A novel nano-structured porous polycaprolactone scaffold improves hyaline cartilage repair in a rabbit model compared to a collagen type I/III scaffold: in vitro and in vivo studies

Harnessing Nanomedicine for Cartilage Repair: Design Considerations and Recent Advances in Biomaterials

Cartilage injuries are escalating worldwide, particularly in aging society. Given its limited self-healing ability, the repair and regeneration of damaged articular cartilage remain formidable challenges. To address this issue, nanomaterials are leveraged to achieve desirable repair outcomes by enhancing mechanical properties, optimizing drug loading and bioavailability, enabling site-specific and targeted delivery, and orchestrating cell activities at the nanoscale. This review presents a comprehensive survey of recent research in nanomedicine for cartilage repair, with a primary focus on biomaterial design considerations and recent advances. The review commences with an introductory overview of the intricate cartilage microenvironment and further delves into key biomaterial design parameters crucial for treating cartilage damage, including microstructure, surface charge, and active targeting. The focal point of this review lies in recent advances in nano drug delivery systems and nanotechnology-enabled 3D matrices for cartilage repair. We discuss the compositions and properties of these nanomaterials and elucidate how these materials impact the regeneration of damaged cartilage. This review underscores the pivotal role of nanotechnology in improving the efficacy of biomaterials utilized for the treatment of cartilage damage.

SOX family transcription factors as therapeutic targets in wound healing: A comprehensive review

The SOX family plays a vital role in determining the fate of cells and has garnered attention in the fields of cancer research and regenerative medicine. It also shows promise in the study of wound healing, as it actively participates in the healing processes of various tissues such as skin, fractures, tendons, and the cornea. However, our understanding of the mechanisms behind the SOX family's involvement in wound healing is limited compared to its role in cancer. Gaining insight into its role, distribution, interaction with other factors, and modifications in traumatized tissues could provide valuable new knowledge about wound healing. Based on current research, SOX2, SOX7, and SOX9 are the most promising members of the SOX family for future interventions in wound healing. SOX2 and SOX9 promote the renewal of cells, while SOX7 enhances the microvascular environment. The SOX family holds significant potential for advancing wound healing research. This article provides a comprehensive review of the latest research advancements and therapeutic tools related to the SOX family in wound healing, as well as the potential benefits and challenges of targeting the SOX family for wound treatment.

Retrograde "Sandwich" Technique and Implantation of Minced Cartilage in a Hyaluronic Acid Scaffold for Deep Osteochondral Knee Lesions

The management of deep osteochondral lesions is a subject of great controversy. Despite multiple studies and research efforts, it has not been possible to establish an ideal technique for their treatment. The main goal of all available treatments is to avoid the progress toward early osteoarthritis. Hence, this article will present a one-step technique for the handling of osteochondral lesions with a depth equal to or greater than 5 mm, with retrograde subchondral bone grafting to reconstruct the subchondral bone, seeking the greatest possible preservation of the subchondral plate, and implantation of autologous minced cartilage plus a hyaluronic acid-based scaffold (HyaloFast; Anika Therapeutics) under arthroscopic surgery.

Collagen Scaffold Application in Arthroscopic Reconstruction of Osteochondral Lesions of the Talus With Autologous Cancellous Bone Grafts

Background

Single-step all-arthroscopic techniques have gained popularity recently in the treatment of osteochondral lesions of the talus (OLT). Concomitant subchondral bone defects led surgeons to add autologous bone grafting to the surgical procedures. Collagen scaffolds have been used widely for stabilization of the reconstruction and regeneration of the articular surface.

Purpose

To compare single-step all-arthroscopic treatment of OLT consisting of debridement, microfracture, autologous bone grafting, and application of fibrin sealant in 2 patient groups: with versus without collagen scaffold.

Study Design

Cohort study; Level of evidence, 3.

Methods

Included were 94 patients who underwent single-step all-arthroscopic treatment for OLT. Autologous bone grafting was applied to 48 patients (BG group), while autologous bone grafting plus collagen scaffold was applied to 46 patients (BG+S group). A fibrin sealant was applied to both groups. Clinical outcomes were assessed with the American Orthopaedic Foot & Ankle Society (AOFAS) score and the visual analog scale (VAS) for pain. Radiological outcomes were evaluated with the magnetic resonance observation of cartilage repair tissue score. The mean follow-up time was 69.3 ± 20.7 months.

Results

Patients in both groups showed statistically significant improvement in pre- to postoperative AOFAS and VAS scores (P < .001 for all), with no difference between groups in AOFAS and VAS score improvement. Complete healing with or without hypertrophy was achieved in 42 patients in the BG group (87.5%) and 38 patients in the BG+S group (82.6%).

Conclusion

The treatment of bone lesions in OLT may be the ultimate goal to obtain successful outcomes, in which case using a collagen scaffold besides grafting may not affect clinical and radiological outcomes.

Comparison of 3 Cell-Free Matrix Scaffolds Used to Treat Osteochondral Lesions in a Rabbit Model

BACKGROUND

Various cell-free scaffolds are already in use for the treatment of osteochondral defects (OCDs); however, a gold standard material has not yet been defined.

PURPOSE

This study compared the macroscopic, histological, and scanning electron microscopy (SEM) characteristics of Chondro-Gide (CG), MaioRegen (MA), and poly-d,l-lactide-co-caprolactone (PLCL) cell-free scaffolds enhanced with small-diameter microfractures (SDMs) for OCDs in a rabbit model.

STUDY DESIGN

Controlled laboratory study.

METHODS

In total, 54 knees from 27 rabbits were used in this study. Three rabbits were sacrificed at the beginning of the study to form an intact cartilage control group (group IC). An OCD model was created at the center of the trochlea, and SDMs were generated in 24 rabbits. Rabbits with OCDs were divided into 4 groups (n = 12 knees per group) according to the cell-free scaffold applied: CG (group CG), MA (group MA), PLCL (group PLCL), and a control group (group SDM). Half of the rabbits were sacrificed at 1 month after treatment, while the other half were sacrificed at 3 months after treatment. Healed cartilage was evaluated macroscopically (using International Cartilage Regeneration & Joint Preservation Society [ICRS] classification criteria) and histopathologically (using modified O'Driscoll scores and collagen staining). Additionally, cell-free scaffold morphologies were compared using SEM analysis.

RESULTS

ICRS and modified O'Driscoll classification and staining with collagen type 1 and type 2 demonstrated significant differences among groups at both 1 and 3 months after treatment (P < .05). The histological characteristics of the group IC samples were superior to those of all other groups, except group PLCL, at 3 months after treatment (P < .05). In addition, the histological properties of group PLCL samples were superior to those of group SDM samples at both 1 and 3 months after treatment in terms of the modified O'Driscoll scores and type 1 collagen staining (P < .05). Concerning type 2 collagen staining intensity, the groups were ranked from highest to lowest at 3 months after treatment as follows: group PLCL (30.3 ± 2.6) > group MA (26.6 ± 1.2) > group CG (23.3 ± 2.3) > group SDM (18.9 ± 0.9).

CONCLUSION

OCDs treated with enhanced SDM using cell-free PLCL scaffolds had superior histopathological and microenvironmental properties, more hyaline cartilage, and more type 2 collagen compared with those treated using CG or MA scaffolds.

CLINICAL RELEVANCE

OCDs treated with PLCL cell-free scaffolds may have superior histopathological properties and contain more type 2 collagen than do OCDs treated with CG or MA cell-free scaffolds.

Autologous Oxygen-Releasing Nano-Biomimetic Scaffold with Chondrocytes Promotes Joint Repair After Trauma

Our study assesses the role of a scaffold constructed by co-culture of autologous oxygen-releasing biomimetic scaffold (AONS) and chondrocytes in joint repair after trauma. A composite scaffold structure was used and a scaffold constructed of AONS and chondrocytes was transplanted into SD rats to create models of patellar cartilage fracture and hip osteochondral fracture, respectively followed by analysis of cell proliferation by immunofluorescence method, osteogenesis-related gene expression by RT-PCR, chondrocytes apoptosis by TUNEL staining. The blank control group and AONS composite chondrocytes have significant differences in apoptosis and cell proliferation of two fracture types (P <0.05). The autologous oxygen-releasing nanometers at 4 and 8 weeks showed a significant difference in the number of PCNA and TUNEL cells between biomimetic scaffold and chondrocytes in two groups (P < 0.05). The AONS and chondrocytes were effective for two types of fractures at 1, 4 and 8 weeks. The expression of various markers of intrachondral osteogenesis was decreased and the markers of hip osteochondral fracture were increased significantly (P < 0.05). Joint recovery was better than patellar cartilage fractures. The AONS composite chondrocyte scaffold promotes repair of patellar cartilage fractures and hip osteochondral fractures with a better effect on hip osteochondral fractures.

