GAG depletion increases the stress-relaxation response of tendon fascicles,but does not influence recovery

Cyclic and static loading regimes are commonly used to study tenocyte metabolism in vitro and to improve our understanding of exercise-associated tendon pathologies. The aims of our study were to investigate if cyclic and static stress relaxation affected the mechanical properties of tendon fascicles differently, if this effect was reversible after a recovery period, and if the removal of glycosaminoglycans (GAGs) affected sample recovery. Tendon fascicles were dissected frombovine-foot extensors and subjected to 14% cyclic (1 Hz) or static tensile strain for 30 min. Additional fascicles were incubated overnight in buffer with 0.5 U chondroitinase ABC or in buffer alone prior to the static stress-relaxation regime. To assess the effect of different stress-relaxation regimes, a quasi-static test to failure was carried out, either directly post loading or after a 2 h recovery period, and compared with unloaded control fascicles. Both stress-relaxation regimes led to a significant reduction in fascicle failure stress and strain, but this was more pronounced in the cyclically loaded specimens. Removal of GAGs led to more stress relaxation and greater reductions in failure stress after static loading compared to controls. The reduction in mechanical properties was partially reversible in all samples, given a recovery period of 2 h. This has implications for mechanical testing protocols, as a time delay between fatiguing specimens and characterization of mechanical properties will affect the results. GAGs appear to protect tendon fascicles from fatigue effects, possibly by enabling sample hydration.     

MMP-1, IL-1β, and COX-2 mRNA Expression is Modulated by Static Load in Rabbit Flexor Tendons

Tendon cells respond to their mechanical environment by synthesizing and degrading the surrounding matrix. This study examined how expression of genes associated with tendon degeneration is affected by static loads. Forty flexor tendons from 10 New Zealand White rabbits were harvested and secured in a tissue loading system. A static load of 0, 2, 4, or 6 MPa was applied to tendons for 20 h. MMP-1, IL-1β, COX-2, GAPDH, and 18s mRNA expression was measured by qRT-PCR. MMP-1 expression in tendons loaded to 6 MPa was significantly increased 259% compared to tendons loaded to 4 MPa. Relative to a 0 MPa load, IL-1β expression was inhibited with load at 4 MPa (48%) while COX-2 expression was increased at 6 MPa (219%). A polynomial regression analysis found a significant positive correlation between creep and expression of MMP-1 (R ² = 0.53, p < 0.001) and IL-1β (R ² = 0.55, p < 0.001). The results of this study indicate that moderate load inhibits IL-1β and high load stimulates COX-2 relative to stress shielding. MMP-1 expression is up-regulated with high loads compared to moderate loads. The correlation between creep and expression suggests that the pathway for MMP-1 and IL-1β expression, leading eventually to tendon degeneration, may be regulated by the biomechanical factor creep.     

Effects of cyclic loading on the tensile properties of human patellar tendon

Bone-patellar tendon-bone (BPTB) graft is a popular choice for ACL reconstruction. These grafts are subjected to cyclic loading during the activities of daily living. Significant knee laxity is observed in reconstructed knee shortly after reconstruction. The source of this laxity is not clear. The change in the tensile properties of the graft due to cyclic loading can be one of the reasons for the change in knee laxity.Twenty patellar tendons from fresh frozen cadaver knees were cyclically loaded at a stress amplitude equivalent to 33% of the failure strength of the contralateral patellar tendon for 5000 cycles at 1.4 Hz. They were then tested in tension to failure. Failure properties and the low load properties such as toe-region modulus were calculated. The results were compared with those of contralateral patellar tendons that were not subjected to cyclic loading before testing to failure.Fatigue loading did not alter the failure and low load properties with the exception of failure strain which decreased by about 10% (P < .05). Cyclically loaded patellar tendons with higher tissue mass density possess higher strength, modulus of elasticity, toughness, and transition stress (P < .05). The results indicate that there is no significant change in graft properties because of cyclic loading with the above load magnitude. The change in knee laxity observed after reconstruction, hence, is not because of change in graft properties due to moderate cyclic loading. Other factors, such as plastic deformation (yielding) of the graft, might play a role in increased knee laxity after reconstruction.     

