Stiffness of photocrosslinked RGD-alginate gels regulates adipose progenitor cell behavior.

Adipose progenitor cells (APCs) are widely investigated for soft tissue reconstruction following tumor resection; however, the long-term success of current approaches is still limited. In order to develop clinically relevant therapies, a better understanding of the role of cell-microenvironment interactions in adipose tissue regeneration is essential. In particular, the effect of extracellular matrix (ECM) mechanics on the regenerative capability of APCs remains to be clarified. We have used artificial ECMs based on photocrosslinkable RGD-alginate to investigate the adipogenic and pro-angiogenic potential of 3T3-L1 preadipocytes as a function of matrix stiffness. These hydrogels allowed us to decouple matrix stiffness from changes in adhesion peptide density or extracellular Ca(2+) concentration and provided a physiologically relevant 3D culture context. Our findings suggest that increased matrix rigidity promotes APC self-renewal and angiogenic capacity, whereas, it inhibits adipose differentiation. Collectively, this study advances our understanding of the role of ECM mechanics in adipose tissue formation and vascularization and will aid in the design of efficacious biomaterial scaffolds for adipose tissue engineering applications.

Methods for photocrosslinking alginate hydrogel scaffolds with high cell viability.

Methods for seeding high-viability (>85%) three-dimensional (3D) alginate-chondrocyte hydrogel scaffolds are presented that employ photocrosslinking of methacrylate-modified alginate with the photoinitiator VA-086. Comparison with results from several other photoinitiators, including Irgacure 2959, highlights the role of solvent, ultraviolet exposure, and photoinitiator cytotoxicity on process viability of bovine chondrocytes in two-dimensional culture. The radicals generated from VA-086 photodissociation are shown to be noncytotoxic at w/v concentrations up to 1.5%, enabling photocrosslinking without significant cell death. The applicability of these photoinitiators for generating 3D tissue-engineered constructs is evaluated by measuring cell viability in 3D constructs with aggregate moduli in the 10-20 kPa range. Hydrogels with encapsulated bovine chondrocytes were constructed with >85% viability using VA-086. While the commonly used Irgacure 2959 is noncytotoxic in its native state and crosslinks the alginate at weight fractions much lower than VA-086, the cytotoxicity of IRG2959's photogenerated radical leads to viabilities below 70% in the conditions tested.