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164-398: A biomaterial is different from a biological material, such as bone , that is produced by a biological system . However, "biomaterial" and "biological material" are often used interchangeably. Further, the word "bioterial" has been proposed as a potential alternate word for biologically-produced materials such as bone, or fungal biocomposites. Additionally, care should be exercised in defining

328-543: A brown-haired person has 110,000, a black-haired person has 100,000, and a redhead has 90,000. Hair growth stops after a human's death. Visible growth of hair on the dead body happens only because of skin drying out due to water loss. The world record for longest hair on a living person stands with Smita Srivastava of Uttar Pradesh, India . At 7 feet and 9 inches long, she broke a Guinness World Record in November 2023, having grown her hair for 32 years. Hair exists in

492-499: A biomaterial as biocompatible , since it is application-specific. A biomaterial that is biocompatible or suitable for one application may not be biocompatible in another. Material exploited in contact with living tissues, organisms, or microorganisms. Biomaterials can be derived either from nature or synthesized in the laboratory using a variety of chemical approaches utilizing metallic components, polymers , ceramics or composite materials . They are often used and/or adapted for

656-599: A biomaterial can be designed to include toxicity for an intended purpose. For example, application of toxic biomaterial is studied during in vivo and in vitro cancer immunotherapy testing. Toxic biomaterials offer an opportunity to manipulate and control cancer cells. One recent study states: "Advanced nanobiomaterials, including liposomes , polymers , and silica , play a vital role in the codelivery of drugs and immunomodulators . These nanobiomaterial-based delivery systems could effectively promote antitumor immune responses and simultaneously reduce toxic adverse effects." This

820-400: A biomaterial. biomaterials can be designed to replicate natural organisms, a process known as biomimetics . The structure of a biomaterial can be observed at different at different levels to better understand a materials properties and function. The arrangement of atoms and ions within a material is one of the most important structural properties of a biomaterial. The atomic structure of

984-405: A construct with impregnated pharmaceutical products can be placed into the body, which permits the prolonged release of a drug over an extended period of time. A biomaterial may also be an autograft , allograft or xenograft used as a transplant material. The ability of an engineered biomaterial to induce a physiological response that is supportive of the biomaterial's function and performance

1148-914: A cotton thread, but is not stiff or rough. It is neither fine nor coarse. Thick strands whose shed strands usually are easily identified. Coarse hair feels hard and wiry. Hair is mainly composed of keratin proteins and keratin-associated proteins (KRTAPs). The human genome encodes 54 different keratin proteins which are present in various amounts in hair. Similarly, humans encode more than 100 different KRTAPs which crosslink keratins in hair. The content of KRTAPs ranges from less than 3% in human hair to 30–40% in echidna quill. Many mammals have fur and other hairs that serve different functions. Hair provides thermal regulation and camouflage for many animals; for others it provides signals to other animals such as warnings, mating, or other communicative displays; and for some animals hair provides defensive functions and, rarely, even offensive protection. Hair also has

1312-435: A flat cross-section, while people of mostly European or Middle Eastern ancestry tend to have hair with a diameter of 70–100 μm and an oval cross-section, and people of mostly Asian or Native American ancestry tend to have hair with a diameter of 90–120 μm and a round cross-section. There are roughly two million small, tubular glands and sweat glands that produce watery fluids that cool the body by evaporation. The glands at

1476-410: A function within the human body. The application of a specific biomaterial must combine the necessary composition, material properties, structure, and desired in vivo reaction in order to perform the desired function. Categorizations of different desired properties are defined in order to maximize functional results. Host response is defined as the "response of the host organism (local and systemic) to

1640-479: A long bone are separated by a growing zone of cartilage (the epiphyseal plate ). At skeletal maturity (18 to 25 years of age), all of the cartilage is replaced by bone, fusing the diaphysis and both epiphyses together (epiphyseal closure). In the upper limbs, only the diaphyses of the long bones and scapula are ossified. The epiphyses, carpal bones, coracoid process, medial border of the scapula, and acromion are still cartilaginous. The following steps are followed in

1804-473: A material can be viewed at different levels, the sub atomic level, atomic or molecular level, as well as the ultra-structure created by the atoms and molecules. Intermolecular forces between the atoms and molecules that compose the material will determine its material and chemical properties. The sub atomic level observes the electrical structure of an individual atom to define its interactions with other atoms and molecules. The molecular structure observes

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1968-405: A material may elicit little or no immune response in a given organism, and may or may not able to integrate with a particular cell type or tissue . Immuno-informed biomaterials that direct the immune response rather than attempting to circumvent the process is one approach that shows promise. The ambiguity of the term reflects the ongoing development of insights into "how biomaterials interact with

2132-447: A medical application, and thus comprise the whole or part of a living structure or biomedical device which performs, augments, or replaces a natural function. Such functions may be relatively passive, like being used for a heart valve , or maybe bioactive with a more interactive functionality such as hydroxy-apatite coated hip implants . Biomaterials are also commonly used in dental applications, surgery, and drug delivery. For example,

2296-509: A mineralized organic matrix. The primary inorganic component of human bone is hydroxyapatite , the dominant bone mineral , having the nominal composition of Ca 10 (PO 4 ) 6 (OH) 2 . The organic components of this matrix consist mainly of type I collagen —"organic" referring to materials produced as a result of the human body—and inorganic components, which alongside the dominant hydroxyapatite phase, include other compounds of calcium and phosphate including salts. Approximately 30% of

2460-419: A more fulfilling and healthier lifestyle. Bone is constantly being created and replaced in a process known as remodeling . This ongoing turnover of bone is a process of resorption followed by replacement of bone with little change in shape. This is accomplished through osteoblasts and osteoclasts. Cells are stimulated by a variety of signals , and together referred to as a remodeling unit. Approximately 10% of

2624-443: A new strategy in chemical synthesis and nanotechnology . Molecular crystals, liquid crystals, colloids, micelles, emulsions , phase-separated polymers, thin films and self-assembled monolayers all represent examples of the types of highly ordered structures, which are obtained using these techniques. The distinguishing feature of these methods is self-organization. Nearly all materials could be seen as hierarchically structured, since

2788-457: A number of anatomical terms to describe the appearance, shape and function of bones. Other anatomical terms are also used to describe the location of bones . Like other anatomical terms, many of these derive from Latin and Greek . Some anatomists still use Latin to refer to bones. The term "osseous", and the prefix "osteo-", referring to things related to bone, are still used commonly today. Some examples of terms used to describe bones include

2952-422: A number of chemical enzymes that either promote or inhibit the activity of the bone remodeling cells, controlling the rate at which bone is made, destroyed, or changed in shape. The cells also use paracrine signalling to control the activity of each other. For example, the rate at which osteoclasts resorb bone is inhibited by calcitonin and osteoprotegerin . Calcitonin is produced by parafollicular cells in

3116-529: A positive correlation between the adaptations of resistance training and bone density. While nutritional and pharmacological approaches may also improve bone health, the strength and balance adaptations from resistance training are a substantial added benefit. Weight-bearing exercise may assist in osteoblast (bone-forming cells) formation and help to increase bone mineral content. High-impact sports, which involve quick changes in direction, jumping, and running, are particularly effective with stimulating bone growth in

3280-613: A prefix—such as osteopathy . In anatomical terminology , including the Terminologia Anatomica international standard, the word for a bone is os (for example, os breve , os longum , os sesamoideum ). Bone is not uniformly solid, but consists of a flexible matrix (about 30%) and bound minerals (about 70%), which are intricately woven and continuously remodeled by a group of specialized bone cells. Their unique composition and design allows bones to be relatively hard and strong, while remaining lightweight. Bone matrix

