Regeneration of osteochondral defects in vivo by a cell-free cylindrical poly(lactide-co-glycolide) scaffold with a radially oriented microstructure

Exploring Biomaterial Scaffolds for Eyelid Reconstruction: A Synthesis of Experimental Findings

This review synthesizes experimental findings on various biomaterial scaffolds used in eyelid reconstruction. It examines the structural properties, cellular responses, and functional outcomes of scaffolds such as chitosan, poly(propylene glycol fumarate)-2-hydroxyethyl methacrylate, poly(propylene glycol fumarate) - type I collagen (PPF-Col), decellularized matrix-polycaprolactone, branched polyethylene, collagen, poly(3-hydroxybutyrate-co-3-hydroxyhexanoate, and poly(lactic-co-glycolic acid. These scaffolds exhibit diverse mechanical and biological properties, with some demonstrating good biocompatibility, tunable properties, and potential for tissue repair. However, there are limitations, including concerns about long-term functionality and a lack of comprehensive evaluations. This review highlights the need for multifunctional scaffolds that combine lid replacement and ocular surface function restoration, as well as the establishment of standardized research methods. The goal is to guide future innovation in the field and improve the quality of life for patients with eyelid defects.

Osteochondral tissue engineering in translational practice: histological assessments and scoring systems

Osteochondral lesions are common pathological alterations in synovial joints. Different techniques have been designed to achieve osteochondral repair, and tissue-engineered osteochondral grafts have shown the most promise. Histological assessments and related scoring systems are crucial for evaluating the quality of regenerated tissue, and the interpretation and comparison of various repair techniques require the establishment of a reliable and widely accepted histological method. To date, there is still no consensus on the type of histological assessment and scoring system that should be used for osteochondral repair. In this review, we summarize common osteochondral staining methods, discuss the criteria regarding high-quality histological images, and assess the current histological scoring systems for osteochondral regeneration. Safranin O/Fast green is the most widely used staining method for the cartilage layer, whereas Gomori and Van Gieson staining detect new bone formation. We suggest including the graft-host interface and more sections together with the basic histological information for images. An ideal scoring system should analyze both the cartilage and bone regions, especially for the subchondral bone plate. Furthermore, histological assessments should be performed over a longer period of time to minimize discrepancies caused by defect size and animal species.

Cell-free chitosan/silk fibroin/bioactive glass scaffolds with radial pore for in situ inductive regeneration of critical-size bone defects

Tissue-engineered is an effective method for repairing critical-size bone defects. The application of bioactive scaffold provides artificial matrix and suitable microenvironment for cell recruitment and extracellular matrix deposition, which can effectively accelerate the process of tissue regeneration. Among various scaffold properties, appropriate pore structure and distribution have been proven to play a crucial role in inducing cell infiltration differentiation and in-situ tissue regeneration. In this study, a chitosan (CS) /silk fibroin (SF) /bioactive glass (BG) composite scaffold with distinctive radially oriented pore structure was constructed. The composite scaffolds had stable physical and chemical properties, a unique pore structure of radial arrangement from the center to the periphery and excellent mechanical properties. In vitro biological studies indicated that the CS/SF/BG scaffold could promote osteogenic differentiation of bone marrow mesenchymal stem cells (BMSCs) and the expression of related genes due to the wide range of connected pore structures and released active elements. Furthermore, in vivo study showed CS/SF/BG scaffold with radial pores was more conducive to the repair of skull defects in rats with accelerated healing speed during the bone tissue remodeling process. These results demonstrated the developed CS/SF/BG scaffold would be a promising therapeutic strategy for the repair of bone defects regeneration.

Azithromycin-carrying and microtubule-orientated biomimetic poly (lactic-co-glycolic acid) scaffolds for eyelid reconstruction

Introduction

Tarsal plate repair is the major challenge of eyelid reconstruction for the oculoplastic surgeon. The ideal synthetic tarsal plate substitute should imitate the microstructure and mechanical strength of the natural eyelid. The aim of this work was to develop a novel bionic substitute for eyelid reconstruction.

