Augmentation of chronic rotator cuff healing using adipose-derived stem cell-seeded human tendon-derived hydrogel

Biomechanical, Histologic, and Micro-Computed Tomography Characterization of Partial-Width Full-Thickness Supraspinatus Tendon Injury in Rats

PURPOSE

Partial rotator cuff tears can cause shoulder pain and dysfunction and are more common than complete tears. However, few studies examine partial injuries in small animals and, therefore a robust, clinically relevant model may be lacking. This study aimed to fully characterize the established rat model of partial rotator cuff injury over time and determine if it models human partial rotator cuff tears.

METHODS

We created a full-thickness, partial-width injury at the supraspinatus tendon-bone interface bilaterally in 31 Sprague-Dawley rats. Rats were euthanized immediately, and at 2-, 3-, 4-, and 8-weeks after surgery. Fourteen intact shoulders were used as controls. Samples were assessed biomechanically, histologically, and morphologically.

RESULTS

Biomechanically, load to failure in controls and 8 weeks after injury was significantly greater than immediately and 3 weeks after injury. Load to failure at 8 weeks was comparable to control. However, the locations of failure were different between intact shoulders and partially injured samples. Bone mineral density at 8 weeks was significantly greater than that at 2 and 3 weeks. Although no animals demonstrated propagation to complete tear and the injury site remodeled histologically, the appearance at 8 weeks was not identical to that in the controls.

CONCLUSIONS

The biomechanical properties and bone quality decreased after the injury and was restored gradually over time with full restoration by 8 weeks after injury. However, the findings were not equivalent to the intact shoulder. This study demonstrated the limitations of the current model in its application to long-term outcome studies, and the need for better models that can be used to assess chronic partial rotator cuff injuries.

CLINICAL RELEVANCE

There is no small animal model that mimics human chronic partial rotator cuff tears, which limits our ability to improve care for this common condition.

Human-Derived collagen hydrogel as an antibiotic vehicle for topical treatment of bacterial biofilms

The complexity of chronic wounds creates difficulty in effective treatments, leading to prolonged care and significant morbidity. Additionally, these wounds are incredibly prone to bacterial biofilm development, further complicating treatment. The current standard treatment of colonized superficial wounds, debridement with intermittent systemic antibiotics, can lead to systemic side-effects and often fails to directly target the bacterial biofilm. Furthermore, standard of care dressings do not directly provide adequate antimicrobial properties. This study aims to assess the capacity of human-derived collagen hydrogel to provide sustained antibiotic release to disrupt bacterial biofilms and decrease bacterial load while maintaining host cell viability and scaffold integrity. Human collagen harvested from flexor tendons underwent processing to yield a gellable liquid, and subsequently was combined with varying concentrations of gentamicin (50-500 mg/L) or clindamycin (10-100 mg/L). The elution kinetics of antibiotics from the hydrogel were analyzed using liquid chromatography-mass spectrometry. The gel was used to topically treat Methicillin-resistant Staphylococcus aureus (MRSA) and Clostridium perfringens in established Kirby-Bauer and Crystal Violet models to assess the efficacy of bacterial inhibition. 2D mammalian cell monolayers were topically treated, and cell death was quantified to assess cytotoxicity. Bacteria-enhanced in vitro scratch assays were treated with antibiotic-embedded hydrogel and imaged over time to assess cell death and mobility. Collagen hydrogel embedded with antibiotics (cHG+abx) demonstrated sustained antibiotic release for up to 48 hours with successful inhibition of both MRSA and C. perfringens biofilms, while remaining bioactive up to 72 hours. Administration of cHG+abx with antibiotic concentrations up to 100X minimum inhibitory concentration was found to be non-toxic and facilitated mammalian cell migration in an in vitro scratch model. Collagen hydrogel is a promising pharmaceutical delivery vehicle that allows for safe, precise bacterial targeting for effective bacterial inhibition in a pro-regenerative scaffold.

Effects of adipose-derived cell supplementation on tendon-bone healing in a rat model of chronic rotator cuff tear with suprascapular nerve injury

OBJECTIVE

To investigate the effect of adipose-derived cells (ADCs) on tendon-bone healing in a rat model of chronic rotator cuff tear (RCT) with suprascapular nerve (SN) injury.

METHODS

Adult rats underwent right shoulder surgery whereby the supraspinatus was detached, and SN injury was induced. ADCs were cultured from the animals' abdominal fat. At 6 weeks post-surgery, the animals underwent surgical tendon repair; the ADC (+ve) group (n = 18) received an ADC injection, and the ADC (-ve) group (n = 18) received a saline injection. Shoulders were harvested at 10, 14, and 18 weeks and underwent histological, fluorescent, and biomechanical analyses.

RESULTS

In the ADC (+ve) group, a firm enthesis, including dense mature fibrocartilage and well-aligned cells, were observed in the bone-tendon junction and fatty infiltration was less than in the ADC (-ve) group. Mean maximum stress and linear stiffness was greater in the ADC (+ve) compared with the ADC (-ve) group at 18 weeks.

CONCLUSION

ADC supplementation showed a positive effect on tendon-bone healing in a rat model of chronic RCT with accompanying SN injury. Therefore, ADC injection may possibly accelerate recovery in massive RCT injuries.

