Design Of Biomaterials Surface Chemistry For Modulating Cellular Behaviors

Cellular microenvironment encompassing extracellular matrix (ECM) plays critical roles in regulating cellular behaviors and tissue/organ homeostasis. Hence, probing cell-biomaterials interactions is of great significance in both gaining profound understanding of cell biology and advancing tissue regeneration. Of note, in order to recapitulate ECM characteristics to achieve desired cellular behaviors, engineering surface chemistry becomes one of the prerequisites for biomaterials design in tissue engineering. Chemistry of ECM essentially encompasses two aspects:chemical composition that dictates properties including wettability, charge density, surface free energy and etc., and spatial distribution of chemical modality.To engineer surface chemistry, introduction of small chemical groups or molecules derived from native ECM onto biomaterials substrate surface represents a convenient and straightforward strategy. In this study, we exploited poly(?-caprolactone) (PCL) and poly(2-hydroxyethyl methacrylate) (PHEMA) as biomaterials substratum, since these synthetic polymers have been extensively applied in tissue engineering. Specifically, PCL was modified with different small chemical groups and PHEMA was modified with varying densities of collagen type I. On these series of surfaces, behaviors of different cells were examined and compared. The major findings are elaborated as followed.Firstly, a series of PCL derivatives were synthesized via ring-opening copolymerization to bear pendant small chemical groups including hydroxyl (-OH), methyl (-CH3), carboxyl (-COOH), amino (-NH2) and carbonyl (-C=O). These polymers including PCL itself were processed into thin films and characterized regarding wettability, surface topology and protein adsorption. It was found that pendant hydrophilic groups reduced the hydrophobicity of PCL and slightly rougher surface was for PCL bearing pendant groups. In addition, a correlation between wettability and serum protein adsorption might be present.Except for PCL-CH3, PCL films with pendant groups promoted adhesion of human amnion mesenchymal stem cells (hAMSCs). Cells on PCL-NH2 and PCL-COOH films slightly outgrew those on others. Importantly, the differentiation of hAMSCs varied on different films, with the best osteogenesis on PCL-NH2 film, PCL and PCL-CH3 films supporting superior adipogenic differentiation, and PCL-COOH and PCL-CH3 film being most favorable for chondrogenesis.Next, this series of polymers were employed as a platform to evaluate the chondrogenesis of both rabbit bone marrow mesenchymal stem cells (rBMSCs) and rabbit articular chondrocytes (rACs, passaged for different generations, P1, P3 and P5). It was found that the presence of hydrophilic groups enhanced both adhesion and proliferation of rACs and rBMSCs. While P1 rACs could deposit a significant amount of glycosaminoglycans (GAG) on PCL-COOH film, these cells dedifferentiated significantly on both pristine PCL and PCL-CH3 films. Interestingly, P3 rACs could regain the chondrocyte phenotype with chondrogenic induction factors in culture medium on all films. However, a better chondrogenesis of rBMSCs and P5 rACs was achieved on less hydrophilic films, including pristine PCL and PCL-CH3 films, although GAG/DNA values were far less than redifferentiated P3 rACs. These findings suggest that biomaterials surface chemistry can be specific to certain cell types and provide a new perspective to developing biomaterials towards cartilage tissue regeneration.In the end, PHEMA polymer substrate was modified with different densities of collagen type I by prior 1,1-carbonyldiimidazole (CDI) treatment. It was found that CDI treatment decreased the hydrophilicity and roughness of PHEMA, while following collagen immobilization increased the hydrophilicity again but had no effect on roughness. Cell attachment and proliferation of human bone marrow mesenchymal stem cells (hBMSCs) were stimulated on collagen-modified surfaces. Notably, while osteogenic differentiation of hMSCs was promoted with increased density of collagen on PHEMA surfaces, the adipogenic and chondrogenic differentiation followed a reversed trend. It was noticed that the effects of collagen density on chondrogenesis were depended on cell types as well. For hBMSCs, GAG production was promoted along with the increase collagen density, while ovine knee cartilage chondrocytes displayed the opposite.In conclusion, PCL and PHEMA with different surface chemistries are successfully engineered surface chemistry modulate cellular behaviors from early adhesion to late proliferation and differentiation. Importantly, different cell types display different requirements for biomaterials surface chemistry. This study highlights the importance of biomaterial surface chemistry in modulating the behaviors of cells and confers a profound understanding in designing biomaterials scaffolds for tissue regeneration.