Tissue engineering of tendons and ligaments by human bone marrow stromal cells in a liquid fibrin matrix in immunodeficient rats: results of a histologic study

Uni-Directionally Oriented Fibro-Porous PLLA/Fibrin Bio-Hybrid Scaffold: Mechano-Morphological and Cell Studies

In this study, we report a biohybrid oriented fibrous scaffold based on nanofibers of poly(l-lactic acid) (PLLA)/fibrin produced by electrospinning and subsequent post-treatment. Induced hydrolytic degradation of the fibers in 0.25 M NaOH solution for various time periods followed by the immobilization of fibrin on the hydrolyzed fiber surfaces was shown to significantly affect the mechanical properties, with the tensile strength (40.6 MPa ± 1.3) and strain at failure (38% ± 4.5) attaining a value within the range of human ligaments and ligament-replacement grafts. Unidirectional electrospinning with a mandrel rotational velocity of 26.4 m/s produced highly aligned fibers with an average diameter of 760 ± 96 nm. After a 20-min hydrolysis treatment in NaOH solution, this was further reduced to an average of 457 ± 89 nm, which is within the range of collagen bundles found in ligament tissue. Based on the results presented herein, the authors hypothesize that a combination of fiber orientation/alignment and immobilization of fibrin can result in the mechanical and morphological modification of PLLA tissue scaffolds for ligament-replacement grafts. Further, it was found that treatment with NaOH enhanced the osteogenic differentiation of hMSCs and the additional inclusion of fibrin further enhanced osteogenic differentiation, as demonstrated by decreased proliferative rates and increased ALP activity.

The effect of fibrin formulation on cell migration in an in vitro tendon repair model

BACKGROUND

The purpose of this study was to determine the effect of fibrinogen concentration on cell viability and migration in a tissue culture tendon healing model.

METHODS

Forty-eight canine flexor digitorum profundus tendons were randomly divided into three groups. In each group the tendons were lacerated and repaired augmented with a canine bone marrow stromal cell seeded fibrin interposition patch using either 5 mg/ml fibrinogen and 25 U/ml thrombin (physiological as a control), 40 mg/ml fibrinogen and 250 U/ml thrombin (low adhesive), or 80 mg/ml fibrinogen and 250 U/ml thrombin (high adhesive). The sutured tendons were cultured for two or four weeks.

RESULTS

Failure load was not significantly different among the groups. Cell-labeling staining showed that the stromal cells migrated across the gap in the control and low adhesive groups, but there was no cell migration in the high adhesive group at two weeks.

CONCLUSION

A high fibrinogen concentration in a fibrin patch or glue may impede early cell migration.

LEVEL OF EVIDENCE

Not applicable because this study was a laboratory study.

American Society for Bone and Mineral Research-Orthopaedic Research Society Joint Task Force Report on Cell-Based Therapies - Secondary Publication

Cell-based therapies, defined here as the delivery of cells in vivo to treat disease, have recently gained increasing public attention as a potentially promising approach to restore structure and function to musculoskeletal tissues. Although cell-based therapy has the potential to improve the treatment of disorders of the musculoskeletal system, there is also the possibility of misuse and misrepresentation of the efficacy of such treatments. The medical literature contains anecdotal reports and research studies, along with web-based marketing and patient testimonials supporting cell-based therapy. Both the American Society for Bone and Mineral Research (ASBMR) and the Orthopaedic Research Society (ORS) are committed to ensuring that the potential of cell-based therapies is realized through rigorous, reproducible, and clinically meaningful scientific discovery. The two organizations convened a multidisciplinary and international Task Force composed of physicians, surgeons, and scientists who are recognized experts in the development and use of cell-based therapies. The Task Force was charged with defining the state-of-the art in cell-based therapies and identifying the gaps in knowledge and methodologies that should guide the research agenda. The efforts of this Task Force are designed to provide researchers and clinicians with a better understanding of the current state of the science and research needed to advance the study and use of cell-based therapies for skeletal tissues. The design and implementation of rigorous, thorough protocols will be critical to leveraging these innovative treatments and optimizing clinical and functional patient outcomes. In addition to providing specific recommendations and ethical considerations for preclinical and clinical investigations, this report concludes with an outline to address knowledge gaps in how to determine the cell autonomous and nonautonomous effects of a donor population used for bone regeneration. © 2020 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 38:485-502, 2020.

American Society for Bone and Mineral Research-Orthopaedic Research Society Joint Task Force Report on Cell-Based Therapies

Cell-based therapies, defined here as the delivery of cells in vivo to treat disease, have recently gained increasing public attention as a potentially promising approach to restore structure and function to musculoskeletal tissues. Although cell-based therapy has the potential to improve the treatment of disorders of the musculoskeletal system, there is also the possibility of misuse and misrepresentation of the efficacy of such treatments. The medical literature contains anecdotal reports and research studies, along with web-based marketing and patient testimonials supporting cell-based therapy. Both the American Society for Bone and Mineral Research (ASBMR) and the Orthopaedic Research Society (ORS) are committed to ensuring that the potential of cell-based therapies is realized through rigorous, reproducible, and clinically meaningful scientific discovery. The two organizations convened a multidisciplinary and international Task Force composed of physicians, surgeons, and scientists who are recognized experts in the development and use of cell-based therapies. The Task Force was charged with defining the state-of-the art in cell-based therapies and identifying the gaps in knowledge and methodologies that should guide the research agenda. The efforts of this Task Force are designed to provide researchers and clinicians with a better understanding of the current state of the science and research needed to advance the study and use of cell-based therapies for skeletal tissues. The design and implementation of rigorous, thorough protocols will be critical to leveraging these innovative treatments and optimizing clinical and functional patient outcomes. In addition to providing specific recommendations and ethical considerations for preclinical and clinical investigations, this report concludes with an outline to address knowledge gaps in how to determine the cell autonomous and nonautonomous effects of a donor population used for bone regeneration. © 2019 American Society for Bone and Mineral Research.