Response of Rabbit Achilles Tendon to Chronic Repetitive Loading

The objective of this work was to assess the response of tendon to chronic repetitive loading. Controlled muscle stimulation was used to load the rabbit Achilles tendon at a frequency of 1.25 Hz for two hours per day, three days per week for a period of 11 weeks. Average peak tendon force was 26 N during the protocol. The loading protocol did not modify the gross morphology of the tissue, nor its water content or cellularity. Increases in mRNA expression of collagen Type III and MMPs were observed, but no signs of injury were detected by histologic examination of tendon and paratenon structures. The lack of a detectable injury response suggests that the tendons were not loaded beyond their capacity for repair. Factors additional to mechanical loading such as aging, illness or stress may be necessary to produce pathology.     

Response of rabbit Achilles tendon to chronic repetitive loading.

The objective of this work was to assess the response of tendon to chronic repetitive loading. Controlled muscle stimulation was used to load the rabbit Achilles tendon at a frequency of 1.25 Hz for two hours per day, three days per week for a period of 11 weeks. Average peak tendon force was 26 N during the protocol. The loading protocol did not modify the gross morphology of the tissue, nor its water content or cellularity. Increases in mRNA expression of collagen Type III and MMPs were observed, but no signs of injury were detected by histologic examination of tendon and paratenon structures. The lack of a detectable injury response suggests that the tendons were not loaded beyond their capacity for repair. Factors additional to mechanical loading such as aging, illness or stress may be necessary to produce pathology.     

Comparison of mechanical properties of rat tibialis anterior tendon evaluated using two different approaches

Tendon injuries may result in variations of its mechanical properties. The published data of the tendon stiffness of small animals, such as mouse and rat, are exclusively obtained by measuring grip-to-grip (g-t-g) displacement. Local strain concentration and relative sliding of the specimens in the clamps might significantly affect the measured tendon deformation. In the present study, the mechanical properties of the rat tibialis anterior tendon measured using the proposed tendon mark method were compared to those evaluated using the g-t-g displacement method. Five male Sprague Dawley rats ( approximately 418 g) were used in this study. For the proposed method, reference marks were made on the tendons using permanent ink. A microscope video system was customized to observe and record the tendon deformation. Pattern recognition software was developed to obtain the displacement time-histories of the reference marks. The distance between the grips was approximately 7 mm; and the distance between the reference marks used for the data processing was approximately 5 mm. The cross-section areas of the specimens were measured using a custom-made slot gauge and by applying a constant compressive stress (0.15 MPa). The tendons were clamped between two custom-made metal grips and stretched on a testing machine at a constant speed (1 mm/s) up to failure. Throughout the tests, the tendon specimens were submerged in a PBS bath at 22 degrees C. The deformation of the specimens was evaluated using the g-t-g displacement method and the proposed method. The stress/strain curves obtained by using the g-t-g displacement can be characterized by an initial toe zone, a quasi-linear zone, and a final failure stage. The stress/strain curves determined using the proposed method are quite different from those obtained using the g-t-g displacement: it has a smaller toe zone and a stress-hardening transition, over which the tendon stiffness increases dramatically with the increasing strain. The tendon stiffness measured by using the g-t-g displacement method may underestimate the actual mechanical properties of tendon by approximately 43%.     

An in vitro scratch tendon tissue injury model: effects of high frequency low magnitude loading

The healing process of ruptured tendons is suboptimal, taking months to achieve tissue with inferior properties to healthy tendon. Mechanical loading has been shown to positively influence tendon healing. However, high frequency low magnitude (HFLM) loads, which have shown promise in maintaining healthy tendon properties, have not been studied with in vitro injury models. Here, we present and validate an in vitro scratch tendon tissue injury model to investigate effects of HFLM loading on the properties of injured rat tail tendon fascicles (RTTFs). A longitudinal tendon tear was simulated using a needle aseptically to scratch a defined length along individual RTTFs. Tissue viability, biomechanical, and biochemical parameters were investigated before and 7 days after culture . The effects of static, HFLM (20 Hz), and low frequency (1 Hz) cyclic loading or no load were also investigated. Tendon viability was confirmed in damaged RTTFs after 7 days of culture, and the effects of a 0.77 ± 0.06 cm scratch on the mechanical property (tangent modulus) and tissue metabolism in damaged tendons were consistent, showing significant damage severity compared with intact tendons. Damaged tendon fascicles receiving HFLM (20 Hz) loads displayed significantly higher mean tangent modulus than unloaded damaged tendons (212.7 ± 14.94 v 92.7 ± 15.59 MPa), and damaged tendons receiving static loading (117.9 ± 10.65 MPa). HFLM stimulation maintained metabolic activity in 7-day cultured damaged tendons at similar levels to fresh tendons immediately following damage. Only damaged tendons receiving HFLM loads showed significantly higher metabolism than unloaded damaged tendons (relative fluorescence units —7021 ± 635.9 v 3745.1 ± 641.7). These validation data support the use of the custom-made in vitro injury model for investigating the potential of HFLM loading interventions in treating damaged tendons.     

