Engineered allogeneic chondrocyte pellet for reconstruction of fibrocartilage zone at bone-tendon junction--a preliminary histological observation

Interposition of acellular amniotic membrane at the tendon to bone interface would be better for healing than overlaying above the tendon to bone junction in the repair of rotator cuff injury

PURPOSE

The retear rate of rotator cuff (RC) after surgery is high, and the rapid and functional enthesis regeneration remains a challenge. Whether acellular amniotic membrane (AAM) helps to promote the healing of tendon to bone and which treatment is better are both unclear. The study aims to investigate the effect of AAM on the healing of RC and the best treatment for RC repair.

METHODS

Thirty-three Sprague Dawley rats underwent RC transection and repair using microsurgical techniques and were randomly divided into the suturing repair only (SRO) group (n = 11), the AAM overlaying (AOL) group (n = 11), and the AAM interposition (AIP) group (n = 11), respectively. Rats were sacrificed at 4 weeks, then examined by subsequent micro-CT, and evaluated by histologic and biomechanical tests. The statistical analyses of one-way ANOVA or Kruskal-Wallis test were performed using with SPSS 23.0. A p < 0.05 was considered a significant difference.

RESULTS

AAM being intervened between tendon and bone (AIP group) or overlaid over tendon to bone junction (AOL group) in a rat model, promoted enthesis regeneration, increased new bone and cartilage generation, and improved collagen arrangement and biomechanical properties in comparison with suturing repair only (SRO group) (AOL vs. SRO, p < 0.001, p = 0.004, p = 0.003; AIP vs. SRO, p < 0.001, p < 0.001, p < 0.001). Compared with the AOL group, the AIP group had better results in micro-CT evaluation, histological score, and biomechanical testing (p = 0 0.039, p = 0.011, p = 0.003, respectively).

CONCLUSION

In the RC repair model, AAM enhanced regeneration of the tendon to bone junction. This regeneration was more effective when the AAM was intervened at the tendon to bone interface than overlaid above the tendon to bone junction.

Outcomes of arthroscopic single-row repair alone vs. repair with human dermal allograft patch augmentation in patients with large to massive, posterosuperior rotator cuff tears: a retrospective comparative study

BACKGROUND

Large to massive rotator cuff tears (RCTs) affect shoulder functions profoundly with unmanageable disability without intervention. The retear rates with arthroscopic rotator cuff repair (ARCR) in these patients are abysmal. Patch augmentation has been credited for preventing retears, improving functions by increasing the strength, and acting as a bioconductive scaffold. This study aimed to assess the retear rates and compare the clinical and radiological outcomes between the ARCR with and without acellular human dermal allograft (HDA) augmentation.

METHODS

This is a retrospective comparative study among patients diagnosed with large to massive, posterosuperior RCTs, operated between January 2020 and December 2021, including 36 patients (group I) with and 131 patients (group II) without HDA augmentation, with a mean follow-up of 20 (range, 12-35) months. The average age was 64 (range, 49-80) and 66 (range, 41-81) years in groups I and II, respectively. In group I, there were 16 male and 20 female patients, whereas in group II, there were 58 male and 73 female patients.

RESULTS

The visual analog scale score improved to 1.1 ± 1.7 in group I and 2.1 ± 1.7 in group II (P = .005). There was a greater improvement in the University of California, Los Angeles shoulder score to 30.1 ± 4.2 in group I compared with 23.2 ± 3.9 in group II (P = .046). Forward flexion (degrees) improved from a mean of 103.2 ± 18.6 to 138.9 ± 23.5 in group I and from 106.4 ± 21.3 to 127.0 ± 19.5 in group II (P = .004). The acromiohumeral interval (mm) measured in anteroposterior radiographs increased to 8.4 ± 1.8 in group I and 8.2 ± 2.0 in group II (P = .006). The satisfaction after the procedure was 4.4 ± 0.6 in group I and 3.1 ± 1.1 in group II (P = .044). The retear rate in the HDA-augmented group was 5.6% as compared with 29.1% in the nonaugmented group, which was statistically significant (P = .007). There were no complications or adverse tissue reactions against HDA seen in any patients.

CONCLUSION

In patients with large to massive, posterosuperior RCTs, patch augmentation with acellular HDA significantly averted the retears after ARCR without any graft-related complications. The augmentation also resulted in improved shoulder function and greater range of motion compared with the nonaugmented group.

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.

Effect of Octacalcium Phosphate Crystals on the Osteogenic Differentiation of Tendon Stem/Progenitor Cells In Vitro

Synthetic octacalcium phosphate (OCP) activates bone tissue-related cells, such as osteoblasts, osteoclasts, and vascular endothelial cells. However, the effect of OCP on tendon-related cell activation remains unknown. This study examined the response of rat tendon stem/progenitor cells (TSPCs) to OCP and related calcium phosphate crystals in vitro. TSPCs were cultured with OCP and Ca-deficient hydroxyapatite (CDHA) obtained from the original OCP hydrolysis to assess the activity of alkaline phosphatase (ALP) and the expression of osteogenesis-related genes. Compared with CDHA, the effect of OCP on promoting the osteogenic differentiation of TSPCs was apparent: the ALP activity and mRNA expression of RUNX2, Col1a1, OCN, and OPN were higher in OCP than in CDHA. To estimate the changes in the chemical environment caused by OCP and CDHA, we measured the calcium ion (Ca²⁺) and inorganic phosphate (Pi) ion concentrations and pH values of the TSPCs medium. The results suggest that the difference in the osteogenic differentiation of the TSPCs is related to the ionic environment induced by OCP and CDHA, which could be related to the progress of OCP hydrolysis into CDHA. These results support the previous in vivo observation that OCP has the healing function of rabbit rotator cuff tendon in vivo.

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.

Type II Collagen Sponges Facilitate Tendon Stem/Progenitor Cells to Adopt More Chondrogenic Phenotypes and Promote the Regeneration of Fibrocartilage-Like Tissues in a Rabbit Partial Patellectomy Model

Objective

Fibrocartilage transition zone (FC) is difficult to regenerate after surgical re-attachment of tendon to bone. Here, we investigated whether type II collagen-sponges (CII-sponges) facilitated tendon stem/progenitor cells (TSPCs) to adopt chondrogenic phenotypes and further observed if this material could increase the FC areas in bone-tendon junction (BTJ) injury model.

Methods

CII-sponges were made as we previously described. The appearance and pore structure of CII-sponges were photographed by camera and microscopies. The viability, proliferation, and differentiation of TSPCs were examined by LIVE/DEAD assay, alamarBlue, and PKH67 in vitro tracking. Subsequently, TSPCs were seeded in CII-sponges, Matrigel or monolayer, and induced under chondrogenic medium for 7 or 14 days before being harvested for qPCR or being transplanted into nude mice to examine the chondrogenesis of TSPCs. Lastly, partial patellectomy (PP) was applied to establish the BTJ injury model. CII-sponges were interposed between the patellar fragment and tendon, and histological examination was used to assess the FC regeneration at BTJ after surgery at 8 weeks.