No Effect of Platelet-Rich Plasma Injections as an Adjuvant to Autologous Cartilage Chips Implantation for the Treatment of Chondral Defects

BACKGROUND

Repair of chondral injuries using cartilage chips has recently demonstrated clinical feasibility. Autologous platelet-rich plasma (PRP) is a potential promising technique for improving healing response during cartilage repair.

PURPOSE

To assess the cartilage repair tissue quality after autologous cartilage chips treatment (CC) with and without repeated local injections of PRP for the treatment of full-thickness focal chondral defects of the knee.

MATERIALS AND METHODS

Two full-thickness chondral defects (Ø = 6 mm) were created in the medial and lateral trochlea facets of each knee in 6 skeletally mature Göttingen minipigs. The 2 treatment groups were (1) CC with 1 weekly PRP injection for 3 weeks (n = 12) and (2) CC alone (n = 12). The animals were euthanized after 6 months. Samples of whole blood and PRP were analyzed for concentrations of platelets and nucleated cells. The composition of the cartilage repair tissue was assessed using gross appearance assessment, histomorphometry, and semiquantitative scoring (ICRS II).

RESULTS

Histological evaluation demonstrated no significant difference in the content of hyaline cartilage (CC + PRP: 18.7% vs. CC: 19.6%), fibrocartilage (CC + PRP: 48.1% vs. CC: 51.8%), or fibrous tissue (CC + PRP: 22.7% vs. CC: 21.8%) between the treatment groups. Macroscopic evaluation did not demonstrate any difference between groups.

CONCLUSIONS

PRP injections after CC in the treatment of full-thickness cartilage injuries demonstrated no beneficial effects in terms of macroscopic and histologic composition of cartilage repair tissue.

Preclinical Testing of New Hydrogel Materials for Cartilage Repair: Overcoming Fixation Issues in a Large Animal Model

Reinforced hydrogels represent a promising strategy for tissue engineering of articular cartilage. They can recreate mechanical and biological characteristics of native articular cartilage and promote cartilage regeneration in combination with mesenchymal stromal cells. One of the limitations of in vivo models for testing the outcome of tissue engineering approaches is implant fixation. The high mechanical stress within the knee joint, as well as the concave and convex cartilage surfaces, makes fixation of reinforced hydrogel challenging. Methods. Different fixation methods for full-thickness chondral defects in minipigs such as fibrin glue, BioGlue®, covering, and direct suturing of nonenforced and enforced constructs were compared. Because of insufficient fixation in chondral defects, superficial osteochondral defects in the femoral trochlea, as well as the femoral condyle, were examined using press-fit fixation. Two different hydrogels (starPEG and PAGE) were compared by 3D-micro-CT (μCT) analysis as well as histological analysis. Results. Our results showed fixation of below 50% for all methods in chondral defects. A superficial osteochondral defect of 1 mm depth was necessary for long-term fixation of a polycaprolactone (PCL)-reinforced hydrogel construct. Press-fit fixation seems to be adapted for a reliable fixation of 95% without confounding effects of glue or suture material. Despite the good integration of our constructs, especially in the starPEG group, visible bone lysis was detected in micro-CT analysis. There was no significant difference between the two hydrogels (starPEG and PAGE) and empty control defects regarding regeneration tissue and cell integration. However, in the starPEG group, more cell-containing hydrogel fragments were found within the defect area. Conclusion. Press-fit fixation in a superficial osteochondral defect in the medial trochlear groove of adult minipigs is a promising fixation method for reinforced hydrogels. To avoid bone lysis, future approaches should focus on multilayered constructs recreating the zonal cartilage as well as the calcified cartilage and the subchondral bone plate.

Does Retrograde Femoral Nailing through a Normal Physis Impair Growth? An Experimental Porcine Model

Materials and methods

The study was carried out using an experimental porcine model. Eleven juvenile female porcines were randomized for insertion of a retrograde femoral nail in one limb. The other limb acted as a control. The animals were housed for 8 weeks before the nail was removed and housed for 8 additional weeks, that is, 16 weeks in total. Growth was assessed by interphyseal distance on 3D magnetic resonance imaging (MRI) after 16 weeks and the operated limb was compared to the non-operated limb. Histomorphometric analysis of the physeal canal was performed.

Results

No difference in longitudinal growth was observed when comparing the operated femur to the non-operated femur using MRI after 16 weeks. No osseous tissue crossing the physis was observed on MRI or histology. The empty canal in the physis after nail removal was filled with fibrous tissue 16 weeks after primary surgery.

Conclusion

Growth was not impaired and no bone bridges were seen on MRI or histology 16 weeks after insertion and later removal of the retrograde femoral nail.

Clinical significance

The insertion of a retrograde intramedullary femoral nail centrally through the physis and later removal might be safe, however, long-term follow-up is needed.

Aim and objective

The insertion of an intramedullary nail may be beneficial in certain cases of leg length discrepancy (LLD) in children. However, it is unknown if the physeal injury due to the surgery may cause bone bridge formation and thereby growth arrest after removal. This study aimed to assess longitudinal interphyseal growth 16 weeks after insertion and later removal of a retrograde femoral nail passing through the physis. Moreover, to analyse the tissue forming in the empty physeal canal after removal of the nail.

How to cite this article

Abood AA, Rahbek O, Olesen ML, et al. Does Retrograde Femoral Nailing through a Normal Physis Impair Growth? An Experimental Porcine Model. Strategies Trauma Limb Reconstr 2021;16(1):8–13.

Review of Synthetic and Hybrid Scaffolds in Cartilage Tissue Engineering

Cartilage tissue is under extensive investigation in tissue engineering and regenerative medicine studies because of its limited regenerative potential. Currently, many scaffolds are undergoing scientific and clinical research. A key for appropriate scaffolding is the assurance of a temporary cellular environment that allows the cells to function as in native tissue. These scaffolds should meet the relevant requirements, including appropriate architecture and physicochemical and biological properties. This is necessary for proper cell growth, which is associated with the adequate regeneration of cartilage. This paper presents a review of the development of scaffolds from synthetic polymers and hybrid materials employed for the engineering of cartilage tissue and regenerative medicine. Initially, general information on articular cartilage and an overview of the clinical strategies for the treatment of cartilage defects are presented. Then, the requirements for scaffolds in regenerative medicine, materials intended for membranes, and methods for obtaining them are briefly described. We also describe the hybrid materials that combine the advantages of both synthetic and natural polymers, which provide better properties for the scaffold. The last part of the article is focused on scaffolds in cartilage tissue engineering that have been confirmed by undergoing preclinical and clinical tests.

Stem Cell Treatment for Knee Articular Cartilage Defects and Osteoarthritis

PURPOSE OF REVIEW

To review the current basic science and clinical literature on mesenchymal stem cell (MSC) therapy for articular cartilage defects and osteoarthritis of the knee.

RECENT FINDINGS

MSCs derived from bone marrow, adipose, and umbilical tissue have the capacity for self-renewal and differentiation into the chondrocyte lineage. In theory, MSC therapy may help restore cartilage focally or diffusely where nascent regenerative potential in the intra-articular environment is limited. Over the last several years, in vitro and animal studies have elucidated the use of MSCs in isolation as injectables, in combination with biological delivery media and scaffolding, and as surgical adjuvants for cartilage regeneration and treatment of knee degenerative conditions. More recently, clinical and translational literature has grown more convincing from early descriptive case series to randomized controlled trials showing promise in efficacy and safety. Studies describing MSC for knee cartilage regeneration applications are numerous and varied in quality. Future research directions should include work on elucidating optimal cell concentration and dosing, as well as standardization in methodology and reporting in prospective trials. Backed by promise from in vitro and animal studies, preliminary clinical evidence on MSC therapy shows promise as a nonoperative therapeutic option or an adjuvant to existing surgical cartilage restoration techniques. While higher quality evidence to support MSC therapy has emerged over the last several years, further refinement of methodology will be necessary to support its routine clinical use.

No effect of platelet-rich plasma as adjuvant to bone marrow stimulation for the treatment of chondral defects in a large animal model

BACKGROUND

Bone marrow stimulation (BMS) remains a dominant treatment strategy for symptomatic full thickness articular cartilage defects. Autologous platelet-rich plasma (PRP), may improve biological cartilage repair as an adjunct to BMS.

OBJECTIVES

To assess the histological quality of cartilage repair after BMS with and without repeated local injections of PRP for the treatment of full-thickness focal chondral defects of the knee.

