Concise Review: Biomimetic Functionalization of Biomaterials to Stimulate the Endogenous Healing Process of Cartilage and Bone Tissue

An Antibacterial Bionic Periosteum with Angiogenesis-Neurogenesis Coupling Effect for Bone Regeneration

The periosteum, rich in neurovascular networks, bone progenitor cells, and stem cells, is vital for bone repair. Current artificial periosteal materials face challenges in mechanical strength, bacterial infection, and promoting osteogenic differentiation and angiogenesis. To address these issues, we adjusted the electrospinning ratio of poly-ε-caprolactone and chitosan and incorporated Zn doping whitlockite with polydopamine coating into a nanofiber membrane. After a series of characterizations, optimal results were achieved with a poly-ε-caprolactone: chitosan ratio of 8:1 and 5% nanoparticle content. In vitro cell experiments and in vivo calvarial defect models, the sustained release of Mg2+ and Ca2+ promoted vascularization and new bone formation, respectively, while the release of Zn2+ was conducive to antibacterial and cooperated with Mg2+ to promote neurovascularization. Consequently, this antibacterial bionic periosteum with an angiogenesis-neurogenesis coupling effect demonstrates a promising potential for bone repair applications.

Systemic Cisplatin Does Not Affect the Bone Regeneration Process in a Critical Size Defect Murine Model

Osteosarcoma (OS) is the most common primary malignant bone tumor, and the current standard of care for OS includes neoadjuvant chemotherapy, followed by an R0 surgical resection of the primary tumor, and then postsurgical adjuvant chemotherapy. Bone reconstruction following OS resection is particularly challenging due to the size of the bone voids and because patients are treated with adjuvant and neoadjuvant systemic chemotherapy, which theoretically could impact bone formation. We hypothesized that an osteogenic material could be used in order to induce bone regeneration when adjuvant or neoadjuvant chemotherapy is given. We utilized a biomimetic, biodegradable magnesium-doped hydroxyapatite/type I collagen composite material (MHA/Coll) to promote bone regeneration in the presence of systemic chemotherapy in a murine critical size defect model. We found that in the presence of neoadjuvant or adjuvant chemotherapy, MHA/Coll is able to enhance and increase bone formation in a murine critical size defect model (11.16 ± 2.55 or 13.80 ± 3.18 versus 8.70 ± 0.81 mm3) for pre-op cisplatin + MHA/Coll (p-value = 0.1639) and MHA/Coll + post-op cisplatin (p-value = 0.1538), respectively, at 12 weeks. These findings indicate that neoadjuvant and adjuvant chemotherapy will not affect the ability of a biomimetic scaffold to regenerate bone to repair bone voids in OS patients. This preliminary data demonstrates that bone regeneration can occur in the presence of chemotherapy, suggesting that there may not be a necessity to modify the current standard of care concerning neoadjuvant and adjuvant chemotherapy for the treatment of metastatic sites or micrometastases.

Biomimetic biphasic scaffolds in osteochondral tissue engineering: Their composition, structure and consequences

Approaches to the design and construction of biomimetic scaffolds for osteochondral tissue, show increasing advances. Considering the limitations of this tissue in terms of repair and regeneration, there is a need to develop appropriately designed scaffolds. A combination of biodegradable polymers especially natural polymers and bioactive ceramics, shows promise in this field. Due to the complicated architecture of this tissue, biphasic and multiphasic scaffolds containing two or more different layers, could mimic the physiology and function of this tissue with a higher degree of similarity. The purpose of this review article is to discuss the approaches focused on the application of biphasic scaffolds for osteochondral tissue engineering, common methods of combining layers and the ultimate consequences of their use in patients were discussed.

Osteochondral Explant Isolation and Culture Under a Compression and Shear Bioreactor

Osteochondral explants harvested from different species are valuable preclinical ex vivo models for tissue engineering research. In this chapter, we describe the isolation of osteochondral plugs from bovine stifle joints, followed by defect creation, and plug preparation in a straightforward manner before mechanical loading using a compression and shear bioreactor. The method can be adapted to isolate osteochondral plugs from any animal species and to load explants in any type of bioreactor.

Adhesive Bioinspired Coating for Enhancing Glass-Ceramics Scaffolds Bioactivity

Bioceramic scaffolds, composed of a biphasic composite containing bioactive glass and hydroxyapatite, were prepared in this work to overcome the intrinsic limits of the two components taken separately (in particular, their specific reactivities and dissolution rates, which should be tunable as a function of the given clinical requirements). To mimic the biological environment and tune the different stages of cellular response, a coating with gelatin and chondroitin sulphate via Layer-by-Layer (LbL) assembly was presented and discussed. The resulting functionalized scaffolds were affected by the coating in terms of microstructure and porosity. In addition, the LbL coating significantly enhanced the seeded cell behaviour, with high adhesion, proliferation and osteogenic activity, as revealed by the alkaline phosphatase activity and overexpression of osteopontin and osteocalcin.

