Effects of biomaterial-induced inflammation on fibrosis and rejection

The effect of incorporation of SDF-1alpha into PLGA scaffolds on stem cell recruitment and the inflammatory response

Despite significant advances in the understanding of tissue responses to biomaterials, most implants are still plagued by inflammatory responses which can lead to fibrotic encapsulation. This is of dire consequence in tissue engineering, where seeded cells and bioactive components are separated from the native tissue, limiting the regenerative potential of the design. Additionally, these interactions prevent desired tissue integration and angiogenesis, preventing functionality of the design. Recent evidence supports that mesenchymal stem cells (MSC) and hematopoietic stem cells (HSC) can have beneficial effects which alter the inflammatory responses and improve healing. The purpose of this study was to examine whether stem cells could be targeted to the site of biomaterial implantation and whether increasing local stem cell responses could improve the tissue response to PLGA scaffold implants. Through incorporation of SDF-1alpha through factor adsorption and mini-osmotic pump delivery, the host-derived stem cell response can be improved resulting in 3X increase in stem cell populations at the interface for up to 2 weeks. These interactions were found to significantly alter the acute mast cell responses, reducing the number of mast cells and degranulated mast cells near the scaffold implants. This led to subsequent downstream reduction in the inflammatory cell responses, and through altered mast cell activation and stem cell participation, increased angiogenesis and decreased fibrotic responses to the scaffold implants. These results support that enhanced recruitment of autologous stem cells can improve the tissue responses to biomaterial implants through modifying/bypassing inflammatory cell responses and jumpstarting stem cell participation in healing at the implant interface.

Biocompatibility of injectable chitosan-phospholipid implant systems

Injectable biomaterials are desirable therapeutic platforms due to minimal invasiveness and improved patient compliance, and are applicable in such areas as compound delivery and tissue engineering. The present work examined the biocompatibility of injectable blends composed of chitosan, phospholipid and lauric aldehyde (PoLi(gel)-LA) or lauric chloride (PoLi(gel)-LCl). In vitro cytotoxicity was evaluated in L929 and HeLa cell lines. Both blends resulted in acceptable biocompatibility, although greater cell viability was seen with PoLi(gel)-LA. In vivo biocompatibility was investigated in healthy CD-1 mice. Subcutaneous injection of the PoLi(gel)-LA blend caused no local or systemic toxicities over a four-week period while the PoLi(gel)-LCl caused immediate local toxicity. Mice injected intraperitoneally with PoLi(gel)-LA did not show physical or behavioural alterations, and body weight changes did not differ from control animals. Furthermore, histological examination of spleen and liver showed unaltered morphology. Interleukin-6 levels in mice injected with PoLi(gel)-LA did not differ from levels of control animals (6.91+/-3.61 pg/mL versus 6.92+/-5.02 pg/mL, respectively). Biodegradation occurred progressively, with 7.4+/-5.02% of the original injected mass remaining after four weeks. Results obtained herein establish the biocompatibility of PoLi(gel)-LA and indicate its potential for use in various localized therapeutic applications.