Mechanical properties of collagen fascicles from in situ frozen and stress-shielded rabbit patellar tendons

Lyophilized bovine acellular tendon linear fiber material for the reconstruction of attachment structure of paraspinous muscles: an animal in vivo study

Low back pain is common after lumbar spine surgery and the injury from extensive detachment of paraspinal muscles during the surgery may play a vital role. Previously, we prepared a bovine acellular tendon fiber (ATF) material through lyophilization and proved that it could retain its original fibrillar structure and mechanical properties. The objective of this study is to evaluate the effectiveness of this new fiber material used for attachment structure reconstruction of paraspinal muscle. Defect of spinous process, interspinous and supraspinous ligament was established on lumbar spine in rabbit and rat and ATF linear material was implanted to reconstruct the attachment structure. Ultrasound showed the cross-sectional area of the paraspinal muscle in ATF group was larger than that of control group in rats. MRI showed the irregular shape and high signal changes in control group, but regular shape and uniform signal in the ATF group in rabbit. For Electromyogram, the frequency of evoked potential in control group was lower than ATF group and normal rats. HE and Masson staining showed good tissue healing, and immunohistochemical results showed the immune rejection of ATF is significantly lower than that of suture. Reconstruction of the attachment structure of paraspinous muscles with ATF linear material could maintain the morphology, volume and function of paraspinal muscle. ATF material has the potential to be used to manufacture personalized ligaments and other tissue engineering scaffolds. Graphical abstract.

Scaffold-based tissue engineering strategies for soft-hard interface regeneration

Repairing injured tendon or ligament attachments to bones (enthesis) remains costly and challenging. Despite superb surgical management, the disorganized enthesis newly formed after surgery accounts for high recurrence rates after operations. Tissue engineering offers efficient alternatives to promote healing and regeneration of the specialized enthesis tissue. Load-transmitting functions thus can be restored with appropriate biomaterials and engineering strategies. Interestingly, recent studies have focused more on microstructure especially the arrangement of fibers since Rossetti successfully demonstrated the variability of fiber underspecific external force. In this review, we provide an important update on the current strategies for scaffold-based tissue engineering of enthesis when natural structure and properties are equally emphasized. We firstly described compositions, structures and features of natural enthesis with their special mechanical properties highlighted. Stimuli for growth, development and healing of enthesis widely used in popular strategies are systematically summarized. We discuss the fabrication of engineering scaffolds from the aspects of biomaterials, techniques and design strategies and comprehensively evaluate the advantages and disadvantages of each strategy. At last, this review pinpoints the remaining challenges and research directions to make breakthroughs in further studies.

Preparation and biological characteristics of a bovine acellular tendon fiber material

Acellular tendon matrix is an ideal substitute for constructing tissue engineering ligaments, but using detergents causes damage to collagen and fibrin during the process of decellularization. In this study, fresh tendons were lyophilized and separated into fresh tendon fiber (FTF) bundles, and then the cellular components in FTF were removed to prepare acellular tendon fiber (ATF) without adding chemical detergent. H&E staining and DAPI fluorescence microscopy showed no nucleus and DNA residue. Compared with FTFs, the DNA content of ATFs was significantly lower without the collagen content change before and after decellularization. The microstructure of collagen fibrils in ATFs was intact under scanning electron microscopy (SEM), and the maximum tensile load and elastic modulus between FTFs and ATFs were not statistically different. The ATF bundles were cultured with SD rat tenocytes for 72 hr and cells attachment to fiber surfaces were observed under SEM. ATF bundles were then implanted into paraspinal muscles, and histological analysis showed fibroblast-like cells within the ATFs and was similar to the control group (fresh tendon autograft) in morphology. H&E staining showed that the number of lymphocytes and plasma cells in ATF was less than that in fresh tendon autograft. ATF bundles were twisted into linear fiber materials by hand, of which the maximum breaking strength was similar to silk with same diameter. These findings demonstrated that ATFs retain their original fibril structure and mechanical properties after decellularization by trypsin and pancreatic deoxyribonuclease without detergent. Lyophilized ATFs linear fiber material provides the possibility of preparing personalized ligament and other tissue engineering scaffolds.

