Three-dimensional gradient porous polymeric composites for osteochondral regeneration

Thermomagneto-responsive injectable hydrogel for chondrogenic differentiation of mesenchymal stem cells

Damaged cartilage tissue has a limited ability to self-heal due to its avascular nature and low cellularity. To effectively engineer cartilage tissue, innovative techniques such as injectable and interactive hydrogels using a minimally invasive approach are required to mimic the natural properties of cartilage. In this study, an injectable hydrogel containing magnetic iron oxide nanoparticles (MNPs) has been rationally designed to induce chondrogenic differentiation in bone marrow mesenchymal stem cells (BMSCs) using an external magnetic field application. The effect of the incorporation of MNPs with the surface functional group of either carboxyl or amine on the properties of the hydrogels (denoted as HS and HA samples, respectively) has been investigated, and compared to control hydrogel without MNPs (denoted as H). The hydrogels demonstrated thermomagnetic-responsive and shear-thinning behavior. Incorporating MNPs in the hydrogel combination resulted in the formation of a more robust network with increased compressive modulus (by 2 and 2.5 times), cell viability (by 24 % and 7 %), swelling ratio (by 97 % and 42 %) for HS and HA, respectively, as well as better cell adhesion. Also, incorporating MNPs resulted in decreased elastic modulus (by 28 and 5 times), biodegradation rate (by 5 % and 9 %), and viscosity (by 4 and 20 times) for HS and HA, respectively. The results of glycosaminoglycans (GAG) staining indicated the synergistic effect of MNP incorporation and magnetic field application in improving chondrogenic differentiation of BMSCs in vitro. The research findings could lead to the development of superior injectable hydrogels and bioinks for tissue engineering applications.

3D-printed PCL scaffolds with anatomy-inspired bionic stratified structures for the treatment of growth plate injuries

The growth plate is a cartilaginous tissue with three distinct zones. Resident chondrocytes are highly organized in a columnar structure, which is critical for the longitudinal growth of immature long bones. Once injured, the growth plate may potentially be replaced by bony bar formation and, consequently, cause limb abnormalities in children. It is well-known that the essential step in growth plate repair is the remolding of the organized structure of chondrocytes. To achieve this, we prepared an anatomy-inspired bionic Poly(ε-caprolactone) (PCL) scaffold with a stratified structure using three-dimensional (3D) printing technology. The bionic scaffold is engineered by surface modification of NaOH and collagen Ⅰ (COL Ⅰ) to promote cell adhesion. Moreover, chondrocytes and bone marrow mesenchymal stem cells (BMSCs) are loaded in the most suitable ratio of 1:3 for growth plate reconstruction. Based on the anatomical structure of the growth plate, the bionic scaffold is designed to have three regions, which are the small-, medium-, and large-pore-size regions. These pore sizes are used to induce BMSCs to differentiate into similar structures such as the growth plate. Remarkably, the X-ray and histological results also demonstrate that the cell-loaded stratified scaffold can successfully rebuild the structure of the growth plate and reduce limb abnormalities, including limb length discrepancies and angular deformities in vivo. This study provides a potential method of preparing a bioinspired stratified scaffold for the treatment of growth plate injuries.

Is 3D Printing Promising for Osteochondral Tissue Regeneration?

Osteochondral tissue regeneration is quite difficult to achieve due to the complexity of its organization. In the design of these complex multilayer structures, a fabrication method, 3D printing, started to be employed, especially by using extrusion, stereolithography and inkjet printing approaches. In this paper, the designs are discussed including biphasic, triphasic, and gradient structures which aim to mimic the cartilage and the calcified cartilage and the whole osteochondral tissue closely. In the first section of the review paper, 3D printing of hydrogels including gelatin methacryloyl (GelMa), alginate, and polyethylene glycol diacrylate (PEGDA) are discussed. However, their physical and biological properties need to be augmented, and this generally is achieved by blending the hydrogel with other, more durable, less hydrophilic, polymers. These scaffolds are very suitable to carry growth factors, such as TGF-β1, to further stimulate chondrogenesis. The bone layer is mimicked by printing calcium phosphates (CaPs) or bioactive glasses together with the hydrogels or as a component of another polymer layer. The current research findings indicate that polyester (i.e. polycaprolactone (PCL), polylactic acid (PLA) and poly(lactide-co-glycolide) (PLGA)) reinforced hydrogels may more successfully mimic the complex structure of osteochondral tissue. Moreover, more recent printing methods such as melt electrowriting (MEW), are being used to integrate polyester fibers to enhance the mechanical properties of hydrogels. Additionally, polyester scaffolds that are 3D printed without hydrogels are discussed after the hydrogel-based scaffolds. In this review paper, the relevant studies are analyzed and discussed, and future work is recommended with support of tables of designed scaffolds. The outcome of the survey of the field is that 3D printing has significant potential to contribute to osteochondral tissue repair.