Histopathological and biomechanical evaluation of tenocyte seeded allografts on rat Achilles tendon regeneration

In vivo study on the repair of rat Achilles tendon injury treated with non-thermal atmospheric-pressure helium microplasma jet

Non-thermal atmospheric-pressure plasma (NTAPP) has been widely studied for clinical applications, e.g., disinfection, wound healing, cancer therapy, hemostasis, and bone regeneration. It is being revealed that the physical and chemical actions of plasma have enabled these clinical applications. Based on our previous report regarding plasma-stimulated bone regeneration, this study focused on Achilles tendon repair by NTAPP. This is the first study to reveal that exposure to NTAPP can accelerate Achilles tendon repair using a well-established Achilles tendon injury rat model. Histological evaluation using the Stoll's and histological scores showed a significant improvement at 2 and 4 weeks, with type I collagen content being substantial at the early time point of 2 weeks post-surgery. Notably, the replacement of type III collagen with type I collagen occurred more frequently in the plasma-treated groups at the early stage of repair. Tensile strength test results showed that the maximum breaking strength in the plasma-treated group at two weeks was significantly higher than that in the untreated group. Overall, our results indicate that a single event of NTAPP treatment during the surgery can contribute to an early recovery of an injured tendon.

Local Injection of Rapamycin-Loaded Pcl-Peg Nanoparticles for Enhanced Tendon Healing in Rotator Cuff Tears via Simultaneously Reducing Fatty Infiltration and Drug Toxicity

As a common cause of shoulder pain, rotator cuff tears (RCTs) are difficult to treat clinically because of their unsatisfactory prognosis due to the fatty infiltration caused by muscle-derived stem cells (MDSCs). Previous studies have found that rapamycin (RAPA) can inhibit fatty infiltration. However, systemic administration of RAPA may cause complications such as infection and nausea, while local administration of RAPA may lead to the cytotoxicity of tendon cells, affecting the healing of rotator cuffs. In this study, biocompatible and clinically approved polycaprolactone-polyethylene glycol (PCL-PEG) is formulated into an injectable nanoparticle for the sustained release of RAPA. The results indicate that the RAPA/PCL-PEG nanoparticles (NPs) can efficiently prolong the release of RAPA and significantly reduce the cytotoxicity of tendon cells caused by RAPA. The study of the fatty infiltration model in rats with delayed rotator cuff repair shows that weekly intraarticular injection of RAPA/PCL-PEG NPs can more effectively reduce the fatty infiltration and muscle atrophy of rat rotator cuffs and leads to better mechanical properties and gait improvements than a daily intraarticular injection of RAPA. These findings imply that local injection of RAPA/PCL-PEG NPs in the shoulder joints can be a potential clinical option for RCTs patients with fatty infiltration.

Dynamic Tensile Stress Promotes Regeneration of Achilles Tendon in a Panda Rope Bridge Technique Mice Model

Regeneration of ruptured Achilles tendon remains a clinical challenge owing to its limited regenerative capacity. Dynamic tensile stress plays a positive role in the regeneration of tendon, although the specific underlying mechanisms remain unclear. In this study, the Achilles tendon defect-regeneration model was created in male C57BL/6 mice aged 8 weeks. The animals were randomly assigned to four groups-repair, non-repair, repair with fixation, and non-repair with fixation. The repair group and repair with fixation group adopted the panda rope bridge technique (PRBT) repair method. Our results demonstrated the presence of more densely aligned and mature collagen fibers, as well as more tendon-related makers, in the repair group at both 2- and 4-week post-surgery. Furthermore, the biomechanical strength of the regenerated tendon in the repair group was highly improved. Most importantly, the expressions of integrin αv and its downstream and the phosphorylation levels of FAK and ERK were remarkably higher in the repair group than in the other groups. Furthermore, blocking FAK or ERK with selective inhibitors PF573228 and U0126 resulted in obvious adverse effects on the histological structure of the regenerated Achilles tendon. In summary, this study demonstrated that dynamic tensile stress based on the PRBT could effectively promote the regeneration of the Achilles tendon, suggesting that dynamic tensile stress enhances the cell proliferation and tenogenic differentiation via the activation of the integrin/FAK/ERK signaling pathway.

