Rotator Cuff Repair With Autologous Tenocytes and Biodegradable Collagen Scaffold: A Histological and Biomechanical Study in Sheep

Fabrication of atelocollagen-coated bioabsorbable suture and the evaluation of its regenerative efficacy in Achilles tendon healing using a rat experimental model

Recently, the incidence of Achilles tendon ruptures (ATRs) has become more common, and repair surgery using a bioabsorbable suture is generally preferred, particularly in the case of healthy patients. Sutures composed of poly(lactic-co-glycolic acid) (PLGA) are commonly used in ATR surgeries. Nevertheless, owing to the inherent limitations of PLGA, novel bioabsorbable sutures that can accelerate Achilles tendon healing are sought. Recently, several studies have demonstrated the beneficial effects of atelocollagen on tendon healing. In this study, poly(3,4-dihydroxy-L-phenylalanine) (pDOPA), a hydrophilic biomimetic material, was used to modify the hydrophobic surface of a PLGA suture (Vicryl, VC) for the stable coating of atelocollagen on its surface. The main objective was to fabricate an atelocollagen-coated VC suture and evaluate its performance in the healing of Achilles tendon using a rat model of open repair for ATR. Structural analyses of the surface-modified suture indicated that the collagen was successfully coated on the VC/pDOPA suture. Postoperative in vivo biomechanical analysis, histological evaluation, ultrastructural/morphological analyses, and western blotting confirmed that the tendons in the VC/pDOPA/Col group exhibit superior healing than those in the VC and VC/pDOPA groups after 1 and 6 weeks following the surgery. The this study suggests that atelocollagen-coated PLGA/pDOPA sutures are preferable for future medical applications, especially in the repair of ATR.

Arthroscopic Repair of Retracted Large and Massive Rotator Cuff Tears With and Without Augmentation With a Bio-Inductive Collagen Implant Reveals Substantial and Comparable Clinical Improvement

PURPOSE

To compare clinical and imaging results after repair of retracted large and massive full-thickness rotator cuff tears, including revision repairs, with and without augmentation with a bio-inductive collagen implant.

METHODS

The study group comprised 24 patients (17 male subjects) with retracted 2 or 3 tendon rotator cuff tears undergoing arthroscopic repair followed by onlay augmentation with a bio-inductive collagen implant. The control group comprised 24 patients (19 male subjects) matched by tear size undergoing repair without augmentation. Mean patient age at repair in both groups was 61 years. Active range of motion and patient-reported outcomes were recorded before and after surgery. Noncontrast high-field magnetic resonance imaging was obtained in 20 of 24 collagen implant patients and 17 of 24 control patients at minimum 6 months' follow-up to assess tendon healing.

RESULTS

American Shoulder and Elbow Surgeons and Simple Shoulder Test scores improved from 35 to 86 and 3.6 to 9.3, respectively, in the collagen implant group and from 39 to 87 and 3.9 to 9.7 in the control group. The visual analog score-pain improved from 6.0 to 0.9 and from 5.9 to 0.9 in the collagen implant and control groups, respectively (P < .001 for all). Overall improvements in range of motion and patient-reported outcomes were similar in both groups. Magnetic resonance imaging revealed intact repairs in 11 of 20 (55%) patients in the patch group and 9 of 17 (53%) in the control group. Two patients in each group were revised to reverse shoulder arthroplasty.

CONCLUSIONS

Arthroscopic repair of retracted large and massive rotator cuff tears, including revision repairs, with and without augmentation using a bio-inductive collagen implant results in substantial and comparable early clinical improvement, although predictable healing remains elusive. Further work is needed to optimize patient selection for massive rotator cuff repair and define more precisely the indications for augmentation of these repairs using the collagen implant.

LEVEL OF EVIDENCE

Level III, retrospective cohort study.

