Composite Spheroid-Laden Bilayer Hydrogel for Engineering Three-Dimensional Osteochondral Tissue

A combination of hydrogels and stem cell spheroids has been used to engineer three-dimensional (3D) osteochondral tissue, but precise zonal control directing cell fate within the hydrogel remains a challenge. In this study, we developed a composite spheroid-laden bilayer hydrogel to imitate osteochondral tissue by spatially controlled differentiation of human adipose-derived stem cells. Meticulous optimization of the spheroid-size and mechanical strength of gelatin methacryloyl (GelMA) hydrogel enables the cells to homogeneously sprout within the hydrogel. Moreover, fibers immobilizing transforming growth factor beta-1 (TGF-β1) or bone morphogenetic protein-2 (BMP-2) were incorporated within the spheroids, which induced chondrogenic or osteogenic differentiation of cells in general media, respectively. The spheroids-filled GelMA solution was crosslinked to create the bilayer hydrogel, which demonstrated a strong interfacial adhesion between the two layers. The cell sprouting enhanced the adhesion of each hydrogel, demonstrated by increase in tensile strength from 4.8 ± 0.4 to 6.9 ± 1.2 MPa after 14 days of culture. Importantly, the spatially confined delivery of BMP-2 within the spheroids increased mineral deposition and more than threefold enhanced osteogenic genes of cells in the bone layer while the cells induced by TGF-β1 signals were apparently differentiated into chondrocytes within the cartilage layer. The results suggest that our composite spheroid-laden hydrogel could be used for the biofabrication of osteochondral tissue, which can be applied to engineer other complex tissues by delivery of appropriate biomolecules.

Advances in Translational 3D Printing for Cartilage, Bone, and Osteochondral Tissue Engineering

The regeneration of 3D tissue constructs with clinically relevant sizes, structures, and hierarchical organizations for translational tissue engineering remains challenging. 3D printing, an additive manufacturing technique, has revolutionized the field of tissue engineering by fabricating biomimetic tissue constructs with precisely controlled composition, spatial distribution, and architecture that can replicate both biological and functional native tissues. Therefore, 3D printing is gaining increasing attention as a viable option to advance personalized therapy for various diseases by regenerating the desired tissues. This review outlines the recently developed 3D printing techniques for clinical translation and specifically summarizes the applications of these approaches for the regeneration of cartilage, bone, and osteochondral tissues. The current challenges and future perspectives of 3D printing technology are also discussed.

Piezoelectric Electrospun Fibrous Scaffolds for Bone, Articular Cartilage and Osteochondral Tissue Engineering

Osteochondral tissue (OCT) related diseases, particularly osteoarthritis, number among the most prevalent in the adult population worldwide. However, no satisfactory clinical treatments have been developed to date to resolve this unmet medical issue. Osteochondral tissue engineering (OCTE) strategies involving the fabrication of OCT-mimicking scaffold structures capable of replacing damaged tissue and promoting its regeneration are currently under development. While the piezoelectric properties of the OCT have been extensively reported in different studies, they keep being neglected in the design of novel OCT scaffolds, which focus primarily on the tissue’s structural and mechanical properties. Given the promising potential of piezoelectric electrospun scaffolds capable of both recapitulating the piezoelectric nature of the tissue’s fibrous ECM and of providing a platform for electrical and mechanical stimulation to promote the regeneration of damaged OCT, the present review aims to examine the current state of the art of these electroactive smart scaffolds in OCTE strategies. A summary of the piezoelectric properties of the different regions of the OCT and an overview of the main piezoelectric biomaterials applied in OCTE applications are presented. Some recent examples of piezoelectric electrospun scaffolds developed for potentially replacing damaged OCT as well as for the bone or articular cartilage segments of this interfacial tissue are summarized. Finally, the current challenges and future perspectives concerning the use of piezoelectric electrospun scaffolds in OCT regeneration are discussed.

Gradient Mineralized and Porous Double-Network Hydrogel Effectively Induce the Differentiation of BMSCs into Osteochondral Tissue In Vitro for Potential Application in Cartilage Repair

At present, it is a considerable challenge to mimic the complex architecture of osteochondral (OC) tissue. In this study, a porous and gradient mineralized double-network hydrogel is synthesized and used to induce bone marrow mesenchymal stem cells (BMSCs) to differentiate into the desired OC tissue depending only on the material and mechanical properties. Physical and chemical characterizations show that hydroxyapatite nanoparticles grow and fill into the pores of the hydrogel, and their content presents a gradient change in different layers of hydrogel. The synthesized hydrogel has excellent mechanical properties and the compression strength with different mineralization degrees varies from 27 to 380 kPa, which fully meets the needs of increased mechanical strength of articular cartilage from the surface to the deep layer. Besides, the synthesized hydrogel has good biocompatibility that can promote the proliferation and growth of BMSCs. More importantly, the results of histochemistry, immunohistochemistry, and real time polymerase chain reaction show that gradient mineralized hydrogel can induce BMSCs to differentiate into the desired chondrocytes and osteoblasts in different layers of hydrogels, indicating that OC tissues can be successfully constructed through a simple induction differentiation of gradient mineralized hydrogel.