Anti-Adhesive Resorbable Indomethacin/Bupivacaine-Eluting Nanofibers for Tendon Rupture Repair: In Vitro and In Vivo Studies

The treatment and surgical repair of torn Achilles tendons seldom return the wounded tendon to its original elasticity and stiffness. This study explored the in vitro and in vivo simultaneous release of indomethacin and bupivacaine from electrospun polylactide-polyglycolide composite membranes for their capacity to repair torn Achilles tendons. These membranes were fabricated by mixing polylactide-polyglycolide/indomethacin, polylactide-polyglycolide/collagen, and polylactide-polyglycolide/bupivacaine with 1,1,1,3,3,3-hexafluoro-2-propanol into sandwich-structured composites. Subsequently, the in vitro pharmaceutic release rates over 30 days were determined, and the in vivo release behavior and effectiveness of the loaded drugs were assessed using an animal surgical model. High concentrations of indomethacin and bupivacaine were released for over four weeks. The released pharmaceutics resulted in complete recovery of rat tendons, and the nanofibrous composite membranes exhibited exceptional mechanical strength. Additionally, the anti-adhesion capacity of the developed membrane was confirmed. Using the electrospinning technique developed in this study, we plan on manufacturing degradable composite membranes for tendon healing, which can deliver sustained pharmaceutical release and provide a collagenous habitat.

Endotenon-Derived Type II Tendon Stem Cells Have Enhanced Proliferative and Tenogenic Potential

Tendon injuries caused by overuse or age-related deterioration are frequent. Incomplete knowledge of somatic tendon cell biology and their progenitors has hindered interventions for the effective repair of injured tendons. Here, we sought to compare and contrast distinct tendon-derived cell populations: type I and II tendon stem cells (TSCs) and tenocytes (TNCs). Porcine type I and II TSCs were isolated via the enzymatic digestion of distinct membranes (paratenon and endotenon, respectively), while tenocytes were isolated through an explant method. Resultant cell populations were characterized by morphology, differentiation, molecular, flow cytometry, and immunofluorescence analysis. Cells were isolated, cultured, and evaluated in two alternate oxygen concentrations (physiological (2%) and air (21%)) to determine the role of oxygen in cell biology determination within this relatively avascular tissue. The different cell populations demonstrated distinct proliferative potential, morphology, and transcript levels (both for tenogenic and stem cell markers). In contrast, all tendon-derived cell populations displayed multipotent differentiation potential and immunophenotypes (positive for CD90 and CD44). Type II TSCs emerged as the most promising tendon-derived cell population for expansion, given their enhanced proliferative potential, multipotency, and maintenance of a tenogenic profile at early and late passage. Moreover, in all cases, physoxia promoted the enhanced proliferation and maintenance of a tenogenic profile. These observations help shed light on the biological mechanisms of tendon cells, with the potential to aid in the development of novel therapeutic approaches for tendon disorders.

Effects of L-carnitine on healing of Achilles tendon in rats

OBJECTIVES

In this experimental study, we aimed to analyze the effects of levocarnitine (L-carnitine) on tendon healing after surgical repair of Achilles tendon rupture in a rat model.

MATERIALS AND METHODS

The study included 40 Wistar Albino rats divided into four groups: Group 1, neither surgical intervention nor substance applications were performed for the Achilles tendons. In the other groups, the right Achilles tendons were cut using a scalpel and repaired with a modified Kessler-type technique with 3/0 monofilament polydioxanone suture. In Group 2, the rats did not receive any additional treatment, except for surgical repair. In Group 3, the same volume similar to Group 4 of saline solution was administered intraperitoneally for seven days. In Group 4, each rat received 300 mg/kg of L-carnitine intraperitoneally for seven days. At Week 6, all rats were sacrificed. All right Achilles tendons were used for biomechanical tests and histopathological evaluations. Biochemical analysis of the matrix metalloproteinase was also performed using the blood specimens.

RESULTS

There were no significant differences among the groups in terms of the histopathological parameters. Although the mean matrix metalloproteinase level was low in the L-carnitine group, it did not reach statistical significance. A significant increase in maximum force, tensile strength, and strength to 2-mm gap was observed in the L-carnitine group.

CONCLUSION

The significant effects of L-carnitine on biomechanical parameters may indicate favorable effects on Achilles tendon healing in rats by reducing matrix metalloproteinase 2 and 9. To improve Achilles tendon healing, further investigation for these markers is needed. Since the effects of L-carnitine on the Achilles tendon cannot be clearly distinguished histopathologically, further studies involving L-carnitine-induced effects are warranted.

