tissue engg appli'n

8/8/2019 Tissue Engg Appli'n

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PRESENTED BYASMITA BENICHATAGEMBT-09039


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Tissue engineering is an interdisciplinary field

that applies the principles of engineering andthe life sciences towards the development of

biological substitutes that restore, maintain,

or improve tissue function.Langer and J. Vacanti Tissue Engineering. Science 1993.


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Engineering at the Genetic and Molecular Level-Towards Genetically Designed Tissues for Regenerative Medicine

- Posttranscriptional Gene Silencing

- Biomolecule Use in Tissue Engineering

Engineering at the Cellular Level- Fetal Tissue Engineering: Regenerative Capacity ofFetal Stem Cells

-Embryonic Stem Cell Use

-The Unrestricted Somatic Stem Cell (USSC) From Cord Blood For Regenerative Medicine

- Mesenchymal Stem Cells: New Insights Into Tissue Engineering and Regenerative Medicine

Engineering at the Tissue Level- Cartilage Engineering

- MuscleTissue Engineering

-

Bone Tissue Engineering- Tendon and Ligament Tissue Engineering: RestoringTendon/Ligament and Its Interfaces

- Neural Tissue Engineering and Regenerative Medicine

Engineering at the Organ Level-Breast Tissue Engineering

-Bioartificial Liver

-Pancreas Engineering

-Tissue-Engineered Urinary Bladder-Cell-Based Regenerative Medicine for Heart Disease


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In Neurology In Maxillofacial Surgery In Dental Implantology In General Surgery Regeneration of Renal Tissues In Plastic Surgery Cardiovascular Substitutes

Skin Substitutes In Orthopedic Surgery In Endocrinology In Hematology


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In vitro tissueengineering

In vivo tissue engineering

Ex vivo tissueengineering

Langer and J.Langer and J. VacantiVacanti TissueTissue

Engineering.Engineering. Science,Science, 1993.1993.


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(1) Start building material (e.g., extracellular matrix,biodegradable polymer)

(2) Shape it as needed(3) Seed it with living cells

(4) Bathe it with growth factors(5) Cells multiply & fill up the scaffold & grow intothree-dimensional tissue

(6) Implanted in the body(7) Cells recreate their intended tissue functions(8) Blood vessels attach themselves to the new tissue

(9) The scaffold dissolves(10)The newly grown tissue eventually blends in with itssurroundings

General Steps For Tissue Engineering


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Our skin is a major organ of the body that acts asa barrier to pathogens and trauma Largestlaminar organ.

Skin defects caused by burns, venous anddiabetic ulcers, or acute injury occasionallyinduce life-threatening situations.

Thus, the need for a functional and cost-effectivepermanent skin substitute for burn victims hasalways been garnered.


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Epidermis (5 layers)Keratinocytes provide protective properties.

Melanocytes provide pigmentation.

Langerhans cells help immune system.

Merkel cells provide sensory receptors.

Dermis (2 layers)Collagen, glycoaminoglycans, elastine, ect.

Fibroblasts are principal cellular constituent.

Vascular structures, nerves, skin appendages.

Hypodermis (fatty layer)Adipose tissue plus connective tissue.

Anchors skin to underlying tissues.

Shook absorber and insulator.


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Essential Design Properties

"The initial replacement material should provide immediatephysiologic wound closure and be eliminated once it has providedsufficient information for reconstitution of neodermis

It should protect the wound by providing a barrier to the outside

It should control water evaporation and protein and electrolyte loss

It should limit excessive heat loss

It should decrease pain and allow early mobilization

It should provide an environment for accelerated wound healing

The risk of infection must be taken into account


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Skin substitutes classified as Permanent or temporary Epidermal, dermal or composite Biological or alloplastic (synthetic)

Temporary-material designed to be placed on a fresh wound (partial

thickness) and left until healed

Semi-permanent-material remaining attached to the excised wound andeventually replaced by autogenous skin grafts

Permanent-incorporation of an epidermal analogue, dermal analogue, or

both as a permanent replacement


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Biologicals (Naturally occurring tissues) Cutaneous allografts Cutaneous xenografts Amniotic membranes

Skin substitutes Synthetic bilaminates Collagen-based composites

Collagen-based dermal analogues Deepithelized allografts

Culture-derived tissue substitues Cultured autologous keratinocytes (sheet grafts, cell suspensions) Bilayer human tissue Polyglycolic or acid mesh Fibroblast-seeded dermal analogs Collagen-glycosaminoglycan matrix Epithelial seeded dermal analogs


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Rapid and effective burn wound closure-imp aspect

Early surgical removal of heat-denatured proteinsand devitalized tissue from a wound

Lack of autograft- overcome by use of synthetic

replacements

Initial use of allografts may undergo immunogenic

rejection


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Rheinwald JG, Green H.Serial cultivation of strains of human epidermal keratinocytes

Human diploid epidermis epidermal cells were successfully grown in serial culture. To initiate colony formation, they require the presence of fibroblasts, but proliferation of

fibroblasts must be controlled so that the epidermal cell population is not overgrown.

