Mechano growth factor (MGF) and transforming growth factor (TGF)-β3 functionalized silk scaffolds enhance articular hyaline cartilage regeneration in rabbit model

Cartilage lacuna-biomimetic hydrogel microspheres endowed with integrated biological signal boost endogenous articular cartilage regeneration

Despite numerous studies on chondrogenesis, the repair of cartilage-particularly the reconstruction of cartilage lacunae through an all-in-one advanced drug delivery system remains limited. In this study, we developed a cartilage lacuna-like hydrogel microsphere system endowed with integrated biological signals, enabling sequential immunomodulation and endogenous articular cartilage regeneration. We first integrated the chondrogenic growth factor transforming growth factor-β3 (TGF-β3) into mesoporous silica nanoparticles (MSNs). Then, TGF-β3@MSNs and insulin-like growth factor 1 (IGF-1) were encapsulated within microspheres made of polydopamine (pDA). In the final step, growth factor-loaded MSN@pDA and a chitosan (CS) hydrogel containing platelet-derived growth factor-BB (PDGF-BB) were blended to produce growth factors loaded composite microspheres (GFs@μS) using microfluidic technology. The presence of pDA reduced the initial acute inflammatory response, and the early, robust release of PDGF-BB aided in attracting endogenous stem cells. Over the subsequent weeks, the continuous release of IGF-1 and TGF-β3 amplified chondrogenesis and matrix formation. μS were incorporated into an acellular cartilage extracellular matrix (ACECM) and combined with a polydopamine-modified polycaprolactone (PCL) structure to produce a tissue-engineered scaffold that mimicked the structure of the cartilage lacunae evenly distributed in the cartilage matrix, resulting in enhanced cartilage repair and patellar cartilage protection. This research provides a strategic pathway for optimizing growth factor delivery and ensuring prolonged microenvironmental remodeling, leading to efficient articular cartilage regeneration.

In vitro determination of osteo-adipogenic lineage choice of bone marrow stromal/stem cells (BMSCs)

Bone marrow stromal/stem cells (BMSCs) are primitive and heterogeneous cells that can be differentiated into osteoblasts, adipocytes and other subsets. Their bone-fat lineage commitment is responsible for the homeostasis of bone marrow microenvironment. However, there are little effective methods and evidence to simultaneously visualise the lineage commitment of BMSCs. Here we provide a bivalent differentiation medium that can enable BMSCs differentiation into osteoblasts and adipocytes in vitro, and establish a method to simultaneously distinguish osteoblasts or adipocytes from the heterogeneous BMSCs based on Alizarin red S and Oil red O staining, which have been used for detection of specific mineralized nodules and lipid droplets, respectively. This assay provides a specifically simple but effective and low-cost method to evaluate the efficiency of osteo-adipogenic (OA) allocation of BMSCs.►Researchers can utilize the bivalent differentiation medium to evaluate the efficiency of osteogenic and adipogenic differentiation of BMSCs in vitro.

TGF-β signaling in health, disease, and therapeutics

Transforming growth factor (TGF)-β is a multifunctional cytokine expressed by almost every tissue and cell type. The signal transduction of TGF-β can stimulate diverse cellular responses and is particularly critical to embryonic development, wound healing, tissue homeostasis, and immune homeostasis in health. The dysfunction of TGF-β can play key roles in many diseases, and numerous targeted therapies have been developed to rectify its pathogenic activity. In the past decades, a large number of studies on TGF-β signaling have been carried out, covering a broad spectrum of topics in health, disease, and therapeutics. Thus, a comprehensive overview of TGF-β signaling is required for a general picture of the studies in this field. In this review, we retrace the research history of TGF-β and introduce the molecular mechanisms regarding its biosynthesis, activation, and signal transduction. We also provide deep insights into the functions of TGF-β signaling in physiological conditions as well as in pathological processes. TGF-β-targeting therapies which have brought fresh hope to the treatment of relevant diseases are highlighted. Through the summary of previous knowledge and recent updates, this review aims to provide a systematic understanding of TGF-β signaling and to attract more attention and interest to this research area.

Endogenus chondrocytes immobilized by G-CSF in nanoporous gels enable repair of critical-size osteochondral defects

Injured articular cartilage is a leading cause for osteoarthritis. We recently discovered that endogenous stem/progenitor cells not only reside in the superficial zone of mouse articular cartilage, but also regenerated heterotopic bone and cartilage in vivo. However, whether critical-size osteochondral defects can be repaired by pure induced chemotatic cell homing of these endogenous stem/progenitor cells remains elusive. Here, we first found that cells in the superficial zone of articular cartilage surrounding surgically created 3 × 1 mm defects in explant culture of adult goat and rabbit knee joints migrated into defect-filled fibrin/hylaro1nate gel, and this migration was significantly more robust upon delivery of exogenous granulocyte-colony stimulating factor (G-CSF). Remarkably, G-CSF-recruited chondrogenic progenitor cells (CPCs) showed significantly stronger migration ability than donor-matched chondrocytes and osteoblasts. G-CSF-recruited CPCs robustly differentiated into chondrocytes, modestly into osteoblasts, and barely into adipocytes. In vivo, critical-size osteochondral defects were repaired by G-CSF-recruited endogenous cells postoperatively at 6 and 12 weeks in comparison to poor healing by gel-only group or defect-only group. ICRS and O'Driscoll scores of articular cartilage were significantly higher for both 6- and 12-week G-CSF samples than corresponding gel-only and defect-only groups. Thus, endogenous stem/progenitor cells may be activated by G-CSF, a Food and Drug Administration (FDA)-cleared bone-marrow stimulating factor, to repair osteochondral defects.

miR-20a-5p regulated SMAD6 to inhibit chondrogenesis of hDPSCs

OBJECTIVES

Chondrogenic differentiation of human dental pulp stem cells (hDPSCs) is highly promising for cartilage repair. The specific mechanism, however, still needs to be explicated.

MATERIALS AND METHODS

In this study, we isolated hDPSCs and transfected cells with lentiviruses containing an over-expression, knock-down, or negative control of miR-20a-5p. Three-D pellet cultures of hDPSCs were used for the chondrogenic induction. Following the pellet culture period, chondrogenesis was assessed by histological and immunohistochemical analysis and expression of chondrogenic-related genes. Dual-luciferase report assay was performed to determine potential targeted genes of miR-20a-5p, and the phosphorylation levels of P65 and IκBα were explored. Animal experiments were performed to determine the effect of miR-20a-5p on cartilage regeneration.

RESULTS

miR-20a-5p was showed to repress the expression of SMAD6 to inhibit the chondrogenic differentiation of hDPSCs. Accordingly, the knock-down of miR-20a-5p promoted cartilage regeneration in the osteochondral defects of rats. Mechanically, it is indicated that NF-κB signaling is the potential down-stream network of miR-20a-5p/Smad6 crosstalk during chondrogenic differentiation.

CONCLUSIONS

miR-20a-5p could target SMAD6 to activate NF-κB signaling pathway, and thus inhibit chondrogenesis of hDPSCs, which provided promising therapeutic target for cartilage defects clinically.

Biomaterial based implants caused remote liver fatty deposition through activated blood-derived macrophages

Understanding the biocompatibility of biomaterials is a prerequisite for the prediction of its clinical application, and the present assessments mainly rely on in vitro cell culture and in situ histopathology. However, remote organs responses after biomaterials implantation is unclear. Here, by leveraging body-wide-transcriptomics data, we performed in-depth systems analysis of biomaterials - remote organs crosstalk after abdominal implantation of polypropylene and silk fibroin using a rodent model, demonstrating local implantation caused remote organs responses dominated by acute-phase responses, immune system responses and lipid metabolism disorders. Of note, liver function was specially disturbed, defined as hepatic lipid deposition. Combining flow cytometry analyses and liver monocyte recruitment inhibition experiments, we proved that blood derived monocyte-derived macrophages in the liver underlying the mechanism of abnormal lipid deposition induced by local biomaterials implantation. Moreover, from the perspective of temporality, the remote organs responses and liver lipid deposition of silk fibroin group faded away with biomaterial degradation and restored to normal at end, which highlighted its superiority of degradability. These findings were further indirectly evidenced by human blood biochemical ALT and AST examination from 141 clinical cases of hernia repair using silk fibroin mesh and polypropylene mesh. In conclusion, this study provided new insights on the crosstalk between local biomaterial implants and remote organs, which is of help for future selecting and evaluating biomaterial implants with the consideration of whole-body response.

