Silk fibroin and hydroxyapatite segmented coating enhances graft ligamentization and osseointegration processes of the polyethylene terephthalate artificial ligament in vitro and in vivo

Anterior Cruciate Ligament Repair Augmented With a Polyethylene Terephthalate Band Supports Biomechanical Stability During the Early Healing Phase in a Rabbit Model

BACKGROUND

Augmented repair is an alternative strategy for the treatment of acute ligament and tendon injuries that imparts time-zero biomechanical strength to allow early loading, thereby protecting the repaired structures during the early healing process.

PURPOSE

To investigate the biomechanical properties and biological healing process after suture repair of acute anterior cruciate ligament (ACL) tears with polyethylene terephthalate (PET) augmentation and compare the findings with those obtained without PET augmentation.

STUDY DESIGN

Controlled laboratory study.

METHODS

A total of 48 rabbits were assigned to 3 groups: a PET-augmented group, a nonaugmented suture repair group, and a natural (control) group. All 3 groups were evaluated at 4, 12, and 16 weeks after surgery. Biomechanical performance was assessed using tensile strength testing, and ACL healing and maturation were assessed using histological assessments.

RESULTS

The PET-augmented group showed less anterior knee laxity at 30° of knee flexion and superior structural continuity compared with the suture group. ACL repair with PET augmentation yielded recovery of the maximum tensile load as early as 4 weeks compared with that of the natural group (110.5 ± 6.5 vs 129.0 ± 8.6 N, respectively; P = .29) and a gradual improvement in linear stiffness from 4 weeks (58.4 ± 3.9 N/mm) to 16 weeks (83.1 ± 5.1 N/mm; P = .04), approaching that of the natural group (106.7 ± 5.8 N/mm). Furthermore, histological analyses revealed that in the PET-augmented group, the ACL healed back to the proximal insertion as early as 4 weeks with angiogenesis and collagen regeneration, and the increased ligament maturity score indicated a gradual healing process from 4 to 16 weeks.

CONCLUSION

Compared with nonaugmented repair, repair augmented with a PET band enhanced early ACL stability and supported healing of ACL tears in a rabbit model.

CLINICAL RELEVANCE

The biomechanical and histological findings support subsequent clinical investigations using PET augmentation in patients with acute ACL tears.

Novel Silk Fibroin Based Bilayer Scaffolds for Bioabsorbable Internal Biliary Stenting

Biliary duct reconstruction is one of the most challenging parts of liver transplantation and accounts for 40%-60% of complications. While current stent-based devices on the market show promising results in reducing complications, they are manufactured from permanent synthetic materials and require a second reintervention for their removal. This exposes the patients to other potential complications and increases healthcare costs. This study develops a fabrication technique to produce a bioabsorbable biliary stent based on silk fibroin. The process used a dip-coating procedure for silk fibroin that produced highly smooth monolayer tubular specimens without the use of any additional surfactants during removal. This process was combined with an electrospinning step to produce bilayer structures through the deposition of electrospun silk fibroin on the outer surface. The structures proved to have promising mechanical, morphological, and cytocompatibility properties for use in the field of biliary stenting. Furthermore, the technique investigated proved to be reproducible, achieving an important requirement for large-scale use even in the presence of a biomaterial derived from a natural source. These results show the possibility of obtaining a completely bioabsorbable internal biliary stent that does not require any second reintervention. This study can be the starting point for further investigations both in vitro and in vivo to assess the suitability of silk fibroin biliary stents for clinical applications.

Strontium-Doped Hydroxyapatite Coating Improves Osteo/Angiogenesis for Ameliorative Graft-Bone Integration via the Macrophage-Derived Cytokines-Mediated Integrin Signal Pathway

Polyethylene terephthalate (PET) artificial ligaments, renowned for their superior mechanical properties, have been extensively adopted in anterior cruciate ligament (ACL) reconstruction surgeries. However, the inherent bio-inertness of PET introduces formidable barriers to graft-bone integration, a critical aspect of rehabilitation. Previous interventions, ranging from surface roughening to chemical modifications, have aimed to address this challenge; however, consistently effective techniques for inducing graft-bone integration remain scarce. Our study employed advanced surface-coating methodologies to introduce strontium-doped hydroxyapatite (SrHA) onto PET ligaments. Detailed scanning electron microscopy (SEM) examinations revealed a uniform and integrative coating of SrHA on PET fibers. Furthermore, spectroscopic analysis confirmed the steady release of strontium ions from the coated surface under physiological conditions. In-depth cellular studies proved that extracellular strontium emanating from SrHA-coated PET (PET@SrHA) ligaments actively steers the M2 macrophage polarization. Additionally, macrophages (Mφs) manifested a heightened secretion of prohealing cytokines when exposed to PET@SrHA. Subsequent investigations showed that these cytokines acted as mediators, activating integrin signaling pathways among macrophages, vascular endothelial cells, and osteoblasts. As a direct consequence, an increased rate of angiogenesis and osteogenic differentiation was observed, vital for graft-bone integration following ACL reconstruction with PET@SrHA ligaments. From a biochemical standpoint, our results pinpoint strontium ions as influential immunomodulators, sculpting the graft-bone interface's immune environment. This insight presents the SrHA-coating technique as a viable therapeutic strategy, holding sound promise for improving angiogenesis and osseointegration outcomes during ACL reconstruction using PET-based grafts.

