PLDLA/PCL-T Scaffold for Meniscus Tissue Engineering

Meniscal repair with additive manufacture of bioresorbable polymer: From physicochemical characterization to implantation of 3D printed poly (L-co-D, L lactide-co-trimethylene carbonate) with autologous stem cells in rabbits

Three-dimensional (3D) structures are actually the state-of-the-art technique to create porous scaffolds for tissue engineering. Since regeneration in cartilage tissue is limited due to intrinsic cellular properties this study aims to develop and characterize three-dimensional porous scaffolds of poly (L-co-D, L lactide-co-trimethylene carbonate), PLDLA-TMC, obtained by 3D fiber deposition technique. The PLDLA-TMC terpolymer scaffolds (70:30), were obtained and characterized by scanning electron microscopy, gel permeation chromatography, differential scanning calorimetry, thermal gravimetric analysis, compression mechanical testing and study on in vitro degradation, which showed its amorphous characteristics, cylindrical geometry, and interconnected pores. The in vitro degradation study showed significant loss of mechanical properties compatible with a decrease in molar mass, accompanied by changes in morphology. The histocompatibility association of mesenchymal stem cells from rabbit's bone marrow, and PLDLA-TMC scaffolds, were evaluated in the meniscus regeneration, proving the potential of cell culture at in vivo tissue regeneration. Nine New Zealand rabbits underwent total medial meniscectomy, yielding three treatments: implantation of the seeded PLDLA-TMC scaffold, implantation of the unseeded PLDLA-TMC and negative control (defect without any implant). After 24 weeks, the results revealed the presence of fibrocartilage in the animals treated with polymer. However, the regeneration obtained with the seeded PLDLA-TMC scaffolds with mesenchymal stem cells had become intimal to mature fibrocartilaginous tissue of normal meniscus both macroscopically and histologically. This study demonstrated the effectiveness of the PLDLA-TMC scaffold in meniscus regeneration and the potential of mesenchymal stem cells in tissue engineering, without the use of growth factors. It is concluded that bioresorbable polymers represent a promising alternative for tissue regeneration.

Current advances in engineering meniscal tissues: insights into 3D printing, injectable hydrogels and physical stimulation based strategies

The knee meniscus is the cushioning fibro-cartilage tissue present in between the femoral condyles and tibial plateau of the knee joint. It is largely avascular in nature and suffers from a wide range of tears and injuries caused by accidents, trauma, active lifestyle of the populace and old age of individuals. Healing of the meniscus is especially difficult due to its avascularity and hence requires invasive arthroscopic approaches such as surgical resection, suturing or implantation. Though various tissue engineering approaches are proposed for the treatment of meniscus tears, three-dimensional (3D) printing/bioprinting, injectable hydrogels and physical stimulation involving modalities are gaining forefront in the past decade. A plethora of new printing approaches such as direct light photopolymerization and volumetric printing, injectable biomaterials loaded with growth factors and physical stimulation such as low-intensity ultrasound approaches are being added to the treatment portfolio along with the contemporary tear mitigation measures. This review discusses on the necessary design considerations, approaches for 3D modeling and design practices for meniscal tear treatments within the scope of tissue engineering and regeneration. Also, the suitable materials, cell sources, growth factors, fixation and lubrication strategies, mechanical stimulation approaches, 3D printing strategies and injectable hydrogels for meniscal tear management have been elaborated. We have also summarized potential technologies and the potential framework that could be the herald of the future of meniscus tissue engineering and repair approaches.

Preclinical Studies and Clinical Trials on Cell-Based Treatments for Meniscus Regeneration

This study aims at performing a thorough review of cell-based treatment strategies for meniscus regeneration in preclinical and clinical studies. The PubMed, Embase, and Web of Science databases were searched for relevant studies (both preclinical and clinical) published from the time of database construction to December 2022. Data related to cell-based therapies for in situ regeneration of the meniscus were extracted independently by two researchers. Assessment of risk of bias was performed according to the Cochrane Handbook for Systematic Reviews of Interventions. Statistical analyses based on the classification of different treatment strategies were performed. A total of 5730 articles were retrieved, of which 72 preclinical studies and 6 clinical studies were included in this review. Mesenchymal stem cells (MSCs), especially bone marrow MSCs (BMSCs), were the most commonly used cell type. Among preclinical studies, rabbit was the most commonly used animal species, partial meniscectomy was the most commonly adopted injury pattern, and 12 weeks was the most frequently chosen final time point for assessing repair outcomes. A range of natural and synthetic materials were used to aid cell delivery as scaffolds, hydrogels, or other morphologies. In clinical trials, there was large variation in the dose of cells, ranging from 16 × 106 to 150 × 106 cells with an average of 41.52 × 106 cells. The selection of treatment strategy for meniscus repair should be based on the nature of the injury. Cell-based therapies incorporating various "combination" strategies such as co-culture, composite materials, and extra stimulation may offer greater promise than single strategies for effective meniscal tissue regeneration, restoring natural meniscal anisotropy, and eventually achieving clinical translation. Impact Statement This review provides an up-to-date and comprehensive overview of preclinical and clinical studies that tested cell-based treatments for meniscus regeneration. It presents novel perspectives on studies published in the past 30 years, giving consideration to the cell sources and dose selection, delivery methods, extra stimulation, animal models and injury patterns, timing of outcome assessment, and histological and biomechanical outcomes, as well as a summary of findings for individual studies. These unique insights will help to shape future research on the repair of meniscus lesions and inform the clinical translation of new cell-based tissue engineering strategies.

Reconstruction of Fibrocartilage with Fibrous Alignment of Type I Collagen in Scaffold-Free Manner

For functional reconstruction of fibrocartilage, it is necessary to reproduce the essential mechanical property exhibited by natural fibrocartilage. The distinctive mechanical property of fibrocartilage is originated from the specific histological features of fibrocartilage composed of highly aligned type I collagen (Col I) and an abundant cartilaginous matrix. While the application of tensile stimulation induces highly aligned Col I, our study reveals that it also exerts an antichondrogenic effect on scaffold-free tissues constructed with meniscal chondrocytes (MCs) and induces downregulation of Sox-9 expression and attenuated glycosaminoglycan production. Modulation of mechanotransduction by blocking nuclear translocation of Yes-associated protein (YAP) ameliorated the antichondrogenic effect in the presence of tensile stimulation. Since MCs subjected to mechanical doses either by surface stiffness or tensile stimulation showed reversibility of YAP status even after a long-term exposure to mechanotransduction, fibrocartilage tissue was constructed by sequentially inducing tissue alignment by tensile stimulation followed by inducing cartilaginous matrix production in a tension-released state. The minimal tensile dose to constitute durable tissue alignment was screened by investigating the alignment of cytoskeleton and Col I after culturing the scaffold-free tissue constructs with various tensile doses (10% static tension for 1, 3, 7, and 10 days) followed by maintaining in a released state for 5 days. Fluorescence-conjugated phalloidin binding and immunofluorescence of Col I indicated that the duration of static tension for more than 7 days resulted in durable tissue alignment for at least 5 days in the tension-released state. The tissues subjected to tensile stimulation for 7 days followed by 14 days in a released state in chondrogenic media resulted in abundant cartilaginous matrix as well as uniaxial anisotropic alignment. Our results show that the optimized tensile dose can facilitate the successful reconstruction of fibrocartilage by modulating the characteristics of matrix production by MCs.

Repairing Avascular Meniscal Lesions by Recruiting Endogenous Targeted Cells Through Bispecific Synovial-Meniscal Aptamers

BACKGROUND

Tissue engineering is a promising treatment option for meniscal lesions in the avascular area, but a favorable cell source and its utilization in tissue-engineered menisci remain uncertain. Therefore, a more controllable and convenient method for cell recruitment is required.

