Development and characterization of an acellular porcine medial meniscus for use in tissue engineering

Decellularized Human Dermis for Orthoplastic Extremity Reconstruction

The reconstruction of patients who possess multi morbid medical histories remains a challenge. With the ever-increasing number of patients with diabetes, infections, and trauma, there is a consistent need for promotion of soft tissue healing and a reliable substrate to assist with every aspect of soft tissue reconstruction, as well as the loss of fascial domain. Several proprietary products filled some of these needs but have failed to fulfill the needs of the clinician when faced with reconstructing multiple soft tissue systems, such as the integument and the musculoskeletal system. In this paper we discuss the use of decellularized human dermis (DermaPure®, Tissue Regenix, Universal City, TX, USA) through which a unique human tissue processing technique (dCELL® technology, Tissue Regenix, Universal City, TX, USA) and the creation of multiple product forms have proven to exhibit versatility in a wide range of clinical needs for successful soft tissue reconstruction. The background of human tissue processing, basic science, and early clinical studies are detailed, which has translated to the rationale for the success of this unique soft tissue substrate in orthoplastic reconstruction, which is also provided here in detail.

Ozone therapy (O2-O3) alleviates the progression of early intervertebral disc degeneration via the inhibition of oxidative stress and the interception of the PI3K/Akt/NF-κB signaling pathway

Intervertebral disc degeneration (IDD) stands for the most frequent cause of low back pain. Finding a cure for this disease is an important challenge as current conservative treatments and surgical interventions fail to bring a solution to this disease. Ozone therapy (O2-O3) has yielded outstanding outcomes in intervertebral disc pathology. The ozone's efficacy in the treatment of IDD remains unconfirmed. This study aimed to assess the effectiveness of intradiscal ozone injection on IDD induced in a rat. Effects of ozone therapy on the viability of nucleus pulposus cells were evaluated by CCK-8 assays. Macrophage immunoreactivity was detected by immunohistochemical, the expression of collagen type II was evaluated by western blot, and measurement of oxidative stress parameters was realized. Molecular docking studies were carried out in order to predict the interaction formed between O3 and the target enzymes, on the one hand, O3 with PI3K and, on the other hand, O3 with COX-2. IRM, X-ray, hematoxylin-eosin, and bleu alcian staining were realized to assess the therapeutic impacts of ozone in the puncture-induced rat model of IDD. In vivo, O3 ameliorated the IDD in the early stage of this disease. It was also displayed in molecular docking that O3 might bind to PI3K to suppress the PI3K/Akt/NF-κB signaling pathway. This study's results show that the O3 should be administered at the low grade of IDD and at an early stage because it cannot restore the advanced inflammatory alteration of the IVD. Our results corroborated also that O3 inhibits the progression of IDD via the PI3K/Akt/NF-κB signaling pathway, which supports O3 as an effective therapeutic option for treating IDD.

A survey on the usage of decellularized tissues in orthopaedic clinical trials

Orthopaedic surgery requires grafts with sufficient mechanical strength. For this purpose, decellularized tissue is an available option that lacks the complications of autologous tissue. However, it is not widely used in orthopaedic surgeries. This study investigated clinical trials of the use of decellularized tissue grafts in orthopaedic surgery. Using the ClinicalTrials.gov (CTG) and the International Clinical Trials Registry Platform (ICTRP) databases, we comprehensively surveyed clinical trials of decellularized tissue use in orthopaedic surgeries registered before 1 September 2022. We evaluated the clinical results, tissue processing methods, and commercial availability of the identified products using academic literature databases and manufacturers' websites. We initially identified 4,402 clinical trials, 27 of which were eligible for inclusion and analysis, including nine shoulder surgery trials, eight knee surgery trials, two ankle surgery trials, two hand surgery trials, and six peripheral nerve graft trials. Nine of the trials were completed. We identified only one product that will be commercially available for use in knee surgery with significant mechanical load resistance. Peracetic acid and gamma irradiation were frequently used for sterilization. Despite the demand for decellularized tissue, few decellularized tissue products are currently commercially available, particularly for the knee joint. To be viable in orthopaedic surgery, decellularized tissue must exhibit biocompatibility and mechanical strength, and these requirements are challenging for the clinical application of decellularized tissue. However, the variety of available decellularized products has recently increased. Therefore, decellularized grafts may become a promising option in orthopaedic surgery.

Characterisation of native and decellularised porcine tendon under tension and compression: A closer look at glycosaminoglycan contribution to tendon mechanics

Decellularised porcine superflexor tendon (pSFT) has been characterised as a suitable scaffold for anterior cruciate ligament replacement, with dimensions similar to hamstring tendon autograft. However, decellularisation of tissues may reduce or damage extracellular matrix components, leading to undesirable biomechanical changes at a whole tissue scale. Although the role of collagen in tendons is well established, the mechanical contribution of glycosaminoglycans (GAGs) is less evident and could be altered by the decellularisation process. In this study, the contribution of GAGs to the tensile and compressive mechanical properties of pSFT was determined and whether decellularisation affected these properties by reducing GAG content or functionality. PSFTs were either enzymatically treated using chondroitinase ABC to remove GAGs or decellularised using previously established methods. Native, GAG-depleted and decellularised pSFT groups were then subjected to quantitative assays and biomechanical characterisation. In tension, specimens underwent stress relaxation and strength testing. In compression, specimens underwent confined compression testing. The GAG-depleted group was found to have circa 86% reduction of GAG content compared to native and decellularised groups. There was no significant difference in GAG content between native (3.75 ± 0.58 μg/mg) and decellularised (3.40 ± 0.37 μg/mg) groups. Stress relaxation testing discovered the time-independent and time-dependent relaxation moduli of the decellularised group were reduced ≥50% compared to native and GAG-depleted groups. However, viscoelastic behaviour of native and GAG-depleted groups resulted similar. Strength testing discovered no differences between native and GAG-depleted group's properties, albeit a reduction ∼20% for decellularised specimens' linear modulus and tensile strength compared to native tissue. In compression testing, the aggregate modulus was found to be circa 74% lower in the GAG-depleted group than the native and decellularised groups, while the zero-strain permeability was significantly higher in the GAG-depleted group (0.86 ± 0.65 mm⁴/N) than the decellularised group (0.03 ± 0.04 mm⁴/N). The results indicate that GAGs may significantly contribute to the mechanical properties of pSFT in compression, but not in tension. Furthermore, the content and function of GAGs in pSFTs are unaffected by decellularisation and the mechanical properties of the tissue remain comparable to native tissue.

Biofabrication, biochemical profiling, and in vitro applications of salivary gland decellularized matrices via magnetic bioassembly platforms

Trending three-dimensional tissue engineering platforms developed via biofabrication and bioprinting of exocrine glands are on the rise due to a commitment to organogenesis principles. Nevertheless, a proper extracellular matrix (ECM) microarchitecture to harbor primary cells is yet to be established towards human salivary gland (SG) organogenesis. By using porcine submandibular gland (SMG) biopsies as a proof-of-concept to mimic the human SG, a new decellularized ECM bioassembly platform was developed herein with varying perfusions of sodium dodecyl sulfate (SDS) to limit denaturing events and ensure proper preservation of the native ECM biochemical niche. Porcine SMG biopsies were perfused with 0.01%, 0.1%, and 1% SDS and bio-assembled magnetically in porous polycarbonate track-etched (PCTE) membrane. Double-stranded DNA (dsDNA), cell removal efficiency, and ECM biochemical contents were analyzed. SDS at 0.1% and 1% efficiently removed dsDNA (< 50 ng/mg) and preserved key matrix components (sulfated glycosaminoglycans, collagens, elastin) and the microarchitecture of native SMG ECM. Bio-assembled SMG decellularized ECM (dECM) perfused with 0.1-1% SDS enhanced cell viability, proliferation, expansion confluency rates, and tethering of primary SMG cells during 7 culture days. Perfusion with 1% SDS promoted greater cell proliferation rates while 0.1% SDS supported higher acinar epithelial expression when compared to basement membrane extract and other substrates. Thus, this dECM magnetic bioassembly strategy was effective for decellularization while retaining the original ECM biochemical niche and promoting SMG cell proliferation, expansion, differentiation, and tethering. Altogether, these outcomes pave the way towards the recellularization of this novel SMG dECM in future in vitro and in vivo applications.

