In attempts to engineer human tissues in the lab, bio-mimicking the cellular arrangement of natural tissues is critical to achieve the required biological and mechanical form and function. Although biofabrication employing cellular bioinks continues to evolve as a promising solution over polymer scaffold based techniques in creating complex multi-cellular tissues, the ability of most current biofabrication processes to mimic the requisite cellular arrangement is limited. In this study, we propose a novel biofabrication approach that uses forces generated by bulk standing acoustic waves (BSAW) to non-deleteriously align cells within viscous bioinks. We computationally determine the acoustic pressure pattern generated by BSAW and experimentally map the effects of BSAW frequency (0.71, 1, 1.5, 2 MHz) on the linear arrangement of two types of human cells (adipose-derived stem cells and MG63) in alginate. Computational results indicate a non-linear relationship between frequency and acoustic pressure amplitude. Experimental results demonstrate that the spacing between adjacent strands of aligned cells is affected by frequency (p < 0.0001), and this effect is independent of the cell type. Lastly, we demonstrate a synergistic technique of gradual crosslinking in tandem with the BSAW-induced alignment to entrap cells within crosslinked hydrogels. This study represents an advancement in engineered tissue biofabrication aimed at bio-mimicry.

A selective ultrasonic foaming (SUF) process was developed to fabricate porous polymer for biomedical applications. The method employs a high intensity focused ultrasound (HIFU) transducer to selectively heat and implode gas-impregnated polymers. This acoustic method is solvent-free and capable of creating interconnected pores that have various topographical features at different length scales. In this paper, we investigate the effects of major process parameters of the SUF process, including the ultrasound power, scanning speed, and the specimen gas concentration. The pore size and interconnectivity of the porous structure were analyzed. The microstructures were characterized using the scanning electron microscopy (SEM) and a dye penetration test. It was found that the scanning speed of the ultrasound had a significant effect on the pore size control, and that low gas concentration was a necessary condition for interconnected porous structures.

A novel technique was developed for the fabrication of porous polymer for biomedical applications using selective ultrasonic foaming. It was found that the gas concentration of saturated polymer samples plays an important role in the creation of open celled, interconnected porous structures. In this paper, we present a concentration-dependent diffusion model for PMMA-CO 2 gas polymer system to understand the open-cell mechanism in the selective ultrasonic foaming process. An explicit finite difference scheme was employed to solve the nonlinear gas diffusion equation. By comparing with the polymer gas saturation data, a necessary condition for open celled structure is established in terms of the gas concentration levels.