On-Chip Formation of Deformable Hydrogel 3D Architectures via Swelling-Driven Buckling

Technology to reproduce the microstructure (channels, folds, etc.) and stimulating environment (mechanical stimuli, chemical stimuli, etc.) of living organisms in vitro is crucial for the fabrication of an organ-on-a-chip capable of advanced cell culture. In particular, if such a biological environment can be constructed on a solid substrate, including a sensor substrate, it can be developed as an organ-on-a-chip platform with potential applications in disease modeling and drug discovery through various types of data acquisition. Hydrogel is the best candidate as a base material because of its excellent permeability, biocompatibility, and ability to mimic the biological environment at the material level. On the other hand, the unique feature of gels, swelling, causes a volume mismatch between them and solid substrates, making it difficult to fabricate hybrid devices due to delamination or fracture.<br/>In this talk, we introduce "buckle delamination", a method to fabricate three-dimensional (3D) architectures of hydrogel films on a chip by using swelling as a driving force. This phenomenon is a type of instability induced by the mismatch between the volume expansion ratio of the thin film and the supporting substrate. This mismatch generates compressive stress, which causes part of the thin film to delaminate and buckle from the substrate, forming a hollow 3D architecture. First, we applied this phenomenon to hydrogel films and proposed a method to precisely control the architecture and position through microfabrication techniques. Using polyacrylamide gel and glass substrates as model materials, we have shown that by chemically controlling the adhesion pattern between the two materials, buckle delamination can be induced at arbitrary locations and continuous channel-like structures can be fabricated. Furthermore, by tuning the physical parameters of the hydrogel, the shape of the 3D architecture can be controlled based on patterns of instability. We then demonstrated that the channel-like architectures can work as a fluidic device. The device is based on a soft and flexible hydrogel film, which can passively expand and contract in the radial direction, like a blood vessel, in response to fluid flow. We have also demonstrated that the permeability and biocompatibility of this device allows for long-term culture of cells and the formation of vascular-like tissue in the channel. Finally, we will show that the architecture formation by "buckle delamination" is a processing method based on a universal physical phenomenon and that it can be applied to various types of swellable hydrogel. Notably, by using a stimulus-responsive gel film, the channel architecture formed on a solid substrate can be deformed quickly, largely, and bio-mimetically like an organ (e.g., peristalsis in the intestinal tract) in response to stimulus patterns. We believe that these results will be useful for designing devices that reproduce the dynamic in vivo environment on solid substrates, and may also contribute to the creation of organ-on-a-chip platforms and soft biomimetic robots.