Cyclical strain improves artificial equine tendon constructs in vitro

Abstract

Tendon injuries are a common cause of morbidity in humans. They also occur frequently in horses, and the horse provides a relevant, large animal model in which to test novel therapies. To develop novel cell therapies that can aid tendon regeneration and reduce subsequent reinjury rates, the mechanisms that control tendon tissue regeneration and matrix remodelling need to be better understood. Although a range of chemical cues have been explored (growth factors, media etc.), the influence of the mechanical environment on tendon cell culture has yet to be fully elucidated. To mimic the in vivo environment, in this study, we have utilised a novel and affordable, custom-made bioreactor to apply a cyclical strain to tendon-like constructs generated in three-dimensional (3D) culture by equine tenocytes. Dynamic shear analysis (DSA), dynamic scanning calorimetry (DSC) and Fourier-transform infrared (FTIR) spectroscopy were used to determine the mechanical and chemical properties of the resulting tendon-like constructs. Our results demonstrate that equine tenocytes exposed to a 10% cyclical strain have an increased amount of collagen gel contraction after 7 and 8 days of culture compared with cells cultured in 3D in the absence of external strain.While all the tendon-like constructs have a very similar chemical composition to native tendon, the application of strain improves their mechanical properties. We envisage that these results will contribute towards the development of improved biomimetic artificial tendon models for the development of novel strategies for equine regenerative therapies. K E Y W O R D S3D culture, dynamic shear analysis, equine, mechanical properties, tendon cells

Spider Silk-Augmented Scaffolds and Adipose-Derived Stromal Cells Loaded with Uniaxial Cyclic Strain: First Investigations of a Novel Approach for Tendon-Like Constructs

“…To further improve cell distribution and induce mechanotransduction, cyclic uniaxial strain was applied. The frequency of the cyclic strain was with 1 Hz lower than the stride frequency found in equine canter, which is approximately 2 Hz, but comparable to the strain used by other studies, in particular for the promotion of stem cell differentiation towards tenocytes [31][32][33]. While some studies applied strain for as little as 15 to 20 min per 24 h, as 15 min per 24 h were sufficient for a notable effect regarding mechanical induction, longer application periods were suggested [33,34].…”

A universal multi-platform 3D printed bioreactor chamber for tendon tissue engineering

“…The design for the frames includes two internal tendon attachment points which avoid the use of grips or clamps to secure the ends of the tissue and were optimised to distribute the mechanical stress through the tissue without breaking the fibrin hydrogel scaffold. 38,45 After 14 days culture in six-well plates, the cell-seeded fibrin hydrogels formed tendon-like tissues between the attachment points which were easily removed from the well plate and slotted into individual wells of the bioreactor chamber. At this stage, two 90° adapter arms were attached (Figure 2(b)) to connected points A and B of the frame to the corresponding points on the bioreactor chamber and six-way tensile arm (Figure 2(d)).…”

“…Researchers use either custom-made tensile bioreactors or commercially available systems such as the EBERS TC-3 and the CellScale MC series. Our search of literature published between January 2016 and April 2020 indicates that of 24 published studies on cyclic loading in tendon tissue engineering, three groups published data generated using a CellScale bioreactor 25 , 28 , 34 and one group published using an EBERS TC-3 bioreactor, 41 with the remaining 20 using custom-designed bioreactors 19 – 24 , 26 , 27 , 29 – 33 , 35 – 40 , 42 , 43 (summarised in Table 1 ). There is a clear requirement for greater reproducibility and consistency in the methodological approach to enable both comparative research and translation towards effective clinical therapies.…”

The Lack of a Representative Tendinopathy Model Hampers Fundamental Mesenchymal Stem Cell Research

“…Optimal for physiological mimicking is, therefore, the application of intermittent cyclic loading ( Cao et al, 2006 ; Scott et al, 2011 ). Different studies show favorable cell characteristics (elongation, metabolic activity, gene levels and protein production) administering intermittent cyclic strain, while a negative influence of continuous cyclic strain is frequently reported ( Cao et al, 2006 ; Riboh et al, 2008 ; Bosworth et al, 2014 ; Youngstrom et al, 2015 ; Atkinson et al, 2020 ). For example, Riboh et al (2008) compared the application of constant versus intermittent cyclic strain in a 2D, Flexcell Strain Unit (Flexcell International; Hillsborough, NC, United States).…”

“… Wu et al (2017) cultured three different cell types (tenocytes, AT-MSCs and HUVECs) on synthetic electrospun fibers (PCL/PLA scaffolds) and stated that dynamic culture in a custom-made mechanical stimulation device promoted collagen production and tenogenic differentiation ( Wu et al, 2017 ). Atkinson et al (2020) demonstrated with the use of a custom-designed bioreactor that equine tendon constructs within collagen I gels, analogous to other species, show improved mechanics when exposed to cyclic strain ( Atkinson et al, 2020 ).…”