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.

A decellularized and sterilized human meniscus allograft for off-the-shelf meniscus replacement

PURPOSE

Meniscus tears are one of the most frequent orthopedic knee injuries, which are currently often treated performing meniscectomy. Clinical concerns comprise progressive degeneration of the meniscus tissue, a change in knee biomechanics, and an early onset of osteoarthritis. To overcome these problems, meniscal transplant surgery can be performed. However, adequate meniscal replacements remain to be a great challenge. In this research, we propose the use of a decellularized and sterilized human meniscus allograft as meniscal replacement.

METHODS

Human menisci were subjected to a decellularization protocol combined with sterilization using supercritical carbon dioxide (scCO₂). The decellularization efficiency of human meniscus tissue was evaluated via DNA quantification and Hematoxylin & Eosin (H&E) and DAPI staining. The mechanical properties of native, decellularized, and decellularized + sterilized meniscus tissue were evaluated, and its composition was determined via collagen and glycosaminoglycan (GAG) quantification, and a collagen and GAG stain. Additionally, cytocompatibility was determined in vitro.

RESULTS

Human menisci were decellularized to DNA levels of ~ 20 ng/mg of tissue dry weight. The mechanical properties and composition of human meniscus were not significantly affected by decellularization and sterilization. Histologically, the decellularized and sterilized meniscus tissue had maintained its collagen and glycosaminoglycan structure and distribution. Besides, the processed tissues were not cytotoxic to seeded human dermal fibroblasts in vitro.

CONCLUSIONS

Human meniscus tissue was successfully decellularized, while maintaining biomechanical, structural, and compositional properties, without signs of in vitro cytotoxicity. The ease at which human meniscus tissue can be efficiently decellularized, while maintaining its native properties, paves the way towards clinical use.

Preparation of hybrid meniscal constructs using hydrogels and acellular matrices

To search for a suitable meniscus repair material, acellular hybrid scaffolds consisting of in situ cross-linkable 3-D interpenetrating network structures were obtained by decellularization of the meniscus tissues followed by integration of the gel system. Decellularization efficiency was confirmed using a DNA quantification assay (82% decrease in DNA content) and histological stainings. In the second part of the study, the gelatin molecule was functionalized by adding methacrylic anhydride and the degree of functionalization was found to be 75% by (Proton-Nuclear Magnetic Resonance) ¹H-NMR. Using this, a series of hybrid constructs named GelMA-Hybrid (G-Hybrid), GELMA/PEGDMA-Hybrid (PG-Hybrid), and GelMA/PEGDMA/HAMA-Hybrid (PGH-Hybrid) were prepared by cross-linking with UVA. Changes in the chemical structure were determined with Fourier Transform Infrared Spectrophotometer (FTIR). Water uptake capacities of cross-linked hybrid structures were measured in swelling studies, and it was found that hybrid scaffolds showed similar swelling properties compared to native counterparts. By compressive mechanical tests, enhanced mechanical properties were revealed in cross-linked scaffolds with PGH-Hybrid having the highest cross-link density. Protein denaturation and decomposition transition temperatures were improved by adding hydrogels to acellular scaffolds according to thermal gravimetric analyses (TGA). Cross-linked acellular scaffolds have exhibited a behavior close to native tissues with below 25% mass loss in phosphate buffer saline (PBS) and enzymatic solution. Cell viability was examined through Alamar Blue on the first day and cell viability in hybrid constructs was found to be above 80% while it was closer to the control group on the 7^th day. It was concluded that the developed biomaterials could be used in meniscus tissue engineering with their tunable physicochemical and mechanical properties.

Tensile mechanical properties of vitrified porcine menisci are superior to frozen and similar to fresh porcine menisci

Vitrification inhibits crystallization of ice and may allow the mechanical properties of menisci to be preserved for transplantation without the damaging consequences of ice crystals formed during freezing. The primary objective of this study was to investigate the differences between fresh, frozen, and vitrified porcine lateral menisci examining tensile mechanical properties along the circumferential-peripheral, circumferential-central, longitudinal, and radial orientations. The secondary objective was to investigate the variations in the tensile mechanical properties of menisci comparing the circumferential-peripheral orientation to the three other orientations: circumferential-central, longitudinal, and radial. Quasi-static tensile testing was conducted to quantify the tensile mechanical properties of fresh, frozen and vitrified menisci. Ultimate tensile strength of frozen menisci were significantly decreased compared with fresh and vitrified menisci along three orientations: circumferential-peripheral, longitudinal, and radial. Along the circumferential-central orientation, tensile modulus of frozen menisci was significantly decreased compared with fresh menisci. The mechanical properties of vitrified menisci were comparable to fresh menisci along all four orientations. For all menisci (fresh, frozen and vitrified), ultimate tensile strength and failure strain along the circumferential-peripheral orientation were significantly increased compared with the three other orientations. Freezing was detrimental to the mechanical properties of menisci but vitrification likely avoided the negative effects of freezing thereby preserving mechanical properties that were comparable to fresh menisci. The findings of this study revealed that vitrification was superior to freezing for preserving mechanical properties of meniscal tissue; hence, vitrification is likely to be a competitive alternative to freezing for meniscal transplantation in the future.

Anisotropic hydrogel fabricated by controlled diffusion as a bio-scaffold for the regeneration of cartilage injury

Controlled fabrication of anisotropic materials has become a hotspot in materials science, particularly biomaterials, since the next generation of tissue engineering is based on the application of heterogeneous structures that can simulate the original biological complexity of the body. The current fabrication method of producing anisotropic materials involves expensive and highly specialized equipment, and not every conventional method can be applied to preparing anisotropic materials for corresponding tissue engineering. Anisotropic materials can be easily applied to a problem in tissue engineering: cartilage injury repairing. The articular cartilage consists of four spatially distinct regions: superficial, transitional, deep, and calcified. Each region has a specific extracellular matrix composition, mechanical properties, and cellular organization; this calls for the application of an anisotropic hydrogel. Controlled diffusion, under the assistance of buoyancy, has been considered a generalized method to prepare materials using a gradient. The diffusion of two solutions can be controlled through the difference in their densities. In addition to providing anisotropy, this method realizes the in situ formation of an anisotropic hydrogel, and simplifies the preparation process, freeing it from the need for expensive equipment such as 3D printing and microfluidics. Herein, an anisotropic hydrogel based on a decellularized extracellular matrix is fabricated and characterized. The as-prepared scaffold possessed specific chemical composition, physical properties, and physiological factor gradient. In vitro experiments ensured its biocompatibility and biological effectiveness; further in vivo experiments confirmed its application in the effective regeneration of cartilage injury.

The biomimetic extracellular matrix: a therapeutic tool for breast cancer research

A deeper knowledge of the functional versatility and dynamic nature of the ECM has improved the understanding of cancer biology. Translational Significance: This work provides an in-depth view of the importance of the ECM to develop more mimetic breast cancer models, which aim to recreate the components and architecture of tumor microenvironment. Special focus is placed on decellularized matrices derived from tissue and cell culture, both in procurement and applications, as they have achieved great success in cancer research and pharmaceutical sector. The extracellular matrix (ECM) is increasingly recognized as a master regulator of cell behavior and response to breast cancer (BC) treatment. During BC progression, the mammary gland ECM is remodeled and altered in the composition and organization. Accumulated evidence suggests that changes in the composition and mechanics of ECM, orchestrated by tumor-stromal interactions along with ECM remodeling enzymes, are actively involved in BC progression and metastasis. Understanding how specific ECM components modulate the tumorigenic process has led to an increased interest in the development of biomaterial-based biomimetic ECM models to recapitulate key tumor characteristics. The decellularized ECMs (dECMs) have emerged as a promising in vitro 3D tumor model, whose recent advances in the processing and application could become the biomaterial by excellence for BC research and the pharmaceutical industry. This review offers a detailed view of the contribution of ECM in BC progression, and highlights the application of dECM-based biomaterials as promising personalized tumor models that more accurately mimic the tumorigenic mechanisms of BC and the response to treatment. This will allow the design of targeted therapeutic approaches adapted to the specific characteristics of each tumor that will have a great impact on the precision medicine applied to BC patients.

