Tendon-to-bone healing using an injectable calcium phosphate cement combined with bone xenograft/BMP composite

Graded Modulation of Inflammation by Metal Ion-Coordinated Peptide-Based Hydrogel Chemical Regulators Promotes Tendon-Bone Junction Regeneration

After rotator cuff injuries, uncontrolled inflammation hinders tendon-bone junction regeneration and induces scar formation in situ. Therefore, precisely controlling inflammation could be a solution to accelerate tendon-bone junction regeneration. In this study, we synthesized a peptide-metal ion complex hydrogel with thermosensitive capability that can be used as a hydrogel chemical regulator. By the coordination complex between Mg2+ and BMP-12, the free and coordinated Mg2+ can be programmability released from the hydrogel. The fast release of free Mg2+ can prevent inflammation at the early stage of injuries, according to the results of RT-qPCR and immunofluorescence staining. Then, the coordinated Mg2+ was slowly released from the hydrogel and provided an anti-inflammatory environment for tendon-bone junction regeneration in the long term. Finally, the hydrogel demonstrated enhanced therapeutic effects in a rat rotator cuff tear model. Overall, the Mg2+/BMP-12 peptide-metal ion complex-based hydrogel effectively addresses the regenerative requirements of the tendon-bone junction across various stages by graded modulating inflammation.

A New Tissue Engineering Strategy to Promote Tendon-bone Healing: Regulation of Osteogenic and Chondrogenic Differentiation of Tendon-derived Stem Cells

In the field of sports medicine, repair surgery for anterior cruciate ligament (ACL) and rotator cuff (RC) injuries are remarkably common. Despite the availability of relatively effective treatment modalities, outcomes often fall short of expectations. This comprehensive review aims to thoroughly examine current strategies employed to promote tendon-bone healing and analyze pertinent preclinical and clinical research. Amidst ongoing investigations, tendon-derived stem cells (TDSCs), which have comparatively limited prior exploration, have garnered increasing attention in the context of tendon-bone healing, emerging as a promising cell type for regenerative therapies. This review article delves into the potential of combining TDSCs with tissue engineering methods, with ACL reconstruction as the main focus. It comprehensively reviews relevant research on ACL and RC healing to address the issues of graft healing and bone tunnel integration. To optimize tendon-bone healing outcomes, our emphasis lies in not only reconstructing the original microstructure of the tendon-bone interface but also achieving proper bone tunnel integration, encompassing both cartilage and bone formation. In this endeavor, we thoroughly analyze the transcriptional and molecular regulatory variables governing TDSCs differentiation, incorporating a retrospective analysis utilizing single-cell sequencing, with the aim of unearthing relevant signaling pathways and processes. By presenting a novel strategy rooted in TDSCs-driven osteogenic and chondrogenic differentiation for tendon-bone healing, this study paves the way for potential future research avenues and promising therapeutic applications. It is anticipated that the findings herein will contribute to advancing the field of tendon-bone healing and foster the exploration of TDSCs as a viable option for regenerative therapies in the future.

Multiphasic bone-ligament-bone integrated scaffold enhances ligamentization and graft-bone integration after anterior cruciate ligament reconstruction

The escalating prevalence of anterior cruciate ligament (ACL) injuries in sports necessitates innovative strategies for ACL reconstruction. In this study, we propose a multiphasic bone-ligament-bone (BLB) integrated scaffold as a potential solution. The BLB scaffold comprised two polylactic acid (PLA)/deferoxamine (DFO)@mesoporous hydroxyapatite (MHA) thermally induced phase separation (TIPS) scaffolds bridged by silk fibroin (SF)/connective tissue growth factor (CTGF)@Poly(l-lactide-co-ε-caprolactone) (PLCL) nanofiber yarn braided scaffold. This combination mimics the native architecture of the ACL tissue. The mechanical properties of the BLB scaffolds were determined to be compatible with the human ACL. In vitro experiments demonstrated that CTGF induced the expression of ligament-related genes, while TIPS scaffolds loaded with MHA and DFO enhanced the osteogenic-related gene expression of bone marrow stem cells (BMSCs) and promoted the migration and tubular formation of human umbilical vein endothelial cells (HUVECs). In rabbit models, the BLB scaffold efficiently facilitated ligamentization and graft-bone integration processes by providing bioactive substances. The double delivery of DFO and calcium ions by the BLB scaffold synergistically promoted bone regeneration, while CTGF improved collagen formation and ligament healing. Collectively, the findings indicate that the BLB scaffold exhibits substantial promise for ACL reconstruction. Additional investigation and advancement of this scaffold may yield enhanced results in the management of ACL injuries.