METHODS

Two full-thickness chondral defects (Ø = 6 mm) were surgically performed in the medial and lateral trochlea of each knee in skeletally mature Göttingen minipigs. The two treatment groups with 12 defect for each groups were (1) BMS with one weekly PRP injection for 4 weeks, and (2) BMS alone. The animals were euthanized after 6 months. Samples of both whole blood and PRP were analysed with an automated hematology analyzer to determine the concentrations of platelets and nucleated cells. The composition of cartilage repair tissue was assessed using gross appearance assessment, histomorphometry and semi-quantitative scoring (ICRS II).

RESULTS

The average fold increase in platelets was 10.2 ± 2.2. Leukocyte concentration increased in PRP samples by an average fold change of 7.2 ± 1.3. Our macroscopic findings showed that the defects in the BMS + PRP-treated group, were filled with an irregular, partially rough tissue similar to the BMS-treated group. No significant difference in amount of hyalin cartilage, fibrocartilage or fibrous tissue content and ICRS II scores was found between the groups.

CONCLUSIONS

Four repeated local injections of leukocyte-rich PRP after BMS in the treatment of full-thickness cartilage injuries demonstrated no beneficial effects in terms of macroscopic and histological cartilage repair tissue quality.

Articular cartilage regeneration and tissue engineering models: a systematic review

INTRODUCTION

Cartilage regeneration and restoration is a major topic in orthopedic research as cartilaginous degeneration and damage is associated with osteoarthritis and joint destruction. This systematic review aims to summarize current research strategies in cartilage regeneration research.

MATERIALS AND METHODS

A Pubmed search for models investigating single-site cartilage defects as well as chondrogenesis was conducted and articles were evaluated for content by title and abstract. Finally, only manuscripts were included, which report new models or approaches of cartilage regeneration.

RESULTS

The search resulted in 2217 studies, 200 of which were eligible for inclusion in this review. The identified manuscripts consisted of a large spectrum of research approaches spanning from cell culture to tissue engineering and transplantation as well as sophisticated computational modeling.

CONCLUSIONS

In the past three decades, knowledge about articular cartilage and its defects has multiplied in clinical and experimental settings and the respective body of research literature has grown significantly. However, current strategies for articular cartilage repair have not yet succeeded to replicate the structure and function of innate articular cartilage, which makes it even more important to understand the current strategies and their impact. Therefore, the purpose of this review was to globally summarize experimental strategies investigating cartilage regeneration in vitro as well as in vivo. This will allow for better referencing when designing new models or strategies and potentially improve research translation from bench to bedside.

Comparison of Fixation Techniques of 3D-Woven Poly(ϵ-Caprolactone) Scaffolds for Cartilage Repair in a Weightbearing Porcine Large Animal Model

Objective To test different fixation methods of a 3-dimensionally woven poly(ϵ-caprolactone) (PCL) scaffold within chondral defects of a weightbearing large animal model. Methods Full thickness chondral defects were made in the femoral condyles of 15 adult male Yucatan mini-pigs. Two surgical approaches were compared including total arthrotomy (traditional) and a retinaculum-sparing, minimally invasive surgery (MIS) approach. Following microfracture (MFX), scaffolds were placed without fixation or were fixed with fibrin glue, suture, or subchondral anchor. Experimental endpoints were between 1 and 6 weeks. Micro-computed tomography and histology were used to assess samples. Results The MIS approach was superior as the traditional approach caused medial condyle cartilage wear. One of 13 (7.7%) of scaffolds without fixation, 4 of 11 (36.3%) fibrin scaffolds, 1 of 4 (25%) of sutured scaffolds, and 9 of 9 (100%) of anchor-fixed scaffolds remained in place. Histology demonstrated tissue filling with some overgrowth of PCL scaffolds. Conclusions Of the methods tested, the MIS approach coupled with subchondral anchor fixation provided the best scaffold retention in a mini-pig chondral defect model. This finding has implications for fixation strategies in future animal studies and potential future human use.

Therapeutic Efficacy of Spherical Aggregated Human Bone Marrow-Derived Mesenchymal Stem Cells Cultured for Osteochondral Defects of Rabbit Knee Joints

BACKGROUND

Engraftment and longevity of transplanted cells are crucial for stem cell-based cartilage treatment.

PURPOSE

To determine whether cultured spherical cell masses of human bone marrow-derived mesenchymal stem cells (hBM-MSCs) could improve engraftment at defect sites and to examine their corresponding effects on osteochondral regeneration.

STUDY DESIGN

Controlled laboratory study.

METHODS

A cylindrical osteochondral defect (5 mm wide × 5 mm deep) was created in trochlear grooves of rabbit knees. The single-cell type of hBM-MSCs with fibrin glue, the spherical type of hBM-MSCs with fibrin glue, and cell-free fibrin glue (control) were each implanted into osteochondral defect sites. A total of 18 rabbit knees were randomly assigned to 1 of the 3 groups (3 rabbits per group). Animals were sacrificed at 6 and 12 weeks after transplantation. Repaired tissues were evaluated via gross examination, histologic examination, and immunofluorescence analysis.

RESULTS

Transplantation with spherical hBM-MSCs exhibited superior overall osteochondral restoration when compared with the single-type group, as evidenced by well-ordered mature collagen fibrils produced during subchondral bone formation in the zonation phenomenon. Immunofluorescence analysis of osteochondral defect areas with human-specific antigen revealed a larger number of mesenchymal stem cells in the spherical-type group than the single cell-type group.

CONCLUSION

Transplantation of spherical hBM-MSCs was better than single cells from monolayer culture in improving osteochondral regeneration.

CLINICAL RELEVANCE

The findings demonstrate a simple strategy for enhancing the potency of stem cells required for restoration of osteochondral defects. Furthermore, this strategy may be implemented with other types of stem/progenitor cell-based therapies.

The importance of factorial design in tissue engineering and biomaterials science: Optimisation of cell seeding efficiency on dermal scaffolds as a case study

This article presents a case study to show the usefulness and importance of using factorial design in tissue engineering and biomaterials science. We used a full factorial experimental design (2 × 2 × 2 × 3) to solve a routine query in every biomaterial research project: the optimisation of cell seeding efficiency for pre-clinical in vitro cell studies, the importance of which is often overlooked. In addition, tissue-engineered scaffolds can be cellularised with relevant cell type(s) to form implantable tissue constructs, where the cell seeding method must be reliable and robust. Our results show the complex relationship between cells and scaffolds and suggest that the optimum seeding conditions for each material may be different due to different material properties, and therefore, should be investigated for individual scaffolds. Our factorial experimental design can be easily translated to other cell types and three-dimensional biomaterials, where multiple interacting variables can be thoroughly investigated for better understanding of cell–biomaterial interactions.

Micro/Nano Scaffolds for Osteochondral Tissue Engineering

To develop an osteochondral tissue regeneration strategy it is extremely important to take into account the multiscale organization of the natural extracellular matrix. The structure and gradients of organic and inorganic components present in the cartilage and bone tissues must be considered together. Another critical aspect is an efficient interface between both tissues. So far, most of the approaches were focused on the development of multilayer or stratified scaffolds which resemble the structural composition of bone and cartilage, not considering in detail a transitional interface layer. Typically, those scaffolds have been produced by the combined use of two or more processing techniques (microtechnologies and nanotechnologies) and materials (organic and inorganic). A significant number of works was focused on either cartilage or bone, but there is a growing interest in the development of the osteochondral interface and in tissue engineering models of composite constructs that can mimic the cartilage/bone tissues. The few works that give attention to the interface between cartilage and bone, as well as to the biochemical gradients observed at the osteochondral unit, are also herein described.

Augmented cartilage regeneration by implantation of cellular versus acellular implants after bone marrow stimulation: a systematic review and meta-analysis of animal studies

Bone marrow stimulation may be applied to regenerate focal cartilage defects, but generally results in transient clinical improvement and formation of fibrocartilage rather than hyaline cartilage. Tissue engineering and regenerative medicine strive to develop new solutions to regenerate hyaline cartilage tissue. This systematic review and meta-analysis provides a comprehensive overview of current literature and assesses the efficacy of articular cartilage regeneration by implantation of cell-laden versus cell-free biomaterials in the knee and ankle joint in animals after bone marrow stimulation. PubMed and EMBASE (via OvidSP) were systematically searched using tissue engineering, cartilage and animals search strategies. Included were primary studies in which cellular and acellular biomaterials were implanted after applying bone marrow stimulation in the knee or ankle joint in healthy animals. Study characteristics were tabulated and outcome data were collected for meta-analysis for studies applying semi-quantitative histology as outcome measure (117 studies). Cartilage regeneration was expressed on an absolute 0–100% scale and random effects meta-analyses were performed. Implantation of cellular biomaterials significantly improved cartilage regeneration by 18.6% compared to acellular biomaterials. No significant differences were found between biomaterials loaded with stem cells and those loaded with somatic cells. Culture conditions of cells did not affect cartilage regeneration. Cartilage formation was reduced with adipose-derived stem cells compared to other cell types, but still improved compared to acellular scaffolds. Assessment of the risk of bias was impaired due to incomplete reporting for most studies. Implantation of cellular biomaterials improves cartilage regeneration compared to acellular biomaterials.