Enthesis repair - State of play

The fibrocartilaginous enthesis is a highly specialised tissue interface that ensures a smooth mechanical transfer between tendon or ligament and bone through a fibrocartilage area. This tissue is prone to injury and often does not heal, even after surgical intervention. Enthesis augmentation approaches are challenging due to the complexity of the tissue that is characterised by the coexistence of a range of cellular and extracellular components, architectural features and mechanical properties within only hundreds of micrometres. Herein, we discuss enthesis repair and regeneration strategies, with particular focus on elegant interfacial and functionalised scaffold-based designs.

Efficacy of transplantation of lipoaspired mesenchymal stem cells in the treatment of chronic rotator cuff tears. Experimental model in rats

BACKGROUND AND AIM

Rotator cuff tears emerge in approximately 30% of the population over 60 years of age. Arthroscopic surgical treatment of these lesions is the treatment of choice, however, despite the improved repair techniques, the rate of re-tears ranges between 11 and 94%. Therefore, researchers seek to improve the biological healing process through the use of different alternatives such as mesenchymal stem cells (MSCs). Our objective is to evaluate the efficacy of a Cellular Therapy Drug made from allogeneic stem cells derived from adipose tissue in a rat model of chronic rotator cuff injury.

MATERIAL AND METHODS

The supraspinatus lesion was created in 48 rats for subsequent suturing at 4 weeks. MSCs in suspension were added to 24 animals after suturing, and HypoThermosol-FRS® (HTS) to 24 animals as a control group. Histology (Åström and Rausing scale) and the maximum load, displacement and elastic constant of the supraspinatus tendon were analyzed in both groups 4 months after the repair.

RESULTS

No statistically significant differences were found in the histological score comparing the tendons treated with MSCs with respect to the tendons treated with HTS (P=.811) nor in the results of maximum load (P=.770), displacement (P=.852) or elastic constant (P=.669) of the tendon in both groups.

CONCLUSIONS

The addition of adipose-derived cells in suspension to the repair of a chronic cuff injury does not improve the histology or biomechanics of the sutured tendon.

[Translated article] Efficacy of transplantation of lipoaspired mesenchymal stem cells in the treatment of chronic rotator cuff tears. Experimental model in rats

BACKGROUND AND AIM

Rotator cuff tears emerge in approximately 30% of the population over 60 years of age. Arthroscopic surgical treatment of these lesions is the treatment of choice, however, despite the improved repair techniques, the rate of re-tears ranges between 11 and 94%. Therefore, researchers seek to improve the biological healing process through the use of different alternatives such as mesenchymal stem cells (MSCs). Our objective is to evaluate the efficacy of a cellular therapy drug made from allogeneic stem cells derived from adipose tissue in a rat model of chronic rotator cuff injury.

MATERIAL AND METHODS

The supraspinatus lesion was created in 48 rats for subsequent suturing at 4 weeks. MSCs in suspension were added to 24 animals after suturing, and HypoThermosol-FRS® (HTS) to 24 animals as a control group. Histology (Åström and Rausing scale) and the maximum load, displacement and elastic constant of the supraspinatus tendon were analysed in both groups 4 months after the repair.

RESULTS

No statistically significant differences were found in the histological score comparing the tendons treated with MSCs with respect to the tendons treated with HTS (P=0.811) nor in the results of maximum load (P=0.770), displacement (P=0.852) or elastic constant (P=0.669) of the tendon in both groups.

CONCLUSIONS

The addition of adipose-derived cells in suspension to the repair of a chronic cuff injury does not improve the histology or biomechanics of the sutured tendon.

Exploring polysaccharide and protein-enriched decellularized matrix scaffolds for tendon and ligament repair: A review

Tissue engineering (TE) has become a primary research topic for the treatment of diseased or damaged tendon/ligament (T/L) tissue. T/L injuries pose a severe clinical burden worldwide, necessitating the development of effective strategies for T/L repair and tissue regeneration. TE has emerged as a promising strategy for restoring T/L function using decellularized extracellular matrix (dECM)-based scaffolds. dECM scaffolds have gained significant prominence because of their native structure, relatively high bioactivity, low immunogenicity, and ability to function as scaffolds for cell attachment, proliferation, and differentiation, which are difficult to imitate using synthetic materials. Here, we review the recent advances and possible future prospects for the advancement of dECM scaffolds for T/L tissue regeneration. We focus on crucial scaffold properties and functions, as well as various engineering strategies employed for biomaterial design in T/L regeneration. dECM provides both the physical and mechanical microenvironments required by cells to survive and proliferate. Various decellularization methods and sources of allogeneic and xenogeneic dECM in T/L repair and regeneration are critically discussed. Additionally, dECM hydrogels, bio-inks in 3D bioprinting, and nanofibers are briefly explored. Understanding the opportunities and challenges associated with dECM-based scaffold development is crucial for advancing T/L repairs in tissue engineering and regenerative medicine.