Strategies to promote tendon-bone healing after anterior cruciate ligament reconstruction: Present and future

At present, anterior cruciate ligament (ACL) reconstruction still has a high failure rate. Tendon graft and bone tunnel surface angiogenesis and bony ingrowth are the main physiological processes of tendon-bone healing, and also the main reasons for the postoperative efficacy of ACL reconstruction. Poor tendon-bone healing has been also identified as one of the main causes of unsatisfactory treatment outcomes. The physiological process of tendon-bone healing is complicated because the tendon-bone junction requires the organic fusion of the tendon graft with the bone tissue. The failure of the operation is often caused by tendon dislocation or scar healing. Therefore, it is important to study the possible risk factors for tendon-bone healing and strategies to promote it. This review comprehensively analyzed the risk factors contributing to tendon-bone healing failure after ACL reconstruction. Additionally, we discuss the current strategies used to promote tendon-bone healing following ACL reconstruction.

Canine ACL reconstruction with an injectable hydroxyapatite/collagen paste for accelerated healing of tendon-bone interface

Healing of an anterior cruciate ligament (ACL) autologous graft in a bone tunnel occurs through the formation of fibrovascular scar tissue, which is structurally and compositionally inferior to normal fibrocartilaginous insertion and thus may increase the reconstruction failure and the rate of failure recurrence. In this study, an injectable hydroxyapatite/type I collagen (HAp/Col Ⅰ) paste was developed to construct a suitable local microenvironment to accelerate the healing of bone-tendon interface. Physicochemical characterization demonstrated that the HAp/Col Ⅰ paste was injectable, uniform and stable. The in vitro cell culture illustrated that the paste could promote MC3T3-E1 cells proliferation and osteogenic expression. The results of a canine ACL reconstruction study showed that the reconstructive ACL had similar texture and color as the native ACL. The average width of the tunnel, total bone volume, bone volume/tissue volume and trabecular number acquired from micro-CT analysis suggested that the healing of tendon-bone interface in experimental group was better than that in control group. The biomechanical test showed the maximal loads in experimental group achieved approximately half of native ACL's maximal load at 24 weeks. According to histological examination, Sharpey fibers could be observed as early as 12 weeks postoperatively while a typical four-layer transitional structure of insertion site was regenerated at 48 weeks in the experimental group. The injectable HAp/Col Ⅰ paste provided a biomimetic scaffold and microenvironment for early cell attachment and proliferation, further osteogenic expression and extracellular matrix deposition, and in vivo structural and functional regeneration of the tendon-bone interface.

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A stable and injectable HAp/Col I paste was designed, optimized and characterized.

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The paste was applied in ACL reconstruction with an established standard operation procedure.

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Provided the safety and efficacy evidence for ACL reconstruction, and healing of tendon-bone interface was accelerated.

Effects of Platelet-Rich Osteoconductive-Osteoinductive Allograft Compound on Tunnel Widening of ACL Reconstruction: A Randomized Blind Analysis Study

The anterior cruciate ligament (ACL) is a commonly injured ligament in the knee. Bone tunnel widening is a known phenomenon after soft-tissue ACL reconstruction and etiology and the clinical relevance has not been fully elucidated. Osteoconductive compounds are biomaterials providing an appropriate scaffold for bone formation such as a demineralized bone matrix. Osteoinductive materials contain growth factors stimulating bone lineage cells and bone growth. A possible application of osteoinductive/osteoconductive (OIC) material is in ACL surgery. We hypothesized that OIC placed in ACL bone tunnels: (1) reduces tunnel widening, (2) improves graft maturation, and (3) reduces tunnel ganglion cyst formation. To test this hypothesis, this study evaluated the osteogenic effects of demineralized bone matrix (DBM) and platelet-rich plasma (PRP) on tunnel widening, graft maturation, and ganglion cyst formation. This was a randomized controlled clinical trial pilot study. A total of 26 patients that elected to have ACL reconstruction surgery were randomized between the OIC and control group. Measurements of tunnel expansion and graft-tunnel incorporation were conducted via the quantitative image analysis of MRI scans performed at six months after surgery for both groups. No patients had adverse post-operative reactions or infections. The use of OIC significantly reduced tunnel widening (p < 0.05) and improved graft maturation (p < 0.05). Patients treated with OIC had a significantly lower prevalence of ganglion cyst compared to the control group (p < 0.05). The use of OIC has measurable effects on the reduction of tunnel widening, improved graft maturation, and decreased size of ganglion cyst after ACL reconstruction. This study explored the utilization of biologics to minimize bone tunnel widening in ACL reconstruction surgery.

Advances in Regenerative Sports Medicine Research

Regenerative sports medicine aims to address sports and aging-related conditions in the locomotor system using techniques that induce tissue regeneration. It also involves the treatment of meniscus and ligament injuries in the knee, Achilles’ tendon ruptures, rotator cuff tears, and cartilage and bone defects in various joints, as well as the regeneration of tendon–bone and cartilage–bone interfaces. There has been considerable progress in this field in recent years, resulting in promising steps toward the development of improved treatments as well as the identification of conundrums that require further targeted research. In this review the regeneration techniques currently considered optimal for each area of regenerative sports medicine have been reviewed and the time required for feasible clinical translation has been assessed. This review also provides insights into the direction of future efforts to minimize the gap between basic research and clinical applications.