Criteria, Challenges, and Opportunities for Acellularized Allogeneic/Xenogeneic Bone Grafts in Bone Repairing

As bone grafts become more commonly needed by patients and as donors become scarcer, acellularized bone grafts (ABGs) are becoming more popular for restorative purposes. While autogeneic grafts are reliable as a gold standard, allogeneic and xenogeneic ABGs have been shown to be of particular interest due to the limited availability of autogeneic resources and reduced patient well-being in long-term surgeries. Because of the complete similarity of their structures with native bone, excellent mechanical properties, high biocompatibility, and similarities of biological behaviors (osteoinductive and osteoconductive) with local bones, successful outcomes of allogeneic and xenogeneic ABGs in both in vitro and in vivo research have raised hopes of repairing patients' bone injuries in clinical applications. However, clinical trials have been delayed due to a lack of standardized protocols pertaining to acellularization, cell seeding, maintenance, and diversity of ABG evaluation criteria. This study sought to uncover these factors by exploring the bone structures, ossification properties of ABGs, sources, benefits, and challenges of acellularization approaches (physical, chemical, and enzymatic), cell loading, and type of cells used and effects of each of the above items on the regenerative technologies. To gain a perspective on the repair and commercialization of products before implementing new research activities, this study describes the differences between ABGs created by various techniques and methods applied to them. With a comprehensive understanding of ABG behavior, future research focused on treating bone defects could provide a better way to combine the treatment approaches needed to treat bone defects.

Tri-Layered Doxycycline-, Collagen- and Bupivacaine-Loaded Poly(lactic-co-glycolic acid) Nanofibrous Scaffolds for Tendon Rupture Repair

Achilles tendon rupture is a severe injury, and its optimal therapy remains controversial. Tissue engineering scaffolds play a significant role in tendon healing and tissue regeneration. In this study, we developed tri-layered doxycycline/collagen/bupivacaine (DCB)-composite nanofibrous scaffolds to repair injured Achilles tendons. Doxycycline, collagen, and bupivacaine were integrated into poly(lactic-co-glycolic acid) (PLGA) nanofibrous membranes, layer by layer, using an electrospinning technique as healing promoters, a 3D scaffold, and painkillers, respectively. After spinning, the properties of the nanofibrous scaffolds were characterized. In vitro drug discharge behavior was also evaluated. Furthermore, the effectiveness of the DCB–PLGA-composite nanofibers in repairing ruptured Achilles tendons was investigated in an animal tendon model with histological analyses. The experimental results show that, compared to the pristine PLGA nanofibers, the biomolecule-loaded nanofibers exhibited smaller fiber size distribution and an enhanced hydrophilicity. The DCB-composite nanofibers provided a sustained release of doxycycline and bupivacaine for over 28 days in vivo. Additionally, Achilles tendons repaired using DCB-composite nanofibers exhibited a significantly higher maximum load-to-failure than normal tendons, suggesting that the biomolecule-incorporated nanofibers are promising scaffolds for repairing Achilles tendons.

Attachment and Growth of Fibroblasts and Tenocytes Within a Porous Titanium Scaffold: A Bioreactor Approach

Background

Direct attachment of tendons to metallic implants is important in orthopedics. Tissue integration depends on scaffold microstructure and composition. This study evaluated the effect of pore size of titanium on the viability and function of fibroblasts and tenocytes in a dynamic bioreactor.

Methods

Standardized Ti porous cylinders with 3 pore sizes (400, 700, and 1000 μm) were seeded with fibroblasts or tenocytes (4500 cells/μL) in silicon tubes. Cells were analyzed via alamarBlue (AB) assay in addition to scanning electron microscopy at day 7 (fibroblasts) or day 8 (tenocytes) and day 15. AB functions as a cell health indicator where functional living cells reduce the resazurin dye (blue) in the solution to resorufin (pink), and cell viability can be quantified via spectroscopy.

