For example, self-folded tubes were developed by using a modified gelatin gel as the hydrophilic layer and polycaprolactone as a hydrophobic portion, at room temperature. Self-folding techniques rely on the difference in strains generated due to differences in swelling rates or extent of materials in aqueous solution, with and without external thermal stimulation. Self-folding is an effective approach to generate scaffolds enabling cell patterning in 3D formats. More importantly, this technology continues to suffer from limits in spatial resolution, and thus nanoscale features in ECM systems cannot be duplicated in 3D printed scaffolds. However, the cross-linking conditions to achieve such an outcome often limit the cell types and growth factors that can be used in the process. By mixing the cells with the printing precursors prior to deposition and cross-linking, the distribution of cells can be controlled within the scaffolds. In this approach, controlling the spatial distribution of each cell type is challenging. ![]() To achieve 3D cultures, these scaffolds are traditionally printed to mimic tissue geometry, followed by culturing a mixture of cells inside the printed scaffolds. As an alternative, 3D-printed scaffolds have also emerged, including integrated polymers and inorganic systems, to provide structural control in 3D formats. However, due to their relatively rapid degradation and poor mechanical properties with respect to orthopedic needs, hydrogel-based scaffolds often cannot support sustained cell growth and functional tissue formation. Mixtures of culture medium and growth factors can be added to each building block, enabling heterogeneous cell cultures towards tissue-related outcomes. With embedded cells inside hydrogels, these building blocks can be patterned to enable 3D tissues. To address these needs, hydrogels have been widely used to support 3D cell growth. For successful tissue regeneration, bioengineered 3D scaffolds should provide features to promote cell growth and facilitate functional recovery, including: (1) adaption of the intrinsic 3D geometry, extracellular matrix (ECM) structure and chemistry of the target tissue, (2) biocompatibility, (3) adequate biomechanics to support tissue growth and function with a biodegradation rate commensurate with new tissue formation to transfer mechanical load, and (4) support for heterogenous cell growth. Tissues are complex systems that house cells which communicate in a heterogeneous environment. These results demonstrate the utility of self-folded silk rolls as efficient scaffold systems for tissue regeneration, while exploiting relatively simple 2D designs programmed to form more complex 3D structures. By utilizing this self-folding method, co-cultures of neurons and hMSCs were achieved by patterning cells on silk films and then converting these materials into a 3D format with rolling, mimicking aspects of the structure of osteons and providing physiologically relevant structures to promote bone regeneration. The osteogenic outcomes were further supported by enhanced biomechanical performance. The 3D silk rolls, with patterns transferred from the initially prepared 2D films, guided the directional outgrowth of neurites, and also promoted the osteogenic differentiation of human mesenchymal stem cells (hMSCs). A simple and robust one-step self-folding approach was developed using bilayers consisting of a hydrogel and silk film in aqueous solution. Towards this goal, we report silk protein-based self-folding scaffolds to support 3D cell culture, while providing directional guidance and promotion of cell growth and differentiation. ![]() Biomaterial scaffold designs are needed for self-organizing features related to tissue formation while also simplifying the fabrication processes involved.
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