Fibrous tissue encapsulation may slow the diffusion of the target analyte to an implanted sensor and compromise the optical signal. Poly(N-isopropylacrylamide) (PNIPAAm) hydrogels are thermoresponsive, exhibiting temperature-modulated swelling behavior that could be used to prevent biofouling. Unfortunately, PNIPAAm hydrogels are limited by poor mechanical strength. In this study, a unique thermoresponsive nanocomposite hydrogel was developed to create a mechanically robust self-cleaning sensor membrane for implantable biosensors. This hydrogel was prepared by the photochemical cure of an aqueous solution of NIPAAm and copoly(dimethylsiloxane/methylvinylsiloxane) colloidal nanoparticles ( approximately 219 nm). At temperatures above the volume phase transition temperature (VPTT) of approximately 33-34 degrees C, the hydrogel deswells and becomes hydrophobic, whereas lowering the temperature below the VPTT causes the hydrogel to swell and become hydrophilic. The potential of this material to minimize biofouling via temperature-modulation while maintaining sensor viability was investigated using glucose as a target analyte. PNIPAAm composite hydrogels with and without poration were compared to a pure PNIPAAm hydrogel and a nonthermoresponsive poly(ethylene glycol) (PEG) hydrogel. Poration led to a substantial increase in diffusion. Cycling the temperature of the nanocomposite hydrogels around the VPTT caused significant detachment of GFP-H2B 3T3 fibroblast cells.

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The finding that C9-deficient sera (C9D) can kill serum sensitive strains of Gram-negative bacteria by us and other investigators, questions the role of C9 in the membrane attack complex as necessary for cell death. In these studies we have demonstrated that C5b-8 complexes generated on E. coli J5 during incubation in C9-depleted and C9-neutralized sera are effective in killing Gram-negative bacteria. In the same study, we extended our investigations to show that the deposition of C5b-7 complexes (from C8-deficient [C8D], C8 depleted and C8-neutralized sera) is also effective in killing Gram-negative bacteria. In all cases, these studies demonstrated that when E. coli J5 was incubated with C8D, C9D and pooled normal human serum [PNHS], deposited C5b-9 complexes from PNHS produced more killing than C5b-7 or C5b-8 complexes alone. These experiments clearly demonstrated that C5b-7 and C5b-8 complexes are bactericidal and that multimeric C9 within C5b-9 is not an absolute requirement for inner membrane damage and cell death of Gram-negative bacteria.

Biomaterials elicit foreign body responses when implanted into living tissue. While biocompatibility has been improved, the fundamental aspects of tissue responses to biomaterials and their in vivo evaluation remain poorly appreciated. Here, we quantified vascularization of porous poly2-hydroxyethylmethacrylate (polyHEMA) with 40 and 80 µm nominal pore sizes at various time points after implantation in rat subcutis. Solid polyHEMA, silicone, and cotton materials were also studied for comparison. We observed vascularization into the material one week after implantation for both 40 and 80 µm porous polyHEMA. The rate of vascularization was greater in 80 µm polyHEMA, with higher vascular density in the material and adjacent tissues one week and one month post-implantation. The vascular density inside 80 µm polyHEMA reached a maximum one month after implantation. In 40 µm polyHEMA, the vascular density increased gradually over the two months following implantation. After two months, vascularization in the material was similar for both 40 and 80 µm polyHEMA. Notably, despite similar levels of vascularization inside both porous materials at two months, the 80 µm polyHEMA elicited greater vascularization in the critical 100 µm margin of tissue around the implant, compared to other materials. In all materials except 80 µm polyHEMA, we observed a narrow margin of significantly reduced vascularity at the implant-tissue interface. We conclude that implanted 80 µm polyHEMA encourages vascularization, underscoring the importance of rigorous evaluation metrics to assess long-term performance of implanted biomaterials and guide future biomaterial optimization.

Implantable devices induce inflammation and collagen formation, which perturb the metabolic microenvironment and reduce mass transport. This study tested whether novel porous biomaterials improve tissue integration and normalize the glucose gradients. Five materials 700μm thick were implanted into rat dorsal subcutis: cotton cloth, solid silicone elastomer, solid polyHEMA, polyHEMA with 40μm pores, polyHEMA with 80μm pores. Specimens with surrounding tissue were explanted and frozen in liquid nitrogen 1, 4, and 8 weeks after implant. Serial sections were quantified for microvascular density (CD31 antibody), collagen (Masson's trichrome), immune cells (nuclear counterstain) and spatial glucose concentration (bioluminescence). Preliminary results indicate neovascularization of 80μm pore size polyHEMA after 1 week, and complete microvascular infiltration of the 80μm matrix after 4 weeks of implantation. Glucose concentrations in the porous polyHEMA after 4 weeks were comparable to those in the surrounding tissue. At that time, a moderate collagen deposition was observed in the 40 and 80 μm porous polyHEMA. While dense vascularization was also observed with cotton, it had the highest immune involvement. These preliminary findings suggest tissue integrates into porous polyHEMA matrix with a high microvessel density after 4 weeks and a more homogeneous glucose distribution.