A review on bioceramics scaffolds for bone defect in different types of animal models: HA and β -TCP

Increased life expectancy has led to an increase in the use of bone substitutes in numerous nations, with over two million bone-grafting surgeries performed worldwide each year. A bone defect can be caused by trauma, infections, and tissue resections which can self-heal due to the osteoconductive nature of the native extracellular matrix components. However, natural self-healing is time-consuming, and new bone regeneration is slow, especially for large bone defects. It also remains a clinical challenge for surgeons to have a suitable bone substitute. To date, there are numerous potential treatments for bone grafting, including gold-standard autografts, allograft implantation, xenografts, or bone graft substitutes. Tricalcium phosphate (TCP) and hydroxyapatite (HA) are the most extensively used and studied bone substitutes due to their similar chemical composition to bone. The scaffolds should be testedin vivoandin vitrousing suitable animal models to ensure that the biomaterials work effectively as implants. Hence, this article aims to familiarize readers with the most frequently used animal models for biomaterials testing and highlight the available literature for in vivo studies using small and large animal models. This review summarizes the bio ceramic materials, particularly HA and β-TCP scaffolds, for bone defects in small and large animal models. Besides, the design considerations for the pre-clinical animal model selection for bone defect implants are emphasized and presented.

Bioactive engineered scaffolds based on PCL-PEG-PCL and tumor cell-derived exosomes to minimize the foreign body reaction

Long-term presence of M1 macrophages causes serious foreign body reaction (FBR), which is the main reason for the failure of biological scaffold integration. Inducing M2 polarization of macrophages near scaffolds to reduce foreign body response has been widely researched. In this work, inspired by the special capability of tumor exosomes in macrophages M2 polarization, we integrate tumor-derived exosomes into biological scaffolds to minimize the FBR. In brief, breast cancer cell-derived exosomes are loaded into polycaprolactone-b-polyethylene glycol-b-polycaprolactone (PCL-PEG-PCL) fiber scaffold through physical adsorption and entrapment to constructed bioactive engineered scaffold. In cellular experiments, we demonstrate bioactive engineered scaffold based on PCL-PEG-PCL and exosomes can promote the transformation of macrophages from M1 to M2 through the PI3K/Akt signaling pathway. In addition, the exosomes release gradually from scaffolds and act on the macrophages around the scaffolds to reduce FBR in a subcutaneous implant mouse model. Compared with PCL-PEG-PCL scaffolds without exosomes, bioactive engineered scaffolds reduce significantly inflammation and fibrosis of tissues around the scaffolds. Therefore, cancer cell-derived exosomes show the potential for constructing engineered scaffolds in inhibiting the excessive inflammation and facilitating tissue formation.

Rotary Jet-Spun Polycaprolactone/Hydroxyapatite and Carbon Nanotube Scaffolds Seeded with Bone Marrow Mesenchymal Stem Cells Increase Bone Neoformation

Clinically, bone tissue replacements and/or bone repair are challenging. Strategies based on well-defined combinations of osteoconductive materials and osteogenic cells are promising to improve bone regeneration but still require improvement. Herein, we combined polycaprolactone (PCL) fibers, carbon nanotubes (CNT), and hydroxyapatite (nHap) nanoparticles to develop the next generation of bone regeneration material. Fibers formed by rotary jet spinning (RJS) instead of traditional electrospinning (ES) with embedded bone marrow mesenchymal stem cells (BMMSCs) showed the best outcomes to repair rat calvarial defects after 6 weeks. To understand this, it was observed that different morphologies were formed depending on the manufacturing method used. RJS fibers presented a particular topography with rough fibers, which allowed for better cellular growth and cell spreading in vitro around and into a three-dimensional (3D) mesh, while fibers made by ES were more smooth and cellular growth was only measured on the 3D mesh surface. The fibers with incorporated nHap/CNT nanoparticles enhanced in vitro cell performance as indicated by more cellular proliferation, alkaline phosphatase activity, proliferation, and deposition of calcium. Greater bone neoformation occurred by combining three characteristics: the presence of nHap and CNT nanoparticles, the topography of the RJS fibers, and the addition of BMMSCs. RJS fibers with nanoparticles and seeded with BMMSCs showed 10 136 mm³ of bone neoformation, meaning a 10-fold increase compared to using RJS only and BMMSCs (0.853 mm³) and a 5-fold increase from using ES only (2054 mm³) after 6 weeks of implantation. Conversely, none of these approaches used individually showed any significant difference for in vivo bone neoformation, suggesting that their combination is essential for optimizing bone formation. In summary, our work generated a potential material composed of well-defined combinations of suitable scaffolds seeded with BMMSCs for enhancing numerous orthopedic tissue engineering applications.

