Patient-specific Scaffolds with a Biomimetic Gradient Environment for Articular Cartilage–Subchondral Bone Regeneration

Mesenchymal stem cells for cartilage regeneration: Insights into molecular mechanism and therapeutic strategies

The use of mesenchymal stem cells (MSCs) in cartilage regeneration has gained significant attention in regenerative medicine. This paper reviews the molecular mechanisms underlying MSC-based cartilage regeneration and explores various therapeutic strategies to enhance the efficacy of MSCs in this context. MSCs exhibit multipotent capabilities and can differentiate into various cell lineages under specific microenvironmental cues. Chondrogenic differentiation, a complex process involving signaling pathways, transcription factors, and growth factors, plays a pivotal role in the successful regeneration of cartilage tissue. The chondrogenic differentiation of MSCs is tightly regulated by growth factors and signaling pathways such as TGF-β, BMP, Wnt/β-catenin, RhoA/ROCK, NOTCH, and IHH (Indian hedgehog). Understanding the intricate balance between these pathways is crucial for directing lineage-specific differentiation and preventing undesirable chondrocyte hypertrophy. Additionally, paracrine effects of MSCs, mediated by the secretion of bioactive factors, contribute significantly to immunomodulation, recruitment of endogenous stem cells, and maintenance of chondrocyte phenotype. Pre-treatment strategies utilized to potentiate MSCs, such as hypoxic conditions, low-intensity ultrasound, kartogenin treatment, and gene editing, are also discussed for their potential to enhance MSC survival, differentiation, and paracrine effects. In conclusion, this paper provides a comprehensive overview of the molecular mechanisms involved in MSC-based cartilage regeneration and outlines promising therapeutic strategies. The insights presented contribute to the ongoing efforts in optimizing MSC-based therapies for effective cartilage repair.

Chitosan/Hyaluronan and Alginate-Nanohydroxyapatite Biphasic Scaffold as a Promising Matrix for Osteoarthritis Disorders

Purpose

Regenerative medicine offers new techniques for osteoarthritis (OA) disorders, especially while considering simultaneous chondral and subchondral regenerations.

Methods

Chitosan and hyaluronan were chemically bound as the chondral phase and the osteogenic layer was prepared with alginate and nano-hydroxyapatite (nHAP). These scaffolds were fixed by fibrin glue as a biphasic scaffold and then examined.

Results

Scanning electron microscopy (SEM) confirmed the porosity of 61.45±4.51 and 44.145±2.81 % for the subchondral and chondral layers, respectively. The composition analysis by energy dispersive X-ray (EDAX) indicated the various elements of both hydrogels. Also, their mechanical properties indicated that the highest modulus and resistance values corresponded to the biphasic hydrogel as 108.33±5.56 and 721.135±8.21 kPa, despite the same strain value as other groups. Their individual examinations demonstrated the proteoglycan synthesis of the chondral layer and also, the alkaline phosphatase (ALP) activity of the subchondral layer as 13.3±2.2 ng. After 21 days, the cells showed a mineralized surface and a polygonal phenotype, confirming their commitment to bone and cartilage tissues, respectively. Immunostaining of collagen I and II represented greater extracellular matrix (ECM) secretion in the biphasic composite group due to the paracrine effect of the two cell types on each other.

Conclusion

For the first time, the ability of this biphasic scaffold to regenerate both tissue types was evaluated and the results showed satisfactory cellular commitment to bone and cartilage tissues. Thus, this scaffold can be considered a new strategy for the preparation of implants for OA.

Advances in mechanically robust and biomimetic polysaccharide-based constructs for cartilage tissue engineering

The purpose of cartilage tissue engineering is to provide artificial constructs with biological functions and mechanical features that resemble native tissue to improve tissue regeneration. Biochemical characteristics of the cartilage extracellular matrix (ECM) microenvironment provide a platform for researchers to develop biomimetic materials for optimal tissue repair. Due to the structural similarity of polysaccharides into physicochemical characteristics of cartilage ECM, these natural polymers capture special attention for developing biomimetic materials. The mechanical properties of constructs play a crucial influence in load-bearing cartilage tissues. Moreover, the addition of appropriate bioactive molecules to these constructs can promote chondrogenesis. Here, we discuss polysaccharide-based constructs that can be used to create substitutes for cartilage regeneration. We intend to focus on newly developed bioinspired materials, fine-tuning the mechanical properties of constructs, the design of carriers loaded by chondroinductive agents, and development of appropriate bioinks as a bioprinting approach for cartilage regeneration.