3444-419: A recent study, there was a strong correlation between calcium intake and BMD across a variety of diverse populations of children and adolescence ultimately coming to the conclusion that fundamentally, achieving optimal bone health is necessary for providing our youth with the ability to undergo hormonal changes as well. They found in a study of over 10,000 children ages 8-19 that in females, African Americans, and

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3608-447: A sensory function, extending the sense of touch beyond the surface of the skin. Guard hairs give warnings that may trigger a recoiling reaction. While humans have developed clothing and other means of keeping warm, the hair found on the head serves primarily as a source of heat insulation and cooling (when sweat evaporates from soaked hair) as well as protection from ultra-violet radiation exposure. The function of hair in other locations

3772-599: A series of regulated tests that material must pass to be certified for use. These include the United States Pharmacopoeia IV (USP Class IV) Biological Reactivity Test and the International Standards Organization 10993 (ISO 10993) Biological Evaluation of Medical Devices. The main objective of biocompatibility tests is to quantify the acute and chronic toxicity of material and determine any potential adverse effects during use conditions, thus

3936-408: A smaller number of randomly oriented collagen fibers, but forms quickly; it is for this appearance of the fibrous matrix that the bone is termed woven . It is soon replaced by lamellar bone, which is highly organized in concentric sheets with a much lower proportion of osteocytes to surrounding tissue. Lamellar bone, which makes its first appearance in humans in the fetus during the third trimester,

4100-401: A strong nutritional plan with adequate amounts of Calcium sources can lead to strong bones but also can be a worth-while strategy into preventing further damage or degradation of bone stores as we age. The connection between Calcium intake & BMD and its effects on youth as a whole is a very world-wide issue and has been shown to affect different ethnicities in a variety of differing ways. In

4264-460: A variety of doctors, including rheumatologists for joints, and orthopedic surgeons, who may conduct surgery to fix broken bones. Other doctors, such as rehabilitation specialists may be involved in recovery, radiologists in interpreting the findings on imaging, and pathologists in investigating the cause of the disease, and family doctors may play a role in preventing complications of bone disease such as osteoporosis. Hair Hair

4428-400: A variety of textures. Three main aspects of hair texture are the curl pattern, volume, and consistency. All mammalian hair is composed of keratin , so the make-up of hair follicles is not the source of varying hair patterns. There are a range of theories pertaining to the curl patterns of hair. Scientists have come to believe that the shape of the hair shaft has an effect on the curliness of

4592-456: A very low shear stress strength (51.6 MPa). This means that bone resists pushing (compressional) stress well, resist pulling (tensional) stress less well, but only poorly resists shear stress (such as due to torsional loads). While bone is essentially brittle , bone does have a significant degree of elasticity , contributed chiefly by collagen . Mechanically, bones also have a special role in hearing . The ossicles are three small bones in

4756-403: Is 90 to 95% composed of elastic collagen fibers, also known as ossein, and the remainder is ground substance . The elasticity of collagen improves fracture resistance. The matrix is hardened by the binding of inorganic mineral salt, calcium phosphate , in a chemical arrangement known as bone mineral , a form of calcium apatite . It is the mineralization that gives bones rigidity. Bone

4920-610: Is a protein filament that grows from follicles found in the dermis . Hair is one of the defining characteristics of mammals . The human body , apart from areas of glabrous skin, is covered in follicles which produce thick terminal and fine vellus hair . Most common interest in hair is focused on hair growth , hair types, and hair care , but hair is also an important biomaterial primarily composed of protein , notably alpha-keratin . Attitudes towards different forms of hair, such as hairstyles and hair removal , vary widely across different cultures and historical periods, but it

5084-491: Is a hip replacement using ivory material which was first recorded in Germany 1891. Valuable criteria for viable natural biomaterials: Examples of natural biomaterials: Biopolymers are polymers produced by living organisms. Cellulose and starch , proteins and peptides , and DNA and RNA are all examples of biopolymers, in which the monomeric units, respectively, are sugars , amino acids , and nucleotides . Cellulose

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5248-423: Is a method which classifies the hair by curl pattern, hair-strand thickness and overall hair volume. Curliness Strands Thin strands that sometimes are almost translucent when held up to the light. Shed strands can be hard to see even against a contrasting background. Fine hair is difficult to feel or it feels like an ultra-fine strand of silk. Strands are neither fine nor coarse. Medium hair feels like

5412-800: Is a prime example of how the biocompatibility of a biomaterial can be altered to produce any desired function. Biodegradable biomaterials refers to materials that are degradable through natural enzymatic reactions . The application of biodegradable synthetic polymers began in the later 1960s. Biodegradable materials have an advantage over other materials, as they have lower risk of harmful effects long term. In addition to ethical advancements using biodegradable materials, they also improve biocompatibility for materials used for implantation. Several properties including biocompatibility are important when considering different biodegradable biomaterials. Biodegradable biomaterials can be synthetic or natural depending on their source and type of extracellular matrix (ECM). Some of

5576-490: Is a trait that may be associated with neoteny . Primates are relatively hairless compared to other mammals, and Hominini such as chimpanzees, have less dense hair than would be expected given their body size for a primate. Evolutionary biologists suggest that the genus Homo arose in East Africa approximately 2 million years ago. Part of this evolution was the development of endurance running and venturing out during

5740-426: Is actively constructed and remodeled throughout life by special bone cells known as osteoblasts and osteoclasts. Within any single bone, the tissue is woven into two main patterns, known as cortical and cancellous bone, each with a different appearance and characteristics. The hard outer layer of bones is composed of cortical bone , which is also called compact bone as it is much denser than cancellous bone. It forms

5904-550: Is affected by the body's response to the foreign material. The body undergoes a cascade of processes defined under the foreign body response (FBR) in order to protect the host from the foreign material. The interactions between the device upon the host tissue/blood as well as the host tissue/blood upon the device must be understood in order to prevent complications and device failure. Tissue injury caused by device implantation causes inflammatory and healing responses during FBR. The inflammatory response occurs within two time periods:

6068-462: Is also called bone in the uncountable sense of that word, is hard tissue , a type of specialised connective tissue . It has a honeycomb -like matrix internally, which helps to give the bone rigidity. Bone tissue is made up of different types of bone cells . Osteoblasts and osteocytes are involved in the formation and mineralisation of bone; osteoclasts are involved in the resorption of bone tissue. Modified (flattened) osteoblasts become

6232-409: Is both the most common biopolymer and the most common organic compound on Earth. About 33% of all plant matter is cellulose. On a similar manner, silk (proteinaceous biopolymer) has garnered tremendous research interest in a myriad of domains including tissue engineering and regenerative medicine, microfluidics, drug delivery. Bone A bone is a rigid organ that constitutes part of

6396-474: Is called "osteoid". Around and inside collagen fibrils calcium and phosphate eventually precipitate within days to weeks becoming then fully mineralized bone with an overall carbonate substituted hydroxyapatite inorganic phase. In order to mineralise the bone, the osteoblasts secrete alkaline phosphatase, some of which is carried by vesicles . This cleaves the inhibitory pyrophosphate and simultaneously generates free phosphate ions for mineralization, acting as

6560-438: Is cognate with terms such as Old Norse and Norwegian : fax . Each strand of hair is made up of the medulla , cortex , and cuticle . The innermost region, the medulla , is an open and unstructured region that is not always present. The highly structural and organized cortex , or second of three layers of the hair, is the primary source of mechanical strength and water uptake. The cortex contains melanin , which colors

6724-418: Is composed of a network of rod- and plate-like elements that make the overall organ lighter and allow room for blood vessels and marrow. Trabecular bone accounts for the remaining 20% of total bone mass but has nearly ten times the surface area of compact bone. The words cancellous and trabecular refer to the tiny lattice-shaped units (trabeculae) that form the tissue. It was first illustrated accurately in