Optimizing Tissue Engineering for Clinical Relevance in Rotator Cuff Repair

Rotator cuff tear (RCT) is the most common cause of disability in the upper extremity. It results in 4.5 million physician visits in the United States every year and is the most common etiology of shoulder conditions evaluated by orthopedic surgeons. Over 460,000 RCT repair surgeries are performed in the United States annually. Rotator cuff (RC) retear and failure to heal remain significant postoperative complications. Literature suggests that the retear rates can range from 29.5% to as high as 94%. Weakened and irregular enthesis regeneration is a crucial factor in postsurgical failure. Although commercially available RC repair grafts have been introduced to augment RC enthesis repair, they have been associated with mixed clinical outcomes. These grafts lack appropriate biological cues such as stem cells and signaling molecules at the bone-tendon interface. In addition, they do little to prevent fibrovascular scar tissue formation, which causes the RC to be susceptible to retear. Advances in tissue engineering have demonstrated that mesenchymal stem cells (MSCs) and growth factors (GFs) enhance RC enthesis regeneration in animal models. These models show that delivering MSCs and GFs to the site of RCT enhances native enthesis repair and leads to greater mechanical strength. In addition, these models demonstrate that MSCs and GFs may be delivered through a variety of methods including direct injection, saturation of repair materials, and loaded microspheres. Grafts that incorporate MSCs and GFs enhance anti-inflammation, osteogenesis, angiogenesis, and chondrogenesis in the RC repair process. It is crucial that the techniques that have shown success in animal models are incorporated into the clinical setting. A gap currently exists between the promising biological factors that have been investigated in animal models and the RC repair grafts that can be used in the clinical setting. Future RC repair grafts must allow for stable implantation and fixation, be compatible with current arthroscopic techniques, and have the capability to deliver MSCs and/or GFs.

Translational Research on Orthobiologics in the Treatment of Rotator Cuff Disease: From the Laboratory to the Operating Room

Rotator cuff disease is one of the most common human tendinopathies and can lead to significant shoulder dysfunction. Despite efforts to improve symptoms in patients with rotator cuff tears and healing rates after rotator cuff repair, high rates of failed healing and persistent shoulder morbidity exist. Increasing interest has been placed on the utilization of orthobiologics-scaffolds, cell-based augmentation, platelet right plasma (platelet-rich plasma), and small molecule-based strategies-in the management of rotator cuff disease and the augmentation of rotator cuff repairs. This is a complex topic that involves novel treatment strategies, including patches/scaffolds, small molecule-based, cellular-based, and tissue-derived augmentation techniques. Ultimately, translational research, with a particular focus on preclinical models, has allowed us to gain some insights into the utility of orthobiologics in the treatment of rotator cuff disease and will continue to be critical to our further understanding of the underlying cellular mechanisms moving forward.

Fibroblast Growth Factor Soaked Collagen Membrane Shows No Biomechanical or Histological Advantages in the Treatment of Chronic Rotator Cuff Tears in a Rabbit Model

PURPOSE

To investigate the histological and biomechanical effects of a fibroblast growth factor (FGF-2)-soaked collagen membrane used to treat a full-thickness chronic rotator cuff (RC) rupture in a rabbit model.

METHODS

Forty-eight shoulders from 24 rabbits were used. At the beginning of the procedure, 8 rabbits were killed to assess the control group (Group IT) with intact tendons. To establish a chronic RC tear model, a full-thickness subscapularis tear was created on both shoulders of the remaining 16 rabbits and left for 3 months. The transosseous mattress suture technique was used to repair tears in the left shoulder (Group R). The tears in the right shoulder (Group CM) were treated using the same approach, with an FGF-soaked collagen membrane inserted and sutured over the repair site. Three months after the procedure, all rabbits were killed. Biomechanical testing was performed on the tendons to determine failure load, linear stiffness, elongation intervals, and displacement. Histologically, the modified Watkins score was used to evaluate tendon-bone healing.

RESULTS

There was no significant difference among the three groups in terms of failure load, displacement, linear stiffness, and elongation (P > .05). The total modified Watkins score was not affected by applying the FGF-soaked collagen membrane to the repair site (P > .05). Fibrocytes, parallel cells, large-diameter fibers, and the total modified Watkins score were significantly lower in both repair groups when compared to the intact tendon group (P < .05).

CONCLUSIONS

In addition to tendon repair, FGF-2 soaked collagen membrane -application at the repair site provides neither biomechanical nor histological advantages in the treatment of chronic RC tears.

CLINICAL RELEVANCE

FGF-soaked collagen membrane augmentation provides no impact on the chronic RC tear healing tissue. The need to investigate alternative methods that may have a positive effect on healing in chronic RC repairs continues.

An Atelocollagen Injection Enhances the Healing of Nonoperatively Treated Achilles Tendon Tears: An Experimental Study in Rats

Background

There is growing interest in nonoperative treatment for the management of Achilles tendon ruptures (ATRs). However, nonoperative treatment is limited by the risk of tendon reruptures and low satisfaction rates. Recently, atelocollagen injections have been reported to have beneficial effects on tendon healing.

Purpose

To evaluate the beneficial effects of injected atelocollagen on Achilles tendon healing and investigate the mechanism of atelocollagen on tendon healing.

Study Design

Controlled laboratory study.

Methods

Percutaneous tenotomy of the right Achilles tendon in 66 rats was performed. The animals were equally divided into the noninjection group (NG) and the collagen injection group (CG). At 1, 3, and 6 weeks, the Achilles functional index, cross-sectional area, load to failure, stiffness, stress, and the modified Bonar score were assessed. Transmission electron microscopy, western blotting, and immunohistochemistry were also performed.

