A Rat Tibial Growth Plate Injury Model to Characterize Repair Mechanisms and Evaluate Growth Plate Regeneration Strategies

Sustained release of MAPK14-targeting siRNA from polyelectrolyte complex hydrogels mitigates MSC osteogenesis in vitro with potential application in growth plate injury

The growth plate is a cartilage structure at the end of long bones which mediates growth in children. When fractured, the formation of bony repair tissue known as a "bony bar" can occur and cause limb deformities. There are currently no effective clinical solutions for the prevention of the bony bar formation or regeneration of healthy growth plate cartilage after a fracture. This study employs previously developed alginate/chitosan polyelectrolyte complex (PEC) hydrogels as a sustained release vehicle for the delivery of short-interfering RNA (siRNA). Specifically, the siRNA targets the p38-MAPK pathway in mesenchymal stem cells (MSCs) to prevent their osteogenic differentiation. In vitro experimental findings show sustained release of siRNA from the hydrogels for 6 months. Flow cytometry and confocal imaging indicate that the hydrogels release siRNA to effectively knockdown GFP expression over a sustained period. MAPK-14 targeting siRNA was used to knockdown the expression of MAPK-14 and correspondingly decrease the expression of other osteogenic genes in MSCs in vitro over the span of 21 days. These hydrogels were used in a rat model of growth plate injury to determine whether siMAPK-14 released from the gels could inhibit bony bar formation. No significant reduction of bony bar formation was seen in vivo at the one concentration of siRNA examined. This PEC hydrogel represents a significant advancement for siRNA sustained delivery, and presents an interesting potential therapeutic delivery system for growth plate injuries and other regenerative medicine applications.

Injectable hydrogel loaded with bilayer microspheres to inhibit angiogenesis and promote cartilage regeneration for repairing growth plate injury

Introduction: The repair and regeneration of growth plate injuries using tissue engineering techniques remains a challenge due to large bone bridge formation and low chondrogenic efficiency. Methods: In this study, a bilayer drug-loaded microspheres was developed that contains the vascular endothelial growth factor (VEGF) inhibitor, Bevacizumab, on the outer layer and insulin-like growth factor-1 (IGF-1), a cartilage repair factor, on the inner layer. The microspheres were then combined with bone marrow mesenchymal stem cells (BMSCs) in the gelatin methacryloyl (GelMA) hydrogel to create a composite hydrogel with good injectability and biocompatibility. Results: The in vitro drug-release profile of bilayer microspheres showed a sequential release, with Bevacizumab released first followed by IGF-1. And this hydrogel simultaneously inhibited angiogenesis and promoted cartilage regeneration. Finally, in vivo studies indicated that the composite hydrogel reduced bone bridge formation and improved cartilage regeneration in the rabbit model of proximal tibial growth plate injury. Conclusion: This bilayer microsphere-based composite hydrogel with sequential controlled release of Bevacizumab and IGF-1 has promising potential for growth plate injury repair.

A new method for modeling rabbit growth plate injury for the study of tissue engineering scaffolds

Establishing a suitable animal model of growth plate injury is necessary to evaluate the effect of tissue engineering scaffolds on repairing the injured growth plate. However, the currently used animal models have limitations. Therefore in this study, we reported and evaluated a new modeling method termed the longitudinal disruption method, which is to make a longitudinal defect in the region of growth plate. In order to compare this new method with the traditional transverse disruption method, we constructed the models by both methods, respectively. To observe whether bone bridges were formed, histological sections were analyzed by HE and Masson staining at three weeks after modeling. The HE and Masson staining results showed the formation of bone bridges in both groups, implying that the two methods successfully injured the growth plate. However, it was unclear whether the exact injury to growth plate caused by both methods was consistent. Therefore, in order to evaluate the accuracy and precision of modeling method, the X-ray and micro-CT were performed immediately after modeling. The percentages of accurate defect position in the longitudinal and transverse modeling groups were 88.89% and 55.56%, respectively. The micro-CT results revealed irregularly shaped defect cross sections in the transverse modeling group, whereas the defects in the longitudinal modeling group had regular shapes. The mean defect areas were 10.06 ± 0.86 and 12.30 ± 2.13 mm² in the longitudinal and transverse modeling groups, respectively, while the difference between the actual area and the expected area were -1.94 ± 0.86 mm² and -7.70 ± 2.13 mm², respectively, showing the high precision of this new method. Altogether, we successfully demonstrated a new method for establishing a rabbit model of growth plate injury,which provides a simple and rapid modeling process, good modeling effect, high modeling accuracy, and convenient scaffold implantation. The new method provides an effective animal model for tissue engineering research on the repair and regeneration of injured growth plate.