Rotator Cuff Augmentation: Its Role and Best Practices

Rotator cuff tears are a common source of pain and impairment in the shoulder. Healing of the rotator cuff tendons following repair has been associated with improved patient outcomes. While there have been many technical improvements in surgical techniques for rotator cuff repair, failure rates are still surprisingly high. Augmentation of these repairs has been shown to help with fixation biomechanics as well as healing rates. The described types of augments include autograft, allograft, xenograft, and synthetic options. This report reviews the commonly available types of augments and some of the outcomes associated with their use.

Microfracture Lateral to the Greater Tuberosity of the Humerus Enhances Tendon-to-Bone Healing in a Rat Rotator Cuff Model

BACKGROUND

Microfracture at the rotator cuff insertion is an established surgical marrow-stimulation technique for enhancing rotator cuff healing. However, the effect of lateralized or medialized microfracture on the insertion is unknown.

PURPOSE

To compare the biomechanical and histologic effects of microfracture at 3 different regions for rotator cuff repair in a rat model.

STUDY DESIGN

Controlled laboratory study.

METHODS

A total of 72 Sprague-Dawley rats with bilateral supraspinatus tendon insertion detachment were allocated into 4 groups with 4 different interventions: no microfracture at the humeral head as a control group (Con), traditional microfracture at the footprint area (MFA), and medialized microfracture to the footprint area (MMFA) on the articular surface of the humerus or lateralized microfracture to the footprint area at the greater tuberosity (LMFA). All underwent immediate repair. Tendon-to-bone healing was assessed by biomechanical and histologic tests 4 and 8 weeks postoperation.

RESULTS

At 4 weeks, the LMFA group showed a significantly superior failure load compared with the other groups (all P < .05). The LMFA and MFA groups showed significantly superior stiffness compared with the Con and MMFA groups (all P < .01). At 8 weeks, superior failure load and stiffness were observed in the LMFA group compared with the control group (all P < .05). Histologic examination revealed that the LMFA group had superior collagen composition and tendon-to-bone maturation at the interface at 4 and 8 weeks compared with the Con group (all P < .05).

CONCLUSION

Lateralized microfracture at the greater tuberosity improved the histologic quality of repair tissue and biomechanical strength at the tendon-to-bone insertion after rotator cuff repair in a rat model.

CLINICAL RELEVANCE

Microfracture lateral to the footprint area might be a better way to enhance rotator cuff healing clinically.

Biomechanical and Biological Characterization of XGel, a Human-Derived Hydrogel for Stem Cell Expansion and Tissue Engineering

Hydrogels are 3D scaffolds used as alternatives to in vivo models for disease modeling and delivery of cells and drugs. Existing hydrogel classifications include synthetic, recombinant, chemically defined, plant- or animal-based, and tissue-derived matrices. There is a need for materials that can support both human tissue modeling and clinically relevant applications requiring stiffness tunability. Human-derived hydrogels are not only clinically relevant, but they also minimize the use of animal models for pre-clinical studies. This study aims to characterize XGel, a new human-derived hydrogel as an alternative to current murine-derived and synthetic recombinant hydrogels that features unique physiochemical, biochemical, and biological properties that support adipocyte and bone differentiation. Rheology studies determine the viscosity, stiffness, and gelation features of XGel. Quantitative studies for quality control support consistency in the protein content between lots. Proteomics studies reveal that XGel is predominantly composed of extracellular matrix proteins, including fibrillin, collagens I-VI, and fibronectin. Electron microscopy of the hydrogel provides phenotypic characteristics in terms of porosity and fiber size. The hydrogel demonstrates biocompatibility as a coating material and as a 3D scaffold for the growth of multiple cell types. The results provide insight into the biological compatibility of this human-derived hydrogel for tissue engineering.

Efficacy of Adipose-Derived Mesenchymal Stem Cells and Stromal Vascular Fraction Alone and Combined to Biomaterials in Tendinopathy or Tendon Injury: Systematic Review of Current Concepts

Background and Objectives: Tendon injury and tendinopathy are among the most frequent musculoskeletal diseases and represent a challenging issue for surgeons as well as a great socio-economic global burden. Despite the current treatments available, either surgical or conservative, the tendon healing process is often suboptimal and impaired. This is due to the inherent scarce ability of tendon tissue to repair and return itself to the original structure. Recently, Adipose-derived mesenchymal stem cells (ADSC) and stromal vascular fraction (SVF) have gained a central interest in the scientific community, demonstrating their effectiveness in treatments of acute and chronic tendon disorders in animals and humans. Either enzymatic or mechanical procedures to obtain ADSC and SVF have been described and used in current clinical practice. However, no unified protocols and processes have been established. Materials and Methods: This systematic review aims at providing a comprehensive update of the literature on the clinical application of ADSC enzymatically or mechanically processed to obtain SVF, alone and in association with biomaterials in the local treatment of tendinopathy and tendon injury in vivo, in animal models and humans. The study was performed according to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA). Results: Thirty-two articles met our inclusion criteria, with a total of 18 studies in animals, 10 studies in humans and 4 studies concerning the application of biomaterials in vivo in animals. The review of the literature suggests that ADSC/SVF therapy can represent a promising alternative in tendonregenerative medicine for the enhancement of tendon healing. Conclusions: Nevertheless, further investigations and randomized control trials are needed to improve the knowledge, standardize the procedures and extend the consensus on their use for such applications.