PEG-PCL-based nanomedicines: A biodegradable drug delivery system and its application

The lack of efficient therapeutic options for many severe disorders including cancer spurs demand for improved drug delivery technologies. Nanoscale drug delivery systems based on poly(ethylene glycol)-poly(ε-caprolactone) copolymers (PEG-PCL) represent a strategy to implement therapies with enhanced drug accumulation at the site of action and decreased off-target effects. In this review, we discuss state-of-the-art nanomedicines based on PEG-PCL that have been investigated in a preclinical setting. We summarize the various synthesis routes and different preparation methods used for the production of PEG-PCL nanoparticles. Additionally, we review physico-chemical properties including biodegradability, biocompatibility, and drug loading. Finally, we highlight recent therapeutic applications investigated in vitro and in vivo using advanced systems such as triggered release, multi-component therapies, theranostics, or gene delivery systems.

Parylene scaffold for cartilage lesion

Evaluate parylene scaffold feasibility in cartilage lesion treatment, introducing a novel paradigm combining a reparative and superficial reconstructive procedure. Fifteen rabbits were used. All animals had both knees operated and the same osteochondral lesion model was created bilaterally. The parylene scaffold was implanted in the right knee, and the left knee of the same animal was used as control. The animals were euthanized at different time points after surgery: four animals at three weeks, three animals at six weeks, four animals at nine weeks, and four animals at 12 weeks. Specimens were analyzed by International Cartilage Repair Society (ICRS) macroscopic evaluation, modified Pineda histologic evaluation of cartilage repair, and collagen II immunostaining. Parylene knees were compared to its matched contra-lateral control knees of the same animal using the Wilcoxon matched-pairs signed rank. ICRS mean ± SD values for parylene versus control, three, six, nine and twelve weeks, respectively: 7.83 ± 1.85 versus 4.42 ± 1.08, p = 0.0005; 10.17 ± 1.17 versus 6.83 ± 1.17, p = 0.03; 10.89 ± 0.60 versus 7.33 ± 2.18, p = 0.007; 10.67 ± 0.78 versus 7.83 ± 3.40, p = 0.03. Modified Pineda mean ± SD values for parylene versus control, six, nine and twelve weeks, respectively: 3.37 ± 0.87 versus 6.94 ± 1.7, p < 0.0001; 5.73 ± 2.05 versus 6.41 ± 1.7, p = 0.007; 3.06 ± 1.61 versus 6.52 ± 1.51, p < 0.0001. No inflammation was seen. Parylene implanted knees demonstrated higher collagen II expression via immunostaining in comparison to the control knees. Parylene scaffolds are a feasible option for cartilage lesion treatment and the combination of a reparative to a superficial reconstructive procedure using parylene scaffolds led to better results than the reparative procedure alone.

Improved cartilage regeneration by implantation of acellular biomaterials after bone marrow stimulation: a systematic review and meta-analysis of animal studies

Microfracture surgery may be applied to treat cartilage defects. During the procedure the subchondral bone is penetrated, allowing bone marrow-derived mesenchymal stem cells to migrate towards the defect site and form new cartilage tissue. Microfracture surgery generally results in the formation of mechanically inferior fibrocartilage. As a result, this technique offers only temporary clinical improvement. Tissue engineering and regenerative medicine may improve the outcome of microfracture surgery. Filling the subchondral defect with a biomaterial may provide a template for the formation of new hyaline cartilage tissue. In this study, a systematic review and meta-analysis were performed to assess the current evidence for the efficacy of cartilage regeneration in preclinical models using acellular biomaterials implanted after marrow stimulating techniques (microfracturing and subchondral drilling) compared to the natural healing response of defects. The review aims to provide new insights into the most effective biomaterials, to provide an overview of currently existing knowledge, and to identify potential lacunae in current studies to direct future research. A comprehensive search was systematically performed in PubMed and EMBASE (via OvidSP) using search terms related to tissue engineering, cartilage and animals. Primary studies in which acellular biomaterials were implanted in osteochondral defects in the knee or ankle joint in healthy animals were included and study characteristics tabulated (283 studies out of 6,688 studies found). For studies comparing non-treated empty defects to defects containing implanted biomaterials and using semi-quantitative histology as outcome measure, the risk of bias (135 studies) was assessed and outcome data were collected for meta-analysis (151 studies). Random-effects meta-analyses were performed, using cartilage regeneration as outcome measure on an absolute 0–100% scale. Implantation of acellular biomaterials significantly improved cartilage regeneration by 15.6% compared to non-treated empty defect controls. The addition of biologics to biomaterials significantly improved cartilage regeneration by 7.6% compared to control biomaterials. No significant differences were found between biomaterials from natural or synthetic origin or between scaffolds, hydrogels and blends. No noticeable differences were found in outcome between animal models. The risk of bias assessment indicated poor reporting for the majority of studies, impeding an assessment of the actual risk of bias. In conclusion, implantation of biomaterials in osteochondral defects improves cartilage regeneration compared to natural healing, which is further improved by the incorporation of biologics.

Viscoelastic, physical, and bio-degradable properties of dermal scaffolds and related cell behaviour

Dermal scaffolds promote healing of debilitating skin injuries caused by burns and chronic skin conditions. Currently available products present disadvantages and therefore, there is still a clinical need for developing new dermal substitutes. This study aimed at comparing the viscoelastic, physical and bio-degradable properties of two dermal scaffolds, the collagen-based and clinically well established Integra(®) and a novel fibrin-based dermal scaffold developed at our laboratory called Smart Matrix(®), to further evaluate our previous published findings that suggested a higher influx of cells, reduced wound contraction and less scarring for Smart Matrix(®) when used in vivo. Rheological results showed that Integra(®) (G'  =  313.74 kPa) is mechanically stronger than Smart Matrix(®) (G'  =  8.26 kPa), due to the presence of the silicone backing layer in Integra(®). Micro-pores were observed on both dermal scaffolds, although nano-pores as well as densely packed nano-fibres were only observed for Smart Matrix(®). Average surface roughness was higher for Smart Matrix(®) (Sa  =  114.776 nm) than for Integra(®) (Sa  =  75.565 nm). Both scaffolds possess a highly porous structure (80-90%) and display a range of pore micro-sizes that represent the actual in vivo scenario. In vitro proteolytic bio-degradation suggested that Smart Matrix(®) would degrade faster upon implantation in vivo than Integra(®). For both scaffolds, the enzymatic digestion occurs via bulk degradation. These observed differences could affect cell behaviour on both scaffolds. Our results suggest that fine-tuning of scaffolds' viscoelastic, physical and bio-degradable properties can maximise cell behaviour in terms of attachment, proliferation and infiltration, which are essential for tissue repair.

Implantation of Autologous Cartilage Chips Improves Cartilage Repair Tissue Quality in Osteochondral Defects: A Study in Göttingen Minipigs

BACKGROUND

Osteochondral injuries have poor endogenous healing potential, and no standard treatment has been established. The use of combined layered autologous bone and cartilage chips for treatment of osteochondral defects has shown promising short-term clinical results.

PURPOSE/HYPOTHESIS

This study aimed to investigate the role of cartilage chips by comparing combined layered autologous bone and cartilage chips with autologous bone implantation alone in a Göttingen minipig model. The hypothesis was that the presence of cartilage chips would improve the quality of the repair tissue.

STUDY DESIGN

Controlled laboratory study.

METHODS

Twelve Göttingen minipigs received 2 osteochondral defects in each knee. The defects were randomized to autologous bone graft (ABG) combined with autologous cartilage chips (autologous dual-tissue transplantation [ADTT]) or ABG alone. Six animals were euthanized at 6 months and 6 animals were euthanized at 12 months. Follow-up evaluation consisted of histomorphometry, immunohistochemistry, semiquantitative scoring (International Cartilage Repair Society II), and computed tomography.