Regenerative Sports Medicine: Past, Present, and Future (Adapted From the PASSOR Legacy Award Presentation; AAPMR; October 2016)

Regenerative medicine has shown dramatic expanse and evolution in the past decade. Within that milieu, physiatrists are taking an active role in research, clinical care delivery, and education. The purpose of this review is to provide a balance among evidence, theory, experience, clinical trends, and the foreseeable future. We focus on the literature that reports the research with the best methodology in each practice area, recognizing that the level of evidence varies substantially among different treatment modalities and conditions. The following elements are included: an overview of the evolution of currently available regenerative techniques, evidence base for each available modality (prolotherapy, platelet rich plasma, bone marrow aspirate concentrate and stem cells, adipose-derived stem cells, and amniotic tissue products), general principles in the application of these treatments, and discussion and a vision of what lies ahead. We expect that practitioners will use this review to facilitate clinical decision making and to provide a core knowledge base to assist when counseling patients. LEVEL OF EVIDENCE: IV.

Bone marrow mesenchymal stem cells do not enhance intra-synovial tendon healing despite engraftment and homing to niches within the synovium

Background

Intra-synovial tendon injuries display poor healing, which often results in reduced functionality and pain. A lack of effective therapeutic options has led to experimental approaches to augment natural tendon repair with autologous mesenchymal stem cells (MSCs) although the effects of the intra-synovial environment on the distribution, engraftment and functionality of implanted MSCs is not known. This study utilised a novel sheep model which, although in an anatomically different location, more accurately mimics the mechanical and synovial environment of the human rotator cuff, to determine the effects of intra-synovial implantation of MSCs.

Methods

A lesion was made in the lateral border of the lateral branch of the ovine deep digital flexor tendon within the digital sheath and 2 weeks later 5 million autologous bone marrow MSCs were injected under ultrasound guidance into the digital sheath. Tendons were recovered post mortem at 1 day, and 1–2, 4, 12 and 24 weeks after MSC injection. For the 1-day and 1–2-week groups, MSCs labelled with fluorescent-conjugated magnetic iron-oxide nanoparticles (MIONs) were tracked with MRI, histology and flow cytometry. The 4, 12 and 24-week groups were implanted with non-labelled cells and compared with saline-injected controls for healing.

Results

The MSCs displayed no reduced viability in vitro to an uptake of 20.0 ± 4.6 pg MIONs per cell, which was detectable by MRI at minimal density of ~ 3 × 10⁴ cells. Treated limbs indicated cellular distribution throughout the tendon synovial sheath but restricted to the synovial tissues, with no MSCs detected in the tendon or surgical lesion.

The lesion was associated with negligible morbidity with minimal inflammation post surgery. Evaluation of both treated and control lesions showed no evidence of healing of the lesion at 4, 12 and 24 weeks on gross and histological examination.

Conclusions

Unlike other laboratory animal models of tendon injury, this novel model mimics the failed tendon healing seen clinically intra-synovially. Importantly, however, implanted stem cells exhibited homing to synovium niches where they survived for at least 14 days. This phenomenon could be utilised in the development of novel physical or biological approaches to enhance localisation of cells in augmenting intra-synovial tendon repair.

Autologous Stem Cells in Achilles Tendinopathy (ASCAT): protocol for a phase IIA, single-centre, proof-of-concept study

INTRODUCTION

Achilles tendinopathy (AT) is a cause of pain and disability affecting both athletes and sedentary individuals. More than 150 000 people in the UK every year suffer from AT.While there is much preclinical work on the use of stem cells in tendon pathology, there is a scarcity of clinical data looking at the use of mesenchymal stem cells to treat tendon disease and there does not appear to be any studies of the use of autologous cultured mesenchymal stem cells (MSCs) for AT. Our hypothesis is that autologous culture expanded MSCs implanted into an area of mid-portion AT will lead to improved pain-free mechanical function. The current paper presents the protocol for a phase IIa clinical study.

METHODS AND ANALYSIS

The presented protocol is for a non-commercial, single-arm, open-label, phase IIa proof-of-concept study. The study will recruit 10 participants and will follow them up for 6 months. Included will be patients aged 18-70 years with chronic mid-portion AT who have failed at least 6 months of non-operative management. Participants will have a bone marrow aspirate collected from the posterior iliac crest under either local or general anaesthetic. MSCs will be isolated and expanded from the bone marrow. Four to 6 weeks after the harvest, participants will undergo implantation of the culture expanded MSCs under local anaesthetic and ultrasound guidance. The primary outcome will be safety as defined by the incidence rate of serious adverse reaction. The secondary outcomes will be efficacy as measured by patient-reported outcome measures and radiological outcome using ultrasound techniques.

ETHICS AND DISSEMINATION

The protocol has been approved by the National Research Ethics Service Committee (London, Harrow; reference 13/LO/1670). Trial findings will be disseminated through peer-reviewed publications and conference presentations.

TRIAL REGISTRATION NUMBER

NCT02064062.

Macroscopic and microscopic analyses in flexor tendons of the tarsometatarso-phalangeal joint of ostrich (Struthio camelus) foot with energy storage and shock absorption

Flexor tendons function as energy storage and shock absorption structures in the tarsometatarso-phalangeal joint (TMTPJ) of ostrich feet during high-speed and heavy-load locomotion. In this study, mechanisms underlying the energy storage and shock absorption of three flexor tendons of the third toe were studied using histology and scanning electron microscopy (SEM). Macroscopic and microscopic structures of the flexor tendons in different positions of TMTPJ were analyzed. Histological slices showed collagen fiber bundles of all flexor tendons in the middle TMTPJ were arranged in a linear-type, but in the proximal and distal TMTPJ, a wavy-type arrangement was found in the tendon of the M. flexor digitorum longus and tendon of the M. flexor perforans et perforatus digiti III, while no regular-type was found in the tendon of the M. flexor perforatus digiti III. SEM showed that the collagen fiber bundles of flexor tendons were arranged in a hierarchically staggered way (horizontally linear-type and vertically linear-type). Linear-type and wavy-type both existed in the proximal TMTPJ for the collagen fiber bundles of the tendon of the M. flexor perforatus digiti III, but only the linear-type was found in the distal TMTPJ. A number of fibrils were distributed among the collagen fiber bundles, which were likely effective in connection, force transmission and other functions. The morphology and arrangement of collagen fiber bundles were closely related to the tendon functions. We present interpretations of the biological functions in different positions and types of the tendons in the TMTPJ of the ostrich feet.