Application of Nondegradable Synthetic Materials for Tendon and Ligament Injury

Tendon and ligament injuries, prevalent requiring surgical intervention, significantly impact joint stability and function. Owing to excellent mechanical properties and biochemical stability, Nondegradable synthetic materials, including polyethylene terephthalate (PET) and polytetrafluoroethylene (PTFE), have demonstrated significant potential in the treatment of tendon and ligament injuries. These above materials offer substantial mechanical support, joint mobility, and tissue healing promotion of the shoulder, knee, and ankle joint. This review conclude the latest development and application of nondegradable materials such as artificial patches and ligaments in tendon and ligament injuries including rotator cuff tears (RCTs), anterior cruciate ligament (ACL) injuries, and Achilles tendon ruptures.

High-Performance Artificial Ligament Made from Helical Polyester Fibers Wrapped with Aligned Carbon Nanotube Sheets

Repairing high-load connective tissues, such as ligaments, by surgically implanting artificial grafts after injury is challenging because they lack biointegration with host bones for stable interfaces. Herein, a high-performance helical composite fiber (HCF) ligament by wrapping aligned carbon nanotube (CNT) sheets around polyester fibers is proposed. Anterior cruciate ligament (ACL) reconstruction surgery shows that HCF grafts could induce effective bone regeneration, thus allowing the narrowing of bone tunnel defects. Such repair of the bone tunnel is in strong contrast to the tunnel enlargement of more than 50% for commercial artificial ligaments made from bare polyester fibers. Rats reconstructed with this HCF ligament show normal jumping, walking, and running without limping. This work allows bone regeneration in vivo through a one-step surgery without seeding cells or transforming growth factors, thereby opening an avenue for high-performance artificial tissues.

Nano-hydroxyapatite/natural polymer composite scaffolds for bone tissue engineering: a brief review of recent trend

Nanostructured inorganic biomaterial emerged as the most essential platform to address traumatic and non-traumatic conditions of hard tissues in the current scenario. Synthetic inorganic biomaterials serve as an efficient and pathogen-free choice that overcomes the obstructions associated with autografts and allografts to promote new tissue regeneration, since nano-hydroxyapatite (nHAp) is a biomaterial that mimics the natural mineral composition of bones and teeth of human hard tissues, which is widely employed in orthopedics and dentistry. The nHAp-based materials exhibit bioactive, biocompatible, and osteoconductive features under in vitro and in vivo conditions. The brittle nature of synthetic nHAp leads to weak mechanical properties, which eventually confines the utility of nHAp in load-bearing applications. Hence, this review focuses on the recent trends in the fabrication and investigation of nHAp-based polymer nanocomposite scaffolds for bone regeneration. Employing different polymers and fabrication strategies would efficiently tailor the physicochemical properties, and tailor-made mechanical properties in competence with biodegradation, thereby enhancing their potential in biomedical utility, and exploring their efficacy under in vitro and in vivo conditions to make "HAp-based smart-biomaterials" for bone tissue engineering.

Sequential intervention of anti-inflammatory and osteogenesis with silk fibroin coated polyethylene terephthalate artificial ligaments for anterior cruciate ligament reconstruction

