Chitosan-polyvinyl pyrrolidone hydrogels as candidate for islet immunoisolation: In vitro biocompatibility evaluation

The success of immunoisolation devices for islet transplantation depends on the nature of semipermeable membranes. which permit the crossover of micro nutrients, glucose, and insulin and prevent the entry of immunocytes and ot her transplant rejection mechanisms. In the present study we examined the p roperties of chitosan-polyvinyl pyrrolidone (PVP) hydrogels for possible ap plication as an immunoisolation device. Hydrogels with two different propor tions of chitosan-PVP (M 1 1:1 and M2 2.1, v/v) were synthesized by cross-l inking with glutaraldehyde. Hydrogels were characterized for their hydrophi lic nature, protein adsorption, diffusion propel ties, cytotoxicity, and is let compatibility. Hydrogel membranes were found to be hydrophilic as deter mined by high octane contact angle value (M1: 142.9 +/- 0.46; M2: 143.6 +/- 0.49). Protein adsorption on the hydrogels was found to be low (0.0143 +/- 0.0027 mg for M1 and 0.0136 +/- 0.0049 mg for M2) compared to tissue cultu re polystyrene (TCPS) (0.0434 +/- 0.001 mg) and pure chitosan (0.0214 +/- 0 .0025 mg) control. Hydrogel M1 was tested as a representative for diffusion studies. M1 allowed regulated transport of insulin and did not allow anti- insulin antibodies to pass through. In vitro biocompatibility of M1 and M2 was found to be excellent with no cytotoxic effects on the HeLa cells as de termined by MTT and NR assay. Mouse islets cultured on the hydrogel membran es retained their integrity and intact morphology as assessed by image anal ysis study. Viability of islets cultured on hydrogels was comparable to tha t of controls (M1: 97%: M2: 90.4%) as assessed by trypan blue dye exclusion test. Islets retained their functionality when cultured on hydrogels, as j udged by insulin secretion in response to glucose challenge (16.0 mM). Alth ough in vivo experiments an awaited, the present study provides sufficient documentation to consider chitosan-PVP membranes as potential candidates fo r immunoisolation of islets.