RESULTS

There was significantly more hyaline cartilage in the ADTT group (25.8%) compared with the ABG group (12.8%) at 6 months after treatment. At 12 months, the fraction of hyaline cartilage in the ABG group had significantly decreased to 4.8%, whereas the fraction of hyaline cartilage in the ADTT group was unchanged (20.1%). At 6 and 12 months, there was significantly more fibrocartilage in the ADTT group (44% and 60.8%) compared with the ABG group (24.5% and 41%). The fraction of fibrous tissue was significantly lower in the ADTT group compared with the ABG group at both 6 and 12 months. The implanted cartilage chips stained >75% positive for collagen type 4 and laminin at both 6 and 12 months. Significant differences were found in a number of International Cartilage Repair Society II subcategories. The volume of the remaining bone defect significantly decreased from 6 to 12 months in both treatment groups; however, no difference in volume was found between the groups at either 6 or 12 months.

CONCLUSION

The presence of cartilage chips in an osteochondral defect facilitated the formation of fibrocartilage as opposed to fibrous tissue at both 6 and 12 months posttreatment. The implanted chips were present in the defect and viable after 12 months.

CLINICAL RELEVANCE

This study substantiates the chondrogenic role of cartilage chips in osteochondral defects.

Dental pulp-derived stromal cells exhibit a higher osteogenic potency than bone marrow-derived stromal cells in vitro and in a porcine critical-size bone defect model

Introduction: The osteogenic differentiation of bone marrow-derived mesenchymal stromal cells (BMSCs) was compared with that of dental pulp-derived stromal cells (DPSCs) in vitro and in a pig calvaria critical-size bone defect model.

Methods: BMSCs and DPSCs were extracted from the tibia bone marrow and the molar teeth of each pig, respectively. BMSCs and DPSCs were cultured in monolayer and on a three-dimensional (3D) polycaprolactone (PCL) – hyaluronic acid – tricalcium phosphate (HT-PCL) scaffold. Population doubling (PD), alkaline phosphatase (ALP) activity, and calcium deposition were measured in monolayer. In the 3D culture ALP activity, DNA content, and calcium deposition were evaluated. Six non-penetrating critical-size defects were made in each calvarium of 14 pigs. Three paired sub-studies were conducted: (1) empty defects vs. HT-PCL scaffolds; (2) PCL scaffolds vs. HT-PCL scaffolds; and (3) autologous BMSCs on HT-PCL scaffolds vs. autologous DPSCs on HT-PCL scaffolds. The observation time was five weeks. Bone volume fractions (BV/TV) were assessed with micro-computed tomography (μCT) and histomorphometry.

Results and discussion: The results from the in vitro study revealed a higher ALP activity and calcium deposition of the DPSC cultures compared with BMSC cultures. Significantly more bone was present in the HT-PCL group than in both the pure PCL scaffold group and the empty defect group in vivo. DPSCs generated more bone than BMSCs when seeded on HT-PCL. In conclusion, DPSCs exhibited a higher osteogenic potential compared with BMSCs both in vitro and in vivo, making it a potential cell source for future bone tissue engineering.

Chondrogenic regeneration using bone marrow clots and a porous polycaprolactone-hydroxyapatite scaffold by three-dimensional printing

Scaffolds play an important role in directing three-dimensional (3D) cartilage regeneration. Our recent study reported the potential advantages of bone marrow clots (MC) in promoting extracellular matrix (ECM) scaffold chondrogenic regeneration. The aim of this study is to build a new scaffold for MC, with improved characteristics in mechanics, shaping, and biodegradability, compared to our previous study. To address this issue, this study prepared a 3D porous polycaprolactone (PCL)-hydroxyapatite (HA) scaffold combined with MC (Group A), while the control group (Group B) utilized a bone marrow stem cell seeded PCL-HA scaffold. The results of in vitro cultures and in vivo implantation demonstrated that although an initial obstruction of nutrient exchange caused by large amounts of fibrin and erythrocytes led to a decrease in the ratio of live cells in Group A, these scaffolds also showed significant improvements in cell adhesion, proliferation, and chondrogenic differentiation with porous recanalization in the later culture, compared to Group B. After 4 weeks of in vivo implantation, Group A scaffolds have a superior performance in DNA content, Sox9 and RunX2 expression, cartilage lacuna-like cell and ECM accumulation, when compared to Group B. Furthermore, Group A scaffold size and mechanics were stable during in vitro and in vivo experiments, unlike the scaffolds in our previous study. Our results suggest that the combination with MC proved to be a highly efficient, reliable, and simple new method that improves the biological performance of 3D PCL-HA scaffold. The MC-PCL-HA scaffold is a candidate for future cartilage regeneration studies.

Collagen Type IV and Laminin Expressions during Cartilage Repair and in Late Clinically Failed Repair Tissues from Human Subjects

OBJECTIVE

To identify the collagen type IV (Col4) isoform in articular cartilage and to evaluate the expressions of Col4 and laminin in the pericellular matrix (PCM) in damaged cartilage and during cartilage repair.

DESIGN

The Col4 isoform was determined in chondrocytes isolated from 6 patients cultured up to 6 days and in 21% O2 or 1% O2, and the gene expression of Col4 α-chains was investigated. The distribution of Col4 and laminin in traumatically damaged cartilage (n = 7) and clinically failed cartilage repair (microfracture, TruFit, autologous chondrocyte implantation; n = 11) were investigated using immunohistochemistry. Normal human cartilage was used as control (n = 8). The distribution during clinical cartilage repair procedures was investigated in a minipig model with 6-month follow-up (untreated chondral, untreated osteochondral, microfracture, autologous chondrocyte implantation; n = 10).

RESULTS

The Col4 isoform in articular cartilage was characterized as α1α1α2, which is an isoform containing antiangiogenic domains in the NC1-terminals (arresten and canstatin). In normal cartilage, laminin and Col4 was exclusively found in the PCM. High amounts (>50%) of Col4 in the PCM significantly decreased in damaged cartilage (P = 0.004) and clinically failed repair tissue (P < 0.001). Laminin was only found with high expression (>50%) in 4/8 of the normal samples, which was not statistically significantly different from damaged cartilage (P = 0.15) or failed cartilage repair (P = 0.054).

CONCLUSIONS

Col4 in cartilage contain antiangiogenic domains and may play a role in the hypoxic environment in articular cartilage. Col4 and laminin was not found in the PCM of damaged and clinically failed repair.

Experimental articular cartilage repair in the Göttingen minipig: the influence of multiple defects per knee

Background

A gold standard treatment for articular cartilage injuries is yet to be found, and a cost-effective and predictable large animal model is needed to bridge the gap between in vitro studies and clinical studies.

Ideally, the animal model should allow for testing of clinically relevant treatments and the biological response should be reproducible and comparable to humans. This allows for a reliable translation of results to clinical studies.This study aimed at verifying the Göttingen minipig as a pre-clinical model for articular cartilage repair by testing existing clinical cartilage repair techniques and evaluating the use of two defects per knee.

Methods

Sixteen fully mature Göttingen minipigs were used. The minipigs received bilateral trochlear osteochondral drill-hole defects or chondral defects (Ø 6 mm), either one defect per knee or two defects per knee. The defects were treated with one of the following: Matrix-induced autologous chondrocyte implantation (MACI), microfracture (MFx), autologous-dual-tissue transplantation (ADTT), autologous bone graft, autologous cartilage chips. Empty chondral and osteochondral defects were used as controls. MRI and CT were performed 3 and 6 month, histology was performed 6 month postoperative.

Results

The repair tissue varied in morphology from non-cartilaginous fibrous tissue to fibrocartilaginous tissue as seen on MRI, CT and histology at 6 month. The worst results were seen in the empty controls, while the best results were achieved with the MACI and ADTT treatment. The use of two defects per knee did not have any significant effect on the repair response.

Conclusion

The outcomes of the applied treatments were consistent with the outcomes in clinical studies and it was possible to apply two defects per knee. The Göttingen minipig model was easy to handle, cost-effective and provided predictable outcome. Based on this study the use of two defects per knee, one in the medial and one in the lateral trochlear facet, in male Göttingen minipigs is recommended.

PVA-chitosan composite hydrogel versus alginate beads as a potential mesenchymal stem cell carrier for the treatment of focal cartilage defects

PURPOSE

To investigate whether mesenchymal stem cells (MSCs) seeded in novel polyvinyl alcohol (PVA)-chitosan composite hydrogel can provide comparable or even further improve cartilage repair outcomes as compared to previously established alginate-transplanted models.

METHODS

Medial femoral condyle defect was created in both knees of twenty-four mature New Zealand white rabbits, and the animals were divided into four groups containing six animals each. After 3 weeks, the right knees were transplanted with PVA-chitosan-MSC, PVA-chitosan scaffold alone, alginate-MSC construct or alginate alone. The left knee was kept as untreated control. Animals were killed at the end of 6 months after transplantation, and the cartilage repair was assessed through Brittberg morphological score, histological grading by O'Driscoll score and quantitative glycosaminoglycan analysis.