Incorporation of kartogenin and silk fibroin scaffolds promotes rat articular cartilage regeneration through enhancement of antioxidant functions

Treating articular cartilage defects in patients remains a challenging task due to the absence of blood vessels within the cartilage tissue. The regenerative potential is further compromised by an imbalance between anabolism and catabolism, induced by elevated levels of reactive oxygen species. However, the advent of tissue engineering introduces a promising strategy for cartilage regeneration, offering viable solutions such as mechanical support and controlled release of chondrogenic molecules or cytokines. In this study, we developed an antioxidant scaffold by incorporating natural silk fibroin (SF) and kartogenin (KGN)-loaded liposomes (SF-Lipo@KGN). The scaffold demonstrated appropriate pore size, connectivity, and water absorption and the sustained release of KGN was achieved through the encapsulation of liposomes. In vitro experiments revealed that the SF-Lipo@KGN scaffolds exhibited excellent biocompatibility, as evidenced by enhanced cell adhesion, migration, and proliferation of chondrocytes. The SF-Lipo@KGN scaffolds were found to stimulate cartilage matrix synthesis through the activation of the nuclear factor erythroid-2-related factor 2/heme oxygenase-1 antioxidant signaling pathway. In vivo experiments demonstrated the effective promotion of articular cartilage regeneration by the SF-Lipo@KGN scaffolds, which enhanced extracellular matrix anabolism and restored the intrinsic redox homeostasis. Overall, this study successfully developed biomimetic KGN-loaded scaffolds that restore cartilage redox homeostasis, indicating promising prospects for cartilage tissue engineering.

Growth factor-loaded sulfated microislands in granular hydrogels promote hMSCs migration and chondrogenic differentiation

Cell-based therapies for articular cartilage lesions are expensive and time-consuming; clearly, a one-step procedure to induce endogenous repair would have significant clinical benefits. Acellular heterogeneous granular hydrogels were explored for their injectability, cell-friendly cross-linking, and ability to promote migration, as well as to serve as a scaffold for depositing cartilage extracellular matrix. The hydrogels were prepared by mechanical sizing of bulk methacrylated hyaluronic acid (HAMA) and bulk HAMA incorporating sulfated HAMA (SHAMA). SHAMA's negative charges allowed for the retention of positively charged growth factors (GFs) (e.g., TGFB3 and PDGF-BB). Mixtures of HAMA and GF-loaded SHAMA microgels were annealed by enzymatic cross-linking, forming heterogeneous granular hydrogels with GF deposits. The addition of GF loaded sulfated microislands guided cell migration and enhanced chondrogenesis. Granular heterogeneous hydrogels showed increased matrix deposition and cartilage tissue maturation compared to bulk or homogeneous granular hydrogels. This advanced material provides an ideal 3D environment for guiding cell migration and differentiation into cartilage. STATEMENT OF SIGNIFICANCE: Acellular materials which promote regeneration are of great interest for repair of cartilage defects, and they are more cost- and time-effective compared to current cell-based therapies. Here we develop an injectable, granular hydrogel system which promotes cell migration from the surrounding tissue, facilitating endogenous repair. The hydrogel architecture and chemistry were optimized to increase cell migration and extracellular matrix deposition. The present study provides quantitative data on the effect of microgel size and chemical modification on cell migration, growth factor retention and tissue maturation.

Engineered biochemical cues of regenerative biomaterials to enhance endogenous stem/progenitor cells (ESPCs)-mediated articular cartilage repair

As a highly specialized shock-absorbing connective tissue, articular cartilage (AC) has very limited self-repair capacity after traumatic injuries, posing a heavy socioeconomic burden. Common clinical therapies for small- to medium-size focal AC defects are well-developed endogenous repair and cell-based strategies, including microfracture, mosaicplasty, autologous chondrocyte implantation (ACI), and matrix-induced ACI (MACI). However, these treatments frequently result in mechanically inferior fibrocartilage, low cost-effectiveness, donor site morbidity, and short-term durability. It prompts an urgent need for innovative approaches to pattern a pro-regenerative microenvironment and yield hyaline-like cartilage with similar biomechanical and biochemical properties as healthy native AC. Acellular regenerative biomaterials can create a favorable local environment for AC repair without causing relevant regulatory and scientific concerns from cell-based treatments. A deeper understanding of the mechanism of endogenous cartilage healing is furthering the (bio)design and application of these scaffolds. Currently, the utilization of regenerative biomaterials to magnify the repairing effect of joint-resident endogenous stem/progenitor cells (ESPCs) presents an evolving improvement for cartilage repair. This review starts by briefly summarizing the current understanding of endogenous AC repair and the vital roles of ESPCs and chemoattractants for cartilage regeneration. Then several intrinsic hurdles for regenerative biomaterials-based AC repair are discussed. The recent advances in novel (bio)design and application regarding regenerative biomaterials with favorable biochemical cues to provide an instructive extracellular microenvironment and to guide the ESPCs (e.g. adhesion, migration, proliferation, differentiation, matrix production, and remodeling) for cartilage repair are summarized. Finally, this review outlines the future directions of engineering the next-generation regenerative biomaterials toward ultimate clinical translation.

Suppressing Chondrocyte Hypertrophy to Build Better Cartilage

Current clinical strategies for restoring cartilage defects do not adequately consider taking the necessary steps to prevent the formation of hypertrophic tissue at injury sites. Chondrocyte hypertrophy inevitably causes both macroscopic and microscopic level changes in cartilage, resulting in adverse long-term outcomes following attempted restoration. Repairing/restoring articular cartilage while minimizing the risk of hypertrophic neo tissue formation represents an unmet clinical challenge. Previous investigations have extensively identified and characterized the biological mechanisms that regulate cartilage hypertrophy with preclinical studies now beginning to leverage this knowledge to help build better cartilage. In this comprehensive article, we will provide a summary of these biological mechanisms and systematically review the most cutting-edge strategies for circumventing this pathological hallmark of osteoarthritis.

Local injection of adipose-derived mesenchymal stem cells in silk fibroin solution on the regeneration of lower esophageal sphincter in an animal model of GERD

Presently, various tissue engineering methods using adult stem cells and biomaterials are being confirmed to regenerate vessels, cardiac muscle, bladder, and intestines. However, there are few studies about the repair of the lower esophageal sphincter (LES) may help alleviate the symptoms of gastroesophageal reflux disease (GERD). This study aims to determine whether Adipose-Derived Stem Cells (ADSCs) combined with regenerated silk fibroin (RSF) solution could regenerate the LES. In vitro, the ADSCs were isolated, identified, and then cultured with an established smooth muscular induction system. In vivo, in the experimental groups, CM-Dil labeled ADSCs or induced ADSCs mixed with RSF solution were injected into the LES of rats after the development of the animal model of GERD respectively. The results showed that ADSCs could be induced into smooth muscular-like cells with the expression of h-caldesmon, calponin, α-smooth muscle actin, and a smooth muscle-myosin heavy chain in vitro. In vivo, the thickness of LES in the experiment rats was much thicker than those in the controlled groups. This result indicated that ADSCs mixed with RSF solution might contribute to the regeneration of the LES, thus reducing the occurrence of GERD.

Injectable TG-linked recombinant human collagen hydrogel loaded with bFGF for rat cranial defect repair

The basic fibroblast growth factor (bFGF) plays a significant role in promoting the process of bone repair, but bFGF cannot keep its biological activity stable under normal physiological conditions. Therefore, the development of better biomaterials to carry bFGF remains a challenge for bone repair and regeneration. Here we designed a novel recombinant human collagen (rhCol), which could be cross-linked by transglutaminase (TG) and loaded bFGF to prepare rhCol/bFGF hydrogels. The rhCol hydrogel possessed a porous structure and good mechanical properties. The assays, including cell proliferation, migration, and adhesion assay, were performed to evaluate the biocompatibility of rhCol/bFGF and the results demonstrated that the rhCol/bFGF promoted cell proliferation, migration and adhesion. The rhCol/bFGF hydrogel degraded and released bFGF controllably, enhancing utilization rate of bFGF and allowing osteoinductive activity. The results of RT-qPCR and immunofluorescence staining also proved that rhCol/bFGF promoted expression of bone-related proteins. The rhCol/bFGF hydrogels were applied in the cranial defect in rats and the results confirmed that it accelerates bone defect repair. In conclusion, rhCol/bFGF hydrogel has excellent biomechanical properties and can continuously release bFGF to promote bone regeneration, suggesting that rhCol/bFGF hydrogel is a potential scaffold in clinic application.

