Tissue engineering for skin

create from raw stuff paper engineer for flake off thread ENGINEERING OF THE SKIN (MECH 5510M) LITERATURE REVIEW SID 200507638ABSTRACT This essay is a literature review on the tissue engineering for peel off substitute, with strike to the clinical need, approaches various commercially- operable products. fur is undoubtedly crucial in the upkeep of the systems internal balance also protecting externally. It gets severely compromised in flares, non-healing ulcers, constructive surgeries etc. bringing down the patients quality of life drastically. Tissue engineering is a more efficient approach than traditional fight implanting. It is a research bea that is forever evolving, where researchers are always working towards virtuoso united goal, i.e. to develop in mess quantities, a scratch modesty that can be handled with less care, integrate faster with the bodys natural matrix and be reasonable. INTRODUCTIONA lot of research has been undertaken in the past to actu alize that it is possible to generate scramble by applying engineering techniques. This is done by growing skin at a faster rate than natural and in an artificial panache4. pare down is the largest approximately widely spread pipe organ in the homosexual body. Its role is to protect the bodys internal environment from clumsiness of the external conditions and restrict entry of microbes, by acting as a barrier4. Several situations diseases arise, due to which the skin gets irreparably damaged, and so requiring interventional help in restoring it back to health. Tissue engineering is the natural covering of engineering techniques to develop biological substitutes1. Burns (acute) ulcers (chronic) are the most common conditions which consume the replacement of skin. In developing countries (Fig 1)2,3, due to lack of knowledge on safety, a very(prenominal) high number of burn accidents occur every year, and mostly of black nature. The fatality is importantly due to pain, infection, loss of body fluids incapability of the body to self-regenerate large amounts of lost skin5. Thus, experimentation in this field was triggered. Many skin diseases, which lead to necrosis, pigmentation problems, also require engineered skin4. CLINICAL NEED FOR SKIN tissue paper ENGINEERINGIn most incidents, both the dermal and dermal layers require replacement. Conventionally, the manipulation regularity involved skin grafting i.e. autologous (self) split-thickness and full-thickness grafting, where good for you(p) skin was taken from other areas of the body and replaced at the injury site. Split-thickness (comprising of the shield a part of the dermis) grafting is not a logical method to white plague, when a large area of the body (50%) is affected less profound skin is acquirable. But, it is todays gold standard approach6. Further trauma, due to grafting, can be painful to a patient who is already in a exact responsibility. Also, scar general anatomyation post-operatively is another reason for its reduced usage. Full-thickness grafts are sufficient to habituate when the burned area is less than 2% of the total area. These problems could be avoided if skin (of full or partial thickness) were grown artificially and substituted in the place of real skin6.LITERATURE REVIEWThe skin can be slackly divided into two layers i.e. the epidermis dermis. The epidermis is made up of several layers and may/may not consist of extra- cubicleular matrix (ECM). The layers from draw close to deep are cornified, granular, spinosal and basalar layers. The most normally found cells here are the keratinocytes melanocytes. The dermis is constituted by GAGs proteins. Within the dermis, fibroblasts are most comm notwithstanding found8. Several skin substitutes exist for injury coverage in tissue engineering4. It can be broadly divided into temporary and permanent skin substitutes. The table below (Table 1) is a list of all the material options availab le for skin replacement Table 1 Temporary and Permanent shin Substitutes8 Permanent tissue engineering of the skin can be broadly divided into three categories6, 8Epidermal replacements Generally, victimisation autologous keratinocyte sheets. Replaces only the epidermis, but take rates are very poor, suitable for picayune burn treatment only. Dermal replacements Replaces only the dermal layer. In most cases, it is applied along with an epidermal graft to improve take rates.Dermo-epidermal (bilayer skin) replacements Replaces both the epidermis and dermis. Suitable for full-thickness burns.Skin replacements commence two main components i.e. cells and the hold up. In wound coverage, three types of cells can be used autologous, allogenic or stem cells. Autologous (self) cell usage is the most preferred as it is easily accepted by the patients body does not need run and anti-immune responses. Allogenic (donor) cells, if used directly can lead to the eventual rejection of the transplant. However, it is used in an acellular fashion, where the donor keratinocytes are removed prior to culturing9. Stem cells have trans-germal pluripotential properties are currently being researched for their poteintial application