Graft-host integration after the anterior cruciate ligament (ACL) reconstruction sequentially follows the prognosis from the inflammation period to the regeneration period. However, due to insufficient bioactivity, polyethylene terephthalate (PET) artificial ligaments often require a long period for graft-host integration. To improve graft-host integration, sequential therapy targeting multifactor is widely advocated. In this study, a multilayer regenerated silk fibroin (RSF) coating loaded with heparin and bone morphogenetic protein binding peptide (BBP) for differentiated release was introduced on the surface of the PET artificial ligament by a stepwise deposition method. The drug release profiles of heparin and BBP on the coated PET artificial ligament indicated the features of differential drug release, i.e., with heparin in the outermost layer releasing a significant amount (more than 60%) during the first 5 days while BBP in the inner layer only releasing a small amount (ca. 30%) within 1 week without burst release. Based on the isometric ACL reconstruction model of rabbits, such drug-loaded RSF coating was verified to be able to modulate the early inflammatory response and promote the maturation of the graft in the articular cavity, meanwhile, it provided a continuous and stable signal of osteogenic induction to improve graft-bone integration. Thus, sequential intervention with heparin and BBP proved to be a reliable combination, and multifunctional RSF-coated PET artificial ligaments hold great potential for improving the clinical efficacy of ACL reconstruction.

Anatomical acromioclavicular joint stabilization with chemically sterilized tendon allografts: A retrospective study

Background

The purpose of this retrospective study was to analyze whether chemically sterilized tendon allografts perform as well as other non-sterilized allografts and autografts as described in the literature for anatomical acromioclavicular joint stabilization for the treatment of Rockwood III-V. Allografts are still described as a factor for higher re-rupture rates.

Methods

Retrospective data were collected from 21 acromioclavicular joint stabilizations performed by a single surgeon and performed between 2011 and 2014 using sterilized semitendinosus allografts. The primary endpoints were re-rupture and complication rates. Secondary endpoints were AC-joint stability, pain level, return to work and sport and the range of motion.

Results

No re-ruptures occurred during the mean follow-up time of 33 months. Zero complications occurred directly after surgery, but three complications later than three weeks after surgery. All cases resolved without further surgery. After surgery, stability significantly improved for all patients. Post-surgery, 19 patients had stable acromioclavicular joints and only two patients showed minor instabilities. Range of motion returned to the range of the healthy shoulders for all patients.

Conclusion

Chemically sterilized semitendinosus allograft use for anatomic AC-joint stabilization is equivalent to the use of other allografts or autografts and required no hardware removal. No donor age or graft size dependence was observed, due to zero re-ruptures.

Constructing high-strength nano-micro fibrous woven scaffolds with native-like anisotropic structure and immunoregulatory function for tendon repair and regeneration

Tendon injuries are common debilitating musculoskeletal diseases with high treatment expenditure in sports medicine. The development of tendon-biomimetic scaffolds may be promising for improving the unsatisfactory clinical outcomes of traditional therapies. In this study, we combined an advanced electrospun nanofiber yarn-generating technique with a traditional textile manufacturing strategy to fabricate innovative nano-micro fibrous woven scaffolds with tendon-like anisotropic structure and high-strength mechanical properties for the treatment of large-size tendon injury. Electrospun nanofiber yarns made from pure poly L-lactic acid (PLLA) or silk fibroin (SF)/PLLA blend were fabricated, and their mechanical properties matched and even exceeded those of commercial PLLA microfiber yarns. The PLLA or SF/PLLA nanofiber yarns were then employed as weft yarns interlaced with commercial PLLA microfiber yarns as warp yarns to generate two new types of nanofibrous scaffolds (nmPLLA and nmSF/PLLA) with a plain-weaving structure. Woven scaffolds made from pure PLLA microfiber yarns (both weft and warp directions) (mmPLLA) were used as controls.In vitroexperiments showed that the nmSF/PLLA woven scaffold with aligned fibrous topography significantly promoted cell adhesion, elongation, proliferation, and phenotypic maintenance of tenocytes compared with mmPLLA and nmPLLA woven scaffolds. Moreover, the nmSF/PLLA woven scaffold exhibited the strongest immunoregulatory functions and effectively modulated macrophages towards the M2 phenotype.In vivoexperiments revealed that the nmSF/PLLA woven scaffold notably facilitated Achilles tendon regeneration with improved structure by macroscopic, histological, and ultrastructural observations six months after surgery, compared with the other two groups. More importantly, the regenerated tissue in the nmSF/PLLA group had excellent biomechanical properties comparable to those of the native tendon. Overall, our study provides an innovative biological-free strategy with ready-to-use features, which presents great potential for clinical translation for damaged tendon repair.

BMSC-derived exosomes promote tendon-bone healing after anterior cruciate ligament reconstruction by regulating M1/M2 macrophage polarization in rats

Background

Recent studies have shown that bone marrow stromal cell-derived exosomes (BMSC-Exos) can be used for tissue repair. However, whether the BMSC-Exos can promote tendon-bone healing after anterior cruciate ligament reconstruction (ACLR) is still unclear. In this study, we observed in vivo and in vitro the effect of rat BMSC-Exos on tendon-bone healing after ACLR and its possible mechanism.

