Emerging strategies to bypass transplant rejection via biomaterial-assisted immunoengineering: Insights from islets and beyond

Novel transplantation techniques are currently under development to preserve the function of impaired tissues or organs. While current technologies can enhance the survival of recipients, they have remained elusive to date due to graft rejection by undesired in vivo immune responses despite systemic prescription of immunosuppressants. The need for life-long immunomodulation and serious adverse effects of current medicines, the development of novel biomaterial-based immunoengineering strategies has attracted much attention lately. Immunomodulatory 3D platforms can alter immune responses locally and/or prevent transplant rejection through the protection of the graft from the attack of immune system. These new approaches aim to overcome the complexity of the long-term administration of systemic immunosuppressants, including the risks of infection, cancer incidence, and systemic toxicity. In addition, they can decrease the effective dose of the delivered drugs via direct delivery at the transplantation site. In this review, we comprehensively address the immune rejection mechanisms, followed by recent developments in biomaterial-based immunoengineering strategies to prolong transplant survival. We also compare the efficacy and safety of these new platforms with conventional agents. Finally, challenges and barriers for the clinical translation of the biomaterial-based immunoengineering transplants and prospects are discussed.

Metal-coordination synthesis of a natural injectable photoactive hydrogel with antibacterial and blood-aggregating functions for cancer thermotherapy and mild-heating wound repair

Photothermal therapy (PTT) is a promising approach for treating cancer. However, it suffers from the formation of local lesions and subsequent bacterial infection in the damaged area. To overcome these challenges, the strategy of mild PTT following the high-temperature ablation of tumors is studied to achieve combined tumor suppression, wound healing, and bacterial eradication using a hydrogel. Herein, Bi₂S₃ nanorods (NRs) are employed as a photothermal agent and coated with hyaluronic acid to obtain BiH NRs with high colloidal stability. These NRs and allantoin are loaded into an injectable Fe³⁺-coordinated hydrogel composed of sodium alginate (Alg) and Farsi gum (FG), which is extracted from Amygdalus scoparia Spach. The hydrogel can be used for localized cancer therapy by high-temperature PTT, followed by wound repair through the combination of mild hyperthermia and allantoin-mediated induction of cell proliferation. In addition, an outstanding blood clotting effect is observed due to the water-absorbing ability and negative charge of FG and Alg as well as the porous structure of hydrogels. The hydrogels also eradicate infection owing to the local heat generation and intrinsic antimicrobial activity of the NRs. Lastly, in vivo studies reveal an efficient photothermal-based tumor eradication and accelerated wound healing by the hydrogel.