Results

The Achilles functional index (-6.8 vs -43.0, respectively; P = .040), load to failure (42.1 vs 27.0 N, respectively; P = .049), and stiffness (18.8 vs 10.3 N/mm, respectively; P = .049) were higher in the CG than those in the NG at 3 weeks. There were no significant differences in histological scores between the 2 groups. Transmission electron microscopy analysis showed that the mean diameter of collagen fibrils in the CG was greater than that in the NG at 3 weeks (117.2 vs 72.6 nm, respectively; P < .001) and 6 weeks (202.1 vs 144.0 nm, respectively; P < .001). Western blot analysis showed that the expression of collagen type I in the CG was higher than that in the NG at 1 week (P = .005) and 6 weeks (P = .001).

Conclusion

An atelocollagen injection had beneficial effects on the healing of nonoperatively treated Achilles tendon injuries. The Achilles tendon of CG rats exhibited better functional, biomechanical, and morphological outcomes compared with NG rats. The molecular data indicated that the mechanism of atelocollagen injections may be associated with an increased amount of collagen type I.

Clinical Relevance

An atelocollagen injection might be a good adjuvant option for the nonoperative treatment of ATRs.

Biomaterials for Tissue-Engineered Treatment of Tendinopathy in Animal Models: A Systematic Review

To conduct a systematic review of studies reporting the treatment of tendon injury using biomaterials in animal models. A systematic search was conducted to retrieve studies involving animal models of tendon repair using biomaterials, in PubMed (database construction to August 2022) and Ovid-Embase (1946 to August 2022). Data related to tendon repair with biomaterials were extracted by two researchers, respectively. Risk of bias was assessed following the Cochrane Handbook for Systematic Reviews of Interventions. A statistical analysis was performed based on the classification of tendon repair biomaterials included in our study. A total of 8413 articles were retrieved, with 78 studies included in our analysis. For tendon repair in animal models using biomaterials, the most commonly seen characteristics were as follows: naturally derived biomaterials, rabbits and rats as animal models, surgery as the injury model, and the Achilles tendon as the injury site. The histology and biomechanical recovery of tendon injury following repair are affected by different biomaterials. Studies of tendon repair in animal models indicate that biomaterials can significantly improve repair outcomes, including tendon structure and biomechanics. Among effective biomaterial strategies are the use of new composites and incorporation of cells or growth factors into the material, both of which provide obvious benefits for tendon healing. More high-quality preclinical studies are required to encourage the translation of biomaterials into clinical practice for tendon repair.

The Effect of Pulling Angle on Rotator Cuff Mechanical Properties in a Canine In Vitro Model

The objective of this study was to examine the effect of pulling angle on time-zero mechanical properties of intact infraspinatus tendon or infraspinatus tendon repaired with the modified Mason-Allen technique in a canine model in vitro. Thirty-six canine shoulder samples were used. Twenty intact samples were randomly allocated into functional pull (135°) and anatomic pull (70°) groups (n = 10 per group). The remaining sixteen infraspinatus tendons were transected from the insertion and repaired using the modified Mason-Allen technique before being randomly allocated into functional pull or anatomic pull groups (n = 8 per group). Load to failure testing was performed on all specimens. The ultimate failure load and ultimate stress of the functional pulled intact tendons were significantly lower compared with anatomic pulled tendons (1310.2 ± 167.6 N vs. 1687.4 ± 228.2 N, p = 0.0005: 55.6 ± 8.4 MPa vs. 67.1 ± 13.3 MPa, p = 0.0334). For the tendons repaired with the modified Mason-Allen technique, no significant differences were observed in ultimate failure load, ultimate stress or stiffness between functional pull and anatomic pull groups. The variance of pulling angle had a significant influence on the biomechanical properties of the rotator cuff tendon in a canine shoulder model in vitro. Load to failure of the intact infraspinatus tendon was lower at the functional pulling position compared to the anatomic pulling position. This result indicates that uneven load distribution across tendon fibers under functional pull may predispose the tendon to tear. However, this mechanical character is not presented after rotator cuff repair using the modified Mason-Allen technique.

Advanced strategies for constructing interfacial tissues of bone and tendon/ligament

Enthesis, the interfacial tissue between a tendon/ligament and bone, exhibits a complex histological transition from soft to hard tissue, which significantly complicates its repair and regeneration after injury. Because traditional surgical treatments for enthesis injury are not satisfactory, tissue engineering has emerged as a strategy for improving treatment success. Rapid advances in enthesis tissue engineering have led to the development of several strategies for promoting enthesis tissue regeneration, including biological scaffolds, cells, growth factors, and biophysical modulation. In this review, we discuss recent advances in enthesis tissue engineering, particularly the use of biological scaffolds, as well as perspectives on the future directions in enthesis tissue engineering.