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6888-419: Is debated. Hats and coats are still required while doing outdoor activities in cold weather to prevent frostbite and hypothermia , but the hair on the human body does help to keep the internal temperature regulated. When the body is too cold, the arrector pili muscles found attached to hair follicles stand up, causing the hair in these follicles to do the same. These hairs then form a heat-trapping layer above

7052-571: Is discovered, others in the same batch may be traced. Calcium sulfate (its α- and β-hemihydrates) is a well known biocompatible material that is widely used as a bone graft substitute in dentistry or as its binder. In the United States, 49% of the 250,000 valve replacement procedures performed annually involve a mechanical valve implant. The most widely used valve is a bileaflet disc heart valve or St. Jude valve. The mechanics involve two semicircular discs moving back and forth, with both allowing

7216-411: Is gauged by the surface biomineralization in which a native layer of hydroxyapatite is formed at the surface. These days, the development of clinically useful biomaterials is greatly enhanced by the advent of computational routines that can predict the molecular effects of biomaterials in a therapeutic setting based on limited in vitro experimentation. Self-assembly is the most common term in use in

7380-441: Is important. The material must be ductile for a similar reason that the tensile strength cannot be too high, ductility allows the material to bend without fracture and also prevents the concentration of stresses in the tissue when the temperature changes. The material property of toughness is also important for dental implants as well as any other rigid, load-bearing implant such as a replacement hip joint . Toughness describes

7544-399: Is in the spatial scale of the unit cell (lattice parameter) in each particular case. Molecular self assembly is found widely in biological systems and provides the basis of a wide variety of complex biological structures. This includes an emerging class of mechanically superior biomaterials based on microstructural features and designs found in nature. Thus, self-assembly is also emerging as

7708-469: Is interpreted in the neocortex , a section of the brain that expanded markedly in animals like Morganucodon and Hadrocodium . The more advanced therapsids could have had a combination of naked skin, whiskers , and scutes . A full pelage likely did not evolve until the therapsid-mammal transition. The more advanced, smaller therapsids could have had a combination of hair and scutes, a combination still found in some modern mammals, such as rodents and

7872-491: Is known as bioactivity. Most commonly, in bioactive glasses and bioactive ceramics this term refers to the ability of implanted materials to bond well with surrounding tissue in either osteo conductive or osseo productive roles. Bone implant materials are often designed to promote bone growth while dissolving into surrounding body fluid. Thus for many biomaterials good biocompatibility along with good strength and dissolution rates are desirable. Commonly, bioactivity of biomaterials

8036-474: Is less dense . This makes it weaker and more flexible. The greater surface area also makes it suitable for metabolic activities such as the exchange of calcium ions. Cancellous bone is typically found at the ends of long bones, near joints, and in the interior of vertebrae. Cancellous bone is highly vascular and often contains red bone marrow where hematopoiesis , the production of blood cells, occurs. The primary anatomical and functional unit of cancellous bone

8200-584: Is less common to see, the necessity for a healthy routine especially when it comes to bone development is essential in our youth. Children that naturally have lower bone mineral density have a lower quality of life and therefore lead a life that is less fulfilling and uncomfortable. Factors such as increases in Calcium intake has been shown to increase BMD stores. Studies have shown that increasing calcium stores whether that be through supplementation or intake via foods and beverages such as leafy greens and milk have pushed

8364-472: Is made of a mineralized hard component (exhibits brittle fracture) and a softer organic component composed primarily of chitin . The brittle component is arranged in a helical pattern. Each of these mineral "rods" (1 μm diameter) contains chitin–protein fibrils with approximately 60 nm diameter. These fibrils are made of 3 nm diameter canals that link the interior and exterior of the shell. Biomaterials are used in: Biomaterials must be compatible with

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8528-478: Is more complex, since not all hair grows at once. Scalp hair was reported to grow between 0.6 cm and 3.36 cm per month. The growth rate of scalp hair somewhat depends on age (hair tends to grow more slowly with age), sex, and ethnicity. Thicker hair (>60 μm) grows generally faster (11.4 mm per month) than thinner (20-30 μm) hair (7.6 mm per month). It was previously thought that Caucasian hair grew more quickly than Asian hair and that

8692-518: Is mostly found in the bone marrow of the femur, the ribs, the vertebrae and pelvic bones . Bone receives about 10% of cardiac output. Blood enters the endosteum , flows through the marrow, and exits through small vessels in the cortex. In humans, blood oxygen tension in bone marrow is about 6.6%, compared to about 12% in arterial blood, and 5% in venous and capillary blood. Bone is metabolically active tissue composed of several types of cells. These cells include osteoblasts , which are involved in

8856-434: Is multiple layers of osteoblasts and osteocytes around a central canal called the osteonic canal . Volkmann's canals at right angles connect the osteons together. The columns are metabolically active, and as bone is reabsorbed and created the nature and location of the cells within the osteon will change. Cortical bone is covered by a periosteum on its outer surface, and an endosteum on its inner surface. The endosteum

9020-527: Is necessary during our childhood as these factors lead to a supportive and healthy lifestyle/bone health. Up till the age of 30, the bone stores that we have will ultimately start to decrease as we surpass this age. Influencing factors that can help us have larger stores and higher amounts of BMD will allow us to see less harmful results as we reach older adulthood. The issue of having fragile bones during our childhood leads to an increase in certain disorders and conditions such as juvenile osteoporosis , though it

9184-451: Is not fully known. Two types of bone can be identified microscopically according to the arrangement of collagen: woven and lamellar. Woven bone is produced when osteoblasts produce osteoid rapidly, which occurs initially in all fetal bones, but is later replaced by more resilient lamellar bone. In adults, woven bone is created after fractures or in Paget's disease . Woven bone is weaker, with

9348-455: Is not just one method to discovering one's hair type. Additionally it is possible, and quite normal to have more than one kind of hair type, for instance having a mixture of both type 3a & 3b curls. The Andre Walker Hair Typing System is the most widely used system to classify hair. The system was created by Oprah Winfrey 's hairstylist, Andre Walker . According to this system there are four types of hair: straight, wavy, curly, kinky. This

9512-448: Is often used to indicate a person's personal beliefs or social position, such as their age, gender , or religion . The word "hair" usually refers to two distinct structures: Hair fibers have a structure consisting of several layers, starting from the outside: The word "hair" is derived from Middle English : heer and hêr , in turn derived from Old English : hǽr and hér , with influence from Old Norse : hár . Both

9676-730: Is stimulated by the secretion of growth hormone by the pituitary , thyroid hormone and the sex hormones ( estrogens and androgens ). These hormones also promote increased secretion of osteoprotegerin. Osteoblasts can also be induced to secrete a number of cytokines that promote reabsorption of bone by stimulating osteoclast activity and differentiation from progenitor cells. Vitamin D , parathyroid hormone and stimulation from osteocytes induce osteoblasts to increase secretion of RANK- ligand and interleukin 6 , which cytokines then stimulate increased reabsorption of bone by osteoclasts. These same compounds also increase secretion of macrophage colony-stimulating factor by osteoblasts, which promotes

9840-561: Is stronger and filled with many collagen fibers parallel to other fibers in the same layer (these parallel columns are called osteons). In cross-section , the fibers run in opposite directions in alternating layers, much like in plywood , assisting in the bone's ability to resist torsion forces. After a fracture, woven bone forms initially and is gradually replaced by lamellar bone during a process known as "bony substitution". Compared to woven bone, lamellar bone formation takes place more slowly. The orderly deposition of collagen fibers restricts