Strategies for promoting tendon-bone healing: Current status and prospects

Tendon-bone insertion (TBI) injuries are common, primarily involving the rotator cuff (RC) and anterior cruciate ligament (ACL). At present, repair surgery and reconstructive surgery are the main treatments, and the main factor determining the curative effect of surgery is postoperative tendon-bone healing, which requires the stable combination of the transplanted tendon and the bone tunnel to ensure the stability of the joint. Fibrocartilage and bone formation are the main physiological processes in the bone marrow tract. Therefore, therapeutic measures conducive to these processes are likely to be applied clinically to promote tendon-bone healing. In recent years, biomaterials and compounds, stem cells, cell factors, platelet-rich plasma, exosomes, physical therapy, and other technologies have been widely used in the study of promoting tendon-bone healing. This review provides a comprehensive summary of strategies used to promote tendon-bone healing and analyses relevant preclinical and clinical studies. The potential application value of these strategies in promoting tendon-bone healing was also discussed.

Therapeutic potential and mechanisms of mesenchymal stem cell-derived exosomes as bioactive materials in tendon-bone healing

Tendon-bone insertion (TBI) injuries, such as anterior cruciate ligament injury and rotator cuff injury, are the most common soft tissue injuries. In most situations, surgical tendon/ligament reconstruction is necessary for treating such injuries. However, a significant number of cases failed because healing of the enthesis occurs through scar tissue formation rather than the regeneration of transitional tissue. In recent years, the therapeutic potential of mesenchymal stem cells (MSCs) has been well documented in animal and clinical studies, such as chronic paraplegia, non-ischemic heart failure, and osteoarthritis of the knee. MSCs are multipotent stem cells, which have self-renewability and the ability to differentiate into a wide variety of cells such as chondrocytes, osteoblasts, and adipocytes. Numerous studies have suggested that MSCs could promote angiogenesis and cell proliferation, reduce inflammation, and produce a large number of bioactive molecules involved in the repair. These effects are likely mediated by the paracrine mechanisms of MSCs, particularly through the release of exosomes. Exosomes, nano-sized extracellular vesicles (EVs) with a lipid bilayer and a membrane structure, are naturally released by various cell types. They play an essential role in intercellular communication by transferring bioactive lipids, proteins, and nucleic acids, such as mRNAs and miRNAs, between cells to influence the physiological and pathological processes of recipient cells. Exosomes have been shown to facilitate tissue repair and regeneration. Herein, we discuss the prospective applications of MSC-derived exosomes in TBI injuries. We also review the roles of MSC-EVs and the underlying mechanisms of their effects on promoting tendon-bone healing. At last, we discuss the present challenges and future research directions.

Assessment of a Synergistic Effect of Platelet-Rich Plasma and Stem Cell-Seeded Hydrogel for Healing of Rat Chronic Rotator Cuff Injuries

Outcomes after repair of chronic rotator cuff injuries remain suboptimal. Type-1 collagen-rich tendon hydrogel was previously reported to improve healing in a rat chronic rotator cuff injury model. Stem cell seeding of the tendon hydrogel improved bone quality in the same model. This study aimed to examine whether there was a synergistic and dose-dependent effect of platelet-rich plasma (PRP) on tendon-bone interface healing by combining PRP with stem cell-seeded tendon hydrogel. Human cadaveric tendons were processed into a hydrogel. PRP was prepared at two different platelet concentrations: an initial concentration (initial PRP group) and a higher concentration (concentrated PRP group). Tendon hydrogel was mixed with adipose-derived stem cells and one of the platelet concentrations. Methylcellulose, as opposed to saline, was used as a negative control due to comparable viscosity. The supraspinatus tendon was detached bilaterally in 33 Sprague-Dawley rats (66 shoulders). Eight weeks later, each detached tendon was repaired, and a hydrogel mixture or control was injected at the repair site. Eight weeks after repair, shoulder samples were harvested and assigned for biomechanical testing (n = 42 shoulders) or a combination of bone morphological and histological assessment (n = 24 shoulders). Biomechanical testing showed significantly higher failure load and stiffness in the concentrated PRP group than in control. Yield load in the initial and concentrated PRP groups were significantly higher than that in the control. There were no statistically significant differences between the initial and concentrated PRP groups. The addition of the highly concentrated PRP to stem cells-seeded tendon hydrogel improved healing biomechanically after chronic rotator cuff injury in rats compared to control. However, synergistic and dose-dependent effects were not seen.

Hydrogel Development for Rotator Cuff Repair

Rotator cuff tears (RCTs) are common in shoulder disease and disability. Despite significant advances in surgical repair techniques, 20–70% of patients still have postoperative rotator cuff dysfunction. These functional defects may be related to retear or rotator cuff quality deterioration due to tendon retraction and scar tissue at the repair site. As an effective delivery system, hydrogel scaffolds may improve the healing of RCTs and be a useful treatment for irreparable rotator cuff injuries. Although many studies have tested this hypothesis, most are limited to laboratory animal experiments. This review summarizes differences in hydrogel scaffold construction, active ingredients, and application methods in recent research. Efforts to determine the indications of hydrogel scaffolds (with different constructions and cargos) for various types of RCTs, as well as the effectiveness and reliability of application methods and devices, are also discussed.