Methods

Three types of poly(lactic-co-glycolic acid) (PLGA) scaffolds (random, oriented, and azithromycin-loaded oriented scaffolds) were prepared using an improved thermal-induced phase separation technique. The microstructure of the scaffolds was examined by scanning electron microscopy. In vitro cytotoxicity was assessed using scaffold extracts. Fibroblast and primary rat meibomian gland epithelial cells (rMGCs) were cultured within the scaffolds, and their behavior was observed using fluorescence staining. Three types of PLGA scaffolds were implanted into rabbit eyelid defect in vivo to evaluate their inductive tissue repair function.

Results

We successfully fabricated three types of PLGA scaffolds with varying pore architectures, and the axially aligned scaffold demonstrated interconnected and vertically parallel channels. In vitro cytotoxicity tests using scaffold extracts revealed no apparent cytotoxicity. Fluorescence staining showed that both Fibroblast and rMGCs could adhere well onto the pore walls, with fibroblast elongating along the axially aligned porous structure. At 8 weeks post-implantation, all scaffolds were well integrated by fibrovascular tissue. The axially aligned scaffold groups exhibited faster degradation compared to the random scaffold group, with smaller fragments surrounded by mature collagen fibers.

Conclusion

The study found that the axially aligned scaffolds could well support and guide cellular activities in vitro and in vivo. Moreover, the axially aligned scaffold group showed a faster degradation rate with a matched integration rate compared to the random scaffold group. The findings suggest that the oriented scaffold is a promising alternative for eyelid tarsal plate substitutes.

The Emerging Use of ASC/Scaffold Composites for the Regeneration of Osteochondral Defects

Articular cartilage is composed of chondrocytes surrounded by a porous permeable extracellular matrix. It has a limited spontaneous healing capability post-injury which, if left untreated, can result in severe osteochondral disease. Currently, osteochondral (OC) defects are treated by bone marrow stimulation, artificial joint replacement, or transplantation of bone, cartilage, and periosteum, while autologous osteochondral transplantation is also an option; it carries the risk of donor site damage and is limited only to the treatment of small defects. Allografts may be used for larger defects; however, they have the potential to elicit an immune response. A possible alternative solution to treat osteochondral diseases involves the use of stromal/stem cells. Human adipose-derived stromal/stem cells (ASCs) can differentiate into cartilage and bone cells. The ASC can be combined with both natural and synthetic scaffolds to support cell delivery, growth, proliferation, migration, and differentiation. Combinations of both types of scaffolds along with ASCs and/or growth factors have shown promising results for the treatment of OC defects based on in vitro and in vivo experiments. Indeed, these findings have translated to several active clinical trials testing the use of ASC-scaffold composites on human subjects. The current review critically examines the literature describing ASC-scaffold composites as a potential alternative to conventional therapies for OC tissue regeneration.

Recent Biomimetic Approaches for Articular Cartilage Tissue Engineering and Their Clinical Applications: Narrative Review of the Literature

Since articular cartilage is lacking blood vessels and nerves, its capacity to heal is extremely limited. This means that ruptured cartilage affects the joint as a whole. A health issue known as osteoarthritis can develop as a result of injury and deterioration. Osteoarthritis development can be speeded up by the widespread deterioration of articular cartilage, which ranks third on the list of musculoskeletal disorders requiring rehabilitation, behind only low back pain and broken bones. The current treatments for cartilage repair are ineffective and rarely restore full function or tissue normalcy. A promising new technology in tissue engineering may help create functional cartilage tissue substitutes. Ensuring that the cell source is loaded with bioactive molecules that promote cellular differentiation and/or maturation is the general approach. This review summarizes recent advances in cartilage tissue engineering, and recent clinical trials have been conducted to provide a comprehensive overview of the most recent research developments and clinical applications in the framework of degenerated articular cartilage and osteoarthritis.

Current Advances in the Regeneration of Degenerated Articular Cartilage: A Literature Review on Tissue Engineering and Its Recent Clinical Translation

Functional ability is the basis of healthy aging. Articular cartilage degeneration is amongst the most prevalent degenerative conditions that cause adverse impacts on the quality of life; moreover, it represents a key predisposing factor to osteoarthritis (OA). Both the poor capacity of articular cartilage for self-repair and the unsatisfactory outcomes of available clinical interventions make innovative tissue engineering a promising therapeutic strategy for articular cartilage repair. Significant progress was made in this field; however, a marked heterogeneity in the applied biomaterials, biofabrication, and assessments is nowadays evident by the huge number of research studies published to date. Accordingly, this literature review assimilates the most recent advances in cell-based and cell-free tissue engineering of articular cartilage and also focuses on the assessments performed via various in vitro studies, ex vivo models, preclinical in vivo animal models, and clinical studies in order to provide a broad overview of the latest findings and clinical translation in the context of degenerated articular cartilage and OA.