Results

CII-sponges were like sponges with interconnected pores. TSPCs could adhere, proliferate, and differentiate in this CII-sponge up to 14 days at least. Both qPCR and immunostaining data showed that compared with TSPCs cultured in monolayer or Matrigel, cells in CII-sponges group adopted more chondrogenic phenotypes with an overall increase of chondrocyte-related genes and proteins. Furthermore, in PP injured model, much more new formed cartilage-like tissues could be observed in CII-sponges group, evidenced by a large amount of positive proteoglycan expression and typical oval or round chondrocytes in this area.

Conclusion

Our study showed that CII-sponges facilitated the TSPCs to differentiate toward chondrocytes and increased the area of FCs, which suggests that CII-sponges are meaningful for the reconstruction of FC at bone tendon junction. However, the link between the two phenomena requires further research and validation.

Low-Intensity Pulsed Ultrasound Augments Tendon, Ligament, and Bone-Soft Tissue Healing in Preclinical Animal Models: A Systematic Review

PURPOSE

To appraise the available animal and human studies investigating low-intensity pulsed ultrasound stimulation (LIPUS) on tendon, ligament, and bone-soft tissue (B-ST) junction healing.

METHODS

A systematic review of PUBMED, EMBASE, and the Cochrane Library was performed for animal and human studies investigating the effects of LIPUS on tendon, ligament, and B-ST junction healing. The systematic search was performed using the key term "low intensity pulsed ultrasound" and any of the following: "tendon," "ligament," "tendon-bone," and "bone-tendon." Inclusion criteria consisted of (1) randomized controlled trials assessing the effect of LIPUS on bone, tendon, and soft tissue in animals or humans and (2) English-language articles.

RESULTS

A total of 28 animal and 2 human studies met inclusion criteria. Animal studies utilized various models, including Achilles and patellar tendon transections, medial collateral ligament transections, and surgical repair of patellar tendon, rotator cuff tendon, and anterior cruciate ligament, to evaluate the effects of LIPUS. Animal studies demonstrated significantly improved collagen content and organization, bone formation, fibrocartilage remodeling, and mechanical strength with LIPUS treatment compared with controls. In human trials, LIPUS treatment of chronic tendinopathies did not improve clinical outcomes.

CONCLUSIONS

In acute injury animal models, LIPUS augmented healing of acute tendon, ligament, and B-ST junction injuries through increased collagen content and organization; increased anti-inflammatory cellular signaling; and increased angiogenesis. However, in 2 human studies investigating chronic tendinopathy, LIPUS did not lead to superior outcomes compared with controls.

CLINICAL RELEVANCE

Animal models suggest that LIPUS may be a promising noninvasive treatment modality for accelerating patient recovery after acute tendon and ligament injuries, as well as after surgical repair of B-ST junction injuries, but this has not been demonstrated in human studies. Randomized clinical trials evaluating LIPUS for acute tendon and ligament injuries are warranted.

Sustained release of collagen-affinity SDF-1α from book-shaped acellular fibrocartilage scaffold enhanced bone-tendon healing in a rabbit model

Rapid and functional bone-tendon (B-T) healing remains a difficulty in clinical practice. Tissue engineering has emerged as a promising strategy to address this problem. However, the majority of tissue engineering scaffolds are loaded with stem cells to enhance the regenerability in B-T healing, which is complicated and inconvenient for clinical application. Accordingly, developing a cell-free scaffold with chemotactic function and chondrogenic inducibility may be an effective approach. In this study, a collagen affinity peptide derived from the A3 domain of von Willebrand factor (a hemostasis factor) was fused into the C-terminal of a stromal cell-derived factor-1α (SDF-1α) to synthesize a recombinant SDF-1α capable of binding collagen and chemotactic activity. The recombinant SDF-1α was then tethered on the collagen fibers of a book-shaped acellular fibrocartilage scaffold (BAFS), thus fabricating a novel scaffold (C-SDF-1α/BAFS) with chemotactic function and chondrogenic inducibility. In vitro tests determined that this scaffold was noncytotoxic and biomimetic, could attract stem cells migrating to the scaffold using sustainably released C-SDF-1α, and inducedthe interacting stem cells down the chondrogenic lineage. In vivo, the C-SDF-1α/BAFS significantly enhanced the B-T healing in a rabbit partial patellectomy model, as shown by the larger cartilaginous metaplasia region, better fibrocartilage regeneration, additional bone formation, and improved biomechanical properties. Therefore, the findings of the study demonstrate that the C-SDF-1α/BAFS could potentially be applied for B-T healing.

FGF2: a key regulator augmenting tendon-to-bone healing and cartilage repair

Ligament/tendon and cartilage injuries are clinically common diseases that perplex most clinicians. Because of the lack of blood vessels and nerves, their self-repairing abilities are rather poor. Therefore, surgeries are necessary and also widely used to treat ligament/tendon or cartilage injuries. However, after surgery, there are still many problems that affect healing. In recent years, it has been found that exogenous FGF2 plays an important role in the repair of ligament/tendon and cartilage injuries and exerts a synergistic effect with endogenous FGF2. Therefore, FGF2 can be used as a new type of biomolecule to accelerate tendon-to-bone healing and cartilage repair after injury.

Frame Coating of Single-Walled Carbon Nanotubes in Collagen on PET Fibers for Artificial Joint Ligaments

The coating formation technique for artificial knee ligaments was proposed, which provided tight fixation of ligaments of polyethylene terephthalate (PET) fibers as a result of the healing of the bone channel in the short-term period after implantation. The coating is a frame structure of single-walled carbon nanotubes (SWCNT) in a collagen matrix, which is formed by layer-by-layer solidification of an aqueous dispersion of SWCNT with collagen during spin coating and controlled irradiation with IR radiation. Quantum mechanical method SCC DFTB, with a self-consistent charge, was used. It is based on the density functional theory and the tight-binding approximation. The method established the optimal temperature and time for the formation of the equilibrium configurations of the SWCNT/collagen type II complexes to ensure maximum binding energies between the nanotube and the collagen. The highest binding energies were observed in complexes with SWCNT nanometer diameter in comparison with subnanometer SWCNT. The coating had a porous structure-pore size was 0.5-6 μm. The process of reducing the mass and volume of the coating with the initial biodegradation of collagen after contact with blood plasma was demonstrated. This is proved by exceeding the intensity of the SWCNT peaks G and D after contact with the blood serum in the Raman spectrum and by decreasing the intensity of the main collagen bands in the SWCNT/collagen complex frame coating. The number of pores and their size increased to 20 μm. The modification of the PET tape with the SWCNT/collagen coating allowed to increase its hydrophilicity by 1.7 times compared to the original PET fibers and by 1.3 times compared to the collagen coating. A reduced hemolysis level of the PET tape coated with SWCNT/collagen was achieved. The SWCNT/collagen coating provided 2.2 times less hemolysis than an uncoated PET implant. MicroCT showed the effective formation of new bone and dense connective tissue around the implant. A decrease in channel diameter from 2.5 to 1.7 mm was detected at three and, especially, six months after implantation of a PET tape with SWCNT/collagen coating. MicroCT allowed us to identify areas for histological sections, which demonstrated the favorable interaction of the PET tape with the surrounding tissues. In the case of using the PET tape coated with SWCNT/collagen, more active growth of connective tissue with mature collagen fibers in the area of implantation was observed than in the case of only collagen coating. The stimulating effect of SWCNT/collagen on the formation of bone trabeculae around and inside the PET tape was evident in three and six months after implantation. Thus, a PET tape with SWCNT/collagen coating has osteoconductivity as well as a high level of hydrophilicity and hemocompatibility.