Advances in Stem Cell Therapies for Rotator Cuff Injuries

Rotator cuff injury is a common upper extremity musculoskeletal disease that may lead to persistent pain and functional impairment. Despite the clinical outcomes of the surgical procedures being satisfactory, the repair of the rotator cuff remains problematic, such as through failure of healing, adhesion formation, and fatty infiltration. Stem cells have high proliferation, strong paracrine action, and multiple differentiation potential, which promote tendon remodeling and fibrocartilage formation and increase biomechanical strength. Additionally, stem cell-derived extracellular vesicles (EVs) can increase collagen synthesis and inhibit inflammation and adhesion formation by carrying regulatory proteins and microRNAs. Therefore, stem cell-based therapy is a promising therapeutic strategy that has great potential for rotator cuff healing. In this review, we summarize the advances of stem cells and stem cell-derived EVs in rotator cuff repair and highlight the underlying mechanism of stem cells and stem cell-derived EVs and biomaterial delivery systems. Future studies need to explore stem cell therapy in combination with cellular factors, gene therapy, and novel biomaterial delivery systems.

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.

Augmentation of Rotator Cuff Healing With Orthobiologics

The limited regenerative capacity of the tendon-bone enthesis after surgical repair poses a significant challenge to achieving desired clinical outcomes. Biologic augmentation of the repair site has the potential to enhance the biomechanical and histological integrity of the enthesis, leading to lower retear rates and greater patient satisfaction. Platelet-rich plasma, stem cells and bone marrow aspirate concentrate, growth factors, biodegradable or biomimetic scaffolds, and amniotic products have been investigated in preclinical and, in some cases, clinical studies aimed at augmenting tendon-bone healing. Although many of these therapies have achieved some degree of success in improving structural, histological, and clinical outcomes after surgical tendon-bone enthesis repair, none have reliably and consistently lead to clinical improvement. High-quality randomized controlled clinical studies are needed to definitively evaluate the efficacy of these biologic therapies and ultimately determine which, if any, are capable of achieving a tendon-bone repair that is structurally noninferior to the native enthesis before injury.

The Evolution of Arthroscopic Rotator Cuff Repair

Over the past 30 years, arthroscopic rotator cuff repair (ARCR) has evolved to become the gold standard in treating rotator cuff pathology. As procedural concepts of ARCR continue to improve, it is also continually compared with the open rotator cuff repair as the historical standard of care. This review highlights the evolution of ARCR, including a historical perspective; the anatomic, clinical, and surgical implications of the development of an arthroscopic approach; how arthroscopy improved some of the problems of the open approach; adaptations in techniques and technologies associated with ARCR; future perspectives in orthobiologics as they pertain to ARCR; and lastly, the clinical improvements, or lack of improvements, with all of these adaptations.

Adipose-Derived Stem Cell Sheets Improve Early Biomechanical Graft Strength in Rabbits After Anterior Cruciate Ligament Reconstruction

BACKGROUND

Although various reconstruction techniques are available for anterior cruciate ligament (ACL) injuries, a long recovery time is required before patients return to sports activities, as the reconstructed ACL requires time to regain strength. To date, several studies have reported use of mesenchymal stem cells in orthopaedic surgery; however, no studies have used adipose-derived stem cell (ADSC) sheets in ACL reconstruction (ACLR).

HYPOTHESIS

ADSC sheet transplantation can improve biomechanical strength of the autograft used in ACLR.

STUDY DESIGN

Controlled laboratory study.

METHODS

A total of 68 healthy Japanese white rabbits underwent unilateral ACLR with a semitendinosus tendon autograft after random enrollment into a control group (no sheet; n = 34) and a sheet group (ADSC sheet; n = 34). At 2, 4, 8, 16, and 24 weeks after surgery, rabbits in each group were sacrificed to evaluate tendon-bone healing using histological staining, micro-computed tomography, and biomechanical testing. At 24 weeks, scanning transmission electron microscopy of the graft midsubstance was performed.

RESULTS

The ultimate failure load for the control and sheet groups, respectively, was as follows: 17.2 ± 5.5 versus 37.3 ± 10.3 (P = .01) at 2 weeks, 28.6 ± 1.9 versus 47.4 ± 10.4 (P = .003) at 4 weeks, 53.0 ± 14.3 versus 48.1 ± 9.3 (P = .59) at 8 weeks, 66.2 ± 9.3 versus 95.2 ± 43.1 (P = .24) at 16 weeks, and 66.7 ± 27.3 versus 85.3 ± 29.5 (P = .39) at 24 weeks. The histological score was also significantly higher in the sheet group compared with the control group at early stages up to 8 weeks. On micro-computed tomography, relative to the control group, the bone tunnel area was significantly narrower in the sheet group at 4 weeks, and the bone volume/tissue volume of the tendon-bone interface was significantly greater at 24 weeks. Scanning transmission electron microscopy at 24 weeks indicated that the mean collagen fiber diameter in the midsubstance was significantly greater, as was the occupation ratio of collagen fibers per field of view, in the sheet group.

CONCLUSION

ADSC sheets improved biomechanical strength, prevented bone tunnel enlargement, and promoted tendon-bone interface healing and graft midsubstance healing in an in vivo rabbit model.