Osteochondral tissue engineering: Perspectives for clinical application and preclinical development

The treatment of osteochondral defects (OCD) remains challenging. Among currently available surgical treatments for OCDs, scaffold-based treatments are promising to regenerate the osteochondral unit. However, there is still no consensus regarding the clinical effectiveness of these scaffold-based therapies for OCDs. Previous reviews have described the gradient physiological characteristics of osteochondral tissue and gradient scaffold design for OCD, tissue engineering strategies, biomaterials, and fabrication technologies. However, the discussion on bridging the gap between the clinical need and preclinical research is still limited, on which we focus in the present review, providing an insight into what is currently lacking in tissue engineering methods that failed to yield satisfactory outcomes, and what is needed to further improve these techniques. Currently available surgical treatments for OCDs are firstly summarized, followed by a comprehensive review on experimental animal studies in recent 5 years on osteochondral tissue engineering. The review will then conclude with what is currently lacking in these animal studies and the recommendations that would help enlighten the community in developing more clinically relevant implants.

The translational potential of this article

This review is attempting to summarize the lessons from clinical and preclinical failures, providing an insight into what is currently lacking in TE methods that failed to yield satisfactory outcomes, and what is needed to further improve these implants.

The Effect of Pore Directionality of Collagen Scaffolds on Cell Differentiation and In Vivo Osteogenesis

Although many bone substitutes have been designed and produced, the development of bone tissue engineering products that mimic the microstructural characteristics of native bone remains challenging. It has been shown that pore orientation within collagen scaffolds influences bone matrix formation by the endochondral route. In addition, that the unidirectional orientation of the scaffolds can limit the growth of blood vessels. However, a comparison between the amount of bone that can be formed in scaffolds with different pore orientations in addition to analyzing the effect of loading osteogenic and proangiogenic factors is still required. In this work we fabricated uni- and multidirectional collagen sponges and evaluated their microstructural, physicochemical, mechanical and biological characteristics. Although the porosity and average pore size of the uni- and multidirectional scaffolds was similar (94.5% vs. 97.1% and 260 µm vs. 269 µm, respectively) the unidirectional sponges had a higher tensile strength, Young's modulus and capacity to uptake liquids than the multidirectional ones (0.271 MPa vs. 0.478 MPa, 9.623 MPa vs. 3.426 MPa and 8000% mass gain vs. 4000%, respectively). Culturing of rat bone marrow mesenchymal stem cells demonstrated that these scaffolds support cell growth and osteoblastic differentiation in the presence of BMP-2 in vitro, although the pore orientation somehow affected cell attachment and differentiation. The evaluation of the ability of the scaffolds to support bone growth when loaded with BMP-2 or BMP-2 + VEGF in an ectopic rat model showed that they both supported bone formation. Histological analysis and quantification of mineralized matrix revealed that the pore orientation of the collagen scaffolds influenced the osteogenic process.

A cell-free ROS-responsive hydrogel/oriented poly(lactide-co-glycolide) hybrid scaffold for reducing inflammation and restoring full-thickness cartilage defectsin vivo

The modulation of inflammation in tissue microenvironment takes an important role in cartilage repair and regeneration. In this study, a novel hybrid scaffold was designed and fabricated by filling a reactive oxygen species (ROS)-scavenging hydrogel (RS Gel) into a radially oriented poly(lactide-co-glycolide) (PLGA) scaffold. The radially oriented PLGA scaffolds were fabricated through a temperature gradient-guided phase separation and freeze-drying method. The RS Gel was formed by crosslinking the mixture of ROS-responsive hyperbranched polymers and biocompatible methacrylated hyaluronic acid (HA-MA). The hybrid scaffolds exhibited a proper compressive modulus, good ROS-scavenging capability, and cell compatibility.In vivotests showed that the hybrid scaffolds significantly regulated inflammation and promoted regeneration of hyaline cartilage after they were implanted into full-thickness cartilage defects in rabbits for 12 w. In comparison with the PLGA scaffolds, the neo-cartilage in the hybrid scaffolds group possessed more deposition of glycosaminoglycans and collagen type II, and were well integrated with the surrounding tissue.