Mechanical Loading Promotes the Migration of Endogenous Stem Cells and Chondrogenic Differentiation in a Mouse Model of Osteoarthritis

Osteoarthritis (OA) is a major health problem, characterized by progressive cartilage degeneration. Previous works have shown that mechanical loading can alleviate OA symptoms by suppressing catabolic activities. This study evaluated whether mechanical loading can enhance anabolic activities by facilitating the recruitment of stem cells for chondrogenesis. We evaluated cartilage degradation in a mouse model of OA through histology with H&E and safranin O staining. We also evaluated the migration and chondrogenic ability of stem cells using in vitro assays, including immunohistochemistry, immunofluorescence, and Western blot analysis. The result showed that the OA mice that received mechanical loading exhibited resilience to cartilage damage. Compared to the OA group, mechanical loading promoted the expression of Piezo1 and the migration of stem cells was promoted via the SDF-1/CXCR4 axis. Also, the chondrogenic differentiation was enhanced by the upregulation of SOX9, a transcription factor important for chondrogenesis. Collectively, the results revealed that mechanical loading facilitated cartilage repair by promoting the migration and chondrogenic differentiation of endogenous stem cells. This study provided new insights into the loading-driven engagement of endogenous stem cells and the enhancement of anabolic responses for the treatment of OA.

The role of TGF-beta3 in cartilage development and osteoarthritis

Articular cartilage serves as a low-friction, load-bearing tissue without the support with blood vessels, lymphatics and nerves, making its repair a big challenge. Transforming growth factor-beta 3 (TGF-β3), a vital member of the highly conserved TGF-β superfamily, plays a versatile role in cartilage physiology and pathology. TGF-β3 influences the whole life cycle of chondrocytes and mediates a series of cellular responses, including cell survival, proliferation, migration, and differentiation. Since TGF-β3 is involved in maintaining the balance between chondrogenic differentiation and chondrocyte hypertrophy, its regulatory role is especially important to cartilage development. Increased TGF-β3 plays a dual role: in healthy tissues, it can facilitate chondrocyte viability, but in osteoarthritic chondrocytes, it can accelerate the progression of disease. Recently, TGF-β3 has been recognized as a potential therapeutic target for osteoarthritis (OA) owing to its protective effect, which it confers by enhancing the recruitment of autologous mesenchymal stem cells (MSCs) to damaged cartilage. However, the biological mechanism of TGF-β3 action in cartilage development and OA is not well understood. In this review, we systematically summarize recent progress in the research on TGF-β3 in cartilage physiology and pathology, providing up-to-date strategies for cartilage repair and preventive treatment.

A Cell-Free Silk Fibroin Biomaterial Strategy Promotes In Situ Cartilage Regeneration Via Programmed Releases of Bioactive Molecules

In situ tissue regeneration using cell-free biofunctional scaffolds has been extensively studied as a promising alternative strategy to promote cartilage repair. In this study, a cartilage-biomimetic silk fibroin (SF)-based scaffold with controlled sequential release of two bioactive molecules is developed. Transforming growth factor-β1 (TGF-β1) is initially loaded onto the SF scaffolds by physical absorption, which are then successively functionalized with bone marrow mesenchymal stem cells (BMSCs)-specific-affinity peptide (E7) via gradient degradation coating of Silk fibroin Methacryloyl (SilMA)/Hyaluronic acid Methacryloyl (HAMA). Such SF-based scaffolds exhibit excellent structural stability and catilage-like mechanical properties, thus providing a desirable 3D microenvironment for cartilage reconstruction. Furthermore, rapid initial release of E7 during the first few days, followed by slow and sustained release of TGF-β1 for as long as few weeks, synergistically induced the recruitment of BMSCs and chondrogenic differentiation of them in vitro. Finally, in vivo studies indicate that the implantation of the biofunctional scaffold markedly promote in situ cartilage regeneration in a rabbit cartilage defect model. It is believed that this cartilage-biomimetic biofunctional SF-based scaffold with sequential controlled release of E7 and TGF-β1 may have a promising potential for improved cartilage tissue engineering.

Are leukocyte-poor or multiple injections of platelet-rich plasma more effective than hyaluronic acid for knee osteoarthritis? A systematic review and meta-analysis of randomized controlled trials

INTRODUCTION

Platelet-rich plasma (PRP) has gained popularity as a treatment option for knee osteoarthritis; however, its efficacy remains controversial. The optimal leukocyte concentration and number of injections have not been well investigated. This study was, therefore, designed to provide clinical evidence on the leukocyte concentration and number of intra-articular injections of PRP via a meta-analysis of randomized controlled trials (RCTs).

METHODS

The MEDLINE, Embase, Cochrane Library, CINAHL, and Scopus databases were searched and RCTs comparing PRP and hyaluronic acid (HA) for treating knee osteoarthritis were included. Clinical outcomes, including visual analog scale (VAS) score, Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC), and adverse reactions, were evaluated.

RESULTS

A total of 138 studies were screened, of which 21 level 1 RCTs (2086 knees; 1077 PRP and 1009 HA) were included. PRPs showed significant improvement in pain according to the VAS score compared to HA at 6 and 12 months, regardless of leukocyte concentration. Both single and multiple injections of PRP improved pain better than HA at 12 months. Regarding function, both single and multiple injections of leukocyte-poor PRP and leukocyte-rich PRP led to significantly better improvement in total WOMAC score compared with HA at 6 months. There was no significant difference in procedure-related knee pain or swelling between the PRP and HA groups. Leukocyte-rich PRP had a significantly higher odds ratio for procedure-related knee pain or swelling compared to HA (odds ratio, 3.3 [95% confidence interval, 1.1-10.2], P = .037).

CONCLUSION

Based on evidence from Level 1 studies, intra-articular injection of PRP improves pain and function in patients with knee osteoarthritis for up to 12 months and is superior to HA, regardless of leukocyte concentration or number of injections. The findings of this study support the routine clinical use of intra-articular injections of PRP for the treatment of knee osteoarthritis, regardless of the type and frequency of PRP injection.

LEVEL OF EVIDENCE

Meta-analysis of level I studies.

Pushing the Natural Frontier: Progress on the Integration of Biomaterial Cues toward Combinatorial Biofabrication and Tissue Engineering

The engineering of fully functional, biological-like tissues requires biomaterials to direct cellular events to a near-native, 3D niche extent. Natural biomaterials are generally seen as a safe option for cell support, but their biocompatibility and biodegradability can be just as limited as their bioactive/biomimetic performance. Furthermore, integrating different biomaterial cues and their final impact on cellular behavior is a complex equation where the outcome might be very different from the sum of individual parts. This review critically analyses recent progress on biomaterial-induced cellular responses, from simple adhesion to more complex stem cell differentiation, looking at the ever-growing possibilities of natural materials modification. Starting with a discussion on native material formulation and the inclusion of cell-instructive cues, the roles of shape and mechanical stimuli, the susceptibility to cellular remodeling, and the often-overlooked impact of cellular density and cell-cell interactions within constructs, are delved into. Along the way, synergistic and antagonistic combinations reported in vitro and in vivo are singled out, identifying needs and current lessons on the development of natural biomaterial libraries to solve the cell-material puzzle efficiently. This review brings together knowledge from different fields envisioning next-generation, combinatorial biomaterial development toward complex tissue engineering.

Functionalized Hydrogels for Cartilage Repair: The Value of Secretome-Instructive Signaling

Cartilage repair has been a challenge in the medical field for many years. Although treatments that alleviate pain and injury are available, none can effectively regenerate the cartilage. Currently, regenerative medicine and tissue engineering are among the developed strategies to treat cartilage injury. The use of stem cells, associated or not with scaffolds, has shown potential in cartilage regeneration. However, it is currently known that the effect of stem cells occurs mainly through the secretion of paracrine factors that act on local cells. In this review, we will address the use of the secretome—a set of bioactive factors (soluble factors and extracellular vesicles) secreted by the cells—of mesenchymal stem cells as a treatment for cartilage regeneration. We will also discuss methodologies for priming the secretome to enhance the chondroregenerative potential. In addition, considering the difficulty of delivering therapies to the injured cartilage site, we will address works that use hydrogels functionalized with growth factors and secretome components. We aim to show that secretome-functionalized hydrogels can be an exciting approach to cell-free cartilage repair therapy.

The Contribution of Silk Fibroin in Biomedical Engineering

Silk fibroin (SF) is a natural protein (biopolymer) extracted from the cocoons of Bombyx mori L. (silkworm). It has many properties of interest in the field of biotechnology, the most important being biodegradability, biocompatibility and robust mechanical strength with high tensile strength. SF is usually dissolved in water-based solvents and can be easily reconstructed into a variety of material formats, including films, mats, hydrogels, and sponges, by various fabrication techniques (spin coating, electrospinning, freeze-drying, and physical or chemical crosslinking). Furthermore, SF is a feasible material used in many biomedical applications, including tissue engineering (3D scaffolds, wounds dressing), cancer therapy (mimicking the tumor microenvironment), controlled drug delivery (SF-based complexes), and bone, eye and skin regeneration. In this review, we describe the structure, composition, general properties, and structure-properties relationship of SF. In addition, the main methods used for ecological extraction and processing of SF that make it a green material are discussed. Lastly, technological advances in the use of SF-based materials are addressed, especially in healthcare applications such as tissue engineering and cancer therapeutics.

