A Bioactive Cartilage Graft of IGF1-Transduced Adipose Mesenchymal Stem Cells Embedded in an Alginate/Bovine Cartilage Matrix Tridimensional Scaffold

Challenges in Application: Gelation Strategies of DAT-Based Hydrogel Scaffolds

Decellularized adipose tissue (DAT) has great clinical applicability, owing to its abundant source material, natural extracellular matrix microenvironment, and nonimmunogenic attributes, rendering it a versatile resource in the realm of tissue engineering. However, practical implementations are confronted with multifarious limitations. Among these, the selection of an appropriate gelation strategy serves as the foundation for adapting to diverse clinical contexts. The cross-linking strategies under varying physical or chemical conditions exert profound influences on the ultimate morphology and therapeutic efficacy of DAT. This review sums up the processes of DAT decellularization and subsequent gelation, with a specific emphasis on the diverse gelation strategies employed in recent experimental applications of DAT. The review expounds upon methodologies, underlying principles, and clinical implications of different gelation strategies, aiming to offer insights and inspiration for the application of DAT in tissue engineering and advance research for tissue engineering scaffold development.

Application of Alginate Hydrogels for Next-Generation Articular Cartilage Regeneration

The articular cartilage has insufficient intrinsic healing abilities, and articular cartilage injuries often progress to osteoarthritis. Alginate-based scaffolds are attractive biomaterials for cartilage repair and regeneration, allowing for the delivery of cells and therapeutic drugs and gene sequences. In light of the heterogeneity of findings reporting the benefits of using alginate for cartilage regeneration, a better understanding of alginate-based systems is needed in order to improve the approaches aiming to enhance cartilage regeneration with this compound. This review provides an in-depth evaluation of the literature, focusing on the manipulation of alginate as a tool to support the processes involved in cartilage healing in order to demonstrate how such a material, used as a direct compound or combined with cell and gene therapy and with scaffold-guided gene transfer procedures, may assist cartilage regeneration in an optimal manner for future applications in patients.

Sequential growth factor exposure of human Ad-MSCs improves chondrogenic differentiation in an osteochondral biphasic implant

Joint cartilage damage affects 10-12% of the world's population. Medical treatments improve the short-term quality of life of affected individuals but lack a long-term effect due to injury progression into fibrocartilage. The use of mesenchymal stem cells (MSCs) is one of the most promising strategies for tissue regeneration due to their ability to be isolated, expanded and differentiated into metabolically active chondrocytes to achieve long-term restoration. For this purpose, human adipose-derived MSCs (Ad-MSCs) were isolated from lipectomy and grown in xeno-free conditions. To establish the best differentiation potential towards a stable chondrocyte phenotype, isolated Ad-MSCs were sequentially exposed to five differentiation schemes of growth factors in previously designed three-dimensional biphasic scaffolds with incorporation of a decellularized cartilage matrix as a bioactive ingredient, silk fibroin and bone matrix, to generate a system capable of being loaded with pre-differentiated Ad-MSCs, to be used as a clinical implant in cartilage lesions for tissue regeneration. Chondrogenic and osteogenic markers were analyzed by reverse transcription-quantitative PCR and cartilage matrix generation by histology techniques at different time points over 40 days. All groups had an increased expression of chondrogenic markers; however, the use of fibroblast growth factor 2 (10 ng/ml) followed by a combination of insulin-like growth factor 1 (100 ng/ml)/TGFβ1 (10 ng/ml) and a final step of exposure to TGFβ1 alone (10 ng/ml) resulted in the most optimal chondrogenic signature towards chondrocyte differentiation and the lowest levels of osteogenic expression, while maintaining stable collagen matrix deposition until day 33. This encourages their possible use in osteochondral lesions, with appropriate properties for use in clinical patients.

Biological perspectives and current biofabrication strategies in osteochondral tissue engineering

Articular cartilage and the underlying subchondral bone are crucial in human movement and when damaged through disease or trauma impacts severely on quality of life. Cartilage has a limited regenerative capacity due to its avascular composition and current therapeutic interventions have limited efficacy. With a rapidly ageing population globally, the numbers of patients requiring therapy for osteochondral disorders is rising, leading to increasing pressures on healthcare systems. Research into novel therapies using tissue engineering has become a priority. However, rational design of biomimetic and clinically effective tissue constructs requires basic understanding of osteochondral biological composition, structure, and mechanical properties. Furthermore, consideration of material design, scaffold architecture, and biofabrication strategies, is needed to assist in the development of tissue engineering therapies enabling successful translation into the clinical arena. This review provides a starting point for any researcher investigating tissue engineering for osteochondral applications. An overview of biological properties of osteochondral tissue, current clinical practices, the role of tissue engineering and biofabrication, and key challenges associated with new treatments is provided. Developing precisely engineered tissue constructs with mechanical and phenotypic stability is the goal. Future work should focus on multi-stimulatory environments, long-term studies to determine phenotypic alterations and tissue formation, and the development of novel bioreactor systems that can more accurately resemble the in vivo environment.

A Cellularized Biphasic Implant Based on a Bioactive Silk Fibroin Promotes Integration and Tissue Organization during Osteochondral Defect Repair in a Porcine Model

In cartilage tissue engineering, biphasic scaffolds (BSs) have been designed not only to influence the recapitulation of the osteochondral architecture but also to take advantage of the healing ability of bone, promoting the implant’s integration with the surrounding tissue and then bone restoration and cartilage regeneration. This study reports the development and characterization of a BS based on the assembly of a cartilage phase constituted by fibroin biofunctionalyzed with a bovine cartilage matrix, cellularized with differentiated autologous pre-chondrocytes and well attached to a bone phase (decellularized bovine bone) to promote cartilage regeneration in a model of joint damage in pigs. BSs were assembled by fibroin crystallization with methanol, and the mechanical features and histological architectures were evaluated. The scaffolds were cellularized and matured for 12 days, then implanted into an osteochondral defect in a porcine model (n = 4). Three treatments were applied per knee: Group I, monophasic cellular scaffold (single chondral phase); group II (BS), cellularized only in the chondral phase; and in order to study the influence of the cellularization of the bone phase, Group III was cellularized in chondral phases and a bone phase, with autologous osteoblasts being included. After 8 weeks of surgery, the integration and regeneration tissues were analyzed via a histology and immunohistochemistry evaluation. The mechanical assessment showed that the acellular BSs reached a Young’s modulus of 805.01 kPa, similar to native cartilage. In vitro biological studies revealed the chondroinductive ability of the BSs, evidenced by an increase in sulfated glycosaminoglycans and type II collagen, both secreted by the chondrocytes cultured on the scaffold during 28 days. No evidence of adverse or inflammatory reactions was observed in the in vivo trial; however, in Group I, the defects were not reconstructed. In Groups II and III, a good integration of the implant with the surrounding tissue was observed. Defects in group II were fulfilled via hyaline cartilage and normal bone. Group III defects showed fibrous repair tissue. In conclusion, our findings demonstrated the efficacy of a biphasic and bioactive scaffold based on silk fibroin and cellularized only in the chondral phase, which entwined chondroinductive features and a biomechanical capability with an appropriate integration with the surrounding tissue, representing a promising alternative for osteochondral tissue-engineering applications.