Injectable hydrogels for islet transplantation: a concise review

Islet cell transplantation is a promising alternative for the treatment of type 1 diabetic mellitus which is caused by complete absence or reduced insulin production by pancreas. After Shapiro and his team carried out successful islet transplantation and achieved positive clinical outcomes, much progress have been made in the procedure from isolation to clinical transplantation. Since 2000, more than 1500 patients have undergone islet transplantation. Thus, this therapeutic approach has progressed from mere curiosity to therapeutic achievement. However, many hurdles have yet to be crossed, such as instant blood-mediated inflammatory reaction, immune reactions, side effects of immunosuppressant drugs, lack of donors, islet quality variability, and others. Isolated islet cells face huge mechanical, immunological and bio-physiological challenges that potentially compromise long-term viability and functionality post-transplantation. In addition, preservation of islet cell microenvironment, including extracellular matrix (ECM), is one of the most challenging aspects of the transplantation. ECM is composed of water, proteins, and polysaccharides, and is essential for biochemical, mechanical, and physiological well-being of organs and tissues. ECM also organizes morphological integrity and physiological function by either binding with growth factors or promoting cell surface interactions that result in signal transduction and the regulation of gene transcription. In general, we can say ECM and other biochemical substances constitute a tissue-specific microenvironment that is responsible for growth and proliferation. In this review, we focus on ECM mimicking scaffolds, injectable natural and synthetic hydrogels, their recent advancements, some drawbacks, and future perspectives.