in skin engineering. slight information is obtained on keratinocyte stem cells. The suggested reason for their longevity is that KSC cycles very soft and is resistant to mutations8. The type of biodegradable scaffold, either natural or semisynthetic permits cells to attach onto them and facilitate handling during transplantation6, 9.Rheinwald Green Experiment8The experiment carried out in 1975 by Rheinwald and Green where valet de chambre (autologous) keratinocytes were attaind in-vitro, proved to be a find in this field and modified versions of this method are used nowadays. Extracted keratinocytes were allowed to form colonies on a plastic substrate. These colonies expanded to form a sheet. Stratifications arose as the daughter cells, u sually at the centre, started multiplying vertically and a 12-cell layer was achieved. To amplification the multiplicative capacity of keratinocytes, a feeder layer (comprising murine Swiss 3T3 lethally irradiated fibroblasts) mitogens were introduced to the polish. Epidermal Replacements A small skin biopsy of the patient is harvested, which is closed to produce a patch. The full-thickness biopsy of the patients skin is cut finely and enzymes are added to cause disaggregation of the skin into cells. A feeder layer, as mentioned previously, is used to burnish these cells in culture flasks. To promote proliferation, epidermal growth factors, enzymes such(prenominal) as insulin, hydrocortisone, cholera-toxin and bovine blood serum are used. After colonies have been formed, trypsin is added. The KCs are gracious to confluence and later, the sheets are removed from the flasks ( utilize dispase) for use8. The result of this method compared to the split-thickness gold standard is q uite poor, as the dermal layer is missing and it depends upon the health of the dermis existing. Also, it is prone to scarring, takes too long, expensive, extremely fragile and has varying take rates6. Dermal Replacements It was claimed, in 1952, that using only pure epidermal sheets, success would be lesser than compared to those with a dermis10. To accentuate the success of the epidermal transplantation, dermal replacements were constructed. A dermal replacement that covered the affected area with cryoprserved allogenic skin was used minus the epidermal layer was used11, 12. Also, an observation that allogenic keratinocytes elicited more anti-immune response than allogenic fibroblasts, was account. To reconstruct the dermis, the two-stage Integra application is most widely used now13. This dermis functions as a scaffold for the attachment of keratinocytes and improves vascularization9. Burke et al (1981) developed a dermal replacement, where a collagen sponge was covered with a silastic layer (synthetic). The sponge behaves as a scaffold for the fibroblast cells. This technique was commercialized into a product (Integra Dermal vicissitude Template) 9, 14. A modification to this employed GAGs along with collagen, in the scaffold. Here, a precipitated commixture of bovine collagen fibres and a chondrotin-6-sulfate (GAG from shark cartilage) was freeze dried. This generated a collagen-GAG sponge scaffold, which had a mean pore size. Cross-linkage to strengthen the matrix was done using gluteraldehyde. Finally, the silastic layer was applied. This is available as a product Integra Artificial Skin (Chamberlain and Yannas, 1999)9, 15. According to Heimbach et al (1988), this is most suitable for burns patients. The concept of using absorbable polymer scaffolds (synthetic) such as polyglactin 910 or polyglycolic acid was the next expediency in dermal replacements. Here, allogenic fibroblasts are enzymatically well-behaved and this culture is mounted on the polymer scaffold for integration). Due to this, an ECM consisting of collagen, growth factors, GAGs etc. is formed, which stays active voice even after it is frozen17. This was commercialized as Dermagraft 8, 16. Two-stage dermis application has shown be results, and now clinical exams are being conducted to examine the applicability of one-stage dermis, such as Matriderm 6. The dermal replacements essentially require an epidermal covering. Dermo-Epidermal ReplacementsThese are available both as autologous or off-the-shelf products. In autologous DED replacements, both keratinocytes and fibroblasts are harvested from the patient and are added to the collagen-GAG scaffold. Cultivation of this in culture medium is for around four weeks. This is a more permanent issue 6, 18, 19. The first model of todays Apligraf was done by Bell et al (1979)20. DEDs use human keratinocytes fibroblast cells (allogenic) within a scaffold. Morphological studies after using Apligraf reported the prese nce of a well-defined epidermis, with all four layers, as in the natural skin, and seeded allogenic fibroblasts aligned in a normal manner within the collagen matrix 8, 21.COMMERCIALLY AVAILABLE PRODUCTSCONCLUSION FUTURE AIMSTissue engineering of the skin was the first to be approved by the FDA has evolved a great deal, from the first application of only cultured keratinocytes to the use of biological skin substitutes. Research is still in-progress to develop