Large animal models for the study of tendinopathy

Tendinopathy has a high incidence in athletes and the aging population. It can cause pain and movement disorders, and is one of the most difficult problems in orthopedics. Animal models of tendinopathy provide potentially efficient and effective means to develop understanding of human tendinopathy and its underlying pathological mechanisms and treatments. The selection of preclinical models is essential to ensure the successful translation of effective and innovative treatments into clinical practice. Large animals can be used in both micro- and macro-level research owing to their similarity to humans in size, structure, and function. This article reviews the application of large animal models in tendinopathy regarding injuries to four tendons: rotator cuff, patellar ligament, Achilles tendon, and flexor tendon. The advantages and disadvantages of studying tendinopathy with large animal models are summarized. It is hoped that, with further development of animal models of tendinopathy, new strategies for the prevention and treatment of tendinopathy in humans will be developed.

Functional biomaterials for tendon/ligament repair and regeneration

With an increase in life expectancy and the popularity of high-intensity exercise, the frequency of tendon and ligament injuries has also increased. Owing to the specificity of its tissue, the rapid restoration of injured tendons and ligaments is challenging for treatment. This review summarizes the latest progress in cells, biomaterials, active molecules and construction technology in treating tendon/ligament injuries. The characteristics of supports made of different materials and the development and application of different manufacturing methods are discussed. The development of natural polymers, synthetic polymers and composite materials has boosted the use of scaffolds. In addition, the development of electrospinning and hydrogel technology has diversified the production and treatment of materials. First, this article briefly introduces the structure, function and biological characteristics of tendons/ligaments. Then, it summarizes the advantages and disadvantages of different materials, such as natural polymer scaffolds, synthetic polymer scaffolds, composite scaffolds and extracellular matrix (ECM)-derived biological scaffolds, in the application of tendon/ligament regeneration. We then discuss the latest applications of electrospun fiber scaffolds and hydrogels in regeneration engineering. Finally, we discuss the current problems and future directions in the development of biomaterials for restoring damaged tendons and ligaments.

Challenges and perspectives of tendon-derived cell therapy for tendinopathy: from bench to bedside

Tendon is composed of dense fibrous connective tissues, connecting muscle at the myotendinous junction (MTJ) to bone at the enthesis and allowing mechanical force to transmit from muscle to bone. Tendon diseases occur at different zones of the tendon, including enthesis, MTJ and midsubstance of the tendon, due to a variety of environmental and genetic factors which consequently result in different frequencies and recovery rates. Self-healing properties of tendons are limited, and cell therapeutic approaches in which injured tendon tissues are renewed by cell replenishment are highly sought after. Homologous use of individual’s tendon-derived cells, predominantly differentiated tenocytes and tendon-derived stem cells, is emerging as a treatment for tendinopathy through achieving minimal cell manipulation for clinical use. This is the first review summarizing the progress of tendon-derived cell therapy in clinical use and its challenges due to the structural complexity of tendons, heterogeneous composition of extracellular cell matrix and cells and unsuitable cell sources. Further to that, novel future perspectives to improve therapeutic effect in tendon-derived cell therapy based on current basic knowledge are discussed.

Effects and Mechanism of Particulate Matter on Tendon Healing Based on Integrated Analysis of DNA Methylation and RNA Sequencing Data in a Rat Model

Exposure to particulate matter (PM) has been linked with the severity of various diseases. To date, there is no study on the relationship between PM exposure and tendon healing. Open Achilles tenotomy of 20 rats was performed. The animals were divided into two groups according to exposure to PM: a PM group and a non-PM group. After 6 weeks of PM exposure, the harvest and investigations of lungs, blood samples, and Achilles tendons were performed. Compared to the non-PM group, the white blood cell count and tumor necrosis factor-alpha expression in the PM group were significantly higher. The Achilles tendons in PM group showed significantly increased inflammatory outcomes. A TEM analysis showed reduced collagen fibrils in the PM group. A biomechanical analysis demonstrated that the load to failure value was lower in the PM group. An upregulation of the gene encoding cyclic AMP response element-binding protein (CREB) was detected in the PM group by an integrated analysis of DNA methylation and RNA sequencing data, as confirmed via a Western blot analysis showing significantly elevated levels of phosphorylated CREB. In summary, PM exposure caused a deleterious effect on tendon healing. The molecular data indicate that the action mechanism of PM may be associated with upregulated CREB signaling.