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.

Scrapie-Responsive Gene 1 Promotes Chondrogenic Differentiation of Umbilical Cord Mesenchymal Stem Cells via Wnt5a

Objective

Repair of cartilage defects, a common condition resulting from many factors, is still a great challenge. Based on their chondrogenic differentiation ability, mesenchymal stem cell- (MSC-) based cartilage regeneration is a promising approach for cartilage defect repair. However, MSC differentiation into chondroblasts or related cell lineages is elaborately controlled by stem cell differentiation stage factors and affected by an array of bioactive elements, which may impede the efficient production of target cells. Thus, identifying a single transcription factor to promote chondrogenic differentiation is critical. Herein, we explored the mechanism by which scrapie-responsive gene 1 (SCRG1), a candidate gene for cartilage regeneration promotion, regulates chondrogenic differentiation of MSCs.

Methods

Expression of SCRG1 was detected in umbilical cord-derived MSCs (UCMSCs) by quantitative reverse transcription polymerase chain reaction (qRT-PCR) and immunohistochemical analysis during chondrogenic differentiation. The function of SCRG1 in chondrogenic potential was evaluated after gene knockdown or overexpression by lentiviral vectors. Finally, a rabbit cartilage defect model was established to evaluate the effect of SCRG1 on cartilage repair in vivo.

Results

Expression of SCRG1 was upregulated during in vitro chondrogenic differentiation of UCMSCs. SCRG1 knockdown inhibited chondrogenic differentiation of UCMSCs, while SCRG1 overexpression promoted chondrogenic differentiation of UCMSCs in vitro. In addition, UCMSC overexpressing SCRG1 promoted cartilage repair in vivo. Mechanistically, SCRG1 promoted chondrogenic differentiation via upregulation of Wnt5a expression and subsequent inhibition of β-catenin.

Conclusion

Our results showed that SCRG1 promotes chondrogenic differentiation of UCMSCs by inhibiting canonical Wnt/β-catenin signaling through Wnt5a. Our findings provide a future target for chondrogenic differentiation and cartilage regeneration.

New Insights into Cartilage Tissue Engineering: Improvement of Tissue-Scaffold Integration to Enhance Cartilage Regeneration

Distinctive characteristics of articular cartilage such as avascularity and low chondrocyte conversion rate present numerous challenges for orthopedists. Tissue engineering is a novel approach that ameliorates the regeneration process by exploiting the potential of cells, biodegradable materials, and growth factors. However, problems exist with the use of tissue-engineered construct, the most important of which is scaffold-cartilage integration. Recently, many attempts have been made to address this challenge via manipulation of cellular, material, and biomolecular composition of engineered tissue. Hence, in this review, we highlight strategies that facilitate cartilage-scaffold integration. Recent advances in where efficient integration between a scaffold and native cartilage could be achieved are emphasized, in addition to the positive aspects and remaining problems that will drive future research.

An Overview on Recent Progress of the Hydrogels: From Material Resources, Properties to Functional Applications

Hydrogels, as the most typical elastomer materials with three-dimensional network structures, have attracted wide attention owing to their outstanding features in fields of sensitive stimulus response, low surface friction coefficient, good flexibility and bio-compatibility. Because of numerous fresh polymer materials (or polymerization monomers), hydrogels with various structure diversities and excellent properties are emerging, and the development of hydrogels is very vigorous over the past decade. This review focuses on state-of-the-art advances, systematically reviews the recent progress on construction of novel hydrogels utilized several kinds of typical polymerization monomers, and explores the main chemical and physical cross-linking methods to develop the diversity of hydrogels. Following the aspects mentioned above, the classification and emerging applications of hydrogels, such as pH response, ionic response, electrical response, thermal response, biomolecular response, and gas response, are extensively summarized. Finally, we have done this review with the promises and challenges for the future evolution of hydrogels and their biological applications. cross-linking methods; functional applications; hydrogels; material resources This article is protected by copyright. All rights reserved.

Anti-Friction MSCs Delivery System Improves the Therapy for Severe Osteoarthritis

Osteoarthritis (OA) is a musculoskeletal disorder disease affecting about 500 million people worldwide and mesenchymal sem cells (MSCs) therapy has been demonstrated as a potential strategy to treat OA. However, the shear forces during direct injection and the harsher shear condition of OA environments would lead to significant cell damage and inhibit the therapeutic efficacy. Herein, DNA supramolecular hydrogel has been applied as delivering material for MSCs to treat severe OA model, which perform extraordinary protection in MSCs against the shear force both in vitro and in vivo. It is demonstrated that the DNA supramolecular hydrogel can promote formation of quality cartilage, reduce osteophyte, and normalize subchondral bone under the high friction condition of OA, whose molecular mechanisms underlying therapeutic effects are also investigated. It can be anticipated that DNA supramolecular hydrogel would be a promising cell delivery system for multiple potential MSCs therapy.

Biomaterial-based delivery of nucleic acids for tissue regeneration

Gene therapy is a promising novel method of tissue regeneration by stimulating or inhibiting key signaling pathways. However, their therapeutic applications in vivo are largely limited by several physiological obstacles, such as degradation of nucleases, impermeability of cell membranes, and transport to the desired intracellular compartments. Biomaterial-based gene delivery systems can overcome the problems of stability and local drug delivery, and can temporarily control the overexpression of therapeutic genes, leading to the local production of physiologically relevant levels of regulatory factors. But the gene delivery of biomaterials for tissue regeneration relies on multi-factor design. This review aims to outline the impact of gene delivery methods, therapeutic genes and biomaterials selection on this strategy, emphatically introduce the latest developments in the design of gene delivery vehicles based on biomaterials, summarize the mechanism of nucleic acid for tissue regeneration, and explore the strategies of nucleic acid delivery vehicles for various tissue regeneration.

Adverse Reactions and Clinical Outcomes for Leukocyte-Poor Versus Leukocyte-Rich Platelet-Rich Plasma in Knee Osteoarthritis: A Systematic Review and Meta-analysis

Background:

Platelet-rich plasma (PRP) has gained attention as a therapeutic option for knee osteoarthritis; however, its efficacy varies widely. Leukocytes in PRP raise the concern of aggravating proinflammatory activity. To date, PRP has rarely been investigated with regard to leukocyte concentration.

Purpose:

To provide clinical evidence of the intra-articular injection of PRPs containing different leukocyte concentrations.

Study Design:

Systematic review; Level of evidence, 4.

Methods:

We systematically searched the MEDLINE, Embase, Cochrane Library, CINAHL, and Scopus databases. PRP was classified into leukocyte-poor (LP-PRP) and leukocyte-rich (LR-PRP). Clinical outcomes including Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC), visual analog scale (VAS) for pain score, International Knee Documentation Committee (IKDC) subjective score, and adverse reactions were evaluated. The Methodological Index for Non-Randomized Studies criteria were used for quality assessment.

Results:

Included were 32 studies with an evidence level between 1 and 4. Both LP-PRP and LR-PRP showed improvements above the minimal clinically important difference (MCID) in VAS pain score. No significant intergroup difference was seen at 3, 6, or 12 months of follow-up. Regarding function, both LP-PRP and LR-PRP showed improvements above the MCID in the WOMAC and IKDC scores, with no significant difference between the groups. Adverse reactions for pain were significantly higher in LR-PRP than in LP-PRP (odds ratio, 1.64; 95% confidence interval, 1.29-2.10; P = .01). After intra-articular PRP injection, LR-PRP showed a significantly higher rate of swelling than LP-PRP (odds ratio, 1.56; 95% confidence interval, 1.22-1.99; P = .02). The mean Methodological Index for Non-Randomized Studies score of the included studies was 18.6 (range, 10-24).

Conclusion:

Intra-articular PRP injection resulted in improvements above the MCID in terms of pain and function in patients with knee osteoarthritis up to 12 months. The risk of local adverse reactions appeared to be increased after LR-PRP compared with LP-PRP injection. The findings of this review can support the potential use of intra-articular PRP injection for the treatment of knee osteoarthritis. In clinical application, clinicians need to consider selecting a specific type of PRP for knee osteoarthritis.

Silk Biomaterials for Bone Tissue Engineering

Silk is a natural fibrous polymer with application potential in regenerative medicine. Increasing interest remains for silk materials in bone tissue engineering due to their characteristics in biocompatibility, biodegradability and mechanical properties. Plenty of the in vitro and in vivo studies confirmed the advantages of silk in accelerating bone regeneration. Silk is processed into scaffolds, hydrogels, and films to facilitate different bone regenerative applications. Bioactive factors such as growth factors and drugs, and stem cells are introduced to silk-based matrices to create friendly and osteogenic microenvironments, directing cell behaviors and bone regeneration. The recent progress in silk-based bone biomaterials is discussed and focused on different fabrication and functionalization methods related to osteogenesis. The challenges and potential targets of silk bone materials are highlighted to evaluate the future development of silk-based bone materials.