Mesenchymal stem cells for tendon healing: what is on the horizon?

Tendon injuries are a noteworthy morbidity but at present there are few effective scientifically proven treatments. In recent decades, a number of new strategies including tissue engineering with mesenchymal stem cells (MSCs) have been proposed to enhance tendon healing. Although MSCs are an interesting and promising approach, many questions regarding their use in tendon repair remain unanswered. This descriptive overview of the literature of the last decade explores the in vivo studies on tendon healing, in small and large animal models, which used MSCs harvested from different tissues, and the state of the art in clinical applications. It was observed that there are still doubts about the optimum amount of MSCs to use and their source and the type of scaffolds to deliver the cells. Thus, further studies are needed to determine the best protocol for MSC use in tendon healing. Copyright © 2016 John Wiley & Sons, Ltd.

Translation of cell therapy into clinical practice: validation of an application procedure for bone marrow progenitor cells and platelet rich plasma

PURPOSE

Tissue regeneration can be improved by local application of autologous bone marrow derived progenitor cells (BMSC) and platelet rich plasma (PRP). However, there is a lack of standardized application procedures for clinical use. Therefore, a technique in accordance with the guidelines for advanced therapies medical products of the European Medicine Agency was developed and established.

METHODS

In detail, a process for the isolation and formulation of autologous bone marrow cells (BMC) and PRP in a clinical setting was validated. To investigate the influence of storage time and temperature on gel formation and gel stability, different concentrations of BMC were stored with and without additional platelets, thrombin and fibrinogen and analyzed over a period of 28 days. In addition, cell vitality using a live-dead staining and migration ability of human mesenchymal stem cells (hMSC) in the gel clot was investigated.

RESULTS

For an optimized stable gel clot, human BMC and PRP should be combined with 10% to 20% fibrinogen (9 mg/mL to 18 mg/mL) and 5% to 20% thrombin (25 I.E. to 100 I.E.). Both freshly prepared and stored cells for 1 to 7 days had a stable consistence over 28 days at 37°C. Different platelet concentrations did not influence gel clot formation. The ratio of living cells did not decrease significantly over the observation period of 5 days in the live-dead staining.

CONCLUSIONS

The study identified an optimal gel texture for local application of BMC and PRP. Seeded hMSC could migrate therein and were able to survive to initiate a healing cascade.

Effect of Fibrin Formulation on Initial Strength of Tendon Repair and Migration of Bone Marrow Stromal Cells in Vitro

BACKGROUND

Cell-based tissue engineering techniques have been introduced to improve tendon repair outcomes. The purpose of this study was to determine optimal concentrations of fibrinogen and thrombin for use as a scaffold to deliver stromal cells to the tendon repair site.

METHODS

Lacerated flexor digitorum profundus tendons from forty canine forepaws underwent simulated repair with fibrin gel interposition. The tendons were divided into five groups with different ratios of fibrinogen (mg/mL) to thrombin (NIH units/mL) used to form the gels. These ratios, which ranged from those found in normal hemostasis to those used clinically as adhesives, were 5:25 (the physiological ratio, used as a control), 40:250 (a low adhesive concentration of fibrinogen and a low adhesive concentration of thrombin [low-low group]), 80:250 (high-low group), 40:500 (low-high group), and 80:500 (high-high group). The failure load and tensile stiffness at time zero, compressive stiffness of the fibrin gel, and cell viability and migration were evaluated.

RESULTS

The failure loads of the high-low and high-high groups were significantly higher than that of the control group. The tensile stiffness of the high-high group was significantly higher than that of the control group. The high-low and high-high groups had significantly higher compressive stiffness than the other groups. While there was no significant difference among the groups regarding cell viability, the cells in the control, low-low, and low-high gels were spindle-shaped whereas those in the high-low and high-high groups were rounded. Cells migrated across scratch gaps within twenty-four hours in the control, low-low, and low-high groups, but not in the high-low and high-high groups.

CONCLUSIONS

Higher concentrations of fibrinogen resulted in stronger and stiffer gels, but the strength was far less than that of a tendon suture and these gels were associated with a more rounded cell morphology and reduced cell migration. Therefore, lower concentrations of fibrinogen should be used if a fibrin gel is employed to deliver cells for tendon repair.

CLINICAL RELEVANCE

Concentrations of fibrinogen lower than those used in fibrin glue may be more appropriate if fibrin is employed to create a cell delivery matrix for tendon repair.

Fibrin matrices: The versatile therapeutic delivery systems

Fibrin sealants, that have been employed for over a century by surgeons to stop post surgery bleeding, are finding novel applications in the controlled delivery of antibiotics and several other therapeutics. Fibrinogen can be easily purified from blood plasma and converted by thrombolysis to fibrin that undergoes spontaneous aggregation to form insoluble clot. During the gelling, fibrin can be formulated into films, clots, threads, microbeads, nanoconstructs and nanoparticles. Whole plasma clots in the form of beads and microparticles can also be prepared by activating endogenous thrombin, for possible drug delivery. Fibrin formulations offer remarkable scope for controlling the porosity as well as in vivo degradability and hence the release of the associated therapeutics. Binding/covalent-linking of therapeutics to the fibrin matrix, crosslinking of the matrix with bifunctional reagents and coentrapment of protease inhibitors have been successful in regulating both in vitro and in vivo release of the therapeutics. The release rates can also be remarkably lowered by preentrapment of therapeutics in insoluble particles like liposomes or by anchoring them to the matrix via molecules that bind them as well as fibrin.

