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Accurately measuring the viscoelastic properties of biomaterials is critical for understanding their functions in biological systems and optimizing their development for specific applications. Conventional methods often require direct physical contact, which hinders longitudinal studies of sterile samples and impose strict requirements in sample preparation. Here, we introduce tensile acoustic rheometry (TAR), a technique for rapid, contactless characterization of soft viscoelastic biomaterials. TAR uses a dual-mode ultrasound approach to apply an upward force impulse, generating oscillatory tensile and compressive motion in a small, free-standing sample (~30 mm3) with its bottom immobilized on a pre-wetted flat surface by capillary stiction. High frequency ultrasound pulse echo detection is employed to track this motion via the movement of the top surface of the sample in real time. In this study, we developed a theoretical framework of the tensile-compression motion of the sample from which Young’s modulus and viscosity of the sample are determined based on the TAR measurements. TAR was validated across a variety of samples, including engineered hydrogels and commercially available natural food products. Results from TAR measurements aligned closely with theoretical predictions, reported values, and shear wave elastography measurements. These findings underscore the versatility and flexibility of TAR as a robust, versatile rheological method for biomaterial characterization with minimal sample preparation requirements. 

Background.Transplantation of human-induced pluripotent stem cell (hiPSC)-derived islet organoids is a promising cell replacement therapy for type 1 diabetes (T1D). It is important to improve the efficacy of islet organoids transplantation by identifying new transplantation sites with high vascularization and sufficient accommodation to support graft survival with a high capacity for oxygen delivery. Methods.A human-induced pluripotent stem cell line (hiPSCs-L1) was generated constitutively expressing luciferase. Luciferase-expressing hiPSCs were differentiated into islet organoids. The islet organoids were transplanted into the scapular brown adipose tissue (BAT) of nonobese diabetic/severe combined immunodeficiency disease (NOD/SCID) mice as the BAT group and under the left kidney capsule (KC) of NOD/SCID mice as a control group, respectively. Bioluminescence imaging (BLI) of the organoid grafts was performed on days 1, 7, 14, 28, 35, 42, 49, 56, and 63 posttransplantation. Results.BLI signals were detected in all recipients, including both the BAT and control groups. The BLI signal gradually decreased in both BAT and KC groups. However, the graft BLI signal intensity under the left KC decreased substantially faster than that of the BAT. Furthermore, our data show that islet organoids transplanted into streptozotocin-induced diabetic mice restored normoglycemia. Positron emission tomography/MRI verified that the islet organoids were transplanted at the intended location in these diabetic mice. Immunofluorescence staining revealed the presence of functional organoid grafts, as confirmed by insulin and glucagon staining. Conclusions.Our results demonstrate that BAT is a potentially desirable site for islet organoid transplantation for T1D therapy.