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.

3D-Bioprinted Difunctional Scaffold for In Situ Cartilage Regeneration Based on Aptamer-Directed Cell Recruitment and Growth Factor-Enhanced Cell Chondrogenesis

Articular cartilage (AC) lesions are fairly common but remain an obstacle for clinicians and researchers due to their poor self-healing capacity. Recently, a promising therapy based on the recruitment of autologous mesenchymal stem cells (MSCs) has been developed for the regeneration of full-thickness cartilage defects in the knee joint. In this study, a 3D-bioprinted difunctional scaffold was developed based on aptamer HM69-mediated MSC-specific recruitment and growth factor-enhanced cell chondrogenesis. The aptamer, which can specifically recognize and recruit MSCs, was first chemically conjugated to the decellularized cartilage extracellular matrix and then mixed with gelatin methacrylate to form a photocrosslinkable bioink ready for 3D bioprinting. Together with the growth factor that promoted cell chondrogenic differentiation, the biodegradable polymer poly(ε-caprolactone) was further chosen to impart mechanical strength to the 3D bioprinted constructs. The difunctional scaffold specifically recruited MSCs, provided a favorable microenvironment for cell adhesion and proliferation, promoted chondrogenesis, and thus greatly improved cartilage repair in rabbit full-thickness defects. In conclusion, this study demonstrated that 3D bioprinting of difunctional scaffolds could be a promising strategy for in situ AC regeneration based on aptamer-directed cell recruitment and growth-factor-enhanced cell chondrogenesis.

Marginal sealing around integral bilayer scaffolds for repairing osteochondral defects based on photocurable silk hydrogels

Osteochondral repair remains a major challenge in current clinical practice despite significant advances in tissue engineering. In particular, the lateral integration of neocartilage into surrounding native cartilage is a difficult and inadequately addressed problem that determines the success of tissue repair. Here, a novel design of an integral bilayer scaffold combined with a photocurable silk sealant for osteochondral repair is reported. First, we fabricated a bilayer silk scaffold with a cartilage layer resembling native cartilage in surface morphology and mechanical strength and a BMP-2-loaded porous subchondral bone layer that facilitated the osteogenic differentiation of BMSCs. Second, a TGF-β3-loaded methacrylated silk fibroin sealant (Sil-MA) exhibiting biocompatibility and good adhesive properties was developed and confirmed to promote chondrocyte migration and differentiation. Importantly, this TGF-β3-loaded Sil-MA hydrogel provided a bridge between the cartilage layer of the scaffold and the surrounding cartilage and then guided new cartilage to grow towards and replace the degraded cartilage layer from the surrounding native cartilage in the early stage of knee repair. Thus, osteochondral regeneration and superior lateral integration were achieved in vivo by using this composite. These results demonstrate that the new approach of marginal sealing around the cartilage layer of bilayer scaffolds with Sil-MA hydrogel has tremendous potential for clinical use in osteochondral regeneration.

Intra-articular Injection of PDGF-BB Explored in a Novel in Vitro Model Mobilizes Mesenchymal Stem Cells From the Synovium Into Synovial Fluid in Rats

BACKGROUND

Drugs that can induce mesenchymal stem cell (MSC) mobilization from synovium into synovial fluid will enable regenerative medicine in joints without use of exogenous MSCs. An in vitro synovial MSC migration model had previously been developed for screening but had problems in practical application. We herein developed a novel in vitro model, explored cytokines for synovial MSC mobilization with this model, and verified whether MSCs in synovial fluid increase following intra-articular injection of the cytokine.

METHODS

Human synovial MSCs embedded in a mixture of Matrigel and type 1 collagen hydrogel were placed on a culture insert and then put in medium containing migration factor. Of the six cytokines, we identified the one that mobilizes the highest number of MSCs. PDGF-BB or PBS was injected into rat knees, and 48 h later, synovial fluid was collected and cultured. The cells were examined for MSC properties.

RESULTS

PDGF-BB was the most effective for synovial MSC mobilization among six cytokines. The effect of PDGF-BB was inhibited by a PRGFR inhibitor. Injection of PDGF-BB into rat knees increased colony-forming cells in the synovial fluid. These cells had surface epitopes and multipotency comparable to MSCs and a higher capacity for proliferation, colony formation, and chondrogenesis.

CONCLUSIONS

This novel in vitro model recapitulated the migration of MSCs from synovium into synovial fluid. Our exploration of cytokines revealed that PDGF-BB strongly induced in vitro synovial MSC migration, while intra-articular injection of PDGF-BB increased in vivo MSC numbers in synovial fluid in rats.

Cell-mediated injectable blend hydrogel-BCP ceramic scaffold for in situ condylar osteochondral repair

The existing approaches for healing mandibular condylar osteochondral defects, which are prevalent in temporomandibular joint disorders (TMD), are sparse and not reparative. To address this, regenerative medicine in situ has transpired as a potential therapeutic solution as it can effectively regenerate composite tissues. Herein, injectable self-crosslinking thiolated hyaluronic acid (HA-SH)/type I collagen (Col I) blend hydrogel and BCP ceramics combined with rabbit bone mesenchymal stem cells (rBMSCs)/chondrocytes were used to fabricate a new bi-layer scaffold to simulate specific structure of rabbit condylar osteochondral defects. The in vitro results demonstrated that the blend hydrogel scaffold provided suitable microenvironment for simultaneously realizing proliferation and chondrogenic specific matrix secretion of both rBMSCs and chondrocytes, while BCP ceramics facilitated rBMSCs proliferation and osteogenic differentiation. The in vivo results confirmed that compared with cell-free implant, the rBMSCs/chondrocytes-loaded bi-layer scaffold could effectively promote the regeneration of both fibrocartilage and subchondral bone, suggesting that the bi-layer scaffold presented a promising option for cell-mediated mandibular condylar cartilage regeneration.

Surface modification of electrospun fibers with mechano-growth factor for mitigating the foreign-body reaction

The implantation of synthetic polymeric scaffolds induced foreign-body reaction (FBR) seriously influence the wound healing and impair functionality recovery. A novel short peptide, mechano-growth factor (MGF), was introduced in this study to modify an electrospun polycaprolactone (PCL) fibrous scaffold to direct the macrophage phenotype transition and mitigate the FBR. In vitro studies discovered the cell signal transduction mechanism of MGF regulates the macrophage polarization via the expression of related genes and proteins. We found that macrophages response the MGF stimuli via endocytosis, then MGF promotes the histone acetylation and upregulates the STAT6 expression to direct an anti-inflammatory phenotype transition. Subsequently, an immunoregulatory electrospun PCL fibrous scaffold was modified by silk fibroin (SF) single-component layer-by-layer assembly, and the SF was decorated with MGF via click chemistry. Macrophages seeded on scaffold to identify the function of MGF modified scaffold in directing macrophage polarization in vitro. Parallelly, rat subcutaneous implantation model and rat tendon adhesion model were performed to detect the immunomodulatory ability of the MGF-modified scaffold in vivo. The results demonstrate that MGF-modified scaffold is beneficial to the transformation of macrophages to M2 phenotype in vitro. More importantly, MGF-functionalized scaffold can inhibit the FBR at the subcutaneous tissue and prevent tissue adhesion.

Clinical Efficacy of Platelet-Rich Plasma Injection and Its Association With Growth Factors in the Treatment of Mild to Moderate Knee Osteoarthritis: A Randomized Double-Blind Controlled Clinical Trial As Compared With Hyaluronic Acid

BACKGROUND

Although platelet-rich plasma (PRP) has potential as a regenerative treatment for knee osteoarthritis, its efficacy varies. Compositional differences among types of PRP could affect clinical outcomes, but the biological characterization of PRP is lacking.

PURPOSE

To assess the efficacy of intra-articular PRP injection in knee osteoarthritis as compared with hyaluronic acid (HA) injection and to determine whether the clinical efficacy of PRP is associated with its biological characteristics.

STUDY DESIGN

Randomized controlled trial; Level of evidence, 1.

METHODS

A total of 110 patients with symptomatic knee osteoarthritis received a single injection of leukocyte-rich PRP (1 commercial kit) or HA. Clinical data were assessed at baseline and at 6 weeks and 3 and 6 months after injection. The primary endpoint was an improvement in the International Knee Documentation Committee (IKDC) subjective score at 6 months, and the secondary endpoints were improvements in scores based on the Patient Global Assessment, the visual analog scale (VAS) for pain, the Western Ontario and McMaster Universities Osteoarthritis Index, and the Samsung Medical Center patellofemoral score. Cell counts and concentrations of growth factors and cytokines in the injected PRP were assessed to determine their association with clinical outcomes.

