In cutting-edge tissue engineering, drug development, and even clinical applications, the construction of in vitro models that mimic in vivo tissue structure and environment are very important conditions, and the way cells or microstructural units are assembled and the extracellular matrix environment plays a key role in the process of tissue functionalization, which has led to the development of three-dimensional tissue structure printing technologies. Among these technologies, projection light-curing and extrusion printing techniques are represented by the use of hydrogels containing cells as bio-ink materials, demonstrating superior biological tissue building capabilities. However, such printing is still limited to printing the bioink as a whole, and the cells in it are randomly distributed, making it difficult to actively form microstructural units on the cells, which is a current challenge for bioprinting.
In recent years, acoustic waves as an easy to integrate, high bioaffinity and high precision control means, in the flexible manipulation of cells and efficient assembly applications have been widely studied, such as the combination of acoustic waves and microfluidics of acoustic flow control and acoustic tweezers technology, especially suitable for manipulating cells to build in vitro models of tissue-like. How to extend the two-dimensional acoustic field manipulation technology to three-dimensional and three-dimensional tissue structure assembly is the challenge that needs to be solved for its advancement to biological 3D printing. Recently, Prof. Lujian Chen and Assistant Prof. Xuejia Hu from Xiamen University and Prof. Yi Yang's group from Wuhan University collaborated to propose a new solution: combining lamellar printing and acoustic manipulation of cellular 3D structure assembly, and published in the journal Biofabrication with the title: Smart acoustic 3D cell construct assembly with high-resolution. Biofabrication.
Drawing on the idea of multilayer light-curing printing, this study proposes the direct manipulation of cell composition feature structures in gel lamellae based on acoustic surface waves and the multilayer assembly of lamellae units, successfully realizing the 3D structure assembly and bionic tissue construction of cells. A schematic diagram of this strategy is shown in Fig. 1. The technique is designed with a six-fold rotationally symmetric transducer configuration on a Z-cut lithium niobate substrate to ensure a large degree of modulation freedom, which enables the assembly of cells in the lamellae into diverse structures through wave vector combination, phase combination and amplitude modulation. And to expand the two-dimensional acoustic field generated by surface waves and two-dimensional cell structures into three-dimensional space, the PμSL high-precision 3D printing technology (nanoArch P150, MUFON Precision) was used to fabricate a high-precision modular frame to couple with the surface wave acoustic field and to realize cell assembly in that frame. gelMA 60, as a bio-ink, is light-cured to form a gel lamella with microstructured gel lamellae. The gel lamellae are then used as two-dimensional units for the alignment and assembly of multiple layers and the fusion of hydrogels to obtain microscopic three-dimensional structures immobilized by the gel matrix.
As a demonstration, a variety of acoustic field structures generated by the modulation of acoustic devices in combination with 3D printed components with different characteristic units, such as the ring-like structure of blood vessels, the honeycomb structure of liver-like lobules, and the dotted structure of dense stacks, etc., and their ability to perform flexible cell assembly was experimentally verified. Through secondary 3D assembly, the researchers have achieved a variety of 3D cellular-scale tissue-like models, including hollow tubular capillary tissue, interwoven tissue structures, and honeycomb-like tissue of liver lobules. The scales of these feature cells depend on the period of the acoustic field and can be designed to vary from tens to hundreds of microns. In three dimensions, the thickness of these lamellae can be as low as 100 μm, thanks to the use of high-precision printed cell structures, which can be designed to fit the needs of different tissue heights with different interlayer distances. These 3D tissue-like models show good activity after culture, and the microscopically tightly connected bionic structures further promote the process of cell and tissue functionalization, such as the experimental verification that the tubular 3D models show interconnected fusion and vascularization tendency during long-term culture.
This acoustic cell 3D assembly technique extends the two-dimensional manipulation capability of acoustic surface waves to three-dimensional space, demonstrating unique advantages such as direct cell assembly, precise construction of tissue structures, flexibility and control, and ease of operation. This study demonstrates the ability to construct microscopic media beyond bio-ink printing, proposing an innovative technological route from a new dimension.