Results

At day 7, fibroblasts cultured on all sizes reduced AB, with significant differences noted between 400 vs 1000 μm (P = .013) and 700 vs 1000 μm (P = .001). At day 15, fibroblasts reduced AB on all sizes with a significant difference noted between 700 vs 1000 μm (P = .004). Fibroblasts on all 3 pore sizes increased AB reduction from day 7 to day 15. Tenocytes reduced AB with significant differences between the 400 vs 700 μm (P = .049) and the 400 vs 1000 μm pore sizes at day 8. In contrast, tenocyte reduction of AB decreased from day 8 to day 15. Scanning electron microscopy performed on fibroblast cylinders showed fibroblasts reached the surface of the cylinders, confirming interconnectivity.

Conclusions

While both fibroblasts and tenocytes penetrated the pores, fibroblasts preferred larger size, whereas tenocytes favored smaller size. Results are encouraging since soft-tissue attachment to a metallic scaffold is difficult but clinically desirable. Future studies could be performed in an in vivo animal model.

Basic Research on Tendon Repair: Strategies, Evaluation, and Development

Tendon is a fibro-elastic structure that links muscle and bone. Tendon injury can be divided into two types, chronic and acute. Each type of injury or degeneration can cause substantial pain and the loss of tendon function. The natural healing process of tendon injury is complex. According to the anatomical position of tendon tissue, the clinical results are different. The wound healing process includes three overlapping stages: wound healing, proliferation and tissue remodeling. Besides, the healing tendon also faces a high re-tear rate. Faced with the above difficulties, management of tendon injuries remains a clinical problem and needs to be solved urgently. In recent years, there are many new directions and advances in tendon healing. This review introduces tendon injury and sums up the development of tendon healing in recent years, including gene therapy, stem cell therapy, Platelet-rich plasma (PRP) therapy, growth factor and drug therapy and tissue engineering. Although most of these therapies have not yet developed to mature clinical application stage, with the repeated verification by researchers and continuous optimization of curative effect, that day will not be too far away.

Repair of Rotator Cuff Tendon Defects in Aged Rats Using a Growth Factor Injectable Gel Scaffold

PURPOSE

To determine if the tendon-specific crosslinking gelatin (Col-Tgel) impregnated with growth factors promotes tendon healing at the bone interface and in a tendon window model.

METHODS

Two different Col-Tgel formulations were first tested in vitro by evaluating cell morphology and tendogenic differentiation. After the optimum formulation was determined, the gel was mixed with either transforming growth factor-β3 (TGF-β3) or growth differentiation factor-7 (GDF-7) growth factor and prepared for injections. Window defects were induced in 12 animals, which were randomized into the following treatments: (1) sham, (2) empty Col-Tgel, (3) Col-Tgel containing TGF-β3, or (4) Col-Tgel containing GDF-7. Based on these results, the sham, empty Col-Tgel, and Col-Tgel containing TGF-β3 were applied to the supraspinatus repair interface. Tendons were analyzed biomechanically and histologically using hematoxylin and eosin and Masson's trichrome staining.

RESULTS

In the window defect model, histologic scores were the best in rats treated with TGF-β3 containing Col-Tgel, followed by the empty Col-Tgel scaffold, and finally the sham control. The GDF-7 Col-Tgel was not further tested because occasional ectopic cartilage and bone formation was found in the prior window defect model. In the supraspinatus repair model, there was no statistical difference (P > .05) in the biomechanical strength among the 3 treatment groups, but load-to-failure ratio improved when TGF-β3 was added to the scaffold, suggesting improved tendon healing.

CONCLUSIONS

This pilot study evaluated the performance of an injectable gel tendon graft in a population of retired breeder rats. The results suggest that Col-Tgel containing TGF-β3 may be a useful adjunctive treatment for surgical repair of full-thickness rotator cuff tears. Histologic and biomechanical scores suggest that Col-Tgel containing TGF-β3 promotes tendon healing.

CLINICAL RELEVANCE

The results of this study suggest that shoulders injected with Col-Tgel may be a useful adjunctive treatment for repair of rotator cuff tears.