Repair of Achilles sleeve avulsion: a new transosseous suture technique

BACKGROUND

Achilles sleeve avulsion usually occurs from pre-existing insertional Achilles tendinopathy, leaving a calcific spur at the insertional site. The purpose of this study was to introduce a new technique using the spur base on the insertional site to drill the suture tunnel to repair Achilles sleeve avulsion.

METHODS

In total, 11 patients diagnosed with Achilles sleeve avulsion underwent this new surgical technique and were followed for a mean time of 40 months. Clinical outcomes were measured using the visual analog scale (VAS), American Orthopaedic Foot and Ankle Society (AOFAS) score, Victorian Institute of Sports Assessment-Achilles (VISA-A) score, Tegner score, and time taken to return to activities. Preoperative and postoperative MRI, the ability to perform heel rise, and complications were also evaluated.

RESULTS

All cases (11/11) had insertional Achilles tendinopathy with calcific spur formation on the tendon's insertion. At final follow-up, the average VAS score improved from 5.3 to 0.1, AOFAS score improved from 44.8 to 97.9, VISA-A score improved from 23.6 to 96.6, and Tegner score improved from 0.9 to 4.9. Tendinopathy symptoms were eliminated. Patients returned to daily activities, work, and sports 3.5 months, 2.8 months, and 12.3months after operation, respectively. Patients took an average of 18.1 weeks after operation to perform the single heel rise test. No severe complications such as infection and rerupture were observed.

CONCLUSION

Our new transosseous suture technique is a promising alternative option in treating Achilles sleeve avulsion. More cases and longer follow up are needed in order to find the best reconstructive option for this pathology.

LEVELS OF EVIDENCE

Level IV.

Thermosensitive Chitosan-Gelatin-Glycerol Phosphate Hydrogels as Collagenase Carrier for Tendon-Bone Healing in a Rabbit Model

Healing of an anterior cruciate ligament graft in bone tunnel yields weaker fibrous scar tissue, which may prolong an already prolonged healing process within the tendon-bone interface. In this study, gelatin molecules were added to thermosensitive chitosan/β-glycerol phosphate disodium salt hydrogels to form chitosan/gelatin/β-glycerol phosphate (C/G/GP) hydrogels, which were applied to 0.1 mg/mL collagenase carrier in the tendon-bone junction. New Zealand white rabbit's long digital extensor tendon was detached and translated into a 2.5-mm diameter tibial plateau tunnel. Thirty-six rabbits underwent bilateral surgery and hydrogel injection treatment with and without collagenase. Histological analyses revealed early healing and more bone formation at the tendon-bone interface after collagenase partial digestion. The area of metachromasia significantly increased in both 4-week and 8-week groups after collagenase treatment (p < 0.01). Micro computed tomography showed a significant increase in total bone volume and bone volume/tissue volume in the 8 weeks after collagenase treatment, compared with the control group. Load-to-failure was significantly higher in the treated group at 8 weeks (23.8 ± 8.13 N vs 14.3 ± 3.9 N; p = 0.008). Treatment with collagenase digestion resulted in a 66% increase in pull-out strength. In conclusion, injection of C/G/GP hydrogel with collagenase improves tendon-to-bone healing in a rabbit model.

FGF-2-Induced Human Amniotic Mesenchymal Stem Cells Seeded on a Human Acellular Amniotic Membrane Scaffold Accelerated Tendon-to-Bone Healing in a Rabbit Extra-Articular Model

Background

FGF-2 (basic fibroblast growth factor) has a positive effect on the proliferation and differentiation of many kinds of MSCs. Therefore, it represents an ideal molecule to facilitate tendon-to-bone healing. Nonetheless, no studies have investigated the application of FGF-2-induced human amniotic mesenchymal stem cells (hAMSCs) to accelerate tendon-to-bone healing in vivo.

Objective

The purpose of this study was to explore the effect of FGF-2 on chondrogenic differentiation of hAMSCs in vitro and the effect of FGF-2-induced hAMSCs combined with a human acellular amniotic membrane (HAAM) scaffold on tendon-to-bone healing in vivo.

Methods

In vitro, hAMSCs were transfected with a lentivirus carrying the FGF-2 gene, and the potential for chondrogenic differentiation of hAMSCs induced by the FGF-2 gene was assessed using immunofluorescence and toluidine blue (TB) staining. HAAM scaffold was prepared, and hematoxylin and eosin (HE) staining and scanning electron microscopy (SEM) were used to observe the microstructure of the HAAM scaffold. hAMSCs transfected with and without FGF-2 were seeded on the HAAM scaffold at a density of 3 × 10⁵ cells/well. Immunofluorescence staining of vimentin and phalloidin staining were used to confirm cell adherence and growth on the HAAM scaffold. In vivo, the rabbit extra-articular tendon-to-bone healing model was created using the right hind limb of 40 New Zealand White rabbits. Grafts mimicking tendon-to-bone interface (TBI) injury were created and subjected to treatment with the HAAM scaffold loaded with FGF-2-induced hAMSCs, HAAM scaffold loaded with hAMSCs only, HAAM scaffold, and no special treatment. Macroscopic observation, imageological analysis, histological assessment, and biomechanical analysis were conducted to evaluate tendon-to-bone healing after 3 months.

Results

In vitro, cartilage-specific marker staining was positive for the FGF-2 overexpression group. The HAAM scaffold displayed a netted structure and mass extracellular matrix structure. hAMSCs or hAMSCs transfected with FGF-2 survived on the HAAM scaffold and grew well. In vivo, the group treated with HAAM scaffold loaded with FGF-2-induced hAMSCs had the narrowest bone tunnel after three months as compared with other groups. In addition, macroscopic and histological scores were higher for this group than for the other groups, along with the best mechanical strength.

Conclusion

hAMSCs transfected with FGF-2 combined with the HAAM scaffold could accelerate tendon-to-bone healing in a rabbit extra-articular model.

