Session Detail

A novel biaxial culture system capable of cyclically stretching planar soft tissues was developed and used to study growth and remodeling of fibroblast-seeded collagen gels in response to dynamic mechanical stimuli. Fibroblast-seeded collagen gels, a simple three-dimensional cell culture model, were subjected to five distinct mechanical conditions for six days: freefloating, static equibiaxial stretching (10%), cyclic equibiaxial stretching at two constant strain magnitudes (CES-7% and CES-20%), and cyclic equibiaxial stretching with incrementally increasing stain magnitude (ICES, 7% -> 15% -> 20% each for two days). The frequency of cyclic stretching was set at 1 Hz. At the end of culture, mechanical properties of the gels were examined by biaxial mechanical testing and checked again upon the removal of seeded cells. Collagen microstructure within the gels was illustrated by multiphoton microscopy. The mRNA levels of collagen type I and type III and fibronectin in the cells were examined by reverse transcription PCR. The protein expression of a-smooth muscle actin was detected by immunohistochemistry. We found that the gels cultured under cyclic stretching were stiffer than those cultured under static stretching. Particularly, the stiffness appeared to be significantly enhanced when the ICES was employed. The enhancement of mechanical properties by cyclic stretching appeared to persist upon cell removal, suggesting an irreversible remodeling of extracellular matrix. Second harmonic generation images showed that collagen fibers became thicker and more compact in the gels cultured under cyclic stretching, which may explain the mechanical findings. The mRNA expression of collagen type I in the cells of the ICES was significantly greater than that of the other groups except for the CES-20%. This study suggests that when cyclic stretching is to be used in engineering soft tissues, incrementally increasing strain magnitude may prove useful in the development of the tissue.

 

Ligamentum flavum (LF) hypertrophy induces the inflammation and fibrosis by mechanical stress. It is the common disorder for the most patient with lumbar spinal canal stenosis. Here, we established a cyclic stretching mircoenvironment to simulate part of the motion condition of LF cells in human body by using two-dimensional and three-dimensional cell culture. We observed directional migration, morphological changes and protein expressions of LF cells after long-term cyclic mechanical stretching. In the future, this study is in a hope to identify the correlation between LFH and mechanical stress.

 

Many studies use ultrasound for diaphragmatic excursion (DE) evaluation. The calculation of DE value requires recording the diaphragm movement, freezing the ultrasound image, re-calling video and measuring target distance which is time consuming. We aimed at using an ultrasound image tracking algorithm (UITA) to trace diaphragm movement and reveal DE values in real time. We tested UITA with 40 young volun-teers under 4 respiration conditions: standing with quiet breathing (SQB), supine with quiet breathing (SuQB), stand-ing with deep breathing (SDB), and supine with deep breath-ing (SuDB). The value of DE during SQB, SuQB, SDB, and SuDB was 24.5 ± 10.2, 31.9 ± 10.5, 68.9 ± 15.9, and 98.1 ± 27.4 mm, respectively. We found displacement of diaphragm can be translated to waveforms like spirometry graphs with real-time DE value. DE decreased about 30% in the standing position than in the supine position. Quiet breathing or deep breathing had similar effect on the percent decrease of DE. Further studies are needed to validate this tracking algorithm as a clinical tool in patients with the diaphragm dysfunction.