Mussel-inspired extracellular matrix-mimicking hydrogel scaffold with high cell affinity and immunomodulation ability for growth factor-free cartilage regeneration

Background

Injury to articular cartilage cause certain degree of disability due to poor self-repair ability of cartilage tissue. To promote cartilage regeneration, it is essential to develop a scaffold that properly mimics the native cartilage extracellular matrix (ECM) in the aspect of compositions and functions.

Methods

A mussel-inspired strategy was developed to construct an ECM-mimicking hydrogel scaffold by incorporating polydopamine-modified hyaluronic acid (PDA/HA) complex into a dual-crosslinked collagen (Col) matrix for growth factor-free cartilage regeneration. The adhesion, proliferation, and chondrogenic differentiation of cells on the scaffold were examined. A well-established full-thickness cartilage defect model of the knee in rabbits was used to evaluated the efficacy and functionality of the engineered Col/PDA/HA hydrogel scaffold.

Results

The PDA/HA complex incorporated-hydrogel scaffold with catechol moieties exhibited better cell affinity than bare negatively-charged HA incorporated hydrogel scaffold. In addition, the PDA/HA complex endowed the scaffold with immunomodulation ability, which suppressed the expression of inflammatory cytokines and effectively activated the polarization of macrophages toward M2 phenotypes. The in vivo results revealed that the mussel-inspired Col/PDA/HA hydrogel scaffold showed strong cartilage inducing ability to promote cartilage regeneration.

Conclusions

The PDA/HA complex-incorporated hydrogel scaffold overcame the cell repellency of negatively-charged polysaccharide-based scaffolds, which facilitated the adhesion and clustering of cells on the scaffold, and therefore enhanced cell-HA interactions for efficient chondrogenic differentiation. Moreover, the hydrogel scaffold modulated immune microenvironment, and created a regenerative microenvironment to enhance cartilage regeneration.

The translational potential of this article

This study gives insight into the mussel-inspired approach to construct the tissue-inducing hydrogel scaffold in a growth-factor-free manner, which show great advantage in the clinical treatment. The hydrogel scaffold composed of collagen and hyaluronic acid as the major component, providing cartilage ECM-mimicking environment, is promising for cartilage defect repair.

Biomimetic Scaffolds Modulate the Posttraumatic Inflammatory Response in Articular Cartilage Contributing to Enhanced Neoformation of Cartilaginous Tissue In Vivo

Focal chondral lesions of the knee are the most frequent type of trauma in younger patients and are associated with a high risk of developing early posttraumatic osteoarthritis. The only current clinical solutions include microfracture, osteochondral grafting, and autologous chondrocyte implantation. Cartilage tissue engineering based on biomimetic scaffolds has become an appealing strategy to repair cartilage defects. Here, a chondrogenic collagen-chondroitin sulfate scaffold is tested in an orthotopic Lapine in vivo model to understand the beneficial effects of the immunomodulatory biomaterial on the full chondral defect. Using a combination of noninvasive imaging techniques, histological and whole transcriptome analysis, the scaffolds are shown to enhance the formation of cartilaginous tissue and suppression of host cartilage degeneration, while also supporting tissue integration and increased tissue regeneration over a 12 weeks recovery period. The results presented suggest that biomimetic materials could be a clinical solution for cartilage tissue repair, due to their ability to modulate the immune environment in favor of regenerative processes and suppression of cartilage degeneration.

Osteogenesis in the presence of chemotherapy: A biomimetic approach

Osteosarcoma (OS) is the most common bone tumor in pediatrics. After resection, allografts or metal endoprostheses reconstruct bone voids, and systemic chemotherapy is used to prevent recurrence. This urges the development of novel treatment options for the regeneration of bone after excision. We utilized a previously developed biomimetic, biodegradable magnesium-doped hydroxyapatite/type I collagen composite material (MHA/Coll) to promote bone regeneration in the presence of chemotherapy. We also performed experiments to determine if human mesenchymal stem cells (hMSCs) seeded on MHA/Coll scaffold migrate less toward OS cells, suggesting that hMSCs will not contribute to tumor growth and therefore the potential of oncologic safety in vitro. Also, hMSCs seeded on MHA/Coll had increased expression of osteogenic genes (BGLAP, SPP1, ALP) compared to hMSCs in the 2D condition, even when exposed to chemotherapeutics. This is the first study to demonstrate that a highly osteogenic scaffold can potentially be oncologically safe because hMSCs on MHA/Coll tend to differentiate and lose the ability to migrate toward tumor cells. Therefore, hMSCs on MHA/Coll could potentially be utilized for bone regeneration after OS excision.