Fibrochondrogenic differentiation potential of tendon-derived stem/progenitor cells from human patellar tendon

Background

Bone–tendon junction (BTJ) is a unique structure connecting tendon and bone through a fibrocartilage zone. Owing to its unique structure, the regeneration of BTJ remains a challenge. Here, we study the fibrochondrogenic differentiation of human tendon-derived stem/progenitor cells (TSPCs) both in vitro and in vivo.

Methods

TSPCs were isolated from human patellar tendon tissues and investigated for their multidifferentiation potential. TSPCs were cultured in chondrogenic medium with transforming growth factor beta 3 (TGF-β3) and BMP-2 in vitro ​and examined for the expression of fibrochondrogenic marker genes by quantitative real-time reverse transcription polymerase chain reaction, enzyme-linked immunosorbent assay, and immunofluorescence. TSPCs pretreated were also seeded in collage II sponge and then transplanted in immunocompromised nude mice to examine if the fibrochondrogenic characteristics were conserved in vivo.

Results

We found that TSPCs were differentiated towards fibrochondrogenic lineage, accompanied by the expression of collagen I, collagen II, SRY-box transcription factor 9 (Sox 9), and tenascin C. Furthermore, after TSPCs were seeded in collagen II sponge and transplanted in immunocompromised nude mice, they expressed fibrochondrogenic genes, including proteoglycan, collagen I, and collagen II.

Conclusion

Taken together, this study showed that TSPCs are capable of differentiating towards fibrocartilage-like cells, and the fibrochondrogenic characteristics were conserved even in vivo, and thus might have the potential application for fibrocartilage regeneration in BTJ repair.

The translational potential of this article

TSPCs are able to differentiate into fibrocartilage-like cells and thus might well be one potential cell source for fibrocartilage regeneration in a damaged BTJ repair.

Dual Function of Glucosamine in Gelatin/Hyaluronic Acid Cryogel to Modulate Scaffold Mechanical Properties and to Maintain Chondrogenic Phenotype for Cartilage Tissue Engineering

Glucosamine (GlcN) fulfills many of the requirements as an ideal component in scaffolds used in cartilage tissue engineering. The incorporation of GlcN in a gelatin/hyaluronic acid (GH) cryogel scaffold could provide biological cues in maintaining the phenotype of chondrocytes. Nonetheless, substituting gelatin with GlcN may also decrease the crosslinking density and modulate the mechanical properties of the cryogel scaffold, which may be beneficial as physical cues for chondrocytes in the scaffold. Thus, we prepared cryogel scaffolds containing 9% GlcN (GH-GlcN9) and 16% GlcN (GH-GlcN16) by carbodiimide-mediated crosslinking reactions at -16 °C. The crosslinking density and the mechanical properties of the cryogel matrix could be tuned by adjusting the content of GlcN used during cryogel preparation. In general, incorporation of GlcN did not influence scaffold pore size and ultimate compressive strain but increased porosity. The GH-GlcN16 cryogel showed the highest swelling ratio and degradation rate in hyaluronidase and collagenase solutions. On the contrary, the Young's modulus, storage modulus, ultimate compressive stress, energy dissipation level, and rate of stress relaxation decreased by increasing the GlcN content in the cryogel. The release of GlcN from the scaffolds in the culture medium of chondrocytes could be sustained for 21 days for GH-GlcN16 in contrast to only 7 days for GH-GlcN9. In vitro cell culture experiments using rabbit articular chondrocytes revealed that GlcN incorporation affected cell proliferation, morphology, and maintenance of chondrogenic phenotype. Overall, GH-GlcN16 showed the best performance in maintaining chondrogenic phenotype with reduced cell proliferation rate but enhanced glycosaminoglycans (GAGs) and type II collagen (COL II) secretion. Quantitative real-time polymerase chain reaction also showed time-dependent up-regulation of cartilage-specific marker genes (COL II, aggrecan and Sox9) for GH-GlcN16. Implantation of chondrocytes/GH-GlcN16 constructs into full-thickness articular cartilage defects of rabbits could regenerate neocartilage with positive staining for GAGs and COL II. The GH-GlcN16 cryogel will be suitable as a scaffold for the treatment of articular cartilage defects.

Early cellular responses of BMSCs genetically modified with bFGF/BMP2 co-cultured with ligament fibroblasts in a three-dimensional model in vitro

Currently, a number of strategies including the implantation of bone marrow-derived mesenchymal stem cells (BMSCs) and growth factors have been developed to regenerate the tendon-to-bone interface after performing anterior cruciate ligament reconstruction. However, the mechanisms behind the interactions of the implanted BMSCs and tendon cells remain to be elucidated. The aim of this study was to evaluate the early cellular responses of BMSCs genetically modified with basic growth factor growth factor (bFGF)/bone morphogenic protein 2 (BMP2) and ligament fibroblasts in a three-dimensional co-culture model. BMSCs and ligament fibroblasts were both isolated from male Wistar rats. The BMSCs were then transfected with an adenoviral vector carrying bFGF or BMP2. The transfected BMSCs and ligament fibroblasts both encapsulated in alginate beads were co-cultured for 6 days in three-dimensional model. On days 0, 3 and 6, cell proliferation was assayed. On day 6, the expression of several tendon-bone related markers was evaluated. In the co-culture system, bFGF and BMP2 were highly expressed at the mRNA and protein level. During the process, bFGF significantly promoted cell proliferation, as well as the expression of scleraxis (SCX) and collagen (COL) type Ⅰ (COL1) in the BMSCs; however, it markedly decreased the expression of phenotype markers in the ligament fibroblasts, including COL1 and COL3. BMP2 markedly increased the expression of alkaline phosphatase and osteocalcin in the BMSCs and ligament fibroblasts, whereas it had no obvious effect on cell proliferation and collagen synthesis in the ligament fibroblasts. The combination of bFGF and BMP2 resulted in the similarly enhanced proliferation of BMSCs and ligament fibroblasts as observed with bFGF alone; however, this combination more potently promoted osteogenic differentiation than did BMP2 alone. The findings of our study demonstrate the superiority of the combined use of growth factors in inducing osteogenic differentiation and provide a theoretical foundation for the regeneration of the tendon-to-bone interface.

Allograft integration in a rabbit transgenic model for anterior cruciate ligament reconstruction

BACKGROUND

Tissue engineering strategies include both cell-based and cell homing therapies. Ligamentous tissues are highly specialized and constitute vital components of the musculoskeletal system. Their damage causes significant morbidity and loss in function.

HYPOTHESIS

The aim of this study is to analyze tendinous graft integration, cell repopulation and ligamentization by using GFP+/- allografts in GFP+/- transgenic New Zealand white (NZW) rabbits.

MATERIAL AND METHODS

Graft implantation was designed to closely mimic anterior cruciate ligament (ACL) repair surgery. Allografts were implanted in 8 NZW rabbits and assessed at 5 days, 3 weeks and 6 weeks through: (1) arthroCT imaging, (2) morphological analysis of the transplanted allograft, (3) histological analysis, (4) collagen type I immunochemistry, and (5) GFP cell tracking. Collagen remodeling was appreciated at 3 and 6 weeks.