Towards the development of osteochondral allografts with reduced immunogenicity

Nowadays, repair and replacement of hyaline articular cartilage still challenges orthopedic surgery. Using a graft of decellularized articular cartilage as a structural scaffold is considered as a promising therapy. So far, successful cell removal has only been possible for small samples with destruction of the macrostructure or loss of biomechanics. Our aim was to develop a mild, enzyme-free chemical decellularization procedure while preserving the biomechanical properties of cartilage. Porcine osteochondral cylinders (diameter: 12 mm; height: 10 mm) were divided into four groups: Native plugs (NA), decellularized plugs treated with PBS, Triton-X-100 and SDS (DC), and plugs additionally treated with freeze-thaw-cycles of -20 °C, -80 °C or shock freezing in nitrogen (N₂) before decellularization. In a non-decalcified HE stain the decellularization efficiency (cell removal, cell size, depth of decellularization) was calculated. For biomechanics the elastic and compression modulus, transition and failure strain as well as transition and failure stress were evaluated. The -20 °C, -80 °C, and N₂ groups showed a complete decellularization of the superficial and middle zone. In the deep zone cells could not be removed in any experimental group. The biomechanical analysis showed only a reduced elastic modulus in all decellularized samples. No significant differences were found for the other biomechanical parameters.

Development of meniscus cartilage using polycaprolactone and decellularized meniscus surface modified by gelatin, hyaluronic acid biomacromolecules: A rabbit model

The lack of vascularization in the white-red and white zone of the meniscus causes these zones of tissue to have low self-healing capacity in case of injury and accelerate osteoarthritis (OA). In this study, we have developed hybrid constructs using polycaprolactone (PCL) and decellularized meniscus extracellular matrix (DMECM) surface modified by gelatin (G), hyaluronic acid (HU) and selenium (Se) nanoparticles (PCL/DMECM/G/HU/Se), following by the cross-linking of the bio-polymeric surface. Material characterization has been performed on the fabricated scaffold using scanning electron microscopy (SEM), Fourier transforms infrared (FTIR) spectroscopy, swelling and degradation analyses, and mechanical tests. In Vitro, investigations have been conducted by C28/I2 human chondrocyte culture into the scaffold and evaluated the cytotoxicity and cell/scaffold interaction. For the in vivo study, the scaffolds were transplanted into the defect sites of female New Zealand white rabbits. Good regeneration was observed after two months. We have concluded that the designed PCL/DMECM/G/HU construct can be a promising candidate as a meniscus tissue engineering scaffold to facilitate healing.

An overview of post transplantation events of decellularized scaffolds

Regenerative medicine and tissue engineering are reasonable techniques for repairing failed tissues and could be a suitable alternative to organ transplantation. One of the most widely used methods for preparing bioscaffolds is the decellularization procedure. Although cell debris and DNA are removed from the decellularized tissues, important compositions of the extracellular matrix including proteins, proteoglycans, and glycoproteins are nearly preserved. Moreover, the obtained scaffolds have a 3-dimensional (3D) structure, appropriate naïve mechanical properties, and good biocompatibility. After transplantation, different types of host cells migrate to the decellularized tissues. Histological and immunohistochemical assessment of the different bioscaffolds after implantation reveals the migration of parenchymal cells, angiogenesis, as well as the invasion of inflammatory and giant foreign cells. In this review, the events after transplantation including angiogenesis, scaffold degradation, and the presence of immune and tissue-specific progenitor cells in the decellularized scaffolds in various hosts, are discussed.

Decellularised human bone allograft from different anatomical sites as a basis for functionally stratified repair material for bone defects

Tissue engineered bone solutions aim to overcome the limitations of autologous and allogeneic grafts. Decellularised tissues are produced by washing cellular components from human or animal tissue to produce an immunologically safe and biocompatible scaffold, capable of integration following implantation. A decellularisation procedure utilising low concentration sodium dodecyl sulphate (0.1% w/v) was applied to trabecular bone from human femoral heads (FH) and tibial plateaus (TP). Biological (histology, DNA quantification), biomechanical (compression testing) and structural (μCT) comparisons were made between decellularised and unprocessed cellular tissue. Total DNA levels of decellularised FH and TP bone were below 50 ng mg^-1 dry tissue weight and nuclear material was removed. No differences were found between cellular and decellularised bone, from each anatomical region, for all the biomechanical and structural parameters investigated. Differences were found between cellular FH and TP and between decellularised FH and TP. Decellularised FH had a higher ultimate compressive stress, Young's modulus and 0.2% proof stress than decellularised TP (p = 0.001, 0.002, 0.001, Mann Whitney U test, MWU). The mineral density of cellular and decellularised TP bone was significantly greater than cellular and decellularised FH bone respectively (cellular: p = 0.001, decellularised: p < 0.001, MWU). The bone volume fraction and trabecular thickness of cellular and decellularised FH bone were significantly greater than cellular and decellularised TP bone respectively (cellular: p = 0.001, 0.005; decellularised: p < 0.001, <0.001, MWU). Characterisation of decellularised trabecular bone from different anatomical regions offers the possibility of product stratification, allowing selection of biomechanical properties to match particular anatomical regions undergoing bone graft procedures.

Biomaterials and Meniscal Lesions: Current Concepts and Future Perspective

Menisci are crucial structures for knee homeostasis. After a meniscal lesion, the golden rule, now, is to save as much meniscus as possible; only the meniscus tissue that is identified as unrepairable should be excised, and meniscal sutures find more and more indications. Several different methods have been proposed to improve meniscal healing. They include very basic techniques, such as needling, abrasion, trephination and gluing, or more complex methods, such as synovial flaps, meniscal wrapping or the application of fibrin clots. Basic research of meniscal substitutes has also become very active in the last decades. The aim of this literature review is to analyze possible therapeutic and surgical options that go beyond traditional meniscal surgery: from scaffolds, which are made of different kind of polymers, such as natural, synthetic or hydrogel components, to new technologies, such as 3-D printing construct or hybrid biomaterials made of scaffolds and specific cells. These recent advances show that there is great interest in the development of new materials for meniscal reconstruction and that, with the development of new biomaterials, there will be the possibility of better management of meniscal injuries

Integration and functional performance of a decellularised porcine superflexor tendon graft in an ovine model of anterior cruciate ligament reconstruction

The objective was to evaluate the performance of decellularised porcine superflexor tendon (pSFT) as an anterior cruciate ligament (ACL) reconstruction device. The ACL of adult sheep was reconstructed with decellularised pSFT or ovine allograft SFT and animals sacrificed at 4, 12 and 26 weeks (n = 4 per group) for biological evaluation and 26 weeks (n = 6) for biomechanical evaluation of the grafts. Both grafts showed good in vivo performance with no major differences at macroscopic evaluation post euthanasia. Histopathology revealed an inflammatory reaction to both grafts at 4 weeks, which reduced by 26 weeks. There was advanced cellular ingrowth from 12 weeks, ligamentisation of intra-articular grafts, ossification and formation of Sharpey's fibers at the graft/bone junctions. Immunohistochemistry showed that at 4 and 12 weeks, the host response was dominated by CD163+ M2 macrophages and a cell infiltrate comprising α-SMA + myofibroblasts, CD34⁺ and CD271+ progenitor cells. At 26 weeks the biomechanical properties of decellularised pSFT and oSFT grafts were comparable, with all grafts failing in the intra-articular region. This study provides new insight into constructive remodelling of tendons used for ACL replacement and evidence of integration and functional performance of a decellularised xenogeneic tendon with potential as an alternative for ACL reconstruction.