Crimped nanofiber scaffold mimicking tendon-to-bone interface for fatty-infiltrated massive rotator cuff repair

Electrospun fibers, with proven ability to promote tissue regeneration, are widely being explored for rotator cuff repairing. However, without post treatment, the microstructure of the electrospun scaffold is vastly different from that of natural extracellular matrix (ECM). Moreover, during mechanical loading, the nanofibers slip that hampers the proliferation and differentiation of migrating stem cells. Here, electrospun nanofiber scaffolds, with crimped nanofibers and welded joints to biomimic the intricate natural microstructure of tendon-to-bone insertion, were prepared using poly(ester-urethane)urea and gelatin via electrospinning and double crosslinking by a multi-bonding network densification strategy. The crimped nanofiber scaffold (CNS) features bionic tensile stress and induces chondrogenic differentiation, laying credible basis for in vivo experimentation. After repairing a rabbit massive rotator cuff tear using a CNS for 3 months, the continuous translational tendon-to-bone interface was fully regenerated, and fatty infiltration was simultaneously inhibited. Instead of micro-CT, μCT was employed to visualize the integrity and intricateness of the three-dimensional microstructure of the CNS-induced-healed tendon-to-bone interface at an ultra-high resolution of less than 1 μm. This study sheds light on the correlation between nanofiber post treatment and massive rotator cuff repair and provides a general strategy for crimped nanofiber preparation and tendon-to-bone interface imaging characterization.

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Electrospun scaffold mimicking the microstructure of ECM was fabricated.

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The translational microstructure of tendon-to-bone interface was regenerated.

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Tendon-to-bone interface was 3D visualized with resolution less than 1 μm.

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Muscle fatty infiltration was inhibited for massive rotator cuff tear.

Biomaterials developed for facilitating healing outcome after anterior cruciate ligament reconstruction: Efficacy, surgical protocols, and assessments using preclinical animal models

Anterior cruciate ligament (ACL) reconstruction is the recommended treatment for ACL tear in the American Academy of Orthopaedic Surgeons (AAOS) guideline. However, not a small number of cases failed because of the tunnel bone resorption, unsatisfactory bone-tendon integration, and graft degeneration. The biomaterials developed and designed for improving ACL reconstruction have been investigated for decades. According to the Food and Drug Administration (FDA) and the International Organization for Standardization (ISO) regulations, animal studies should be performed to prove the safety and bioeffect of materials before clinical trials. In this review, we first evaluated available biomaterials that can enhance the healing outcome after ACL reconstruction in animals and then discussed the animal models and assessments for testing applied materials. Furthermore, we identified the relevance and knowledge gaps between animal experimental studies and clinical expectations. Critical analyses and suggestions for future research were also provided to design the animal study connecting basic research and requirements for future clinical translation.

Osteoprotegerin/bone morphogenetic protein 2 combining with collagen sponges on tendon-bone healing in rabbits

INTRODUCTION

The aim was to investigate the effect of collagen sponges (CS) as a delivery device for osteoprotegerin (OPG)/bone morphogenetic protein 2 (BMP-2) and support matrix on the tendon-bone healing after anterior crusicate ligament (ACL) reconstruction in modeled rabbits.

MATERIALS AND METHODS

Sixty New Zealand white rabbits were randomly divided into four groups based on treatments they received at the tendon-bone interface after left knee ACL reconstruction: the control group, OPG/BMP-2, CS, and OPG/BMP-2/CS combination. At 4, 8 and 12 weeks post-surgery, five rabbits from each group were euthanized to examine the tendon-bone healing. Levels of OPG and BMP-2 in synovial fluid, the bone tunnel enlargement value, the histomorphological typing of tendon-bone interface, and the bone tunnel area of the tendon-bone interface were compared among different treatments.

RESULTS

The OPG/BMP-2/CS combination treatment group had the highest levels of OPG and BMP-2 in synovial fluid (both P < 0.05), the greatest number of Sharpey-like collagen fibers at all test points (P < 0.05), the most fibrocartilage enthesis on week 12, the greatest bone tunnel area (P < 0.05), and the greatest decrease in bone tunnel enlargement on week 12 (P < 0.05). Histomorphological typing of tendon-bone interface of all groups showed changes varying from tendon-bone separation to firm healing, and the change was most significant in the OPG/BMP-2/CS combination treatment group.

CONCLUSION

CS treatment alone serves as a fixing support, and CS combining with growth factors OPG/BMP-2 ensures slow and stable release of OPG/BMP-2, significantly improves the tendon-bone healing in the rabbit ACL model.

A Synthetic Graft With Multilayered Co-Electrospinning Nanoscaffolds for Bridging Massive Rotator Cuff Tear in a Rat Model

BACKGROUND

Graft bridging is used in massive rotator cuff tear (MRCT); however, the integration of graft-tendon and graft-bone is still a challenge.

HYPOTHESIS

A co-electrospinning nanoscaffold of polycaprolactone (PCL) with an "enthesis-mimicking" (EM) structure could bridge MRCT, facilitate tendon regeneration, and improve graft-bone healing.

STUDY DESIGN

Controlled laboratory study.