Engineering Tendon: Scaffolds, Bioreactors, and Models of Regeneration

Tendons bridge muscle and bone, translating forces to the skeleton and increasing the safety and efficiency of locomotion. When tendons fail or degenerate, there are no effective pharmacological interventions. The lack of available options to treat damaged tendons has created a need to better understand and improve the repair process, particularly when suitable autologous donor tissue is unavailable for transplantation. Cells within tendon dynamically react to loading conditions and undergo phenotypic changes in response to mechanobiological stimuli. Tenocytes respond to ultrastructural topography and mechanical deformation via a complex set of behaviors involving force-sensitive membrane receptor activity, changes in cytoskeletal contractility, and transcriptional regulation. Effective ex vivo model systems are needed to emulate the native environment of a tissue and to translate cell-matrix forces with high fidelity. While early bioreactor designs have greatly expanded our knowledge of mechanotransduction, traditional scaffolds do not fully model the topography, composition, and mechanical properties of native tendon. Decellularized tendon is an ideal scaffold for cultivating replacement tissue and modeling tendon regeneration. Decellularized tendon scaffolds (DTS) possess high clinical relevance, faithfully translate forces to the cellular scale, and have bulk material properties that match natural tissue. This review summarizes progress in tendon tissue engineering, with a focus on DTS and bioreactor systems.

Complete stress shielding of the Achilles tendon: ultrastructure and level of interleukin-1 and TGF-β

Few studies emphasize the collagen metabolism-related cytokines and ultrastructure of the completely stress-shielded Achilles tendon. In this study, we used a rat model with complete stress shielding of the Achilles tendon to observe the changes in the ultrastructure of the Achilles tendon and concentration of IL-1 and TGF-β 3 weeks after stress shielding. The model group comprised 12 male Sprague-Dawley rats. The stress of the Achilles tendon of the left hind limb was shielded through tendon cerclage combined with sciatic nerve transection, and the right served as a normal control. Three weeks later, the ultrastructure of the Achilles tendon was observed under electron microscopy and IL-1 and TGF-β levels were determined by enzyme-linked immunosorbent assay. Compared with the control side, collagen fibrils of the shielded Achilles tendons were irregularly arranged and loose. The number of small-diameter collagen fibrils increased significantly with the decrease of the average diameter of collagen fibrils. At the same time, IL-1 concentrations increased significantly in the model group as compared to that in the control group, but no significant difference was found in TGF-β levels. These results suggest that IL-1 may play an important role in the change of ultrastructure after stress shielding.

Viscoelastic and failure properties of spine ligament collagen fascicles

The microstructural volume fractions, orientations, and interactions among components vary widely for different ligament types. If these variations are understood, however, it is conceivable to develop a general ligament model that is based on microstructural properties. This paper presents a part of a much larger effort needed to develop such a model. Viscoelastic and failure properties of porcine posterior longitudinal ligament (PLL) collagen fascicles were determined. A series of subfailure and failure tests were performed at fast and slow strain rates on isolated collagen fascicles from porcine lumbar spine PLLs. A finite strain quasi-linear viscoelastic model was used to fit the fascicle experimental data. There was a significant strain rate effect in fascicle failure strain (P < 0.05), but not in failure force or failure stress. The corresponding average fast-rate and slow-rate failure strains were 0.098 ± 0.062 and 0.209 ± 0.081. The average failure force for combined fast and slow rates was 2.25 ± 1.17 N. The viscoelastic and failure properties in this paper were used to develop a microstructural ligament failure model that will be published in a subsequent paper.

Biomechanical Properties of Vaginal Tissue. Part 1: New Experimental Protocol

PURPOSE

We established a reliable experimental protocol to characterize the biomechanical properties of vaginal tissue and guarantee good test repeatability.

MATERIALS AND METHODS

Because of the large quantities of tissue required to establish the protocol, we worked on ewes according to animal ethics laws. To study the mechanical properties of ewe vaginal tissue we used unidirectional tension tests at a constant deformation rate. Rupture tests were performed under different experimental conditions to analyze the influence of each condition.

RESULTS

Tissue underwent exhaustive tests. The parameters studied were sampling, freezing, preservation conditions, hygrometry and temperature during vaginal tissue tests, and the rate of deformation during tests. As previously noted, vaginal tissue is anisotropic and the collection has been tested previously. We noted that freezing tissue had no consequences on the mechanical response of tissue during unidirectional tension testing. The experimental conditions that we defined (temperature, hygrometry and rate of deformation) allowed us to have reproducible tests.

CONCLUSIONS

Results and analyses allowed us to determine the best reference protocol.

