Biocompatibility and physicochemical characteristics of alginate-polycation microcapsules

There is a need for better understanding of the biocompatibility of alginate-polycation microcapsules based on their physicochemical characteristics. Microcapsules composed of alginate with 44% (IntG) or 71% (HiG) guluronate, gelled with calcium (Ca) or barium (Ba) and coated with poly-l-lysine (PLL) or poly-l-ornithine (PLO), followed by IntG alginate were compared. For microcapsules with an IntG(Ca) gel core, using PLO instead of PLL resulted in less immune cell adhesion after 2 days in C57BL/6J mice. The PLO microcapsules were also characterized by greater hydrophilicity and superior resistance to swelling and damage under osmotic stress. For microcapsules with a PLL membrane, replacing the IntG(Ca) gel core with IntG(Ba) or HiG(Ca) gel resulted in stronger immune responses (p < 0.05). This was explained by poor penetration of PLL into the gel, as demonstrated by Fourier transform infrared spectroscopy analyses and membrane rupturing during osmotic swelling. X-ray photoelectron spectroscopy analyses show that all microcapsules had the same amount of polycation at their surface. Moreover, alginate coatings had non-significant effects on the biocompatibility and physicochemical properties of the microcapsules. Thus, alginate-polycation interactions for membrane formation are more important for biocompatibility than either the quantity of polycation at the surface or the alginate coating.