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New conductive hydrogels with superior biocompatibility continue to be developed in order to serve as bioactive scaffolds capable of modulating cellular functionality for tissue engineering applications. We developed an electrically conductive gelatin methacrylate-poly(aniline) (GelMA-PANi) hydrogel that is permissive of matrix mineralization by encapsulated osteoblast-like cells. Incorporation of PANi clusters within the GelMA matrix increases the electro-conductivity of the composite gel, while maintaining the osteoid-like soft mechanical properties that allows three-dimensional encapsulation of living cells. Viability of human osteogenic cells encapsulated within GelMA-PANi hydrogels was similar to that of GelMA. Cells within GelMA-PANi also demonstrated the capability of depositing mineral within the hydrogel matrix after being chemically induced for two weeks, although the total mineral content was lower as compared to GelMA. Additionally, we demonstrated that the GelMA-PANi-composite hydrogel could be printed in complex, user-defined geometries using digital projection stereolithography.

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Despite the promise of stem cell engineering and the new advances in bioprinting technologies, one of the major challenges in the manufacturing of large scale bone tissue scaffolds is the inability to perfuse nutrients throughout thick constructs. Here, we report a scalable method to create thick, perfusable bone constructs using a combination of cell-laden hydrogels and a 3D printed sacrificial polymer. Osteoblast-like Saos-2 cells were encapsulated within a gelatin methacrylate (GelMA) hydrogel and 3D printed polyvinyl alcohol pipes were used to create perfusable channels. A custom-built bioreactor was used to perfuse osteogenic media directly through the channels in order to induce mineral deposition which was subsequently quantified via micro-CT. Histological staining was used to verify mineral deposition around the perfused channels, while COMSOL modeling was used to simulate oxygen diffusion between adjacent channels. This information was used to design a scaled-up construct containing a 3D array of perfusable channels within cell-laden GelMA. Progressive matrix mineralization was observed by cells surrounding perfused channels as opposed to random mineral deposition in static constructs. Micro-CT confirmed that there was a direct relationship between channel mineralization within perfused constructs and time within the bioreactor. Furthermore, the scalable method presented in this work serves as a model on how large-scale bone tissue replacement constructs could be made using commonly available 3D printers, sacrificial materials, and hydrogels.