Advances in electrospun scaffolds for meniscus tissue engineering and regeneration

The meniscus plays a critical role in maintaining the homeostasis, biomechanics, and structural stability of the knee joint. Unfortunately, it is predisposed to damages either from sports-related trauma or age-related degeneration. The meniscus has an inherently limited capacity for tissue regeneration. Self-healing of injured adult menisci only occurs in the peripheral vascularized portion, while the spontaneous repair of the inner avascular region seems never happens. Repair, replacement, and regeneration of menisci through tissue engineering strategies are promising to address this problem. Recently, many scaffolds for meniscus tissue engineering have been proposed for both experimental and preclinical investigations. Electrospinning is a feasible and versatile technique to produce nano- to micro-scale fibers that mimic the microarchitecture of native extracellular matrix and is an effective approach to prepare nanofibrous scaffolds for constructing engineered meniscus. Electrospun scaffolds are reported to be capable of inducing colonization of meniscus cells by modulating local extracellular density and stimulating endogenous regeneration by driving reprogramming of meniscus wound microenvironment. Electrospun nanofibrous scaffolds with tunable mechanical properties, controllable anisotropy, and various porosities have shown promises for meniscus repair and regeneration and will undoubtedly inspire more efforts in exploring effective therapeutic approaches towards clinical applications. In this article, we review the current advances in the use of electrospun nanofibrous scaffolds for meniscus tissue engineering and repair and discuss prospects for future studies.

Fabrication of decellularized meniscus extracellular matrix according to inner cartilaginous, middle transitional, and outer fibrous zones result in zone-specific protein expression useful for precise replication of meniscus zones

Meniscus is a fibrocartilage composite tissue with three different microstructual zones, inner fibrocartilage, middle transitional, and outer fibrous zone. We hypothesized that decellularized meniscus extracellular matrix (DMECM) would have different characteristics according to zone of origin. We aimed to compare zone-specific DMECM in terms of biochemical characteristics and cellular interactions associated with tissue engineering. Micronized DMECM was fabricated from porcine meniscus divided into three microstructural zones. Characterization of DMECM was done by biochemical and proteomic analysis. Inner DMECM showed the highest glycosaminoglycan content, while middle DMECM showed the highest collagen content among groups. Proteomic analysis showed significant differences among DMECM groups. Inner DMECM showed better adhesion and migration potential to meniscus cells compared to other groups. DMECM resulted in expression of zone-specific differentiation markers when co-cultured with synovial mesenchymal stem cells (SMSCs). SMSCs combined with inner DMECM showed the highest glycosaminoglycan in vivo. Outer DMECM constructs, on the other hand, showed more fibrous tissue features, while middle DMECM constructs showed both inner and outer zone characteristics. In conclusion, DMECM showed different characteristics according to microstructural zones, and such material may be useful for zone-specific tissue engineering of meniscus.

A review of strategies for development of tissue engineered meniscal implants

The meniscus is a key stabilizing tissue of the knee that facilitates proper tracking and movement of the knee joint and absorbs stresses related to physical activity. This review article describes the biology, structure, and functions of the human knee meniscus, common tears and repair approaches, and current research and development approaches using modern methods to fabricate a scaffold or tissue engineered meniscal replacement. Meniscal tears are quite common, often resulting from sports or physical training, though injury can result without specific contact during normal physical activity such as bending or squatting. Meniscal injuries often require surgical intervention to repair, restore basic functionality and relieve pain, and severe damage may warrant reconstruction using allograft transplants or commercial implant devices. Ongoing research is attempting to develop alternative scaffold and tissue engineered devices using modern fabrication techniques including three-dimensional (3D) printing which can fabricate a patient-specific meniscus replacement. An ideal meniscal substitute should have mechanical properties that are close to that of natural human meniscus, and also be easily adapted for surgical procedures and fixation. A better understanding of the organization and structure of the meniscus as well as its potential points of failure will lead to improved design approaches to generate a suitable and functional replacement.

Augmentation of the insufficient tissue bed for surgical repair of hypospadias using acellular matrix grafts: A proof of concept study

Acellular matrices produced by tissue decellularisation are reported to have tissue integrative properties. We examined the potential for incorporating acellular matrix grafts during procedures where there is an inadequate natural tissue bed to support an enduring surgical repair. Hypospadias is a common congenital defect requiring surgery, but associated with long-term complications due to deficiencies in the quality and quantity of the host tissue bed at the repair site. Biomaterials were implanted as single on-lay grafts in a peri-urethral position in male pigs. Two acellular tissue matrices were compared: full-thickness porcine acellular bladder matrix (PABM) and commercially-sourced cross-linked acellular matrix from porcine dermis (Permacol™). Anatomical and immunohistological outcomes were assessed 3 months post-surgery. There were no complications and surgical sites underwent full cosmetic repair. PABM grafts were fully incorporated, whilst Permacol™ grafts remained palpable. Immunohistochemical analysis indicated a non-inflammatory, remodelling-type response to both biomaterials. PABM implants showed extensive stromal cell infiltration and neovascularisation, with a significantly higher density of cells (p < 0.001) than Permacol™, which showed poor cellularisation and partial encapsulation. This study supports the anti-inflammatory and tissue-integrative nature of non-crosslinked acellular matrices and provides proof-of-principle for incorporating acellular matrices during surgical procedures, such as in primary complex hypospadias repair.

An Exploratory Study into the Implantation of Arytenoid Cartilage Scaffold in the Horse

Respiratory function in the horse can be severely compromised by arytenoid chondritis, or arytenoid chondropathy, a pathologic condition leading to deformity and dysfunction of the affected cartilage. Current treatment in cases unresponsive to medical management is removal of the cartilage, which can improve the airway obstruction, but predisposes the patient to other complications like tracheal penetration of oropharyngeal content and dynamic collapse of the now unsupported soft tissue lateral to the cartilage. A tissue engineering approach to reconstructing the arytenoid cartilage would represent a significant advantage in the management of arytenoid chondritis. In this study, we explored if decellularized matrix could potentially be incorporated into the high motion environment of the arytenoid cartilages of horses. Equine arytenoid cartilages were decellularized and a portion of the resultant acellular scaffolds was implanted in a full-thickness defect created in the arytenoids of eight horses. The implantation was performed bilaterally in each horse, with one side randomly selected to receive an implant seeded with autologous bone marrow-derived nucleated cells (BMNCs). Arytenoids structure and function were monitored up to 4 months. In vivo assessments included laryngeal ultrasound, and laryngeal endoscopy at rest and during exercise on a high-speed treadmill. Histologic evaluation of the arytenoids was performed postmortem. Implantation of the cartilaginous graft had no adverse effect on laryngeal respiratory function or swallowing, despite induction of a transient granuloma on the medial aspect of the arytenoids. Ultrasonographic monitoring detected a postoperative increase in the thickness and cross-sectional area of the arytenoid body that receded faster in the arytenoids not seeded with BMNCs. The explanted tissue showed epithelialization of the mucosal surface, integration of the implant into the native arytenoid, with minimal adverse cellular reaction. Remodeling of the scaffold material was evident by 2 months after implantation. Preseeding the scaffold with BMNCs increased the rate of scaffold degradation and incorporation. Replacement of arytenoid portion with a tissue-engineered cartilaginous graft preseeded with BMNCs is surgically feasible in the horse, is well tolerated, and results in appropriate integration within the native tissue, also preventing laryngeal tissue collapse during exercise.