RESULTS

Morphological and histological analyses showed significant (p < 0.05) tissue repair when treated with PVA-chitosan-MSC or alginate MSC as compared to the scaffold only and untreated control. In addition, safranin O staining and the glycosaminoglycan (GAG) content were significantly higher (p < 0.05) in MSC treatment groups than in scaffold-only or untreated control group. No significant difference was observed between the PVA-chitosan-MSC- and alginate-MSC-treated groups.

CONCLUSION

PVA-chitosan hydrogel seeded with mesenchymal stem cells provides comparable treatment outcomes to that of previously established alginate-MSC construct implantation. This study supports the potential use of PVA-chitosan hydrogel seeded with MSCs for clinical use in cartilage repair such as traumatic injuries.

A Stereological Method for the Quantitative Evaluation of Cartilage Repair Tissue

OBJECTIVE

To implement stereological principles to develop an easy applicable algorithm for unbiased and quantitative evaluation of cartilage repair.

DESIGN

Design-unbiased sampling was performed by systematically sectioning the defect perpendicular to the joint surface in parallel planes providing 7 to 10 hematoxylin-eosin stained histological sections. Counting windows were systematically selected and converted into image files (40-50 per defect). The quantification was performed by two-step point counting: (1) calculation of defect volume and (2) quantitative analysis of tissue composition. Step 2 was performed by assigning each point to one of the following categories based on validated and easy distinguishable morphological characteristics: (1) hyaline cartilage (rounded cells in lacunae in hyaline matrix), (2) fibrocartilage (rounded cells in lacunae in fibrous matrix), (3) fibrous tissue (elongated cells in fibrous tissue), (4) bone, (5) scaffold material, and (6) others. The ability to discriminate between the tissue types was determined using conventional or polarized light microscopy, and the interobserver variability was evaluated.

RESULTS

We describe the application of the stereological method. In the example, we assessed the defect repair tissue volume to be 4.4 mm(3) (CE = 0.01). The tissue fractions were subsequently evaluated. Polarized light illumination of the slides improved discrimination between hyaline cartilage and fibrocartilage and increased the interobserver agreement compared with conventional transmitted light.

CONCLUSION

We have applied a design-unbiased method for quantitative evaluation of cartilage repair, and we propose this algorithm as a natural supplement to existing descriptive semiquantitative scoring systems. We also propose that polarized light is effective for discrimination between hyaline cartilage and fibrocartilage.

Evaluation of Cartilage Repair by Mesenchymal Stem Cells Seeded on a PEOT/PBT Scaffold in an Osteochondral Defect

The main objective of this study was to evaluate the effectiveness of a mesenchymal stem cell (MSC)-seeded polyethylene-oxide-terephthalate/polybutylene-terephthalate (PEOT/PBT) scaffold for cartilage tissue repair in an osteochondral defect using a rabbit model. Material characterisation using scanning electron microscopy indicated that the scaffold had a 3D architecture characteristic of the additive manufacturing fabrication method, with a strut diameter of 296 ± 52 μm and a pore size of 512 ± 22 μm × 476 ± 25 μm × 180 ± 30 μm. In vitro optimisation revealed that the scaffold did not generate an adverse cell response, optimal cell loading conditions were achieved using 50 μg/ml fibronectin and a cell seeding density of 25 × 10(6) cells/ml and glycosaminoglycan (GAG) accumulation after 28 days culture in the presence of TGFβ3 indicated positive chondrogenesis. Cell-seeded scaffolds were implanted in osteochondral defects for 12 weeks, with cell-free scaffolds and empty defects employed as controls. On examination of toluidine blue staining for chondrogenesis and GAG accumulation, both the empty defect and the cell-seeded scaffold appeared to promote repair. However, the empty defect and the cell-free scaffold stained positive for collagen type I or fibrocartilage, while the cell-seeded scaffold stained positive for collagen type II indicative of hyaline cartilage and was statistically better than the cell-free scaffold in the blinded histological evaluation. In summary, MSCs in combination with a 3D PEOT/PBT scaffold created a reparative environment for cartilage repair.

Functionalization of polycaprolactone scaffolds with hyaluronic acid and β-TCP facilitates migration and osteogenic differentiation of human dental pulp stem cells in vitro

In this study, we sought to assess the osteogenic potential of human dental pulp stem cells (DPSCs) on three different polycaprolactone (PCL) scaffolds. The backbone structure of the scaffolds was manufactured by fused deposition modeling (PCL scaffold). The composition and morphology was functionalized in two of the scaffolds. The first underwent thermal induced phase separation of PCL infused into the pores of the PCL scaffold. This procedure resulted in a highly variable micro- and nanostructured porous (NSP), interconnected, and isotropic tubular morphology (NSP-PCL scaffold). The second scaffold type was functionalized by dip-coating the PCL scaffold with a mixture of hyaluronic acid and β-TCP (HT-PCL scaffold). The scaffolds were cylindrical and measured 5 mm in height and 10 mm in diameter. They were seeded with 1×10(6) human DPSCs, a cell type known to express bone-related markers, differentiate into osteoblasts-like cells, and to produce a mineralized bone-like extracellular matrix. DPSCs were phenotypically characterized by flow cytometry for CD90(+), CD73(+), CD105(+), and CD14(-). DNA, ALP, and Ca(2+) assays and real-time quantitative polymerase chain reaction for genes involved in osteogenic differentiation were analyzed on day 1, 7, 14, and 21. Cell viability and distribution were assessed on day 1, 7, 14, and 21 by fluorescent-, scanning electron-, and confocal microscopy. The results revealed that the DPSCs expressed relevant gene expression consistent with osteogenic differentiation. The NSP-PCL and HT-PCL scaffolds promoted osteogenic differentiation and Ca(2+) deposition after 21 days of cultivation. Different gene expressions associated with mature osteoblasts were upregulated in these two scaffold types, suggesting that the methods in which the scaffolds promote osteogenic differentiation, depends on functionalization approaches. However, only the HT-PCL scaffold was also able to support cell proliferation and cell migration resulting in even cell dispersion throughout the scaffold. In conclusion, DPSCs could be a possible alternate cell source for bone tissue engineering. The HT-PCL scaffold showed promising results in terms of promoting cell migration and osteogenic differentiation, which warrants future in vivo studies.

Chondrogenic differentiation of marrow clots after microfracture with BMSC-derived ECM scaffold in vitro

Repairing articular cartilage by combining microfracture and various scaffolds has been extensively performed in in vivo animal models. We previously described a novel extracellular matrix (ECM) scaffold for cartilage tissue engineering. The aim of this study was to investigate the effect of a bone marrow-derived mesenchymal stem cells-derived ECM (BMSC-dECM) scaffold on the chondrogenic differentiation of marrow clots following microfracture in vitro. In this study, we manufactured the BMSC-dECM scaffold using a freeze-drying method. To obtain the marrow clots, a full-thickness cartilage defect was established and microholes were created in the trochlear groove of New Zealand white rabbits. The samples were divided and cultured in vitro for 1, 2, 4, and 8 weeks. The samples included a culture of the marrow clot alone (Group 1), a culture of the marrow clot with transforming growth factor-beta 3 (TGF-β3) (Group 2), a culture of the composite of the BMSC-dECM scaffold and the marrow clot alone (Group 3), and a culture of the composite with TGF-β3 (Group 4). A smooth and glossy surface was observed in Group 2 and Group 4 over time, but the surface for Group 4 was larger from week 1 onward. Compressive strength gradually increased in Groups 2 and 4, and greater increases were observed in Group 4 during the 8-week culture period. Enhanced cartilage-like matrix deposition of glycosaminoglycan (GAG) and type II collagen were confirmed by Safranin O and immunohistochemistry staining, respectively, in Groups 2 and 4. The GAG and collagen contents also gradually increased over time in Groups 2 and 4; the increase was greater in Group 4. In addition, real-time-polymerase chain reaction demonstrated that the expression of chondrogenic genes, such as COL2, ACAN, and SOX9, was gradually upregulated in Groups 2 and 4. However, greater increases in the expression of these cartilage-like genes were observed in Group 4 from week 4 onward. Our results suggest that the BMSC-dECM scaffold may favor the chondrogenesis of marrow clots following microfracture in vitro. In conclusion, these tissue engineering-like constructs could be potential candidates for cartilage repair.

Osteochondral regeneration using a novel aragonite-hyaluronate bi-phasic scaffold in a goat model

PURPOSE

The objective of this study was to examine whether different mechanical modifications and/or impregnation of hyaluronic acid (HA) might enhance aragonite-based scaffold properties for the regeneration of cartilage and bone in an animal model.