METHODS

First, we analyzed the cytocompatibility of the electrospinning nanoscaffolds, including aligned PCL (aPCL), nonaligned PCL (nPCL), aPCL-collagen I, nPCL-collagen II, and nPCL-nanohydroxyapatite (nHA). Second, for the EM condition, nPCL-collagen II and nPCL-nHA were electrospun layer by layer at one end of the aPCL-collagen I; for the control condition, the nPCL was electrospun on the aPCL. In 40 mature male rats, resection of both the supraspinatus and infraspinatus tendons was performed to create MRCT, and the animals were divided randomly into EM and control groups. In both groups, one end of the layered structure was fixed on the footprint of the rotator cuff, whereas the other end of the layered structure was sutured with the tendon stump. The animals were euthanized for harvesting of tissues for histologic and biomechanical analysis at 4 weeks or 8 weeks postoperatively.

RESULTS

All scaffolds showed good cytocompatibility in vitro. The graft-tendon tissue in the EM group had more regularly arranged cells, denser tissue, a significantly higher tendon maturing score, and more birefringence compared with the control group at 8 weeks after operation. Newly formed fibrocartilage could be observed at the graft-bone interface in both groups by 8 weeks, but the EM group had a higher graft-bone healing score and significantly more newly formed fibrocartilage than the control group. An enthesis-like structure with transitional layers was observed in the EM group at 8 weeks. Biomechanically, the values for maximum failure load and stiffness of the tendon-graft-bone complex were significantly higher in the EM group than in the control group at 8 weeks.

CONCLUSION

The co-electrospinning nanoscaffold of aPCL-collagen I could be used as a bridging graft to improve early graft-tendon healing for MRCT in a rat model and enhance early enthesis reconstruction in combination with a multilayered structure of nPCL-collagen II and nPCL-nHA.

CLINICAL RELEVANCE

We constructed a graft to bridge MRCT, enhance graft-tendon healing and graft-bone healing, and reconstruct the enthesis structure.

Evaluation of a bioengineered ACL matrix's osteointegration with BMP-2 supplementation

A poly (l-lactic) acid bioengineered anterior cruciate ligament (ACL) matrix has previously demonstrated the ability to support tissue regeneration in a rabbit ACL reconstruction model. The matrix was designed for optimal bone and ligament regeneration by developing a matrix with differential pore sizes in its bone and ligament compartments. Building upon past success, we designed a new bioengineered ACL matrix that is easier to install and can be used with endobutton fixation during ACL reconstruction. To achieve this, a new braiding procedure was developed to allow the matrix to be folded in half, making two-limbs, while maintaining its bone and ligament compartments. The osteointegration of the matrix with and without bone morphogenetic protein 2 (BMP-2) supplementation was evaluated in a rabbit ACL reconstruction model. Two doses of BMP-2 were evaluated, 1 and 10 μg, and delivered by saline injection into the bone tunnel at the end of surgery. A fibrous matrix-to-bone interface with occasional Sharpey’s fibers was the primary mode of osteointegration observed. The matrix was also found to support a fibrocartilage matrix-to-bone interface. In some cases, the presence of chondrocyte-like cells was observed at the aperture of the bone tunnel and the center of the matrix within the bone tunnel. Treatment with BMP-2 was associated with a trend towards smaller bone tunnel cross-sectional areas, and 1 μg of BMP-2 was found to significantly enhance osteoid seam width in comparison with no BMP-2 or 10 μg of BMP-2 treatment. Regenerated tissue was well organized within the bioengineered ACL matrix and aligned with the poly (l-lactic) acid fibers. Disorganized tissue was found between the two-limbs of the bioengineered ACL matrix and hypothesized to be due to a lack of structural scaffolding. This study suggests that the bioengineered ACL matrix can undergo similar modes of osteointegration as current autografts and allografts, and that BMP-2 treatment may enhance osteoblastic activity within the bone tunnels.

[Research progress of structured repair of tendon-bone interface]

In sports system, the tendon-bone interface has the effect of tensile and bearing load, so the effect of healing plays a crucial role in restoring joint function. The process of repair is the formation of scar tissue, so it is difficult to achieve the ideal effect for morphology and biomechanical strength. The tissue engineering method can promote the tendon-bone interface healing from the seed cells, growth factors, and scaffolds, and is a new direction in the field of development of the tendon-bone interface healing.

In vitro behavior of tendon stem/progenitor cells on bioactive electrospun nanofiber membranes for tendon-bone tissue engineering applications

Purpose

In order to accelerate the tendon-bone healing processes and achieve the efficient osteointegration between the tendon graft and bone tunnel, we aim to design bioactive electrospun nanofiber membranes combined with tendon stem/progenitor cells (TSPCs) to promote osteogenic regeneration of the tendon and bone interface.

Methods

In this study, nanofiber membranes of polycaprolactone (PCL), PCL/collagen I (COL-1) hybrid nanofiber membranes, poly(dopamine) (PDA)-coated PCL nanofiber membranes and PDA-coated PCL/COL-1 hybrid nanofiber membranes were successfully fabricated by electrospinning. The biochemical characteristics and nanofibrous morphology of the membranes, as well as the characterization of rat TSPCs, were defined in vitro. After co-culture with different types of electrospun nanofiber membranes in vitro, cell proliferation, viability, adhesion and osteogenic differentiation of TSPCs were evaluated at different time points.