Editorial Commentary: Allogenic Dermal Fibroblasts in Collagen Matrix Scaffold Enhance Rotator Cuff Repair in an Animal Model

There has been a recent surge of interest on the use of biologic supplements to facilitate rotator cuff repair healing. Experimental evidence appears to support use of allogenic dermal fibroblasts (ADFs), either in the form of local injection or tenocytes embedded in collagen matrix scaffold, to enhance healing of a repaired rotator cuff tendon tear in an animal model. When compared with the ADFs, the platelet-rich plasma (PRP)-induced response seems to be limited in terms of the specific increases in local collagen 1 concentration, thus resulting in a bone-tendon healing response that is inferior in both biology and biomechanical behavior under the same laboratory conditions. While on the one hand, there is pilot data supporting use of dermal fibroblast in the clinical setting, thus reinforcing the animal study findings, on the other hand, we are also aware of the encouraging biologic changes that occurred in the retrieved acellular dermal matrix (ADM) allograft that was used for superior capsular reconstruction as a treatment of irreparable rotator cuff tears. In theory, ADFs locally instilled as an injection should further enhance the healing response compared to the ADM. However, this needs to be further studied to be able to be widely applicable clinically.

Design of an electrospun tubular construct combining a mechanical and biological approach to improve tendon repair

Hand tendon injuries represent a major clinical problem and might dramatically diminish a patient's life quality. In this study, a targeted solution for flexor tendon repair was developed by combining a mechanical and biological approach. To this end, a novel acrylate-endcapped urethane-based polymer (AUP) was synthesized and its physico-chemical properties were characterized. Next, tubular repair constructs were developed using electrospinning of the AUP material with incorporated naproxen and hyaluronic acid (i.e. anti-inflammatory and anti-adhesion compounds, respectively), and with a tubular braid as mechanical reinforcement. Tensile testing of the repair constructs using ex vivo sheep tendons showed that the developed repair constructs fulfilled the required mechanical properties for tendon repair (i.e. minimal ultimate stress of 4 MPa), with an ultimate stress of 6.4 ± 0.6 MPa. Moreover, in vitro biological assays showed that the developed repair tubes and the incorporated bioactive components were non-cytotoxic. In addition, when equine tenocytes and mesenchymal stem cells were co-cultured with the repair tubes, an increased production of collagen and non-collagenous proteins was observed. In conclusion, this novel construct in which a mechanical approach (fulfilling the required mechanical properties) was combined with a biological approach (incorporation of bioactive compounds), shows potential as flexor tendon repair application. Graphical abstract.

In Vitro Biocompatibility and Degradation Analysis of Mass-Produced Collagen Fibers

Automation and mass-production are two of the many limitations in the tissue engineering industry. Textile fabrication methods such as electrospinning are used extensively in this field because of the resemblance of the extracellular matrix to the fiber structure. However, electrospinning has many limitations, including the ability to mass-produce, automate, and reproduce products. For this reason, this study evaluates the potential use of a traditional textile method such as spinning. Apart from mass production, these methods are also easy, efficient, and cost-effective. This study uses bovine-derived collagen fibers to create yarns using the traditional ring spinning method. The collagen yarns are proven to be biocompatible. Enzymatic biodegradability was also confirmed for its potential use in vivo. The results of this study prove the safety and efficacy of the material and the fabrication method. The material encourages higher cell proliferation and migration compared to tissue culture-treated plastic plates. The process is not only simple but is also streamlined and replicable, resulting in standardized products that can be reproduced.

Injection of adipose stem cells in the treatment of rotator cuff disease - a narrative review of current evidence

The purpose of this study is to summarize evidence for the use of adipose stem cell (ASC) injections in the treatment of rotator cuff tears (RCT) and identify future areas of study. A thorough literature search was performed to identify studies investigating the use of ASC injections in the treatment of RCTs. Among animal trials, it is unclear whether ASCs are of benefit for rotator cuff repair. In clinical trials, ASC injection may reduce retear rate with otherwise equivocal clinical outcomes. Although ASC injection may be safe, the literature does not provide a clear consensus as to the efficacy of ASC injections, nor does it delineate which patients would benefit most from this treatment.

Translational therapy from preclinical animal models for muscle degeneration after rotator cuff injury

Chronic rotator cuff tears are debilitating diseases which significantly affect patients’ quality of life and pose substantial financial burden to the society. The intraoperative reparability of injured tendon and postoperative probability of tendon retear are highly associated with the quality of torn muscles, specifically, the severity of muscle atrophy and fatty infiltration. Animal models that reproduce the characteristic muscle pathology after rotator cuff injury have been developed and used to provide insight into the underlying biology and pathophysiology. In this review, we briefly summarize the current information obtained from preclinical animal studies regarding the degenerative change of cuff muscle subsequent to tendon release and/or suprascapular nerve denervation. Importantly, we focus on the potential translational therapeutic targets or agents for the prevention or reversal of muscle atrophy and fatty infiltration. While further studies are warranted to assess the safety and efficacy of novel therapies derived from these preclinical animal research, we believe that their clinical translation for the treatment of rotator cuff disorders is on the horizon.