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.

Ex-vivo recellularisation and stem cell differentiation of a decellularised rat dental pulp matrix

Implementing the principles of tissue engineering within the clinical management of non-vital immature permanent teeth is of clinical interest. However, the ideal scaffold remains elusive. The aim of this work was to assess the feasibility of decellularising rat dental pulp tissue and evaluate the ability of such scaffold to support stem cell repopulation. Rat dental pulps were retrieved and divided into control and decellularised groups. The decellularisation protocol incorporated a low detergent concentration and hypotonic buffers. After decellularisation, the scaffolds were characterised histologically, immunohistochemistry and the residual DNA content quantified. Surface topography was also viewed under scanning electron microscopy. Biocompatibility was evaluated using cytotoxicity assays utilising L-929 cell line. Decellularised scaffolds were recellularised with human dental pulp stem cells up to 14 days in vitro. Cellular viability was assessed using LIVE/DEAD stain kit and the recellularised scaffolds were further assessed histologically and immunolabelled using makers for odontoblastic differentiation, cytoskeleton components and growth factors. Analysis of the decellularised scaffolds revealed an acellular matrix with histological preservation of structural components. Decellularised scaffolds were biocompatible and able to support stem cell survival following recellularisation. Immunolabelling of the recellularised scaffolds demonstrated positive cellular expression against the tested markers in culture. This study has demonstrated the feasibility of developing a biocompatible decellularised dental pulp scaffold, which is able to support dental pulp stem cell repopulation. Clinically, decellularised pulp tissue could possibly be a suitable scaffold for use within regenerative (reparative) endodontic techniques.

Injectable ECM hydrogel for delivery of BMSCs enabled full-thickness meniscus repair in an orthotopic rat model

Meniscal injuries have poor intrinsic healing capability and are associated with the development of osteoarthritis. Decellularized meniscus extracellular matrix (mECM) has been suggested to be efficacious for the repair of meniscus defect. However, main efforts to date have been focused on the concentration, crosslinking density and anatomical region dependence of the mECM hydrogels on regulation of proliferation and differentiation of adult mesenchymal stem cells (MSCs) in vitro 2D or 3D culture. A systematic investigation and understanding of the effect of mECM on encapsulated MSCs response and integrative meniscus repair by in vivo rat subcutaneous implantation and orthotopic meniscus injury model will be highly valuable to explore its potential for clinical translation. In this study, we investigated the in situ delivery of rat BMSCs in an injectable mECM hydrogel to a meniscal defect in a SD rat model. Decellularized mECM retained essential proteoglycans and collagens, and significantly upregulated expression of fibrochondrogenic markers by BMSCs versus collagen hydrogel alone in vitro 3D cell culture. When applied to an orthotopic model of meniscal injury in SD rat, mECM is superior than collagen I scaffold in reduction of osteophyte formation and prevention of joint space narrowing and osteoarthritis development as evidenced by histology and micro-CT analysis. Taken together, these results indicate mECM hydrogel is a highly promising carrier to deliver MSCs for long-term repair of meniscus tissue, while preventing the development of osteoarthritis.

Decellularized Intervertebral Discs: A Potential Replacement for Degenerate Human Discs

Intervertebral disc (IVD) degeneration is a major cause of back pain. Current surgical interventions have limitations. An alternative approach is to replace degenerated IVDs with a natural biological scaffold. The removal of cellular components from human IVDs should render them nonimmunogenic upon implantation. The aim of this initial proof of technical feasibility study was to develop a decellularization protocol on bovine IVDs with endplates (EPs) and assess protocol performance before application of the protocol to human IVDs with attached EP and vertebral bone (VB). A decellularization protocol based on hypotonic low concentration sodium dodecyl sulfate (0.1% w/v) with proteinase inhibitors, freeze/thaw cycles, and nuclease and sonication treatments was applied to IVDs. Histological, biochemical, and biomechanical comparisons were made between cellular and decellularized tissue. Cell removal from bovine IVDs was demonstrated and total DNA levels of the decellularized inner annulus fibrosus (iAF), outer annulus fibrosus (oAF), and EP were 40.7 (±11.4), 25.9 (±3.8), and 29.3 (±3.1) ng.mg⁻¹ dry tissue weight, respectively (n = 6, ±95% confidence level [CL]). These values were significantly lower than in cellular tissue. No significant difference in DNA levels between bovine cellular and decellularized nucleus pulposus (NP) was found. Glycosaminoglycans (GAGs) were largely retained in the NP, iAF, and oAF. Cyclic compression testing showed sufficient sensitivity to detect an increase in stiffness of bovine IVD postdecellularization (2957.2 ± 340.8 N.mm⁻¹) (predecellularization: 2685.4 ± 263.1 N.mm⁻¹; n = 5, 95% CL), but the difference was within natural tissue variation. Total DNA levels for all decellularized tissue regions of human IVDs (NP, iAF, oAF, EP, and VB) were below 50 ng.mg⁻¹ dry tissue weight (range: 2 ng.mg⁻¹, iAF to 29 ng.mg⁻¹, VB) and the tissue retained high levels of GAGs. Further studies to assess the biocompatibility and regenerative potential of decellularized human IVDs in vitro and in vivo are now required; however, proof of technical feasibility has been demonstrated and the retention of bone in the IVD samples would allow incorporation of the tissue into the recipient spine.

3D cell-printing of biocompatible and functional meniscus constructs using meniscus-derived bioink

Meniscus injuries are prevalent in orthopedic diagnosis. The reconstruction of the structural inhomogeneity and anisotropy of the meniscus is a major challenge in clinical practice. Meniscal tissue engineering has emerged as a potential alternative for the treatment of various meniscal diseases and injuries. In this study, we developed three-dimensional (3D) cell-printed meniscus constructs using a mixture of polyurethane and polycaprolactone polymers and cell-laden decellularized meniscal extracellular matrix (me-dECM) bioink with high controllability and durable architectural integrity. The me-dECM bioink provided 3D cell-printed meniscus constructs with a conducive biochemical environment that supported growth and promoted the proliferation and differentiation of encapsulated stem cells toward fibrochondrogenic commitment. In addition, we investigated the in vivo performance of the 3D cell-printed meniscus constructs, which exhibited biocompatibility, excellent mechanical properties, and improved biological functionality. These attributes were similar to those of the native meniscus. Collectively, the 3D cell-printing technology and me-dECM bioink facilitate the recapitulation of meniscus tissue specificity in the aspect of the shape and microenvironment for meniscus regeneration. Further, the developed constructs can potentially be applied in clinical practice.

Cell-derived decellularized extracellular matrix scaffolds for articular cartilage repair

Articular cartilage repair remains a great clinical challenge. Tissue engineering approaches based on decellularized extracellular matrix (dECM) scaffolds show promise for facilitating articular cartilage repair. Traditional regenerative approaches currently used in clinical practice, such as microfracture, mosaicplasty, and autologous chondrocyte implantation, can improve cartilage repair and show therapeutic effect to some degree; however, the long-term curative effect is suboptimal. As dECM prepared by proper decellularization procedures is a biodegradable material, which provides space for regeneration tissue growth, possesses low immunogenicity, and retains most of its bioactive molecules that maintain tissue homeostasis and facilitate tissue repair, dECM scaffolds may provide a biomimetic microenvironment promoting cell attachment, proliferation, and chondrogenic differentiation. Currently, cell-derived dECM scaffolds have become a research hotspot in the field of cartilage tissue engineering, as ECM derived from cells cultured in vitro has many advantages compared with native cartilage ECM. This review describes cell types used to secrete ECM, methods of inducing cells to secrete cartilage-like ECM and decellularization methods to prepare cell-derived dECM. The potential mechanism of dECM scaffolds on cartilage repair, methods for improving the mechanical strength of cell-derived dECM scaffolds, and future perspectives on cell-derived dECM scaffolds are also discussed in this review.