10004-587: Is the Young's Modulus, E , which describes a material's elastic response to stresses . The Young's Moduli of the tissue and the device that is being coupled to it must closely match for optimal compatibility between device and body, whether the device is implanted or mounted externally. Matching the elastic modulus makes it possible to limit movement and delamination at the biointerface between implant and tissue as well as avoiding stress concentration that can lead to mechanical failure . Other important properties are

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10168-403: Is the flexural rigidity, D . Flexural rigidity will determine how well the device surface can maintain conformal contact with the tissue surface, which is especially important for devices that are measuring tissue motion ( strain ), electrical signals ( impedance ), or are designed to stick to the skin without delaminating , as in epidermal electronics. Since flexural rigidity depends on

10332-533: Is the trabecula . The trabeculae are aligned towards the mechanical load distribution that a bone experiences within long bones such as the femur . As far as short bones are concerned, trabecular alignment has been studied in the vertebral pedicle . Thin formations of osteoblasts covered in endosteum create an irregular network of spaces, known as trabeculae. Within these spaces are bone marrow and hematopoietic stem cells that give rise to platelets , red blood cells and white blood cells . Trabecular marrow

10496-438: Is the boundary between the cortical bone and the cancellous bone. The primary anatomical and functional unit of cortical bone is the osteon . Cancellous bone or spongy bone , also known as trabecular bone , is the internal tissue of the skeletal bone and is an open cell porous network that follows the material properties of biofoams . Cancellous bone has a higher surface-area-to-volume ratio than cortical bone and it

10660-458: Is the building block of the organic matrix , a triple helix with diameter of 1.5 nm. These tropocollagen molecules are intercalated with the mineral phase ( hydroxyapatite , calcium phosphate) forming fibrils that curl into helicoids of alternating directions. These " osteons " are the basic building blocks of bones, with the volume fraction distribution between organic and mineral phase being about 60/40. In another level of complexity,

10824-409: Is the outer covering. Its complex structure slides as the hair swells and is covered with a single molecular layer of lipid that makes the hair repel water. The diameter of human hair varies from 0.017 to 0.18 millimeters (0.00067 to 0.00709 in). Some of these characteristics in humans' head hair vary by race: people of mostly African ancestry tend to have hair with a diameter of 60–90 μm and

10988-476: Is through the crystal lattice , which is a three-dimensional representation of the location of a repeating factor ( unit cell ) in the structure denoted with lattices . There are 14 different configurations of atom arrangement in a crystalline structure, and are all represented under Bravais lattices . During the formation of a crystalline structure, different impurities, irregularities, and other defects can form. These imperfections can form through deformation of

11152-492: Is very minimal. Being able to consistently meet calcium needs while also engaging in weight-bearing exercise is essential for building a strong initial bone foundation at which to build upon. Being able to reach our daily value of 1300mg for ages 9-18 is becoming more and more necessary and as we progress in health, the chance that osteoporosis and other factors such as bone fragility or potential for stunted growth can be greatly reduced through these resources, ultimately leading to

11316-545: The Upper Permian , shows smooth, hairless skin with what appears to be glandular depressions, though as a semi-aquatic species it might not have been particularly useful to determine the integument of terrestrial species. The oldest undisputed known fossils showing unambiguous imprints of hair are the Callovian (late middle Jurassic ) Castorocauda and several contemporary haramiyidans , both near-mammal cynodonts , giving

11480-441: The anagen , catagen , and telogen phases. Each strand of hair on the human body is at its own stage of development. Once the cycle is complete, it restarts and a new strand of hair begins to form. The growth rate of hair varies from individual to individual depending on their age, genetic predisposition and a number of environmental factors. It is commonly stated that hair grows about 1 cm per month on average; however reality

11644-409: The epidermis called the hair follicle . The bulb of hair consists of fibrous connective tissue, glassy membrane, external root sheath, internal root sheath composed of epithelium stratum ( Henle's layer ) and granular stratum ( Huxley's layer ), cuticle, cortex and medulla. All natural hair colors are the result of two types of hair pigments. Both of these pigments are melanin types, produced inside

11808-517: The epidermis . This process is formally called piloerection , derived from the Latin words 'pilus' ('hair') and 'erectio' ('rising up'), but is more commonly known as 'having goose bumps ' in English. This is more effective in other mammals whose fur fluffs up to create air pockets between hairs that insulate the body from the cold. The opposite actions occur when the body is too warm; the arrector muscles make

11972-418: The fiber based on the number, distribution and types of melanin granules. The melanin may be evenly spaced or cluster around the edges of the hair. The shape of the follicle determines the shape of the cortex, and the shape of the fiber is related to how straight or curly the hair is. People with straight hair have round hair fibers. Oval and other shaped fibers are generally more wavy or curly. The cuticle

12136-412: The human body at birth, approximately 300 bones are present. Many of these fuse together during development, leaving a total of 206 separate bones in the adult, not counting numerous small sesamoid bones . The largest bone in the body is the femur or thigh-bone, and the smallest is the stapes in the middle ear . The Greek word for bone is ὀστέον (" osteon "), hence the many terms that use it as

12300-433: The human body " and eventually "how those interactions determine the clinical success of a medical device (such as pacemaker or hip replacement )". Modern medical devices and prostheses are often made of more than one material, so it might not always be sufficient to talk about the biocompatibility of a specific material. Surgical implantation of a biomaterial into the body triggers an organism-inflammatory reaction with

12464-724: The middle ear which are involved in sound transduction. The cancellous part of bones contain bone marrow . Bone marrow produces blood cells in a process called hematopoiesis . Blood cells that are created in bone marrow include red blood cells , platelets and white blood cells . Progenitor cells such as the hematopoietic stem cell divide in a process called mitosis to produce precursor cells. These include precursors which eventually give rise to white blood cells , and erythroblasts which give rise to red blood cells. Unlike red and white blood cells, created by mitosis, platelets are shed from very large cells called megakaryocytes . This process of progressive differentiation occurs within

12628-406: The opossum . The high interspecific variability of the size, color, and microstructure of hair often enables the identification of species based on single hair filaments. In varying degrees most mammals have some skin areas without natural hair. On the human body, glabrous skin is found on the ventral portion of the fingers , palms , soles of feet and lips , which are all parts of

12792-429: The skeleton in most vertebrate animals. Bones protect the various other organs of the body, produce red and white blood cells , store minerals , provide structure and support for the body, and enable mobility . Bones come in a variety of shapes and sizes and have complex internal and external structures. They are lightweight yet strong and hard and serve multiple functions . Bone tissue (osseous tissue), which

12956-427: The tensile and compressive strengths which quantify the maximum stresses a material can withstand before breaking and may be used to set stress limits that a device may be subject to within or external to the body. Depending on the application, it may be desirable for a biomaterial to have high strength so that it is resistant to failure when subjected to a load, however in other applications it may be beneficial for

13120-420: The thyroid gland , and can bind to receptors on osteoclasts to directly inhibit osteoclast activity. Osteoprotegerin is secreted by osteoblasts and is able to bind RANK-L, inhibiting osteoclast stimulation. Osteoblasts can also be stimulated to increase bone mass through increased secretion of osteoid and by inhibiting the ability of osteoclasts to break down osseous tissue . Increased secretion of osteoid

13284-445: The 12-15 adolescent groups that at 2.6-2.8g/kg of body weight, they began to see a decrease in BMD. They elaborate on this by determining that this is strongly influenced by a lower baseline in calcium intake throughout puberty. Genetic factors have also been shown to influence lower acceptance of calcium stores. Ultimately, the window that youth have for accruing and building resilient bones

13448-461: The EDAR locus, a region of the modern human genome that contributes to hair texture variation among most individuals of East Asian descent, support the hypothesis that (East Asian) straight hair likely developed in this branch of the modern human lineage subsequent to the original expression of tightly coiled natural afro-hair . Specifically, the relevant findings indicate that the EDAR mutation coding for