HYPOTHESIS

Circular bispecific synovial-meniscal (S-M) aptamers with a gelatin methacryloyl (GelMA) hydrogel can recruit endogenous synovial and meniscal cells to the site of the defect, thereby promoting in situ meniscal regeneration and chondroprotection.

STUDY DESIGN

Controlled laboratory study.

METHODS

Synovial and meniscal aptamers were filtered through systematic evolution of ligands by exponential enrichment (SELEX) and cross-linked to synthesize the S-M aptamer. A GelMA-aptamer system was constructed. An in vitro analysis of the bi-recruitment of synovial and meniscal cells was performed, and the migration and proliferation of the GelMA-aptamer hydrogel were also tested. For the in vivo assay, rabbits (n = 90) with meniscal defects in the avascular zone were divided into 3 groups: repair with the GelMA-aptamer hydrogel (GelMA-aptamer group), repair with the GelMA hydrogel (GelMA group), and no repair (blank group). Regeneration of the repaired meniscus and degeneration of the cartilage were assessed by gross and histological evaluations at 4, 8, and 12 weeks postoperatively. The mechanical properties of repaired menisci were also evaluated.

RESULTS

In vitro synovial and meniscal cells were recruited simultaneously by the S-M aptamer with high affiliation and specificity. The GelMA-aptamer hydrogel promoted the migration of targeted cells. Compared with the other groups, the GelMA-aptamer group showed enhanced fibrocartilaginous regeneration, lower cartilage degeneration, and better mechanical strength at 12 weeks after meniscal repair.

CONCLUSION/CLINICAL RELEVANCE

Bispecific S-M aptamers could be used for avascular meniscal repair by recruiting endogenous synovial and meniscal cells and promoting fibrocartilaginous regeneration.

Applications and prospects of different functional hydrogels in meniscus repair

The meniscus is a kind of fibrous cartilage structure that serves as a cushion in the knee joint to alleviate the mechanical load. It is commonly injured, but it cannot heal spontaneously. Traditional meniscectomy is not currently recommended as this treatment tends to cause osteoarthritis. Due to their good biocompatibility and versatile regulation, hydrogels are emerging biomaterials in tissue engineering. Hydrogels are excellent candidates in meniscus rehabilitation and regeneration because they are fine-tunable, easily modified, and capable of delivering exogenous drugs, cells, proteins, and cytokines. Various hydrogels have been reported to work well in meniscus-damaged animals, but few hydrogels are effective in the clinic, indicating that hydrogels possess many overlooked problems. In this review, we summarize the applications and problems of hydrogels in extrinsic substance delivery, meniscus rehabilitation, and meniscus regeneration. This study will provide theoretical guidance for new therapeutic strategies for meniscus repair.

Breast Tissue Restoration after the Partial Mastectomy Using Polycaprolactone Scaffold

As breast conserving surgery increases in the surgical treatment of breast cancer, partial mastectomy is also increasing. Polycaprolactone (PCL) is a polymer that is used as an artifact in various parts of the human body based on the biocompatibility and mechanical properties of PCL. Here, we hypothesized that a PCL scaffold can be utilized for the restoration of breast tissue after a partial mastectomy. To demonstrate the hypothesis, a PCL scaffold was fabricated by 3D printing and three types of spherical PCL scaffold including PCL scaffold, PCL scaffold with collagen, and the PCL scaffold with breast tissue fragment were implanted in the rat breast defect model. After 6 months of implantation, the restoration of breast tissue was observed in the PCL scaffold and the expression of collagen in the PCL scaffold with collagen was seen. The expression of TNF-α was significantly increased in the PCL scaffold, but the expression of IL-6 showed no significant difference in all groups. Through this, it showed the possibility of using it as a method to conveniently repair tissue defects after partial mastectomy of the human body.

Treatment strategies for meniscal lesions: from past to prospective therapeutics

Menisci play an important role in the biomechanics of knee joint function, including loading transmission, joint lubrication, prevention of soft tissue impingement during motion and joint stability. Meniscal repair presents a challenge due to a lack of vascularization that limits the healing capacity of meniscal tissue. In this review, the authors aimed to untangle the available treatment options for repairing meniscal tears. Various surgical procedures have been developed to treat meniscal tears; however, clinical outcomes are limited. Consequently, numerous researchers have focused on different treatments such as the application of exogenous and/or autologous growth factors, scaffolds including tissue-derived matrix, cell-based therapy and miRNA-210. The authors present current and prospective treatment strategies for meniscal lesions.

Bioinspired Protein/Peptide Loaded 3D Printed PLGA Scaffold Promotes Bone Regeneration

Background: This study was aimed to investigate the effect of three dimensional (3D)printed poly lactide-co-glycolide (PLGA) scaffolds combined with Gly-Phe-Hyp-Gly-Arg (GFOGER) and bone morphogenetic protein 9 (BMP-9) on the repair of large bone defects.

Methods: 3D printing method was used to produce PLGA scaffolds, and the sample was viewed by both optical microscopy and SEM, XRD analysis, water absorption and compressive strength analysis, etc. The rabbits were divided into six groups randomly and bone defect models were constructed (6 mm in diameter and 9 mm in depth): control group (n = 2), sham group (n = 4), model group (n = 4) and model + scaffold group (n = 4 rabbits for each group, 0%,2% and 4%). The rabbits were sacrificed at the 4th and 12th weeks after surgery, and the samples were collected for quantitative analysis of new bone mineral density by micro-CT, histopathological observation, immunohistochemistry and Western blot to detect the protein expression of osteoblast-related genes.

Results: This scaffold presented acceptable mechanical properties and slower degradation rates. After surface modification with GFOGER peptide and BMP-9, the scaffold demonstrated enhanced new bone mineral deposition and density over the course of a 12 week in vivo study. Histological analysis and WB confirmed that this scaffold up-regulated the expression of Runx7, OCN, COL-1 and SP7, contributing to the noted uniform trabeculae formation and new bone regeneration.

Conclusions: The application of this strategy in the manufacture of composite scaffolds provided extensive guidance for the application of bone tissue engineering.

Effects of low-intensity pulsed ultrasound stimulation on cell seeded 3D hybrid scaffold as a novel strategy for meniscus regeneration: An in vitro study

Menisci are fibrocartilaginous structures in the knee joint with an inadequate regenerative capacity, which causes low healing potential and further leads to osteoarthritis. Recently, three-dimensional (3D) printing techniques and ultrasound treatment have gained plenty of attention for meniscus tissue engineering. The present study investigates the effectiveness of low-intensity pulsed ultrasound stimulations (LIPUS) on the proliferation, viability, morphology, and gene expression of the chondrocytes seeded on 3D printed polyurethane scaffolds dip-coated with gellan gum, hyaluronic acid, and glucosamine. LIPUS stimulation was performed at 100, 200, and 300 mW/cm² intensities for 20 min/day. A faster gap closure (78.08 ± 2.56%) in the migration scratch assay was observed in the 200 mW/cm² group after 24 h. Also, inverted microscopic and scanning electron microscopic images showed no cell morphology changes during LIPUS exposure at different intensities. The 3D cultured chondrocytes under LIPUS treatment revealed a promotion in cell proliferation rate and viability as the intensity doses increased. Additionally, LIPUS could stimulate chondrocytes to overexpress the aggrecan and collagen II genes and improve their chondrogenic phenotype. This study recommends that the combination of LIPUS treatment and 3D hybrid scaffolds can be considered as a valuable treatment for meniscus regeneration based on our in vitro data.

