Decellularized scaffolds for skin tissue engineering School of Advanced Technologies in medicine, Tehran University of Medical Sciences Decellularized scaffolds for skin tissue engineering Prof. Jafar Ai Dr. Somayeh Ebrahimi Dr. Somayeh Ebrahimi

The skin is the largest organ in the human body. It consists of about 10% of our body mass. Dr. Somayeh Ebrahimi

The Anatomy of Human Skin 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. Dr. Somayeh Ebrahimi

Keratinocytes and Fibroblasts

Skin defects caused by burns, venous and diabetic ulcers, or acute injury occasionally induce life-threatening situations. Many burned people die, their body couldn’t produce new skin Dr. Somayeh Ebrahimi

Burn Classification Dr. Somayeh Ebrahimi Skin defects can be divided based on their depth of injury as: I) epidermal II) superficial partial-thickness III) deep partial-thickness and full-thickness skin wounds Dr. Somayeh Ebrahimi

Skin Grafting Dr. Somayeh Ebrahimi In the past, a burn victims only option for repair was a method known as a skin graph. This requires doctors to surgically cut a piece of unburned skin from your body and place it on the burned area. This can cause bleeding, infection, nerve damage, and in some cases, a repeat graph is required. Dr. Somayeh Ebrahimi

Tissue engineering scaffolds Growth factors cells Organ transplantation is an approach for the repair and replacement of unhealthy tissues or organs, but is often hindered by death of donor tissues/organs and immunological problems associated with infectious diseases. scaffolds Growth factors cells

Decellularized scaffolds The process of decellularization of a scaffold involves the discharge of cellular contents from the tissues or organs, retaining only the components of the native ECM. The decellularized scaffolds can later be recellularized with suitable cells for the purpose of creating tissue-engineered grafts suitable for tissue/organ transplantation.

In addition, it can be tailor-made with all the characteristic features of an ideal scaffold, such as: Biocompatibility Biodegradability Non-immunogenicity and the ability to provide structural, mechanical, biochemical and biological cues for cell adhesion, proliferation, migration, differentiation and continued function, with a hope of potential clinical translation. Therefore, the decellularized scaffold can be considered to be an attractive system for tissue engineering.

Current state of decellularization methodologies Physicals Chemicals Enzymatic

Physical methods

Chemical methods Acids and bases Non-ionic detergents (Triton X-100) Ionic detergents (SDS) Zwitterionic detergents (CHAPS and SB-10/SB-16) Tri(n-butyl)phosphate (TnBP) Hypotonic and hypertonic treatments Chelating agents Alcohols and acetone

Enzymatic methods Protease Trypsin: cleaves peptide bonds on the C-side of Arg and Lys Dispase: selectively cleaves specific peptides, mainly fibronectin and collagen IV Nuclease DNase RNase Lipase

Protease inhibitors Protease inhibitors such as phenylmethylsulfonylfluoride (PMSF), Aprotonin, and Leupeptin A buffered solution of pH 7–8 further inhibits many proteases Control of temperature and time of exposure to the lysis solutions can also limit the activity of the proteases.

The advantages of decellularization Minimizes immunological response upon implantation Allows for the use of xenogeneic materials Ability to conserve the mechanical integrity of native tissue Ability to retain the biochemical composition of native tissue Ability to retain the three-dimensional microarchitecture of native tissue Retains the bio inductive properties (cryptic peptides) to facilitate tissue remodeling Widely applicable and economical Long-term storage capability Potential for an off-the-shelf product

Small Intestine Sub-mucosal layer (SIS) Reagents SDS, TritonX-100, SDC, per-acetic acid Decellularization method Immersion, agitation, perfusion

Before processing After processing

Recellularization Tissue-engineered skin exists as cells grown in vitro and subsequently seeded onto a scaffold or some porous material which is then placed in vivo at the site of injury.

Process of Skin Engineering Patient has a skin biopsy The skin is then peeled and separated into the epidermis and dermis. Keratinocytes and Fibroblasts are then isolated from one another. Transferred into a culture on top of a scaffold. The final skin is finished after about 3 to 4 weeks.

Towards the Future Dr. Somayeh Ebrahimi Skin engineering still has much room to evolve. More dermo-epidermal substitutes will be created that will speed the process and the wait time for the patient. An increase of “off the shelf” dermal and epidermal substitutes will allow patients quick and easy access to repairing their burns or wounds. A skin that includes sweat glands and hair follicles to help mimic real skin is also being created. In the future, engineered skin will replace skin graphs as the predominant method for treating skin defects. Dr. Somayeh Ebrahimi

Thanks for your attention Dr. Somayeh Ebrahimi