Assessment of stem cell carriers for tendon tissue engineering in pre-clinical models

Tendon injuries are prevalent and problematic, especially among young and otherwise healthy individuals. The inherently slow innate healing process combined with the inevitable scar tissue formation compromise functional recovery, imposing the need for the development of therapeutic strategies. The limited number of low activity/reparative capacity tendon-resident cells has directed substantial research efforts towards the exploration of the therapeutic potential of various stem cells in tendon injuries and pathophysiologies. Severe injuries require the use of a stem cell carrier to enable cell localisation at the defect site. The present study describes advancements that injectable carriers, tissue grafts, anisotropically orientated biomaterials, and cell-sheets have achieved in preclinical models as stem cell carriers for tendon repair.

Biologics for tendon repair

Tendon injuries are common and present a clinical challenge to orthopedic surgery mainly because these injuries often respond poorly to treatment and require prolonged rehabilitation. Therapeutic options used to repair ruptured tendons have consisted of suture, autografts, allografts, and synthetic prostheses. To date, none of these alternatives has provided a successful long-term solution, and often the restored tendons do not recover their complete strength and functionality. Unfortunately, our understanding of tendon biology lags far behind that of other musculoskeletal tissues, thus impeding the development of new treatment options for tendon conditions. Hence, in this review, after introducing the clinical significance of tendon diseases and the present understanding of tendon biology, we describe and critically assess the current strategies for enhancing tendon repair by biological means. These consist mainly of applying growth factors, stem cells, natural biomaterials and genes, alone or in combination, to the site of tendon damage. A deeper understanding of how tendon tissue and cells operate, combined with practical applications of modern molecular and cellular tools could provide the long awaited breakthrough in designing effective tendon-specific therapeutics and overall improvement of tendon disease management.

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

Tendon injuries represent a significant clinical burden on healthcare systems worldwide. As the human population ages and the life expectancy increases, tendon injuries will become more prevalent, especially among young individuals with long life ahead of them. Advancements in engineering, chemistry and biology have made available an array of three-dimensional scaffold-based intervention strategies, natural or synthetic in origin. Further, functionalisation strategies, based on biophysical, biochemical and biological cues, offer control over cellular functions; localisation and sustained release of therapeutics/biologics; and the ability to positively interact with the host to promote repair and regeneration. Herein, we critically discuss current therapies and emerging technologies that aim to transform tendon treatments in the years to come.

A review on the use of cell therapy in the treatment of tendon disease and injuries

Tendon disease and injuries carry significant morbidity worldwide in both athletic and non-athletic populations. It is estimated that tendon injuries account for 30%−50% of all musculoskeletal injuries globally. Current treatments have been inadequate in providing an accelerated process of repair resulting in high relapse rates. Modern concepts in tissue engineering and regenerative medicine have led to increasing interest in the application of cell therapy for the treatment of tendon disease. This review will explore the use of cell therapy, by bringing together up-to-date evidence from in vivo human and animal studies, and discuss the issues surrounding the safety and efficacy of its use in the treatment of tendon disease.

Repairing damaged tendon and muscle: are mesenchymal stem cells and scaffolds the answer?

Mesenchymal stem cells (MSCs) have become an area of intense interest in the treatment of musculoskeletal conditions, such as muscle and tendon injury, as various animal and human trials have demonstrated that implantation with MSCs leads to improved healing and function. However, these trials have usually been relatively small scale and lacking in adequate controls. Additionally, the optimum source of these cells has yet to be determined, partly due to a lack of understanding as to how MSCs produce their beneficial effects when implanted. Scaffolds have been shown to improve tissue-engineering repairs but require further work to optimize their interactions with both native tissue and implanted MSCs. Robust, well-controlled trials are therefore required to determine the usefulness of MSCs in musculoskeletal tissue repair.

Stem cell-bearing suture improves Achilles tendon healing in a rat model

BACKGROUND

Tendon healing is a slow and complicated process that results in inferior structural and functional properties when compared to healthy tendon tissue. It may be possible to improve outcomes of tendon healing with enhancement of biological aspects of the repair including tissue structure, organization, and composition. The purpose of this study was to determine whether use of a stem cell-bearing suture improves Achilles tendon healing in a rat model.

METHODS

The Achilles tendon was transected in 108 bilateral hind limbs from 54 rats. Each limb was randomized to repair with suture only (SO), suture plus injection (SI) of mesenchymal stem cells (MSCs) at the repair site, or suture loaded with MSCs (suture with stem cells, SCS). One half of the animals were randomly sacrificed at 14 and 28 days after surgery and the Achilles tendon was harvested. From each repair group at each time point, 12 limbs were randomized to biomechanical testing and 6 to histologic analysis. Tendons were loaded using a 223-N load cell at 0.17 mm/s. A blinded pathologist scored the histology sections.

RESULTS

Ultimate failure strength (N/mm(2)) was significantly higher in the SI and SCS groups versus the SO group. In the SI group, ultimate failure strength decreased significantly at 28 days versus 14 days. Histology score in the SCS group was significantly lower (better) than in both other groups (P ≤ .001). Histology findings at day 28 were significantly higher versus day 14 for all groups (P = .01).

CONCLUSIONS

Both the SI and the SCS groups had significantly higher ultimate failure strength versus the SO group, and strength was maintained at 28 days in the SCS group but not in the SI group. Histology in the SCS group was significantly better than in both other groups.

CLINICAL RELEVANCE

These findings in a rat model suggest that the use of stem cells enhances healing after Achilles repair and that embedding of stem cells directly into suture offers sustained early benefit to tendon healing.

Distribution of injected technetium(99m)-labeled mesenchymal stem cells in horses with naturally occurring tendinopathy

This study aimed to investigate immediate cell survival and distribution following different administration routes of mesenchymal stem cells (MSCs) into naturally occurring tendon injuries. Ten million MSCs, labeled with technetium-99m hexamethylpropyleneamine oxime, were implanted into 13 horses with naturally occurring tendon or ligament injuries intra-lesionally, intravenously and by regional perfusion, and traced for up to 48 h using planar gamma scintigraphy. Labeling efficiencies varied between 1.8% and 18.5% (mean 9.3%). Cells were retained in the damaged area after intra-lesional administration but only 24% of cells were still present within the tendon after 24 h. After intravenous injection, cells largely distributed to the lung fields, with no detectable cells in the tendon lesions. Significant labeling of the tendon lesions was observed in 11/12 horses following regional perfusion but at a lower level to intra-lesional injection. The highest cell numbers were retained after intra-lesional injection, although with considerable cell loss, while regional perfusion may be a viable alternative for MSC delivery. Cells did not "home" to damaged tendon in large numbers after intravenous administration. Cells were detected in the lungs most frequently after intravascular administration, although with no adverse effects. Low cell retention has important implications for designing effective clinical therapies for human clinical use.