Canine tendon studies. II. Biomechanical evaluation of normal and regrown canine tendons.

Some of the mechanical properties of regrown canine tendons are compared to those of normal tendons of young and mature animals. Patellar and Achilles tendons from 12 beagle dogs were removed and studied with their bone origin and insertions. Mechanical tests were performed within 24 hr and test conditions simulated the physiological function of the tendon in vivo at room temperature. Specimens were soaked in Ringers solution and mounted in an Instron testing machine with load deflection curves plotted automatically. The parameters used for analysis were load extension, stress relaxation, elastic limit, and strain rate dependence. The regrown tendons in young animals appeared to quickly adjust in dimension and structure so that their properties were not significantly different from those of normal tendons on a load extension basis. The normal tendons were stiffer than regrown ones but the modulus of elasticity increased with age. The Achilles were stiffer than patellar tendons. Cyclic loading with 25 kg did not affect reconstructed tendon models, although some increase in stiffness was noted. The elastic modulus decreased with an increase in ambient temperature and increasing strain rate.     

Mechanical properties of achilles tendon in rats induced to experimental diabetes

The aim of this study was to quantify the effect of chemically induced diabetes mellitus (DM) on the mechanical properties of the Achilles tendon of rats and correlate it with metabolic and biomechanical findings. Adult rats were selected randomly and assigned to two groups, the diabetic group consisted of animals receiving a dose of streptozotocin to induce type I diabetes and the control group. The animals were placed in metabolic cages for analysis of metabolism. Ten weeks after diabetes induction, the Achilles tendon of both groups were collected and submitted to a traction test in a conventional testing machine. The measurements of mechanical properties indicated that the elastic modulus (MPa) was significantly higher in the control group (p < 0.01). In Maximum tension (MPa), the groups did not have differences (p > 0.01). Energy/tendon area (N mm/mm²), specific strain (%) and maximum specific strain (mm) were higher in tendon tests of the diabetic group (p < 0.01). We observed that the mechanical properties of tendons have correlations with metabolic properties of the diabetic animals. These results showed that induced DM in rats have an important negative effect on the mechanical properties of the Achilles tendon.     

The effect of acute exercise on collagen turnover in human tendons: influence of prior immobilization period

Mechanical loading of human tendon stimulates collagen synthesis, but the relationship between acute loading responses and training status of the tendon is not clear. We tested the effect of prolonged load deprivation on the acute loading-induced collagen turnover in human tendons, by applying the same absolute load to a relative untrained Achilles tendon (2-week immobilization period prior to acute loading) and a habitually loaded contra-lateral Achilles tendon, respectively, within the same individuals. Eight untrained, healthy males had one lower limb totally immobilized for 2 weeks, whereas the contra-lateral leg was used habitually. Following the procedure both Achilles tendons and calf muscles were loaded with the same absolute load during a 1-h treadmill run. Tissue collagen turnover was measured by microdialysis performed post-immobilization but pre-exercise around both Achilles tendons and compared to values obtained by 72-h post-exercise. Power Doppler was used to monitor alterations in intratendinous blood flow velocity of the Achilles tendon and MRI used to quantitate changes in tendon cross-section area. Acute loading resulted in an increased collagen synthesis 72 h after the run in both Achilles tendons (p < 0.05) with no significant difference. No signs of acute tendon overloading were demonstrated by Power Doppler, and tendon cross-section area did not change as a result of immobilization and reloading. The present study indicates that 2 weeks of tendon load deprivation is not sufficient to affect the normal adaptive response to loading determined as increased collagen synthesis of peritendinous Achilles tendon tissue in humans.     