Methods

Highly expressed miRNAs in rat BMSC-Exos were selected by bioinformatics and verified in vitro. The effect of overexpressed miRNA in BMSC-Exos on M2 macrophage polarization was observed. A rat model of ACLR was established. The experimental components were divided into three groups: the control group, the BMSC-Exos group, and the BMSC-Exos with miR-23a-3p overexpression (BMSC-Exos mimic) group. Biomechanical tests, micro-CT, and histological staining were performed for analysis.

Results

Bioinformatics analysis showed that miR-23a-3p was highly expressed in rat BMSC-Exos and could target interferon regulatory factor 1 (IRF1, a crucial regulator in M1 macrophage polarization). In vitro, compared with the control group or the BMSC-Exos group, the BMSC-Exos mimic more significantly promoted the polarization of macrophages from M1 to M2. In vivo, at 2 weeks, the number of M2 macrophages in the early local stage of ACLR was significantly increased in the BMSC-Exos mimic group; at 4 and 8 weeks, compared with the control group or the BMSC-Exos group, the bone tunnels of the tibia and femur sides of the rats in the BMSC-Exos mimic group were significantly smaller, the interface between the graft and the bone was narrowed, the bone volume/total volume ratio (BV/TV) increased, the collagen type II alpha 1 level increased, and the mechanical strength increased.

Conclusions

BMSC-Exos promoted M1 macrophage to M2 macrophage polarization via miR-23a-3p, reduced the early inflammatory reaction at the tendon-bone interface, and promoted early healing after ACLR.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13287-022-02975-0.

A regeneration process-matching scaffold with appropriate dynamic mechanical properties and spatial adaptability for ligament reconstruction

Ligament regeneration is a complicated process that requires dynamic mechanical properties and allowable space to regulate collagen remodeling. Poor strength and limited space of currently available grafts hinder tissue regeneration, yielding a disappointing success rate in ligament reconstruction. Matching the scaffold retreat rate with the mechanical and spatial properties of the regeneration process remains challenging. Herein, a scaffold matching the regeneration process was designed via regulating the trajectories of fibers with different degradation rates to provide dynamic mechanical properties and spatial adaptability for collagen infiltration. This core-shell structured scaffold exhibited biomimetic fiber orientation, having tri-phasic mechanical behavior and excellent strength. Besides, by the sequential material degradation, the available space of the scaffold increased from day 6 and remained stable on day 24, consistent with the proliferation and deposition phase of the native ligament regeneration process. Furthermore, mature collagen infiltration and increased bone integration in vivo confirmed the promotion of tissue regeneration by the adaptive space, maintaining an excellent failure load of 67.65% of the native ligament at 16 weeks. This study proved the synergistic effects of dynamic strength and adaptive space. The scaffold matching the regeneration process is expected to open new approaches in ligament reconstruction.

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Regeneration process-matching scaffold was made via regulating fiber trajectory.

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The scaffold showed tri-phasic mechanical behavior and fatigue properties.

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Matching repair process with dynamic mechanical property and spatial adaptability.

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A feasible substitute for the T/L reconstruction by spatial adaptability.

Effects of bioactive strontium-substituted hydroxyapatite on osseointegration of polyethylene terephthalate artificial ligaments

The insufficient bioactivity of polyethylene terephthalate (PET) artificial ligaments severely weakens the ligament-bone healing in anterior cruciate ligament (ACL) reconstruction, while osteogenic modification is a prevailing method to enhance osseointegration of PET artificial ligaments. In the present study, strontium-substituted hydroxyapatite (SrHA) nanoparticles with different strontium (Sr) contents were synthesized via microwave-hydrothermal method and subsequently were coated on the surface of PET artificial ligaments. The results of XRD, FT-IR, TEM and ICP-OES revealed that the doping of Sr ions had no great influences on the phase composition, morphology and particle size of HA, but affected its chemical compositions and crystallinity. The SEM images showed that nanoparticles were successfully deposited on the surface of PET grafts, the surface hydrophilicity of which was significantly improved by the prepared coatings. The in vitro study revealed that the osteogenic activity of rat bone marrow mesenchymal stem cells (rBMSCs) was affected by varying concentrations of Sr ions in coatings and the optimal osteogenic differentiation was observed in the 2SrHA-PET group, which significantly up-regulated the expression of BMP-2, OCN, Col-I and VEGF. The enhanced osteogenic ability of the 2SrHA-PET group was further demonstrated through an in vivo study, which obviously promoted ligament-bone integration compared with that of PET and HA-PET groups, thus improving the biomechanical strength of the graft-bone complex. This study confirms that SrHA coatings can facilitate osseointegration in the repair of ligament injury in rabbits and thus offers a prospective method for ACL reconstruction by using Sr-containing biomaterial-modified PET artificial ligaments.

