Monitoring the adhesion process of tendon stem cells using shear-horizontal surface acoustic wave sensors

Cell adhesion to a substrate or extracellular matrix (ECM) plays an important role in a variety of cellular functions, such as cell migration, proliferation, differentiation, and tissue formation. Shear-horizontal surface acoustic wave (SH-SAW) sensors can detect cell behaviors in liquid in a non-invasive, simple and quantitative manner. As the key part of SH-SAW, acoustic-wave guiding layer plays a crucial role in improving sensor performance. Parylene-C (poly(2-chloro-p-xylylene)) has been proven as ideal guiding layer due to its good uniformity, compactness and adhesion to substrate. Of comparable cell and protein compatibility to the tissue culture substrate, parylene-C films also have preferable effects as the bio-sensitive interface on SH-SAW sensors. In this study, SH-SAW sensor with parylene-C acoustic-wave guiding layer was adopted to monitor the adhesion process of tendon stem cells (TSCs), a newly discovered stem cell type in tendons. TSC suspensions of different concentrations (0.5×10⁵, 1.0×10⁵, 2.0×10⁵, 4.0×10⁵ cell/ml) were added to collagen-coated PDMS wells successively. The cells were maintained in the incubator for 10 hr, during which corresponding S₂₁ spectrums were recorded every 1 min. The results indicated that there was a sharp increase in S₂₁ loss in the beginning of incubation. With incubation continued, the increase rate reduced gradually, and S₂₁ loss tended to be stable. S₂₁ phase decreased continuously at first, and then entered a plateau with continued incubation. These changes are considered to be related to the integrin-ECM protein interactions and focal adhesion formation occurring in TSC adhesion process. In addition, as TSC suspension concentration increased, the final value of S₂₁ loss change due to TSC adhesion was increased. SH-SAW sensors exhibit high sensitivity and stability in TSC adhesion monit- ring, indicating their potential for investigating cell biology in general and cell adhesion in particular.