Optical Microscopy and Electron Microscopy for the Morphological Evaluation of Tendons: A Mini Review

The morphological characteristics of tendons have been thoroughly evaluated via microscopy. Optical microscopy and electron microscopy are the most commonly used techniques for tendon tissue observation. According to the principles of both microscopy types, preparation and evaluation methods vary. Simple optical microscopy is commonly used in the observation of cells and extracellular matrix, and many stains, including hematoxylin–eosin, Van Gieson, Prussian blue, Alcian blue, and toluidine blue, are used for evaluating cells, collagen fiber arrangement, and noncollagenous proteins. Histological scoring systems have been used in many studies for semi‐quantification. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) are the most commonly used electron microscopy types, and special consideration is needed for the fixation and embedding protocols. Glutaraldehyde followed by osmium is most commonly used in the chemical fixation of tendon tissue, followed by epoxy resin embedment. Longitudinal sections captured in SEM images show the arrangement of collagen fibrils and the cells and lipid drops among them, while cross sections captured in TEM images show the diameter and distribution of collagen fibrils. SEM and TEM are used together for comprehensive evaluations. This mini review is focused on the preparation methodology and related evaluation indexes for the morphological evaluation of tendons.

Current Progress in Tendon and Ligament Tissue Engineering

Background

Tendon and ligament injuries accounted for 30% of all musculoskeletal consultations with 4 million new incidences worldwide each year and thus imposed a significant burden to the society and the economy. Damaged tendon and ligament can severely affect the normal body movement and might lead to many complications if not treated promptly and adequately. Current conventional treatment through surgical repair and tissue graft are ineffective with a high rate of recurrence.

Methods

In this review, we first discussed the anatomy, physiology and pathophysiology of tendon and ligament injuries and its current treatment. Secondly, we explored the current role of tendon and ligament tissue engineering, describing its recent advances. After that, we also described stem cell and cell secreted product approaches in tendon and ligament injuries. Lastly, we examined the role of the bioreactor and mechanical loading in in vitro maturation of engineered tendon and ligament.

Results

Tissue engineering offers various alternative ways of treatment from biological tissue constructs to stem cell therapy and cell secreted products. Bioreactor with mechanical stimulation is instrumental in preparing mature engineered tendon and ligament substitutes in vitro.

Conclusions

Tissue engineering showed great promise in replacing the damaged tendon and ligament. However, more study is needed to develop ideal engineered tendon and ligament.

Augmenting endogenous repair of soft tissues with nanofibre scaffolds

As our ability to engineer nanoscale materials has developed we can now influence endogenous cellular processes with increasing precision. Consequently, the use of biomaterials to induce and guide the repair and regeneration of tissues is a rapidly developing area. This review focuses on soft tissue engineering, it will discuss the types of biomaterial scaffolds available before exploring physical, chemical and biological modifications to synthetic scaffolds. We will consider how these properties, in combination, can provide a precise design process, with the potential to meet the requirements of the injured and diseased soft tissue niche. Finally, we frame our discussions within clinical trial design and the regulatory framework, the consideration of which is fundamental to the successful translation of new biomaterials.

An overview of decellularisation techniques of native tissues and tissue engineered products for bone, ligament and tendon regeneration

Decellularised tissues and organs have been successfully used in a variety of tissue engineering/regenerative medicine applications. Because of the complexity of each tissue (size, porosity, extracellular matrix (ECM) composition etc.), there is no standardised protocol and the decellularisation methods vary widely, thus leading to heterogeneous outcomes. Physical, chemical, and enzymatic methods have been developed and optimised for each specific application and this review describes the most common strategies utilised to achieve decellularisation of soft and hard tissues. While removal of the DNA is the primary goal of decellularisation, it is generally achieved at the expense of ECM preservation due to the harsh chemical or enzymatic processing conditions. As denaturation of the native ECM has been associated with undesired host responses, decellularisation conditions aimed at effectively achieving simultaneous DNA removal and minimal ECM damage will be highlighted. Additionally, the utilisation of decellularised matrices in regenerative medicine is explored, as are the most recent strategies implemented to circumvent challenges in this field. In summary, this review focusses on the latest advancements and future perspectives in the utilisation of natural ECM for the decoration of synthetic porous scaffolds.

Biological analysis of flexor tendon repair-failure stump tissue: A potential recycling of tissue for tendon regeneration

Objectives

Re-rupture is common after primary flexor tendon repair. Characterization of the biological changes in the ruptured tendon stumps would be helpful, not only to understand the biological responses to the failed tendon repair, but also to investigate if the tendon stumps could be used as a recycling biomaterial for tendon regeneration in the secondary grafting surgery.