Meniscus Regeneration With Multipotent Stromal Cell Therapies

Meniscus is a semilunar wedge-shaped structure with fibrocartilaginous tissue, which plays an essential role in preventing the deterioration and degeneration of articular cartilage. Lesions or degenerations of it can lead to the change of biomechanical properties in the joints, which ultimately accelerate the degeneration of articular cartilage. Even with the manual intervention, lesions in the avascular region are difficult to be healed. Recent development in regenerative medicine of multipotent stromal cells (MSCs) has been investigated for the significant therapeutic potential in the repair of meniscal injuries. In this review, we provide a summary of the sources of MSCs involved in repairing and regenerative techniques, as well as the discussion of the avenues to utilizing these cells in MSC therapies. Finally, current progress on biomaterial implants was reviewed.

A Versatile Surgical Method for Studying Meniscus Implantation in a Rabbit Model

Meniscus injury is a health problem that greatly affects people's quality of life. In recent years, the number of diagnosed meniscus injury is increasing year by year. If not treated in time and correctly, it causes severe damages to the cartilage. Owing to the meniscus' limited healing ability, synthetic/tissue-engineered meniscus has emerged as a new treatment modality in recent years. Rabbit models, which have been proved to be a feasible animal model, have been extensively used to study meniscus implantation. However, there is not a unified and minimally invasive surgical method for meniscus implantation in rabbits, and the current surgical methods have unsolved problems, such as long incisions, patella valgus, and cutting of the medial collateral ligament. Therefore, the goal of this study is to provide a minimally invasive and versatile meniscus implantation method. Compared with the control group, our study showed less trauma to the animal model, and we believe that it has the application significance on tissue-engineered meniscus implantation. Impact statement Meniscal injury is a central area of sports medicine research because of the high and increasing global rate. With its profound potential implications for patients' functions and the subsequent development of arthritis, there is a great need for the synthetic/tissue-engineered menisci. Animal meniscus implantation models allow studying meniscus implantation with synthetic/tissue-engineered meniscus, and the rabbit model is a gold method for meniscus implantation in the laboratory. However, there has not yet been a minimally invasive and versatile surgical technique describing this surgery method. This article, therefore, provides a detailed description of the rabbit meniscus implantation method, including step-by-step surgical instructions and accompanying pictures.

Meniscal Regenerative Scaffolds Based on Biopolymers and Polymers: Recent Status and Applications

Knee menisci are structurally complex components that preserve appropriate biomechanics of the knee. Meniscal tissue is susceptible to injury and cannot heal spontaneously from most pathologies, especially considering the limited regenerative capacity of the inner avascular region. Conventional clinical treatments span from conservative therapy to meniscus implantation, all with limitations. There have been advances in meniscal tissue engineering and regenerative medicine in terms of potential combinations of polymeric biomaterials, endogenous cells and stimuli, resulting in innovative strategies. Recently, polymeric scaffolds have provided researchers with a powerful instrument to rationally support the requirements for meniscal tissue regeneration, ranging from an ideal architecture to biocompatibility and bioactivity. However, multiple challenges involving the anisotropic structure, sophisticated regenerative process, and challenging healing environment of the meniscus still create barriers to clinical application. Advances in scaffold manufacturing technology, temporal regulation of molecular signaling and investigation of host immunoresponses to scaffolds in tissue engineering provide alternative strategies, and studies have shed light on this field. Accordingly, this review aims to summarize the current polymers used to fabricate meniscal scaffolds and their applications in vivo and in vitro to evaluate their potential utility in meniscal tissue engineering. Recent progress on combinations of two or more types of polymers is described, with a focus on advanced strategies associated with technologies and immune compatibility and tunability. Finally, we discuss the current challenges and future prospects for regenerating injured meniscal tissues.

Tannic acid/Sr2+-coated silk/graphene oxide-based meniscus scaffold with anti-inflammatory and anti-ROS functions for cartilage protection and delaying osteoarthritis

Tissue engineering method provides a promising solution for meniscus repair and regeneration. However, the inflammatory environment that persists after meniscus injury in the knee joint impedes meniscus tissue regeneration. The purpose of this study was to investigate the applicability of silk/graphene oxide (GO)-based meniscus scaffold modified with tannic acid (TA)/Sr²⁺ coating for the elimination of inflammatory cytokines and reactive oxygen species (ROS) under osteoarthritis (OA) environment along with cartilage protection by using a rat model. The self-assembled coating composed of a series of TA-Sr²⁺ complex concentrations was formed by a facile, rapid, and efficient method on the scaffold. The phenolic hydroxyl groups on the coating endowed the meniscus scaffold with excellent anti-inflammatory and ROS scavenging capacities. We also found that the coating could promote cell migration in a mock wound model and could increase extracellular matrix secretion in vitro. Moreover, the coating components at a certain concentration played an effective role in delaying OA and providing cartilage protection in the rat model. The expression of inflammation cytokines (e.g., IL-6, IL-8, and MMPs) in rat knee tissue was significantly downregulated, and cartilage degeneration and OA damage were also inhibited according to tissue staining results and the OARSI (Osteoarthritis Research Society International) scoring system. Combining these performances, we suggest that this silk/GO-based scaffold modified with TA/Sr²⁺ coating could have broader application prospects by virtue of its effective and user-friendly properties. STATEMENT OF SIGNIFICANCE: The biological properties of the meniscus play a role in activating and regulating the metabolic and inflammatory responses that influence the homeostasis of joint health and ultimately lead to knee osteoarthritis (OA). The inflammation condition of the knee joint may exacerbate the degeneration of meniscus and cartilage. The present study aimed to develop a functional coating composed of tannic acid/Sr²⁺ complex on a silk/graphene oxide-based meniscus scaffold and to endow the scaffold with anti-inflammatory and ROS elimination capacities during the meniscus regeneration process to protect cartilage and delay OA development. The in vitro cytocompatibility study and the in vivo rat OA model study revealed that the coating was effective in promoting cell migration, facilitating ECM secretion, inhibiting inflammation, and delaying OA development.

Biosynthetic scaffolds for partial meniscal loss: A systematic review from animal models to clinical practice

Acute or degenerative meniscus tears are the most common knee lesions. Meniscectomy provides symptomatic relief and functional recovery only in the short- to mid-term follow-up but significantly increases the risk of osteoarthritis. For this reason, preserving the meniscus is key, although it remains a challenge. Allograft transplants present many disadvantages, so during the last 20 years preclinical and clinical research focused on developing and investigating meniscal scaffolds. The aim of this systematic review was to collect and evaluate all the available evidence on biosynthetic scaffolds for meniscus regeneration both in vivo and in clinical studies. Three databases were searched: 46 in vivo preclinical studies and 30 clinical ones were found. Sixteen natural, 15 synthetic, and 15 hybrid scaffolds were studied in vivo. Among them, only 2 were translated into clinic: the Collagen Meniscus Implant, used in 11 studies, and the polyurethane-based scaffold Actifit®, applied in 19 studies. Although positive outcomes were described in the short- to mid-term, the number of concurrent procedures and the lack of randomized trials are the major limitations of the available clinical literature. Few in vivo studies also combined the use of cells or growth factors, but these augmentation strategies have not been applied in the clinical practice yet. Current solutions offer a significant but incomplete clinical improvement, and the regeneration potential is still unsatisfactory. Building upon the overall positive results of these “old” technologies to address partial meniscal loss, further innovation is urgently needed in this field to provide patients better joint sparing treatment options.

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Animal studies employed natural, synthetic and hybrid natural/synthetic scaffolds.

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Only in a few animal studies scaffold augmentation with cells or GFs was tested.

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Only two meniscal scaffolds have reached clinical application: CMI and Actifit.