Results

Among all the membranes, the performance of the PCL/COL-1 (volume ratio: 2:1 v/v) group was superior in terms of its ability to support the adhesion, proliferation, and osteogenic differentiation of TSPCs. No benefit was found in this study to include PDA coating on cell adhesion, proliferation and osteogenic differentiation of TSPCs.

Conclusion

The PCL/COL-1 hybrid electrospun nanofiber membranes are biocompatible, biomimetic, easily fabricated, and are capable of supporting cell adhesion, proliferation, and osteogenic differentiation of TSPCs. These bioactive electrospun nanofiber membranes may act as a suitable functional biomimetic scaffold in tendon-bone tissue engineering applications to enhance tendon-bone healing abilities.

Promotion of osteogenesis by bioactive glass-ceramic coating: Possible involvement of the Hedgehog signaling pathway

PURPOSE

Bioactive glass-ceramic (BGC) coatings have been extensively studied and clinically used as bone substitute materials because of their osteogenesis, osteoinduction, and osteoconduction characteristics. Although the Hedgehog (Hh) signaling pathway plays an important role in skeletal development, the relationship between BGC coatings and the Hh signaling pathway is unknown.

METHODS

In this study, a BGC coating is fabricated by furnace sintering, and its surface is investigated by a scanning electron microscope (SEM) and a transmission electron microscope (TEM). Furthermore, the expression of Ki67 is evaluated using immunofluorescence, and osteogenesis-related factors and Hh signaling pathway molecules on the BGC coating are examined by real-time reverse transcription polymerase chain reaction (real-time RT-PCR) and Western blotting in bone marrow mesenchymal stem cells (BMSCs).

RESULTS

The SEM and the TEM show that the BGC coating surface is smooth, without cracks, and composed of particles with mesoporous structure. The expression of Ki67 positive BMSCs of the BGC group is higher than that of the control group. Real-time RT-PCR and Western blotting assay reveal that the expression levels of osteoblast-related genes (BMP2, Osteocalcin, ALP, Runx2) and Hh signaling pathway molecules (Gli1, Smo) are much higher for the BGC coating group than those for the control group. Furthermore, after treating with Smo inhibitor cyclopamine, the Smo and Gli1 expressions in BMSCs are dramatically down-regulation for the BGC coating compared to those for the control group. Both mRNA and protein expression levels of osteogenesis-related factors was downregulated after treating Smo inhibitor cyclopamine in BMSCs with the BGC coating.

CONCLUSIONS

The BGC coatings promote osteogenesis probably via the Hh signaling pathway, which provides a theory reference for future clinical application of bone formation.

Promoting tendon to bone integration using graphene oxide-doped electrospun poly(lactic-co-glycolic acid) nanofibrous membrane

Background

These normal entheses are not reestablished after repair despite significant advances in surgical techniques. There is a significant need to develop integrative biomaterials, facilitating functional tendon-to-bone integration.

Materials and methods

We fabricated a highly interconnective graphene oxide-doped electrospun poly(lactide-co-glycolide acid) (GO-PLGA) nanofibrous membrane by electrospinning technique and evaluated them using in vitro cell assays. Then, we established rabbit models, the PLGA and GO-PLGA nanofibrous membranes were used to augment the rotator cuff repairs. The animals were killed postoperatively, which was followed by micro-computed tomography, histological and biomechanical evaluation.

Results

GO was easily mixed into PLGA filament without changing the three dimensional microstructure. An in vitro evaluation demonstrated that the PLGA membranes incorporated with GO accelerated the proliferation of BMSCs and furthered the Osteogenic differentiation of BMSCs. In addition, an in vivo assessment further revealed that the local application of GO-PLGA membrane to the gap between the tendon and the bone in a rabbit model promoted the healing enthesis, increased new bone and cartilage generation, and improved collagen arrangement and biomechanical properties in comparison with repair with PLGA only.

Conclusion

The electrospun GO-PLGA fibrous membrane provides an effective approach for the regeneration of tendon to bone enthesis.

Biological augmentation of graft healing in anterior cruciate ligament reconstruction: a systematic review

Aims

The success of anterior cruciate ligament reconstruction (ACLR) depends on osseointegration at the graft-tunnel interface and intra-articular ligamentization. Our aim was to conduct a systematic review of clinical and preclinical studies that evaluated biological augmentation of graft healing in ACLR.

Materials and Methods

In all, 1879 studies were identified across three databases. Following assessment against strict criteria, 112 studies were included (20 clinical studies; 92 animal studies).

