Mechanical Stimulation Increases Collagen Type I and Collagen Type III Gene Expression of Stem Cell–Collagen Sponge Constructs for Patellar Tendon Repair

Abstract

Our group has shown that mechanical stimulation increases the stiffness of stem cell-collagen sponge constructs at 14 days in culture and subsequent rabbit patellar tendon repairs at 12 weeks postsurgery. What remains unclear is which genes might be responsible for this increase in stiffness. Therefore, the objective of this study was to determine how a tensile stimulus affects the gene expression of stem cell-collagen sponge constructs used to repair rabbit central patellar tendon defects. Tissue-engineered constructs were created by seeding mesenchymal stem cells (MSCs) from 10 adult rabbits at 0.14 x 10(6) cells/construct in type I collagen sponges. Half of the constructs were mechanically stimulated once every 5 min for 8 h/d to a peak strain of 2.4% for 2 weeks. The other half remained in an incubator without mechanical stimulation for 2 weeks. After 14 days in culture, half of the stimulated and nonstimulated constructs were prepared to determine the expression of collagen type I, collagen type III, decorin, fibronectin, and glyceraldehyde-3-phosphate dehydrogenase genes using real-time quantitative reverse transcriptase polymerase chain reaction. The remaining constructs were mechanically tested to determine their mechanical properties. Two weeks of in vitro mechanical stimulation significantly increased collagen type I and collagen type III gene expression of the stem cell-collagen sponge constructs. Stimulated constructs showed 3 and 4 times greater collagen type I (p = 0.0001) and collagen type III gene expression (p = 0.001) than nonstimulated controls. Stimulated constructs also had 2.5 times the linear stiffness and 4 times the linear modulus of nonstimulated constructs. However, mechanical stimulation did not significantly increase decorin or fibronectin gene expression (p = 0.2) after 14 days in culture. This study shows that mechanical stimulation of cell-sponge constructs produces similar increases in the expression of 2 structural genes, as well as linear stiffness and linear modulus.

The Role of Mechanical Loading in Tendon Development, Maintenance, Injury, and Repair

“…The results showed that mechanical stimulation improved repair tissue maximum force, linear stiffness, maximum stress, and linear modulus to 70%, 85%, 70%, and 50%, respectively, of the values in the normal, uninjured central third of patellar tendons 134 . Mechanical stimulation increased collagen type-I and type-III gene expression three and four times greater than in nonstimulated controls, respectively 135 . Additionally, the stimulated tissue-engineered constructs were 2.5 times stiffer than nonstimulated controls 135 .…”

“…Mechanical stimulation increased collagen type-I and type-III gene expression three and four times greater than in nonstimulated controls, respectively 135 . Additionally, the stimulated tissue-engineered constructs were 2.5 times stiffer than nonstimulated controls 135 .…”

“…Tissue engineers are incorporating mechanical stimulation to enhance tendon tissue augmentations and replacements [134][135][136][137][138][139][140][141][142][143][144][145][146] . By mechanically preconditioning the tissue-engineered construct cell population prior to in vivo implantation, the cells may be better equipped to enhance the repair since they have been exposed to the appropriate mechanical environment 134,135 .…”

“…By mechanically preconditioning the tissue-engineered construct cell population prior to in vivo implantation, the cells may be better equipped to enhance the repair since they have been exposed to the appropriate mechanical environment 134,135 . Further elucidating the cellular processes involved in the response to the normal and abnormal mechanical environments will improve tissue engineering therapies.…”

The past, present and future in scaffold-based tendon treatments

“…Advancements in engineering, chemistry and biology have made available numerous technologies that allow fabrication of hierarchical threedimensional scaffolds that closely imitate native tendon architectural features and mechanical properties, whilst enabling localised and sustained delivery of therapeutics [350]. Collagen sponges, for example, with or without aligned tracks and loaded with GAGs, growth factors and various cell populations have demonstrated enhanced cell motility and phenotype maintenance in vitro and increased collagen expression levels in small animal models [351][352][353][354][355]. However, such scaffold conformations cannot provide adequate mechanical resistance, in such a high mechanical demand environment [356].…”