The Translational potential of this article

Novel therapeutic strategies described in this review from preclinical animal studies hold a great translational potential for preventing or reversing rotator cuff muscle pathology, while further assessments on their safety and efficacy are warranted.

Decellularized Human Umbilical Cord Wharton Jelly Scaffold Improves Tendon Regeneration in a Rabbit Rotator Cuff Tendon Defect Model

BACKGROUND

Owing to limited self-healing capacity, failure of rotator cuff tendon healing is a common complication after surgery. Biological scaffolds have garnered attention owing to their potential to enhance healing outcomes.

PURPOSE

To verify the effect of the decellularized umbilical cord Wharton jelly (DUCWJ) scaffold as a bridging scaffold in a rabbit model of acute rotator cuff tendon defect.

STUDY DESIGN

Controlled laboratory study.

METHODS

We fabricated a DUCWJ scaffold using a physicochemical decellularized method, evaluating changes in the umbilical cord Wharton jelly before and after decellularization. Scanning electron microscopy and biomechanical testing were performed to determine the microstructure and mechanical properties. We assessed cytocompatibility and cell regulatory behavior of the scaffold toward tendon stem/progenitor cells (TSPCs). A supraspinatus tendon defect was created in 54 New Zealand White rabbits, allocated to the DUCWJ scaffold repair group and the negative control group (without scaffold). Histology, reverse transcription polymerase chain reaction, and biomechanical tensile strength were assessed at 4, 8, and 12 weeks postoperatively.

RESULTS

Decellularization completely removed cells from the umbilical cord Wharton jelly, retained a considerable amount of glycosaminoglycan and collagen, and preserved the microstructure and tensile strength. The DUCWJ scaffold facilitated migration and proliferation of TSPCs in vitro. Tendon-related gene expression revealed that the DUCWJ scaffold could maintain the tenocyte phenotype of TSPCs. In the in vivo study, the DUCWJ scaffold improved tendon healing and enhanced the biomechanical strength of repaired tendons. Histological evaluation scores of the DUCWJ group were significantly higher than those of the negative control at 4, 8, and 12 weeks after surgery (P < .05). In repaired tendon tissues, reverse transcription polymerase chain reaction findings revealed that the DUCWJ scaffold stimulated tendon development and maturation. Furthermore, an overall increase in ultimate load and tensile modulus was noted over time; the DUCWJ group presented better results than the negative control group (P < .05).

CONCLUSION

The DUCWJ scaffold has an excellent 3-dimensional porous structure, good biocompatibility, and fundamental biomechanical characteristics, and it promotes migration, attachment, and proliferation of TSPCs. The in vivo animal study demonstrated that the DUCWJ scaffold has potential for tendon regeneration in an acute rotator cuff tendon defect model.

CLINICAL RELEVANCE

DUCWJ scaffolds have potential as a regenerative material to augment rotator cuff healing in the clinical setting.

Tendon midsubstance trauma as a means for the development of translatable chronic rotator cuff degeneration in an ovine model

BACKGROUND

Chronic degeneration of rotator cuff tendons is a major contributing factor to the unacceptably high prevalence of rotator cuff repair surgery failures. The etiology of chronic rotator cuff degeneration is not well understood, and current therapies are not effective, necessitating preclinical research to fill this knowledge gap. Unfortunately, current large animal models rely on enthesis disruption as a means of model generation, which is not representative of human patients with chronic rotator cuff degeneration prior to full-thickness tears. Following, the goal of this study was to develop and characterize a translational large-animal model of chronic rotator cuff degeneration without enthesis release.

METHODS

A midsubstance damage model [i.e., "combed fenestration" (CF)] in adult sheep was generated by creating 16 longitudinal cuts within the top third of the infraspinatus tendon thickness. Tendon integrity was characterized through exhaustive non-destructive biomechanical stress relaxation testing [peak stress, peak load, percent relaxation, and cross-sectional area (CSA)], followed by histopathological degeneration scoring and analysis (Bonar score), histomorphological analysis of collagen organization and fatty atrophy (percent adipose area), and gene expression analyses.

RESULTS

The CF model tendons exhibited significantly decreased mechanical properties as evidenced by decreased peak stress (P<0.025) and increased percent relaxation (18-week vs. Control, P<0.035) at multiple strain magnitudes and across all timepoints. At all timepoints, the CF tendons exhibited pathological changes aligned with tendon degeneration, as evidenced by increased Bonar scoring (P<0.001) and decreased collagen organization (6-week vs. Control, P=0.013). Increases in intramuscular adipose content were also documented through histomorphology analysis (6- and 18-week vs. Control, P<0.077). Significant changes in gene expression were noted at all timepoints.

