A combinatorial study of nanocomposite hydrogels: on-chip mechanical/viscoelastic and pre-osteoblast interaction characterization†
Nanocomposite hydrogels were prepared in a combinatorial way with chitosan, bioglass nanoparticles (BG-NPs) and distinct amounts of crosslinker (genipin), in a total of 30 formulations. Such miniaturized hydrogels were prepared by dispensing the precursor solutions in wettable spots previously patterned onto superhydrophobic surfaces. The chips were used as platforms to analyze the biomaterials on-chip both for mechanical/viscoelastic and cell–biomaterial interactions. We adapted a mechanical dynamic analyzer (DMA) in order to perform the in situ totally unconfined solid-state rheological characterization of biomaterials under physiological-like conditions. We concluded that the viscoelastic properties of the hydrogels are dependent on the three factors studied. Besides influencing biomaterials' mechanical properties, bioglass fillers also confer bioactivity. We immersed the chips with 20 distinct biomaterial formulations in a cell suspension of MC3T3-E1 pre-osteoblasts and quantified – using image analysis compatible with the maintenance of the integrity of the chip – selective cell adhesion after 1 day of cell culture, as well as cell proliferation and cell morphology at day 3. Linear regression studies showed that for the range of conditions studied herein, neither cell adhesion nor proliferation depended directly on the biomaterials' mechanical/viscoelastic properties. Rather, cell proliferation was favoured in the presence of an intermediate amount of BGNPs (12.5% w/w) for all chitosan/genipin conditions, especially in softer hydrogels (2% (w/v) chitosan, 2.5% (w/w) genipin). This hit-spotted condition also favoured cell spreading. Interestingly, the elastic modulus measured for this formulation meets the values reported for the granulation tissue occurring during bone regeneration, where fibroblasts produce collagen. We believe that this approach will facilitate the complete on-chip rapid study of miniaturized biomaterials, in order to get more adequate formulations to be used in tissue engineering or other biomedical applications.