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Clinical results are promising, but complete meniscus regeneration has not been achieved.

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There is urgent need for technological innovation in the field of meniscal regeneration.

Development of biological meniscus scaffold: Decellularization method and recellularization with meniscal cell population derived from mesenchymal stem cells

Tissue engineering approaches which include a combination of cells and scaffold materials provide an alternative treatment for meniscus regeneration. Decellularization and recellularization techniques are potential treatment options for transplantation. Maintenance of the ultrastructure composition of the extracellular matrix and repopulation with cells are important factors in constructing a biological scaffold and eliminating immunological reactions.The aim of the study is to develop a method to obtain biological functional meniscus scaffolds for meniscus regeneration. For this purpose, meniscus tissue was decellularized by our modified method, a combination of physical, chemical, and enzymatic methods and then recellularized with a meniscal cell population composed of fibroblasts, chondrocytes and fibrochondrocytes that obtained from mesenchymal stem cells. Decellularized and recellularized meniscus scaffolds were analysed biochemically, biomechanically and histologically. Our results revealed that cellular components of the meniscus were successfully removed by preserving collagen and GAG structures without any significant loss in biomechanical properties. Recellularization results showed that the meniscal cells were localized in the empty lacuna on the decellularized meniscus, and also well distributed and proliferated consistently during the cell culture period (p < 0.05). Furthermore, a high amount of DNA, collagen, and GAG contents (p < 0.05) were obtained with the meniscal cell population in recellularized meniscus tissue.The study demonstrates that our decellularization and recellularization methods were effective to develop a biological functional meniscus scaffold and can mimic the meniscus tissue with structural and biochemical features. We predict that the obtained biological meniscus scaffolds may provide avoidance of adverse immune reactions and an appropriate microenvironment for allogeneic or xenogeneic recipients in the transplantation process. Therefore, as a promising candidate, the obtained biological meniscus scaffolds might be verified with a transplantation experiment.

Facile Strategy on Hydrophilic Modification of Poly(ε-caprolactone) Scaffolds for Assisting Tissue-Engineered Meniscus Constructs In Vitro

Poly(ε-caprolactone) (PCL) derived scaffolds have been extensively explored in the field of tissue-engineered meniscus (TEM) originating from their good biosafety and biomechanical properties. However, the poor intrinsic hydrophobicity severely hindered their wide applications for the scaffold-assisted tissue regeneration. Herein, we developed a simple strategy on surface modification of three-dimensional (3D) PCL scaffolds via a simply soaking treatment of sodium hydroxide (NaOH) solutions to increase the hydrophilicity and roughness of scaffolds' surfaces. We investigated the effect of hydrolysis degree mediated by NaOH solutions on mechanical properties of 3D scaffolds, considering the importance of scaffolds' resistance to internal force. We also investigated and analyzed the biological performances of mesenchymal stromal cells (MSCs) and meniscal fibrocartilage cells (MFCs) onto the scaffolds treated or untreated by NaOH solutions. The results indicated that hydrophilic modification could improve the proliferation and attachment of cells on the scaffolds. After careful screening process condition, structural fabrication, and performance optimization, these modified PCL scaffolds possessed roughened surfaces with inherent hierarchical pores, enhanced hydrophilicity and preferable biological performances, thus exhibiting the favorable advantages on the proliferation and adhesion of seeded cells for TEM. Therefore, this feasible hydrophilic modification method is not only beneficial to promote smarter biomedical scaffold materials but also show great application prospect in tissue engineering meniscus with tunable architectures and desired functionalities.

In-vivo histocompatibility and osteogenic potential of biodegradable PLDLA composites containing silica-based bioactive glass fiber

The purpose of this two-year study was to evaluate the histocompatibility and osteogenic properties of a composite material consisting of poly(l-co-d,l lactide) (PLDLA) and silica-based bioactive glass fibers in vivo. PLDLA and PLDLA/silica-based bioactive glass fibers pins were implanted into the erector spinae muscles and femurs of beagles. Muscle and bone tissue samples were harvested 6, 12, 16, 26, 52, 78, and 104 weeks after implantation. Histology analysis was used to assess the histocompatibility, angiogenesis, and bone-implant contact. Micro-computed tomography was used to evaluate bone formation around the pins. Immunohistochemistry and western blotting revealed the expression level of the osteogenesis-related proteins. Addition of bioactive glass was demonstrated to possess better histocompatibility and reduce the inflammatory reactions in vivo. Moreover, PLDLA/silica-based bioactive glass fibers pins were demonstrated to promote angiogenesis and increase osteogenesis-related proteins expression, and thus played a positive role in osteogenesis and osseointegration after implantation. Our findings indicated that a composite of PLDLA and silica-based bioactive glass fiber is a promising biodegradable material for clinical use.

3D-Printed Poly-Caprolactone Scaffolds Modified With Biomimetic Extracellular Matrices for Tarsal Plate Tissue Engineering

Tarsal plate regeneration has always been a challenge in the treatment of eyelid defects. The commonly used clinical treatments such as hard palate mucosa grafts cannot achieve satisfactory repair effects. Tissue engineering has been considered as a promising technology. However, tarsal plate tissue engineering is difficult to achieve due to its complex structure and lipid secretion function. Three-dimensional (3D) printing technology has played a revolutionary role in tissue engineering because it can fabricate complex scaffolds through computer aided design (CAD). In this study, it was novel in applying 3D printing technology to the fabrication of tarsal plate scaffolds using poly-caprolactone (PCL). The decellularized matrix of adipose-derived mesenchymal stromal cells (DMA) was coated on the surface of the scaffold, and its biofunction was further studied. Immortalized human SZ95 sebocytes were seeded on the scaffolds so that neutral lipids were secreted for replacing meibocytes. In vitro experiments revealed excellent biocompatibility of DMA-PCL scaffolds with sebocytes. In vivo experiments revealed excellent sebocytes proliferation on the DMA-PCL scaffolds. Meanwhile, sebocytes seeded on the scaffolds secreted abundant neutral lipid in vitro and in vivo. In conclusion, a 3D-printed PCL scaffold modified with DMA was found to be a promising substitute for tarsal plate tissue engineering.

Cell Bioprinting: The 3D-Bioplotter™ Case

The classic cell culture involves the use of support in two dimensions, such as a well plate or a Petri dish, that allows the culture of different types of cells. However, this technique does not mimic the natural microenvironment where the cells are exposed to. To solve that, three-dimensional bioprinting techniques were implemented, which involves the use of biopolymers and/or synthetic materials and cells. Because of a lack of information between data sources, the objective of this review paper is, to sum up, all the available information on the topic of bioprinting and to help researchers with the problematics with 3D bioprinters, such as the 3D-Bioplotter™. The 3D-Bioplotter™ has been used in the pre-clinical field since 2000 and could allow the printing of more than one material at the same time, and therefore to increase the complexity of the 3D structure manufactured. It is also very precise with maximum flexibility and a user-friendly and stable software that allows the optimization of the bioprinting process on the technological point of view. Different applications have resulted from the research on this field, mainly focused on regenerative medicine, but the lack of information and/or the possible misunderstandings between papers makes the reproducibility of the tests difficult. Nowadays, the 3D Bioprinting is evolving into another technology called 4D Bioprinting, which promises to be the next step in the bioprinting field and might promote great applications in the future.

