Effects of Mechanical Stimulation on the Biomechanics and Histology of Stem Cell–Collagen Sponge Constructs for Rabbit Patellar Tendon Repair

Abstract

The objective of this study was to determine how mechanical stimulation affects the biomechanics and histology of stem cell-collagen sponge constructs used to repair central rabbit patellar tendon defects. Autogenous tissue-engineered constructs were created for both in vitro and in vivo analyses by seeding mesenchymal stem cells from 10 adult rabbits at 0.14x10(6) cells/construct in type I collagen sponges. Half of these constructs were mechanically stimulated once every 5 min for 8 h/day to a peak strain of 4% for 2 weeks. The other half remained in an incubator without mechanical stimulation for 2 weeks. Samples allocated for in vitro testing revealed that mechanically stimulated constructs had 2.5 times the linear stiffness of nonstimulated constructs. The remaining paired constructs for in vivo studies were implanted in bilateral full-thickness, full-length defects in the central third of rabbit patellar tendons. Twelve weeks after surgery, repair tissues were assigned for biomechanical (7 pairs) and histologic (3 pairs) analyses. Maximum force, linear stiffness, maximum stress, and linear modulus for the stimulated (vs. nonstimulated) repairs averaged 70% (vs. 55%), 85% (vs. 55%), 70% (vs. 50%), and 50% (vs. 40%) of corresponding values for the normal central third of the patellar tendons. The average force-elongation curve for the mechanically stimulated repairs also matched the corresponding curve for the normal patellar tendons, up to 150% of the peak in vivo force values recorded in a previous study. Construct and repair linear stiffness and linear modulus were also positively correlated (r = 0.6 and 0.7, respectively). Histologically both repairs showed excellent cellular alignment and mild staining for decorin and collagen type V, and moderate staining for fibronectin and collagen type III. This study shows that mechanical stimulation of stem cell-collagen sponge constructs can significantly improve tendon repair biomechanics up to and well beyond the functional limits of in vivo loading.

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

“…The tissue-engineered constructs were implanted into defects in the central third of rabbit patellar tendons, and repair tissues were harvested at twelve weeks following surgery. 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 .…”

“…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.…”

“…Others have sought to improve tendon repair by creating tissue-engineered constructs using autologous progenitor cells derived from the bone marrow of New Zealand White rabbits seeded on a bovine-derived type-I collagen sponge and incorporating a mechanical stimulation profile at a frequency of 1 Hz, for eight hours per day, at a peak strain of 2.4% for a total of twelve days 134 . The tissue-engineered constructs were implanted into defects in the central third of rabbit patellar tendons, and repair tissues were harvested at twelve weeks following surgery.…”

Design and Performance of an Optically Accessible, Low-Volume, Mechanobioreactor for Long-Term Study of Living Constructs

“…43 Cyclic traction devices have demonstrated an increase in mechanical properties over nonstimulated samples by *150% for collagen-based constructs for tendon repair. 44 Given this successful proliferation of devices and improvements of outcome, it is clear that bioreactors will play a critical role in the field of tissue engineering. Experimental results from loading bioreactors have shown that mechanical stimulation of tissues and engineered constructs results in increases in cell proliferation, protein production, molecular incorporation, and higher levels of structural organization, in general, leading to enhanced mechanical properties.…”