CONCLUSIONS

These data reveal that this new ovine CF model of chronic rotator cuff degeneration results in tendons with decreased mechanical properties, degenerative pathology characteristics, and gene expression profiles that aligned with the degenerative changes that have been noted in humans with tendinopathy. For these reasons, we believe this novel large animal model of chronic rotator cuff degeneration is a translational platform in which to test devices, therapies, and/or technologies aimed at repairing damage to the shoulder.

Electronic Drugs: Spatial and Temporal Medical Treatment of Human Diseases

Recent advances in diagnostics and medicines emphasize the spatial and temporal aspects of monitoring and treating diseases. However, conventional therapeutics, including oral administration and injection, have difficulties meeting these aspects due to physiological and technological limitations, such as long-term implantation and a narrow therapeutic window. As an innovative approach to overcome these limitations, electronic devices known as electronic drugs (e-drugs) have been developed to monitor real-time body signals and deliver specific treatments to targeted tissues or organs. For example, ingestible and patch-type e-drugs could detect changes in biomarkers at the target sites, including the gastrointestinal (GI) tract and the skin, and deliver therapeutics to enhance healing in a spatiotemporal manner. However, medical treatments often require invasive surgical procedures and implantation of medical equipment for either short or long-term use. Therefore, approaches that could minimize implantation-associated side effects, such as inflammation and scar tissue formation, while maintaining high functionality of e-drugs, are highly needed. Herein, the importance of the spatial and temporal aspects of medical treatment is thoroughly reviewed along with how e-drugs use cutting-edge technological innovations to deal with unresolved medical challenges. Furthermore, diverse uses of e-drugs in clinical applications and the future perspectives of e-drugs are discussed.

The role of MicroRNAs in tendon injury, repair, and related tissue engineering

Tendon injuries are one of the most common musculoskeletal disorders that cause considerable morbidity and significantly compromise the patients' quality of life. The innate limited regenerative capacity of tendon poses a substantial treating challenge for clinicians. MicroRNAs (miRNAs) are a family of small non-coding RNAs that play a vital role in orchestrating many biological processes through post-transcriptional regulation. Increasing evidence reveals that miRNA-based therapeutics may serve as an innovative strategy for the treatment of tendon pathologies. In this review, we briefly present miRNA biogenesis, the role of miRNAs in tendon cell biology and their involvement in tendon injuries, followed by a summary of current miRNA-based approaches in tendon tissue engineering with a special focus on attenuating post-injury fibrosis. Next, we discuss the advantages of miRNA-functionalized scaffolds in achieving sustained and localized miRNA administration to minimize off-target effects, and thus hoping to inspire the development of effective miRNA delivery platforms specifically for tendon tissue engineering. We envision that advancement in miRNA-based therapeutics will herald a new era of tendon tissue engineering and pave a way for clinical translation for the treatments of tendon disorders.

Current Biological Strategies to Enhance Surgical Treatment for Rotator Cuff Repair

Rotator cuff tear is one of the most common shoulder problems encountered by orthopedic surgeons. Due to the slow healing process and high retear rate, rotator cuff tear has distressed millions of people all around the world every year, especially for the elderly and active athletes. This disease significantly impairs patients' motor ability and reduces their quality of life. Besides conservative treatment, open and arthroscopic surgery contributes a lot to accelerate the healing process of rotator cuff tear. Currently, there are many emerging novel treatment methods to promote rotator cuff repair. A variety of biological stimulus has been utilized in clinical practice. Among them, platelet-rich plasma, growth factors, stem cells, and exosomes are the most popular biologics in laboratory research and clinical trials. This review will focus on the biologics of bioaugmentation methods for rotator cuff repair and tendon healing, including platelet-rich plasma, growth factors, exosomes and stem cells, etc. Relevant studies are summarized in this review and future research perspectives are introduced.

Enthesis trauma as a means for the development of translatable chronic rotator cuff degeneration in an ovine model

BACKGROUND

Untreated rotator cuff tears lead to irreversible tendon degeneration, resulting in unacceptable repair prognosis. The inability of current animal models of degenerated rotator cuff tendons to more fully emulate the manifestation and degree of pathology seen in humans with a previously torn rotator cuff tendon (s) significantly impairs the development of novel therapeutics. Therefore, the objective of this study was to develop a large-animal translational model of enthesis damage to the rotator cuff tendons to mimic the chronic degenerative changes that occur in patients that demonstrate clinical manifestations of tendinopathy.