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.

Recent Progress on Biodegradable Tissue Engineering Scaffolds Prepared by Thermally-Induced Phase Separation (TIPS)

Porous biodegradable scaffolds provide a physical substrate for cells allowing them to attach, proliferate and guide the formation of new tissues. A variety of techniques have been developed to fabricate tissue engineering (TE) scaffolds, among them the most relevant is the thermally-induced phase separation (TIPS). This technique has been widely used in recent years to fabricate three-dimensional (3D) TE scaffolds. Low production cost, simple experimental procedure and easy processability together with the capability to produce highly porous scaffolds with controllable architecture justify the popularity of TIPS. This paper provides a general overview of the TIPS methodology applied for the preparation of 3D porous TE scaffolds. The recent advances in the fabrication of porous scaffolds through this technique, in terms of technology and material selection, have been reviewed. In addition, how properties can be effectively modified to serve as ideal substrates for specific target cells has been specifically addressed. Additionally, examples are offered with respect to changes of TIPS procedure parameters, the combination of TIPS with other techniques and innovations in polymer or filler selection.

Poly(lactic-co-glycolic acid)-based composite bone-substitute materials

Research and development of the ideal artificial bone-substitute materials to replace autologous and allogeneic bones for repairing bone defects is still a challenge in clinical orthopedics. Recently, poly(lactic-co-glycolic acid) (PLGA)-based artificial bone-substitute materials are attracting increasing attention as the benefit of their suitable biocompatibility, degradability, mechanical properties, and capabilities to promote bone regeneration. In this article, we comprehensively review the artificial bone-substitute materials made from PLGA or the composites of PLGA and other organic and inorganic substances, elaborate on their applications for bone regeneration with or without bioactive factors, and prospect the challenges and opportunities in clinical bone regeneration.

Influence of the Mechanical Environment on the Regeneration of Osteochondral Defects

Articular cartilage is a highly specialised connective tissue of diarthrodial joints which provides a smooth, lubricated surface for joint articulation and plays a crucial role in the transmission of loads. In vivo cartilage is subjected to mechanical stimuli that are essential for cartilage development and the maintenance of a chondrocytic phenotype. Cartilage damage caused by traumatic injuries, ageing, or degradative diseases leads to impaired loading resistance and progressive degeneration of both the articular cartilage and the underlying subchondral bone. Since the tissue has limited self-repairing capacity due its avascular nature, restoration of its mechanical properties is still a major challenge. Tissue engineering techniques have the potential to heal osteochondral defects using a combination of stem cells, growth factors, and biomaterials that could produce a biomechanically functional tissue, representative of native hyaline cartilage. However, current clinical approaches fail to repair full-thickness defects that include the underlying subchondral bone. Moreover, when tested in vivo, current tissue-engineered grafts show limited capacity to regenerate the damaged tissue due to poor integration with host cartilage and the failure to retain structural integrity after insertion, resulting in reduced mechanical function. The aim of this review is to examine the optimal characteristics of osteochondral scaffolds. Additionally, an overview on the latest biomaterials potentially able to replicate the natural mechanical environment of articular cartilage and their role in maintaining mechanical cues to drive chondrogenesis will be detailed, as well as the overall mechanical performance of grafts engineered using different technologies.

A radial 3D polycaprolactone nanofiber scaffold modified by biomineralization and silk fibroin coating promote bone regeneration in vivo

The treatment and repair of large bone defects remains a major therapeutic challenge in the clinical setting. Nanofiber scaffolds fabricated via the electrospinning technique have been developed as a universal method for bone regeneration due to their suitable properties. However, traditional two-dimensional (2D) nanofiber mats are usually too dense, which may prevent cell infiltration and growth, thereby restricting their application. Herein, a three-dimensional (3D) polycaprolactone nanofiber scaffold was developed, modified by biomineralization and silk fibroin coating. The scaffold possessed a parallel array of nanofiber surfaces, mimicking the parallel structure of fibrils in natural bone tissue. Furthermore, the fabricated radially or laterally interconnected macrochannels were investigated to elucidate the effect of the scaffold structure on bone regeneration. In vitro studies revealed that the scaffolds could guide cell arrangement and that the radially aligned scaffold demonstrated a stronger ability to promote cell proliferation. In vivo results showed that the radially aligned scaffold could guide tissue arrangement and remodeling and support a significantly faster regeneration rate of bone tissue. Therefore, 3D-mineralized polycaprolactone nanofiber scaffolds with radially interconnected macrochannels and aligned nanofibers are expected to be used in tissue engineering, including in the repair of bone defects, cartilage or other composite tissues.