RESULTS

PRP showed significantly improvement in IKDC subjective scores at 6 months (11.5 in the PRP group vs 6.3 in the HA group; P = .029). There were no significant differences between groups in other clinical outcomes. The Patient Global Assessment score at 6 months was better in the PRP group (P = .035). The proportion of patients who scored above the minimal clinically important difference (MCID) for VAS at 6 months was significantly higher in the PRP group (P = .044). Within the PRP group, the concentrations of platelet-derived growth factors were high in patients with a score above the MCID for VAS at 6 months. The incidence of adverse events did not differ between the groups (P > .05).

CONCLUSION

PRP had better clinical efficacy than HA. High concentrations of growth factors were observed in patients who scored above the MCID for clinical outcomes in the PRP group. These findings indicate that concentration of growth factors needs to be taken into consideration for future investigations of PRP in knee osteoarthritis.

REGISTRATION

NCT02211521 (ClinicalTrials.gov identifier).

Molecular mechanisms of mechanical load-induced osteoarthritis

INTRODUCTION

Mechanical loading enhances the progression of osteoarthritis. However, its molecular mechanisms have not been established.

OBJECTIVE

The aim of this review was to summarize the probable mechanisms of mechanical load-induced osteoarthritis.

METHODS

A comprehensive search strategy was used to search PubMed and EMBASE databases (from the 15th of January 2015 to the 20th of October 2020). Search terms included "osteoarthritis", "mechanical load", and "mechanism".

RESULTS

Abnormal mechanical loading activates the interleukin-1β, tumour necrosis factor-α, nuclear factor kappa-B, Wnt, transforming growth factor-β, microRNAs pathways, and the oxidative stress pathway. These pathways induce the pathological progression of osteoarthritis. Mechanical stress signal receptors such as integrin, ion channel receptors, hydrogen peroxide-inducible clone-5, Gremlin-1, and transient receptor potential channel 4 are present in the articular cartilages.

CONCLUSION

This review highlights the molecular mechanisms of mechanical loading in inducing chondrocyte apoptosis and extracellular matrix degradation. These mechanisms provide potential targets for osteoarthritis prevention and treatment.

Cartilage Repair by Mesenchymal Stem Cell-Derived Exosomes: Preclinical and Clinical Trial Update and Perspectives

Osteoarthritis (OA) and other degenerative joint diseases are characterized by articular cartilage destruction, synovial inflammation, sclerosis of subchondral bone, and loss of extracellular matrix (ECM). Worldwide, these diseases are major causes of disability. Cell therapies have been considered to be the best therapeutic strategies for long-term treatment of articular cartilage diseases. It has been suggested that the mechanism of stem cell-based therapy is related to paracrine secretion of extracellular vesicles (EVs), which are recognized as the main secretion factors of stem cells. EVs, and in particular the subclass exosomes (Exos), are novel therapeutic approaches for treatment of cartilage lesions and OA. The results of recent studies have shown that EVs isolated from mesenchymal stem cells (MSCs) could inhibit OA progression. EVs isolated from various stem cell sources, such as MSCs, may contribute to tissue regeneration of the limbs, skin, heart, and other tissues. Here, we summarize recent findings of preclinical and clinical studies on different MSC-derived EVs and their effectiveness as a treatment for damaged cartilage. The Exos isolation techniques in OA treatment are also highlighted.

Composition and Mechanism of Three-Dimensional Hydrogel System in Regulating Stem Cell Fate

Three-dimensional (3D) hydrogel systems integrating different types of stem cells and scaffolding biomaterials have an important application in tissue engineering. The biomimetic hydrogels that pattern cell suspensions within 3D configurations of biomaterial networks allow for the transport of bioactive factors and mimic the stem cell niche in vivo, thereby supporting the proliferation and differentiation of stem cells. The composition of a 3D hydrogel system determines the physical and chemical characteristics that regulate stem cell function through a biological mechanism. Here, we discuss the natural and synthetic hydrogel compositions that have been employed in 3D scaffolding, focusing on their characteristics, fabrication, biocompatibility, and regulatory effects on stem cell proliferation and differentiation. We also discuss the regulatory mechanisms of cell-matrix interaction and cell-cell interaction in stem cell activities in various types of 3D hydrogel systems. Understanding hydrogel compositions and their cellular mechanisms can yield insights into how scaffolding biomaterials and stem cells interact and can lead to the development of novel hydrogel systems of stem cells in tissue engineering and stem cell-based regenerative medicine. Impact statement Three-dimensional hydrogel system of stem cell mimicking the stemcell niche holds significant promise in tissue engineering and regenerative medicine. Exactly how hydrogel composition regulates stem cell fate is not well understood. This review focuses on the composition of hydrogel, and how the hydrogel composition and its properties regulate the stem cell adhesion, growth, and differentiation. We propose that cell-matrix interaction and cell-cell interaction are important regulatory mechanisms in stem cell activities. Our review provides key insights into how the hydrogel composition regulates the stem cell fate, untangling the engineering of three-dimensional hydrogel systems for stem cells.

Elastin-like polypeptide modified silk fibroin porous scaffold promotes osteochondral repair

Silk fibroin (SF) is considered biocompatible and biodegradable for osteochondral repair. However, it lacks a bioactive domain for cell adhesion, proliferation and differentiation, limiting its therapeutic efficacy. To revamp SF as a biomimicking and bioactive microenvironment to regulate cell behaviours, we engineered an elastin-like polypeptide (ELP, Val-Pro-Gly-Xaa-Gly) to modify SF fibers via simple and green dehydrothermal (DHT) treatment. Our results demonstrated that the ELP successfully bound to SF, and the scaffold was reinforced by the fusion of the silk fiber intersections with ELP (S-ELP-DHT) via the DHT treatment. Both bone mesenchymal stem cells (BMSCs) and chondrocytes exhibited improved spreading and proliferation on the S-ELP-DHT scaffolds. The ex vivo and in vivo experiments further demonstrated enhanced mature bone and cartilage tissue formation using the S-ELP-DHT scaffolds compared to the naked SF scaffolds. These results indicated that a recombinant ELP-modified silk scaffold can mimic three-dimensional (3D) cell microenvironment, and improve bone and cartilage regeneration. We envision that our scaffolds have huge clinical potential for osteochondral repair.

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Elastin-like polypeptide (ELP) modified silk fibroin (SF) scaffold was developed via dehydrothermal treatment (S-ELP-DHT).

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The S-ELP-DHT scaffold provided a beneficial cell microenvironment for osteochondral repair.

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Greater mature bone and cartilage tissue formation were achieved.

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Improved repair efficacy for articular osteochondral defects was confirmed.

Endogenous cell recruitment strategy for articular cartilage regeneration

In the absence of timely and proper treatments, injuries to articular cartilage (AC) can lead to cartilage degeneration and ultimately result in osteoarthritis. Regenerative medicine and tissue engineering techniques are emerging as promising approaches for AC regeneration and repair. Although the use of cell-seeded scaffolds prior to implantation can regenerate and repair cartilage lesions to some extent, these approaches are still restricted by limited cell sources, excessive costs, risks of disease transmission and complex manufacturing practices. Recently developed acellular scaffold approaches that rely on the recruitment of endogenous cells to the injured sites avoid these drawbacks and offer great promise for in situ AC regeneration. Multiple endogenous stem/progenitor cells (ESPCs) are found in joint-resident niches and have the capability to migrate to sites of injury to participate in AC regeneration. However, the natural recruitment of ESPCs is insufficient, and the local microenvironment is hostile after injury. Hence, an endogenous cell recruitment strategy based on the combination of chemoattractants and acellular scaffolds to effectively and specifically recruit ESPCs and improve local microenvironment may provide new insights into in situ AC regeneration. This review provides a brief overview of: (1) the status of endogenous cell recruitment strategy; (2) the subpopulations, potential migration routes (PMRs) of joint-resident ESPCs and their immunomodulatory and reparative effects; (3) chemoattractants and their potential adverse effects; (4) scaffold-based drug delivery systems (SDDSs) that are utilized for in situ AC regeneration; and (5) the challenges and future perspectives of endogenous cell recruitment strategy for AC regeneration. STATEMENT OF SIGNIFICANCE: Although the endogenous cell recruitment strategy for articular cartilage (AC) regeneration has been investigated for several decades, much work remains to be performed in this field. Future studies should have the following aims: (1) reporting the up-to-date progress in the endogenous cell recruitment strategies; (2) determining the subpopulations of ESPCs, the cellular and molecular mechanisms underlying the migration of these cells and their anti-inflammatory, immunomodulatory and reparative effects; (3) elucidating the chemoattractants that enhance ESPC recruitment and their potential adverse effects; and (4) developing advanced SDDSs for chemoattractant dispatch. Herein, we present a systematic overview of the aforementioned issues to provide a better understanding of endogenous cell recruitment strategies for AC regeneration and repair.