METHODS

A partial enthesis tear model (i.e., sharp transection) in adult sheep was created by cutting the tendon fibers perpendicularly through the enthesis midpoint, while leaving the other portion of the tendon in-tact. To assess tendon integrity, non-destructive biomechanical tests were performed, followed by histopathological, histomorphological, and gene expression analysis. Samples of degenerated human rotator cuff tendons obtained from patients undergoing reverse total shoulder arthroplasty to use for comparative pathological analysis.

RESULTS

In the sheep model, transected tendons at all timepoints had significantly decreased mechanical properties. Histopathologic evaluation and Bonar scoring revealed that the tendons in sheep underwent degenerative changes similar in magnitude and manifestation as the degenerated human tendon samples. Furthermore, similar levels of collagen disorganization were noted between the 6 and 12-week ovine samples and the degenerated human samples.

CONCLUSIONS

These findings indicate that the new sheep model of rotator cuff injury reliably recapitulates the structural and cellular changes that occur clinically in humans with chronic rotator cuff tendon injuries and suggest that this new model is well suited to evaluation of new therapeutic interventions.

Cell-Free Book-Shaped Decellularized Tendon Matrix Graft Capable of Controlled Release of BMP-12 to Improve Tendon Healing in a Rat Model

BACKGROUND

Achilles tendon (AT) defects often occur in traumatic and chronic injuries. Currently, no graft can satisfactorily regenerate parallel tendinous tissue at the defect site to completely restore AT function.

PURPOSE

To develop a cell-free functional graft by tethering bone morphogenetic protein 12 (BMP-12) on a book-shaped decellularized tendon matrix (BDTM) and to determine whether this graft is more beneficial for AT defect healing than an autograft.

STUDY DESIGN

Controlled laboratory study.

METHODS

Canine patellar tendon was sectioned into a book shape and decellularized to fabricate a BDTM. The collagen-binding domain (CBD) was fused into the N-terminus of BMP-12 to synthesize a recombinant BMP-12 (CBD-BMP-12), which was tethered to the BDTM to prepare a cell-free functional graft (CBD-BMP-12/BDTM). After its tensile resistance, tenogenic inducibility, and BMP-12 release dynamics were evaluated, the efficacy of the graft for tendon regeneration was determined in a rat model. A total of 140 mature male Sprague-Dawley rats underwent AT tenotomy. The defect was reconstructed with reversed AT (autograft group), native BMP-12 tethered to an intact decellularized tendon matrix (IDTM; NAT-BMP-12/IDTM group), native BMP-12 tethered to a BDTM (NAT-BMP-12/BDTM group), CBD-BMP-12 tethered on an IDTM (CBD-BMP-12/IDTM group), and CBD-BMP-12 tethered on a BDTM (CBD-BMP-12/BDTM group). The rats were sacrificed 4 or 8 weeks after surgery to harvest AT specimens. Six specimens from each group at each time point were used for histological evaluation; the remaining 8 specimens were used for biomechanical testing.

RESULTS

In vitro CBD-BMP-12/BDTM was noncytotoxic, showed high biomimetics with native tendons, was suitable for cell adhesion and growth, and had superior tenogenic inducibility. In vivo the defective AT in the CBD-BMP-12/BDTM group regenerated more naturally than in the other groups, as indicated by more spindle-shaped fibroblasts embedded in a matrix of parallel fibers. The biomechanical properties of the regenerated AT in the CBD-BMP-12/BDTM group also increased more significantly than in the other groups.

CONCLUSION

CBD-BMP-12/BDTM is more beneficial than autograft for healing AT defects in a rat model.

CLINICAL RELEVANCE

The findings of this study demonstrate that CBD-BMP-12/BDTM can serve as a practical graft for reconstructing AT defects.

Tendon tissue engineering: Cells, growth factors, scaffolds and production techniques

Tendon injuries are a global health problem that affects millions of people annually. The properties of tendons make their natural rehabilitation a very complex and long-lasting process. Thanks to the development of the fields of biomaterials, bioengineering and cell biology, a new discipline has emerged, tissue engineering. Within this discipline, diverse approaches have been proposed. The obtained results turn out to be promising, as increasingly more complex and natural tendon-like structures are obtained. In this review, the nature of the tendon and the conventional treatments that have been applied so far are underlined. Then, a comparison between the different tendon tissue engineering approaches that have been proposed to date is made, focusing on each of the elements necessary to obtain the structures that allow adequate regeneration of the tendon: growth factors, cells, scaffolds and techniques for scaffold development. The analysis of all these aspects allows understanding, in a global way, the effect that each element used in the regeneration of the tendon has and, thus, clarify the possible future approaches by making new combinations of materials, designs, cells and bioactive molecules to achieve a personalized regeneration of a functional tendon.