METHODS

Bi-phasic osteochondral scaffolds were prepared using coralline aragonite with different modifications, including 1- to 2-mm-deep drilled channels in the cartilage phase (Group 1, n = 7) or in the bone phase (Group 2, n = 8), and compared with unmodified coral cylinders (Group 3, n = 8) as well as empty control defects (Group 4, n = 4). In each group, four of the implants were impregnated with HA to the cartilage phase. Osteochondral defects (6 mm diameter, 8 mm depth) were made in medial and lateral femoral condyles of 14 goats, and the scaffolds were implanted according to a randomization chart. After 6 months, cartilage and bone regeneration were evaluated macroscopically and histologically by an external laboratory.

RESULTS

Group 1 implants were replaced by newly formed hyaline cartilage and subchondral bone (combined histological evaluation according to the ICRS II-2010 and O'Driscoll et al. 34 ± 4 n = 7). In this group, the cartilaginous repair tissue showed a smooth contour and was well integrated into the adjacent native cartilage, with morphological evidence of hyaline cartilage as confirmed by the marked presence of proteoglycans, a marked grade of collagen type II and the absence of collagen type I. The average scores in other groups were significantly lower (Group 2 (n = 8) 28.8 ± 11, Group 3 (n = 8) 23 ± 9 and Group 4 (empty control, n = 4) 19.7 ± 15).

CONCLUSIONS

The implants with the mechanical modification and HA impregnation in the cartilage phase outperformed all other types of implant. Although native coral is an excellent material for bone repair, as a stand-alone material implant, it does not regenerate hyaline cartilage. Mechanical modification with drilled channels and impregnation of HA within the coral pores enhanced the scaffold's cartilage regenerative potential. The modified implant shows young hyaline cartilage regeneration. This implant might be useful for the treatment of both chondral and osteochondral defects in humans.

Use of cell-free collagen type I matrix implants for the treatment of small cartilage defects in the knee: clinical and magnetic resonance imaging evaluation

PURPOSE

Articular cartilage defects of the knee are a common condition for which several repair techniques have been described. The aim of the present study was to assess medium-term results of a one-step procedure using a cell-free collagen type I matrix.

METHODS

Fifteen patients with articular cartilage defects of the knee were treated with an 11-mm-diameter cell-free collagen type 1 matrix implant. The matrices were implanted in a press-fit manner into the defect after careful debridement down to the subchondral bone but without penetration of this margin. Follow-up examinations were carried out at 6 weeks, 6 months, and at 12, 24, 36, and 48 months after implantation. Clinical assessment included the visual analogue scale (VAS), the Tegner activity scale, and the International Knee Documentation Committee (IKDC) score. Radiological assessment for graft attachment and tissue regeneration was performed using the magnetic observation of cartilage repair tissue (MOCART) score.

RESULTS

A total of 15 patients (males: n = 6 and females: n = 9) with a mean age of 26.4 years (range 19-40) were treated. The mean VAS improved significantly when compared to the preoperative values (P < 0.05). Six weeks after implantation, IKDC values were slightly lower than the preoperative values (n.s.), but increased significantly at final follow-up (P < 0.05). At 24 months, there were no significant differences in the median Tegner score between the post-operative values and the preoperative values (n.s.). However, after 36 months, a significant improvement was noted that lasted at least up to 48 months (P < 0.05). The MOCART score improved consistently up to 4 years after implantation, with significant improvements already observed after 12 months (P < 0.05). No correlation between the clinical scores and the MOCART score could be perceived.

CONCLUSION

The present study showed that the use of cell-free collagen type I matrix implants led to a significant and durable improvement in all the clinical and imaging scores investigated 4 years after implantation.

LEVEL OF EVIDENCE

IV.

Increased Adipogenic and Decreased Chondrogenic Differentiation of Adipose Derived Stem Cells on Nanowire Surfaces

Despite many advances in tissue engineering, there are still significant challenges associated with restructuring, repairing, or replacing damaged tissue in the body. Currently, a major obstacle has been trying to develop a scaffold for cartilage tissue engineering that provides the correct mechanical properties to endure the loads associated with articular joints as well as promote cell-scaffold interactions to aid in extracellular matrix deposition. In addition, adipogenic tissue engineering is widely growing due to an increased need for more innovative reconstructive therapies following adipose tissue traumas and cosmetic surgeries. Recently, lipoaspirate tissue has been identified as a viable alternative source for mesenchymal stem cells because it contains a supportive stroma that can easily be isolated. Adipose derived stem cells (ADSCs) can differentiate into a variety of mesodermal lineages including the adipogenic and chondrogenic phenotypes. Biodegradable polymeric scaffolds have been shown to be a promising alternative and stem cells have been widely used to evaluate the compatibility, viability, and bioactivity of these materials. Polycaprolactone is a bioresorbable polymer, which has been widely used for biomedical and tissue engineering applications. The fundamental concept behind successful synthetic tissue-engineered scaffolds is to promote progenitor cell migration, adhesion, proliferation, and induce differentiation, extracellular matrix synthesis, and finally integration with host tissue. In this study, we investigated the adhesion, proliferation, and chondrogenic and adipogenic differentiation of ADSCs on nanowire surfaces. A solvent-free gravimetric template technique was used to fabricate polycaprolactone nanowires surfaces. The results indicated that during the growth period i.e., initial 7 days of culture, the nanowire surfaces (NW) supported adhesion and proliferation of the cells that had elongated morphologies. However, cell on surfaces without nanowires had non-elongated morphologies. Further, immunofluorescence imaging of marker proteins showed that the nanowires surfaces did not appear to support chondrogenic differentiation whereas supported adipogenic differentiation of ADSCs.

Current concepts: tissue engineering and regenerative medicine applications in the ankle joint

Tissue engineering and regenerative medicine (TERM) has caused a revolution in present and future trends of medicine and surgery. In different tissues, advanced TERM approaches bring new therapeutic possibilities in general population as well as in young patients and high-level athletes, improving restoration of biological functions and rehabilitation. The mainstream components required to obtain a functional regeneration of tissues may include biodegradable scaffolds, drugs or growth factors and different cell types (either autologous or heterologous) that can be cultured in bioreactor systems (in vitro) prior to implantation into the patient. Particularly in the ankle, which is subject to many different injuries (e.g. acute, chronic, traumatic and degenerative), there is still no definitive and feasible answer to ‘conventional’ methods. This review aims to provide current concepts of TERM applications to ankle injuries under preclinical and/or clinical research applied to skin, tendon, bone and cartilage problems. A particular attention has been given to biomaterial design and scaffold processing with potential use in osteochondral ankle lesions.

Scaffold-assisted cartilage tissue engineering using infant chondrocytes from human hip cartilage

OBJECTIVE

Studies about cartilage repair in the hip and infant chondrocytes are rare. The aim of our study was to evaluate the use of infant articular hip chondrocytes for tissue engineering of scaffold-assisted cartilage grafts.

METHOD

Hip cartilage was obtained from five human donors (age 1-10 years). Expanded chondrocytes were cultured in polyglycolic acid (PGA)-fibrin scaffolds. De- and re-differentiation of chondrocytes were assessed by histological staining and gene expression analysis of typical chondrocytic marker genes. In vivo, cartilage matrix formation was assessed by histology after subcutaneous transplantation of chondrocyte-seeded PGA-fibrin scaffolds in immunocompromised mice.

RESULTS

The donor tissue was heterogenous showing differentiated articular cartilage and non-differentiated tissue and considerable expression of type I and II collagens. Gene expression analysis showed repression of typical chondrocyte and/or mesenchymal marker genes during cell expansion, while markers were re-induced when expanded cells were cultured in PGA-fibrin scaffolds. Cartilage formation after subcutaneous transplantation of chondrocyte loaded PGA-fibrin scaffolds in nude mice was variable, with grafts showing resorption and host cell infiltration or formation of hyaline cartilage rich in type II collagen. Addition of human platelet rich plasma (PRP) to cartilage grafts resulted robustly in formation of hyaline-like cartilage that showed type II collagen and regions with type X collagen.

CONCLUSION

These results suggest that culture of expanded and/or de-differentiated infant hip cartilage cells in PGA-fibrin scaffolds initiates chondrocyte re-differentiation. The heterogenous donor tissue containing immature chondrocytes bears the risk of cartilage repair failure in vivo, which may be possibly overcome by the addition of PRP.