Validation of the 1,4-butanediol thermoplastic polyurethane as a novel material for 3D bioprinting applications

Tissue engineering (TE) seeks to fabricate implants that mimic the mechanical strength, structure, and composition of native tissues. Cartilage TE requires the development of functional personalized implants with cartilage-like mechanical properties capable of sustaining high load-bearing environments to integrate into the surrounding tissue of the cartilage defect. In this study, we evaluated the novel 1,4-butanediol thermoplastic polyurethane elastomer (b-TPUe) derivative filament as a 3D bioprinting material with application in cartilage TE. The mechanical behavior of b-TPUe in terms of friction and elasticity were examined and compared with human articular cartilage, PCL, and PLA. Moreover, infrapatellar fat pad-derived human mesenchymal stem cells (MSCs) were bioprinted together with scaffolds. in vitro cytotoxicity, proliferative potential, cell viability, and chondrogenic differentiation were analyzed by Alamar blue assay, SEM, confocal microscopy, and RT-qPCR. Moreover, in vivo biocompatibility and host integration were analyzed. b-TPUe demonstrated a much closer compression and shear behavior to native cartilage than PCL and PLA, as well as closer tribological properties to cartilage. Moreover, b-TPUe bioprinted scaffolds were able to maintain proper proliferative potential, cell viability, and supported MSCs chondrogenesis. Finally, in vivo studies revealed no toxic effects 21 days after scaffolds implantation, extracellular matrix deposition and integration within the surrounding tissue. This is the first study that validates the biocompatibility of b-TPUe for 3D bioprinting. Our findings indicate that this biomaterial can be exploited for the automated biofabrication of artificial tissues with tailorable mechanical properties including the great potential for cartilage TE applications.

Cell-Free Biomimetic Scaffold with Cartilage Extracellular Matrix-Like Architectures for In Situ Inductive Regeneration of Osteochondral Defects

The development of a biomimetic scaffold designed to provide a native extracellular matrix (ECM)-like microenvironment is a potential strategy for cartilage repair. The ECM in native articular cartilage is structurally composed of three different architectural zones, i.e., horizontally aligned, randomly arranged, and vertically aligned collagen fibers. However, the effects of scaffolds with these three different ECM-like architectures on in vivo cartilage regeneration are not clear. In this study, we aim to systematically investigate and compare their in situ inductive regenerative efficacy on cartilage defects. ECM-mimetic silk fibroin scaffolds with horizontally aligned, vertically aligned, and random pore architectures are fabricated using the controlled directional freezing technique. All of these scaffolds exhibit similar pore area, swelling ratio, and in vitro degradation behavior. Nevertheless, the aligned scaffolds have a higher pore aspect ratio and hydrophilicity, and increase the proliferation of bone marrow-derived mesenchymal stem cells (BMSCs) in vitro. When implanted into rabbit osteochondral defects, the scaffold with vertically aligned pore architectures provides a more cell-favorable microenvironment conducive to endogenous BMSCs than other scaffolds and supports the simultaneous regeneration of cartilage and subchondral bone. These findings indicate that scaffolds with vertically aligned ECM-like architectures serve as an effective cell-free and growth factor-free scaffold for enhanced endogenous osteochondral regeneration.

Bioinspired Scaffold Designs for Regenerating Musculoskeletal Tissue Interfaces

The musculoskeletal system works at a very advanced level of synchrony, where all the physiological movements of the body are systematically performed through well-organized actions of bone in conjunction with all the other musculoskeletal soft tissues, such as ligaments, tendons, muscles, and cartilage through tissue-tissue interfaces. Interfaces are structurally and compositionally complex, consisting of gradients of extracellular matrix components, cell phenotypes as well as biochemical compositions and are important in mediating load transfer between the distinct orthopedic tissues during body movement. When an injury occurs at interface, it must be re-established to restore its function and stability. Due to the structural and compositional complexity found in interfaces, it is anticipated that they presuppose a concomitant increase in the complexity of the associated regenerative engineering approaches and scaffold designs to achieve successful interface regeneration and seamless integration of the engineered orthopedic tissues. Herein, we discuss the various bioinspired scaffold designs utilized to regenerate orthopedic tissue interfaces. First, we start with discussing the structure-function relationship at the interface. We then discuss the current understanding of the mechanism underlying interface regeneration, followed by discussing the current treatment available in the clinic to treat interface injuries. Lastly, we comprehensively discuss the state-of-the-art scaffold designs utilized to regenerate orthopedic tissue interfaces.