Tendon-bioinspired wavy nanofibrous scaffolds provide tunable anisotropy and promote tenogenesis for tendon tissue engineering

The development of tendon-biomimetic nanofibrous scaffolds with mesenchymal stem cells may represent a promising strategy to improve the unsatisfactory outcomes of traditional treatments in tendon repair. In the present study, the nanofibrous scaffolds comprised of poly(p-dioxanone) (PPDO) and silk fibroin (SF) composites were fabricated by using electrospinning technique and subsequent thermal ethanol treatment. The PPDO/SF composite scaffolds presented parallel fiber arrangement with crimped features and nonlinear mechanical properties, which mimic the structure-function relationship of native tendon tissue mechanics. We demonstrated that the fiber crimp degree and mechanical properties of as-prepared PPDO/SF wavy nanofibrous scaffolds (WNSs) could be tunable by adjusting the mass ratio of PPDO/SF. The biological tests revealed that the addition of SF obviously promoted the cell adhesion, proliferation, and phenotypic maintenance of human tenocytes on the WNSs. A preliminary study on the subcutaneous implantation showed that the PPDO/SF WNSs notably decreased the inflammatory response compared with pure PPDO WNSs. More importantly, a combination of growth factor induction and mechanical stimulation was found to notably enhance the tenogenic differentiation of human adipose derived mesenchymal stem cells on the PPDO/SF WNSs by upregulating the expressions of tendon-associated protein and gene markers. Overall, this study demonstrated that our PPDO/SF WNSs could provide a beneficial microenvironment for various cell activities, making them an attractive candidate for tendon tissue engineering research.

Acceleration of ligamentization and osseointegration processes after anterior cruciate ligament reconstruction with autologous tissue-engineered polyethylene terephthalate graft

Background

Despite the advantages of excellent mechanical properties for rapid return to sports and early rehabilitation after anterior cruciate ligament (ACL) reconstruction with polyethylene terephthalate (PET) artificial ligament, the graft failure rate during long-term follow-up is relatively high due to poor graft-host incorporation. The purpose of the present study was to investigate the effect of autologous tissue-engineered PET (ATE-PET) grafts on osseointegration and ligamentization after ACL reconstruction.

Methods

Forty-eight New Zealand white rabbits were randomly divided into PET group (n=24) and ATE-PET group (n=24). In the ATE-PET group, the rabbits initially underwent subcutaneous implantation of the PET ligament. Two weeks later, unilateral ipsilateral ACL reconstruction was performed using an ATE-PET graft. In the PET group, the rabbits underwent ACL reconstruction using PET grafts as controls. Macroscopic observation, micro-computed tomography, histological and immunofluorescent staining, and biomechanical tests were conducted to evaluate the effects at 4 and 12 weeks postoperatively.

Results

The ATE-PET graft was highly pre-vascularized with myofibroblast aggregation after two weeks of subcutaneous implantation. With regard to the intraosseous part of the graft, the ATE-PET group had significantly higher bone mineral density and bone volume/total volume ratio at 12 weeks. Histologically, the width of the interface between the graft and bone was smaller. Regarding the intra-articular part, thicker tissue coverage with a glossy appearance was observed in the ATE-PET group at 12 weeks on macroscopic observation. Histological staining also showed more collagen fibers grew in the grafts with fewer inflammatory reactions of the ATE-PET group at both 4 and 12 weeks. Immunofluorescently, both α-SMA-positive vessels and α-SMA-positive myofibroblasts were found to be significantly greater around the graft in the ATE-PET group at 4 weeks and markedly declined at 12 weeks. Moreover, the ATE-PET group presented significantly greater failure load and stiffness than the PET group at 12 weeks (53.7±5.4 vs. 42.5±4.5 N, P<0.01; 12.9±3.0 vs. 9.8±1.3 N/mm, P=0.04).

Conclusions

The ATE-PET artificial ligament with pre-vascularization and myofibroblast aggregation could effectively accelerate intra-articular graft ligamentization and intraosseous graft osseointegration, thus enhancing the biomechanical properties after ACL reconstruction in a rabbit model.