Immunoengineering the next generation of arthritis therapies

Immunoengineering continues to revolutionize healthcare, generating new approaches for treating previously intractable diseases, particularly in regard to cancer immunotherapy. In joint diseases, such as osteoarthritis (OA) and rheumatoid arthritis (RA), biomaterials and anti-cytokine treatments have previously been at that forefront of therapeutic innovation. However, while many of the existing anti-cytokine treatments are successful for a subset of patients, these treatments can also pose severe risks, adverse events and off-target effects due to continuous delivery at high dosages or a lack of disease-specific targets. The inadequacy of these current treatments has motivated the development of new immunoengineering strategies that offer safer and more efficacious alternative therapies through the precise and controlled targeting of specific upstream immune responses, including direct and mechanistically-driven immunoengineering approaches. Advances in the understanding of the immunomodulatory pathways involved in musculoskeletal disease, in combination with the growing emphasis on personalized medicine, stress the need for carefully considering the delivery strategies and therapeutic targets when designing therapeutics to better treat RA and OA. Here, we focus on recent advances in biomaterial and cell-based immunomodulation, in combination with genetic engineering, for therapeutic applications in joint diseases. The application of immunoengineering principles to the study of joint disease will not only help to elucidate the mechanisms of disease pathogenesis but will also generate novel disease-specific therapeutics by harnessing cellular and biomaterial responses. STATEMENT OF SIGNIFICANCE: It is now apparent that joint diseases such as osteoarthritis and rheumatoid arthritis involve the immune system at both local (i.e., within the joint) and systemic levels. In this regard, targeting the immune system using both biomaterial-based or cellular approaches may generate new joint-specific treatment strategies that are well-controlled, safe, and efficacious. In this review, we focus on recent advances in immunoengineering that leverage biomaterials and/or genetically engineered cells for therapeutic applications in joint diseases. The application of such approaches, especially synergistic strategies that target multiple immunoregulatory pathways, has the potential to revolutionize our understanding, treatment, and prevention of joint diseases.

Chondrogenic Potential of Human Dental Pulp Stem Cells Cultured as Microtissues

Several tissue engineering stem cell-based procedures improve hyaline cartilage repair. In this work, the chondrogenic potential of dental pulp stem cell (DPSC) organoids or microtissues was studied. After several weeks of culture in proliferation or chondrogenic differentiation media, synthesis of aggrecan and type II and I collagen was immunodetected, and SOX9, ACAN, COL2A1, and COL1A1 gene expression was analysed by real-time RT-PCR. Whereas microtissues cultured in proliferation medium showed the synthesis of aggrecan and type II and I collagen at the 6^th week of culture, samples cultured in chondrogenic differentiation medium showed an earlier and important increase in the synthesis of these macromolecules after 4 weeks. Gene expression analysis showed a significant increase of COL2A1 after 3 days of culture in chondrogenic differentiation medium, while COL1A1 was highly expressed after 14 days. Cell-cell proximity promotes the chondrogenic differentiation of DPSCs and important synthesis of hyaline chondral macromolecules.

Endogenous Repair and Regeneration of Injured Articular Cartilage: A Challenging but Promising Therapeutic Strategy

Articular cartilage (AC) has a very limited intrinsic repair capacity after injury or disease. Although exogenous cell-based regenerative approaches have obtained acceptable outcomes, they are usually associated with complicated procedures, donor-site morbidities and cell differentiation during ex vivo expansion. In recent years, endogenous regenerative strategy by recruiting resident mesenchymal stem/progenitor cells (MSPCs) into the injured sites, as a promising alternative, has gained considerable attention. It takes full advantage of body's own regenerative potential to repair and regenerate injured tissue while avoiding exogenous regenerative approach-associated limitations. Like most tissues, there are also multiple stem-cell niches in AC and its surrounding tissues. These MSPCs have the potential to migrate into injured sites to produce replacement cells under appropriate stimuli. Traditional microfracture procedure employs the concept of MSPCs recruitment usually fails to regenerate normal hyaline cartilage. The reasons for this failure might be attributed to an inadequate number of recruiting cells and adverse local tissue microenvironment after cartilage injury. A strategy that effectively improves local matrix microenvironment and recruits resident MSPCs may enhance the success of endogenous AC regeneration (EACR). In this review, we focused on the reasons why AC cannot regenerate itself in spite of potential self-repair capacity and summarized the latest developments of the three key components in the field of EACR. In addition, we discussed the challenges facing in the present EACR strategy. This review will provide an increasing understanding of EACR and attract more researchers to participate in this promising research arena.

Immune Cell Membrane-Coated Biomimetic Nanoparticles for Targeted Cancer Therapy

Nanotechnology has provided great opportunities for managing neoplastic conditions at various levels, from preventive and diagnostic to therapeutic fields. However, when it comes to clinical application, nanoparticles (NPs) have some limitations in terms of biological stability, poor targeting, and rapid clearance from the body. Therefore, biomimetic approaches, utilizing immune cell membranes, are proposed to solve these issues. For example, macrophage or neutrophil cell membrane coated NPs are developed with the ability to interact with tumor tissue to suppress cancer progression and metastasis. The functionality of these particles largely depends on the surface proteins of the immune cells and their preserved function during membrane extraction and coating process on the NPs. Proteins on the outer surface of immune cells can render a wide range of activities to the NPs, including prolonged blood circulation, remarkable competency in recognizing antigens for enhanced targeting, better cellular interactions, gradual drug release, and reduced toxicity in vivo. In this review, nano-based systems coated with immune cells-derived membranous layers, their detailed production process, and the applicability of these biomimetic systems in cancer treatment are discussed. In addition, future perspectives and challenges for their clinical translation are also presented.

