A Multicenter Large-Sample Shear Wave Ultrasound Elastographic Study of the Achilles Tendon in Chinese Adults.

OBJECTIVES: The changes in the viscoelasticity of the Achilles tendon are related to tendinopathy. Therefore, constructing a data model in the healthy population is essential to understanding the key factors affecting the viscoelasticity of the Achilles tendon. The purpose of our research was to obtain large sample data, construct a data model, and determine parameters that affect the elastic modulus of the Achilles tendon in healthy Chinese adults. METHODS: We designed a prospective multicenter clinical trial to evaluate the viscoelasticity of the Achilles tendon by using shear wave elastography. A total of 1165 healthy adult participants from 17 Chinese hospitals were recruited for the assessment. The necessary parameters (age, height, weight, and body mass index) were recorded. The elastic modulus (Young modulus) was obtained from the middle of the Achilles tendon and calculated with feet in naturally relaxed, dorsal, and plantar positions. The thickness and perimeter of the Achilles tendon were measured via cross section on the same site. A multiple linear regression was performed to find the key factors affecting the Young modulus of the Achilles tendon. RESULTS: The Young modulus of the left Achilles tendon in the natural relaxed position followed a normal distribution (P > .05) with a mean ± SD of 374.24 ± 106.12 kPa. The regression equations showed a positive correlation between the Young modulus and weight and a negative correlation between the Young modulus and the circumference or thickness of the left Achilles tendon (P < .05). CONCLUSIONS: The Young modulus of the Achilles tendon as measured by shear wave elastography is related to body weight as well as the perimeter or thickness of the tendon.

Preferential sensing and response to microenvironment stiffness of human dermal fibroblast cultured on protein micropatterns fabricated by 3D multiphoton biofabrication.

While cells are known to sense and respond to their niche including the matrix and the mechanical microenvironment, whether they preferentially sense and react to the stiffness of their microenvironment regardless of its intrinsic material properties is unknown. In this work, protein micropillar arrays with independently controllable stiffness via alterations in pillar height and elastic modulus via laser power used during photochemical cross-linking, were fabricated using a recently developed multiphoton-based 3D protein micro-patterning technology. Human dermal fibroblasts were cultured on these micropillar arrays and the specific interactions between cells and the protein micropatterns particularly on the formation and maturation of the cell-matrix adhesions, were investigated via immunofluorescence staining of the major molecular markers of the adhesions and the measurement of their cluster size, respectively. Our results showed that the cluster size of focal adhesions increased as the stiffness of the micropillar arrays increased, but it was insensitive to the elastic modulus of the protein micropillars that is one of the intrinsic material properties. This finding provides evidence to the notion that cells preferentially sense and react to the stiffness, but not the elastic modulus of their microenvironment.

Nanomechanical measurement of adhesion and migration of leukemia cells with phorbol 12-myristate 13-acetate treatment.

The adhesion and traction behavior of leukemia cells in their microenvironment is directly linked to their migration, which is a prime issue affecting the release of cancer cells from the bone marrow and hence metastasis. In assessing the effectiveness of phorbol 12-myristate 13-acetate (PMA) treatment, the conventional batch-cell transwell-migration assay may not indicate the intrinsic effect of the treatment on migration, since the treatment may also affect other cellular behavior, such as proliferation or death. In this study, the pN-level adhesion and traction forces between single leukemia cells and their microenvironment were directly measured using optical tweezers and traction-force microscopy. The effects of PMA on K562 and THP1 leukemia cells were studied, and the results showed that PMA treatment significantly increased cell adhesion with extracellular matrix proteins, bone marrow stromal cells, and human fibroblasts. PMA treatment also significantly increased the traction of THP1 cells on bovine serum albumin proteins, although the effect on K562 cells was insignificant. Western blots showed an increased expression of E-cadherin and vimentin proteins after the leukemia cells were treated with PMA. The study suggests that PMA upregulates adhesion and thus suppresses the migration of both K562 and THP1 cells in their microenvironment. The ability of optical tweezers and traction-force microscopy to measure directly pN-level cell-protein or cell-cell contact was also demonstrated.

Multiphoton photochemical crosslinking-based fabrication of protein micropatterns with controllable mechanical properties for single cell traction force measurements.

Engineering 3D microstructures with predetermined properties is critical for stem cell niche studies. We have developed a multiphoton femtosecond laser-based 3D printing platform, which generates complex protein microstructures in minutes. Here, we used the platform to test a series of fabrication and reagent parameters in precisely controlling the mechanical properties of protein micropillars. Atomic force microscopy was utilized to measure the reduced elastic modulus of the micropillars, and transmission electron microscopy was used to visualize the porosity of the structures. The reduced elastic modulus of the micropillars associated positively and linearly with the scanning power. On the other hand, the porosity and pore size of the micropillars associated inversely and linearly with the scanning power and reagent concentrations. While keeping the elastic modulus constant, the stiffness of the micropillars was controlled by varying their height. Subsequently, the single cell traction forces of rabbit chondrocytes, human dermal fibroblasts, human mesenchymal stem cells, and bovine nucleus pulposus cells (bNPCs) were successfully measured by culturing the cells on micropillar arrays of different stiffness. Our results showed that the traction forces of all groups showed positive relationship with stiffness, and that the chondrocytes and bNPCs generated the highest and lowest traction forces, respectively.