Preparation and Properties of Antibacterial Polydopamine and Nano-Hydroxyapatite Modified Polyethylene Terephthalate Artificial Ligament

Due to its great biomechanical property, the polyethylene terephthalate (PET) artificial ligament has become one of the most promising allografts for anterior cruciate ligament (ACL) reconstruction. However, because of its chemical and biological inertness, PET is not a favored scaffold material for osteoblast growth, which promotes the ligament-bone healing. Meanwhile, in consideration of prevention of potential infection, the prophylactic injection of antibiotic was used as a post-operative standard procedure but also has the increasing risk of bacterial resistance. To face these two contradictions, in this article we coated a polydopamine (PDA) nano-layer on the PET ligament and used the coating as the adhesion interlayer to introduce nano-hydroxyapatite (nHA) and silver atoms to the surface of PET ligament. Because of the mild self-polymerization reaction of dopamine, the thermogravity analysis (TGA), Raman spectrum, and tensile test results show that the modification procedure have no negative effects on the chemical stability and mechanical properties of the PET. The results of NIH3T3 cell culture show that the PDA and nHA could effectively improve the biocompatibility of PET artificial ligament for fibroblast growth, and staphylococcus aureus antibacterial test results show that the Ag atom provided an antibacterial effect for PET ligament. As shown in this paper, the nano-PDA coating modification procedure could not only preserve the advantages of PET but also introduce new performance characteristics to PET, which opens the door for further functionalization of PET artificial ligament for its advanced development and application.

Natural Biomineralization-Inspired Magnesium Silicate Composite Coating Upregulates Osteogenesis, Enabling Strong Anterior Cruciate Ligament Graft-Bone Healing In Vivo

Artificial ligaments prepared from polyethylene terephthalate (PET) are widely accepted for clinical anterior cruciate ligament (ACL) reconstruction to recover the native function of knee joints. However, due to the chemical inertness and hydrophobicity of PET, improving its bioactivity and promoting graft-bone integration are still great challenges. Inspired by the natural biomineralization process on the surface of a historical stone, in this study, a bioactive organic/inorganic composite coating that is composed of poly(allylamine hydrochloride) and chondroitin sulfate with magnesium silicate (MgSiO₃) doping is developed for surface modification of PET (MSPC-PET). This composite coating promotes adhesion and proliferation of bone marrow mesenchymal stem cells (BMSCs) and its bioactive inorganic components (MgSiO₃) could induce osteogenic differentiation of BMSCs. Furthermore, an in vivo experiment indicated that this composite coating might afford superior graft-bone integration between MSPC-PET and the host bone tunnel, and fibrous scar tissue formation was also inhibited. More importantly, a biomechanical analysis proved that there was a strong integration between the MSPC-PET graft and the bone tunnel, which will improve biomechanical properties for the restoration of ACL function. This study shows that this bioactive composite coating-modified PET graft for the ACL reconstruction can effectively achieve good integration of ACL artificial grafts and bone tunnels and prevent surgical failure.

An Autograft for Anterior Cruciate Ligament Reconstruction Results in Better Biomechanical Performance and Tendon-Bone Incorporation Than Does a Hybrid Graft in a Rat Model

BACKGROUND

The biomechanical and tendon-bone incorporation properties of allograft-augmented hybrid grafts for anterior cruciate ligament (ACL) reconstruction compared with traditional autografts are unknown.

HYPOTHESIS

Using an autograft for ACL reconstruction yields better results on biomechanical testing, radiographic analysis, and histological evaluation versus using a hybrid graft.

STUDY DESIGN

Controlled laboratory study.

METHODS

A total of 66 adult male Sprague Dawley rats underwent unilateral ACL reconstruction with an autograft (AT group; n = 33) or a hybrid graft (HB group; n = 33). The grafts used in both groups were harvested from the peroneus longus tendon and were fixed by suturing to the surrounding periosteum. Samples were harvested for biomechanical testing, micro-computed tomography (CT), and histological evaluation at 4, 8, and 12 weeks postoperatively. Bone tunnels on the femoral and tibial sides were divided into 3 subregions: intra-articular (IA), midtunnel (MT), and extra-articular (EA). A cylinder-like volume of interest in the bone tunnel and a tubular-like volume of interest around the bone tunnel were used to evaluate new bone formation and bone remodeling, respectively, via micro-CT.