Engineered scaffold-free tendon tissue produced by tendon-derived stem cells

Most of the exogenous biomaterials for tendon repair have limitations including lower capacity for inducing cell proliferation and differentiation, poorer biocompatibility and remodeling potentials. To avoid these shortcomings, we intend to construct an engineered tendon by stem cells and growth factors without exogenous scaffolds. In this study, we produced an engineered scaffold-free tendon tissue (ESFTT) in vitro and investigated its potentials for neo-tendon formation and promoting tendon healing in vivo. The ESFTT, produced via tendon-derived stem cells (TDSCs) by treatment of connective tissue growth factor (CTGF) and ascorbic acid in vitro, was characterized by histology, qRT-PCR and immunohistochemistry methods. After ESFTT implanted into the nude mouse, the in vivo fluorescence imaging, histology and immunohistochemistry examinations showed neo-tendon formation. In a rat patellar tendon window injury model, the histology, immunohistochemistry and biomechanical testing data indicated ESFTT could significantly promote tendon healing. In conclusion, this is a proof-of-concept study demonstrating that ESFTT could be a potentially new approach for tendon repair and regeneration.

Smad8/BMP2-engineered mesenchymal stem cells induce accelerated recovery of the biomechanical properties of the Achilles tendon

Tendon tissue regeneration is an important goal for orthopedic medicine. We hypothesized that implantation of Smad8/BMP2-engineered MSCs in a full-thickness defect of the Achilles tendon (AT) would induce regeneration of tissue with improved biomechanical properties. A 2 mm defect was created in the distal region of murine ATs. The injured tendons were then sutured together or given implants of genetically engineered MSCs (GE group), non-engineered MSCs (CH3 group), or fibrin gel containing no cells (FG group). Three weeks later the mice were killed, and their healing tendons were excised and processed for histological or biomechanical analysis. A biomechanical analysis showed that tendons that received implants of genetically engineered MSCs had the highest effective stiffness (>70% greater than natural healing, p < 0.001) and elastic modulus. There were no significant differences in either ultimate load or maximum stress among the treatment groups. Histological analysis revealed a tendon-like structure with elongated cells mainly in the GE group. ATs that had been implanted with Smad8/BMP2-engineered stem cells displayed a better material distribution and functional recovery than control groups. While additional study is required to determine long-term effects of GE MSCs on tendon healing, we conclude that genetically engineered MSCs may be a promising therapeutic tool for accelerating short-term functional recovery in the treatment of tendon injuries.

Growth and Development Symposium: Stem cell therapy in equine tendon injury

Tendon injuries affect all levels of athletic horses and represent a significant loss to the equine industry. Accumulation of microdamage within the tendon architecture leads to formation of core lesions. Traditional approaches to tendon repair are based on an initial period of rest to limit the inflammatory process followed by a controlled reloading program designed to promote the maturation and linear arrangement of scar tissue within the lesion. However, these treatment protocols are inefficient, resulting in prolonged recovery periods and frequent recurrence. Current alternative therapies include the use of bone marrow-derived mesenchymal stem cells (BMSC) and a population of nucleated cells from adipose containing adipose-derived mesenchymal stem cells (AdMSC). Umbilical cord blood-derived stem cells (UCB) have recently received attention for their increased plasticity in vitro and potential as a therapeutic aid. Both BMSC and AdMSC require expansion in culture before implantation to obtain a pure stem cell population, limiting the time frame for implantation. Collected at parturition, UCB can be cryopreserved for future use. Furthermore, the low immunogenicity of the UCB population allows for allogeneic implantation. Current research indicates that BMSC, AdMSC, and UCB can differentiate into tenocyte-like cells in vitro, increasing expression of scleraxis, tenascin c, and extracellular matrix proteins. When implanted, BMSC and AdMSC engraft into the tendon and improve tendon architecture. However, treatment with these stem cells does not decrease recovery period. Furthermore, the resulting regeneration is not optimal, as the resulting tissue is still inferior to native tendon. Umbilical cord blood-derived stem cells may provide an alternate source of stem cells that promote improved regeneration of tendon tissue. A more naïve cell population, these cells may have a greater rate of engraftment as well as an increased ability to secrete bioactive factors and recruit additional reparative cells. Further work should clarify the role of distinct stem cell sources in the regenerating tendon and the need for a naïve or differentiated cell type for implantation.

Exploring the application of stem cells in tendon repair and regeneration

PURPOSE

To conduct a systematic review of the current evidence for the effects of stem cells on tendon healing in preclinical studies and human studies.

METHODS

A systematic search of the PubMed, CINAHL (Cumulative Index to Nursing and Allied Health Literature), Cochrane, and Embase databases was performed for stem cells and tendons with their associated terminology. Data validity was assessed, and data were collected on the outcomes of trials.

RESULTS

A total of 27 preclinical studies and 5 clinical studies met the inclusion criteria. Preclinical studies have shown that stem cells are able to survive and differentiate into tendon cells when placed into a new tendon environment, leading to regeneration and biomechanical benefit to the tendon. Studies have been reported showing that stem cell therapy can be enhanced by molecular signaling adjunct, mechanical stimulation of cells, and the use of augmentation delivery devices. Studies have also shown alternatives to the standard method of bone marrow-derived mesenchymal stem cell therapy. Of the 5 human studies, only 1 was a randomized controlled trial, which showed that skin-derived tendon cells had a greater clinical benefit than autologous plasma. One cohort study showed the benefit of stem cells in rotator cuff tears and another in lateral epicondylitis. Two of the human studies showed how stem cells were successfully extracted from the humerus and, when tagged with insulin, became tendon cells.