Increased expression of IGF-1Ec with increasing colonic polyp dysplasia and colorectal cancer

PURPOSE

IGF-1Ec is an isoform of Insulin-like growth factor 1 (IGF-1) and has recently been identified to be overexpressed in cancers including prostate and neuroendocrine tumours. The aim of this paper is to investigate the expression of IGF-1Ec in colorectal cancer and polyps compared to normal colon tissues and its association with recurrent disease using semi-quantitative immunohistochemistry.

METHODS

Immunohistochemistry for IGF-1Ec expression was performed for colorectal cancer, colorectal polyps and normal colonic tissues. The quantification of IGF-1Ec expression was performed with the use of Image J software and the IHC profiler plugin. Following ethics approval from the National Research Ethics Service (Reference 11/LO/1521), clinical information including recurrent disease on follow-up was collected for patients with colorectal cancer.

RESULTS

Immunohistochemistry was performed in 16 patients with colorectal cancer and 11 patients with colonic polyps and compared to normal colon tissues and prostate adenocarcinoma (positive control) tissues. Significantly increased expression of IGF-1Ec was demonstrated in colorectal cancer (p < 0.001) and colorectal polyps (p < 0.05) compared to normal colonic tissues. Colonic adenomas with high-grade dysplasia had significantly higher expression of IGF-1Ec compared to low-grade dysplastic adenomas (p < 0.001). Colorectal cancers without lymph node metastases at the time of presentation had significantly higher IGF-1Ec expression compared to lymph node-positive disease (p < 0.05). No correlation with recurrent disease was identified with IGF-1Ec expression.

CONCLUSION

IGF-1Ec is significantly overexpressed in colorectal cancer and polyps compared to normal colon tissues offering a potential target to improve colonoscopic identification of colorectal polyps and cancer and intraoperative identification of colorectal tumours.

Mechanisms of TGFβ3 Action as a Therapeutic Agent for Promoting the Synthesis of Extracellular Matrix Proteins in Hyaline Cartilage

Hyaline cartilage is a nonvascular connective tissue covering the joint surface. It consists mostly of the extracellular matrix proteins and a small number of highly differentiated chondrocytes. At present, various techniques for repairing joint surfaces damage, for example, the use of modified cell cultures and biodegradable scaffolds, are under investigation. Molecular mechanisms of cartilage tissue proliferation have been also actively studied in recent years. TGFβ3, which plays a critical role in the proliferation of normal cartilage tissue, is one of the most important protein among cytokines and growth factors affecting chondrogenesis. By interacting directly with receptors on the cell membrane surface, TGFβ3 triggers a cascade of molecular interactions involving transcription factor Sox9. In this review, we describe the effects of TGFβ3 on the receptor complex activation and subsequent intracellular trafficking of Smad proteins and analyze the relation between these processes and upregulation of expression of major extracellular matrix genes, such as col2a1 and acan.

Synergistic Effects of Kartogenin and Transforming Growth Factor-β3 on Chondrogenesis of Human Umbilical Cord Mesenchymal Stem Cells In Vitro

OBJECTIVE

To explore the effect of kartogenin (KGN) on proliferation and chondrogenic differentiation of human umbilical cord mesenchymal stem cells (hUCMSC) in vitro, and the synergistic effects of KGN and transforming growth factor (TGF)-β3 on hUCMSC.

METHODS

Human umbilical cord mesenchymal stem cells were isolated and cultured. Then the differentiation properties were identified by flow cytometry analysis. HUCMSC were divided into four groups: control group, KGN group, TGF-β3 group, and TK group (with TGF-β3 and KGN added into the medium simultaneously). Cells in all groups were induced for 21 days using the suspension ball culture method. Hematoxylin and eosin, immunofluorescence, and Alcian blue staining were used to analyze chondrogenic differentiation. Real-time reverse transcriptase polymerase chain reaction was performed to investigate genes associated with chondrogenic differentiation.

RESULT

Hematoxylin and eosin staining showed that cells in the TGF-β3 group and the TK group had formed cartilage-like tissue after 21 days of culture. The results of immunofluorescence and Alcian blue staining showed that compared with the control group, cells in the KGN and TGF-β3 groups demonstrated increased secretion of aggrecan after 21 days of culture. In addition, cells in the group combining KGN with TGF-β3 (5.587 ± 0.27, P < 0.01) had more collagen II secretion than cells in the TGF-β3 alone group (2.86 ± 0.141, P < 0.01) or the KGN group (1.203 ± 0.215, P < 0.01). The expression of aggrecan (2.468 ± 0.097, P < 0.05) and SRY-Box 9 (4.08 ± 0.13, P < 0.05) in cells in the group combining KGN with TGF-β3 was significantly higher than those in the TGF-β3 group (2.216 ± 0.09, 3.02 ± 0.132, P < 0.05).'

CONCLUSION

The combination of KGN and TGF-β3 had synergistic effects and induced hUCMSC chondrogenesis. This could represent a new approach for clinical application and studies on cartilage repair and regeneration.

Exosomes Derived from Bone Marrow Stromal Cells (BMSCs) Enhance Tendon-Bone Healing by Regulating Macrophage Polarization

Background

Inflammation after tendon-bone junction injury results in the formation of excessive scar tissue and poor biomechanical properties. Recent research has shown that exosomes derived from bone marrow stromal cells (BMSCs) can modulate inflammation during tissue healing. Thus, our study aimed to enhance tendon-bone healing by use of BMSC-derived exosomes (BMSC-Exos).

Material/Methods

The mouse tendon-bone reconstruction model was established, and the mice were randomly divided into 3 groups: the control group, the hydrogel group, and the hydrogel+exosome group, with 30 mice in each group. At 7 days, 14 days, and 1 month after surgery, tendon-bone junction samples were harvested, and the macrophage polarization and tendon-bone healing were evaluated based on histology, immunofluorescence, and quantitative RT-PCR (qRT-PCR) analysis.

Results

In the early phase, we observed significantly higher numbers of M2 macrophages and more anti-inflammatory and chondrogenic-related factors in the hydrogel+BMSC-Exos group compared with the control group and the hydrogel group. The M1 macrophages and related proinflammatory factors decreased. Cell apoptosis decreased in the hydrogel+BMSC-Exos group, while cell proliferation increased; in particular, the CD146+ stem cells substantially increased. At 1 month after surgery, there was more fibrocartilage in the hydrogel+BMSC-Exos group than in the other groups. Biomechanical testing showed that the maximum force, strength, and elastic modulus were significantly improved in the hydrogel+BMSC-Exos group.

Conclusions

Our study provides evidence that the local administration of BMSC-Exos promotes the formation of fibrocartilage by increasing M2 macrophage polarization in tendon-to-bone healing, leading to improved biomechanical properties. These findings provide a basis for the potential clinical use of BMSC-Exos in tendon-bone repair.

Ginsenoside Rb1/TGF-β1 loaded biodegradable silk fibroin-gelatin porous scaffolds for inflammation inhibition and cartilage regeneration

Creating a microenvironment with low inflammation and favorable for the chondrogenic differentiation of endogenous stem cells plays an essential role in cartilage repairing. In the present study, we design a novel ginsenoside Rb1/TGF-β1 loaded silk fibroin-gelatin porous scaffold (GSTR) with the function of attenuating inflammation and promoting chondrogenesis. The scaffold has porous microstructure, proper mechanical strength, degradation rate and sustained release of Rb1 and TGF-β1. Rat bone marrow-derived mesenchymal stem cells (rBMSCs) seeded into GSTR scaffolds are homogeneously distributed and display a higher proliferation rate than non-loaded scaffolds (GS). GSTR scaffolds promote the chondrogenic differentiation of rBMSCs and suppress the expression of inflammation genes. Under the stimulation of IL-1β, the inflammation level of the chondrocytes seeded in GSTR scaffolds is also significantly down-regulated. Moreover, GSTR scaffolds implanted into the osteochondral defects in rats effectively promote the regeneration of hyaline cartilage 12 weeks after surgery when compared with other groups. It is demonstrated that this scaffold loaded with Rb1 and TGF-β1 can synergistically create a microenvironment favorable for cartilage regeneration by promoting the chondrogenesis and suppressing the inflammation levels in vivo. These results prove it has a great potential to develop this Rb1/TGF-β1 releasing scaffold into a novel and promising therapeutic for cartilage repair.