Results

Seven categories of biological interventions were identified: growth factors, biomaterials, stem cells, gene therapy, autologous tissue, biophysical/environmental, and pharmaceuticals. The methodological quality of animal studies was moderate in 97%, but only 10% used clinically relevant outcome measures. The most interventions in clinical trials target the graft-tunnel interface and are applied intraoperatively. Platelet-rich plasma is the most studied intervention, but the clinical outcomes are mixed, and the methodological quality of studies was suboptimal. Other biological therapies investigated in clinical trials include: remnant-augmented ACLR; bone substitutes; calcium phosphate-hybridized grafts; extracorporeal shockwave therapy; and adult autologus non-cultivated stem cells.

Conclusion

There is extensive preclinical research supporting the use of biological therapies to augment ACLR. Further clinical studies that meet the minimum standards of reporting are required to determine whether emerging biological strategies will provide tangible benefits in patients undergoing ACLR. Cite this article: Bone Joint J 2018;100-B:271-84.

Biological Activity of an Injectable Biphasic Calcium Phosphate/PMMA Bone Cement for Induced Osteogensis in Rabbit Model

Polymethylmethacrylate (PMMA) bone cement is widely used in repair of vertebral fracture because of its good biomechanical properties and fast curing. However, the bioinertness of PMMA cement may cause interfacial loosening, fatigue, fracture, and ultimate failure. In this study, biphasic calcium phosphate (BCP) is introduced into PMMA cement to prepare an injectable composite bone cement (BCP_x /PMMA) and the content of BCP is optimized to achieve appropriate rate of absorption that matches the bone regeneration. The compressive strength of BCP_x /PMMA bone cement is found to comply with the International Standardization Organization standard 5833, and can promote biomineralization as well as adhesion, proliferation, and osteogenic differentiation of Sprague-Dawley rat bone marrow mesenchymal stem cells in vitro. Furthermore, in vivo test performed on a rabbit radius defect model demonstrates that the presence of BCP can significantly improve the osteogenic efficacy of PMMA cement. Therefore, it is anticipated that BCP_x /PMMA bone cement, as a promising injectable biomaterial, is of great potential in bone tissue regeneration.

Enhanced biological fixation of ligaments to bone tissues utilizing chitin fabrics

In ligament reconstruction involving anterior cruciate ligament surgery, biological fixation between the transferred ligament and bone tissue is critical for achieving successful outcomes. Here, we administered chitin fabrics into the bone tunnels and evaluated their efficacy in promoting biological fixation. An animal model on the rat's patellar ligament was employed. First, bone tunnels were created in the lateral condyle of the femur. The ligament was then separated from the tibial tuberosity, and half was inserted into the tunnel and fixed with the use of end button. Animals in the experimental group were treated with microfiber nonwoven chitin fabric, whereas control animals received no treatment. Specimens were collected at 2, 4, and 6 weeks after surgery, and the fixation strength was measured by mechanical tests. Histological sections were prepared from samples prepared 4 weeks after surgery, and the diameter of bone tunnel and the width ratio of collagenous tissue in the bone tunnel were measured. Administration of chitin significantly increased the mean fixation strength at 4 and 6 weeks after surgery. Furthermore, chitin also promoted bone formation in the bone tunnel and increased the density of collagen fibers. Thus, microfiber nonwoven chitin fabric enhanced the biological fixation of the ligament to the bone tissue. © 2017 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 106B: 2355-2360, 2018.

Anterior Cruciate Ligament-Derived Stem Cells Transduced With BMP2 Accelerate Graft-Bone Integration After ACL Reconstruction

BACKGROUND

Strong graft-bone integration is a prerequisite for successful graft remodeling after reconstruction of the anterior cruciate ligament (ACL) using soft tissue grafts. Novel strategies to accelerate soft tissue graft-bone integration are needed to reduce the need for bone-tendon-bone graft harvest, reduce patient convalescence, facilitate rehabilitation, and reduce total recovery time after ACL reconstruction.

HYPOTHESIS

The application of ACL-derived stem cells with enhanced expression of bone morphogenetic protein 2 (BMP2) onto soft tissue grafts in the form of cell sheets will both accelerate and improve the quality of graft-bone integration after ACL reconstruction in a rat model.

STUDY DESIGN

Controlled laboratory study.

METHODS

ACL-derived CD34+ cells were isolated from remnant human ACL tissues, virally transduced to express BMP2, and embedded within cell sheets. In a rat model of ACL injury, bilateral single-bundle ACL reconstructions were performed, in which cell sheets were wrapped around tendon autografts before reconstruction. Four groups containing a total of 48 rats (96 knees) were established (n = 12 rats; 24 knees per group): CD34+BMP2 (100%), CD34+BMP2 (25%), CD34+ (untransduced), and a control group containing no cells. Six rats from each group were euthanized 2 and 4 weeks after surgery, and each graft was harvested for immunohistochemical and histological analyses. The remaining 6 rats in each group were euthanized at 4 and 8 weeks to evaluate in situ tensile load to failure in each femur-graft-tibia complex.