The effect of dry needling and treadmill running on inducing pathological changes in rat Achilles tendon

Achilles tendinopathy is a common degenerative condition without a definitive treatment. An adequate chronic animal model of Achilles tendinopathy has not yet been developed. The purpose of this study was to evaluate the individual and combined effects of dry needling and treadmill running on the Achilles tendon of rats. Percutaneous dry needling, designed to physically replicate microrupture of collagen fibers in overloaded tendons, was performed on the right Achilles tendon of 80 Sprague–Dawley rats. The rats were randomly divided into two groups: a treadmill group, which included rats that underwent daily uphill treadmill running (n?=?40), and a cage group, which included rats that could move freely within their cages (n?=?40). At the end of weeks 1 and 4, 20 rats from each group were sacrificed, and bilateral Achilles tendons were collected. The harvested tendons were subjected to mechanical testing and histological analysis. Dry needling induced histological and mechanical changes in the Achilles tendons at week 1, and the changes persisted at week 4. The needled Achilles tendons of the treadmill group tended to show more severe histological and mechanical changes than those of the cage group, although these differences were not statistically significant. Dry needling combined with free cage activity or treadmill running produced tendinopathy-like changes in rat Achilles tendons up to 4 weeks after injury. Dry needling is an easy procedure with a short induction period and a high success rate, suggesting it may have relevance in the design of an Achilles tendinopathy model.     

Changes in stiffness induced by hindlimb suspension in rat Achilles tendon

The aim of this study was to measure the effects of hindlimb suspension on mechanical properties of the rat Achilles tendon. Adult male Wistar rats were randomly assigned to groups to be either suspended, or a control. After 21 days, Achilles tendons were removed for mechanical analysis. Classical tests of tensile performance were made, and mechanical parameters were derived from a stress-strain relationship. The tendons of animals that had been suspended presented values for maximal stress and tangent modulus which were 37.5% (P < 0.01) and 41% (P < 0.01), respectively, lower than the tendons of the control rats. In a similar way, the energy absorption capacity had largely decreased in animals that had been suspended. However, the maximal strain was similar in the two groups. These results showed that hindlimb suspension in rats has an important detrimental effect on mechanical properties of the Achilles tendon. Differences in tendon stiffness obtained here, along with those found by other investigators, encourage the hypothesis that homeostatic responses of soft tissues are due to changes in limb loadings. This study may be useful in providing a better understanding of the adaptation of human skeletal muscle when exposed to microgravity. Accepted: 3 September 1999     

Fatigue is More Damaging than Creep in Ligament Revealed by Modulus Reduction and Residual Strength

Following injury of a complementary joint restraint, ligaments can be subjected to higher than normal stresses. Normal ligaments are exposed to static (creep) and cyclic (fatigue) loading from which damage can accumulate at these higher than normal stresses. This study tracked damage accumulation during creep and fatigue loading of normal rabbit medial collateral ligaments (MCLs) over a range of stresses, using modulus reduction as a marker of damage. Creep tests were interrupted occasionally with unloading/reloading cycles to measure modulus. Test stresses were normalized to ultimate tensile strength (UTS): 60%, 30%, and 15% UTS. Not all creep and fatigues tests progressed until rupture but were stopped and followed by an assessment of the residual strength of that partially damaged ligament using a monotonic failure test. Fatigue loading caused earlier modulus reduction than creep. Modulus reduction occurred at lower increases in strain (strain relative to initial strain) for fatigue than creep. In other words, at the same time or increase in strain, fatigue is more damaging than creep because the modulus ratio reduction is greater. These findings suggest that creep and fatigue have different strain and damage mechanisms. Ligaments exposed to creep or fatigue loading which produced a modulus reduction had decreased residual strength and increased toe-region strain in a subsequent monotonic failure test. This finding confirmed that modulus reduction during creep and fatigue is a suitable marker of partial damage in ligament. Cyclic loading caused damage earlier than static loading, likely an important consideration when ligaments are loaded to higher than normal magnitudes following injury of a complementary joint restraint.     