Methods

A canine flexor tendon repair and failure model was used. Following six weeks of repair failure, the tendon stumps were analyzed and characterized as isolated tendon-derived stem cells (TDSCs).

Results

Failed-repair stump tissue showed cellular accumulation of crumpled and disoriented collagen fibres. Compared with normal tendon, stump tissue had significantly higher gene expression of collagens I and III, matrix metalloproteinases (MMPs), vascular endothelial growth factor (VEGF), platelet-derived growth factor (PDGF), and insulin-like growth factor (IGF). The stump TDSCs presented both mesenchymal stem and haematopoietic cell markers with significantly increased expression of CD34, CD44, and CD90 markers. Stump TDSCs exhibited similar migration but a lower proliferation rate, as well as similar osteogenic differentiation but a lower chondrogenic/adipogenic differentiation capability, compared with normal TDSCs. Stump TDSCs also showed increasing levels of SRY-box 2 (Sox2), octamer-binding transcription factor 4 (Oct4), tenomodulin (TNMD), and scleraxis (Scx) protein and gene expression.

Conclusion

We found that a failed repair stump had increased cellularity that preserved both mesenchymal and haematopoietic stem cell characteristics, with higher collagen synthesis, MMP, and growth factor gene expression. This study provides evidence that tendon stump tissue has regenerative potential.

Cite this article: C-C. Lu, T. Zhang, R. L. Reisdorf, P. C. Amadio, K-N. An, S. L. Moran, A. Gingery, C. Zhao. Biological analysis of flexor tendon repair-failure stump tissue: A potential recycling of tissue for tendon regeneration. Bone Joint Res 2019;8:232–245. DOI: 10.1302/2046-3758.86.BJR-2018-0239.R1.

-Book-shaped decellularized tendon matrix scaffold combined with bone marrow mesenchymal stem cells-sheets for repair of achilles tendon defect in rabbit

Tissue-engineering approaches have great potential to improve the treatment of tendon injuries which are major musculoskeletal disorders. The purpose of this study was to assess the tissue engineering potential of a novel multilayered decellularized tendon "book" scaffold with bone marrow mesenchymal stem cells (BMSCs) sheets for repair of an Achilles tendon defect in a rabbit model. In this study, we developed a novel book-shaped decellularized scaffold derived from the extracellular matrix of tendon tissues from New Zealand white rabbits. Hematoxylin and eosin (H&E) staining, 4', 6-diamidino-2-phenylindole (DAPI) staining, DNA quantitation, and scanning electron microscopy (SEM) confirmed the efficiency of decellularization. After culturing BMSCs on decellularized scaffolds, 3-(4, 5-dimethylthiazol-2-yl)-2, 5-diphenyltetrazolium bromide (MTT) assay, SEM, quantitative real time polymerase chain reaction (qRT-PCR), and immunofluorescence analysis demonstrated that decellularized scaffolds have the capacity to yield homogeneous distribution and alignment of BMSCs, as well as support their differentiation into tendon. Tenomodulin and Alpha-1 collagen type I are important indicators for evaluating tenogenic differentiation of BMSCs. When decellularized "book" scaffolds with BMSCs sheets were used to repair a 1 mm Achilles tendon defect, histomorphological analysis, immunohistochemical assessment, and biomechanical testing showed that the book-shaped decellularized tendon matrix scaffold and BMSCs sheets could promote the regeneration of type I collagen at the wound site during healing, and improve the mechanical properties of the repaired tendon. Therefore, the results of this study suggest that the novel decellularized "book" tendon scaffolds combined with BMSCs sheets have therapeutic effects on improving the healing quality of the Achilles tendon. © 2019 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 9999:1-11, 2019.

Orthotopic Transplantation of Achilles Tendon Allograft in Rats: With or without Incorporation of Autologous Mesenchymal Stem Cells

