In-Petri-dish traveling and standing acoustic wave-assisted fabrication of anisotropic collagen hydrogels

Anisotropic biomaterials containing oriented collagen fibers have shown great potential for various biomedical research areas, such as wound dressing, corneal grafting, and the study of cancer cell invasion in biomimetic microenvironments. To fabricate such anisotropic biomaterials, previous studies have used electric, microfluidic, magnetic, and mechanical methods to align collagen fibers during the fabrication process. In this study, we put forward traveling and standing acoustic wave-based approaches that enable the rapid in-Petri-dish fabrication of anisotropic biomaterials containing acoustically arranged collagen fibers. To develop these approaches, we investigated the effects of traveling and standing acoustic waves on collagen self-assembly and the micro/nanoscale architectures of the fabricated collagen-based biomaterials. Our results reveal that traveling acoustic wave-induced fluid streaming can transport collagen molecules, thereby influencing the collagen self-assembly process, while standing acoustic waves can accumulate self-assembled collagen fibers, increasing their concentrations in acoustic potential valleys periodically distributed. Using our acoustics-assisted approach, we successfully manufactured anisotropic collagen hydrogels containing aligned collagen fibers, which provide anisotropic microenvironments for cell growth and development. Notably, we demonstrated the functionality of these fabricated anisotropic collagen hydrogels in facilitating cell elongation along the acoustically aligned collagen fibers. Compared to previous methods, our acoustics-based approaches are easy to operate without requiring customized chambers for loading collagen and are capable of rapidly fabricating anisotropic collagen hydrogels directly in commercial Petri dishes, thus allowing our approaches to be readily integrated into existing laboratory workflows and combined with other test protocols. In the long run, we expect this work to inspire the development of useful tools that will benefit biomedical researchers working in tissue engineering, regenerative medicine, biomaterials, and bioprinting.