Corticosteroids reduce the tensile strength of isolated collagen fascicles

BACKGROUND

Overuse tendon injuries are frequent. Corticosteroid injections are commonly used as treatment, although their direct effects on the material properties of the tendon are poorly understood.

PURPOSE

To examine the influence of corticosteroids on the tensile strength of isolated collagen fascicles.

STUDY DESIGN

Controlled laboratory study.

METHODS

Single strands (300-500 mum) of rat-tail collagen fascicles were incubated in either high (1 mL of 40 mgmL(-1) mixed with 0.5 mL saline 9%) or low (1 mL of 40 mgmL(-1) mixed with 2 mL saline 9%) concentration of methylprednisolone acetate (Depomedrol) for 3 or 7 days, while the control segment from the same fascicle was kept in saline (N = 64). After the incubation period, the fascicles underwent displacement to failure in a mechanical test rig at 0.13 mm/s, and thereafter hydroxylysyl pyridinoline and lysyl pyridinoline cross-link content was evaluated in a high-performance liquid chromatography system. Data for each group were analyzed with a 2-way analysis of variance (time x incubation) for ultimate stress (mean +/- standard deviation).

RESULTS

In the high-concentration groups, strength was reduced after 3 (16.6 +/- 4.6 MPa) and 7 (8.6 +/- 1.7 MPa) days compared to the controls (30.2 +/- 5.0 MPa and 25.6 +/- 4.6 MPa, respectively; P < .05). In the low-concentration groups, strength was reduced after 3 (12.0 +/- 3.1 MPa) and 7 days (10.9 +/- 2.5 MPa) compared to the controls (31.5 +/- 5.0 MPa and 32.4 +/- 5.6 MPa, respectively; P < .05). The amount of cross-linking was unaffected by the intervention.

CONCLUSION

Data show that the tensile strength of isolated fascicles is markedly reduced after 3- and 7-day incubation in both high and low concentration of corticosteroids, although the observed effect on whole tendon remains unknown.

CLINICAL RELEVANCE

Corticosteroids may weaken specific regions of the injected tendon and leave it more prone to rupture. This weakening effect is manifested in the individual collagen fascicles that constitute the tendon.

Biomechanical and immunohistochemical analysis of high hydrostatic pressure-treated Achilles tendons

BACKGROUND

Reconstruction of bone defects caused by malignant tumors is carried out in different ways. At present, tumor-bearing bone segments are devitalized mainly by extracorporeal irradiation or autoclaving, but both methods have substantial disadvantages. In this regard, high hydrostatic pressure (HHP) treatment of the bone is a new, advancing technology that has been used in preclinical testing to inactivate normal cells and tumor cells without altering the biomechanical properties of the bone. The aim of this study was to examine the biomechanical and immunohistochemical properties of tendons after exposure to HHP and to evaluate whether preservation of the bony attachment of tendons and ligaments is possible.

METHODS

For this, 19 paired Achilles tendons were harvested from both hindlimbs of 4-month-old pigs. After preparation, the cross-sectional area of each tendon was determined by magnetic resonance imaging (MRI). For each animal, one of the two tendons was taken at random and exposed to a pressure of 300 MPa (n = 9) or 600 MPa (n = 10).

RESULTS

The contralateral tendon served as an untreated control. The biomechanical properties of the tendons remained unchanged with respect to the tested parameters: Young's modulus (MPa) and tensile strength (MPa). This finding is in line with immunohistochemical labeling results, as no difference in the labeling pattern of collagen I and versican was observed when comparing the HHP group (at 600 MPa) to the untreated control group.

CONCLUSIONS

We anticipate that during orthopedic surgery HHP can serve as a novel, promising methodical approach to inactivate Achilles tendon and bone cells without altering the biomechanical properties of the tendons. This should allow one to preserve the attachment of tendon and ligaments to the devitalized bone and to facilitate functional reconstruction.