The biology and function of orthotopic transplantation of Achilles tendon allograft are unknown. Particularly, the revitalization of Achilles allograft is a clinical concern. Achilles allografts were harvested from donor rats and stored at -80 °C. Subcutaneous adipose tissue was harvested from the would-be allograft recipient rats for isolation of mesenchymal stem cells (MSCs). MSCs were cultured with growth differentiation factor-5 (GDF-5) and applied onto Achilles allografts on the day of transplantation. After the native Achilles tendon was resected from the left hind limb of the rats, Achilles allograft, with or without autologous MSCs, was implanted and sutured with calf muscles proximally and calcaneus distally. Animal gait was recorded presurgery and postsurgery weekly. The animals were sacrificed at week 4, and the transplanted Achilles allografts were collected for biomechanical testing and histology. The operated limbs had altered gait. By week 4, the paw print intensity, stance time, and duty cycle (percentage of the stance phase in a step cycle) of the reconstructed limbs were mostly recovered to the baselines recorded before surgery. Maximum load of failure was not different between Achilles allografts, with or without MSCs, and the native tendons. The Achilles allograft supplemented with MSCs had higher cellularity than the Achilles allograft without MSCs. Deposition of fine collagen (type III) fibers was active in Achilles allograft, with or without MSCs, but it was more evenly distributed in the allografts that were incubated with MSCs. In conclusion, orthotopically transplanted Achilles allograft healed with host tissues, regained strength, and largely restored Achilles function in 4 wk in rats. It is therefore a viable option for the reconstruction of a large Achilles tendon defect. Supplementation of MSCs improved repopulation of Achilles allograft, but large animal models, with long-term follow up and cell tracking, may be required to fully appreciate the functional benefits of MSCs.

Electrospun Heparin-Loaded Core-Shell Nanofiber Sutures for Achilles Tendon Regeneration In Vivo

Achilles tendon reconstruction surgery is the primary clinical method for repairing acute Achilles tendon ruptures. However, the efficacy of the postoperative healing process and the recovery of physiological function are inadequate. This study examines the healing mechanism of ruptured rat Achilles tendons seamed with heparin-loaded core-shell fiber sutures fabricated via near-field electrospinning. High-heparin-concentration sutures (PPH3.0) perform better than the low-heparin-concentration sutures and commercial sutures (CSs). The PPH3.0 suture recruits fewer inflammatory cells and shows good histocompatibility in peritoneal implantation experiments. Staining of the Achilles tendon rupture repair zone demonstrates that a high heparin concentration in sutures reduces immune-inflammatory responses. Immunohistochemical analysis reveals that the transforming growth factor-β staining scores of the PPH3.0 sutures are not significantly different from those of the corresponding control group but are significantly different from those of the CSs and non-heparin-loaded-suture groups. According to vascular endothelial growth factor (VEGF) analysis, the concentration of VEGF in the group treated with the PPH3.0 suture increases by 37.5% compared with that in its control group. No significant difference in tension strength is observed between the PPH3.0 group and healthy Achilles tendons. These findings illustrate that this novel method effectively treats Achilles tendon rupture and promotes healing and regeneration.

Tissue engineering strategies for the treatment of tendon injuries: a systematic review and meta-analysis of animal models

OBJECTIVES

Recently, the field of tissue engineering has made numerous advances towards achieving artificial tendon substitutes with excellent mechanical and histological properties, and has had some promising experimental results. The purpose of this systematic review is to assess the efficacy of tissue engineering in the treatment of tendon injuries.

METHODS

We searched MEDLINE, Embase, and the Cochrane Library for the time period 1999 to 2016 for trials investigating tissue engineering used to improve tendon healing in animal models. The studies were screened for inclusion based on randomization, controls, and reported measurable outcomes. The RevMan software package was used for the meta-analysis.

RESULTS

A total of 388 references were retrieved and 35 studies were included in this systematic review. The different biomaterials developed were analyzed and we found that they improve the biomechanical and histological characteristics of the repaired tendon. At meta-analysis, despite a high heterogeneity, it revealed a statistically significant effect in favour of the maximum load, the maximum stress, and the Young's modulus between experimental and control groups. In the forest plot, the diamond was on the right side of the vertical line and did not intersect with the line, favouring experimental groups.

CONCLUSIONS

This review of the literature demonstrates the heterogeneity in the tendon tissue engineering literature. Several biomaterials have been developed and have been shown to enhance tendon healing and regeneration with improved outcomes.Cite this article: D. González-Quevedo, I. Martínez-Medina, A. Campos, F. Campos, V. Carriel. Tissue engineering strategies for the treatment of tendon injuries: a systematic review and meta-analysis of animal models. Bone Joint Res 2018;7:318-324. DOI: 10.1302/2046-3758.74.BJR-2017-0326.