The Challenge of Cartilage Integration: Understanding a Major Barrier to Chondral Repair

Articular cartilage defects caused by injury frequently lead to osteoarthritis, a painful and costly disease. Despite widely used surgical methods to treat articular cartilage defects and a plethora of research into regenerative strategies as treatments, long-term clinical outcomes are not satisfactory. Failure to integrate repair tissue with native cartilage is a recurring issue in surgical and tissue-engineered strategies, seeing eventual degradation of the regenerated or surrounding tissue. This review delves into the current understanding of why continuous and robust integration with native cartilage is so difficult to achieve. Both the intrinsic limitations of chondrocytes to remodel injured cartilage, and the significant challenges posed by a compromised biomechanical environment are described. Recent scaffold and cell-based techniques to repair cartilage are also discussed, and limitations of existing methods to evaluate integrative repair. In particular, the importance of evaluating the mechanical integrity of the interface between native and repair tissue is highlighted as a meaningful assessment of any strategy to repair this load-bearing tissue. Impact statement The failure to integrate grafts or biomaterials with native cartilage is a major barrier to cartilage repair. An in-depth understanding of the reasons cartilage integration remains a challenge is required to inform cartilage repair strategies. In particular, this review highlights that integration of cartilage repair strategies is frequently assessed in terms of the continuity of tissue, but not the mechanical integrity. Given the load-bearing nature of cartilage, evaluating integration in terms of interfacial strength is essential to assessing the potential success of cartilage repair methods.

Characterization of Chitosan-Based Scaffolds Seeded with Sheep Nasal Chondrocytes for Cartilage Tissue Engineering

The treatment of cartilage defect remains a challenging issue in clinical practice. Chitosan-based materials have been recognized as a suitable microenvironment for chondrocyte adhesion, proliferation and differentiation forming articular cartilage. The use of nasal chondrocytes to culture articular cartilage on an appropriate scaffold emerged as a promising novel strategy for cartilage regeneration. Beside excellent properties, chitosan lacks in biological activity, such as RGD-sequences. In this work, we have prepared pure and protein-modified chitosan scaffolds of different deacetylation degree and molecular weight as platforms for the culture of sheep nasal chondrocytes. Fibronectin (FN) was chosen as an adhesive protein for the improvement of chitosan bioactivity. Prepared scaffolds were characterised in terms of microstructure, physical and biodegradation properties, while FN interactions with different chitosans were investigated through adsorption-desorption studies. The results indicated faster enzymatic degradation of chitosan scaffolds with lower deacetylation degree, while better FN interactions with material were achieved on chitosan with higher number of amine groups. Histological and immunohistochemical analysis of in vitro engineered cartilage grafts showed presence of hyaline cartilage produced by nasal chondrocytes.

Computational study on electromechanics of electroactive hydrogels for cartilage-tissue repair

BACKGROUND AND OBJECTIVE

The self-repair capability of articular cartilage is limited because of non-vascularization and low turnover of its extracellular matrix. Regenerating hyaline cartilage remains a significant clinical challenge as most non-surgical and surgical treatments provide only mid-term relief. Eventually, further pain and mobility loss occur for many patients in the long run due to further joint deterioration. Repair of articular cartilage tissue using electroactive scaffolds and biophysical stimuli like electrical and osmotic stimulation may have the potential to heal cartilage defects occurring due to trauma, osteoarthritis, or sport-related injuries. Therefore, the focus of the current study is to present a computational model of electroactive hydrogels for the cartilage-tissue repair as a first step towards an optimized experimental design.

METHODS

The multiphysics transport model that mainly includes the Poisson-Nernst-Planck equations and the mechanical equation is used to find the electrical stimulation response of the polyelectrolyte hydrogels. Based upon this, a numerical model on electromechanics of electroactive hydrogels seeded with chondrocytes is presented employing the open-source software FEniCS, which is a Python library for finite-element analysis.

RESULTS

We analyzed the ionic concentrations and electric potential in a hydrogel sample and the cell culture medium, the osmotic pressure created due to ionic concentration variations and the resulting hydrogel displacement. The proposed mathematical model was validated with examples from literature.

CONCLUSIONS

The presented model for the electrical and osmotic stimulation of a hydrogel sample can serve as a useful tool for the development and analysis of a cartilaginous scaffold employing electrical stimulation. By analyzing various parameters, we pave the way for future research on a finer scale using open-source software.

