Title: Regenerating skin tissue by utilizing bioink in 3D printing
In the past few years, advances in 3D printing and especially in bioprinting, have given a broad overview of the exponential amount of possibilities that can be the future of the regenerative medicine. Despite these technological advances, complications continue to challenge the development of fully functional models that recapitulate natural complexities in the native tissue. Presently, there has not been a perfectly successful design of 3D printed skin. This proposal will delineate new strategies for designing skin to further the research and development in this field.
Bioprinting is an additive manufacturing advancement, where it can deposit living cells, biomaterials and growth factors into complex 3D structures Bioprinting processes aim to produce biological structures similar to native tissues or organs in terms of their functions and morphology using scaffold based or scaffold free approaches. Current bioinks for skin printing rely on homogeneous biomaterial, which has several shortcomings such as insufficient mechanical properties. 
Collagen is a widely used bioink in skin regeneration due to its good biocompatibility and biodegradability. It is used as biomaterial for skin tissue engineering because of its low risk of an allergic response or disease transmission[6, 7] However, the poor mechanical properties of collagen that results in fast degradation, severe contraction, and limited lifespan limit its application as a skin substitute.Other skin cell types such as: endothelial cells, adipocytes, hair follicles, and melanocytes have similar properties to collagen.
Recently, polyamidoamine dendrimers (PAMAM) were blended into a gelatine-based scaffolds for skin tissue engineering. The study demonstrated that addition of PAMAM did not significantly alter the porosity of the scaffolds. However, water adsorption potential and collagenase mediated degradation significantly enhanced over period of the study. . Due to PAMAM’s low cytotoxicity level, perfectly controllable size, and ease of modification, it has long been used in biomedical fields. Despite their immense popularity in biological related fields such as drug delivery, molecular imaging, and multivalent display; dendrimers have been under-utilized in the field of tissue engineering and wound repair. 
A research team in Madrid, recently developed a modified extrusion bioprinter using a combination of plasma, fibroblasts, calcium chloride and keratinocytes.The printed product was polymerised on a plate before being grafted on to the backs of immunodeficient mice for eight weeks; the longest experiment of its kind to date. There is a clear indication of proper and complete differentiation of the grafted printed skin. The biggest breakthrough of the experiment was the ability to complete the print in less than 35 minutes.
1) Can different type skin cell types replace collagen scaffolds for better mechanical properties and preventing vascularity?
2) Can using polyamidoamine dendrimers as bioink provide support to other natural materials that assist in wound healing?
3) Can I use stem cells in bioprinting to increase regenerative properties of skin for wound healing?
Skin is the largest organ in the human body and injury or damage to tissue and organs is a major health problem, resulting in about half of the world’s annual healthcare expenditure every year. Approximately 67 million people (1% to 5% of the world’s population) worldwide suffer from chronic skin wounds. Recently, new developments have enabled the potential for 3D printers to produce skin, with a biomaterial, bioprinted membrane that provides the capability to heal wounds, trauma and even disease. Many teams all over the world are trying to develop the world’s first 3D printed skin with all the same mechanical properties as native skin; this discovery will profoundly affect the medical field.
Connection to current body of knowledge:
Last week a journal investigated the tissue-specific bioink that makes up 3D cell printing. I am going to replace the most popular bioink to date, collagen with a different type of skin cell. Collagen has excellent biocompatibility but lacks in every other property. Endothelial cells are the interior surface of the blood vessel and will allow for more complex skin to be printed as other skin cells cannot modify blood vessels; this shall help with vascularity. This addresses my first research question.
Recently, a study has shown that blending polyamidoamine dendrimers (PAMAM) into matrix scaffold of synthetic polymers could provide an additional support to scaffold assisted wound healing. Gelatine is very popular; however, its poor mechanical strength, low elasticity and thermal stability limit its application requiring PAMAM to strengthen and support it. Due to its low cytotoxicity level, perfectly controllable size, and ease of modification, PAMAM dendrimers have been under-utilized in the field of tissue engineering and wound repair . I am going to implement PAMAM into bioink so that it can directly be 3D printed within skin. This shall interact with other natural materials such as: collagen or keratinocyte to generate skin with the ideal properties for wound healing and regeneration . This addresses my second research question.
Furthermore, in Madrid researchers’ have developed a modified extrusion bioprinter. The results showed a clear indication of grafted printed skin in an astonishing 35 minutes. However, the mechanical properties of the skin printed are not promising for future skin regeneration. I am going to use the technique of the extrusion bioprinter but change the material In their experiment they used proteins and plasma, instead I shall use stem cells. Stem cells’ maintains the skin epidermis and promotes healing. Combining the stratified method of the printer with biomaterials that not only within the skin but have mechanical properties designed for skin regeneration is the optimum way to print skin quickly and accurately. This addresses my third research question.
In this research proposal I have presented new strategies for 3D printing skin tissue with differing materials. This proposal is to ensure the quality of life for so many people suffering with burn wounds, skin diseases and trauma. Furthermore, the problems I have identified and potentially solved should path a way for future research into this field.
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