Regulated macrophage immune microenvironment in 3D printed scaffolds for bone tumor postoperative treatment

The 3D printing technique is suitable for patient-specific implant preparation for bone repair after bone tumor resection. However, improving the survival rate due to tumor recurrence remains a challenge for implants. The macrophage polarization induction to M2-type tumor-associated macrophages (TAMs) by the tumor microenvironment is a key factor of immunosuppression and tumor recurrence. In this study, a regenerative scaffold regulating the macrophage immune microenvironment and promoting bone regeneration in a dual-stage process for the postoperative treatment of bone tumors was constructed by binding a colony-stimulating factor 1 receptor (CSF-1R) inhibitor GW2580 onto in situ cosslinked hydroxybutylchitosan (HBC)/oxidized chondroitin sulfate (OCS) hydrogel layer covering a 3D printed calcium phosphate scaffold based on electrostatic interaction. The hydrogel layer on scaffold surface not only supplied abundant sulfonic acid groups for stable loading of the inhibitor, but also acted as the cover mask protecting the bone repair part from exposure to unhealthy growth factors in the microenvironment at the early treatment stage. With local prolonged release of inhibitor being realized via the functional material design, CSF-1R, the main pathway that induces polarization of TAMs, can be efficiently blocked, thus regulating the immunosuppressive microenvironment and inhibiting tumor development at a low therapeutic dose. At the later stage of treatment, calcium phosphate component of the scaffold can facilitate the repair of bone defects caused by tumor excision. In conclusion, the difunctional 3D printed bone repair scaffold regulating immune microenvironment in stages proposed a novel approach for bone tumor postoperative treatment.

Recent Advances in "Functional Engineering of Articular Cartilage Zones by Polymeric Biomaterials Mediated with Physical, Mechanical, and Biological/Chemical Cues"

Articular cartilage (AC) plays an unquestionable role in joint movements but unfortunately the healing capacity is restricted due to its avascular and acellular nature. While cartilage tissue engineering has been lifesaving, it is very challenging to remodel the complex cartilage composition and architecture with gradient physio-mechanical properties vital to proper tissue functions. To address these issues, a better understanding of the intrinsic AC properties and how cells respond to stimuli from the external microenvironment must be better understood. This is essential in order to take one step closer to producing functional cartilaginous constructs for clinical use. Recently, biopolymers have aroused much attention due to their versatility, processability, and flexibility because the properties can be tailored to match the requirements of AC. This review highlights polymeric scaffolds developed in the past decade for reconstruction of zonal AC layers including the superficial zone, middle zone, and deep zone by means of exogenous stimuli such as physical, mechanical, and biological/chemical signals. The mimicked properties are reviewed in terms of the biochemical composition and organization, cell fate (morphology, orientation, and differentiation), as well as mechanical properties and finally, the challenges and potential ways to tackle them are discussed.

Zonally Stratified Decalcified Bone Scaffold with Different Stiffness Modified by Fibrinogen for Osteochondral Regeneration of Knee Joint Defect

Articular cartilage is generally known to be a complex tissue with multiple layers. Each layer has different composition, structure, and mechanical properties, making regeneration after knee joint defects a troubling clinical problem. A novel integrated stratified decalcified bone matrix (SDBM) scaffold with different stiffness to mimic the mechanical properties of articular cartilage is presented herein. This SDBM scaffold was modified using fibrinogen (Fg) (Fg + SDBM) to enhance its vascularization ability and improve its repair efficiency for osteochondral defects of knee joints. A Fg + SDBM scaffold with different elastic modulus in each layer (high-stiffness DBM (HDBM) layer, 174.208 ± 44.330 MPa (Fg + HDBM); medium-stiffness DBM (MDBM) layer, 21.214 ± 6.922 MPa (Fg + MDBM); and low-stiffness DBM (LDBM) layer, 0.678 ± 0.269 MPa (Fg + LDBM)) was constructed by controlling the stratified decalcification time with layered embedding paraffin (0, 3, and 5 days). The low- and medium-stiffness layers of the Fg + SDBM scaffold remarkably promoted the cartilage differentiation of bone marrow mesenchymal stem cells in vitro. Subcutaneous transplantation and rabbit knee joint osteochondral defect repair experiments revealed that the low- and medium-stiffness layers of the Fg + SDBM scaffold exhibited wonderful cartilage capacity, whereas the high-stiffness layer of Fg + SDBM scaffold exhibited good osteogenesis ability. Furthermore, this scaffold could promote blood vessel formation in subchondral bone area. This study presents a feasible strategy for osteochondral regeneration of defective knee joints, which is of great clinical value for tissue repair.

