Acoustic modification of collagen hydrogels facilitates cellular remodeling

Abstract Developing tunable biomaterials that have the capacity to recreate the physical and biochemical characteristics of native extracellular matrices (ECMs) with spatial fidelity is important to a variety of biomedical, biological, and clinical applications. Several factors have made the ECM protein, collagen I an attractive biomaterial, including its ease of isolation, low antigenicity and toxicity, and biodegradability. However, current collagen gel formulations fail to recapitulate the range of collagen structures observed in native tissues, presenting a significant challenge to achieving the full potential of collagen-based biomaterials. Collagen fiber structure can be manipulated in vitro through mechanical forces, environmental factors, or thermal mechanisms. Here, we describe a new ultrasound-based fabrication technology that exploits the ability of ultrasound to generate localized mechanical forces in order to control collagen fiber microstructure non-invasively. Results indicate that exposing soluble collagen to ultrasound (7.8 or 8.8 MHz; 3.2 – 10 W/cm 2 ) during hydrogel formation leads to local variations in collagen fiber structure and organization that support increased levels of cell migration. Further, multiphoton imaging revealed increased cell-mediated collagen remodeling of ultrasound- but not sham-exposed hydrogels, including formation of multicellular aggregates, collagen fiber bundle contraction, and increased binding of collagen hybridizing peptides. Skin explants cultures obtained from diabetic mice showed similar enhancement of cell-mediated remodeling of ultrasound- but not sham-exposed collagen hydrogels. Utilizing the mechanical forces associated with ultrasound to induce local changes in collagen fibril structure and organization in order to functionalize native biomaterials is a promising non-invasive and non-toxic technology for tissue engineering and regenerative medicine.