Effect of surface roughness on fibrinogen adsorption onto alginate-chitosan-alginate microcapsules

Alginate-chitosan-alginate (ACA) microcapsule has been widely investigated for applications such as cell transplantation, biosensors and enzyme immobilization. However, the pericapsular fibrotic overgrowth restricts long-term survival of graft and thus their potential clinical application. It is generally believed that protein adsorption onto the surface of implanted devices is the first event after contact of body fluids [1] and that the adsorbed protein layer controls further biological reactions [2]. Recent studies [3] have recognized that surface topography could affect protein adsorption. In this work, the influence of alginate and chitosan on the surface topography of ACA microcapsule was evaluated and the effect of surface roughness on protein adsorption was analyzed. The surface roughness was monitored using SEM. Bovine fibrinogen (Fgn, 340 kDa) was used for adsorption test, for fibrinogen is relevant to blood coagulation. The adsorption experiment was carried out by gently shaking Fgn solution of known concentration containing pre-weighed microcapsules at 37 ± 0.5 oC for 24 hours. Then, the Fgn solution without any microcapsules was collected and the remaining concentration of Fgn was assayed by the Bradford method. The results showed that alginate viscosity greatly affected the surface roughness of ACA microcapsule. Microcapsules made of low-viscosity sodium alginates had smoother membranes. The surface roughness was also influenced by the chitosan solution concentration. Microcapsules made of chitosans with concentration of 0.25% (w/v) had smoother topographical membrane surface than that of 0.5% (w/v). But the degree of deacetylation and molecular weight of chitosan had little effect on the surface roughness. In each case, the amount of adsorbed of fibrinogen was smaller for microcapsules with smoother membrane. It can be concluded that both alginate viscosity and chitosan solution concentration influence the surface roughness of ACA microcapsules, in turn, the surface roughness make protein adsorption increase