CONCLUSIONS

The current evidence shows that stem cells can have a positive effect on tendon healing. This is most likely because stem cells have regeneration potential, producing tissue that is similar to the preinjury state, but the results can be variable. The use of adjuncts such as molecular signaling, mechanical stimulation, and augmentation devices can potentially enhance stem cell therapy. Initial clinical trials are promising, with adjuncts for stem cell therapy in development.

Synergy of tendon stem cells and platelet-rich plasma in tendon healing

Injured rat Achilles tendons were treated with botulism toxin to create a mechanically unloaded condition (unloaded) or left untreated (loaded), and then treated with phosphate-buffered saline (PBS), platelet-rich plasma (PRP), tendon stem cells (TSCs), or a combination (TSCs + PRP). mRNA and protein expression of collagen I, collagen III, tenascin C, and Smad 8 were determined by real time PCR and immunostaining, respectively. Loaded tendons treated with PBS, PRP, or TSCs for 3 or 14 days had higher collagen I mRNA expression than unloaded tendons. Loaded tendons treated with PBS for 3 or 14 days or with PRP for 3 days had higher collagen I protein levels than unloaded tendons. Loaded tendons treated for 3 days with PBS, for 14 days with PRP or TSCs or TSCs + PRP for 3 or 14 days had higher collagen III protein levels than unloaded tendons. Collagen I mRNA levels were higher in TSCs + PRP-treated loaded tendons compared to PBS-treated loaded tendons on day 3 of treatment. Based on changes in the expression of tendon-healing genes, our data suggest that the combination of TSCs and PRP has synergistic effects on tendon healing under both loaded and unloaded conditions, and loaded conditions improve tendon healing.

Tendon-derived stem cells (TDSCs): from basic science to potential roles in tendon pathology and tissue engineering applications

Traditionally, tendons are considered to only contain tenocytes that are responsible for the maintenance, repair and remodeling of tendons. Stem cells, which are termed tendon-derived stem cells (TDSCs), have recently been identified in tendons. This review aims to summarize the current information about the in vitro characteristics of TDSCs, including issues related to TDSC isolation and culture, their cell morphology, immunophenotypes, proliferation and differentiation characteristics and senescence during in vitro passaging. The challenges in studying the functions of these cells are also discussed. The niche where TDSCs resided essentially provides signals that are conducive to the maintenance of definitive stem cell properties of TDSCs. Yet the niche may also induce pathologies by imposing an aberrant function on TDSCs or other targets. The possible niche factors of TDSCs are herein discussed. We presented current evidences supporting the potential pathogenic role of TDSCs in the development of tendinopathy with reference to the recent findings on the altered biological responses of these cells in response to their potential niche factors. The use of resident stem cells may promote engraftment and differentiation of transplanted cells in tendon and tendon-bone junction repair because the tendon milieu is an ideal and familiar environment to the transplanted cells. Evidences are presented to show the potential advantages and results of using TDSCs as a new cell source for tendon and tendon-bone junction repair. Issues pertaining to the use of TDSCs for tissue repair are also discussed.

Cell-based therapies for tendon and ligament injuries

Tendon and ligament injuries have proved difficult to treat effectively. Cell-based therapies offer the potential to harness the complex protein synthetic machinery of the cell to induce a regenerative response rather than fibrous scarring. This article reviews the current state of play with respect to the clinically used cell preparations for the treatment of tendon and ligaments overstrain injuries.

Uso de células mononucleares da medula óssea no tratamento de tendinites induzidas experimentalmente em equinos

Foram induzidas lesões no tendão flexor digital superficial (TFDS) de ambos os membros anteriores de seis equinos, seguidas de implante autólogo de células da fração mononuclear de medula óssea em apenas um membro de cada animal. Os animais foram avaliados por parâmetros clínicos, ultrassonográficos, histopatológico e imunoistoquímico. Paralelamente, realizou-se o cultivo de novas amostras para a caracterização das células utilizando-se marcadores CD34 e CD45 por meio da citometria de fluxo, confirmando a presença de células mesenquimais na fração mononuclear. A caracterização das fibras colágenas tipo I e tipo III no tecido neoformado mostrou melhora na qualidade da cicatrização tendínea dos membros tratados. A terapia com implante autólogo das células da fração mononuclear melhorou a organização tecidual e a sua qualidade, apresentando maior expressão significativa para colágeno tipo I.

Implantation of bone marrow-derived mesenchymal stem cells demonstrates improved outcome in horses with overstrain injury of the superficial digital flexor tendon

REASONS FOR PERFORMING STUDY

Mesenchymal stem (progenitor; stromal) cell (MSC) therapy has gained popularity for the treatment of equine tendon injuries but without reports of long-term follow-up.

OBJECTIVES

To evaluate the safety and reinjury rate of racehorses after intralesional MSC injection in a large study of naturally occurring superficial digital flexor tendinopathy and to compare these data with those published for other treatments.

METHODS

Safety was assessed clinically, ultrasonographically, scintigraphically and histologically in a cohort of treated cases: 141 client-owned treated racehorses followed-up for a minimum of 2 years after return to full work. Reinjury percentages were compared to 2 published studies of other treatments with similar selection criteria and follow-up. The number of race starts, discipline, age, number of MSCs injected and interval between injury and treatment were analysed.

RESULTS

There were no adverse effects of the treatment with no aberrant tissue on histological examination. The reinjury percentage of all racehorses with follow-up (n = 113) undergoing MSC treatment was 27.4%, with the rate for flat (n = 8) and National Hunt (n = 105) racehorses being 50 and 25.7%, respectively. This was significantly less than published for National Hunt racehorses treated in other ways. No relationship between outcome and age, discipline, number of MSCs injected or injury to implantation interval was found.

CONCLUSIONS

Whilst recognising the limitations of historical controls, this study has shown that MPC implantation is safe and appears to reduce the reinjury rate after superficial digital flexor tendinopathy, especially in National Hunt racehorses.