Fabrication of a Polycaprolactone/Alginate Bipartite Hybrid Scaffold for Osteochondral Tissue Using a Three-Dimensional Bioprinting System

Osteochondral defects, including damage to both the articular cartilage and the subchondral bone, are challenging to repair. Although many technological advancements have been made in recent years, there are technical difficulties in the engineering of cartilage and bone layers, simultaneously. Moreover, there is a great need for a valuable in vitro platform enabling the assessment of osteochondral tissues to reduce pre-operative risk. Three-dimensional (3D) bioprinting systems may be a promising approach for fabricating human tissues and organs. Here, we aimed to develop a polycaprolactone (PCL)/alginate bipartite hybrid scaffold using a multihead 3D bioprinting system. The hybrid scaffold was composed of PCL, which could improve the mechanical properties of the construct, and alginate, encapsulating progenitor cells that could differentiate into cartilage and bone. To differentiate the bipartite hybrid scaffold into osteochondral tissue, a polydimethylsiloxane coculture system for osteochondral tissue (PCSOT) was designed and developed. Based on evaluation of the biological performance of the novel hybrid scaffold, the PCL/alginate bipartite scaffold was successfully fabricated; importantly, our findings suggest that this PCSOT system may be applicable as an in vitro platform for osteochondral tissue engineering.

Toward zonally tailored scaffolds for osteochondral differentiation of synovial mesenchymal stem cells

Synovium-derived mesenchymal stem cells (SMSCs) are an emerging cell source for regenerative medicine applications, including osteochondral defect (OCD) repair. However, in contrast to bone marrow MSCs, scaffold compositions which promote SMSC chondrogenesis/osteogenesis are still being identified. In the present manuscript, we examine poly(ethylene) glycol (PEG)-based scaffolds containing zonally-specific biochemical cues to guide SMSC osteochondral differentiation. Specifically, SMSCs were encapsulated in PEG-based scaffolds incorporating glycosaminoglycans (hyaluronan or chondroitin-6-sulfate [CSC]), low-dose of chondrogenic and osteogenic growth factors (TGFβ1 and BMP2, respectively), or osteoinductive poly(dimethylsiloxane) (PDMS). Initial studies suggested that PEG-CSC-TGFβ1 scaffolds promoted enhanced SMSC chondrogenic differentiation, as assessed by significant increases in Sox9 and aggrecan. Conversely, PEG-PDMS-BMP2 scaffolds stimulated increased levels of osteoblastic markers with significant mineral deposition. A "Transition" zone formulation was then developed containing a graded mixture of the chondrogenic and osteogenic signals present in the PEG-CSC-TGFβ1 and PEG-PDMS-BMP2 constructs. SMSCs within the "Transition" formulation displayed a phenotypic profile similar to hypertrophic chondrocytes, with the highest expression of collagen X, intermediate levels of osteopontin, and mineralization levels equivalent to "bone" formulations. Overall, these results suggest that a graded transition from PEG-CSC-TGFβ1 to PEG-PDMS-BMP2 scaffolds elicits a gradual SMSC phenotypic shift from chondrocyte to hypertrophic chondrocyte to osteoblast-like. As such, further development of these scaffold formulations for use in SMSC-based OCD repair is warranted. © 2018 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater 107B: 2019-2029, 2019.

Advances of nanotechnology in osteochondral regeneration

In the past few decades, nanotechnology has proven to be one of the most powerful engineering strategies. The nanotechnologies for osteochondral tissue engineering aim to restore the anatomical structures and physiological functions of cartilage, subchondral bone, and osteochondral interface. As subchondral bone and articular cartilage have different anatomical structures and the physiological functions, complete healing of osteochondral defects remains a great challenge. Considering the limitation of articular cartilage to self-healing and the complexity of osteochondral tissue, osteochondral defects are in urgently need for new therapeutic strategies. This review article will concentrate on the most recent advancements of nanotechnologies, which facilitates chondrogenic and osteogenic differentiation for osteochondral regeneration. Moreover, this review will also discuss the current strategies and physiological challenges for the regeneration of osteochondral tissue. Specifically, we will summarize the latest developments of nanobased scaffolds for simultaneously regenerating subchondral bone and articular cartilage tissues. Additionally, perspectives of nanotechnology in osteochondral tissue engineering will be highlighted. This review article provides a comprehensive summary of the latest trends in cartilage and subchondral bone regeneration, paving the way for nanotechnologies in osteochondral tissue engineering. This article is categorized under: Implantable Materials and Surgical Technologies > Nanomaterials and Implants Nanotechnology Approaches to Biology > Nanoscale Systems in Biology Implantable Materials and Surgical Technologies > Nanotechnology in Tissue Repair and Replacement.

Ectopic implantation of juvenile osteochondral tissues recapitulates endochondral ossification

Subcutaneous implantation in a mouse can be used to investigate tissue maturation in vivo. Here we demonstrate that this simple model can recapitulate endochondral ossification associated with native skeletal development. By histological and micro-computed tomography analysis we investigated morphological changes of immature bovine osteochondral tissues over the course of subcutaneous implantation in immunocompromised mice for up to 10 weeks. We observed multiple similarities between the ectopic process and native endochondral ossification: (i) permanent cartilage retention in the upper zones; (ii) progressive loss of transient cartilage accompanied by bone formation at the interface; and (iii) remodelling of nascent endochondral bone into mature cancellous bone. Importantly, these processes were mediated by osteoclastogenesis and vascularization. Taken together, these findings advance our understanding of how the simple ectopic model can be used to study phenotypic changes associated with endochondral ossification of native and engineered osteochondral tissues in vivo.

Integrating three-dimensional printing and nanotechnology for musculoskeletal regeneration

The field of tissue engineering is advancing steadily, partly due to advancements in rapid prototyping technology. Even with increasing focus, successful complex tissue regeneration of vascularized bone, cartilage and the osteochondral interface remains largely illusive. This review examines current three-dimensional printing techniques and their application towards bone, cartilage and osteochondral regeneration. The importance of, and benefit to, nanomaterial integration is also highlighted with recent published examples. Early-stage successes and challenges of recent studies are discussed, with an outlook to future research in the related areas.