Controlling Gel Structure to Modulate Cell Adhesion and Spreading on the Surface of Microcapsules

The surface properties of implanted materials or devices play critical roles in modulating cell behavior. However, the surface properties usually affect cell behaviors synergetically so that it is still difficult to separately investigate the influence of a single property on cell behavior in practical applications. In this study, alginate–chitosan (AC) microcapsules with a dense or loose gel structure were fabricated to understand the effect of gel structure on cell behavior. Cells preferentially adhered and spread on the loose gel structure microcapsules rather than on the dense ones. The two types of microcapsules exhibited nearly identical surface positive charges, roughness, stiffness, and hydrophilicity; thus, the result suggested that the gel structure was the principal factor affecting cell behavior. X-ray photoelectron spectroscopy analyses demonstrated that the overall percentage of positively charged amino groups was similar on both microcapsules. The different gel structures led to different states and distributions of the positively charged amino groups of chitosan, so we conclude that the loose gel structure facilitated greater cell adhesion and spreading mainly because more protonated amino groups remained unbound and exposed on the surface of these microcapsules

In-Situ Grafting MPEG on the Surface of Cell-Loaded Microcapsules for Protein Repellency

<div><p>The protein repelled alginate-graft-BAT/chitosan/MPEG-norbornene (A_BCP_N) hydrogel microcapsules were achieved by copper-free ‘click’ reaction between azides from BAT and alkylenes from norbornene. The MPEG modified polyelectrolyte microcapsules showed significant resistance to immune protein adsorption and good biocompatibility in vivo. Moreover, the mild reaction condition made it feasible that the microcapsules could be formed and modified <i>in situ</i> even when live cells were encapsulated, and precluded the damage cause by other voilent modifications methods to transplanted cells or tissues.</p></div

Enhancement of Surface Graft Density of MPEG on Alginate/Chitosan Hydrogel Microcapsules for Protein Repellency

Alginate/chitosan/alginate (ACA) hydrogel microcapsules were modified with methoxy poly­(ethylene glycol) (MPEG) to improve protein repellency and biocompatibility. Increased MPEG surface graft density (<i>n</i>_S) on hydrogel microcapsules was achieved by controlling the grafting parameters including the buffer layer substrate, membrane thickness, and grafting method. X-ray photoelectron spectroscopy (XPS) model was employed to quantitatively analyze <i>n</i>_S on this three-dimensional (3D) hydrogel network structure. Our results indicated that neutralizing with alginate, increasing membrane thickness, and in situ covalent grafting could increase <i>n</i>_S effectively. ACAC_PEG was more promising than ACC_PEG in protein repellency because alginate supplied more −COO^– negative binding sites and prevented MPEG from diffusing. The <i>n</i>_S increased with membrane thickness, showing better protein repellency. Moreover, the in situ covalent grafting provided an effective way to enhance <i>n</i>_S, and 1.00 ± 0.03 chains/nm² was achieved, exhibiting almost complete immunity to protein adsorption. This antifouling hydrogel biomaterial is expected to be useful in transplantation in vivo