13612-461: The Old English and Old Norse words derive from Proto-Germanic : * hēran and are related to terms for hair in other Germanic languages such as Swedish : här , Dutch and German : haar , and Old Frisian : her . The now broadly obsolete word "fax" refers specifically to head hair and is found in compounds such as Fairfax and Halifax . It is derived from Old English : feax and

13776-420: The acellular component of bone consists of organic matter, while roughly 70% by mass is attributed to the inorganic phase. The collagen fibers give bone its tensile strength , and the interspersed crystals of hydroxyapatite give bone its compressive strength . These effects are synergistic . The exact composition of the matrix may be subject to change over time due to nutrition and biomineralization , with

13940-422: The acute phase, and the chronic phase. The acute phase occurs during the initial hours to days of implantation, and is identified by fluid and protein exudation along with a neutrophilic reaction. During the acute phase, the body attempts to clean and heal the wound by delivering excess blood, proteins, and monocytes are called to the site. Continued inflammation leads to the chronic phase, which can be categorized by

14104-445: The age as no later than ≈220 ma based on the modern phylogenetic understanding of these clades. More recently, studies on terminal Permian Russian coprolites may suggest that non-mammalian synapsids from that era had fur. If this is the case, these are the oldest hair remnants known, showcasing that fur occurred as far back as the latest Paleozoic . Some modern mammals have a special gland in front of each orbit used to preen

14268-420: The arrangement of atoms within the material. Finally the ultra-structure observes the 3-D structure created from the atomic and molecular structures of the material. The solid-state of a material is characterized by the intramolecular bonds between the atoms and molecules that comprise the material. Types of intramolecular bonds include: ionic bonds , covalent bonds , and metallic bonds . These bonds will dictate

14432-424: The associated healing of the damaged tissue. Depending upon the composition of the implanted material, the surface of the implant, the mechanism of fatigue, and chemical decomposition there are several other reactions possible. These can be local as well as systemic. These include immune response, foreign body reaction with the isolation of the implant with a vascular connective tissue, possible infection, and impact on

14596-414: The belly and lower tail of a pelycosaur , possibly Haptodus shows the basal synapsid stock bore transverse rows of rectangular scutes , similar to those of a modern crocodile , so the age of acquirement of hair logically could not have been earlier than ≈299 ma, based on the current understanding of the animal's phylogeny. An exceptionally well-preserved skull of Estemmenosuchus , a therapsid from

14760-493: The body most closely associated with interacting with the world around us, as are the labia minora and glans penis . There are four main types of mechanoreceptors in the glabrous skin of humans: Pacinian corpuscles , Meissner's corpuscles , Merkel's discs , and Ruffini corpuscles . The naked mole-rat ( Heterocephalus glaber ) has evolved skin lacking in general, pelagic hair covering, yet has retained long, very sparsely scattered tactile hairs over its body. Glabrousness

14924-408: The body, and there are often issues of biocompatibility , which must be resolved before a product can be placed on the market and used in a clinical setting. Because of this, biomaterials are usually subjected to the same requirements as those undergone by new drug therapies. All manufacturing companies are also required to ensure traceability of all of their products, so that if a defective product

15088-416: The bone marrow. After the cells are matured, they enter the circulation . Every day, over 2.5 billion red blood cells and platelets, and 50–100 billion granulocytes are produced in this way. As well as creating cells, bone marrow is also one of the major sites where defective or aged red blood cells are destroyed. Determined by the species, age, and the type of bone, bone cells make up to 15 percent of

15252-548: The bone matrix. The release of these growth factors from the bone matrix could cause the proliferation of osteoblast precursors. Essentially, bone growth factors may act as potential determinants of local bone formation. Cancellous bone volume in postmenopausal osteoporosis may be determined by the relationship between the total bone forming surface and the percent of surface resorption. A number of diseases can affect bone, including arthritis, fractures, infections, osteoporosis and tumors. Conditions relating to bone can be managed by

15416-429: The bone. Growth factor storage—mineralized bone matrix stores important growth factors such as insulin -like growth factors, transforming growth factor, bone morphogenetic proteins and others. Strong bones during our youth is essential for preventing osteoporosis and bone fragility as we age. The importance of insuring factors that could influence increases in BMD while lowering our risks for further bone degradation

15580-426: The breakdown of bones by the process of bone resorption . New bone is then formed by the osteoblasts. Bone is constantly remodeled by the resorption of osteoclasts and created by osteoblasts. Osteoclasts are large cells with multiple nuclei located on bone surfaces in what are called Howship's lacunae (or resorption pits ). These lacunae are the result of surrounding bone tissue that has been reabsorbed. Because

15744-458: The cartilage called "primary ossification centers". They mostly appear during fetal development, though a few short bones begin their primary ossification after birth . They are responsible for the formation of the diaphyses of long bones, short bones and certain parts of irregular bones. Secondary ossification occurs after birth and forms the epiphyses of long bones and the extremities of irregular and flat bones. The diaphysis and both epiphyses of

15908-403: The changes in spatial scale bring about different mechanisms of deformation and damage. However, in biological materials, this hierarchical organization is inherent to the microstructure. One of the first examples of this, in the history of structural biology, is the early X-ray scattering work on the hierarchical structure of hair and wool by Astbury and Woods. In bone, for example, collagen

16072-425: The circulation of cool air onto the scalp. Further, wet Afro-hair does not stick to the neck and scalp unless totally drenched and instead tends to retain its basic springy puffiness because it less easily responds to moisture and sweat than straight hair does. In this sense, the trait may enhance comfort levels in intense equatorial climates more than straight hair (which, on the other hand, tends to naturally fall over

16236-453: The condition of the strand. Fine hair has the smallest circumference, coarse hair has the largest circumference, and medium hair is anywhere between the other two. Coarse hair has a more open cuticle than thin or medium hair causing it to be the most porous. There are various systems that people use to classify their curl patterns. Being knowledgeable of an individual's hair type is a good start to knowing how to take care of one's hair. There

16400-447: The conversion of cartilage to bone: Bone development in youth is extremely important in preventing future complications of the skeletal system. Regular exercise during childhood and adolescence can help improve bone architecture, making bones more resilient and less prone to fractures in adulthood. Physical activity, specifically resistance training, stimulates growth of bones by increasing both bone density and strength. Studies have shown

16564-567: The creation and mineralization of bone tissue, osteocytes , and osteoclasts , which are involved in the reabsorption of bone tissue. Osteoblasts and osteocytes are derived from osteoprogenitor cells, but osteoclasts are derived from the same cells that differentiate to form macrophages and monocytes . Within the marrow of the bone there are also hematopoietic stem cells . These cells give rise to other cells, including white blood cells , red blood cells , and platelets . Osteoblasts are mononucleate bone-forming cells. They are located on

16728-515: The damage is so extreme that it is impossible to use the patient's own cells, artificial tissue cells are grown. The difficulty is in finding a scaffold that the cells can grow and organize on. The characteristics of the scaffold must be that it is biocompatible, cells can adhere to the scaffold, mechanically strong and biodegradable . One successful scaffold is a copolymer of lactic acid and glycolic acid . As discussed previously, biomaterials are used in medical devices to treat, assist, or replace

16892-641: The differentiation of progenitor cells into osteoclasts, and decrease secretion of osteoprotegerin. Bone volume is determined by the rates of bone formation and bone resorption. Certain growth factors may work to locally alter bone formation by increasing osteoblast activity. Numerous bone-derived growth factors have been isolated and classified via bone cultures. These factors include insulin-like growth factors I and II, transforming growth factor-beta, fibroblast growth factor, platelet-derived growth factor, and bone morphogenetic proteins. Evidence suggests that bone cells produce growth factors for extracellular storage in