Alternative Cutaneous Substitutes Based on Poly(l-co-d,l-lactic acid-co-trimethylene carbonate) with Schinus terebinthifolius Raddi Extract Designed for Skin Healing

The search for new therapies and drugs that act as topical agents to relieve pain and control the inflammatory processes in burns always attracted interest in clinical trials. As an alternative to synthetic drugs, natural extracts are useful in the development of new strategies and formulations for improving the quality of life. The aim of this study was to develop a wound dressing using poly(l-co-d,l-lactic acid-co-trimethylene carbonate) (PLDLA-TMC) containing Schinus terebinthifolius Raddi (S.T.R.). S.T.R. is a native Brazilian plant known for its strong anti-inflammatory responses. The membrane of PLDLA-TMC + S. terebinthifolius Raddi was prepared at different concentrations of S.T.R. (5, 10, 15, and 50%). The Fourier transform infrared results showed no change in the PLDLA-TMC spectrum after S.T.R. addition, whereas the swelling test showed changes only in PLDLA-TMC + S.T.R. at 50%. The wettability measurements showed a mass loss due to the decrease in the contact angle in all samples after the S.T.R. addition in the polymer, whereas the S.T.R. release test showed a linear delivery pattern. The scanning electron microscopy analysis showed that S.T.R. was homogeneously distributed at only 5 and 10%. Tensile tests demonstrated an increase in Young's modulus and a reduction in the elongation till rupture of PLDLA-TMC after the addition of S.T.R. The biocompatibility in vitro evaluation with rat fibroblast cells seeded in the membranes of PLDLA-TMC + S.T.R. showed that although S.T.R. interfered in cell morphology, all concentrations tested showed that cells were able to adhere and proliferate during 7 days. Thus, S.T.R. at 50% was chosen to be tested for in vivo trials. The histological and immunohistochemistry results revealed an accelerated skin healing at 7 days after controlled secondary burns were introduced in the dorsal skin, with a striking total recovery of the epidermis and high rates of molecular activation of cell proliferation. Due to the known biocompatibility properties of PLDLA-TMC and its stable release of S.T.R., we strongly recommend S.T.R.-containing PLDLA-TMC as a curative device to favor skin healing.

A three-dimensional printed silk-based biomimetic tri-layered meniscus for potential patient-specific implantation

Employing tissue engineering principles aided by three-dimensional (3D) printing strategies to fabricate meniscus tissue constructs could help patients with meniscus injury regain mobility, improve pain management and reduce the risk of development of knee osteoarthritis. Here we report a 3D printed meniscus scaffold that biomimics the internal and bulk architecture of the menisci. A shear-thinning novel silk fibroin-gelatin-based bioink with high print fidelity was optimized for the fabrication of scaffolds to serve as potential meniscus implants. Physicochemical characterization of the fabricated scaffolds shows optimum swelling, degradation and mechanical properties. Further, the scaffolds were seeded with meniscus fibrochondrocytes to validate their bioactivity. Fibrochondrocytes seeded on the scaffolds maintained their phenotype and proliferation, and enhanced glycosaminoglycan and total collagen synthesis was observed. Gene expression profile, biochemical quantification and histological studies confirmed the ability of the scaffolds to form meniscus-like tissue constructs. The scaffolds were found to possess amenable immunocompatibility in vitro as well as in vivo. Due to their excellent biological and physicochemical characteristics, these 3D printed scaffolds may be fine-tuned into viable alternatives to the present clinical treatment approaches to meniscus repair.

Polymer-tetrodotoxin conjugates to induce prolonged duration local anesthesia with minimal toxicity

There is clinical and scientific interest in developing local anesthetics with prolonged durations of effect from single injections. The need for such is highlighted by the current opioid epidemic. Site 1 sodium channel blockers such as tetrodotoxin (TTX) are extremely potent, and can provide very long nerve blocks but the duration is limited by the associated systemic toxicity. Here we report a system where slow release of TTX conjugated to a biocompatible and biodegradable polymer, poly(triol dicarboxylic acid)-co-poly(ethylene glycol) (TDP), is achieved by hydrolysis of ester linkages. Nerve block by the released TTX is enhanced by administration in a carrier with chemical permeation enhancer (CPE) properties. TTX release can be adjusted by tuning the hydrophilicity of the TDP polymer backbone. In vivo, 1.0–80.0 µg of TTX released from these polymers produced a range of durations of nerve block, from several hours to 3 days, with minimal systemic or local toxicity.

There is interest in developing long-lasting local anaesthetics for a range of applications. Here, the authors report on the application of tetrodotoxin conjugated to amphiphilic biodegradable polymer to reduce systemic toxicity, achieve sustained release and investigate application as a local anaesthetic.

Functional Biomolecule Delivery Systems and Bioengineering in Cartilage Regeneration

Osteoarthritis (OA) is a common degenerative disease which involves articular cartilage, and leads to total joint disability in the advanced stages. Due to its avascular and aneural nature, damaged cartilage cannot regenerate itself. Stem cell therapy and tissue engineering represent a promising route in OA therapy, in which cooperation of mesenchymal stem cells (MSCs) and three-dimensional (3D) scaffolds contribute to cartilage regeneration. However, this approach still presents some limits such as poor mechanical properties of the engineered cartilage. The natural dynamic environment of the tissue repair process involves a collaboration of several signals expressed in the biological system in response to injury. For this reason, tissue engineering involving exogenous "influencers" such as mechanostimulation and functional biomolecule delivery systems (BDS), represent a promising innovative approach to improve the regeneration process. BDS provide a controlled release of biomolecules able to interact between them and with the injured tissue. Nano-dimensional BDS is the future hope for the design of personalized scaffolds, able to overcome the delivery problems. MSC-derived extracellular vesicles (EVs) represent an attractive alternative to BDS, due to their innate targeting abilities, immunomodulatory potential and biocompatibility. Future advances in cartilage regeneration should focus on multidisciplinary strategies such as modular assembly strategies, EVs, nanotechnology, 3D biomaterials, BDS, mechanobiology aimed at constructing the functional scaffolds for actively targeted biomolecule delivery. The aim of this review is to run through the different approaches adopted for cartilage regeneration, with a special focus on biomaterials, BDS and EVs explored in terms of their delivery potential, healing capabilities and mechanical features.

A collagen-coated sponge silk scaffold for functional meniscus regeneration

Tissue engineering is a promising solution for meniscal regeneration after meniscectomy. However, in situ reconstruction still poses a formidable challenge due to multifunctional roles of the meniscus in the knee. In this study, we fabricate a silk sponge from 9% (w/v) silk fibroin solution through freeze drying and then coat its internal space and external surface with collagen sponge. Subsequently, various characteristics of the silk-collagen scaffold are evaluated, and cytocompatibility of the construct is assessed in vitro and subcutaneously. The efficacy of this composite scaffold for meniscal regeneration is evaluated through meniscus reconstruction in a rabbit meniscectomy model. It is found that the internally coated collagen sponge enhances the cytocompatibility of the silk sponge, and the external layer of collagen sponge significantly improves the initial frictional property. Additionally, the silk-collagen composite group shows more tissue ingrowth and less cartilage wear than the pure silk sponge group at 3 months postimplantation in situ. These findings thus demonstrate that the composite scaffold had less damage to the joint surface than the silk alone through promoting functional meniscal regeneration after meniscectomy, which indicates its clinical potential in meniscus reconstruction.

Surgical Feasibility of a One-Stage Cell-Based Arthroscopic Procedure for Meniscus Regeneration: A Cadaveric Study

IMPACT STATEMENT

Meniscus injury remains the most common indication for orthopedic surgery, but loss of functioning meniscus tissue is strongly correlated with development of early osteoarthritis. However, current clinical options for tissue engineering of the meniscus are limited. This study demonstrates the feasibility of combining human meniscus cells with mesenchymal stromal cells to enhance a meniscus scaffold for meniscus regeneration in a one-stage solution for partial meniscal deficiency.