CLINICAL RELEVANCE

ADSC sheets may be useful for early tendon-bone healing and graft maturation in ACLR.

Stem cell therapies in tendon-bone healing

Tendon-bone insertion injuries such as rotator cuff and anterior cruciate ligament injuries are currently highly common and severe. The key method of treating this kind of injury is the reconstruction operation. The success of this reconstructive process depends on the ability of the graft to incorporate into the bone. Recently, there has been substantial discussion about how to enhance the integration of tendon and bone through biological methods. Stem cells like bone marrow mesenchymal stem cells (MSCs), tendon stem/progenitor cells, synovium-derived MSCs, adipose-derived stem cells, or periosteum-derived periosteal stem cells can self-regenerate and potentially differentiate into different cell types, which have been widely used in tissue repair and regeneration. Thus, we concentrate in this review on the current circumstances of tendon-bone healing using stem cell therapy.

Adipose-derived stem cell exosomes facilitate rotator cuff repair by mediating tendon-derived stem cells

Aim: To evaluate the potential capability of adipose-derived stem cell exosomes (ADSC-exos) on rotator cuff repair by mediating the tendon-derived stem cells (TDSCs) and explored the mechanism. Methods: First, we investigated the growth, survival and migration of TDSCs in the presence of ADSC-exos in vitro. Using a rat rotator cuff injury model to analyze the ability of the ADSC-exos to promote rotator cuff healing in vivo. Results: The hydrogel with ADSC-exos significantly improved the osteogenic and adipogenesis differentiation and enhanced the expression of RUNX2, Sox-9, TNMD, TNC and Scx and the mechanical properties of the articular portion. Conclusion: The ADSC-exos have the potential to promote the rotator cuff repair by mediating the TDSCs.

Conditioned medium of human bone marrow-derived stem cells promotes tendon-bone healing of the rotator cuff in a rat model

Rotator cuff repair is a common surgery in sports medicine. During the surgery, torn tendon was re-fixed onto the bony surface. The majority of patients gain good results. However, re-tear occurs in some patients. The reason under this phenomenon is that the normal tendon-bone enthesis cannot be reconstructed. In order to strengthen the tendon-bone healing and promote enthesis regeneration, numerous manners are tested, among which stem cell related therapies are preferred. Stem cells, due to the ability of multi-lineage differentiation, are widely used in regenerative medicine. However, safety and ethics concerns limit its clinical use. Recent studies found that it is the secretome of stem cells that is biologically effective. On ground of this, we, in the current study, collected the conditioned medium of human bone marrow-derived stem cells (hBMSC-CM) and tested whether this acellular method could promote tendon-bone healing in a rat model of rotator cuff repair. By using histological, radiological, and biomechanical methods, we found that hBMSC-CM promoted tendon-bone healing of the rat rotator cuff. Then, we noticed that hBMSC-CM exerted an impact on macrophage polarization both in vivo and in vitro by inhibiting M1 phenotype and promoting M2 phenotype. Further, we proved that the benefit of hBMSC-CM on tendon-bone healing was related to its regulation on macrophage. Finally, we proved that, hBMSC-CM influenced macrophage polarization, which was, at least partially, related to Smad2/3 signaling pathway. Based on the experiments above, we confirmed the benefit of hBMSC-CM on tendon-bone healing, which relied on its immune-regulative property. Considering the accessibility and safety of acellular hBMSC-CM, we believe it is a promising candidate clinically for tendon-bone healing.

Homing of Adipose-Derived Stem Cells to a Tendon-Derived Hydrogel: A Potential Mechanism for Improved Tendon-Bone Interface and Tendon Healing

PURPOSE

Tendons are difficult to heal owing to their hypocellularity and hypovascularity. Our laboratory has developed a tendon-derived hydrogel (tHG) that significantly improves tendon healing in an animal model. We hypothesized that a potential mechanism for improved healing with tHG is through the attraction of systemic stem cells.

METHODS

Homing of systemic adipose-derived stem cells (ADSCs) to tendon injuries was assessed with acute and chronic injury models. Injury sites were treated with saline or tHG, and animals given a tail vein injection (TVI) of labeled ADSCs 1 week after treatment. One week following TVI, rats were harvested for histology. To further evaluate a potential difference in homing to tHG, a subcutaneous injection (SQI) model was used. Rats were treated with an SQI of saline, silicone, ADSCs in media, tHG, tHG + fibroblasts (FBs), or tHG + ADSCs on day 0. One week after SQI, rats underwent TVI with labeled ADSCs. Samples were harvested 2 or 3 weeks after SQI for analysis. Flow cytometry confirmed homing in the SQI model.

RESULTS

Systemically delivered ADSCs homed to both acute tendon and chronic tendon-bone interface (TBI) injury sites. Despite their presence at the injury site, there was no difference in the number of macrophages, amount of cell proliferation, or angiogenesis 1 week after stem cell delivery. In an SQI model, ADSCs homed to tHG. There was no difference in the number of ADSCs homing to tHG alone versus tHG + ADSCs. However, there was an increase in the number of living cells, general immune cells, and T-cells present at tHG + ADSC versus tHG alone.