17056-506: The ears and neck to a degree that provides slightly enhanced comfort levels in cold climates relative to tightly coiled hair). Further, it is notable that the most pervasive expression of this hair texture can be found in sub-Saharan Africa; a region of the world that abundant genetic and paleo-anthropological evidence suggests, was the relatively recent (≈200,000-year-old) point of origin for modern humanity. In fact, although genetic findings (Tishkoff, 2009) suggest that sub-Saharan Africans are

17220-457: The edges of the eyelid and protects the eye from dirt. The eyelash is to humans, camels, horses, ostriches etc., what whiskers are to cats ; they are used to sense when dirt, dust , or any other potentially harmful object is too close to the eye. The eye reflexively closes as a result of this sensation . Eyebrows and eyelashes do not grow beyond a certain length (eyelashes are rarely more than 10 mm long). However, trichomegaly can cause

17384-453: The engravings of Crisóstomo Martinez . Bone marrow , also known as myeloid tissue in red bone marrow, can be found in almost any bone that holds cancellous tissue . In newborns , all such bones are filled exclusively with red marrow or hematopoietic marrow, but as the child ages the hematopoietic fraction decreases in quantity and the fatty/ yellow fraction called marrow adipose tissue (MAT) increases in quantity. In adults, red marrow

17548-560: The equator, straight hair may have (initially) evolved to aid the entry of UV light into the body during the transition from dark, UV-protected skin to paler skin. Jablonski's assertions suggest that the adjective "woolly" in reference to Afro-hair is a misnomer in connoting the high heat insulation derivable from the true wool of sheep. Instead, the relatively sparse density of Afro-hair, combined with its springy coils actually results in an airy, almost sponge-like structure that in turn, Jablonski argues, more likely facilitates an increase in

17712-491: The first years of life. Hair grows everywhere on the external body except for mucous membranes and glabrous skin, such as that found on the palms of the hands, soles of the feet, and lips. The body has different types of hair, including vellus hair and androgenic hair , each with its own type of cellular construction. The different construction gives the hair unique characteristics, serving specific purposes, mainly, warmth and protection. The three stages of hair growth are

17876-421: The flow of blood as well as the ability to form a seal against backflow. The valve is coated with pyrolytic carbon and secured to the surrounding tissue with a mesh of woven fabric called Dacron (du Pont's trade name for polyethylene terephthalate ). The mesh allows for the body's tissue to grow, while incorporating the valve. Most of the time, artificial tissue is grown from the patient's own cells. However, when

18040-410: The foci for calcium and phosphate deposition. Vesicles may initiate some of the early mineralization events by rupturing and acting as a centre for crystals to grow on. Bone mineral may be formed from globular and plate structures, and via initially amorphous phases. Five types of bones are found in the human body: long, short, flat, irregular, and sesamoid. In the study of anatomy , anatomists use

18204-410: The formation of bone from cartilage . Intramembranous ossification mainly occurs during formation of the flat bones of the skull but also the mandible, maxilla, and clavicles; the bone is formed from connective tissue such as mesenchyme tissue rather than from cartilage. The process includes: the development of the ossification center , calcification , trabeculae formation and the development of

18368-590: The formation of osteoid to about 1 to 2  μm per day. Lamellar bone also requires a relatively flat surface to lay the collagen fibers in parallel or concentric layers. The extracellular matrix of bone is laid down by osteoblasts , which secrete both collagen and ground substance. These cells synthesise collagen alpha polypetpide chains and then secrete collagen molecules. The collagen molecules associate with their neighbors and crosslink via lysyl oxidase to form collagen fibrils. At this stage, they are not yet mineralized, and this zone of unmineralized collagen fibrils

18532-425: The fur, called the harderian gland . Imprints of this structure are found in the skull of the small early mammals like Morganucodon , but not in their cynodont ancestors like Thrinaxodon . The hairs of the fur in modern animals are all connected to nerves, and so the fur also serves as a transmitter for sensory input. Fur could have evolved from sensory hair (whiskers). The signals from this sensory apparatus

18696-475: The groundwork for bone health later in life, reducing the risk of bone-related conditions such as osteoporosis. Bones have a variety of functions: Bones serve a variety of mechanical functions. Together the bones in the body form the skeleton . They provide a frame to keep the body supported, and an attachment point for skeletal muscles , tendons , ligaments and joints , which function together to generate and transfer forces so that individual body parts or

18860-420: The growth rate of women's hair was faster than that of men. However, more recent research has shown that the growth rate of hair in men and women does not significantly differ and that the hair of Chinese people grew more quickly than the hair of French Caucasians and West and Central Africans. The quantity of hair hovers in a certain range depending on hair colour. An average blonde person has 150,000 hairs,

19024-514: The hair follicle and packed into granules found in the fibers. Eumelanin is the dominant pigment in brown hair and black hair , while pheomelanin is dominant in red hair . Blond hair is the result of having little pigmentation in the hair strand. Gray hair occurs when melanin production decreases or stops, while poliosis is white hair (and often the skin to which the hair is attached), typically in spots that never possessed melanin at all, or ceased for natural reasons, generally genetic, in

19188-415: The hair follicle include the oil producing sebaceous gland which lubricates the hair and the arrector pili muscles, which are responsible for causing hairs to stand up. In humans with little body hair, the effect results in goose bumps . The root of the hair ends in an enlargement, the hair bulb , which is whiter in color and softer in texture than the shaft and is lodged in a follicular involution of

19352-423: The hair follicle shape determines curl pattern, the hair follicle size determines thickness. While the circumference of the hair follicle expands, so does the thickness of the hair follicle. An individual's hair volume, as a result, can be thin, normal, or thick. The consistency of hair can almost always be grouped into three categories: fine, medium, and coarse. This trait is determined by the hair follicle volume and

19516-520: The hair lie flat on the skin which allows heat to leave. In some mammals, such as hedgehogs and porcupines , the hairs have been modified into hard spines or quills. These are covered with thick plates of keratin and serve as protection against predators. Thick hair such as that of the lion's mane and grizzly bear's fur do offer some protection from physical damages such as bites and scratches. Displacement and vibration of hair shafts are detected by hair follicle nerve receptors and nerve receptors within

19680-460: The hard exterior (cortex) of bones. The cortical bone gives bone its smooth, white, and solid appearance, and accounts for 80% of the total bone mass of an adult human skeleton . It facilitates bone's main functions—to support the whole body, to protect organs, to provide levers for movement, and to store and release chemical elements, mainly calcium. It consists of multiple microscopic columns, each called an osteon or Haversian system. Each column

19844-501: The hot times of the day that required efficient thermoregulation through perspiration . The loss of heat through heat of evaporation by means of sweat glands is aided by air currents next to the skin surface, which are facilitated by the loss of body hair. Another factor in human evolution that also occurred in the prehistoric past was a preferential selection for neoteny , particularly in females. The idea that adult humans exhibit certain neotenous (juvenile) features, not evinced in

20008-568: The hydroxyapatite crystals are mineral platelets that have a diameter of approximately 70 to 100 nm and thickness of 1 nm. They originally nucleate at the gaps between collagen fibrils. Similarly, the hierarchy of abalone shell begins at the nanolevel, with an organic layer having a thickness of 20 to 30 nm. This layer proceeds with single crystals of aragonite (a polymorph of CaCO 3 ) consisting of "bricks" with dimensions of 0.5 and finishing with layers approximately 0.3 mm (mesostructure). Crabs are arthropods, whose carapace

20172-407: The implanted material or device". Most materials will have a reaction when in contact with the human body. The success of a biomaterial relies on the host tissue's reaction with the foreign material. Specific reactions between the host tissue and the biomaterial can be generated through the biocompatibility of the material. The in vivo functionality and longevity of any implantable medical device