POTENTIAL RELEVANCE

This study has provided evidence for the long-term efficacy of MSC treatment for tendinopathy in racehorses and provides support for translation to human tendon injuries.

Tenogenic differentiation of stem cells for tendon repair-what is the current evidence?

Tendon/ligament injuries are very common in sports and other rigorous activities. Tendons regenerate and repair slowly and inefficiently in vivo after injury. The limited ability of tendon to self-repair and the general inefficiencies of current treatment regimes have hastened the motivation to develop tissue-engineering strategies for tissue repair. Of particular interest in recent years has been the use of adult mesenchymal stem cells (MSCs) to regenerate functional tendons and ligaments. Different sources of MSCs have been studied for their effects on tendon repair. However, ectopic bone and tumour formation has been reported in some special circumstances after transplantation of MSCs. The induction of MSCs to differentiate into tendon-forming cells in vitro prior to transplantation is a possible approach to avoid ectopic bone and tumour formation while promoting tendon repair. While there are reports about the factors that might promote tenogenic differentiation, the study of tenogenic differentiation is hampered by the lack of definitive biomarkers for tendons. This review aims to summarize the cell sources currently used for tendon repair as well as their advantages and limitations. Factors affecting tenogenic differentiation were summarized. Molecular markers currently used for assessing tenogenic differentiation or neotendon formation are summarized and their advantages and limitations are commented upon. Finally, further directions for promoting and assessing tenogenic differentiation of stem cells for tendon repair are discussed.

Genipin-crosslinked fibrin hydrogels as a potential adhesive to augment intervertebral disc annulus repair

Treatment of damaged intervertebral discs is a significant clinical problem and, despite advances in the repair and replacement of the nucleus pulposus, there are few effective strategies to restore defects in the annulus fibrosus. An annular repair material should meet three specifications: have a modulus similar to the native annulus tissue, support the growth of disc cells, and maintain adhesion to tissue under physiological strain levels. We hypothesized that a genipin crosslinked fibrin gel could meet these requirements. Our mechanical results showed that genipin crosslinked fibrin gels could be created with a modulus in the range of native annular tissue. We also demonstrated that this material is compatible with the in vitro growth of human disc cells, when genipin:fibrin ratios were 0.25:1 or less, although cell proliferation was slower and cell morphology more rounded than for fibrin alone. Finally, lap tests were performed to evaluate adhesion between fibrin gels and pieces of annular tissue. Specimens created without genipin had poor handling properties and readily delaminated, while genipin crosslinked fibrin gels remained adhered to the tissue pieces at strains exceeding physiological levels and failed at 15-30%. This study demonstrated that genipin crosslinked fibrin gels show promise as a gap-filling adhesive biomaterial with tunable material properties, yet the slow cell proliferation suggests this biomaterial may be best suited as a sealant for small annulus fibrosus defects or as an adhesive to augment large annulus repairs. Future studies will evaluate degradation rate, fatigue behaviors, and long-term biocompatibility.

Tissue engineering solutions for tendon repair

Tendon injuries range from acute traumatic ruptures and lacerations to chronic overuse injuries, such as tendinosis. Even with improved nonsurgical, surgical, and rehabilitation techniques, outcomes following tendon repair are inconsistent. Primary repair remains the standard of care. However, repaired tendon tissue rarely achieves functionality equal to that of the preinjured state. Poor results have been linked to alterations in cellular organization within the tendon that occur at the time of injury and throughout the early stages of healing. Enhanced understanding of the biology of tendon healing is needed to improve management and outcomes. The use of growth factors and mesenchymal stem cells and the development of biocompatible scaffolds could result in enhanced tendon healing and regeneration. Recent advances in tendon bioengineering may lead to improved management following tendon injury.

Cell therapy in tendon disorders: what is the current evidence?

BACKGROUND

Various types of tissue-derived cells are being experimented with for the treatment of tendinopathy, tendon repair, and use in tissue engineering.

PURPOSE

The aim of this systematic review is to explore the current evidence with a view to evaluate the potential of this therapeutic intervention.

STUDY DESIGN

Systematic review.

METHODS

A review of the literature was conducted using PubMed. Search criteria included keywords "tendinopathy," "tendinitis," "tendinosis," "epicondylitis," "stem cell," and "cell therapy." Articles not written in English language were excluded.

RESULTS

A total number of 379 articles were identified and a critical appraisal of the relevant articles was undertaken, which encompassed human and animal research. The review included articles related to various tissue-derived cells such as tendon progenitors, adipose tissue, synovium, muscle, bone marrow, and skin. The utility of cell therapy in tissue engineering and rotator cuff repair was also assessed.

CONCLUSION

With the limitation of the available evidence, the literature suggests that cell therapy is applicable and may be effective for the treatment of tendinopathy. However, further research into the precise biological mechanisms, long-term implications, and cost-effectiveness is needed.

Fibrin as a delivery system for therapeutic drugs and biomolecules

Fibrin is a natural biopolymer involved in the coagulation cascade. It acts as a reservoir for growth factors, cells, and enzymes during wound healing and provides a scaffold for the synthesis of extracellular matrix. Thus, the use of fibrin has expanded in recent years from traditional use as a sealant for surgical applications, to a tissue engineering scaffold capable of providing nature's cues for tissue regeneration. This paper reviews the advantageous biological aspects of fibrin, the history of the scaffold material, and its present role in the delivery of drugs, growth factors, cells, and gene vectors. Examples are given of studies where the structure and form of the scaffold have been manipulated for optimal release of the therapeutic agent, optimal cellular activity, and investigation into stem cell differentiation. It is evident from the body of literature presented that the benefits of fibrin are being exploited for a vast range of tissue engineering applications and that fibrin remains a key scaffold material for the delivery of drugs and biomolecules.