Thermo-responsive injectable naringin-loaded hydrogel polymerised sodium alginate/bioglass delivery for articular cartilage

In the human body, joint cartilage is of great importance. It has long been a big therapeutic problem to fix joint cartilage lesions as it appears due to different conditions. Recent stories have shown that the cartilage replacement process must delay the extracellular (ECM) cartilage deterioration and modulate the host's inflammation response. For the reconstruction of the articular cartilage, drug-loaded injectable hydrogels were developed. This hydrogel could retain the chondrocyte phenotype, but the host's inflammatory reaction could also be controlled. The bioglass (BG)/sodium alginate (SA) injectable hydrogels was combined with agarose (AG)/Naringin hydrogel in injectable thermal response for articular cartilage regeneration with a non-chargeable hydrogel that contains both Naringin and BG (Naringin–BG hydrogels). The Naringin–BG hydrogel has an adequate swelling ratio that encourages the fusion of tissue formed with host tissue and enables the gradual release of Naringin bioavailabilities enhanced in situ. The Naringin–BG hydrogel can upgrade the typical chondrocyte phenotype by upregulating aggrecan, SRY-box 9, and collagen type II alpha one chain. It may also stimulate the polarization of M2 macrophage, lower inflammations, and prevent ECM degradations through the decrease of the expressions of the indictable metalloproteinase-13 matrix, nitric oxide synthase, and metalloproteinase-1 matrix. The formed tissues were identical to normal tissues and firmly incorporated with the surrounding tissue after administering the Naringin–BG hydrogels into the rat model articular cartilage defects. Then the injectable Naringin–BG hydrogel increases the bioavailable content of Naringin and retains the chondrocyte phenotype.

Enhanced In Vitro and In Vivo Efficacy of Alginate/Silk Protein/Hyaluronic Acid with Polypeptide Microsphere Delivery for Tissue Regeneration of Articular Cartilage

Alginate/Silk fibroin/hyaluronic acid (ALG/SF/HA) nanocomposites were synthesised using blending, inter-linking, and lyophilization methods. We investigated the physicochemical properties of the resulting nanocomposites, including their water retention, weight loss, porosity and cytocompatibility. The optimum ratios of the ALG/SF/HA scaffolding were 3:6.5:0.5. Nanocomposites with optimum ratios were then prepared by integrating pilose antler polypeptides (PAPS) to poly(lactic-co-glycolic acid) (PLGA) microspheres, and the performance was investigated. PAPS-ALG/SF/HA nanocomposites exhibited desirable adhesions and proliferations. Rabbit cartilage deficiencies was developed by the animal model. The cartilage repair effects deficiencies were detected and analyzed between PAPS-SF/ALG/ALG/SF/HA, and control activity classes. The deficiencies were virtually fully remedied after 13 weeks in the presence of PAPS-ALG/SF/HA class, suggesting that the PAPS-ALG/SF/HA nanocomposites had a positive effects on joint cartilage repair.

Multiscale porosity in a 3D printed gellan-gelatin composite for bone tissue engineering

The aim of this work was to develop a complex-shaped gelatin-gellan composite scaffold with multiscale porosity using a combination of cryogenic 3D printing and lyophilization for bone tissue engineering. Cryogenic 3D printing was used to fabricate a low-concentration composite of complex-shaped macroporous gelatin-gellan structures with a pore size of 919 ± 89 µm. This was followed by lyophilization to introduce micropores of size 20-250 µm and nanometre-level surface functionalities, thus achieving a hierarchical porous structure. These multiscale porous scaffolds (GMu) were compared with two other types of scaffolds having only microporosity (GMi) and macroporosity (GMa) with regard to their physical andin vitrobiological properties. GMu scaffolds were found to be better than GMi and GMa in terms of swelling percentage, degradation rate, uniform pore distribution, cellular infiltration, attachment, proliferation, protein generation and mineralization. In conclusion, we have developed a controlled hierarchical bone-like structure, biomimicking natural bone, together with a reproducible process of manufacture by coupling soft hydrogel 3D printing with lyophilization. This enables the development of complex-shaped patient-specific 3D printed hydrogel scaffolds with enhanced performancein vitroand great potential in the fields of tissue engineering, bioprinting and regenerative medicine.