Preparation and Characterization of an Optimized Meniscal Extracellular Matrix Scaffold for Meniscus Transplantation

Many studies have sought to construct a substitute to partially replace irreparably damaged meniscus. Only the meniscus allograft has been used in clinical practice as a useful substitute, and there are concerns about its longevity and inherent limitations, including availability of donor tissue and possibility of disease transmission. To overcome these limitations, we developed an acellular xenograft from whole porcine meniscus. Samples were treated with 2% Triton X-100 for 10 days and 2% sodium dodecyl sulfate for 6 days. The DNA content of extracellular matrix (ECM) scaffolds was significantly decreased compared with that of normal porcine menisci (p < 0.001). Histological analysis confirmed the maintenance of ECM integrity and anisotropic architecture in the absence of nuclei. Biochemical and biomechanical assays of the scaffolds indicated the preservation of collagen (p = 0.806), glycosaminoglycan (p = 0.188), and biomechanical properties (elastic modulus and transition stress). The scaffolds possessed good biocompatibility and supported bone marrow mesenchymal stem cells (BMSCs) proliferation for 2 weeks in vitro, with excellent region-specific recellularization in vivo. The novel scaffold has potential value for application in recellularization and transplantation strategies.

Acellular matrix hydrogel for repair of the temporomandibular joint disc

Application of tissue-derived extracellular matrix (ECM) biomaterials in the repair of the temporomandibular joint (TMJ) disc is a promising approach for the treatment of disc abrasion and perforation, particularly for the young patient population. Although decellularized ECM (dECM) scaffolds preserve tissue-specific structures as well as biological and biomechanical properties, they require surgical implantation. To address this issue, we prepared porcine TMJ discs into decellularized ECM with serial detergent and enzyme treatments, and the TMJ disc-derived ECM was then processed into hydrogels via pepsin digestion. The decellularization efficiency was assessed by quantification of the DNA and matrix component contents. The fibrous ultrastructure of the hydrogel was observed by scanning electron microscopy (SEM). Rheological characterization and mechanical properties were measured. in vitro experiments with costal chondrocytes ensured the cellular proliferative capacity and compatibility in the injectable disc-derived ECM hydrogel. The results showed that a large amount of DNA (>95%) was removed after decellularization; but, the collagen was retained. SEM of the hydrogels demonstrated a multiaperture fiber ultrastructure. Rheological studies revealed a rapid gelation temperature (37°C) and injectable properties. The mechanical properties of the hydrogels were adjusted by changing the ECM concentration. The in vitro studies revealed that the hydrogels are not cytotoxic, but instead showed good cytocompatibility. The hydrogel also showed good injectability and degradability through an in vivo study. Overall, these results suggest the great potential of injectable disc-derived hydrogels for TMJ disc repair and regeneration applications.

Re-Differentiation of Human Meniscus Fibrochondrocytes Differs in Three-Dimensional Cell Aggregates and Decellularized Human Meniscus Matrix Scaffolds

Decellularized matrix (DCM) derived from native tissues may be a promising supporting material to induce cellular differentiation by sequestered bioactive factors. However, no previous study has investigated the use of human meniscus-derived DCM to re-differentiate human meniscus fibrochondrocytes (MFCs) to form meniscus-like extracellular matrix (ECM). We expanded human MFCs and seeded them upon a cadaveric meniscus-derived DCM prepared by physical homogenization under hypoxia. To assess the bioactivity of the DCM, we used conditions with and without chondrogenic factor TGF-β3 and set up a cell pellet culture model as a biomaterial-free control. We found that the DCM supported chondrogenic re-differentiation and ECM formation of MFCs only in the presence of exogenous TGF-β3. Chondrogenic re-differentiation was more robust at the protein level in the pellet model as MFCs on the DCM appeared to favour a more proliferative phenotype. Interestingly, without growth factors, the DCM tended to promote expression of hypertrophic differentiation markers relative to the pellet model. Therefore, the human meniscus-derived DCM prepared by physical homogenization contained insufficient bioactive factors to induce appreciable ECM formation by human MFCs.

Decellularized Extracellular Matrix as a Potent Natural Biomaterial for Regenerative Medicine

Decellularization technique is a favorable method used to fabricate natural and tissue-like scaffolds. This technique is important because of its remarkable ability to perfectly mimic the natural extracellular matrix (ECM). ECM-based scaffolds/hydrogels provide structural support for cell differentiation and maturation. Therefore, novel natural-based bioinks, ECM-based hydrogels, and particulate forms of the ECM provide promising strategies for whole organ regeneration. Despite its efficacious characteristics, removal of residual detergent and the presence of various protocols make this technique challenging for scientists and regenerative medicine-related programs. This chapter reviews the most effective physical, chemical, and enzymatic protocols used to remove the cellular components and their challenges. We discuss the applications of decellularized ECM (dECM) in tissue engineering and regenerative medicine with an emphasis on hard tissues.

Applications of decellularized materials in tissue engineering: advantages, drawbacks and current improvements, and future perspectives

Decellularized materials (DMs) are attracting more and more attention in tissue engineering because of their many unique advantages, and they could be further improved in some aspects through various means.

Tissue-derived decellularized extracellular matrices toward cartilage repair and regeneration

The inability of cartilage tissue to self-heal due to its avascular nature often leads to conditions such as osteoarthritis, traumatic rupture of cartilage, and osteochondrosis. The cartilage provides cushioning effects between the joints and avoids bone frictions. The extracellular matrix (ECM) of cartilage consists predominantly of collagens, elastin, proteoglycans and glycoproteins. A number of tissue engineered ECM derived biological scaffolds and matrices are available for cartilage regeneration. The decellularized tissues provide appropriate bioactive cues in the absence of cellular components, hence avoiding immunological issue. However, the decellularization process involves several cellular disruption techniques that may alter the ECM architecture affecting bioactivity. Therefore, development of cell-free cartilage biomaterials with unaltered ECM integrity and bioactivity is of paramount necessity by smart selection of modified techniques and agents. Herein, we described about various decellularization methods, agents, techniques, and their applications in tissue/cartilage decellularization. It also contemplates various difficulties and future perspectives to troubleshoot the existing obstructions in tissue-derived cartilage matrices and their applications.

Comparison of High-Hydrostatic-Pressure Decellularized Versus Freeze-Thawed Porcine Menisci

The meniscus functions as a load distributor and secondary stabilizer in the knee, and the loss of the meniscus increases the risk of osteoarthritis. Freeze-thawed menisci are used in clinical practice to replace defective menisci; however, the disadvantages of freeze-thawed tissues include disease transmission and immune rejection. In this study, we decellularized menisci using high hydrostatic pressure (HHP) and compared the decellularized menisci with freeze-thawed menisci. Porcine menisci were either pressurized at 1,000 MPa for 10 min and then washed with DNase solution or frozen at -80°C for 2 days and thawed. These menisci then underwent in vitro histological, biochemical, and biomechanical comparisons with native menisci. The HHP-treated and freeze-thawed menisci were also subcutaneously implanted in a pig, and later harvested for histological analysis. The numbers of histologically detected cells were significantly lower and the amount of biochemically detected DNA was approximately 100-fold lower in HHP-treated than in native and freeze-thawed menisci. The compression strength of the HHP-decellularized menisci was decreased after 1 and 50 cycles at 20% strain but was unchanged in the freeze-thawed menisci. After implantation, the numbers of multinucleated giant cells were significantly lower around the HHP-treated menisci than around the freeze-thawed menisci. Recellularization of the HHP-decellularized menisci was confirmed. Thus, although the HHP-decellularized menisci were mechanically inferior to the freeze-thawed meniscus in vitro, they were immunologically superior. Our study is the first to demonstrate the use of HHP for decellularization of the meniscus. © 2019 The Authors. Journal of Orthopaedic Research^® published by Wiley Periodicals, Inc. on behalf of Orthopaedic Research Society. J Orthop Res 37:2466-2475, 2019.