Cell-Free Strategies for Repair and Regeneration of Meniscus Injuries through the Recruitment of Endogenous Stem/Progenitor Cells

The meniscus plays a vital role in protecting the articular cartilage of the knee joint. The inner two-thirds of the meniscus are avascular, and injuries to this region often fail to heal without intervention. The use of tissue engineering and regenerative medicine techniques may offer novel and effective approaches to repairing meniscal injuries. Meniscal tissue engineering and regenerative medicine typically use one of two techniques, cell-based or cell-free. While numerous cell-based strategies have been applied to repair and regenerate meniscal defects, these techniques possess certain limitations including cellular contamination and an increased risk of disease transmission. Cell-free strategies attempt to repair and regenerate the injured tissues by recruiting endogenous stem/progenitor cells. Cell-free strategies avoid several of the disadvantages of cell-based techniques and, therefore, may have a wider clinical application. This review first compares cell-based to cell-free techniques. Next, it summarizes potential sources for endogenous stem/progenitor cells. Finally, it discusses important recruitment factors for meniscal repair and regeneration. In conclusion, cell-free techniques, which focus on the recruitment of endogenous stem and progenitor cells, are growing in efficacy and may play a critical role in the future of meniscal repair and regeneration.

Human Knee Meniscus Regeneration Strategies: a Review on Recent Advances

PURPOSE OF REVIEW

Lack of vascularity in the human knee meniscus often leads to surgical removal (total or partial meniscectomy) in the case of severe meniscal damage. However, complete recovery is in question after such removal as the meniscus plays an important role in knee stability. Thus, meniscus tissue regeneration strategies are of intense research interest in recent years.

RECENT FINDINGS

The structural complexity and inhomogeneity of the meniscus have been addressed with processing technologies for precisely controlled three dimensional (3D) complex porous scaffold architectures, the use of biomolecules and nanomaterials. The regeneration and replacement of the total meniscus have been studied by the orthopedic and scientific communities via successful pre-clinical trials towards mimicking the biomechanical properties of the human knee meniscus. Researchers have attempted different regeneration strategies which contribute to in vitro regeneration and are capable of repairing meniscal tears to some extent. This review discusses the present state of the art of these meniscus tissue engineering aspects.

Current Concepts in Meniscus Tissue Engineering and Repair

The meniscus is the most commonly injured structure in the human knee. Meniscus deficiency has been shown to lead to advanced osteoarthritis (OA) due to abnormal mechanical forces, and replacement strategies for this structure have lagged behind other tissue engineering endeavors. The challenges include the complex 3D structure with individualized size parameters, the significant compressive, tensile and shear loads encountered, and the poor blood supply. In this progress report, a review of the current clinical treatments for different types of meniscal injury is provided. The state-of-the-art research in cellular therapies and novel cell sources for these therapies is discussed. The clinically available cell-free biomaterial implants and the current progress on cell-free biomaterial implants are reviewed. Cell-based tissue engineering strategies for the repair and replacement of meniscus are presented, and the current challenges are identified. Tissue-engineered meniscal biocomposite implants may provide an alternative solution for the treatment of meniscal injury to prevent OA in the long run, because of the limitations of the existing therapies.

Porous Poly(vinyl alcohol)-Based Hydrogel for Knee Meniscus Functional Repair

The meniscus has a key role within the knee joint, conferring stability, absorbing and redistributing loads, and influencing the overall movement proprioception. Recent developments in the treatment of meniscal injury have progressively shifted the focus from general resection to functional repair, with the recognition that restoring the biomechanical meniscal function helps to prevent degenerative changes in the knee joint and the insurgence of osteoarthritis. To address this clinical need, we have developed a biomimetic implant based on a porous poly(vinyl alcohol) (PVA) hydrogel. Such hydrogels are stable, biocompatible, and suitable to surgical translation, and their mechanical properties can be tuned to reduce the mismatch in the case of partial meniscectomy. The PVA implant structure is porous and permeable, allowing fluid flows and facilitating anatomical integration in situ. Here, we present a chemo-physical characterization of PVA porous hydrogels, focusing on their tunable morphology and associated viscoelastic properties. Biocompatibility was evaluated using primary bovine meniscal fibrochondrocytes, and integration with native tissues was assessed in an ex vivo model. Overall, our results suggest that a synthetic meniscal implant based on a porous PVA hydrogel could restore the physiological function of the meniscus and represent a promising clinical alternative to current resection treatments.

* The Ovine Model for Meniscus Tissue Engineering: Considerations of Anatomy, Function, Implantation, and Evaluation

Meniscus injuries represent one of the most-common intra-articular knee injuries. The current treatment options include meniscectomy and allograft transplantation, both with poor long-term outcomes. Therefore, there is a need for regenerative techniques to restore meniscal function. To preclinically test scaffolds for meniscus replacement, large animal models need to be established and standardized. This review establishes the anatomical and compositional similarities between human and sheep menisci and provides guidance for implantation and evaluation of such devices. The ovine meniscus represents a scaled-down version of the human meniscus, with only slight structural differences that can be addressed during device fabrication. Implantation protocols in sheep remain a challenge, as the meniscus cannot be visualized with the arthroscopic-assisted procedures commonly performed in human patients. Thus, we recommend the appropriate implantation protocols for meniscus visualization, ligamentous restoration, and surgical fixation of both total and partial meniscus replacement devices. Last, due to the lack of standardization in evaluation techniques, we recommend a comprehensive battery of tests to evaluate the efficacy of meniscus replacement implants. We recommend other investigators utilize these surgical and testing techniques to establish the ovine model as the gold standard for preclinical evaluation of meniscus replacement devices.

Large Animal Models of Meniscus Repair and Regeneration: A Systematic Review of the State of the Field

Injury to the meniscus is common, but few viable strategies exist for its repair or regeneration. To address this, animal models have been developed to translate new treatment strategies toward the clinic. However, there is not yet a regulatory document guiding such studies. The purpose of this study was to carry out a systematic review of the literature on meniscus treatment methods and outcomes to define the state of the field. Public databases were queried by using search terms related to animal models and meniscus injury and/or repair over the years 1980-2015. Identified peer-reviewed manuscripts were screened by using Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines. One of nine reviewers read each manuscript and scored them based on whether the publication described a series of predefined study descriptors and outcome measures. Additional data were extracted to identify common assays used. A total of 128 full-length peer-reviewed manuscripts were identified. The number of publications increased over the time frame analyzed, with 48% focused on augmented repair. Rabbit was, by far, the most prevalent species utilized (46%), with dog (21%) and sheep (20%) being the next most common. Analysis of study descriptors revealed that most studies appropriately documented details of the animal used, the surgical approach, and defect and implant characteristics (e.g., 63% of studies identified clearly the defect size). In terms of outcome parameters, most studies carried out macroscopic (85%), histologic (90%), and healing/integration (83%) analyses of the meniscus. However, many studies did not provide further analysis beyond these fundamental measures, and less than 40% reported on the adjacent cartilage and synovium, as well as joint function. There is intense interest in the field of meniscus repair. However, given the current lack of guidance documentation in this area, preclinical animal models are not performed in a standardized fashion. The development of a "Best Practices" document would increase reproducibility and external validity of experiments, while accelerating advancements in translational research. Advancement is of paramount importance given the high prevalence of meniscal injuries and the paucity of effective repair or regenerative strategies.