Recent Advances in Biomaterials for the Treatment of Bone Defects

Bone defects or fractures generally heal in the absence of major interventions due to the high regenerative capacity of bone tissue. However, in situations of severe/large bone defects, these orchestrated regeneration mechanisms are impaired. With advances in modern medicine, natural and synthetic bio-scaffolds from bioceramics and polymers that support bone growth have emerged and gained intense research interest. In particular, scaffolds that recapitulate the molecular cues of extracellular signals, particularly growth factors, offer potential as therapeutic bone biomaterials. The current challenges for these therapies include the ability to engineer materials that mimic the biological and mechanical properties of the real bone tissue matrix, whilst simultaneously supporting bone vascularization. In this review, we discuss the very recent innovative strategies in bone biomaterial technology, including those of endogenous biomaterials and cell/drug delivery systems that promote bone regeneration. We present our understanding of their current value and efficacy, and the future perspectives for bone regenerative medicine.

Mechanical Stress Inhibits Early Stages of Endogenous Cell Migration: A Pilot Study in an Ex Vivo Osteochondral Model

Cell migration has a central role in osteochondral defect repair initiation and biomaterial-mediated regeneration. New advancements to reestablish tissue function include biomaterials and factors promoting cell recruitment, differentiation and tissue integration, but little is known about responses to mechanical stimuli. In the present pilot study, we tested the influence of extrinsic forces in combination with biomaterials releasing chemoattractant signals on cell migration. We used an ex vivo mechanically stimulated osteochondral defect explant filled with fibrin/hyaluronan hydrogel, in presence or absence of platelet-derived growth factor-BB or stromal cell-derived factor 1, to assess endogenous cell recruitment into the wound site. Periodic mechanical stress at early time point negatively influenced cell infiltration compared to unloaded samples, and the implementation of chemokines to increase cell migration was not efficient to overcome this negative effect. The gene expression at 15 days of culture indicated a marked downregulation of matrix metalloproteinase (MMP)13 and MMP3, a decrease of β1 integrin and increased mRNA levels of actin in osteochondral samples exposed to complex load. This work using an ex vivo osteochondral mechanically stimulated advanced platform demonstrated that recurrent mechanical stress at early time points impeded cell migration into the hydrogel, providing a unique opportunity to improve our understanding on management of joint injury.

Local SDF-1α application enhances the therapeutic efficacy of BMSCs transplantation in osteoporotic bone healing

Bone defect healing is markedly impaired in osteoporotic patient due to poor bone regeneration ability. Stromal cell derived factor-1α (SDF-1α) plays a pivotal role in the repair of various injured tissues including bone. Here, we definite that SDF-1α hydrogels potentiates in vivo osteogenesis of bone marrow-derived stromal stem cells (BMSCs) in osteoporosis. The characteristics of rat primary BMSCs including superficial markers by flow cytometry and multi-lineage differentiation by induction were determined. At different time intervals, the release media from the SDF-1α-releasing hydrogels were collected to identificate SDF-1α exhibited a sustained release profile and maintained its bioactivity after release from the hydrogels to stimulate chemotaxis of BMSCs in a time dependent manner. Bilateral alveolar defects were operated in ovariectomized (OVX) rats and repaired with systemic BMSCs transplantation with or without the hydrogels. Local administration of SDF-1α significantly enhanced BMSCs recruitment and promoted more bone regeneration as well as the expression of OCN and Runx2 compared with the effect of BMSCs transplantation alone. Moreover, after BMSCs transplantation with SDF-1α delivery, macrophage polarization was promoted toward the M2 phenotype, that is identified as an important symbol in tissue regeneration process. Taken together, local SDF-1α application enhances the efficacy of BMSCs transplantation therapy in osteoporotic bone healing, suggesting clinical potential of SDF-1α to serve as a therapeutic drug target for osteoporosis treatment.

Evaluation of biomimetic hyaluronic-based hydrogels with enhanced endogenous cell recruitment and cartilage matrix formation