Enhanced regeneration of osteochondral defects by using an aggrecanase-1 responsively degradable and N-cadherin mimetic peptide-conjugated hydrogel loaded with BMSCs

Due to the poor self-repair capabilities of articular cartilage, chondral or osteochondral injuries are difficult to be recovered. In this study, an N-cadherin mimetic peptide sequence HAVDIGGGC (HAV) was conjugated to direct cell-cell interactions, and an aggrecanase-1 cleavable peptide sequence CRDTEGE-ARGSVIDRC (ACpep) was used to crosslink hyperbranched PEG-based multi-acrylate polymer (HBPEG) with cysteamine-modified chondroitin sulfate (Cys-CS), obtaining an aggrecanase-1 responsively degradable and HAV-conjugated hydrogel ((HAV-HBPEG)-CS-ACpep). A HBPEG-CS-ACpep hydrogel without the HAV motif was also prepared. The two hydrogels exhibited similar equilibrium swelling ratios, elastic moduli and pore sizes after lyophilization, indicating the negligible influence of conjugated HAV on the crosslinking networks and mechanical properties of the hydrogels. After being degraded in PBS, aggrecanase-1 (ADAMTS4) and trypsin, the HBPEG-CS-ACpep hydrogel exhibited significantly decreased elastic moduli with a much lower value when incubated in enzyme solutions. The two hydrogels could maintain the viability of encapsulated bone marrow-derived mesenchymal stem cells (BMSCs), and the (HAV-HBPEG)-CS-ACpep hydrogel better promoted the cell-cell interactions. After being implanted into osteochondral defects in rabbits for 18 weeks, the two cell-laden hydrogel groups achieved better repair effects than the blank control group. Moreover, hyaline cartilage was formed in the (HAV-HBPEG)-CS-ACpep/BMSCs hydrogel group, while a hybrid of hyaline cartilage and fibrocartilage was found in the HBPEG-CS-ACpep/BMSCs hydrogel group.

Evaluation of a Cell-Free Collagen Type I-Based Scaffold for Articular Cartilage Regeneration in an Orthotopic Rat Model

The management of chondral defects represents a big challenge because of the limited self-healing capacity of cartilage. Many approaches in this field obtained partial satisfactory results. Cartilage tissue engineering, combining innovative scaffolds and stem cells from different sources, emerges as a promising strategy for cartilage regeneration. The aim of this study was to evaluate the capability of a cell-free collagen I-based scaffold to promote cartilaginous repair after orthotopic implantation in vivo. Articular cartilage lesions (ACL) were created at the femoropatellar groove in rat knees and cell free collagen I-based scaffolds (S) were then implanted into right knee defect for the ACL-S group. No scaffold was implanted for the ACL group. At 4-, 8- and 16-weeks post-transplantation, degrees of cartilage repair were evaluated by morphological, histochemical and gene expression analyses. Histological analysis shows the formation of fibrous tissue, at 4-weeks replaced by a tissue resembling the calcified one at 16-weeks in the ACL group. In the ACL-S group, progressive replacement of the scaffold with the newly formed cartilage-like tissue is shown, as confirmed by Alcian Blue staining. Immunohistochemical and quantitative real-time PCR (qRT-PCR) analyses display the expression of typical cartilage markers, such as collagen type I and II (ColI and ColII), Aggrecan and Sox9. The results of this study display that the collagen I-based scaffold is highly biocompatible and able to recruit host cells from the surrounding joint tissues to promote cartilaginous repair of articular defects, suggesting its use as a potential approach for cartilage tissue regeneration.

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.