Mechanical function near defects in an aligned nanofiber composite is preserved by inclusion of disorganized layers: Insight into meniscus structure and function

The meniscus is comprised of circumferentially aligned fibers that resist the tensile forces within the meniscus (i.e., hoop stress) that develop during loading of the knee. Although these circumferential fibers are severed by radial meniscal tears, tibial contact stresses do not increase until the tear reaches ∼90% of the meniscus width, suggesting that the severed circumferential fibers still bear load and maintain the mechanical functionality of the meniscus. Recent data demonstrates that the interfibrillar matrix can transfer strain energy to disconnected fibrils in tendon fascicles. In the meniscus, interdigitating radial tie fibers, which function to stabilize and bind the circumferential fibers together, are hypothesized to function in a similar manner by transmitting load to severed circumferential fibers near a radial tear. To test this hypothesis, we developed an engineered fibrous analog of the knee meniscus using poly(ε-caprolactone) to create aligned scaffolds with variable amounts of non-aligned elements embedded within the scaffold. We show that the tensile properties of these scaffolds are a function of the ratio of aligned to non-aligned elements, and change in a predictable fashion following a simple mixture model. When measuring the loss of mechanical function in scaffolds with a radial tear, compared to intact scaffolds, the decrease in apparent linear modulus was reduced in scaffolds containing non-aligned layers compared to purely aligned scaffolds. Increased strains in areas adjacent to the defect were also noted in composite scaffolds. These findings indicate that non-aligned (disorganized) elements interspersed within an aligned network can improve overall mechanical function by promoting strain transfer to nearby disconnected fibers. This finding supports the notion that radial tie fibers may similarly promote tear tolerance in the knee meniscus, and will direct changes in clinical practice and provide guidance for tissue engineering strategies.

STATEMENT OF SIGNIFICANCE

The meniscus is a complex fibrous tissue, whose architecture includes radial tie fibers that run perpendicular to and interdigitate with the predominant circumferential fibers. We hypothesized that these radial elements function to preserve mechanical function in the context of interruption of circumferential bundles, as would be the case in a meniscal tear. To test this hypothesis, we developed a biomaterial analog containing disorganized layers enmeshed regularly throughout an otherwise aligned network. Using this material formulation, we showed that strain transmission is improved in the vicinity of defects when disorganized fiber layers were present. This supports the idea that radial elements within the meniscus improve function near a tear, and will guide future clinical interventions and the development of engineered replacements.

3D-Printed Poly(ε-caprolactone) Scaffold Augmented With Mesenchymal Stem Cells for Total Meniscal Substitution: A 12- and 24-Week Animal Study in a Rabbit Model

BACKGROUND

Total meniscectomy leads to knee osteoarthritis in the long term. The poly(ε-caprolactone) (PCL) scaffold is a promising material for meniscal tissue regeneration, but cell-free scaffolds result in relatively poor tissue regeneration and lead to joint degeneration.

HYPOTHESIS

A novel, 3-dimensional (3D)-printed PCL scaffold augmented with mesenchymal stem cells (MSCs) would offer benefits in meniscal regeneration and cartilage protection.

STUDY DESIGN

Controlled laboratory study.

METHODS

PCL meniscal scaffolds were 3D printed and seeded with bone marrow-derived MSCs. Seventy-two New Zealand White rabbits were included and were divided into 4 groups: cell-seeded scaffold, cell-free scaffold, sham operation, and total meniscectomy alone. The regeneration of the implanted tissue and the degeneration of articular cartilage were assessed by gross and microscopic (histological and scanning electron microscope) analysis at 12 and 24 weeks postoperatively. The mechanical properties of implants were also evaluated (tensile and compressive testing).

RESULTS

Compared with the cell-free group, the cell-seeded scaffold showed notably better gross appearance, with a shiny white color and a smooth surface. Fibrochondrocytes with extracellular collagen type I, II, and III and proteoglycans were found in both seeded and cell-free scaffold implants at 12 and 24 weeks, while the results were significantly better for the cell-seeded group at week 24. Furthermore, the cell-seeded group presented notably lower cartilage degeneration in both femur and tibia compared with the cell-free or meniscectomy group. Both the tensile and compressive properties of the implants in the cell-seeded group were significantly increased compared with those of the cell-free group.

CONCLUSION

Seeding MSCs in the PCL scaffold increased its fibrocartilaginous tissue regeneration and mechanical strength, providing a functional replacement to protect articular cartilage from damage after total meniscectomy.

CLINICAL RELEVANCE

The study suggests the potential of the novel 3D PCL scaffold augmented with MSCs as an alternative meniscal substitution, although this approach requires further improvement before being used in clinical practice.

Cell-Based Meniscus Repair and Regeneration: At the Brink of Clinical Translation?: A Systematic Review of Preclinical Studies

Background:

Meniscus damage can be caused by trauma or degeneration and is therefore common among patients of all ages. Repair or regeneration of the menisci could be of great importance not only for pain relief or regaining function but also to prevent degenerative disease and osteoarthritis. Current treatment does not offer consistent long-term improvement. Although preclinical research focusing on augmentation of meniscal tear repair and regeneration after meniscectomy is encouraging, clinical translation remains difficult.

Purpose:

To systematically evaluate the literature on in vivo meniscus regeneration and explore the optimal cell sources and conditions for clinical translation. We aimed at thorough evaluation of current evidence as well as clarifying the challenges for future preclinical and clinical studies.

Study Design:

Systematic review.

Methods:

A search was conducted using the electronic databases of MEDLINE, Embase, and the Cochrane Collaboration. Search terms included meniscus, regeneration, and cell-based.

Results:

After screening 81 articles based on title and abstract, 51 articles on in vivo meniscus regeneration could be included; 2 additional articles were identified from the references. Repair and regeneration of the meniscus has been described by intra-articular injection of multipotent mesenchymal stromal (stem) cells from adipose tissue, bone marrow, synovium, or meniscus or the use of these cell types in combination with implantable or injectable scaffolds. The use of fibrochondrocytes, chondrocytes, and transfected myoblasts for meniscus repair and regeneration is limited to the combination with different scaffolds. The comparative in vitro and in vivo studies mentioned in this review indicate that the use of allogeneic cells is as successful as the use of autologous cells. In addition, the implantation or injection of cell-seeded scaffolds increased tissue regeneration and led to better structural organization compared with scaffold implantation or injection of a scaffold alone. None of the studies mentioned in this review compare the effectiveness of different (cell-seeded) scaffolds.

Conclusion:

There is heterogeneity in animal models, cell types, and scaffolds used, and limited comparative studies are available. The comparative in vivo research that is currently available is insufficient to draw strong conclusions as to which cell type is the most promising. However, there is a vast amount of in vivo research on the use of different types of multipotent mesenchymal stromal (stem) cells in different experimental settings, and good results are reported in terms of tissue formation. None of these studies compare the effectiveness of different cell-scaffold combinations, making it hard to conclude which scaffold has the greatest potential.

Regeneration of meniscus tissue using adipose mesenchymal stem cells-chondrocytes co-culture on a hybrid scaffold: In vivo study

The meniscus has poor intrinsic regenerative capacity and its damage inevitably leads to articular cartilage degeneration. We focused on evaluating the effects of Polyvinyl alcohol/Chitosan (PVA/Ch) scaffold seeded by adipose-derived mesenchymal stem cell (ASC) and articular chondrocytes (AC) in meniscus regeneration. The PVA/Ch scaffolds with different molar contents of Ch (Ch1, Ch2, Ch4 and Ch8) were cross-linked by pre-polyurethane chains. By increasing amount of Ch tensile modulus was increased from 83.51 MPa for Ch1 to 110 MPa for Ch8 while toughness showed decrease from 0.33 mJ/mm³ in Ch1 to 0.11 mJ/mm³ in Ch8 constructs. Moreover, swelling ratio and degradation rate increased with an increase in Ch amount. Scanning electron microscopy imaging was performed for pore size measurement and cell attachment. At day 21, Ch4 construct seeded by AC showed the highest expression with 24.3 and 22.64 folds increase in collagen II and aggrecan (p ≤ 0.05), respectively. Since, the mechanical properties, water uptake and degradation rate of Ch4 and Ch8 compositions had no statistically significant differences, Ch4 was selected for in vivo study. New Zealand rabbits were underwent unilateral total medial meniscectomy and AC/scaffold, ASC/scaffold, AC-ASC (co-culture)/scaffold and cell-free scaffold were engrafted. At 7 months post-implantation, macroscopic, histologic, and immunofluorescent studies for regenerated meniscus revealed better results in AC/scaffold group followed by AC-ASC/scaffold and ASC/scaffold groups. In the cell-free scaffold group, there was no obvious meniscus regeneration. Articular cartilages were best preserved in AC/scaffold group. The best histological score was observed in AC/scaffold group. Our results support that Ch4 scaffold seeded by AC alone can successfully regenerate meniscus in tearing injury and ASC has no significant contribution in the healing process.