Development of decellularized meniscus extracellular matrix and gelatin/chitosan scaffolds for meniscus tissue engineering

BACKGROUND

Meniscus tissue engineering has provided a great potential treatment for meniscal injuries. However, few scaffolds in meniscus tissue engineering have matched the mechanical properties of native meniscus.

OBJECTIVE

In this study, we developed a composite scaffold using decellularized meniscus extracellular matrix (DMECM) and gelatin/chitosan (G/C) to explore a preferable ratio to enhance the elastic modulus and cytotoxicity properties of scaffolds.

METHODS

The microstructure, porosity, cytotoxicity, and strength of the composite scaffolds were evaluated. The micro-architectures of the samples were evaluated using scanning electron microscope (SEM). Fourier Transform Infrared analysis (FTIR) was used to confirm the chemical structure with different type composite scaffolds. The compressive elastic modulus of all the scaffolds were measured by the universal tensile testing machine DNS300. Calcein-AM (fluorescent green) and propidium iodide (fluorescent red) were used to stain live cells and dead cells. Morphology and spatial distribution of cells within scaffolds were observed by confocal laser scanning microscopy FV 1000.

RESULTS

SEM showed that the composite scaffolds had suitable porous structure. CCK-8 and live/dead staining demonstrated that the composite scaffolds had no cytotoxicity and could promote bone marrow mesenchymal stem cells (BMSCs) proliferation. The FTIR results demonstrated the successful mixing of these two elements, and the addition of DMECM improved the elastic modulus and cytotoxicity of G/C composite scaffolds.

CONCLUSIONS

This study developed a composite scaffold using DMECM and G/C, and demonstrated that it might be suitable for meniscal tissue engineering application.

Development of decellularized meniscus using closed sonication treatment system: potential scaffolds for orthopedics tissue engineering applications

PURPOSE

Meniscus is a fibrocartilagenous tissue that cannot effectively heal due to its complex structure and presence of avascular zone. Thus, tissue engineering and regenerative medicine offer an alternative for the regeneration of meniscus tissues using bioscaffolds as a replacement for the damaged one. The aim of this study was to prepare an ideal meniscus bioscaffold with minimal adverse effect on extracellular matrix components (ECMs) using a sonication treatment system.

METHODS

The decellularization was achieved using a developed closed sonication treatment system for 10 hrs, and continued with a washing process for 5 days. For the control, a simple immersion treatment was set as a benchmark to compare the decellularization efficiency. Histological and biochemical assays were conducted to investigate the cell removal and retention of the vital extracellular matrix. Surface ultrastructure of the prepared scaffolds was evaluated using scanning electron microscope at 5,000× magnification viewed from cross and longitudinal sections. In addition, the biomechanical properties were investigated through ball indentation testing to study the stiffness, residual forces and compression characteristics. Statistical significance between the samples was determined with p-value =0.05.

RESULTS

Histological and biochemical assays confirmed the elimination of antigenic cellular components with the retention of the vital extracellular matrix within the sonicated scaffolds. However, there was a significant removal of sulfated glycosaminoglycans. The surface histoarchitecture portrayed the preserved collagen fibril orientation and arrangement. However, there were minor disruptions on the structure, with few empty micropores formed which represented cell lacunae. The biomechanical properties of bioscaffolds showed the retention of viscoelastic behavior of the scaffolds which mimic native tissues. After immersion treatment, those scaffolds had poor results compared to the sonicated scaffolds due to the inefficiency of the treatment.

CONCLUSION

In conclusion, this study reported that the closed sonication treatment system had high capabilities to prepare ideal bioscaffolds with excellent removal of cellular components, and retained extracellular matrix and biomechanical properties.

Meniscus-Derived Matrix Scaffolds Promote the Integrative Repair of Meniscal Defects

Meniscal tears have a poor healing capacity, and damage to the meniscus is associated with significant pain, disability, and progressive degenerative changes in the knee joint that lead to osteoarthritis. Therefore, strategies to promote meniscus repair and improve meniscus function are needed. The objective of this study was to generate porcine meniscus-derived matrix (MDM) scaffolds and test their effectiveness in promoting meniscus repair via migration of endogenous meniscus cells from the surrounding meniscus or exogenously seeded human bone marrow-derived mesenchymal stem cells (MSCs). Both endogenous meniscal cells and MSCs infiltrated the MDM scaffolds. In the absence of exogenous cells, the 8% MDM scaffolds promoted the integrative repair of an in vitro meniscal defect. Dehydrothermal crosslinking and concentration of the MDM influenced the biochemical content and shear strength of repair, demonstrating that the MDM can be tailored to promote tissue repair. These findings indicate that native meniscus cells can enhance meniscus healing if a scaffold is provided that promotes cellular infiltration and tissue growth. The high affinity of cells for the MDM and the ability to remodel the scaffold reveals the potential of MDM to integrate with native meniscal tissue to promote long-term repair without necessarily requiring exogenous cells.

Intact vitreous humor as a potential extracellular matrix hydrogel for cartilage tissue engineering applications

Decellularisation of tissues, utilising their biochemical cues, poses exciting tissue engineering (TE) opportunities. However, removing DNA from cartilage (dCart) requires harsh treatments due to its dense structure, causing loss of bioactivity and limiting its application as a cartilaginous extra cellular matrix (ECM). In this study, we demonstrate for the first time the successful application of vitreous humor (VH), a highly hydrated tissue closely resembling the glycosaminoglycan (GAG) and collagen composition of cartilage, as an ECM hydrogel to support chondrogenic differentiation. Equine VH was extracted followed by biochemical quantifications, histological examinations, cytotoxicity (human mesenchymal stromal cells, hMSCs and human articular chondrocytes, hACs) and U937 cell proliferation studies. VH was further seeded with hACs or hMSCs and cultured for 3-weeks to study chondrogenesis compared to scaffold-free micro-tissue pellet cultures and collagen-I hydrogels. Viability, metabolic activity, GAG and DNA content, chondrogenic gene expression (aggrecan, collagen I/II mRNA) and mechanical properties were quantified and matrix deposition was visualised using immunohistochemistry (Safranin-O, collagen I/II). VH was successfully extracted, exhibiting negligible amounts of DNA (0.4 ± 0.4 µg/mg dry-weight) and notable preservation of ECM components. VH displayed neither cytotoxic responses nor proliferation of macrophage-like U937 cells, instead enhancing both hMSC and hAC proliferation. Interestingly, encapsulated cells self-assembled the VH-hydrogel into spheroids, resulting in uniform distribution of both GAGs and collagen type II with increased compressive mechanical properties, rendering VH a permissive native ECM source to fabricate cartilaginous hydrogels for potential TE applications. STATEMENT OF SIGNIFICANCE: Fabricating bioactive and cell-instructive cartilage extracellular matrix (ECM) derived biomaterials and hydrogels has over recent years proven to be a challenging task, often limited by poor retention of inherent environmental cues post decellularisation due to the dense and avascular nature of native cartilage. In this study, we present an alternative route to fabricate highly permissive and bioactive ECM hydrogels from vitreous humor (VH) tissue. This paper specifically reports the discovery of optimal VH extraction protocols and cell seeding strategy enabling fabrication of cartilaginous matrix components into a hydrogel support material for promoting chondrogenic differentiation. The work showcases a naturally intact and unmodified hydrogel design that improves cellular responses and may help guide the development of cell instructive and stimuli responsive hybrid biomaterials in a number of TERM applications.