RESULTS

Graft repopulation with host cells, chondrocyte-like cells at the tendon-bone interface and graft corticalization in the bone tunnels were noticed at 3 weeks. By contrast we noticed a central necrosis aspect in the allografts intra-articularly at 6 weeks with a cell migration towards the graft edge near the synovium.

DISCUSSION

Our study has served to gain a better understanding of tendinous allograft bone integration, ligamentization and allograft repopulation. We believe that both cell-based therapies and cell homing therapies are beneficial in ligament tissue engineering. Future studies may elucidate whether cell repopulation occurs with pre-differentiated or progenitor cells. We believe that both cell-based therapies and cell homing therapies are beneficial in ligament tissue engineering.

LEVEL OF EVIDENCE

Level V (animal study).

Tissue engineering of ligaments for reconstructive surgery

PURPOSE

The use of musculoskeletal bioengineering and regenerative medicine applications in orthopaedic surgery has continued to evolve. The aim of this systematic review was to address tissue-engineering strategies for knee ligament reconstruction.

METHODS

A systematic review of PubMed/Medline using the terms "knee AND ligament" AND "tissue engineering" OR "regenerative medicine" was performed. Two authors performed the search, independently assessed the studies for inclusion, and extracted the data for inclusion in the review. Both preclinical and clinical studies were reviewed, and the articles deemed most relevant were included in this article to provide relevant basic science and recent clinical translational knowledge concerning "tissue-engineering" strategies currently used in knee ligament reconstruction.

RESULTS

A total of 224 articles were reviewed in our initial PubMed search. Non-English-language studies were excluded. Clinical and preclinical studies were identified, and those with a focus on knee ligament tissue-engineering strategies including stem cell-based therapies, growth factor administration, hybrid biomaterial, and scaffold development, as well as mechanical stimulation modalities, were reviewed.

CONCLUSIONS

The body of knowledge surrounding tissue-engineering strategies for ligament reconstruction continues to expand. Presently, various tissue-engineering techniques have some potential advantages, including faster recovery, better ligamentization, and possibly, a reduction of recurrence. Preclinical research of these novel therapies continues to provide promising results. There remains a need for well-designed, high-powered comparative clinical studies to serve as a foundation for successful translation into the clinical setting going forward.

LEVEL OF EVIDENCE

Level IV, systematic review of Level IV studies.

Cell-assembled graphene biocomposite for enhanced chondrogenic differentiation

Graphene-based nanomaterials are increasingly being explored for use as biomaterials for drug delivery and tissue engineering applications due to their exceptional physicochemical and mechanical properties. However, the two-dimensional nature of graphene makes it difficult to extend its applications beyond planar tissue culture. Here, graphene-cell biocomposites are used to pre-concentrate growth factors for chondrogenic differentiation. Bone marrow-derived mesenchymal stem cells (MSCs) are assembled with graphene flakes in the solution to form graphene-cell biocomposites. Increasing concentrations of graphene (G) and porous graphene oxide (pGO) are found to correlate positively with the extent of differentiation. However, beyond a certain concentration, especially in the case of graphene oxide, it will lead to decreased chondrogenesis due to increased diffusional barrier and cytotoxic effects. Nevertheless, these findings indicate that both G and pGO could serve as effective pre-concentration platforms for the construction of tissue-engineered cartilage and suspension-based cultures in vitro.

Intermittently administered parathyroid hormone [1-34] promotes tendon-bone healing in a rat model

The objective of this study was to investigate whether intermittent administration of parathyroid hormone [1–34] (PTH[1–34]) promotes tendon-bone healing after anterior cruciate ligament (ACL) reconstruction in vivo. A rat model of ACL reconstruction with autograft was established at the left hind leg. Every day, injections of 60 μg PTH[1–34]/kg subcutaneously were given to the PTH group rats (n = 10) for four weeks, and the controls (n = 10) received saline. The tendon-bone healing process was evaluated by micro-CT, biomechanical test, histological and immunohistochemical analyses. The effects of PTH[1–34] on serum chemistry, bone microarchitecture and expression of the PTH receptor (PTH1R) and osteocalcin were determined. Administration of PTH[1–34] significantly increased serum levels of calcium, alkaline phosphatase (AP), osteocalcin and tartrate-resistant acid phosphatase (TRAP). The expression of PTH1R on both osteocytes and chondrocyte-like cells at the tendon-bone interface was increased in the PTH group. PTH[1–34] also enhanced the thickness and microarchitecture of trabecular bone according to the micro-CT analysis. The results imply that systematically intermittent administration of PTH[1–34] promotes tendon-bone healing at an early stage via up-regulated PTH1R. This method may enable a new strategy for the promotion of tendon-bone healing after ACL reconstruction.

Effects of Sox9 gene therapy on the healing of bone-tendon junction: An experimental study

BACKGROUND

Sox9 is an operon that positively regulates the transcription of type II collagen. The generation of type II collagen plays a critical role in the healing process of the bone-tendon junction (BTJ).

MATERIALS AND METHODS

Sox9 was injected into an established bone-tendon healing model in order to observe its effect on the healing by determining the biomechanical properties of the BTJ. In addition, the recombinant adenovirus Sox9 was used to transduce the animal model samples and in vivo observations of the effect of the adenovirus-mediated Sox9 transduction as well as its promotion of the healing properties were made.

RESULTS

Sox9 was not only able to promote the healing, but also increased the biomechanical strength. The recombinant Sox9 delivered by adenoviral vector can be expressed at a high level in the damaged tissues of the bone-tendon junction, which can stimulate the production of type II collagen and improve the healing of the BTJ.

CONCLUSIONS

Based on the results of this study, we considered that gene therapy may be applicable in the healing process of the bone-tendon junction.

Cellular therapy in bone-tendon interface regeneration

The intrasynovial bone-tendon interface is a gradual transition from soft tissue to bone, with two intervening zones of uncalcified and calcified fibrocartilage. Following injury, the native anatomy is not restored, resulting in inferior mechanical properties and an increased risk of re-injury. Recent in vivo studies provide evidence of improved healing when surgical repair of the bone-tendon interface is augmented with cells capable of undergoing chondrogenesis. In particular, cellular therapy in bone-tendon healing can promote fibrocartilage formation and associated improvements in mechanical properties. Despite these promising results in animal models, cellular therapy in human patients remains largely unexplored. This review highlights the development and structure-function relationship of normal bone-tendon insertions. The natural healing response to injury is discussed, with subsequent review of recent research on cellular approaches for improved healing. Finally, opportunities for translating in vivo findings into clinical practice are identified.