RESULTS

In vitro, BMP2 transduction promoted the osteogenic differentiation of ACL-derived CD34+ cells while retaining their intrinsic multipotent capabilities. Osteoblast densities were greatest in the BMP2 (100%) and BMP2 (25%) groups. Bone tunnels in the CD34+BMP2 (100%) and CD34+BMP2 (25%) groups had the smallest cross-sectional areas according to micro-computed tomography analyses. Graft-bone integration occurred most rapidly in the CD34+BMP2 (25%) group. Tensile load to failure was significantly greater in the groups containing stem cells at 4 and 8 weeks after surgery. Tensile strength was greatest in the CD34+BMP2 (100%) group at 4 weeks, and in the CD34+BMP2 (25%) group at 8 weeks.

CONCLUSION

ACL-derived CD34+ cells transduced with BMP2 accelerated graft-bone integration after ACL reconstruction using soft tissue autografts in a rat model, as evidenced by improved histological appearance and graft-bone interface biology along with tensile load to failure at each time point up to 8 weeks after surgery.

CLINICAL RELEVANCE

A primary disadvantage of using soft tissue grafts for ACL reconstruction is the prolonged time required for bony ingrowth, which delays the initiation of midsubstance graft remodeling. The lack of consistent correlation between the appearance of a "healed" ACL on postoperative magnetic resonance imaging and readiness to return to sport results in athletes being released to sport before the graft is ready to handle high-intensity loading. Therefore, it is desirable to identify strategies that accelerate graft-bone integration, which would reduce the time to biologic fixation, improve the reliability of biologic fixation, allow for accelerated rehabilitation, and potentially reduce the incidence of early graft pullout and late midsubstance failure.

Biological enhancement of graft-tunnel healing in anterior cruciate ligament reconstruction

The sites where graft healing occurs within the bone tunnel and where the intra-articular ligamentization process takes place are the two most important sites of biological incorporation after anterior cruciate ligament (ACL) reconstruction, since they help to determine the mechanical behavior of the femur-ACL graft-tibia complex. Graft-tunnel healing is a complex process influenced by several factors, such as type of graft, preservation of remnants, bone quality, tunnel length and placement, fixation techniques and mechanical stress. In recent years, numerous experimental and clinical studies have been carried out to evaluate potential strategies designed to enhance and optimize the biological environment of the graft-tunnel interface. Modulation of inflammation, tissue engineering and gene transfer techniques have been applied in order to obtain a direct-type fibrocartilaginous insertion of the ACL graft, similar to that of native ligament, and to accelerate the healing process of tendon grafts within the bone tunnel. Although animal studies have given encouraging results, clinical studies are lacking and their results do not really support the use of the various strategies in clinical practice. Further investigations are therefore needed to optimize delivery techniques, therapeutic concentrations, maintenance of therapeutic effects over time, and to reduce the risk of undesirable effects in clinical practice.

Three-dimensional printing akermanite porous scaffolds for load-bearing bone defect repair: An investigation of osteogenic capability and mechanical evolution

Some Ca-Mg-silicate ceramics have been widely investigated to be highly bioactive and biodegradable, whereas their osteogenic potential and especially biomechanical response in the early stage in vivo are scarcely demonstrated. Herein, the osteogenesis capacity and mechanical evolution of the akermanite (Ca₂MgSi₂O₇) porous materials manufactured by ceramic ink writing three-dimensional printing technique were investigated systematically in a critical size femur defect model, in comparison with the clinically available β-tricalcium phosphate porous bioceramic. Such three-dimensional printed akermanite scaffolds possess fully interconnected pores of ∼280 × 280 µm in size and over 50% porosity with appreciable compressive strength (∼71 MPa), that is 7-fold higher than that of the β-tricalcium phosphate porous bioceramics (∼10 MPa). After 6 weeks and 12 weeks of implantation, the percentage of newly formed bone and more new bone was observed in the akermanite group as compared with the β-tricalcium phosphate group (p < 0.01). Moreover, significant higher mRNA expressions of osteogenic genes were detected in the akermanite group by PCR analysis (p < 0.01). The in vivo mechanical strength decreased during the process of implantation, but maintained a relative high level (∼14 MPa) which was still higher than that of the host cancellous bone (5-10 MPa) at 12 weeks post-implantation. On the contrary, the β-tricalcium phosphate scaffold always exhibited a very low mechanical strength (∼8 MPa). These results suggest that the three-dimensional printed akermanite scaffolds are promising for the bone tissue regeneration and repair of load-bearing bone defects.

bFGF- and CaPP-Loaded Fibrin Clots Enhance the Bioactivity of the Tendon-Bone Interface to Augment Healing

BACKGROUND

Tendon-to-bone healing is a complex and slow process, and the rate of poor healing remains high. In recent years, several new strategies have been developed that enhance tendon-to-bone healing by increasing the bioactivity. Fibrin clots have been widely used to improve tissue healing and tissue engineering,

HYPOTHESIS

Modified fibrin clots can improve the bioactivity of the tendon-bone interface and histological appearance.

STUDY DESIGN

Controlled laboratory study.