Novel decellularized animal conchal cartilage graft for application in human patient

Restoration of the external ear and nose in human patients, in either congenital deformity or acquired defects, is a challenge in reconstructive surgery. Optimization of the currently available materials is necessary for rhinoplasty and microtia correction to avoid intraoperative manoeuvring and early rejection. The aim of this study was to develop cross-linked decellularized caprine conchal cartilages as biocompatible, robust, and non-toxic matrix template. The characterization of the decellularized tissue encompasses in vitro lymphoproliferation assay, cytotoxicity test, agar gel precipitation test, in vivo immunocompatibility study, histology, and determination of pro-inflammatory cytokines in animal model. Decellularized cartilage was implanted in human volunteer at R. G. Kar Medical College and Hospital, Kolkata, India, and samples were assessed histologically by retrieving those after 4 months. The processed cartilages were implanted in rhinoplasty (nine) and microtia patients (six) keeping autogenous cartilage graft as control up to 18 months after surgery. Primary outcomes were viability and safety of the material, both in animal model and human pre-application in actual site. Secondary outcomes included self-assessed clinical findings on gross examination. This study is under the ethical approval no. RKC/14 dated January 27, 2012. The in vitro cellular reactivity was less in processed cartilage protein than control. Histology of retrieved tissues in animal model and human volunteer showed no adverse reactions. Production of IL-2, IL-6, and TNF-α cytokines was lower at 4 weeks. The rhinoplasty and microtia operation in clinical patients utilizing the processed cartilage showed satisfactory recovery with improved facial look. These low cost, easily available, biocompatible, safe xenocartilage biomatrices of caprine conchal cartilage origin are very flexible in shape and size, enabling them as potential bioimplant for repair of nasal and auricular structure without any rejection or diverse biomedical applications.

Short cracks in knee meniscus tissue cause strain concentrations, but do not reduce ultimate stress, in single-cycle uniaxial tension

Tears are central to knee meniscus pathology and, from a mechanical perspective, are crack-like defects (cracks). In many materials, cracks create stress concentrations that cause progressive local rupture and reduce effective strength. It is currently unknown if cracks in meniscus have these consequences; if they do, this would have repercussions for management of meniscus pathology. The objective of this study was to determine if a short crack in meniscus tissue, which mimics a preclinical meniscus tear, (a) causes crack growth and reduces effective strength, (b) creates a near-tip strain concentration and (c) creates unloaded regions on either side of the crack. Specimens with and without cracks were tested in uniaxial tension and compared in terms of macroscopic stress-strain curves and digital image correlation strain fields. The strain fields were used as an indicator of stress concentrations and unloaded regions. Effective strength was found to be insensitive to the presence of a crack (potential effect < 0.86 s.d.; β = 0.2), but significant strain concentrations, which have the potential to lead to long-term accumulation of tissue or cell damage, were observed near the crack tip.

Development and characterisation of a large diameter decellularised vascular allograft

The aims of this study were to develop a biological large diameter vascular graft by decellularisation of native human aorta to remove the immunogenic cells whilst retaining the essential biomechanical, and biochemical properties for the ultimate benefit of patients with infected synthetic grafts. Donor aortas (n = 6) were subjected to an adaptation of a propriety decellularisation process to remove the cells and acellularity assessed by histological analysis and extraction and quantification of total DNA. The biocompatibility of the acellular aortas was determined using standard contact cytotoxicity tests. Collagen and denatured collagen content of aortas was determined and immunohistochemistry was used to determine the presence of specific extracellular matrix proteins. Donor aortas (n = 6) were divided into two, with one half subject to decellularisation and the other half retained as native tissue. The native and decellularised aorta sections were then subject to uniaxial tensile testing to failure [axial and circumferential directions] and suture retention testing. The data was compared using a paired t-test. Histological evaluation showed an absence of cells in the treated aortas and retention of histoarchitecture including elastin content. The decellularised aortas had less than 15 ng mg-1 total DNA per dry weight (mean 94% reduction) and were biocompatible as determined by in vitro contact cytotoxicity tests. There were no gross changes in the histoarchitecture [elastin and collagen matrix] of the acellular aortas compared to native controls. The decellularisation process also reduced calcium deposits within the tissue. The uniaxial tensile and suture retention testing revealed no significant differences in the material properties (p > 0.05) of decellularised aorta. The decellularisation procedure resulted in minimal changes to the biological and biomechanical properties of the donor aortas. Acellular donor aorta has excellent potential for use as a large diameter vascular graft.

Efficient decellularization of rabbit trachea to generate a tissue engineering scaffold biomatrix

OBJECTIVES

Most tracheal decellularization protocols are lengthy and can lead to reduced biomechanical stability. The objectives of this study were: 1) to generate a tracheal extracellular matrix scaffold using an efficient decellularization process and 2) to characterize the decellularized scaffold to assess its suitability for tissue engineering applications.

METHODS

Twelve rabbit tracheae underwent a decellularization process that involved enzymatic-detergent treatments. For characterization, fresh (control) and decellularized tissues underwent histological, immunohistochemical, and biochemical analyses. Tensile testing, scanning electron microscopy, and biocompatibility assay were also conducted.

RESULTS

Post-decellularization, the tracheal tissue had significantly less genetic material while the structural integrity was maintained. Specifically, the deoxyribonucleic acid content was significantly reduced and the glycosaminoglycan content was unchanged. Cell and cellular components were largely removed; at the same time the tensile properties and surface ultrastructural characteristics were unaltered. Biocompatibility was confirmed by contact cytotoxicity assay.

CONCLUSIONS

Overall, an efficient decellularization process was used to treat rabbit tracheal tissue. The effectiveness of the decellularization process was demonstrated and at the same time there was preservation of the underlying extracellular matrix structure. This decellularized material may serve as a potential scaffold for tracheal tissue engineering.

Platelet-derived growth factor-coated decellularized meniscus scaffold for integrative healing of meniscus tears

The aim of this study was to examine the potential of platelet-derived growth factor (PDGF)-coated decellularized meniscus scaffold in mediating integrative healing of meniscus tears by inducing endogenous cell migration. Fresh bovine meniscus was chemically decellularized and covalently conjugated with heparin and PDGF-BB. In vitro PDGF release kinetics was measured. The scaffold was transplanted into experimental tears in avascular bovine meniscus explants and cultured for 2 and 4 weeks. The number migrating and proliferating cells at the borderline between the scaffold and injured explant and PDGF receptor-β (PDGFRβ) expressing cells were counted. The alignment of the newly produced ECM and collagen was analyzed by Safranin-O, picrosirius red staining, and differential interference contrast (DIC). Tensile testing of the explants was performed after culture for 2 and 4 weeks. Heparin conjugated scaffold showed immobilization of high levels of PDGF-BB, with sustained release over 2 weeks. Insertion of the PDGF-BB treated scaffold in defects in avascular meniscus led to increased PDGFRβ expression, cell migration and proliferation into the defect zone. Safranin-O, picrosirius red staining and DIC showed tissue integration between the scaffold and injured explants. Tensile properties of injured explants treated with PDGF-BB coated scaffold were significantly higher than in the scaffold without PDGF. In conclusion, PDGF-BB-coated scaffold increased PDGFRβ expression and promoted migration of endogenous meniscus cells to the defect area. New matrix was formed that bridged the space between the native meniscus and the scaffold and this was associated with improved biomechanical properties. The PDGF-BB-coated scaffold will be promising for clinical translation to healing of meniscus tears.

STATEMENT OF SIGNIFICANCE

Meniscus tears are the most common injury of the knee joint. The most prevalent forms that occur in the inner third typically do not spontaneously heal and represent a major risk factor for the development of knee osteoarthritis. The goal of this project was to develop an approach that is readily applicable for clinical use. We selected a natural and readily available decellularized meniscus scaffold and conjugated it with PDGF, which we had previously found to have strong chemotactic activity for chondrocytes and progenitor cells. The present results show that insertion of the PDGF-conjugated scaffold in defects in avascular meniscus led to endogenous cell migration and proliferation into the defect zone with tissue integration between the scaffold and injured explants and improved tensile properties. This PDGF-conjugated scaffold will be promising for a translational approach to healing of meniscus tears.