Biomaterials play a pivotal role in cell-free cartilage repair approaches, where cells must migrate through the scaffold, fill the defect, and then proliferate and differentiate facilitating tissue remodeling. Here we used multiple assays to test the influence of chemokines and growth factors on cell migration and cartilage repair in two different hyaluronan (HA)-based hydrogels. We first investigated bone marrow Mesenchymal Stromal Cells (BMSC) migration in vitro, in response to different concentrations of platelet-derived growth factor-BB (PDGF-BB), chemokine ligand 5 (CCL5/RANTES) and stromal cell-derived factor 1 (SDF-1), using a 3D spheroid-based assay. PDGF-BB was selected as most favourable chemotactic agent, and MSC migration was assessed in the context of physical impediment to cell recruitment by testing Fibrin-HA and HA-Tyramine hydrogels of different cross-linking densities. Supplementation of PDGF-BB stimulated progressive migration of MSC through the gels over time. We then investigated in situ cell migration into the hydrogels with and without PDGF-BB, using a cartilage-bone explant model implanted subcutaneously in athymic mice. In vivo studies show that when placed into an osteochondral defect, both hydrogels supported endogenous cell infiltration and provided an amenable microenvironment for cartilage production. These processes were best supported in Fibrin-HA hydrogel in the absence of PDGF-BB. This study used an advanced preclinical testing platform to select an appropriate microenvironment provided by implanted hydrogels, demonstrating that HA-based hydrogels can promote the initial and critical step of endogenous cell recruitment and circumvent some of the clinical challenges in cartilage tissue repair. STATEMENT OF SIGNIFICANCE: The challenge of articular cartilage repair arises from its complex structure and architecture, which confers the unique mechanical behavior of the extracellular matrix. The aim of our research is to identify biomaterials for implants that can support migration of endogenous stem and progenitor cell populations from cartilage and bone tissue, in order to permanently replace damaged cartilage with the original hyaline structure. Here, we present an in vitro 3D spheroid-based migration assay and an osteochondral defect model, which provide the opportunity to assess biomaterials and biomolecules, and to get stronger experimental evidence of the not well-characterized dynamic process of endogenous cells colonization in an osteochondral defect. Furthermore, the delicate step of early cell migration into biomaterials towards functional tissue engineering is reproduced. These tests can be used for pre-clinical testing of newly developed material designs in the field of scaffold engineering.

TNX deficiency results in bone loss due to an increase in multinucleated osteoclasts

Tenascin-X (TNX), a glycoprotein of the extracellular matrix (ECM), is expressed in various tissues and plays an important role in ECM architecture. The TNXB gene encoding TNX is known as the gene responsible for classic-like Ehlers-Danlos syndrome (clEDS). To date, the role of TNX in dermal, muscular and obstetric features has been reported, but its role in bone homeostasis remains to be clarified. In this study, we found significant bone loss and upregulation of osteoclast marker gene expression in TNX-deficient mice. Further, TNX deficiency in the bone marrow promoted multinucleation of osteoclasts and resulted in increased bone resorption activity. These results indicate that multinucleated osteoclasts are the cause of bone loss in a TNX-deficient environment. Our findings provide new insight into the mechanism of osteoclast differentiation mediated by TNX and the pathology of clEDS.

Repopulation of an auricular cartilage scaffold, AuriScaff, perforated with an enzyme combination

Biomaterials currently in use for articular cartilage regeneration do not mimic the composition or architecture of hyaline cartilage, leading to the formation of repair tissue with inferior characteristics. In this study we demonstrate the use of "AuriScaff", an enzymatically perforated bovine auricular cartilage scaffold, as a novel biomaterial for repopulation with regenerative cells and for the formation of high-quality hyaline cartilage. AuriScaff features a traversing channel network, generated by selective depletion of elastic fibers, enabling uniform repopulation with therapeutic cells. The complex collagen type II matrix is left intact, as observed by immunohistochemistry, SEM and TEM. The compressive modulus is diminished, but three times higher than in the clinically used collagen type I/III scaffold that served as control. Seeding tests with human articular chondrocytes (hAC) alone and in co-culture with human adipose-derived stromal/stem cells (ASC) confirmed that the network enabled cell migration throughout the scaffold. It also guides collagen alignment along the channels and, due to the generally traverse channel alignment, newly deposited cartilage matrix corresponds with the orientation of collagen within articular cartilage. In an osteochondral plug model, AuriScaff filled the complete defect with compact collagen type II matrix and enabled chondrogenic differentiation inside the channels. Using adult articular chondrocytes from bovine origin (bAC), filling of even deep defects with high-quality hyaline-like cartilage was achieved after 6 weeks in vivo. With its composition and spatial organization, AuriScaff provides an optimal chondrogenic environment for therapeutic cells to treat cartilage defects and is expected to improve long-term outcome by channel-guided repopulation followed by matrix deposition and alignment. STATEMENT OF SIGNIFICANCE: After two decades of tissue engineering for cartilage regeneration, there is still no optimal strategy available to overcome problems such as inconsistent clinical outcome, early and late graft failures. Especially large defects are dependent on biomaterials and their scaffolding, guiding and protective function. Considering the currently used biomaterials, structure and mechanical properties appear to be insufficient to fulfill this task. The novel scaffold developed within this study is the first approach enabling the use of dense cartilage matrix, repopulate it via channels and provide the cells with a compact collagen type II environment. Due to its density, it also provides better mechanical properties than materials currently used in clinics. We therefore think, that the auricular cartilage scaffold (AuriScaff) has a high potential to improve future cartilage regeneration approaches.