Both conditions can be achieved by the use of lethally irradiated 3T3 cells at the correctdensity. When trypsinized human skin cells are plated together with the 3T3 cells, the growth of the

human fibroblasts is largely suppressed, but epidermal cells grow from single cells intocolonies.

Each colony consists of keratinocytes ultimately forming a stratified squamous epithelium inwhich the dividing cells are confined to the lowest layer(s).

Hydrocortisone is added to the medium, to make the colony morphology more oderly and

distinctive, and maintains proliferation at a slightly greater rate. Under given culture conditions, it is possible to isolate keratinocyte clones free of viable

fibroblasts. Like human diploid fibroblasts, human diploid keratinocytes appear to have a finite culture

lifetime. The plating efficiency and culture lifetime were lower for keratinocytes of older persons.


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Epidermis Anatomy- Here are four major layers of keratinocytes(the structural cells) in the epidermis.

The stratum basale, has cells that are shaped like columns.In this layer the cells divide and push already formed cells into

higher layers.As cells move into the higher layers, they flatten and eventually

die.


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This technique allows growth of the epidermis from a singlesmall skin biopsy within 34 weeks

2 culture of isolated colonies of epithelial cells

Approaches for skin culture substitutes in vitro

3 Cell culture ofmultilayered epithelial transplants (commonlytermed sheet grafts)

3 Growth and construction ofcompositemultilayered dermal-epidermal analogues

3 Growth and transplantation ofpre-confluent cell grafts (culturedor non-cultured)


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The growth of multilayered cultured epithelialsheets of human autologous keratinocytes-Permanent substitute

Affecting factors High cost Hospital readmissions for reconstruction of

contractures

Wound infection- fragile epithelium and partiallydeveloped dermoepidermal junction

Thus 2 devices necessary to manipulate CEA tohandle fragile cell layers

Less adherence to wound region


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Such keratinocyte-fibrin suspensions(KFSs) canbe made available for grafting within 10 days ofseeding

Thus KFSs preferred over CEA (3-4 weeks) Lack of dermal structures using keratinocyte

alone lead to combination of a preliminary wound bed preparation by

allografts, followed by subsequent KFS transplantation

together with meshed split-thickness allograftskin as an overlay


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Problems with purely epithelial cell grafts have induced thecombination of cultured autologous keratinocytes with variousalloplastic dermal regeneration templates

trypsinized whole-skin-cell suspensions (uncultured keratinocytes

and fibroblasts) centrifuged into a collagen-glycosaminoglycan (C-GAG) matrix and grafted onto guinea pigs were able to facilitatethe regeneration of a healthy epidermis

Compound materials has been propagated for reconstructive andburn surgery that consists of

(1) a well-characterized, so-called dermal portion that consists of

a porous lattice of fibres of a cross-linked bovine collagen andGAG that is supposed to be replaced by new collagensynthesized by fibroblasts that grow in on fullthickness wounds

(2) a so-called epidermal cover of synthetic polysiloxane polymer(silicone)

Collagen integrates into wound bed, silicone layer peeled off


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Pre-confluent human keratinocyte monolayergrafts have also been used in combination withbiological carrier materials

proliferating basal cells which are responsible forthe initial reformation of an epithelium can betransplanted upside down with the carrier on topas a bio-dressing

One of the most common materials has been C-GAG, with or without the cover of a gas-permeable silastic membrane that serves as abarrier to fluid loss


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Many unsolved mysteries yet to solve Research aim is to replace with a truly

functional skin inclusive of all dermalappendages that are of permanent skin-likequality

perhaps the definitive breakthrough will

come through the ability to replace worn out,defective or damaged body parts usingtechnologies that resemble naturalregeneration.


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Fundamentals of Tissue Engineering and

Regenerative Medicine, by U. Meyeret al

Essentials of Stem Cell Biology, by RobertLanza

Rheinwald JG, Green H. Serial cultivation of

strains of human epidermal keratinocytes: the

formation of keratinizing colonies from single

cells. Cell 6 (3): 33143, 1975


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