skin in bulk quantities, mainly for burns patients, and to mimic all the mechanical and properties and functions of the natural skin. The state of the art results can be achieved now by using cultured keratinocyte cells with the dermal replacement, Integra, in full-thickness, small and clean wounds. This has shown optimal results in cosmesis and wound closure8. However, this branch of tissue engineering is still very much in a developing level. Studies to analyse how to reduce various risks in patients, who notice donor cell s should be done. Also, a main difficulty is in acquiring the cells to attach to the dermis, post-transplantation. Burns patients are highly susceptible to various problems, thus there is a need for materials that present lower risk than living creature/human materials. Mainly, it is ideal if the graft starts to behave like natural skin soon after grafting, which is possible only with rapid vascularization and cell implantation. Also, low expense of these products is extremely desirable.REFERENCESNerem R M. 1992. Tissue engineering in the USA. Medical Biological Engineering Computing, Vol 30, pp. CE8-CE 12.Burn Incidence and Treatment in the United States 1999 Fact Sheet (The Burn Foundation, Philadelphia, 1999).Rose, J. K. Herndon, D. N. Advances in the treatment of burn patients. Burns 23 (suppl. 1), S19-S26 (1997).McNeil S. 2007. Progress and opportunities for tissue-engineered skin. Nature. Vol 445 (22), pp. 874-880.Pomahac B, T. Svensj, F. Yao, H. Brown and E. Eriksson. 1998 . Critical Reviews in viva voce Bioogy and Medicine. Vol9 pp. 333-344.Bottcher-Haberzeth S, T Bedermann, E Reichmann. 2009. Tissue engineering of skin. Burns, doi10.1016/j.burns.2009.08.016Burn flaw Occurrence is higher in Developing Countries. gettable from http//en.wikipedia.org/wiki/Burn value R, E Anthony, S Myers and H Navsaria. Chapter 17 Tissue engineering for Skin Transplantation. In Clemens van Blitterswijk, Peter Thomsen, Anders Lindahl, Jeffrey Hubbell, David F. Williams, Ranieri Cancedda, Joost D. de Bruijn and Jrme Sohier eds., Tissue Engineering. Elsevier Inc, Pp. 507-532.Morgan J R, R L Sheridian, R G Tompkins, M L Yarmush and J F Burke. 2004. Chapter 7 Applications of Materials in Medicine, Biology and Artificial Organs (7.12). In B D Ratner, A S Hoffman, F J Schoen and J E Lemons eds., Biomaterials Science. Elsevier Academic Press, pp. 602-614.Billingham, R.E. and Reynolds, J. 1952. Transplantation studies on sheets of pure epidermal epithelial tissue and on epi dermal cell suspensions. British daybook of Plastic Surgery, Vol 5, pp. 25 36.Cuono , C.B. , Langdon , R. , e t al. 1987. Composite autologous-allogeneic skin replacement development and clinical application. Plastic Reconstruction Surgery, Vol 80, pp 626 637.Heck , E.L. , Bergstresser , P.R. , e t al. 1985. Composite skin graft frozen dermal allografts support the engraftment and expansion of autologous epidermis . Journal of Trauma, Vol 25, pp. 106 112.Heimbach, D .M., W arden, G .D., e t al. ( 2003 ). Multicenter postapproval clinical trial of Integra dermal regeneration template for burn treatment. Journal of Burn parcel out Rehabilitation, Vol 24, pp. 42 48 .Burke, J.F. , Yannas , I.V. , e t al. ( 1981 b ). Successful use of a physiologically acceptable artificial skin in the treatment of extensive burn injury. Annals of Surgery, Vol 194, pp. 413 428.Chamberlain L J, Yannas I V. 1999. Preparation of collagen-glycosaminoglycan copolymers for tissue regeneration. In Method s in Tissue Engineering, J R Morgan and M L Yarmush eds. Humana Press, pp. 3-17.Hansbrough, J.F. , Cooper , M.L., et al. 1992a. Evaluation of a biodegradable matrix containing cultured human fibroblasts as a dermal replacement beneath meshed skin grafts on athymic mice. Surgery, Vol. 111, pp. 438 446.Cooper , M.L. , Hansbrough , J.F. , e t al. 1991. In vivo optimization of a living dermal substitute employing cultured human fibroblasts on a biodegradable polyglycolic acid or polyglactin mesh. Biomaterials, Vol. 12, pp. 243 248.Pham C, Greenwood J, Cleland H, Woodruff P, Maddern G. 2007. Bioengineered skin substitutes for the management of burns a systematic review. Burns Vol. 33, pp. 946-57.Boyce ST. 2001 Design principles for composition and performance of cultured skin substitutes. Burns Vol. 27, pp. 523-33.Bell , E. , Ivarsson , B. , e t al. 1979. Production of a tissue like structure by contraction of collagen lattices by human fibroblasts of different proliferative potential in vitro. Proceedings of the National Academy of Science, Vol. 76, pp. 1274 1278.Parenteau , N.L. , Bilbo , P. , et al. 1992. The organotypic culture of human skin keratinocytes and fibroblasts to achieve form and function. Cytotechnology, Vol. 9, pp. 163 171.Apligraf Structure vs. Skin Structure. Available from http//www.organogenesis.com/images/apligraf_main3.jpgFig. 3, Collagen GAG scaffolds for Tissue Engineering. Pek et al, 2004, Biomaterials. Available from http//web.mit.edu/dmse/csg/Tissue_Regeneration.htmlFig. 3, Collagen GAG scaffolds for Tissue Engineering. OBrien et al, 2004, Biomaterials. Available fromhttp//web.mit.edu/dmse/csg/Tissue_Regeneration.html