cell-matrix. These unique characteristics render spheroids the optimal candidate for numerous fundamental studies and biomedical applications including the development of pre-clinical models for drug discovery, regenerative medicine, and tissue engineering. [1,2] Spheroids of cancer cells, also known as tumoroids, are emerging as preferred models for the investigation of anticancer therapeutics' response, as they provide analogous spatial architecture, diffusion gradient, tumor dynamics, metabolic activity, and drug resistance behavior of solid tumors. [3][4][5] In a similar vein, spheroids of stem cells are also largely investigated owing to their higher cell viability, proliferation, stemness, and regenerative characteristic compared to 2D culture. [2,6] Cell spheroids have also been trending as tissue engineering building blocks to replace single-cell printing, [7] where their complex composition, prolonged survival and fusion capacity are used to reconstruct various tissues, from branched blood vessel [8] to thyroid gland [9] and osteochondral interface. [10] The scalable application of spheroids in the above-mentioned studies necessitates a high-throughput production method with consistent physiological and morphological characteristics. The standard spheroid formation methods include hanging droplets, agitation-based systems, culture on non-adherent surfaces, and scaffold-based fabrication. [11,12] These methods are generally labor-intensive, low-yield, time-consuming, and show heterogeneous spheroids in shape and size due to poor control of the process which limits their scaled-up application. [13,14] Microfluidics has shown the capacity to overcome some of the technical hurdles in spheroid formation by offering controlled physical conditions, minimized cells and reagent consumption, high sensitivity in drug screening, precise manipulation of cells, continuous perfusion, and regulation of the nutrients and oxygen supply. [15][16][17] These advantages coupled with decreasing user-device interaction, compatibility for automation, low fabrication and operation costs make microfluidics an attractive tool for producing high throughput and uniform spheroids desirable for clinical translation. [18,19] Generally, spheroid formation starts with the physical agglomeration of cells. Next, cell-membrane integrins bind to long-chain extracellular matrix (ECM) fibers of adjoining cells 3D cell spheroid culture has emerged as a more faithful recreation of cell growth environment compared to conventional 2D culture, as it can maintain tissue structures, physicochemical characteristics, and cell phenotypes. The majority of current spheroid formation methods are limited to a physical agglomeration of the desired cell type, and then relying on cell capacity to secrete extracellular matrix to form coherent spheroids. Hence, apart from being time-consuming, their success in leading to functional spheroid formation is also cell-type dependent. In this study, a boundarydriven acoustic microstreaming tool is presented that can si...

Acoustofluidic applications in biosciences; acoustic biosensing; acoustic trigger as a functional mechanical stimulus; cell separation and sorting; therapeutics development and delivery; cell patterning and assembly for tissue engineering.

Objective:To evaluate shear bond strength (SBS) of the orthodontic brackets bonded to fluorosed and nonfluorosed teeth using Light Bond with and without adhesion promoters and compare their enamel damages following debonding.Materials and Methods:In this study, 30 fluorosed (Thylstrup and Fejerskov Index = 4–5) and 30 nonfluorosed teeth were randomly distributed between two subgroups according to the bonding materials: Group 1, fluorosed teeth bonded with Light Bond; Group 2, fluorosed teeth bonded with adhesion promoters and Light Bond; Group 3, nonfluorosed teeth bonded with Light Bond; Group 4, nonfluorosed bonded with adhesion promoters and Light Bond. After bonding, the SBS of the brackets was tested with a universal testing machine. Stereomicroscopic evaluation was performed by unbiased stereology in all teeth to determine the amount of adhesive remnants and the number and length of enamel cracks before bonding and after debonding. The data were analyzed using two-way analysis of variance, Kruskal–Wallis, Wilcoxon Signed Rank, and Mann–Whitney test.Results:While fluorosis reduced the SBS of orthodontic bracket (P = 0.017), Enhance Locus Ceruleus LC significantly increased the SBS of the orthodontic bracket in fluorosed and nonfluorosed teeth (P = 0.039). Significant increasing in the number and length of enamel crack after debonding was found in all four groups. There were no significant differences in the length of enamel crack increased after debonding among four groups (P = 0.768) while increasing in the number of enamel cracks after debonding was significantly different among the four groups (P = 0.023). Teeth in Group 2 showed the highest enamel damages among four groups following debonding.Conclusion:Adhesion promoters could improve the bond strength of orthodontic brackets, but conservative debonding methods for decreasing enamel damages would be necessary.

Acoustofluidics has shown great potential for label-free bioparticle patterning with excellent biocompatibility. Acoustofluidic patterning enables the induction of cell–cell interactions, which play fundamental roles in organogenesis and tissue development. One of the current challenges in tissue engineering is not only the control of the spatial arrangement of cells but also the preservation of cell patterns over time. In this work, we developed a standing surface acoustic wave-based platform and demonstrated its capability for the well-controlled and rapid cell patterning of adipose-derived mesenchymal stem cells in a high-density homogenous collagen hydrogel. This biocompatible hydrogel is easily UV crosslinked and can be retrieved within 3 min. Acoustic waves successfully guided the cells toward pressure nodal lines, creating a contactless alignment of cells in <5 s in culture media and <1 min in the hydrogel. The acoustically patterned cells in the hydrogel did not show a decrease in cell viability (>90%) 48 h after acoustic induction. Moreover, 45.53% and 30.85% increases in metabolic activity were observed in growth and differentiation media, respectively, on Day 7. On Day 14, a 32.03% change in metabolic activity was observed using growth media, and no significant difference was observed using differentiation media. The alkaline phosphatase activity showed an increase of 80.89% and 24.90% on Days 7 and 14, respectively, for the acoustically patterned cells in the hydrogel. These results confirm the preservation of cellular viability and improved cellular functionality using the proposed high-resolution acoustic patterning technique and introduce unique opportunities for the application of stem cell regenerative patches for the emerging field of tissue engineering.

In this paper, we introduce a SAW-based platform that generates acoustic microstreaming and Bjerknes forces to enhance the delivery of nanoparticles on the spheroid's surface and improve their penetration into deeper layers of spheroids.