ACL graft healing and biologics

Operative reconstruction of a torn anterior cruciate ligament (ACL) has become the most broadly accepted treatment. An important, but underreported, outcome of ACL reconstruction is graft failure, which poses a challenge for the orthopedic surgeon. An understanding of the tendon-bone healing and the intra-articular ligamentization process is crucial for orthopedic surgeons to make appropriate graft choices and to be able to initiate optimal rehabilitation protocols after surgical ACL reconstruction. This article focuses on the current understanding of the tendon-to-bone healing process for both autografts and allografts and discusses strategies to biologically augment healing.

Extracorporeal shock wave therapy is not useful after arthroscopic rotator cuff repair

PURPOSE

Extracorporeal shock wave therapy (ESWT) is known to accelerate the healing of musculoskeletal tissue. The purpose of this study was to test the hypothesis that ESWT stimulates rotator cuff healing after arthroscopic repair.

METHODS

Seventy-one consecutive patients with a small- to large-sized rotator cuff tear underwent arthroscopic rotator cuff repair. The patients were randomized into two groups: 35 patients underwent ESWT at 6 weeks after surgery (ESWT group) and 36 patients did not (control group). Cuff integrity was evaluated with computed tomographic arthrography at 6 months after surgery. Constant and UCLA scores were measurable outcomes.

RESULTS

All patients were available for a minimum one-year follow-up. The mean age of the ESWT and control groups was 59.4 (SD: 7.7) and 58.6 years (SD: 7.8) (n.s.). There were no significant differences in tear size and repair method between the two groups (n.s.). The mean Constant and UCLA scores, respectively, increased from 54.6 to 90.6 (P < 0.001) and from 18.5 to 27.4 (P < 0.001) in the ESWT group, and from 58.9 to 89.3 (P < 0.001) and 18.5 to 27.4 in the control group. Computed tomographic arthrography was performed in 26 patients from the ESWT group and 24 from the control group, and cuff integrity was maintained in 46 out of 50 patients. Definite re-tear was observed in two patients of the ESWT group and four of the controls. There were no complications associated with ESWT.

CONCLUSION

This study failed to prove that ESWT stimulates rotator cuff healing after arthroscopic rotator cuff repair. Additional ESWT after rotator cuff repair could theoretically be advantageous, and it was proven to be safe in this study.

LEVEL OF EVIDENCE

II.

Higher BMP receptor expression and BMP-2-induced osteogenic differentiation in tendon-derived stem cells compared with bone-marrow-derived mesenchymal stem cells

PURPOSE

Surgical reattachment of tendon to bone often fails due to regeneration failure of the specialised tendon-bone junction (TBJ). The use of mesenchymal stem cells for TBJ regeneration has been reported with promising results. Tendon-derived stem cells (TDSCs) with high proliferative and multi-lineage differentiation potential have been isolated. As stem cells residing in tendons, TDSCs can be considered a new cell source for TBJ repair. Bone morphogenic protein 2 (BMP-2) is a potent osteogenic factor with roles in normal bone healing and pathological ectopic bone formation in soft tissues. The use of BMP-2 to promote TBJ repair has been well reported. This study aimed to compare TDSCs to the gold standard bone-marrow-derived mesenchymal stem cells (BMSCs) with respect to osteogenic response to BMP-2 in vitro.

METHOD

The clonogenicity and multi-differentiation potential of TDSCs and BMSCs were identified by colony-forming-unit assay, osteogenic, adipogenic and chondrogenic differentiation assays. Their osteogenic response to BMP-2 in vitro was examined by alkaline phosphatase (ALP) cytochemical staining, ALP activity assay and Alizarin red S staining of calcium nodule formation. Messenger RNA (mRNA) and BMP receptor (types IA, IB and II) protein expression were examined by quantitative real-time reverse-transcriptase polymerase chain reaction (qRT-PCR) and Western blotting.

RESULTS

Our results showed that both TDSCs and BMSCs exhibited stem cell properties, including clonogenicity and multi-differentiation potential. TDSCs expressed higher mRNA and protein levels of BMP receptors IA, IB and II. They also exhibited higher osteogenic differentiation with and without BMP-2 stimulation compared with BMSCs.

CONCLUSIONS

TDSCs with/without BMP-2 might be an attractive source for TBJ repair compared with BMSCs.

The effect of platelet rich plasma from bone marrow aspirate with added bone morphogenetic protein-2 on the Achilles tendon-bone junction in rabbits

Background

To determine if exogenously injected bone marrow derived platelet-rich plasma (PRP) plus bone morphogenetic protein (BMP)-2 could accelerate the healing of bone-tendon junction injuries and increase the junction holding strength during the early regeneration period.

Methods

A direct injury model of the bone-tendon junction was made using an Achilles tendon-calcaneus bone junction in a rabbit. In the PRP/BMP-2/fibrin group, 0.05 mL of bone marrow derived PRP and 100 ng/mL of BMP-2 both incorporated into 0.1 mL of fibrin glue were injected into Achilles tendon-calcaneus bone junctions. The effect of the intervention was tested by comparing the results of an intervention group to a control group. The results of biomechanical testing, and histological and gross analyses were compared between the 2 groups at the following time points after surgery: 2 weeks, 4 weeks, and 8 weeks.

Results

Histologic examinations showed that woven bone developed in tendon-bone junctions at 2 weeks after surgery in the PRP/BMP-2/fibrin group. Mechanical test results showed no significant difference between the PRP/BMP-2/fibrin and control groups at 2 and 4 weeks after surgery, but the mean maximal load in the PRP/BMP-2/fibrin group was significantly higher than in the control group (p < 0.05) at 8 weeks after surgery.

Conclusions

Bone marrow derived PRP and BMP-2 in fibrin glue accelerated healing in a rabbit model of tendon-bone junction injury.

Use of allogeneic scaffold-free chondrocyte pellet in repair of osteochondral defect in a rabbit model

Cell-based therapies are currently being used in treating osteochondral defect (OCD), but technical advances are needed to tackle the problems of scaffold and grafting technique. This study aimed to test the potential of allogeneic scaffold-free bioengineered chondrocyte pellet (BCP) in treating OCD. BCP was fabricated from rabbit costal cartilage and implanted into 3 mm × 3 mm OCD in medial femoral condyle of 20 rabbits. Samples were harvested at 2, 4, 8, and 16 weeks for histology, histological scoring and histomorphometric analysis. At treated side, cartilage score was significantly better at week 4 (p = 0.027), and cartilage thickness measured in histomorphometric analysis was significantly thicker at week 4 (p = 0.028) and week 16 (p = 0.028) compared to the empty controls. At treated side, bone score remained significantly lower from week 8 onwards (p = 0.024 at week 8, p = 0.02 at week 16) whereas bone area was significantly smaller from week 4 onwards compared to the empty controls (p = 0.028 at week 4, 8, 16). No immunorejection was observed throughout the experiment. The results demonstrated that the BCP enhanced cartilage repair at early stage. Press-fitting of allogeneic BCP was a simple method for OCD repair without immunorejection. Further optimization of the treatment is required before clinical application.