Biomaterials for In Situ Tissue Regeneration: A Review

This review focuses on a somewhat unexplored strand of regenerative medicine, that is in situ tissue engineering. In this approach manufactured scaffolds are implanted in the injured region for regeneration within the patient. The scaffold is designed to attract cells to the required volume of regeneration to subsequently proliferate, differentiate, and as a consequence develop tissue within the scaffold which in time will degrade leaving just the regenerated tissue. This review highlights the wealth of information available from studies of ex-situ tissue engineering about the selection of materials for scaffolds. It is clear that there are great opportunities for the use of additive manufacturing to prepare complex personalized scaffolds and we speculate that by building on this knowledge and technology, the development of in situ tissue engineering could rapidly increase. Ex-situ tissue engineering is handicapped by the need to develop the tissue in a bioreactor where the conditions, however optimized, may not be optimum for accelerated growth and maintenance of the cell function. We identify that in both methodologies the prospect of tissue regeneration has created much promise but delivered little outside the scope of laboratory-based experiments. We propose that the design of the scaffolds and the materials selected remain at the heart of developments in this field and there is a clear need for predictive modelling which can be used in the design and optimization of materials and scaffolds.

Biomaterials for In Situ Tissue Regeneration: A Review

This review focuses on a somewhat unexplored strand of regenerative medicine, that is in situ tissue engineering. In this approach manufactured scaffolds are implanted in the injured region for regeneration within the patient. The scaffold is designed to attract cells to the required volume of regeneration to subsequently proliferate, differentiate, and as a consequence develop tissue within the scaffold which in time will degrade leaving just the regenerated tissue. This review highlights the wealth of information available from studies of ex-situ tissue engineering about the selection of materials for scaffolds. It is clear that there are great opportunities for the use of additive manufacturing to prepare complex personalized scaffolds and we speculate that by building on this knowledge and technology, the development of in situ tissue engineering could rapidly increase. Ex-situ tissue engineering is handicapped by the need to develop the tissue in a bioreactor where the conditions, however optimized, may not be optimum for accelerated growth and maintenance of the cell function. We identify that in both methodologies the prospect of tissue regeneration has created much promise but delivered little outside the scope of laboratory-based experiments. We propose that the design of the scaffolds and the materials selected remain at the heart of developments in this field and there is a clear need for predictive modelling which can be used in the design and optimization of materials and scaffolds.

Restoration of osteochondral defects by implanting bilayered poly(lactide-co-glycolide) porous scaffolds in rabbit joints for 12 and 24 weeks

BACKGROUND

With the ageing of the population and the increase of sports injuries, the number of joint injuries has increased greatly. Tissue engineering or tissue regeneration is an important method to repair articular cartilage defects. While it has recently been paid much attention to use bilayered porous scaffolds to repair both cartilage and subchondral bone, it is interesting to examine to what extent a bilayer scaffold composed of the same kind of the biodegradable polymer poly(lactide-co-glycolide) (PLGA) can restore an osteochondral defect. Herein, we fabricated bilayered PLGA scaffolds and used a rabbit model to examine the efficacy of implanting the porous scaffolds with or without bone marrow mesenchymal stem cells (BMSCs). The present manuscript reports the regenerative potential up to 24 weeks.

METHODS

The osteochondral defect, 4 mm in diameter and 5 mm in depth, was created in the medial condyle of each knee in 23 rabbits. The bilayered PLGA scaffolds with a pore size of 100-200 μm in the chondral layer and a pore size of 300-450 μm in the osseous layer, seeded with or without BMSCs in the chondral layer, were then transplanted into the osteochondral defect of each knee. The osteochondral defect created in the same manner was untreated to act as the control. At 12 and 24 weeks postoperatively, condyles were harvested and analyzed using histology, immunohistochemistry, real-time polymerase chain reaction, and biomechanical testing to evaluate the efficacy of osteochondral repair.

RESULTS

No joint erosion, inflammation, swelling, or deformity was observed, and all animals maintained a full range of motion. Compared with the untreated blank group, the groups implanting the bilayered scaffolds with or without cells exhibited much better resurfacing, similar to the surrounding normal tissue. The histological scores of neotissues repaired by the scaffold with cells were closer to that of normal tissue. Although the biomechanical properties of neotissues were not as good as the normal tissue, no significant difference was found between the gene levels of neotissues repaired by the scaffold with or without cells and that of the normal tissue. The repair of the osteochondral defect tends to be stable 12 weeks after implantation.