CONCLUSIONS

The ADSCs home to tendon injury sites and tHG. We believe the attraction of additional systemic ADSCs is one mechanism for improved tendon and TBI healing with tHG.

CLINICAL RELEVANCE

Treatment of tendon and TBI injuries with tHG can augment healing via homing of systemic stem cells.

Engineered Cell Sheets for the Effective Delivery of Adipose-Derived Stem Cells for Tendon-to-Bone Healing

BACKGROUND

Efforts are being made to treat rotator cuff tears (RCTs) that exhibit poor healing and high retear rates. Tendon-to-bone healing using mesenchymal stem cells is being explored, but research is needed to establish effective delivery options.

PURPOSE

To evaluate the effects of an adipose-derived stem cell (ADSC) sheet on mesenchymal stem cell delivery for tendon-to-bone healing of a chronic RCT in rats and to demonstrate that ADSC sheets enhance tendon-to-bone healing.

STUDY DESIGN

Controlled laboratory study.

METHODS

Mesenchymal stem cells were obtained from rat adipose tissue, and a cell sheet was prepared using a temperature-responsive dish. To evaluate the efficacy of stem cells produced in a sheet for the lesion, the experiment was conducted with 3 groups: repair group, cell sheet transplantation after repair group, and cell sheet-only group. Histological, biomechanical, and micro-computed tomography (micro-CT) results were compared among the groups.

RESULTS

Hematoxylin and eosin staining for histomorphological analysis revealed that the cell sheet transplantation after repair group (5.75 ± 0.95) showed statistically significant higher scores than the repair (2.75 ± 0.50) and cell sheet-only (3.25 ± 0.50) groups (P < .001). On safranin O staining, the cell sheet transplantation after repair group (0.51 ± 0.04 mm²) had a larger fibrocartilage area than the repair (0.31 ± 0.06 mm²) and cell sheet-only (0.32 ± 0.03 mm²) groups (P = .001). On micro-CT, bone volume/total volume values were significantly higher in the cell sheet transplantation after repair group (23.98% ± 1.75%) than in the other groups (P < .039); there was no significant difference in the other values. On the biomechanical test, the cell sheet transplantation after repair group (4 weeks after repair) showed significantly higher results than the other groups (P < .005).

CONCLUSION

Our study shows that engineered stem cells are a clinically feasible stem cell delivery tool for rotator cuff repair.

CLINICAL RELEVANCE

This laboratory study provides evidence that ADSCs are effective in repairing RCTs, which are common sports injuries.

Success Criteria and Preclinical Testing of Multifunctional Hydrogels for Tendon Regeneration

Tendon injuries are difficult to heal, in part, because intrinsic tendon healing, which is dominated by scar tissue formation, does not effectively regenerate the native structure and function of healthy tendon. Further, many current treatment strategies also fall short of producing regenerated tendon with the native properties of healthy tendon. There is increasing interest in the use of cell-instructive strategies to limit the intrinsic fibrotic response following injury and improve the regenerative capacity of tendon in vivo. We have established multifunctional, cell-instructive hydrogels for treating injured tendon that afford tunable control over the biomechanical, biochemical, and structural properties of the cell microenvironment. Specifically, we incorporated integrin-binding domains (RGDS) and assembled multifunctional collagen mimetic peptides that enable cell adhesion and elongation of stem cells within synthetic hydrogels of designed biomechanical properties and evaluated these materials using targeted success criteria developed for testing in mechanically demanding environments such as tendon healing. The in vitro and in situ success criteria were determined based on systematic reviews of the most commonly reported outcome measures of hydrogels for tendon repair and established standards for testing of biomaterials. We then showed, using validation experiments, that multifunctional and synthetic hydrogels meet these criteria. Specifically, these hydrogels have mechanical properties comparable to developing tendon; are noncytotoxic both in two-dimensional bolus exposure (hydrogel components) and three-dimensional encapsulation (full hydrogel); are formed, retained, and visualized within tendon defects over time (2-weeks); and provide mechanical support to tendon defects at the time of in situ gel crosslinking. Ultimately, the in vitro and in situ success criteria evaluated in this study were designed for preclinical research to rigorously test the potential to achieve successful tendon repair before in vivo testing and indicate the promise of multifunctional and synthetic hydrogels for continued translation. Impact statement Tendon healing results in a weak scar that forms due to poor cell-mediated repair of the injured tissue. Treatments that tailor the instructions experienced by cells during healing afford opportunities to regenerate the healthy tendon. Engineered cell-instructive cues, including the biomechanical, biochemical, and structural properties of the cell microenvironment, within multifunctional synthetic hydrogels are promising therapeutic strategies for tissue regeneration. In this article, the preclinical efficacy of multifunctional synthetic hydrogels for tendon repair is tested against rigorous in vitro and in situ success criteria. This study indicates the promise for continued preclinical translation of synthetic hydrogels for tissue regeneration.