Biology and augmentation of tendon-bone insertion repair

Surgical reattachment of tendon and bone such as in rotator cuff repair, patellar-patella tendon repair and anterior cruciate ligament (ACL) reconstruction often fails due to the failure of regeneration of the specialized tissue ("enthesis") which connects tendon to bone. Tendon-to-bone healing taking place between inhomogenous tissues is a slow process compared to healing within homogenous tissue, such as tendon to tendon or bone to bone healing. Therefore special attention must be paid to augment tendon to bone insertion (TBI) healing. Apart from surgical fixation, biological and biophysical interventions have been studied aiming at regeneration of TBI healing complex, especially the regeneration of interpositioned fibrocartilage and new bone at the healing junction. This paper described the biology and the factors influencing TBI healing using patella-patellar tendon (PPT) healing and tendon graft to bone tunnel healing in ACL reconstruction as examples. Recent development in the improvement of TBI healing and directions for future studies were also reviewed and discussed.

Mesenchymal stem cell therapy regenerates the native bone-tendon junction after surgical repair in a degenerative rat model

Background

The enthesis, which attaches the tendon to the bone, naturally disappears with aging, thus limiting joint mobility. Surgery is frequently needed but the clinical outcome is often poor due to the decreased natural healing capacity of the elderly. This study explored the benefits of a treatment based on injecting chondrocyte and mesenchymal stem cells (MSC) in a new rat model of degenerative enthesis repair.

Methodology

The Achilles' tendon was cut and the enthesis destroyed. The damage was repaired by classical surgery without cell injection (group G1, n = 52) and with chondrocyte (group G2, n = 51) or MSC injection (group G3, n = 39). The healing rate was determined macroscopically 15, 30 and 45 days later. The production and organization of a new enthesis was assessed by histological scoring of collagen II immunostaining, glycoaminoglycan production and the presence of columnar chondrocytes. The biomechanical load required to rupture the bone-tendon junction was determined.

Principal Findings

The spontaneous healing rate in the G1 control group was 40%, close to those observed in humans. Cell injection significantly improved healing (69%, p = 0.0028 for G2 and p = 0.006 for G3) and the load-to-failure after 45 days (p<0.05) over controls. A new enthesis was clearly produced in cell-injected G2 and G3 rats, but not in the controls. Only the MSC-injected G3 rats had an organized enthesis with columnar chondrocytes as in a native enthesis 45 days after surgery.

Conclusions

Cell therapy is an efficient procedure for reconstructing degenerative entheses. MSC treatment produced better organ regeneration than chondrocyte treatment. The morphological and biomechanical properties were similar to those of a native enthesis.

Isolation and characterization of multipotent rat tendon-derived stem cells

Stem cells have recently been isolated from humans and mice but not from rat tendon tissue. This study reports the isolation and characterization of stem cells from rat tendon. Nucleated cells isolated from rat flexor tendon tissues after collagenase digestion were plated at a low cell density to allow the selective proliferation of tendon-derived stem cells. About 1-2% of the cells isolated under this optimized culturing condition showed clonogenicity, high proliferative potential at low seeding density, and osteogenic, chondrogenic, and adipogenic multidifferentiation potential. These cells were CD44(+), CD90(+), CD34(-), and CD31(-). Although they shared some common properties with mesenchymal stem cells, they also exhibited their unique characteristics by expressing tenogenic and chondrogenic markers. There was expression of tenogenic markers, including alpha-smooth muscle actin, tenascin C, and tenomodulin, but not collagen type I at passage 0 (P0) and P3. Expression of a chondrogenic marker, aggrecan, was observed at P0 and P3, whereas expression of collagen type II was observed in few cells only at P3. The successful isolation of tendon-derived stem cells under the optimized growth and differentiation conditions was useful for future stem-cell-based tissue regenerative studies as well as studies on their roles in tendon physiology, healing, and disorders using the rat model.

Low intensity pulsed ultrasound increases the mechanical properties of the healing tissues at bone-tendon junction

The re-establishment of bone-tendon junction (BTJ) tissues is involved in many trauma and reconstructive surgeries. A direct BTJ repair requires a long period of immobilization which may be associated with a postoperative weak knee. In this study, we investigated if low-intensity pulsed ultrasound treatment increases the material properties of healing tissues at bone-tendon junction (BTJ) after partial patellectomy using rabbit models. Standard partial patellectomy was conducted on one knee of twenty four rabbits which were randomly divided into an ultrasound group and a control group. The bony changes of BTJ complexes around the BTJ healing interface were measured by anteroposterior x-ray radiographs; then the volumetric bone-mineral density (BMD) of the new bone was assessed using a peripheral computed tomography scanner (pQCT). The stiffness of patellar cartilage, fibrocartilage at the healing interface and the tendon were measured in situ using a novel noncontact ultrasound water jet indentation system. Not only significantly more newly formed bone at the BTJ healing interface but also increased stiffness of the junction tissues were found in the ultrasound group compared with the controls at week 18. In addition, the ultrasound group also showed significantly 44% higher BMD at week 6 than controls.

In vivo evaluation of 3-dimensional polycaprolactone scaffolds for cartilage repair in rabbits

BACKGROUND

Cartilage tissue engineering using synthetic scaffolds allows maintaining mechanical integrity and withstanding stress loads in the body, as well as providing a temporary substrate to which transplanted cells can adhere.

PURPOSE

This study evaluates the use of polycaprolactone (PCL) scaffolds for the regeneration of articular cartilage in a rabbit model.

STUDY DESIGN

Controlled laboratory study.

METHODS

Five conditions were tested to attempt cartilage repair. To compare spontaneous healing (from subchondral plate bleeding) and healing due to tissue engineering, the experiment considered the use of osteochondral defects (to allow blood flow into the defect site) alone or filled with bare PCL scaffold and the use of PCL-chondrocytes constructs in chondral defects. For the latter condition, 1 series of PCL scaffolds was seeded in vitro with rabbit chondrocytes for 7 days and the cell/scaffold constructs were transplanted into rabbits' articular defects, avoiding compromising the subchondral bone. Cell pellets and bare scaffolds were implanted as controls in a chondral defect.

RESULTS

After 3 months with PCL scaffolds or cells/PCL constructs, defects were filled with white cartilaginous tissue; integration into the surrounding native cartilage was much better than control (cell pellet). The engineered constructs showed histologically good integration to the subchondral bone and surrounding cartilage with accumulation of extracellular matrix including type II collagen and glycosaminoglycan. The elastic modulus measured in the zone of the defect with the PCL/cells constructs was very similar to that of native cartilage, while that of the pellet-repaired cartilage was much smaller than native cartilage.

CONCLUSION

The results are quite promising with respect to the use of PCL scaffolds as aids for the regeneration of articular cartilage using tissue engineering techniques.