Fibrin: a versatile scaffold for tissue engineering applications

Tissue engineering combines cell and molecular biology with materials and mechanical engineering to replace damaged or diseased organs and tissues. Fibrin is a critical blood component responsible for hemostasis, which has been used extensively as a biopolymer scaffold in tissue engineering. In this review we summarize the latest developments in organ and tissue regeneration using fibrin as the scaffold material. Commercially available fibrinogen and thrombin are combined to form a fibrin hydrogel. The incorporation of bioactive peptides and growth factors via a heparin-binding delivery system improves the functionality of fibrin as a scaffold. New technologies such as inkjet printing and magnetically influenced self-assembly can alter the geometry of the fibrin structure into appropriate and predictable forms. Fibrin can be prepared from autologous plasma, and is available as glue or as engineered microbeads. Fibrin alone or in combination with other materials has been used as a biological scaffold for stem or primary cells to regenerate adipose tissue, bone, cardiac tissue, cartilage, liver, nervous tissue, ocular tissue, skin, tendons, and ligaments. Thus, fibrin is a versatile biopolymer, which shows a great potential in tissue regeneration and wound healing.

Bone marrow stromal cells in a liquid fibrin matrix improve the healing process of patellar tendon window defects

Following injury, ligaments and tendons do not regain their normal biological and biomechanical status. This study analyzed whether an injection of human bone marrow stromal cells (BMSC) or human fibroblast in a liquid fibrin matrix influences the histological results, ultrastructural morphology, mRNA expression of essential extracellular matrix proteins, and material properties of the healing tissue. Standardized full-thickness, full-length defects of the central portion of patellar tendons were created in 96 immunodeficient rats, and filled with human BMSC in a fibrin matrix (BMSC group), human fibroblasts in a fibrin matrix (fibroblast group), or fibrin matrix only (matrix group), or left untreated (defect group). Histological sections revealed more mature tissue formation with more regular patterns of cell distribution in the BMSC group, without signs of ectopic tissue formation into bone or cartilage. Mean collagen fibril diameter and relative area covered by collagen fibrils were significantly higher at 10 and 20 days postoperatively in the BMSC group compared to the defect and matrix groups, and comparable to normal tendon tissue. Further, collagen I mRNA expression, collagen I/collagen III mRNA ratio, and Young's modulus were significantly increased at 20 days postoperatively in comparison to the defect and matrix groups. In the fibroblast group, only mean collagen fibril diameter was significantly higher compared to the defect group, whereas the other biological and biomechanical parameters were not significantly improved. This study reveals that an injection of BMSC in a liquid fibrin matrix stimulates histological, ultrastructural, molecular biologic, and biomechanical parameters of patellar tendon healing, whereas injection of fibroblasts in fibrin matrix had only minor effects on the stimulation of tendon healing.

Mesenchymal stem cell therapy for equine tendinopathy

Optimal management of tendon overuse injuries in equine and human athletes should avoid the formation of excessive scar tissue, regenerate normal tendon matrix, and reduce re-injury rates. We hypothesized that the implantation of marrow-derived stromal stem cells (BM-MSCs), in far greater numbers than are present normally within tendon tissue, would synthesize a matrix more closely resembling tendon matrix than scar tissue, and hence increase the capacity to return to performance successfully. This article reviews the technique used clinically in the horse and the current outcome data for horses treated by the autologous implantation of BM-MSCs into moderate to severe acute superficial digital flexor tendon (SDFT) injuries. Bone marrow was aspirated from the sternum under standing sedation. The nucleated adherent cell population (containing the BM-MSCs) were isolated and expanded so that, after approximately three weeks, the cells were re-suspended in the supernatant from the bone marrow and implanted into injured SDFT under ultrasonographic guidance. The horses then entered a 48-week rehabilitation period consisting of an ascending exercise regime. By September 2006, 168 racehorses had undergone this regimen. For horses which had returned to full work, 18% had re-injured, which compared favourably to previous studies on conventional management (56% re-injury rate). No adverse effects were noted other than needle tracts visible ultrasonographically. Autologous implantation of mesenchymal stem cells into tendon injuries may therefore improve clinical outcome although definitive proof of efficacy, which is still lacking, will require randomized controlled trials.

The therapeutic applications of multipotential mesenchymal/stromal stem cells in skeletal tissue repair

Four decades after the first isolation and characterization of clonogenic bone marrow stromal cells or mesenchymal stem cells (MSC) in the laboratory of Dr. Alexander Friedenstien, the therapeutic application of their progeny following ex vivo expansion are only now starting to be realized in the clinic. The multipotency, paracrine effects, and immune-modulatory properties of MSC present them as an ideal stem cell candidate for tissue engineering and regenerative medicine. In recent years it has come to light that MSC encompass plasticity that extends beyond the conventional bone, adipose, cartilage, and other skeletal structures, and has expanded to the differentiation of liver, kidney, muscle, skin, neural, and cardiac cell lineages. This review will specifically focus on the skeletal regenerative capacity of bone marrow derived MSC alone or in combination with growth factors, biocompatible scaffolds, and following genetic modification.

Engineering of extensor tendon complex by an ex vivo approach

Engineering of extensor tendon complex remains an unexplored area in tendon engineering research. In addition, less is known about the mechanism of mechanical loading in human tendon development and maturation. In the current study, an ex vivo approach was developed to investigate these issues. Human fetal extensor tenocytes were isolated, expanded and seeded on polyglycolic acid (PGA) fibers that formed a scaffold with a shape mimicking human extensor tendon complex. After in vitro culture for 6 weeks, 7 cell-scaffold constructs were further in vitro cultured with dynamic mechanical loading for another 6 weeks in a bioreactor. The other 14 constructs were in vivo implanted subcutaneously to nude mice for another 14 weeks. Seven of them were implanted without loading, whereas the other 7 were sutured to mouse fascia and animal movement provided a natural dynamic loading in vivo. The results demonstrated that human fetal cells could form an extensor tendon complex structure in vitro and become further matured in vivo by mechanical stimulation. In contrast to in vitro loaded and in vivo non-loaded tendons, in vivo loaded tendons exhibited bigger tissue volume, better aligned collagen fibers, more mature collagen fibril structure with D-band periodicity, and stronger mechanical properties. These findings indicate that an extensor tendon complex like structure is possible to generate by an ex vivo approach and in vivo mechanical loading might be an optimal niche for engineering functional extensor tendon.