20336-438: The individual's hair. A very round shaft allows for fewer disulfide bonds to be present in the hair strand. This means the bonds present are directly in line with one another, resulting in straight hair. The flatter the hair shaft becomes, the curlier hair gets, because the shape allows more cysteines to become compacted together resulting in a bent shape that, with every additional disulfide bond, becomes curlier in form. As

20500-423: The interactions of a biomaterial with the host living system. Important surface properties: In addition to a material being certified as biocompatible , biomaterials must be engineered specifically to their target application within a medical device . This is especially important in terms of mechanical properties which govern the way that a given biomaterial behaves. One of the most relevant material parameters

20664-429: The lashes to grow remarkably long and prominent (in some cases the upper lashes grow to 15 mm long). Hair has its origins in the common ancestor of mammals, the synapsids , about 300 million years ago. It is currently unknown at what stage the synapsids acquired mammalian characteristics such as body hair and mammary glands , as the fossils only rarely provide direct evidence for soft tissues. Skin impression of

20828-410: The lifespan of the implant. Graft-versus-host disease is an auto- and alloimmune disorder, exhibiting a variable clinical course. It can manifest in either acute or chronic form, affecting multiple organs and tissues and causing serious complications in clinical practice, both during transplantation and implementation of biocompatible materials. A biomaterial should perform its intended function within

20992-461: The lining cells that form a protective layer on the bone surface. The mineralised matrix of bone tissue has an organic component of mainly collagen called ossein and an inorganic component of bone mineral made up of various salts. Bone tissue is mineralized tissue of two types, cortical bone and cancellous bone . Other types of tissue found in bones include bone marrow , endosteum , periosteum , nerves , blood vessels and cartilage . In

21156-516: The living body without negatively affecting other bodily tissues and organs. In order to prevent unwanted organ and tissue interactions, biomaterials should be non-toxic . The toxicity of a biomaterial refers to the substances that are emitted from the biomaterial while in vivo . A biomaterial should not give off anything to its environment unless it is intended to do so. Nontoxicity means that biomaterial is: noncarcinogenic, nonpyrogenic , nonallergenic , blood compatible, and noninflammatory . However,

21320-490: The macrostructure reveals properties such as cavities , porosity , gas bubbles, stratification , and fissures . The material's strength and elastic modulus are both independent of the macrostructure. Biomaterials can be constructed using only materials sourced from plants and animals in order to alter, replace, or repair human tissue/organs. Use of natural biomaterials were used as early as ancient Egypt, where indigenous people used animal skin as sutures. A more modern example

21484-419: The material to be low strength. There is a careful balance between strength and stiffness that determines how robust to failure the biomaterial device is. Typically, as the elasticity of the biomaterial increases, the ultimate tensile strength will decrease and vice versa. One application where a high-strength material is undesired is in neural probes ; if a high-strength material is used in these applications

21648-415: The material's ability to deform under applied stress without fracturing and having a high toughness allows biomaterial implants to last longer within the body, especially when subjected to large stress or cyclically loaded stresses , like the stresses applied to a hip joint during running. For medical devices that are implanted or attached to the skin, another important property requiring consideration

21812-511: The modern scientific community to describe the spontaneous aggregation of particles (atoms, molecules, colloids , micelles , etc.) without the influence of any external forces. Large groups of such particles are known to assemble themselves into thermodynamically stable, structurally well-defined arrays, quite reminiscent of one of the seven crystal systems found in metallurgy and mineralogy (e.g., face-centered cubic, body-centered cubic, etc.). The fundamental difference in equilibrium structure

21976-493: The most commonly-used biocompatible materials (or biomaterials) are polymers due to their inherent flexibility and tunable mechanical properties . Medical devices made of plastics are often made of a select few including: cyclic olefin copolymer (COC), polycarbonate (PC), polyetherimide (PEI), medical grade polyvinylchloride (PVC), polyethersulfone (PES), polyethylene (PE), polyetheretherketone (PEEK) and even polypropylene (PP). To ensure biocompatibility , there are

22140-510: The most genetically diverse continental group on Earth, Afro-textured hair approaches ubiquity in this region. This points to a strong, long-term selective pressure that, in stark contrast to most other regions of the genomes of sub-Saharan groups, left little room for genetic variation at the determining loci. Such a pattern, again, does not seem to support human sexual aesthetics as being the sole or primary cause of this distribution. A group of studies have recently shown that genetic patterns at

22304-607: The most successful species on the planet (and which also is very vulnerable at birth) was arguably a more urgent issue (axillary hair in the underarms and groin were also retained as signs of sexual maturity). Sometime during the gradual process by which Homo erectus began a transition from furry skin to the naked skin expressed by Homo sapiens , hair texture putatively gradually changed from straight hair (the condition of most mammals, including humanity's closest cousins—chimpanzees) to Afro-textured hair or 'kinky' (i.e. tightly coiled). This argument assumes that curly hair better impedes

22468-487: The notion that prepuberty or even early pubertal children will see increases in BMD with the addition of increase Calcium intake. Another research study goes on to show that long-term calcium intake has been proven to significantly contribute to overall BMD in children without certain conditions or disorders. This data shows that ensuring adequate calcium intake in children reinforces the structure and rate at which bones will begin to densify. Further detailing how structuring

22632-406: The opening of the hair produce a fatty secretion that lubricates the hair. Hair growth begins inside the hair follicle . The only "living" portion of the hair is found in the follicle. The hair that is visible is the hair shaft, which exhibits no biochemical activity and is considered "dead". The base of a hair's root (the "bulb") contains the cells that produce the hair shaft. Other structures of

22796-478: The osteoblast puts up collagen fibers. These collagen fibers are used as a framework for the osteoblasts' work. The osteoblast then deposits calcium phosphate which is hardened by hydroxide and bicarbonate ions. The brand-new bone created by the osteoblast is called osteoid . Once the osteoblast is finished working it is actually trapped inside the bone once it hardens. When the osteoblast becomes trapped, it becomes known as an osteocyte. Other osteoblasts remain on

22960-502: The osteoclasts are derived from a monocyte stem-cell lineage, they are equipped with phagocytic -like mechanisms similar to circulating macrophages . Osteoclasts mature and/or migrate to discrete bone surfaces. Upon arrival, active enzymes, such as tartrate-resistant acid phosphatase , are secreted against the mineral substrate. The reabsorption of bone by osteoclasts also plays a role in calcium homeostasis . Bones consist of living cells (osteoblasts and osteocytes) embedded in

23124-456: The osteocyte cell processes occupy channels called canaliculi. The many processes of osteocytes reach out to meet osteoblasts, osteoclasts, bone lining cells, and other osteocytes probably for the purposes of communication. Osteocytes remain in contact with other osteocytes in the bone through gap junctions—coupled cell processes which pass through the canalicular channels. Osteoclasts are very large multinucleate cells that are responsible for

23288-595: The other great apes, is about a century old. Louis Bolk made a long list of such traits, and Stephen Jay Gould published a short list in Ontogeny and Phylogeny . In addition, paedomorphic characteristics in women are often acknowledged as desirable by men in developed countries. For instance, vellus hair is a juvenile characteristic. However, while men develop longer, coarser, thicker, and darker terminal hair through sexual differentiation , women do not, leaving their vellus hair visible. Jablonski asserts head hair

23452-424: The passage of UV light into the body relative to straight hair (thus curly or coiled hair would be particularly advantageous for light-skinned hominids living at the equator). It is substantiated by Iyengar's findings (1998) that UV light can enter into straight human hair roots (and thus into the body through the skin) via the hair shaft. Specifically, the results of that study suggest that this phenomenon resembles