Gelatin microspheres containing TGF-beta3 enhance the chondrogenesis of mesenchymal stem cells in modified pellet culture

The study is to investigate the chondrogenesis of a kind of modified cell pellet formed using mesenchymal stem cells (MSCs) and gelatin microspheres containing transforming growth factor beta3 (TGF-beta3). The gelatin microspheres loaded with TGF-beta3 (MS-TGF) were prepared and showed the controlled release of cytokine in a biphasic fashion. Then the mixture of MSCs and MS-TGF was centrifuged to form pellet. The pellet was cultured over 4 weeks to determine the effects of MS-TGF on cartilage matrix production by biochemical analysis, immunohistochemistry staining, and Western blot test. The transcription level of cartilage-related genes was also evaluated by real-time quantitative RT-PCR assay. After 4 weeks of culture, the MSCs were distributed uniformly in the pellet and had good viability. Cells showed faster proliferation and higher DNA content compared to MSCs in a conventional pellet. The production of collagen and glycosaminoglycan also increased significantly. The immunohistochemistry staining and alcian blue staining confirmed the synthesis of cartilage extracellular matrix (ECM). Furthermore, the differentiated MSCs located in lacunae within the metachromatic staining matrix exhibited the typical chondrocyte morphology. The chondrogenic differentiation of MSCs was proved by the expression of collagen II gene in mRNA and protein level. The results indicate that MS-TGF can induce chondrogenic differentiation of MSCs and increase cartilage ECM production, which result in a bigger cartilage pellet. In conclusion, this modified pellet culture can provide an easy and effective way to construct the tissue-engineered cartilage in vitro.

Extracorporeal shock wave therapy in treatment of delayed bone-tendon healing

BACKGROUND

Extracorporeal shock wave therapy is indicated for treatment of chronic injuries of soft tissues and delayed fracture healing and nonunion. No investigation has been conducted to study the effect of shock wave on delayed healing at the bone-tendon junction.

HYPOTHESIS

Shock wave promotes osteogenesis, regeneration of fibrocartilage zone, and remodeling of healing tissue in delayed healing of bone-tendon junction surgical repair.

STUDY DESIGN

Controlled laboratory study.

METHODS

Twenty-eight mature rabbits were used for establishing a delayed healing model at the patella-patellar tendon complex after partial patellectomy and then divided into control and shock wave groups. In the shock wave group, a single shock wave treatment was given at week 6 postoperatively to the patella-patellar tendon healing complex. Seven samples were harvested at week 8 and 7 samples at week 12 for radiologic, densitometric, histologic, and mechanical evaluations.

RESULTS

Radiographic measurements showed 293.4% and 185.8% more new bone formation at the patella-patellar tendon healing junction in the shock wave group at weeks 8 and 12, respectively. Significantly better bone mineral status was found in the week 12 shock wave group. Histologically, the shock wave group showed more advanced remodeling in terms of better alignment of collagen fibers and thicker and more mature regenerated fibrocartilage zone at both weeks 8 and 12. Mechanical testing showed 167.7% and 145.1% higher tensile load and strength in the shock wave group at week 8 and week 12, respectively, compared with controls.

CONCLUSION

Extracorporeal shock wave promotes osteogenesis, regeneration of fibrocartilage zone, and remodeling in the delayed bone-to-tendon healing junction in rabbits.

CLINICAL RELEVANCE

These results provide a foundation for future clinical studies toward establishment of clinical indication for treatment of delayed bone-to-tendon junction healing.

Secretion and organization of a cornea-like tissue in vitro by stem cells from human corneal stroma

PURPOSE

To investigate the potential of human corneal stromal stem cells to assume a keratocyte phenotype and to organize extracellular matrix (ECM) in vitro similar to corneal stromal tissue.

METHODS

Human corneal stromal stem cells (hCSSC) were isolated as side population cells by flow cytometry. Cloned hCSSC were cultured as free-floating pellets in serum-free media for 3 weeks. Gene expression was examined using gene array, quantitative RT-PCR, immunostaining, and immunoblotting. Transmission electron microscopy showed collagen fibril size and alignment.

RESULTS

Pellet cultures of hCSSC in serum-free media upregulated the expression of keratocyte-specific genes and secreted substantial ECM containing characteristic stromal components: keratocan, keratan sulfate, collagen I, collagen V, and collagen VI. Abundant connexin 43 and cadherin 11 in pellets demonstrated cell-cell junctions typical of keratocytes in vivo. Electron microscopy of the pellet cultures revealed abundant fibrillar collagen, some of which was aligned in parallel arrays similar to those of stromal lamellae. Gene array identified expression in pellets of several genes highly expressed by keratocytes. Transcripts for these keratocyte genes -- FLJ30046, KERA, ALDH3A1, CXADR, PTGDS, PDK4, MTAC2D1, F13A1 -- were increased by as much as 100-fold in pellets compared with hCSSC. Simultaneously, expression of stem cell genes BMI1, KIT, NOTCH1, SIX2, PAX6, ABCG2, SPAG10, and OSIL was reduced by a similar factor in pellets compared with hCSSC.

CONCLUSIONS

Scaffolding-free pellet culture of hCSSC induces keratocyte gene expression patterns in these cells and secretion of an organized stroma-like ECM. These cells offer a novel potential for corneal bioengineering.

Techniques for biological characterization of tissue-engineered tendon and ligament

Injuries to tendons and ligaments are prevalent and result in a significant decrease in quality of patient life. Tissue-engineering strategies hold promise as alternatives to current treatments for these injuries, which often fail to fully restore proper joint biomechanics and produce significant donor site morbidity. Commonly, tissue engineering involves the use of a three-dimensional scaffold seeded with cells that can be directed to form tendon/ligament tissue. When determining the success of such approaches, the viability and proliferation of the cells in the construct, as well as extracellular matrix production and structure should be taken into account. Histology and histochemistry, microscopy, colorimetric assays, and real-time reverse transcriptase-polymerase chain reaction (RT-PCR) are techniques that are employed to assess these biological characteristics. This review provides an overview of each of these methods, including specific examples of how they have been used in evaluation of tissue-engineered tendon and ligament tissue. Basic physical principles underlying each method and advantages and disadvantages of the various techniques are summarized.

The role of transforming growth factor-beta and bone morphogenetic protein with fibrin glue in healing of bone-tendon junction injury

Bone-tendon junction injuries have poor healing potential. This study evaluated the role of TGF-beta and BMP-2 in a fibrin glue carrier in healing of injuries at bone-tendon junction. Seventy-two skeletally mature male rabbits were divided into 4 groups. The tendo-Achilles was surgically transected at its insertion and reattached with a pullout suture. Group 1 served as a control. In groups 2, 3, and 4, fibrin glue, a mixture of TGF-beta and fibrin glue, and a mixture of BMP-2 and fibrin glue were injected into the bone-tendon junction. The animals were sacrificed at 2, 4 and 8 weeks after surgical procedure. The addition of TGF-beta to fibrin glue did not significantly improve the biomechanical properties of repair tissue. BMP-2 in combination with fibrin glue accelerates healing in a bone-tendon injury and also improves the histological and biomechanical properties of the repair tissue so formed.