RESULTS

In the AT group, there were significantly higher failure loads and stiffness at 8 weeks (failure load: 3.04 ± 0.40 vs 2.09 ± 0.54 N, respectively; P = .006) (stiffness: 3.43 ± 0.56 vs 1.75 ± 0.52 N/mm, respectively; P < .001) and 12 weeks (failure load: 9.10 ± 1.13 vs 7.14 ± 0.94 N, respectively; P = .008) (stiffness: 4.45 ± 0.75 vs 3.36 ± 0.29 N/mm, respectively; P = .008) than in the HB group. With regard to new bone formation in the bone tunnel, in the AT group, the bone volume/total volume (BV/TV) was significantly higher than in the HB group on the tibial side at 8 weeks (IA: 22.21 ± 4.98 vs 5.16 ± 3.98, respectively; P < .001) (EA: 19.66 ± 7.19 vs 10.85 ± 2.16, respectively; P = .030) and 12 weeks (IA: 30.50 ± 5.04 vs 17.11 ± 7.31, respectively; P = .010) (MT: 21.15 ± 2.58 vs 15.55 ± 4.48, respectively; P = .041) (EA: 20.75 ± 3.87 vs 10.64 ± 3.94, respectively; P = .003). With regard to bone remodeling around the tunnel, the BV/TV was also significantly higher on the tibial side at 8 weeks (MT: 33.17 ± 8.05 vs 15.21 ± 7.60, respectively; P = .007) (EA: 25.19 ± 6.38 vs 13.94 ± 7.10, respectively; P = .030) and 12 weeks (IA: 69.46 ± 4.45 vs 47.80 ± 6.16, respectively; P < .001) (MT: 33.15 ± 3.88 vs 13.76 ± 4.07, respectively; P < .001) in the AT group than in the HB group. Sharpey-like fibers had formed at 8 weeks in the AT group. A large number of fibroblasts withdrew at 12 weeks. In the AT group, the width of the interface was significantly narrower at 4 weeks (85.86 ± 17.49 vs 182.97 ± 14.35 μm, respectively; P < .001), 8 weeks (58.86 ± 10.99 vs 90.15 ± 11.53 μm, respectively; P = .002), and 12 weeks (42.70 ± 7.96 vs 67.29 ± 6.55 μm, respectively; P = .001) than in the HB group.

CONCLUSION

Using an autograft for ACL reconstruction may result in improved biomechanical properties and tendon-bone incorporation compared with a hybrid graft.

CLINICAL RELEVANCE

Augmenting small autografts with allograft tissue may result in decreased biomechanical performance and worse tendon-bone incorporation, increasing the risk of graft failure.

Controlled Cryogelation and Catalytic Cross-Linking Yields Highly Elastic and Robust Silk Fibroin Scaffolds

Silk biomaterials with tunable mechanical properties and biological properties are of special importance for tissue engineering. Here, we fabricated silk fibroin (SF, from Bombyx mori silk) scaffolds from cryogelation under controlled temperature and catalytic cross-linking conditions. Structurally, the cryogelled scaffolds demonstrated a greater β-sheet content but significantly smaller β-sheet domains compared to that without chemical cross-linking and catalyst. Mechanically, the cryogelled scaffolds were softer and highly elastic under tension and compression. The 120% tensile elongation and >85% recoverable compressive strain were among the best properties reported for SF scaffolds. Cyclic compression tests proved the robustness of such scaffolds to resist fatigue. The mechanical properties, as well as the degradation rate of the scaffolds, can be fine-tuned by varying the concentrations of the catalyst and the cross-linker. For biological responses, in vitro rat bone mesenchymal stem cell (rBMSC) culture studies demonstrated that cryogelled SF scaffolds supported better cell attachment and proliferation than the routine freeze-thawed scaffolds. The in vivo subcutaneous implantation results showed excellent histocompatibility and tissue ingrowth for the cryogelled SF scaffolds. This straightforward approach of enhanced elasticity of SF scaffolds and fine-tunability in mechanical performances, suggests a promising strategy to develop novel SF biomaterials for soft tissue engineering and regenerative medicine.