Ultrastructural Determinants of Murine Achilles Tendon Strength During Healing

The mechanisms by which tendon strength is established during growth and development and restored following injury are not completely understood and are likely to be complex, multifactorial processes. Several studies examining the relationship between mechanical behavior and ultrastructural characteristics of tendons and ligaments during growth and maturation suggest that collagen fibril diameter is strongly correlated with tendon strength. Because of the similarities between development and repair processes of musculoskeletal tissues, increases in tendon strength during healing may be related to increases in fibril ultrastructural parameters such as fibril size, numerical density, and area fraction. In this study, we compared murine Achilles tendons at various time points after tenotomy with sham-operated controls in tensile tests to failure and examined tendons using electron microscopy to assess collagen fibril ultrastructure. We found that in the 6-week period following Achilles tenotomy, fibril mean diameter remained significantly smaller than sham-side diameter by a factor of 2–3. Despite the persistently small fibril size, increasing numerical density resulted in a gradual increase in fibril area fraction. Biomechanical strength did not reach that of intact tendons until some time between 5 and 7 weeks, approximately the same time period when fibril area fraction began to approach sham values. These data suggest that parameters other than collagen fibril size are most responsible for increased tendon strength during healing.     

Role of moderate exercising on Achilles tendon collagen crimping patterns and proteoglycans

Abstract

In this study, the morphological and morphometric changes in the collagen crimping pattern of Achilles tendon and metabolism/expression of tenocytes explanted from tendons of running (RUN) and sedentary (SED) rats were investigated to assess the effects of 12 weeks moderate running exercise. The number, the top angle width and the base length of each crimp in three different regions (proximal, central and distal) of RUN and SED tendons were measured with a polarized light microscope. The most significant morphometric differences in the crimps were detectable in the central region of the RUN tendons. In this region, crimps were fewer, larger and more flattened than those of other regions as a consequence of a functional adaptation of extracellular matrix to running, in order to increase tendon stiffness and force transmission efficiency. Conversely, the top angle width of the crimps reduced in proximal and distal regions of the RUN tendons, suggesting that these crimps might act as more reactive mechanical springs, able to store and improve the release of the stored strain energy in most loaded regions. Tenocytes explanted from Achilles tendons of both RUN and SED groups were cultured. Running influenced tenocytes which showed a significant increase in collagen type-I synthesis and proteoglycans production, suggesting enhancement of the loading transmission efficiency and facilitate inter-fibril and inter-fiber sliding.     

Ultrastructural determinants of murine achilles tendon strength during healing

The mechanisms by which tendon strength is established during growth and development and restored following injury are not completely understood and are likely to be complex, multifactorial processes. Several studies examining the relationship between mechanical behavior and ultrastructural characteristics of tendons and ligaments during growth and maturation suggest that collagen fibril diameter is strongly correlated with tendon strength. Because of the similarities between development and repair processes of musculoskeletal tissues, increases in tendon strength during healing may be related to increases in fibril ultrastructural parameters such as fibril size, numerical density, and area fraction. In this study, we compared murine Achilles tendons at various time points after tenotomy with sham-operated controls in tensile tests to failure and examined tendons using electron microscopy to assess collagen fibril ultrastructure. We found that in the 6-week period following Achilles tenotomy, fibril mean diameter remained significantly smaller than sham-side diameter by a factor of 2-3. Despite the persistently small fibril size, increasing numerical density resulted in a gradual increase in fibril area fraction. Biomechanical strength did not reach that of intact tendons until some time between 5 and 7 weeks, approximately the same time period when fibril area fraction began to approach sham values. These data suggest that parameters other than collagen fibril size are most responsible for increased tendon strength during healing.     

Prostaglandin E2, collagenase,and cell death responses depend on cyclical load magnitude in an explant model of tendinopathy

Tendinopathy is a significant clinical problem that can result from repetitive activity. While the precise etiology of this condition remains unclear, the cellular response to cyclical loading is believed to have a contributory role to the pathology of tendinopathy. This study examined the short-term biochemical response of avian flexor digitorum profundus tendon to repetitive cyclic loadings of varying magnitude. An in vitro tendon explant model was utilized to apply four levels of haversine tensile stress (peak stress of 0, 3, 12, and 18 MPa) at 1.0 Hz, 8 hr/day for 3 days. The 12 and 18 MPa levels were known to cause significant mechanical damage based on previous work. Tissue media was recovered and analyzed for prostaglandin E₂ (PGE₂), lactate dehydrogenase (LDH, measure of cell death), and collagenase levels. Tissue samples were recovered and analyzed for cell viability, total collagen, and sulfated glycosaminoglycan content. Collagenase, LDH, and PGE₂ levels were found to be influenced by loading magnitude (p < 0.05) with higher levels being present at higher load magnitudes. Varying cyclical load magnitude caused minimal compositional changes as collagen content and glycosaminoglycan did not change. These results indicate that elevated cyclical mechanical loading of tendon quickly results in altered biochemical tissue responses indicative of tissue injury. More sustained cyclical loading over time may be required for these initial responses to induce more dramatic tissue changes as observed in clinical tendinopathy.     