Exosome-loaded extracellular matrix-mimic hydrogel with anti-inflammatory property Facilitates/promotes growth plate injury repair

Growth plate cartilage has limited self-repair ability, leading to poor bone bridge formation post-injury and ultimately limb growth defects in children. The current corrective surgeries are highly invasive, and outcomes can be unpredictable. Following growth plate injury, the direct loss of extracellular matrix (ECM) coupled with further ECM depletion due to the inhibitory effects of inflammation on the cartilage matrix protein greatly hinder chondrocyte regeneration. We designed an exosome (Exo) derived from bone marrow mesenchymal stem cells (BMSCs) loaded ECM-mimic hydrogel to promote cartilage repair by directly supplementing ECM and anti-inflammatory properties. Aldehyde-functionalized chondroitin sulfate (OCS) was introduced into gelatin methacryloyl (GM) to form GMOCS hydrogel. Our results uncovered that GMOCS hydrogel could significantly promote the synthesis of ECM due to the doping of OCS. In addition, the GMOCS-Exos hydrogel could further promote the anabolism of chondrocytes by inhibiting inflammation and ultimately promote growth plate injury repair through ECM remodeling.

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Chondrocytes are difficult to regenerate after growth plate injury due to extensive degradation of ECM (extracellular matrix).

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GMOCS-Exos can promote the synthesis of ECM by directly supplementing ECM and anti-inflammatory properties.

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GMOCS-Exos can boost cartilage regeneration after growth plate injury and reduce bone bridge formation.

Emulsion-free chitosan-genipin microgels for growth plate cartilage regeneration

The growth plate is a cartilage tissue near the ends of children's long bones and is responsible for bone growth. Injury to the growth plate can result in the formation of a 'bony bar' which can span the growth plate and result in bone growth abnormalities in children. Biomaterials such as chitosan microgels could be a potential treatment for growth plate injuries due to their chondrogenic properties, which can be enhanced through loading with biologics. They are commonly fabricated via an emulsion method, which involves solvent rinses that are cytotoxic. Here, we present a high throughput, non-cytotoxic, non-emulsion-based method to fabricate chitosan-genipin microgels. Chitosan was crosslinked with genipin to form a hydrogel network, and then pressed through a syringe filter using mesh with various pore sizes to produce a range of microgel particle sizes. The microgels were then loaded with chemokines and growth factors and their release was studied in vitro. To assess the applicability of the microgels for growth plate cartilage regeneration, they were injected into a rat growth plate injury. They led to increased cartilage repair tissue and were fully degraded by 28 days in vivo. This work demonstrates that chitosan microgels can be fabricated without solvent rinses and demonstrates their potential for the treatment of growth plate injuries.

Enlightenment of Growth Plate Regeneration Based on Cartilage Repair Theory: A Review

The growth plate (GP) is a cartilaginous region situated between the epiphysis and metaphysis at the end of the immature long bone, which is susceptible to mechanical damage because of its vulnerable structure. Due to the limited regeneration ability of the GP, current clinical treatment strategies (e.g., bone bridge resection and fat engraftment) always result in bone bridge formation, which will cause length discrepancy and angular deformity, thus making satisfactory outcomes difficult to achieve. The introduction of cartilage repair theory and cartilage tissue engineering technology may encourage novel therapeutic approaches for GP repair using tissue engineered GPs, including biocompatible scaffolds incorporated with appropriate seed cells and growth factors. In this review, we summarize the physiological structure of GPs, the pathological process, and repair phases of GP injuries, placing greater emphasis on advanced tissue engineering strategies for GP repair. Furthermore, we also propose that three-dimensional printing technology will play a significant role in this field in the future given its advantage of bionic replication of complex structures. We predict that tissue engineering strategies will offer a significant alternative to the management of GP injuries.