Muscle performance during maximal isometric and dynamic contractions is influenced by the stiffness of the tendinous structures

Contractile force is transmitted to the skeleton through tendons and aponeuroses, and, although it is appreciated that the mechanocharacteristics of these tissues play an important role for movement performance with respect to energy storage, the association between tendon mechanical properties and the contractile muscle output during high-force movement tasks remains elusive. The purpose of the study was to investigate the relation between the mechanical properties of the connective tissue and muscle performance in maximal isometric and dynamic muscle actions. Sixteen trained men participated in the study. The mechanical properties of the vastus lateralis tendon-aponeurosis complex were assessed by ultrasonography. Maximal isometric knee extensor force and rate of torque development (RTD) were determined. Dynamic performance was assessed by maximal squat jumps and countermovement jumps on a force plate. From the vertical ground reaction force, maximal jump height, jump power, and force-/velocity-related determinants of jump performance were obtained. RTD was positively related to the stiffness of the tendinous structures ( r = 0.55, P < 0.05), indicating that tendon mechanical properties may account for up to 30% of the variance in RTD. A correlation was observed between stiffness and maximal jump height in squat jumps and countermovement jumps ( r = 0.64, P < 0.05 and r = 0.55, P < 0.05). Power, force, and velocity parameters obtained during the jumps were significantly correlated to tendon stiffness. These data indicate that muscle output in high-force isometric and dynamic muscle actions is positively related to the stiffness of the tendinous structures, possibly by means of a more effective force transmission from the contractile elements to the bone.

Region-specific mechanical properties of the human patella tendon

The present study investigated the mechanical properties of tendon fascicles from the anterior and posterior human patellar tendon. Collagen fascicles from the anterior and posterior human patellar tendon in healthy young men (mean ± SD, 29.0 ± 4.6 yr, n = 6) were tested in a mechanical rig. A stereoscopic microscope equipped with a digital camera recorded elongation. The fascicles were preconditioned five cycles before the failure test based on pilot data on rat tendon fascicle. Human fascicle length increased with repeated cycles ( P < 0.05); cycle 5 differed from cycle 1 ( P < 0.05), but not cycles 2–4. Peak stress and yield stress were greater for anterior (76.0 ± 9.5 and 56.6 ± 10.4 MPa, respectively) than posterior fascicles (38.5 ± 3.9 and 31.6 ± 2.9 MPa, respectively), P < 0.05, while yield strain was similar (anterior 6.8 ± 1.0%, posterior 8.7 ± 1.4%). Tangent modulus was greater for the anterior (1,231 ± 188 MPa) than the posterior (583 ± 122 MPa) fascicles, P < 0.05. In conclusion, tendon fascicles from the anterior portion of the human patellar tendon in young men displayed considerably greater peak and yield stress and tangent modulus compared with the posterior portion of the tendon, indicating region-specific material properties.

Étude objective de résistance des ligaments pelviens utilisés dans les cures de prolapsus et d'incontinence urinaire d'effort

OBJECTIVE

Underline the objective strength of the pelvic ligaments.

PATIENTS AND METHODS

Twenty nine human female pelvis cadavers, whose storage conditions differed, were used in our study. In each cadaver we dissected all the ligaments used in pelvic surgery. A subjective clinical evaluation of the ligament properties was performed by visual observation as well as by finger palpation. Ligaments were classified into three groups in terms of thickness and apparent strength following finger palpation, high, doubtful and low apparent quality ligaments. Then a suture taking the entire ligament switched the ligaments and a force was applied on the vagina axis until tearing. The device used for strength measurement during traction was a Samson type force gauge, which was developed for the purpose of our study. Results were given in Newtons.

RESULTS

We found a great variability in the values obtained at tearing with maximal values at 200 newtons and minimal at 22. Individually measured, ligament strength varied between individuals, and for a same patient between the type of ligaments and the side. The pre-vertebral ligament was on average the strongest. For bilateral ligaments, there was no difference between the left and right side. The iliopectineal ligament was statistically significantly stronger than sacrospinous and arcus tendineus of pelvic fascia. There was a correlation between subjective evaluation and objective strength measurements.

DISCUSSION AND CONCLUSION

We performed the only study of the strength of pelvic ligaments at tearing. These are, however, routinely used in the cure of prolapse and urinary incontinence. Our results show that there is a great variability in strength between individuals, and for a same patient between the types of ligaments and side. These observations could explain some of the surgical intervention failures and demonstrate the importance of per-operative strength evaluation. Per-operative subjective evaluation on strength is related to objective measurements and could be used to determine the type of ligaments to be used for surgical assembly suspension.

A biomechanical study of the strength of vaginal tissues. Results on 16 post-menopausal patients presenting with genital prolapse

AIMS

Measurements of the tensile and bending strength of samples of vaginal tissue collected during corrective surgery of prolapse.

