3D-Printed Scaffolds with Independently Tunable Multiscale Properties

About This Grant

PROJECT SUMMARY Biomaterials for tissue engineering must simultaneously provide mechanical support at the tissue level and local biochemical and physical cues at the cellular level to promote functional tissue regeneration. However, these multiscale requirements often conflict with each other. For example, hydrogels designed to mimic cartilage extracellular matrix typically lack sufficient mechanical strength to withstand forces applied in vivo. Solid scaffolds with load-bearing capability are significantly stiffer than native cartilage. Both examples result in unwanted changes in cellular response that leads to the formation of functionally inferior scar-like tissue. These challenges highlight the critical need for biomaterials with properties that can be independently tuned across multiple length scales to direct functional tissue regeneration. To address this need, a versatile 3D printing approach has been developed to independently control biochemical and physical properties within a single biomaterial. Prior work demonstrated that printing inks containing peptide-functionalized polymer conjugates enabled control of bioactive peptide concentration on the surface without altering scaffold modulus or architecture. In addition, printing with different ratios of polymer molecular weight resulted in scaffolds with significantly different mechanical properties without affecting scaffold architecture, surface chemistry, or crystallinity. Relevant to the proposed work, human mesenchymal stromal cells (hMSCs) cultured in high stiffness scaffolds under chondrogenic (cartilage-promoting) conditions differentiated towards unwanted hypertrophic and osteogenic (bone) lineages while low stiffness scaffolds promoted more stable chondrogenesis. These findings underscore how biochemical and mechanical cues can have competing or synergistic effects and must be optimized independently to direct stem cell fate. The proposed project aims to expand and refine this biomaterial platform using hMSC differentiation toward cartilage as a model system. Specifically, a new approach will be developed to functionalize the surface of 3D-printed solid scaffolds with soft, hydrophilic peptide-polymer bottlebrushes to independently control surface and bulk properties across length scales within a single construct. It is hypothesized that the surface-grafted bottlebrushes will create a soft, hydrogel-like microenvironment for cells without compromising bulk scaffold modulus, and that including bioactive cartilage-promoting peptides will synergistically enhance hMSC differentiation into cartilage cells. This hypothesis will be tested through two Specific Aims: (1) demonstrate that surface properties can be tuned independently of bulk scaffold modulus, and (2) demonstrate that surface-grafted peptide-polymer bottlebrushes enhance hMSC differentiation. This work will provide a powerful and adaptable platform for future biomaterial designs by enabling independent control of cell- material interactions at multiple length scales. The proposed strategy can be broadly applied to other tissue applications by varying peptide sequences, bottlebrush compositions, and bulk scaffold materials.