Adipose-derived stromal vascular fraction prevent bone bridge formation on growth plate injury in rat (in vivo studies) an experimental research

The growth plate is cartilage tissue found at the end of long bones in children, responsible for longitudinal bone growth. Injuries to the growth plate cartilage often lead to unwanted bony repair, resulting in growth disturbances such as limb length discrepancy and angulation deformity in children. There is currently no clinical treatment that can fully repair an injured growth plate. Tissue engineering is promising for regeneration of growth plate. Adipose-derived stromal vascular fraction highlight the promising potential as tissue engineering therapy for inducing regeneration of injured growth plate and able to reduce the formation of bony repair that can lead to deformity and limb length discrepancy. Using an animal model of growth plate injury, bone bridge formation is evaluated after 28 days using Enzyme-linked Immunoassay, radiology, histopathology and Immunofloresence examination. Radiological analyses performed by evaluation of grey value using ImageJ software and diameter bone bridge measured from the end to end distance between uninjured growth plate evaluated by histopatology examination. Enzyme-linked Immunoassay and immunofloresence are used to evaluate chondrocyte and chondrogenic marker within the defect. The result shows in group with Adipose-derived stromal vascular fraction have a significant lower bone bridge formation compare to positive control group. This current study represents the first work that has utilized this animal model to investigate whether Adipose-derived stromal vascular fraction can be used to initiate regeneration at the injured growth plate.

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Injuries to the growth plate cartilage often lead to unwanted bony repair, resulting in growth disturbances

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There is currently no clinical treatment that can fully repair an injured growth plate

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Tissue engineering is promising for regeneration of growth plate.

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Adipose-derived stromal vascular fraction (AD-SVF) highlight the promising potential as tissue engineering therapy

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AD-SVF decrease bone bridge formation on growth plate injuries model on Rat

Rabbit Model of Physeal Injury for the Evaluation of Regenerative Medicine Approaches

Physeal injuries can lead to bony repair tissue formation, known as a bony bar. This can result in growth arrest or angular deformity, which is devastating for children who have not yet reached their full height. Current clinical treatment involves resecting the bony bar and replacing it with a fat graft to prevent further bone formation and growth disturbance, but these treatments frequently fail to do so and require additional interventions. Novel treatments that could prevent bone formation but also regenerate the injured physeal cartilage and restore normal bone elongation are warranted. To test the efficacy of these treatments, animal models that emulate human physeal injury are necessary. The rabbit model of physeal injury quickly establishes a bony bar, which can then be resected to test new treatments. Although numerous rabbit models have been reported, they vary in terms of size and location of the injury, tools used to create the injury, and methods to assess the repair tissue, making comparisons between studies difficult. The study presented here provides a detailed method to create a rabbit model of proximal tibia physeal injury using a two-stage procedure. The first procedure involves unilateral removal of 25% of the physis in a 6-week-old New Zealand white rabbit. This consistently leads to a bony bar, significant limb length discrepancy, and angular deformity within 3 weeks. The second surgical procedure involves bony bar resection and treatment. In this study, we tested the implantation of a fat graft and a photopolymerizable hydrogel as a proof of concept that injectable materials could be delivered into this type of injury. At 8 weeks post-treatment, we measured limb length, tibial angle, and performed imaging and histology of the repair tissue. By providing a detailed, easy to reproduce methodology to perform the physeal injury and test novel treatments after bony bar resection, comparisons between studies can be made and facilitate translation of promising therapies toward clinical use. Impact Statement This study provides details to create a rabbit model of physeal injury that can facilitate comparisons between studies and test novel regenerative medicine approaches. Furthermore, this model mimics the human, clinical situation that requires a bony bar resection followed by treatment. In addition, identification of a suitable treatment can be seen in the correction of the growth deformity, allowing this model to facilitate the development of novel physeal cartilage regenerative medicine approaches.