Functional tissue-engineered microtissue derived from cartilage extracellular matrix for articular cartilage regeneration

We developed a promising cell carrier prepared from articular cartilage slices, designated cartilage extracellular matrix (ECM)-derived particles (CEDPs), through processes involving physical pulverization, size screening, and chemical decellularization. Rabbit articular chondrocytes (ACs) or adipose-derived stem cells (ASCs) rapidly attached to the surface of the CEDPs and proliferated with high cell viability under microgravity (MG) condition in a rotary cell culture system (RCCS) or static condition. Gene profiling results demonstrated that ACs expanded on CEDPs exhibited significantly enhanced chondrogenic phenotypes compared with monolayer culture, and that ASCs differentiated into a chondrogenic phenotype without the use of exogenous growth factors. Moreover, MG culture conditions in a RCCS bioreactor were superior to static culture conditions in terms of maintaining the chondrogenic phenotype of ACs and inducing ACS chondrogenesis. With prolonged expansion, functional microtissue aggregates of AC- or ASC-laden CEDPs were formed. Further, AC- or ASC-based microtissues were directly implanted in vivo to repair articular osteochondral defects in a rabbit model. Histological results, biomechanical evaluations, and radiographic assessments indicated that AC- and ASC-based microtissues displayed equal levels of superior hyaline cartilage repair, whereas the other two treatment groups, in which osteochondral defects were treated with CEDPs alone or fibrin glue, exhibited primarily fibrous tissue repair. These findings provide an alternative method for cell culture and stem cell differentiation and a promising strategy for constructing tissue-engineered cartilage microtissues for cartilage regeneration.

STATEMENT OF SIGNIFICANCE

Despite the remarkable progress in cartilage tissue engineering, cartilage repair still remains elusive. In the present study, we developed a cell carrier, namely cartilage extracellular matrix-derived particles (CEDPs), for cell proliferation of articular chondrocytes (ACs) and adipose-derived stem cells (ASCs), which improved the maintenance of chondrogenic phenotype of ACs, and induced chondrogenesis of ASCs. Moreover, the functional microtissue aggregates of AC- or ASC-laden CEDPs induced equal levels of superior hyaline cartilage repair in a rabbit model. Therefore, our study demonstrated an alternative method for chondrocyte culture and stem cell differentiation, and a promising strategy for constructing tissue-engineered cartilage microtissues for in vivo articular cartilage repair and regeneration.

Biomimetic Tissue Engineering: Tuning the Immune and Inflammatory Response to Implantable Biomaterials

Regenerative medicine technologies rely heavily on the use of well-designed biomaterials for therapeutic applications. The success of implantable biomaterials hinges upon the ability of the chosen biomaterial to negotiate with the biological barriers in vivo. The most significant of these barriers is the immune system, which is composed of a highly coordinated organization of cells that induce an inflammatory response to the implanted biomaterial. Biomimetic platforms have emerged as novel strategies that aim to use the principle of biomimicry as a means of immunomodulation. This principle has manifested itself in the form of biomimetic scaffolds that imitate the composition and structure of biological cells and tissues. Recent work in this area has demonstrated the promising potential these technologies hold in overcoming the barrier of the immune system and, thereby, improve their overall therapeutic efficacy. In this review, a broad overview of the use of these strategies across several diseases and future avenues of research utilizing these platforms is provided.

Nanoscaled and microscaled parallel topography promotes tenogenic differentiation of ASC and neotendon formation in vitro

Background

Topography at different scales plays an important role in directing mesenchymal stem cell differentiation including adipose-derived stem cells (ASCs) and the differential effect remains to be investigated.

Purpose

This study aimed to investigate the similarity and difference between micro- and nanoscaled aligned topography for inducing tenogenic differentiation of human ASCs (hASCs).

Methods

Parallel microgrooved PDMS membrane and a parallel aligned electrospun nanofibers of gelatin/poly-ε-caprolactone mixture were employed as the models for the study.

Results

Aligned topographies of both microscales and nanoscales could induce an elongated cell shape with parallel alignment, as supported by quantitative cell morphology analysis (cell area, cell body aspect, and cell body major axis angle). qPCR analysis also demonstrated that the aligned topography at both scales could induce the gene expressions of various tenogenic markers at the 7th day of in vitro culture including tenomodulin, collagen I and collagen VI, decorin, tenascin-C and biglycan, but with upregulated expression of scleraxis and tenascin-C only in microscaled topography. Additionally, tenogenic differentiation at the 3rd day was confirmed only at microscale. Furthermore, microscaled topography was confirmed for its tenogenic induction at tissue level as neotendon tissue was formed with the evidence of mature type I collagen fibers only in parallel aligned polyglycolic acid (PGA) microfibers after in vitro culture with mouse ASCs. Instead, only fat tissue was formed in random patterned PGA microfibers.

Conclusion

Both microscaled and nanoscaled aligned topographies could induce tenogenic differentiation of hASCs and micro-scaled topography seemed better able to induce elongated cell shape and stable tenogenic marker expression when compared to nanoscaled topography. The microscaled inductive effect was also confirmed at tissue level by neotendon formation in vitro.