Anisotropy in the viscoelastic response of knee meniscus cartilage

BACKGROUND

The knee meniscus is instrumental to stability, shock absorption, load transmission and stress distribution within the knee joint. Such functions are mechanically demanding, and replacement constructs used in meniscus repair often fail because of a poor match with the surrounding tissue. This study focused on the native structure-mechanics relationships and on their anisotropic behavior in meniscus, to define the target biomechanical viscoelastic properties required by scaffolds upon loading.

METHODS

To show regional orientation of the collagen fibers and their viscoelastic behavior, bovine lateral menisci were characterized by second harmonic generation microscopy and through time-dependent mechanical tests. Furthermore, their dynamic viscoelastic response was analyzed over a wide range of frequencies.

RESULTS AND CONCLUSIONS

Multilevel characterization aims to expand the biomimetic approach from the structure itself, to include the mechanical characteristics that give the meniscus its peculiar properties, thus providing tools for the design of novel, effective scaffolds. An example of modeling of anisotropic open-cell porous material tailored to fulfill the measured requirements is presented, leading to a definition of additional parameters for a better understanding of the load transmission mechanism and for better scaffold functionality.

An Overview of Scaffold Design and Fabrication Technology for Engineered Knee Meniscus

Current surgical treatments for meniscal tears suffer from subsequent degeneration of knee joints, limited donor organs and inconsistent post-treatment results. Three clinical scaffolds (Menaflex CMI, Actifit® scaffold and NUsurface® Meniscus Implant) are available on the market, but additional data are needed to properly evaluate their safety and effectiveness. Thus, many scaffold-based research activities have been done to develop new materials, structures and fabrication technologies to mimic native meniscus for cell attachment and subsequent tissue development, and restore functionalities of injured meniscus for long-term effects. This study begins with a synopsis of relevant structural features of meniscus and goes on to describe the critical considerations. Promising advances made in the field of meniscal scaffolding technology, in terms of biocompatible materials, fabrication methods, structure design and their impact on mechanical and biological properties are discussed in detail. Among all the scaffolding technologies, additive manufacturing (AM) is very promising because of its ability to precisely control fiber diameter, orientation, and pore network micro-architecture to mimic the native meniscus microenvironment.

Poly (lactic acid)-based biomaterials for orthopaedic regenerative engineering

Regenerative engineering converges tissue engineering, advanced materials science, stem cell science, and developmental biology to regenerate complex tissues such as whole limbs. Regenerative engineering scaffolds provide mechanical support and nanoscale control over architecture, topography, and biochemical cues to influence cellular outcome. In this regard, poly (lactic acid) (PLA)-based biomaterials may be considered as a gold standard for many orthopaedic regenerative engineering applications because of their versatility in fabrication, biodegradability, and compatibility with biomolecules and cells. Here we discuss recent developments in PLA-based biomaterials with respect to processability and current applications in the clinical and research settings for bone, ligament, meniscus, and cartilage regeneration.

Caracterização de pinos da blenda poli(L-co-D,L ácido láctico)/poli(caprolactona triol) (PLDLA/PCL-T) e análise das propriedade mecânicas dos pinos durante degradação in vitro

Resumo Os dispositivos de fixação óssea, metálicos convencionais, usados em cirurgia crâniomaxilofacial têm apresentado alguns problemas, tais como, corrosão, inflamação e infecção, além de neoformação de estrutura óssea mecanicamente inferior devido à atrofia gerada pela diferença de módulo elástico entre metal e osso, razões que têm levado ao aumento do interesse por dispositivos poliméricos bioarreabsorvíveis. Os polímeros biorreabsorvíveis mais utilizados nesta aplicação pertencem à família dos poli (α-hidroxi ácidos), que têm como característica degradarem por hidrólise de suas ligações ésteres, tal como copolímero poli (L-ácido láctico-co-D, L ácido láctico), PLDLA. Neste trabalho foram investigados alguns efeitos da adição de poli (caprolactona triol), PCL-T sobre PLDLA. Foram preparados pinos por fusão de blendas nas seguintes composições 100/0, 90/10, 70/30 and 50/50 (m/m), PLDLA/PCL-T. Os pinos foram caracterizados por diferentes técnicas (DSC, MEV e ensaio mecânico). A degradação in vitro dos pinos foi investigada, sendo observado que a adição de PCL-T no PLDLA modificou suas propriedades mecânicas e morfológicas. Tais mudanças podem apresentar potencial para outras aplicações do material, onde a questão da flexibilidade se faça necessária.

Cell-Based Strategies for Meniscus Tissue Engineering

Meniscus injuries remain a significant challenge due to the poor healing potential of the inner avascular zone. Following a series of studies and clinical trials, tissue engineering is considered a promising prospect for meniscus repair and regeneration. As one of the key factors in tissue engineering, cells are believed to be highly beneficial in generating bionic meniscus structures to replace injured ones in patients. Therefore, cell-based strategies for meniscus tissue engineering play a fundamental role in meniscal regeneration. According to current studies, the main cell-based strategies for meniscus tissue engineering are single cell type strategies; cell coculture strategies also were applied to meniscus tissue engineering. Likewise, on the one side, the zonal recapitulation strategies based on mimicking meniscal differing cells and internal architectures have received wide attentions. On the other side, cell self-assembling strategies without any scaffolds may be a better way to build a bionic meniscus. In this review, we primarily discuss cell seeds for meniscus tissue engineering and their application strategies. We also discuss recent advances and achievements in meniscus repair experiments that further improve our understanding of meniscus tissue engineering.

Poly (γ-glutamic acid)/beta-TCP nanocomposites via in situ copolymerization: Preparation and characterization

A series biodegradable poly (γ-glutamic acid)/beta-tricalcium phosphate (γ-PGA/TCP) nanocomposites were prepared which were composed of poly-γ-glutamic acid polymerized in situ with β-tricalcium phosphate and physiochemically characterized as bone graft substitutes. The particle size via dynamic light scattering, the direct morphological characterization via transmission electron microscopy and field emission scanning electron microscope, which showed that γ-PGA and β-TCP were combined compactly at 80℃, and the γ-PGA/TCP nanocomposites had homogenous and nano-sized grains with narrow particle size distributions. The water uptake and retention abilities, in vitro degradation properties, cytotoxicity in the simulated medium, and protein release of these novel γ-PGA/TCP composites were investigated. Cell proliferation in composites was nearly twice than β-TCP when checked in vitro using MC3T3 cell line. We also envision the potential use of γ-PGA/TCP systems in bone growth factor or orthopedic drug delivery applications in future bone tissue engineering applications. These observations suggest that the γ-PGA/TCP are novel nanocomposites with great potential for application in the field of bone tissue engineering.