A bioactivated nano-layered hydrogel for dermal regeneration in hard-to-heal ulcers

The goal of the project within material-guided tissue regeneration (so-called tissue engineering) in wound care is to develop a material that promotes complete and scar-free regeneration of tissue to recreate a functional outer barrier (for example mucosa or skin). In humans, mucous membranes and skin represent approximately one seventh of body mass. Almost all trauma, infection or surgical procedures involve breaching this outer barrier and producing a wound. In healthy people and under normal conditions, the skin and mucous membrane regenerate quickly and restore the integrity of the tissue with full cell coverage. However, should the situation be challenged by extensive trauma, burns, infections, chronic inflammation, metabolic disease or other disease processes, the result is a wound that heals slowly or not at all, often with life-impairing or even life-threatening consequences. By gathering complementary material expertise and biological expertise, the BioNaNOR project has managed to construct a layered, nanostructured and fiber-reinforced aqueous gel (so-called hydrogel) based on a chemically modified version of the marine product chitosan. This layered gel is completely biodegradable and is well suited for the ingrowth and organization of skin cells and at the same time has properties that makes it suitable for clinical use. This synthetic skin analogue have structure and properties similar to normal skin and is made with an inside facing the wound surface, which can also act as a depot for biological signals that summon stem cells from surrounding tissues and provide instructions for normal cell maturation and ultimately complete regeneration og the depper dermal layers. In addition, the surface layer that faces the outside, has been added with biological molecules that promote the migration and growth of the skin's surface cells, so that the material quickly acquires a covering of skin. This advanced hydrogel is degradable in the body and is completely replaced during wound healing by natural skin. During this process, the material thus slowly releases the embedded bioactive molecules together with chitosan metabolites known to support regeneration by reducing inflammation and protecting against invading microbes. In order to safeguard the skin's strength and integrity during clinical use and in the healing phase, the project has also focused heavily on mechanical stability and the material's ability to withstand physical challenges such as stretching, compression and fluid flow. By optimizing the spinning process for chitosan fibres, it has succeeded in producing a fibre-reinforced material which satisfies clinical requirements and at the same time safeguards the biological and medical properties. By arranging the nano-fibres in distinct layers and directions, the material has been designed with a 3D structure that mimics skin and which can support cell growth and regeneration of skin and mucous membranes. The physical strength of the new fibers is three times higher than previously known chitosan-based ones and gives the new material the toughness and tensile strength that are necessary for easy clinical application.

The BioNaNOR material design could constitute a paradigm shift in wound care. Given successful animal and clinical trials, the material could be the first synthetic tissue nano-engineering material for wound care that have an architecture, biochemical composition and biomechanical strength that mimic natural skin and at the same time be both clinically and industrally applicable. If the material meet the clinical requirement, it will be a big step towards an optimized guided regeneration of skin and mucosa in hard-to-heal ulcers, burns and trauma. Also, the new, advanced, biomimicking material design demonstrated here include principles for designing layered, reinforced nano-level organized hydro-gels for other biomedical applications for tissue regeneration where tissue architecture and/or strength and volume stability and loadability are important features. Thirdly, the non-reinforced layered design of the gel makes its suitable for use as laboratory model(s) for large screening for new wound-care drugs and to study in 4D the invasion, migration and maturation of cells during regeneration of tissues. This could contribute significantly contribute to new discoveries in regenerative medicine and reduce the need for animal experiments and early clinical trials. Last, the new methodology developed in the project, producing significantly stronger fibers from marine chitosan and being able to orient the fibers in 3D, may open new green and sustainable possibilities for other applications in regenerative medicine, food and drug preservation and water treatment to mention some. The natural origin of the material and the complete bio-resorbability combined with the increased strength makes the fibers interesting for designing and producing sustainable plastic-analogues that could contribute to reduce the environmental impact of human medical and industrial activities.

Several strategies have been developed to restore dermal function. These include collagen membranes, decellularized dermis from donors or synthetic graft alternatives. So far, these approaches have been unreliable at best and auto-grafts and transplants (that both create their own problems with donor site morbidity, risk for disease transfer and infections and graft rejection) remain the only predictable method for treating hard-to-heal ulcers today. The major reasons for the failures of these approaches are most probably lack of physical strength combined with poor integration with the subjacent tissues and lack of biological signals that can home in precursor cells (e.g. stem cells and fibroblasts) from surrounding healthy tissues, and finally, the lack of biological signals for epidermis formation. The BioNaNOR project aims at using a dermis-matrix-mimicking hydrogel based on nano-layered and chemically modified chitosan. This artificial dermis analogue will be designed with one “deeper” part that provide biological signals for homing and differentiation of mesoderm derived stem cells, and one “superficial” part that includes molecules that stimulate epithelial cell growth and migration. The nano-layered chitosan matrix is bio-degradable and is ultimately replaced by natural dermal tissue that is later covered by epidermis. During this process, the material slowly releases the embedded bioactive molecules together with chitosan metabolites that are known to favour healing by reducing inflammation and supressing bacterial growth. Moreover, as treatment for hard-to-heal “Full-thickness” ulcers also requires a material that immediately restores and maintain the barrier function and provide tissue strength, stability and elasticity during healing, the BioNaNOR approach include an ultra-strong, nano-layered material that interacts well with the underlaying stratum and restore the tissue barrier until the healing tissues have restored their normal function.