Search for: All records

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. 

3D bioprinting has been evolving as an important strategy for the fabrication of engineered tissues for clinical, diagnostic, and research applications. A major advantage of bioprinting is the ability to recapitulate the patient-specific tissue macro-architecture using cellular bioinks. The effectiveness of bioprinting can be significantly enhanced by incorporating the ability to preferentially organize cellular constituents within 3D constructs to mimic the intrinsic micro-architectural characteristics of native tissues. Accordingly, this work focuses on a new non-contact and label-free approach called ultrasound-assisted bioprinting (UAB) that utilizes acoustophoresis principle to align cells within bioprinted constructs. We describe the underlying process physics and develop and validate computational models to determine the effects of ultrasound process parameters (excitation mode, excitation time, frequency, voltage amplitude) on the relevant temperature, pressure distribution, and alignment time characteristics. Using knowledge from the computational models, we experimentally investigate the effect of selected process parameters (frequency, voltage amplitude) on the critical quality attributes (cellular strand width, inter-strand spacing, and viability) of MG63 cells in alginate as a model bioink system. Finally, we demonstrate the UAB of bilayered constructs with parallel (0°–0°) and orthogonal (0°–90°) cellular alignment across layers. Results of this work highlight the key interplay between the UAB process design and characteristics of aligned cellular constructs, and represent an important next step in our ability to create biomimetic engineered tissues.

 

Structural anisotropy, often observed in naturally occurring materials such as wood and human tissues, is central to the function in several engineered and non-engineered applications. In this study, we present the theory and proof-of-concept demonstration of an ultrasound-assisted non-contact manufacturing approach to create well-defined spatial patterns of micro-particles within a fluid matrix. A chamber with opposing pair of ultrasonic transducers was designed and prototyped based on standing bulk acoustic wave theory, and it was used to study the effects of ultrasound frequency (1, 1.5, 2, 3 MHz) and voltage amplitude (80, 160 mVpp) on alignment characteristics of polymer micro-particles (mean Ø = 8 μm) suspended in water (0.01 g/ml). The experimental results were consistent with theory in that the micro-particles aligned along linear strands, with the inter-strand spacing reducing with increasing frequency (p < 0.05). Increasing voltage amplitude reduced the time taken to align the particles, but it did not significantly change the observed spacing (p > 0.05). The observed spacing, however, was higher than the theoretical spacing of half-wavelength, for each frequency and amplitude. The alignment of living human adipose derived stem cells in viscous alginate hydrogel matrix was also successfully demonstrated. The approach presented herein can be scaled up into manufacturing processes, including layered manufacturing, to create highly functional mechanically and/or electrically anisotropic composites through controlled spatial geometry, as well as to biofabricate engineered tissues with aligned cells and extracellular matrix components to mimic natural tissues.