METHODS

A total of 27 male New Zealand White rabbits were used. Of these, 3 were used for cell isolation, and the remaining 24 rabbits were divided into 2 groups (12 per group) for an in vivo partial patellectomy study. The setting time, degradation time, and basic fibroblast growth factor (bFGF) and ceramide-activated protein phosphatase (CaPP) release kinetics of bFGF- and CaPP-loaded fibrin clots were modified appropriately for early tendon-to-bone healing. In an in vitro experiment, the bFGF- and CaPP-loaded fibrin clots were assessed for cell migration and proliferation by microscopy, MTT (3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyltetrazolium bromide) assay, and DAPI (4',6-diamidino-2-phenylindole) assay. Quantitative real-time reverse transcription polymerase chain reaction and a Western blot assay were performed to test for an induction effect of the bFGF- and CaPP-loaded fibrin clots. Finally, for the in vivo experiment, the rabbits were divided into 2 treatment groups: one with bFGF- and CaPP-loaded fibrin clots and one without bFGF- and CaPP-loaded fibrin clots after partial patellectomy in patella-patellar tendon sutured sites. A histological evaluation was performed at 2, 4, and 6 weeks after surgery.

RESULTS

The sitting time and degradation time of the bFGF- and CaPP-loaded fibrin clots were set at 15 seconds and more than 2 weeks, respectively, and the porosity was minimized to achieve the highest levels of cell migration and growth. In the bFGF-CaPP group of the in vitro experiment, cell proliferation increased to a greater extent relative to the control group (P < .05); the mRNA expression of osteopontin, alkaline phosphatase, runt-related transcription factor 2, vascular endothelial growth factor, and collagen type I was upregulated (P < .05); and the relative protein expression of these factors was enhanced (P < .05). In vivo, hematoxylin and eosin staining showed that the tendon-to-bone connections were more mature and more arranged when treated with bFGF- and CaPP-loaded fibrin clots than when untreated, and the histological scores were higher.

CONCLUSION

bFGF- and CaPP-loaded fibrin clots enhanced cell migration and proliferation and the expression of related genes and proteins, which increased the bioactivity of the tendon-bone interface and resulted in the histological improvement of tendon-to-bone healing.

CLINICAL RELEVANCE

As fibrin clots have already been used in clinical practice, bFGF- and CaPP-loaded fibrin clots can be further used to augment healing in the early stages of tendon-to-bone healing.

3D Printing Surgical Implants at the clinic: A Experimental Study on Anterior Cruciate Ligament Reconstruction

Desktop three-dimensional (3D) printers (D3DPs) have become a popular tool for fabricating personalized consumer products, favored for low cost, easy operation, and other advantageous qualities. This study focused on the potential for using D3DPs to successfully, rapidly, and economically print customized implants at medical clinics. An experiment was conducted on a D3DP-printed anterior cruciate ligament surgical implant using a rabbit model. A well-defined, orthogonal, porous PLA screw-like scaffold was printed, then coated with hydroxyapatite (HA) to improve its osteoconductivity. As an internal fixation as well as an ideal cell delivery system, the osteogenic scaffold loaded with mesenchymal stem cells (MSCs) were evaluated through both in vitro and in vivo tests to observe bone-ligament healing via cell therapy. The MSCs suspended in Pluronic F-127 hydrogel on PLA/HA screw-like scaffold showed the highest cell proliferation and osteogenesis in vitro. In vivo assessment of rabbit anterior cruciate ligament models for 4 and 12 weeks showed that the PLA/HA screw-like scaffold loaded with MSCs suspended in Pluronic F-127 hydrogel exhibited significant bone ingrowth and bone-graft interface formation within the bone tunnel. Overall, the results of this study demonstrate that fabricating surgical implants at the clinic (fab@clinic) with D3DPs can be feasible, effective, and economical.

Systematic Review of Biological Modulation of Healing in Anterior Cruciate Ligament Reconstruction

Background:

Whether biological modulation is effective to promote healing in anterior cruciate ligament (ACL) reconstruction remains unclear.

Purpose:

To perform a systematic review of both clinical and experimental evidence of preclinical animal studies on biological modulation to promote healing in ACL reconstruction.

Study Design:

Systematic review; Level of evidence, 2.

Methods:

A systematic search was performed using the PubMed, Ovid, and Scopus search engines. Inclusion criteria were clinical and animal studies involving subjects with ACL injury with the use of biological modulation to promote healing outcomes. Methodological quality of clinical studies was evaluated using the Critical Appraisal Skill Programme (CASP) appraisal tool, and animal studies were evaluated by a scoring system based on a published checklist of good animal studies.

Results:

Ten clinical studies and 50 animal studies were included. Twenty-five included studies were regarded as good quality, with a methodological score ≥5. These studies suggested that transforming growth factor–beta (TGF-β), mesenchymal stem cells, osteogenic factors, and modalities that reduce local inflammation may be beneficial to promote graft healing in ACL reconstruction.

Conclusion:

This systematic review suggests that biological modulation is able to promote healing on top of surgical treatment for ACL injuries. This treatment strategy chiefly works through promotion of healing at the tunnel-graft interface, but the integrity of the intra-articular midsubstance of the graft would be another target for biological modulation.