The Effect of Overuse Activity on Achilles Tendon in an Animal Model: A Biomechanical Study

Musculoskeletal soft tissue injuries from athletic activities are common in the rotator cuff tendons, lateral epicondyle of the elbow, the patella tendon, and the Achilles tendon. Despite the fact that the Achilles tendon is the largest and strongest tendon in the human body, it is frequently injured in the athletic setting. To study the etiology and pathogenesis of Achilles tendon injuries, our goal was to develop a model of Achilles tendon overuse by evaluating the Achilles tendons from animals subjected to the exercise protocol previously described as overuse for the supraspinatus tendon. We hypothesized that the same exercise protocol would produce injuries to the Achilles tendon as demonstrated by changes in the cross-sectional area and biomechanical properties. While a significant injury was induced into the supraspinatus tendon, we found no changes in the Achilles tendons of these exercised animals based on gross observation, geometric measurements, and mechanical testing analyses. Although surprising, there are many possible explanations for these findings including differences in potential injury mechanisms, functional capabilities of the differing tendons, and other factors.     

Mechanical conditioning of cell-seeded small intestine submucosa: a potential tissue-engineering strategy for tendon repair

Our long-term objective is to enhance tendon repair by delivering cells on natural biologic scaffolds to the repair site. Clinical outcomes may be improved by first preconditioning these cell-seeded constructs in bioreactors to enhance their properties at implantation and to deliver cells expressing a desired phenotype. In this work, we have investigated the effect of in vitro mechanical conditioning on small-intestine submucosa (SIS) scaffolds seeded with primary tendon cells (tenocytes). SIS scaffolds (with and without cells) were conditioned under various loading regimes over a 2-week period. In vitro cyclic loading significantly increased the biomechanical properties (e.g., stiffness) of cell-seeded SIS constructs (129.1 +/- 10.2%) from time 0. The stiffness change of cyclically loaded constructs without cells was 33.9 +/- 13.8% and of statically loaded constructs with cells was 34.0 +/- 15.2% and without cells was 33.4 +/- 10.7%. In the cell-seeded groups, our data demonstrate a direct role (e.g., cell tensioning) for cells in construct stiffening. In addition, the initial stiffness of the cell-seeded, cyclically loaded constructs was found to be a strong predictor of the change in construct stiffness. Despite the mechanical integrity of these constructs being significantly less than native tendon, our data show that structural properties can be improved with in vitro mechanical conditioning. These data provide the basis for future studies investigating in vitro conditioning (mechanical, chemical) of cell-seeded ECM scaffolds and the use of such constructs for enhancing tendon repair in vivo.     

Tendon tissue engineering using cell-seeded umbilical veins cultured in a mechanical stimulator

The goal of this study was to investigate the effect of cyclic mechanical stimulation on mesenchymal stem cells (MSCs) seeded within human umbilical veins (HUVs), and to determine the potential of the engineered constructs to function as tendon tissue replacement models. Decellularized HUVs were seeded with MSCs embedded in type I collagen hydrogel. A mechanical stimulator for tissue engineering applications was specifically designed to cyclically tension the constructs for durations up to 2 weeks, where controls were left untensioned. This HUV model system seeded with a cellular collagen gel, coupled with mechanical stimulation, resulted in improved mechanical properties compared to other tendon tissue engineered constructs composed of cellular collagen gel alone, without any additional supporting scaffold. After 2 weeks of culture an increase in cell number was measured for both tensioned and untensioned constructs; however, the increase was at least eightfold higher for stimulated samples. Microscopically, cyclically tensioned samples showed parallel orientation of collagen fibers and spindle-shaped cell nuclei mimicking the morphology of native tendons. Moreover, mechanostimulation resulted in significantly stronger (156%) and stiffer (109%) constructs compared to untensioned samples. This engineered tendon model had an ultimate tensile strength value only one order of magnitude lower than human tendons and strain values in the range of human tendons. The results documented are promising and can be further improved by optimizing potentially critical culture parameters such as seeding density, loading regimes, and mechanostimulation durations.