Multiscale Design and Synthesis of Bioinspired Protein/Mineral System

Natural systems often outperform synthetic materials for their heterogeneous hierarchical architectures. These biological composites are usually comprised of soft and hard phases in complex pattern and structures, with dimension ranging from nanoscale to macroscale, although built in ambient environments from limited components. The resulting systems enable distinct integration of strength and toughness, leading to elegant structures with tissue-specific functions. For example, continuous macroscale gradients present at the osteochondral tissue interface with nano-/micro-scale patterns, reflect complex biological functions and involve changes in extracellular matrix (ECM) composition, cell types and mechanical properties.;To mimic these natural gradient hierarchical architectures, this dissertation provides bioinspired mineralization strategies to create novel protein/mineral composite systems via hierarchical assembly of nano-building blocks onto polymeric templates. Silk protein-based composites, coupled with selective peptides R5 with mineralization domains, were created to mimic the soft-to-hard transition in osteochondral interfaces. The gradient composites supported continuous transition in composition and structural and mechanical properties corresponding to the spatial concentration gradient of the mineralization domains. The biocompatible and biodegradable gradient silicified silk/R5 composites promoted and regulated osteogenic and chondrogenic differentiation of human mesenchymal stem cells in an osteoinductive and chondroinductive environment in vitro, respectively, in a manner consistent with the cellularity and ECM gradients at osteochondral interfaces.;In addition, natural composites are usually complex and anisotropic at the microscopic scale. Well-designed micropatterns present in native tissues and organs involve changes in ECM compositions, cell types and mechanical properties to reflect complex biological functions. However, the design and fabrication of these micropatterns in vitro to meet task-specific biomedical applications remains a challenge. In this dissertation, I also present a de novo design strategy to code bio-functional micropatterns to engineer cell alignment through integration of aqueous-peptide inkjet printing and site-specific biomineralization. Inkjet printing allows for the direct writing of macroscopic R5 peptide patterns with microscale resolution on the surface of silk hydrogels. This is combined with in situ biomineralization of the R5 peptide for site-specific growth of silica nanoparticles on the micropatterns, while avoiding the use of harsh chemicals or complex processing. The resulting mineralized micropatterned systems were used to align human mesenchymal stem cells and bovine serum albumin in vitro.;In conclusion, this dissertation explored the feasibility of using silk as a template to combine selective mineralization domains to mimic the hierarchical architecture in biological systems from the molecular level to microscale and ultimately macroscale. The bioinspired multiscale design of mineral assembles on polymeric templates offers a useful approach to develop complex heterogeneous organic/inorganic composites for a wide range of applications in tissue engineering and regenerative medicine, especially osteochondral tissue engineering.