CONCLUSIONS

Our bilayered PLGA porous scaffold supports long-term osteochondral repair via in vivo tissue engineering or regeneration, and its effect can be further facilitated under the scaffold seeded with allogenic BMSCs.

THE TRANSLATIONAL POTENTIAL OF THIS ARTICLE

The bilayered PLGA porous scaffold can facilitate the repair of osteochondral defects and has potential for application in osteochondral tissue engineering.

Desktop-stereolithography 3D printing of a radially oriented extracellular matrix/mesenchymal stem cell exosome bioink for osteochondral defect regeneration

Mitochondrial dysfunction and oxidative stress damage are hallmarks of osteoarthritis (OA). Mesenchymal stem cell (MSC)-derived exosomes are important in intercellular mitochondria communication. However, the use of MSC exosomes for regulating mitochondrial function in OA has not been reported. This study aimed to explore the therapeutic effect of MSC exosomes in a three dimensional (3D) printed scaffold for early OA therapeutics. Methods: We first examined the mitochondria-related proteins in normal and OA human cartilage samples and investigated whether MSC exosomes could enhance mitochondrial biogenesis in vitro. We subsequently designed a bio-scaffold for MSC exosomes delivery and fabricated a 3D printed cartilage extracellular matrix (ECM)/gelatin methacrylate (GelMA)/exosome scaffold with radially oriented channels using desktop-stereolithography technology. Finally, the osteochondral defect repair capacity of the 3D printed scaffold was assessed using a rabbit model. Results: The ECM/GelMA/exosome scaffold effectively restored chondrocyte mitochondrial dysfunction, enhanced chondrocyte migration, and polarized the synovial macrophage response toward an M2 phenotype. The 3D printed scaffold significantly facilitated the cartilage regeneration in the animal model. Conclusion: This study demonstrated that the 3D printed, radially oriented ECM/GelMA/exosome scaffold could be a promising strategy for early OA treatment.

[The application and research progress of in-situ tissue engineering technology in bone and cartilage repair]

Objective

To review the application and research progress of in-situ tissue engineering technology in bone and cartilage repair.

Methods

The original articles about in-situ tissue engineering technology in bone and cartilage repair were extensively reviewed and analyzed.

Results

In-situ tissue engineering have been shown to be effective in repairing bone defects and cartilage defects, but biological mechanisms are inadequate. At present, most of researches are mainly focused on animal experiments, and the effect of clinical repair need to be further studied.

Conclusion

In-situ tissue engineering technology has wide application prospects in bone and cartilage tissue engineering. However, further study on the mechanism of related cytokines need to be conducted.

Regeneration of different types of tissues depends on the interplay of stem cells-laden constructs and microenvironments in vivo

The ability of repair and regeneration of tissues or organs has been significantly improved by using biomaterials-based constructs. Our previous studies found the regeneration of both articular cartilage and subchondral bone by implantation of a poly(lactide-co-glycolide) (PLGA)/fibrin gel/bone marrow stem cells (BMSCs)/(lipofectamine/pDNA-transforming growth factor (TGF)-β1) construct in vivo, without the step of pre-induced differentiation of the laden stem cells in vitro. To substantiate the ability to regenerate multi-types of tissues by the same constructs, in this study the constructs were implanted into three types of tissues or tissue defects in vivo, including subcutaneous fascia layer, and ear cartilage and eyelid tarsal plate defects. The ear cartilage and eyelid tarsal plate defects were fully regenerated 8 w post-implantation, showing a similar morphology to the corresponding native tissues. In the neo ear cartilage, abundant chondrocytes with obvious lacunas and cartilage-specific extracellular matrices (ECMs) were found. Neo eyelid tarsal plate with mature meibomian gland acinar units was regenerated. Furthermore, expressions of the ECMs-specific genes and proteins, as well as the cell behavior modulatory factors, Sry related HMG box 9 (Sox9) and TGF-β1 were significantly up-regulated in the regenerated ear cartilages and eyelid tarsal plate than those in the subcutaneously implanted constructs, which were filled with fibrocytes, inflammatory cells, obvious vascularization and slight ECMs deposition. These results confirm firmly the ability to regenerate multi-types of tissues by a stem cells-laden construct via adapting to the microenvironments of corresponding tissues.