MATERIALS AND METHODS

Our measurements were conducted on two samples of vaginal tissue 2 cm x 2 cm collected during surgical correction of prolapse by vaginal route in 16 post-menopausal patients. The samples were collected from posterior vaginal fundus, were orientated, and then fixed on a plate holding the edges and allowing the tissue to be stretched over an orifice of 1 cm. The tensile measurements were made using a suture passed over this distance of 1 cm in one of the two samples by recording the strength curve in order to evaluate the force at rupture of the collagen fibres. The second sample was prepared in the same way and a piston of 1 cm diameter was made to penetrate to determine the strength of breakage of the fibres. The pressure and tensile strength curves were recorded up to rupture of the sample, as was the value of the tissue elongation.

RESULTS

There was a great variability in the measurements of maximum strength at rupture of the vaginal samples and in the elongation before rupture of the samples. The mean rupture values in tensile tests were 44 and 59 N in bending with extremes of 12 and 130 N. The values of elongation before rupture of a 10 mm sample were 23 mm in tensile tests and 11 mm in bending tests. There was a great variability of results from one patient to another. There was no relation between the values observed and the patient age. There was a statistical relation between the elongation values of the samples and the maximum force before rupture in both the tensile and bending tests. There was also a relation between the measurement of the maximum force at rupture in bending and in tensile tests although there was no such relation in terms of the values of elongation before rupture.

DISCUSSION

There is no published reference concerning the strength at rupture or the tensile strength curves for human vaginal tissues. Vaginal tissues are however commonly used as a suspension component in the vast majority of operations for correcting prolapse or urinary incontinence. These suspensions are made by passing a suture through the thickness of the vaginal tissue. The results that we report do however show that these vaginal tissues are very variable in strength from one patient to another. The same finding was made in terms of the elongation values for the vaginal tissue before rupture. The values in bending tests showed that the highest rupture force values and the greatest mean elongation before rupture were lower than in tensile tests.

CONCLUSIONS

These findings could explain some failures of these surgical procedures, which are all based on the tensile strength properties. Finally these results could be included in modelling of the reaction of vaginal tissues to the pressure experienced within the vagina.

A study of pelvic ligament strength

OBJECTIVES

To measure the strength at tearing of pelvic ligaments used in the cure of prolapse and urinary incontinence.

MATERIAL AND METHODS

We performed our measurements on pelvis ligaments from cadaveric specimens. We dissected 29 human female pelvis cadavers of which storage conditions differed. Ten were frozen, 10 fresh and 9 were stored in formalin. In each cadaver we dissected pre-vertebral ligaments at promontory and right and left symmetrical ligaments. These were the iliopectineal, sacrospinous and arcus tendineus of pelvic fascia. A subjective clinical evaluation of the ligament properties was performed by visual observation as well as finger palpation. Ligaments were classified into three groups. Group A contained high quality ligaments, in terms of thickness and apparent strength following finger palpation. Ligaments of doubtful quality were classified in group B and low apparent quality ligaments in group C. Then the ligaments were stitched by a suture taking the entire ligament and a force was applied on the vagina axis until tearing. The device used for strength measurement during traction was a SAMSON type force gauge, model EASY, serial number SMS-R-ES 300N manufactured by Andilog that was developed for the purpose of our study. Measurements were given in Newton (N).

RESULTS

There was a great variability in the values obtained at tearing with minimal values at around 20N and maximal values at 200N. Individually measured, ligament strength varied between individuals, and for the same patient between the type of ligaments and the side. The pre-vertebral ligament was on average the strongest. There was no significant difference according to the storage condition except for the pre-vertebral ligament in formalin cadavers. For bilateral ligaments, there was no difference between the left and right side. The iliopectineal ligament was statistically significantly stronger than the sacrospinous and arcus tendineus of pelvic fascia. There was a correlation between subjective evaluation and objective strength measurements.

DISCUSSION

No papers have been published on the strength of pelvic ligaments at tearing. These are however routinely used in the cure of prolapse and urinary incontinence. Our results show that there is a great variability in strength between individuals, and for a same patient between the types of ligaments and side. These observations could explain some of the surgical intervention failures and demonstrate the importance of per-operative strength evaluation. Per-operative subjective evaluation of strength is related to objective measurements and could be used to determine the type of ligaments to be used for surgical suspension. Freezing does not damage pre-vertebral ligament strength and further studies are required to evaluate elasticity of pelvic ligaments.