Tissue engineering stratified scaffolds for articular cartilage and subchondral bone defects repair

Due to their good biocompatibility and mechanical integrity, tissue engineering scaffolds have become a principal method of repair and regeneration of osteochondral defects. To improve their intrinsic properties, control their degenerative times, and enhance their cell adhesion and differentiation, numerous scaffold architectures and formation methods have been developed and tested, but the ideal scaffold design is still controversial. Moreover, scaffold fixation has a significant influence on repair and regeneration after implantation. The authors analyzed relative studies to address the latest scaffold designs, including biphasic scaffold, multilayered scaffold, and continuous nonstratified scaffold, and this article compares their advantages and disadvantages. In addition, the authors introduce a novel modified method for scaffold fixation known as magnetic fixation. Both stratified and nonstratified scaffolds can repair osteochondral defects, but continuous nonstratified scaffolds are more biomimetic compared with the native osteochondral structures, and they lead to a better regeneration of hyaline-like cartilage and structured bone tissue. Therefore, the authors suggest continuous nonstratified scaffolds are an effective option for treating osteochondral defects.

Surface-modified functionalized polycaprolactone scaffolds for bone repair: in vitro and in vivo experiments

A porcine calvaria defect study was carried out to investigate the bone repair potential of three-dimensional (3D)-printed poly-ε-caprolactone (PCL) scaffolds embedded with nanoporous PCL. A microscopic grid network was created by rapid prototyping making a 3D-fused deposition model (FDM-PCL). Afterward, the FDM-PCL scaffolds were infused with a mixture of PCL, water, and 1,4-dioxane and underwent a thermal-induced phase separation (TIPS) followed by lyophilization. The TIPS process lead to a nanoporous structure shielded by the printed microstructure (NSP-PCL). Sixteen Landrace pigs were divided into two groups with 8 and 12 weeks follow-up, respectively. A total of six nonpenetrating holes were drilled in the calvaria of each animal. The size of the cylindrical defects was h 10 mm and Ø 10 mm. The defects were distributed randomly using following groups: (a) NSP-PCL scaffold, (b) FDM-PCL scaffold, (c) autograft, (d) empty defect, (a1) NSP-PCL scaffold + autologous mononuclear cells, and (a2) NSP-PCL scaffold + bone morphogenetic protein 2. Bone volume to total volume was analyzed using microcomputed tomography (µCT) and histomorphometry. The µCT and histological data showed significantly less bone formation in the NSP-PCL scaffolds in all three variations after both 8 and 12 weeks compared to all other groups. The positive autograft control had significantly higher new bone formation compared to all other groups except the FDM-PCL when analyzed using histomorphometry. The NSP-PCL scaffolds were heavily infiltrated with foreign body giant cells suggesting an inflammatory response and perhaps active resorption of the scaffold material. The unmodified FDM-PCL scaffold showed good osteoconductivity and osseointegration after both 8 and 12 weeks.

Exogenous bFGF promotes articular cartilage repair via up-regulation of multiple growth factors

OBJECTIVE

To investigate the roles of exogenous basic fibroblast growth factor (bFGF) on the repair of full-thickness articular cartilage defects in rabbits.

DESIGN

In the present study, a double-layered collagen membrane sandwiched with bFGF-loaded-nanoparticles between a dense layer and a loose layer was implanted into full-thickness articular cartilage defects in rabbits. By grafting the membrane in a different direction, the dense layer or the loose layer facing the surface of the subchondral bone, the effects of the released bFGF on the defects and the profiles of nine growth factors (GFs) in synovial fluid (SF) were investigated using histological methods and antibody arrays, respectively.

RESULTS

In the group with the loose layer facing the surface of the subchondral bone, fast release of bFGF was observed, and early high levels of endogenous transforming growth factor-β2 (TGF-β2), vascular endothelial growth factor (VEGF), bFGF, bone morphogenetic protein 2 (BMP-2), BMP-3, and BMP-4 in SF were detected by antibody arrays, especially on day 3. Chondrocyte-like cells were also observed in this group at an early stage. As a result, this group showed better levels of repair, as compared to the other groups in which low GF levels were detected at an early stage, and chondrocyte-like cells appeared much later.

CONCLUSIONS

Our study suggests that exogenous bFGF promotes articular cartilage repair by up-regulating the levels of multiple GFs, but administration at an early stage is required.

Repair of osteochondral defects with recombinant human type II collagen gel and autologous chondrocytes in rabbit

OBJECTIVE

Recombinant human type II collagen (rhCII) gels combined with autologous chondrocytes were tested as a scaffold for cartilage repair in rabbits in vivo.

METHOD

Autologous chondrocytes were harvested, expanded and combined with rhCII-gel and further pre-cultivated for 2 weeks prior to transplantation into a 4 mm diameter lesion created into the rabbit's femoral trochlea (n = 8). Rabbits with similar untreated lesions (n = 7) served as a control group.

RESULTS

Six months after the transplantation the repair tissue in both groups filled the lesion site, but in the rhCII-repair the filling was more complete. Both repair groups also had high proteoglycan and type II collagen contents, except in the fibrous superficial layer. However, the integration to the adjacent cartilage was incomplete. The O'Driscoll grading showed no significant differences between the rhCII-repair and spontaneous repair, both representing lower quality than intact cartilage. In the repair tissues the collagen fibers were abnormally organized and oriented. No dramatic changes were detected in the subchondral bone structure. The repair cartilage was mechanically softer than the intact tissue. Spontaneously repaired tissue showed lower values of equilibrium and dynamic modulus than the rhCII-repair. However, the differences in the mechanical properties between all three groups were insignificant.

CONCLUSION

When rhCII was used to repair cartilage defects, the repair quality was histologically incomplete, but still the rhCII-repairs showed moderate mechanical characteristics and a slight improvement over those in spontaneous repair. Therefore, further studies using rhCII for cartilage repair with emphasis on improving integration and surface protection are required.

Increased chondrocyte seeding density has no positive effect on cartilage repair in an MPEG-PLGA scaffold

PURPOSE

This study investigates the effect of cell seeding density on cartilage repair in matrix-assisted chondrocyte implantation in vitro and in vivo.

METHODS

In vitro: Four different cell seeding densities of human chondrocytes were seeded onto a porous methoxy-polyethylene glycol-polylactic-co-glycolic acid scaffold (MPEG-PLGA) polymer scaffold ASEED™ (1.2 × 10(6), 4.0 × 10(6), 1.2 × 10(7) and 2.0 × 10(7) cells/cm(3)). The cartilage repair response was evaluated by relative gene expression of the chondrogenic markers sox9, collagen types I, II and X, and aggrecan, total DNA content and sulphated glycosaminoglycan synthesis. In vivo: Using a New Zealand white rabbit intercondylar osteochondral defect model, three different cell seeding densities (1.2 × 10(6), 4.0 × 10(6) and 1.2 × 10(7) cells/cm(3)) were tested with an empty scaffold as control. The cartilage repair response was evaluated using O'Driscoll score.

RESULTS

In vitro: A significant difference (p < 0.05) in total DNA content was found at day 2 but not at day 7. The low cell seeding densities yielded the highest GAG content (p < 0.001) at day 7. Collagen type I was highest (p < 0.01) at the lowest density at day 7. In vivo: No significant difference was found between the 4 groups.

CONCLUSIONS

No positive effect on cartilage repair was found using increased cell seeding density.

LEVEL OF EVIDENCE

Controlled experimental study, Level II.

Dermatan sulphate in methoxy polyethylene glycol-polylactide-co-glycolic acid scaffolds upregulates fibronectin gene expression but has no effect on in vivo osteochondral repair

PURPOSE

The purpose of the study was to investigate the effect of dermatan sulphate (DS) addition to biodegradable methoxy polyethylene glycol (MPEG) substituted polylactide-co-glycolic acid (PLGA) scaffolds for cartilage repair in vitro and in vivo.

METHODS

Human chondrocytes from eight patients undergoing anterior cruciate ligament reconstruction were isolated and cultured in 5% oxygen on MPEG-PLGA scaffolds±DS for one, three, seven and 14 days. Analyses were performed using quantitative gene expression analysis for chondrogenic and cell attachment markers. An osteochondral drill hole defect was created in the intertrochlear groove of the distal femur in 20 New Zealand white rabbits (defects n=20). When bleeding was observed, the defects were treated with MPEG-PLGA scaffolds±DS. Twelve weeks after surgery the rabbits were sacrificed and the defects were analysed using histological grading with O'Driscoll scoring.

RESULTS

DS addition to MPEG-PLGA scaffolds resulted in a significant upregulation of fibronectin gene expression on day 1. No differences were observed in chondrogenic gene expression. There were no differences between the two groups in histological grading (+DS 10.3 and -DS 9.6).

CONCLUSIONS

Upregulation of fibronectin in vitro indicating early cell-scaffold interaction and attachment did not result in improved cartilage repair in an osteochondral defect model in rabbits.