23616-426: The passage of light through fiber optic tubes (which do not function as effectively when kinked or sharply curved or coiled). In this sense, when hominids (i.e. Homo erectus ) were gradually losing their straight body hair and thereby exposing the initially pale skin underneath their fur to the sun, straight hair would have been an adaptive liability. By inverse logic, later, as humans traveled farther from Africa and/or

23780-427: The periosteum. Endochondral ossification occurs in long bones and most other bones in the body; it involves the development of bone from cartilage. This process includes the development of a cartilage model, its growth and development, development of the primary and secondary ossification centers , and the formation of articular cartilage and the epiphyseal plates . Endochondral ossification begins with points in

23944-518: The physical and chemical properties of the material, as well as determine the type of material ( ceramic , metal , or polymer ). The microstructure of a material refers to the structure of an object, organism, or material as viewed at magnifications exceeding 25 times. It is composed of the different phases of form, size, and distribution of grains, pores, precipitates, etc. The majority of solid microstructures are crystalline , however some materials such as certain polymers will not crystallize when in

24108-612: The predominant East Asian 'coarse' or thick, straight hair texture arose within the past ≈65,000 years, which is a time frame that covers from the earliest of the 'Out of Africa' migrations up to now. Ringworm is a fungal disease that targets hairy skin. Premature greying of hair is another condition that results in greying before the age of 20 years in Europeans, before 25 years in Asians, and before 30 years in Africans. Hair care involves

24272-410: The presence of monocytes, macrophages, and lymphocytes. In addition, blood vessels and connective tissue form in order to heal the wounded area. Biocompatibility is related to the behavior of biomaterials in various environments under various chemical and physical conditions. The term may refer to specific properties of a material without specifying where or how the material is to be used. For example,

24436-684: The ratio of calcium to phosphate varying between 1.3 and 2.0 (per weight), and trace minerals such as magnesium , sodium , potassium and carbonate also be found. Type I collagen composes 90–95% of the organic matrix, with the remainder of the matrix being a homogenous liquid called ground substance consisting of proteoglycans such as hyaluronic acid and chondroitin sulfate , as well as non-collagenous proteins such as osteocalcin , osteopontin or bone sialoprotein . Collagen consists of strands of repeating units, which give bone tensile strength, and are arranged in an overlapping fashion that prevents shear stress. The function of ground substance

24600-578: The skeletal mass of an adult is remodelled each year. The purpose of remodeling is to regulate calcium homeostasis , repair microdamaged bones from everyday stress, and to shape the skeleton during growth. Repeated stress, such as weight-bearing exercise or bone healing, results in the bone thickening at the points of maximum stress ( Wolff's law ). It has been hypothesized that this is a result of bone's piezoelectric properties, which cause bone to generate small electrical potentials under stress. The action of osteoblasts and osteoclasts are controlled by

24764-602: The skin. Hairs can sense movements of air as well as touch by physical objects and they provide sensory awareness of the presence of ectoparasites . Some hairs, such as eyelashes , are especially sensitive to the presence of potentially harmful matter. The eyebrows provide moderate protection to the eyes from dirt , sweat and rain . They also play a key role in non-verbal communication by displaying emotions such as sadness, anger, surprise and excitement. In many other mammals, they contain much longer, whisker-like hairs that act as tactile sensors. The eyelash grows at

24928-443: The solid state. Crystalline structure is the composition of ions, atoms, and molecules that are held together and ordered in a 3D shape. The main difference between a crystalline structure and an amorphous structure is the order of the components. Crystalline has the highest level of order possible in the material where amorphous structure consists of irregularities in the ordering pattern. One way to describe crystalline structures

25092-402: The solid, rapid cooling, or high energy radiation. Types of defects include point defects, line defects, as well as edge dislocation. Macrostructure refers to the overall geometric properties that will influence the force at failure, stiffness, bending, stress distribution, and the weight of the material. It requires little to no magnification to reveal the macrostructure of a material. Observing

25256-469: The surface of osteon seams and make a protein mixture known as osteoid , which mineralizes to become bone. The osteoid seam is a narrow region of a newly formed organic matrix, not yet mineralized, located on the surface of a bone. Osteoid is primarily composed of Type I collagen . Osteoblasts also manufacture hormones , such as prostaglandins , to act on the bone itself. The osteoblast creates and repairs new bone by actually building around itself. First,

25420-450: The term "foramen" to describe a hole through which something passes, and a "canal" or "meatus" to describe a tunnel-like structure. A protrusion from a bone can be called a number of terms, including a "condyle", "crest", "spine", "eminence", "tubercle" or "tuberosity", depending on the protrusion's shape and location. In general, long bones are said to have a "head", "neck", and "body". When two bones join, they are said to "articulate". If

25584-430: The tests required for a given material are dependent on its end-use (i.e. blood, central nervous system, etc.). Two properties that have a large effect on the functionality of a biomaterial is the surface and bulk properties . Bulk properties refers to the physical and chemical properties that compose the biomaterial for its entire lifetime. They can be specifically generated to mimic the physiochemical properties of

25748-479: The thickness of the material, h , to the third power ( h ), it is very important that a biomaterial can be formed into thin layers in the previously mentioned applications where conformality is paramount. The molecular composition of a biomaterial determines the physical and chemical properties of a biomaterial. These compositions create complex structures that allow the biomaterial to function, and therefore are necessary to define and understand in order to develop

25912-416: The tissue that the material is replacing. They are mechanical properties that are generated from a material's atomic and molecular construction. Important bulk properties: Surface properties refers to the chemical and topographical features on the surface of the biomaterial that will have direct interaction with the host blood/tissue. Surface engineering and modification allows clinicians to better control

26076-544: The tissue will always fail before the device does (under applied load ) because the Young's Modulus of the dura mater and cerebral tissue is on the order of 500 Pa . When this happens, irreversible damage to the brain can occur, thus the biomaterial must have an elastic modulus less than or equal to brain tissue and a low tensile strength if an applied load is expected. For implanted biomaterials that may experience temperature fluctuations , e.g., dental implants , ductility

26240-417: The top of the new bone and are used to protect the underlying bone, these become known as bone lining cells. Osteocytes are cells of mesenchymal origin and originate from osteoblasts that have migrated into and become trapped and surrounded by a bone matrix that they themselves produced. The spaces the cell body of osteocytes occupy within the mineralized collagen type I matrix are known as lacunae , while

26404-418: The two bones have a fibrous connection and are relatively immobile, then the joint is called a "suture". The formation of bone is called ossification . During the fetal stage of development this occurs by two processes: intramembranous ossification and endochondral ossification . Intramembranous ossification involves the formation of bone from connective tissue whereas endochondral ossification involves

26568-430: The whole body can be manipulated in three-dimensional space (the interaction between bone and muscle is studied in biomechanics ). Bones protect internal organs, such as the skull protecting the brain or the ribs protecting the heart and lungs . Because of the way that bone is formed, bone has a high compressive strength of about 170  MPa (1,700  kgf/cm ), poor tensile strength of 104–121 MPa, and

26732-421: The youth. Sports such as soccer, basketball, and tennis have shown to have positive effects on bone mineral density as well as bone mineral content in teenagers. Engaging in physical activity during childhood years, particularly in these high-impact osteogenic sports, can help to positively influence bone mineral density in adulthood. Children and adolescents who participate in regular physical activity will place

26896-410: Was evolutionarily advantageous for pre-humans to retain because it protected the scalp as they walked upright in the intense African (equatorial) UV light . While some might argue that, by this logic, humans should also express hairy shoulders because these body parts would putatively be exposed to similar conditions, the protection of the head, the seat of the brain that enabled humanity to become one of

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