Topical Antibiotic Elution in a Collagen-Rich Hydrogel Successfully Inhibits Bacterial Growth and Biofilm Formation In Vitro

Chronic wounds are a prominent concern, accounting for $25 billion of health care costs annually. Biofilms have been implicated in delayed wound closure, but they are susceptible to developing antibiotic resistance and treatment options continue to be limited. A novel collagen-rich hydrogel derived from human extracellular matrix presents an avenue for treating chronic wounds by providing appropriate extracellular proteins for healing and promoting neovascularization. Using the hydrogel as a delivery system for localized secretion of a therapeutic dosage of antibiotics presents an attractive means of maximizing delivery while minimizing systemic side effects. We hypothesize that the hydrogel can provide controlled elution of antibiotics leading to inhibition of bacterial growth and disruption of biofilm formation. The rate of antibiotic elution from the collagen-rich hydrogel and the efficacy of biofilm disruption was assessed with Pseudomonas aeruginosa Bacterial growth inhibition, biofilm disruption, and mammalian cell cytotoxicity were quantified using in vitro models. The antibiotic-loaded hydrogel showed sustained release of antibiotics for up to 24 h at therapeutic levels. The treatment inhibited bacterial growth and disrupted biofilm formation at multiple time points. The hydrogel was capable of accommodating various classes of antibiotics and did not result in cytotoxicity in mammalian fibroblasts or adipose stem cells. The antibiotic-loaded collagen-rich hydrogel is capable of controlled antibiotic release effective for bacteria cell death without native cell death. A human-derived hydrogel that is capable of eluting therapeutic levels of antibiotic is an exciting prospect in the field of chronic wound healing.

In Vitro Cultures of Adipose-Derived Stem Cells: An Overview of Methods, Molecular Analyses, and Clinical Applications

Adipose-derived stem cells (ASCs) exhibiting mesenchymal stem cell (MSC) characteristics, have been extensively studied in recent years. Because they have been shown to differentiate into lineages such as osteogenic, chondrogenic, neurogenic or myogenic, the focus of most of the current research concerns either their potential to replace bone marrow as a readily available and abundant source of MSCs, or to employ them in regenerative and reconstructive medicine. There is close to consensus regarding the methodology used for ASC isolation and culture, whereas a number of molecular analyses implicates them in potential therapies of a number of pathologies. When it comes to clinical application, there is a range of examples of animal trials and clinical studies employing ASCs, further emphasizing the advancement of studies leading to their more widespread use. Nevertheless, in vitro studies will most likely continue to play a significant role in ASC studies, both providing the molecular knowledge of their ex vivo properties and possibly serving as an important step in purification and application of those cells in a clinical setting. Therefore, it is important to consider current methods of ASC isolation, culture, and processing. Furthermore, molecular analyses and cell surface properties of ASCs are essential for animal studies, clinical studies, and therapeutic applications of the MSC properties.

A Randomized Controlled Trial of the Treatment of Rotator Cuff Tears with Bone Marrow Concentrate and Platelet Products Compared to Exercise Therapy: A Midterm Analysis

Injectable regenerative therapies such as bone marrow concentrate (BMC) and platelet-rich plasma (PRP) may represent a safe alternative in the treatment of rotator cuff tears. This is a midterm review of a randomized, crossover trial comparing autologous BMC and platelet product injections versus exercise therapy in the treatment of partial and full-thickness supraspinatus tears. Patients enrolled into the study were between 18 and 65 years of age presenting to an outpatient orthopedic clinic with partial to full thickness, nonretracted supraspinatus tendon tears. Enrolled patients were randomized to either ultrasound-guided autologous BMC with PRP and platelet lysate (PL) percutaneous injection treatment or exercise therapy. Patients could cross over to BMC treatment after at least 3 months of exercise therapy. Patients completed the Disability of the Arm, Shoulder and Hand (DASH) scores as the primary outcome measure. Secondary outcomes included the numeric pain scale (NPS), a modified Single Assessment Numeric Evaluation (SANE), and a blinded MRI review. At this midterm review, results from 25 enrolled patients who have reached at least 12-month follow-up are presented. No serious adverse events were reported. Significant differences were seen in patient reported outcomes for the BMC treatment compared to exercise therapy at 3 and 6 months for pain, and for function and reported improvement (SANE) at 3 months (p < .05). Patients reported a mean 89% improvement at 24 months, with sustained functional gains and pain reduction. MRI review showed a size decrease of most tears post-BMC treatment. These findings suggest that ultrasound-guided BMC and platelet product injections are a safe and useful alternative to conservative exercise therapy of torn, nonretracted supraspinatus tendons. This trial is registered with NCT01788683.

Tendon and Ligament Healing and Current Approaches to Tendon and Ligament Regeneration

Ligament and tendon injuries are common problems in orthopedics. There is a need for treatments that can expedite nonoperative healing or improve the efficacy of surgical repair or reconstruction of ligaments and tendons. Successful biologically-based attempts at repair and reconstruction would require a thorough understanding of normal tendon and ligament healing. The inflammatory, proliferative, and remodeling phases, and the cells involved in tendon and ligament healing will be reviewed. Then, current research efforts focusing on biologically-based treatments of ligament and tendon injuries will be summarized, with a focus on stem cells endogenous to tendons and ligaments. Statement of clinical significance: This paper details mechanisms of ligament and tendon healing, as well as attempts to apply stem cells to ligament and tendon healing. Understanding of these topics could lead to more efficacious therapies to treat ligament and tendon injuries. © 2019 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 38:7-12, 2020.