Injectable double-crosslinked hydrogels with kartogenin-conjugated polyurethane nano-particles and transforming growth factor β3 for in-situ cartilage regeneration

Articular cartilage has a limited ability for self-repair after injury. Implantation of scaffolds functionalized with bioactive molecules that could induce the migration and chondrogenesis of endogenous mesenchymal stem cells (MSCs) provides a convenient alternative for in-situ cartilage regeneration. In this study, we found the synergistic effects of kartogenin (KGN) and transforming growth factor β3 (TGF-β3) on chondrogenesis of MSCs in vitro, indicating that KGN and TGF-β3 are a good match for cartilage regeneration. Furthermore, we confirmed that KGN promoted the chondrogenesis of MSCs through attenuating the degradation of Runx1, which physically interacted with p-Smad3 in nuclei of MSCs. Meanwhile, we designed an injectable double-crosslinked hydrogel with superior mechanical property and longer support for cartilage regeneration by modifying sodium alginate and gelatin. When loaded with KGN conjugated polyurethane nanoparticles (PN-KGN) and TGF-β3, this hydrogel showed biological functions by the release of KGN and TGF-β3, which promoted the MSC migration and cartilage regeneration in one system. In conclusion, the cell-free hydrogel, along with PN-KGN and TGF-β3, provides a promising strategy for cartilage repair by attracting endogenous MSCs and inducing chondrogenesis of recruited cells in a single-step procedure.

Influence of pore architectures of silk fibroin/collagen composite scaffolds on the regeneration of osteochondral defects in vivo

The aligned scaffolds facilitate migration of endogenous reparative cells, leading to better regeneration of osteochondral defects.

The Scaffold-Articular Cartilage Interface: A Combined In Vitro and In Silico Analysis Under Controlled Loading Conditions

The optimal method to integrate scaffolds with articular cartilage has not yet been identified, in part because of our lack of understanding about the mechanobiological conditions at the interface. Our objective was to quantify the effect of mechanical loading on integration between a scaffold and articular cartilage. We hypothesized that increased number of loading cycles would have a detrimental effect on interface integrity. The following models were developed: (i) an in vitro scaffold-cartilage explant system in which compressive sinusoidal loading cycles were applied for 14 days at 1 Hz, 5 days per week, for either 900, 1800, 3600, or 7200 cycles per day and (ii) an in silico inhomogeneous, biphasic finite element model (bFEM) of the scaffold-cartilage construct that was used to characterize interface micromotion, stress, and fluid flow under the prescribed loading conditions. In accordance with our hypothesis, mechanical loading significantly decreased scaffold-cartilage interface strength compared to unloaded controls regardless of the number of loading cycles. The decrease in interfacial strength can be attributed to abrupt changes in vertical displacement, fluid pressure, and compressive stresses along the interface, which reach steady-state after only 150 cycles of loading. The interfacial mechanical conditions are further complicated by the mismatch between the homogeneous properties of the scaffold and the depth-dependent properties of the articular cartilage. Finally, we suggest that mechanical conditions at the interface can be more readily modulated by increasing pre-incubation time before the load is applied, as opposed to varying the number of loading cycles.

Variability of the Composition of Growth Factors and Cytokines in Platelet-Rich Plasma From the Knee With Osteoarthritis

PURPOSE

To investigate the composition and concentration of growth factors and cytokines in platelet-rich plasma (PRP) with knee osteoarthritis and to explore the association of the concentration of growth factors and cytokines with the platelet count of PRPs.

METHODS

Patients who visited outpatient clinic with symptomatic knee osteoarthritis (Kellgren-Lawrence grades 1 to 3) and had no blood dyscrasia were enrolled from October 2014 to March 2015. PRPs were obtained using a commercial system. Concentrations of growth factors and cytokines were measured with an enzyme-linked immunosorbent assay. Anabolic factors (platelet-derived growth factor [PDGF]-AA, -BB, and -AB, transforming growth factor-β, vascular endothelial growth factor [VEGF], epidermal growth factor [EGF], basic fibroblast growth factor [bFGF], and insulin-like growth factor 1), catabolic factors (interleukin [IL]-1β and matrix metalloproteinase 13), and catabolic blockers (IL-1 receptor antagonist) were included. The degree of variation was determined by coefficient of variation (CoV).

RESULTS

105 patients were included. Growth factors and cytokines showed wide variation. bFGF showed the highest variation (CoV 78.45), and transforming growth factor-β1 showed the lowest variation (CoV 5.30). Platelet count in PRP showed a positive correlation with PDGF-BB and -AB, and VEGF (r = 0.270, P = .005; r = 0.231, P = .018; and r = 0.200, P = .041, respectively) and was negatively correlated with IL-1β (r = -0.220, P = .025).

CONCLUSION

Growth factors and cytokines in PRPs obtained from patients with knee osteoarthritis show a wide variation; the highest variation was shown in bFGF. Platelet counts associated positively with PDGF-AB and -BB and VEGF and negatively with IL-1β.

CLINICAL RELEVANCE

This information leads to the concept that variation and association of specific factors needs to be taken into consideration for future investigations of PRPs in clinical application in patients with knee osteoarthritis.

Decellularized cartilage matrix scaffolds with laser-machined micropores for cartilage regeneration and articular cartilage repair

Decellularized allogeneic and xenogeneic articular cartilage matrix scaffolds (CMS) are considered ideal scaffolds for cartilage regeneration owing to their heterogeneous architecture, and biochemical and biomechanical properties of native articular cartilage. However, the dense structure of the articular cartilage extracellular matrix, particularly the arrangement of collagen fibers, limits cellular infiltration, leading to poor cartilage regeneration. In addition, the incomplete removal of xenograft cells is associated with immunogenic reaction in the host. To facilitate the migration of chondrocytes into scaffolds and the rate of decellularization processing, we applied a carbon dioxide laser technique to modify the surface of porcine CMS while retaining major properties of the scaffold. By optimizing the laser parameters, we introduced orderly, lattice-arranged conical micropores of suitable depth and diameter onto the cartilage scaffold surface without affecting the cartilage shape or mechanical properties. We found that laser-modified CMS (LM-CMS) could enhance the degree of decellularization and were conducive to cell adhesion, as compared with the intact CMS. Decellularized scaffolds were seeded with rabbit-derived chondrocytes and cultured for 8 weeks in vitro. We found that cell-scaffold constructs formed cartilage-like tissue within the micropores and on the scaffold surface. In vivo, we found that cell-scaffold constructs subcutaneously implanted into the flanks of nude mice formed ivory-white neocartilage with high contents of DNA and cartilage matrix components, as well as good mechanical strength as compared with native CMS. Furthermore, scaffolds combined with autogenous chondrocytes induced neocartilage and better structural restoration at 8 weeks after transplantation into rabbit knee articular cartilage defects. In conclusion, decellularized xenogeneic CMS with laser-machined micropores offers an ideal scaffold with high fidelity for the functional reconstruction of articular cartilage.

Aptamer-Functionalized Bioscaffold Enhances Cartilage Repair by Improving Stem Cell Recruitment in Osteochondral Defects of Rabbit Knees

BACKGROUND

Recruitment of endogenous stem cells has been considered an alternative to cell injection/implantation in articular cartilage repair.

PURPOSE

(1) To develop a cartilage tissue-engineering scaffold with clinically available biomaterials and functionalize the scaffold with an aptamer (Apt19s) that specifically recognizes pluripotent stem cells. (2) To determine whether this scaffold could recruit joint-resident mesenchymal stem cells (MSCs) when implanted into an osteochondral defect in a rabbit model and to examine the effects of cartilage regeneration.

STUDY DESIGN

Controlled laboratory study.

METHODS

The reinforced scaffold was fabricated by embedding a silk fibroin sponge into silk fibroin/hyaluronic acid-tyramine hydrogel and characterized in vitro. A cylindrical osteochondral defect (3.2 mm wide × 4 mm deep) was created in the trochlear grooves of rabbit knees. The rabbits were randomly assigned into 3 groups: Apt19s-functionalized scaffold group, scaffold-only group, and control group. Animals were sacrificed at 6 and 12 weeks after transplantation. Repaired tissues were evaluated via gross examination, histologic examination, and immunohistochemistry.

RESULTS

In vitro, this aptamer-functionalized scaffold could recruit bone marrow-derived MSCs and support cell adhesion. In vivo, the aptamer-functionalized scaffold enhanced cell homing in comparison with the aptamer-free scaffold. The aptamer-functionalized scaffold group also exhibited superior cartilage restoration when compared with the scaffold-only group and the control group.

CONCLUSION

The Apt19s-functionalized scaffold exhibited the ability to recruit MSCs both in vitro and in vivo and achieved a better outcome of cartilage repair than the scaffold only or control in an osteochondral defect model.

CLINICAL RELEVANCE

The findings demonstrate a promising strategy of using aptamer-functionalized bioscaffolds for restoration of chondral/osteochondral defects via aptamer-introduced homing of MSCs.