The Use of Cocultured Mesenchymal Stem Cells with Tendon-Derived Stem Cells as a Better Cell Source for Tendon Repair

The management of tendon tissue injury presents a significant clinical challenge due to the unique properties of tendons. Cell-based therapy provides a new alternative for regenerating functional tendons, such as in tendon rupture repair, but largely remains at the preclinical research stage. A cell source for graft preparation is essential for successful clinic application. In this study, a novel cell coculture system of bone marrow mesenchymal stem cells (BMSCs) and tendon-derived stem cells (TDSCs) was developed and investigated. BMSCs and TDSCs were cultured separately or in combination at ratios of 20:1, 10:1, 5:1, and 1:1 in vitro, and the cocultured cells showed an enhanced proliferation and collagenous protein production. The coculture system promoted tenogenic differentiation with enhanced tenogenic marker gene expression and collagen matrix production, particularly in the groups with a ratio of 1:1. Using a rat patellar tendon window injury model, we demonstrated that the cell sheets formed by cocultured cells promoted tendon healing significantly, compared to those with a single-cell source. Our study suggests that BMSCs and TDSCs cocultured at the 1:1 ratio may be an improved cell source/preparation for tendon tissue engineering.

Automated freeze-thaw cycles for decellularization of tendon tissue - a pilot study

Background

Decellularization of tendon tissue plays a pivotal role in current tissue engineering approaches for in vitro research as well as for translation of graft-based tendon restoration into clinics. Automation of essential decellularization steps like freeze-thawing is crucial for the development of more standardized decellularization protocols and commercial graft production under good manufacturing practice (GMP) conditions in the future.

Methods

In this study, a liquid nitrogen-based controlled rate freezer was utilized for automation of repeated freeze-thawing for decellularization of equine superficial digital flexor tendons. Additional tendon specimens underwent manually performed freeze-thaw cycles based on an established procedure. Tendon decellularization was completed by using non-ionic detergent treatment (Triton X-100). Effectiveness of decellularization was assessed by residual nuclei count and calculation of DNA content. Cytocompatibility was evaluated by culturing allogeneic adipose tissue-derived mesenchymal stromal cells on the tendon scaffolds.

Results

There were no significant differences in decellularization effectiveness between samples decellularized by the automated freeze-thaw procedure and samples that underwent manual freeze-thaw cycles. Further, we inferred no significant differences in the effectiveness of decellularization between two different cooling and heating rates applied in the automated freeze-thaw process. Both the automated protocols and the manually performed protocol resulted in roughly 2% residual nuclei and 13% residual DNA content. Successful cell culture was achieved with samples decellularized by automated freeze-thawing as well as with tendon samples decellularized by manually performed freeze-thaw cycles.

Conclusions

Automated freeze-thaw cycles performed by using a liquid nitrogen-based controlled rate freezer were as effective as previously described manual freeze-thaw procedures for decellularization of equine superficial digital flexor tendons. The automation of this key procedure in decellularization of large tendon samples is an important step towards the processing of large sample quantities under standardized conditions. Furthermore, with a view to the production of commercially available tendon graft-based materials for application in human and veterinary medicine, the automation of key procedural steps is highly required to develop manufacturing processes under GMP conditions.

Decellularized and Engineered Tendons as Biological Substitutes: A Critical Review

Tendon ruptures are a great burden in clinics. Finding a proper graft material as a substitute for tendon repair is one of the main challenges in orthopaedics, for which the requirement of a biological scaffold would be different for each clinical application. Among biological scaffolds, the use of decellularized tendon-derived matrix increasingly represents an interesting approach to treat tendon ruptures. We analyzed in vitro and in vivo studies focused on the development of efficient protocols for the decellularization and for the cell reseeding of the tendon matrix to obtain medical devices for tendon substitution. Our review considered also the proper tendon source and preclinical animal models with the aim of entering into clinical trials. The results highlight a wide panorama in terms of allogenic or xenogeneic tendon sources, specimen dimensions, physical or chemical decellularization techniques, and the cell type variety for reseeding from terminally differentiated to undifferentiated mesenchymal stem cells and their static or dynamic culture employed to generate implantable constructs tested in different animal models. We try to identify the most efficient approach to achieve an optimal biological scaffold for biomechanics and intrinsic properties, resembling the native tendon and being applicable in clinics in the near future, with particular attention to the Achilles tendon substitution.

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.