Artificial ligament made from silk protein/Laponite hybrid fibers

With developments in tissue engineering, artificial ligaments are expected to be future materials for anterior cruciate ligament (ACL) reconstruction. However, poor healing of the intraosseous part after ACL reconstruction significantly hinders their applications in this field. In this study, a bioactive clay Laponite (LAP) was introduced into the regenerated silk fibroin (RSF) spinning dope to produce functional RSF/LAP hybrid fibers by wet-spinning. These RSF/LAP hybrid fibers were then woven into artificial ligament for ACL reconstruction. The structure and mechanical properties of RSF/LAP hybrid fibers were extensively studied by different means. Results confirmed the presence of LAP in RSF fibers and revealed that the addition of LAP slightly deteriorated the comprehensive mechanical properties of RSF fibers. However, they were still much tougher (with higher breaking energy) than those of degummed natural silkworm silk that was earlier used for making artificial ligament. The artificial ligament woven from RSF/LAP hybrid fibers showed better cytocompatibility and osteogenic differentiation with mouse pre-osteoblasts in vitro than those made from degummed natural silkworm silks and pure RSF fibers. Furthermore, in vivo study in a rat ACL reconstruction model demonstrated that the presence of LAP in the artificial ligament could significantly enhance the graft osseointegration process and also improve the corresponding biomechanical properties of the artificial ligament. Based upon these results, the RSF/LAP hybrid fibers, which can be mass produced by wet-spinning process, are believed to have a great potential for use as artificial ligament materials for ACL reconstruction. STATEMENT OF SIGNIFICANCE: In this study, we successfully introduced Laponite (LAP), a kind of clay that has the function of osteogenic induction, into regenerated silk fibroin (RSF) fibers, which was prepared by a mature wet-spinning method developed in our lab. We believe that through artificial spinning, additional functional components can be added into RSF fibers, which one can hardly achieve with natural silks. We showed that the artificial ligament woven from RSF/LAP hybrid fibers had better cytocompatibility and osteogenic differentiation for mouse pre-osteoblasts in vitro, and significantly enhanced the graft osseointegration process and improved the corresponding biomechanical properties in a rat ACL reconstruction model in vivo, compared to those artificial ligaments made from degummed natural silkworm silks and pure RSF fibers.

A novel knitted scaffold made of microfiber/nanofiber core–sheath yarns for tendon tissue engineering

PCL-SF/PLCL microfiber/nanofiber yarns with core-sheath architecture were fabricated and knitted into a 3D scaffold for tendon tissue engineering.

Stem Cell-Conditioned Medium Promotes Graft Remodeling of Midsubstance and Intratunnel Incorporation After Anterior Cruciate Ligament Reconstruction in a Rat Model

BACKGROUND

Stem cell-conditioned medium (CM) has been increasingly used in regenerative medicine. However, its effect on graft-host integration after anterior cruciate ligament (ACL) reconstruction (ACLR) remains unclear.

PURPOSE

To examine the effect of human bone marrow stem cell (hBMSC)-CM on graft-bone integration and graft midsubstance ligamentization in a rat model of ACLR.

STUDY DESIGN

Controlled laboratory study.

METHODS

CM was obtained from the supernatant of commercially available hBMSCs in serum-free Dulbecco's modified Eagle medium (DMEM). In a rat model of an ACL injury, isometric ACLR was performed. Three groups were established: CM injection group (CM; n = 40), control injection group (CI; n = 40) with serum-free DMEM injections, and no injection group (NI; n = 40). An intra-articular injection was performed weekly. Micro-computed tomography was conducted at 2, 4, and 8 weeks postoperatively. Histological and biomechanical analyses were conducted at 4 and 8 weeks postoperatively. The NIH3T3 fibroblast was utilized as a model in vitro to examine the effect of CM using the cell counting kit-8 (CCK-8) assay and immunofluorescence staining of Ki-67, α-smooth muscle actin (α-SMA), and collagen 1 (Col 1).

RESULTS

At 4 and 8 weeks, the femoral and tibial bone tunnel areas as well as the interface between the graft and host bone were smaller, while the bone volume/total volume ratio was higher, in the CM group. Sharpey-like fibers formed at 8 weeks in the CM group. At 4 and 8 weeks, more Col 1 was noticed in the CM group than in the NI group (both P < .001) or CI group (both P < .001). Immunohistochemically, the α-SMA-positive area was up-regulated at the graft-bone interface at 4 weeks (P < .001) and declined at 8 weeks (P < .001) in the CM group compared with the other 2 groups. At the midsubstance, α-SMA expression decreased from 4 to 8 weeks in all groups and was significantly lower in the CM group than in the NI group (P < .01) or CI group (P < .05) at 8 weeks. The CCK-8 assay showed that CM increased NIH3T3 viability (P < .001) and the level of Ki-67 (P < .05), α-SMA (P < .001), and Col 1 (P < .001) in CM-educated NIH3T3 cells.

CONCLUSION

hBMSC-CM accelerates graft-bone incorporation and midsubstance ligamentization and enhances the proliferation, differentiation, and collagen synthesis of fibroblasts.

CLINICAL RELEVANCE

Graft-host integration is essential after ACLR. The current study identified a novel agent, that is, hBMSC-CM, as a candidate for promoting integration.

The regenerated silk fibroin hydrogel with designed architecture bioprinted by its microhydrogel

The regenerated silk fibroin microhydrogel with thixotropic property could be bioprinted and then ripened to a tough hydrogel because of the change in “the second network” of the microhydrogel.