Chondrogenic phenotype in responses to poly(ɛ-caprolactone) scaffolds catalyzed by bioenzymes: effects of surface topography and chemistry

3D-printed constructs deliver bioactive cargos to expedite cartilage regeneration

Cartilage is solid connective tissue that recovers slowly from injury, and pain and dysfunction from cartilage damage affect many people. The treatment of cartilage injury is clinically challenging and there is no optimal solution, which is a hot research topic at present. With the rapid development of 3D printing technology in recent years, 3D bioprinting can better mimic the complex microstructure of cartilage tissue and thus enabling the anatomy and functional regeneration of damaged cartilage. This article reviews the methods of 3D printing used to mimic cartilage structures, the selection of cells and biological factors, and the development of bioinks and advances in scaffold structures, with an emphasis on how 3D printing structure provides bioactive cargos in each stage to enhance the effect. Finally, clinical applications and future development of simulated cartilage printing are introduced, which are expected to provide new insights into this field and guide other researchers who are engaged in cartilage repair.

Development of chondrocyte-laden alginate hydrogels with modulated microstructure and properties for cartilage regeneration

Alginate hydrogel is an attractive biomaterial for cell microencapsulation. The microarchitecture of hydrogels can regulate cellular functions. This study aims to investigate the applicability of sodium citrate buffer (SCB) as a culture medium supplement for modulating the microstructure of alginate microbeads to provide a favorable microenvironment for chondrogenic induction. The chondrocyte-laden microbeads, with and without TGF-β3 incorporation, were produced through an encapsulator. The obtained small-sized microbeads (~300 μm) were exposed to a treatment medium containing SCB, composed of varied concentrations of sodium citrate (1.10-1.57 mM), sodium chloride (3.00-4.29 mM), and ethylenediaminetetraacetic acid (0.60-0.86 mM) to partially degrade their crosslinked structure for 3 days, followed by culture in a normal medium until day 21. Scanning electron microscope micrographs demonstrated a loose hydrogel network with an enhanced pore size in the SCB-treated microbeads. Increasing the concentration of SCB in the treatment medium reduced the calcium content of the microbeads via a Na⁺ /Ca²⁺ exchange process and improved the water absorption of the microbeads, resulting in a higher swelling ratio. All the tested SCB concentrations were non-cytotoxic. Increases in aggrecan and type II collagen gene expression and their corresponding extracellular matrix accumulation, glycosaminoglycans, and type II collagen were vividly detected in the TGF-β3-containing microbeads with increasing SCB concentrations in the treatment medium. Our findings highlighted that the combination of SCB treatment and TGF-β3 incorporation in the chondrocyte-laden microbeads is a promising strategy for enhancing cartilage regeneration, which may contribute to a versatile application in cell delivery and tissue engineering.

Importance of the pig as a human biomedical model

[Figure: see text].

Porous 3D Scaffolds Enhance MSC Vitality and Reduce Osteoclast Activity

In the context of an aging population, unhealthy Western lifestyle, and the lack of an optimal surgical treatment, deep osteochondral defects pose a great challenge for the public health system. Biodegradable, biomimetic scaffolds seem to be a promising solution. In this study we investigated the biocompatibility of porous poly-((D,L)-lactide-ε-caprolactone)dimethacrylate (LCM) scaffolds in contrast to compact LCM scaffolds and blank cell culture plastic. Thus, morphology, cytotoxicity and metabolic activity of human mesenchymal stromal cells (MSC) seeded directly on the materials were analyzed after three and six days of culturing. Further, osteoclastogenesis and osteoclastic activity were assessed using reverse-transcriptase real-time PCR of osteoclast-specific genes, EIA and morphologic aspects after four, eight, and twelve days. LCM scaffolds did not display cytotoxic effects on MSC. After three days, metabolic activity of MSC was enhanced on 3D porous scaffolds (PS) compared to 2D compact scaffolds (CS). Osteoclast activity seemed to be reduced at PS compared to cell culture plastic at all time points, while no differences in osteoclastogenesis were detectable between the materials. These results indicate a good cytocompatibility of LCM scaffolds. Interestingly, porous 3D structure induced higher metabolic activity of MSC as well as reduced osteoclast activity.

Marginal sealing around integral bilayer scaffolds for repairing osteochondral defects based on photocurable silk hydrogels

Osteochondral repair remains a major challenge in current clinical practice despite significant advances in tissue engineering. In particular, the lateral integration of neocartilage into surrounding native cartilage is a difficult and inadequately addressed problem that determines the success of tissue repair. Here, a novel design of an integral bilayer scaffold combined with a photocurable silk sealant for osteochondral repair is reported. First, we fabricated a bilayer silk scaffold with a cartilage layer resembling native cartilage in surface morphology and mechanical strength and a BMP-2-loaded porous subchondral bone layer that facilitated the osteogenic differentiation of BMSCs. Second, a TGF-β3-loaded methacrylated silk fibroin sealant (Sil-MA) exhibiting biocompatibility and good adhesive properties was developed and confirmed to promote chondrocyte migration and differentiation. Importantly, this TGF-β3-loaded Sil-MA hydrogel provided a bridge between the cartilage layer of the scaffold and the surrounding cartilage and then guided new cartilage to grow towards and replace the degraded cartilage layer from the surrounding native cartilage in the early stage of knee repair. Thus, osteochondral regeneration and superior lateral integration were achieved in vivo by using this composite. These results demonstrate that the new approach of marginal sealing around the cartilage layer of bilayer scaffolds with Sil-MA hydrogel has tremendous potential for clinical use in osteochondral regeneration.

Novel Ultrathin Films Based on a Blend of PEG-b-PCL and PLLA and Doped with ZnO Nanoparticles

In this paper, a novel nanofilm type is proposed based on a blend of poly(ethylene glycol)-block-poly(ε-caprolactone) methyl ether (PEG-b-PCL) and poly(l-lactic acid), doped with zinc oxide nanoparticles (ZnO NPs) at different concentrations (0.1, 1, and 10 mg/mL). All nanofilm types were featured by a thickness value of ∼500 nm. Increasing ZnO NP concentrations implied larger roughness values (∼22 nm for the bare nanofilm and ∼67 nm for the films with 10 mg/mL of NPs), larger piezoelectricity (average d₃₃ coefficient for the film up to ∼1.98 pm/V), and elastic modulus: the nanofilms doped with 1 and 10 mg/mL of NPs were much stiffer than the nondoped controls and nanofilms doped with 0.1 mg/mL of NPs. The ZnO NP content was also directly proportional to the material melting point and crystallinity and inversely proportional to the material degradation rate, thus highlighting the stabilization role of ZnO particles. In vitro tests were carried out with cells of the musculoskeletal apparatus (fibroblasts, osteoblasts, chondrocytes, and myoblasts). All cell types showed good adhesion and viability on all substrate formulations. Interestingly, a higher content of ZnO NPs in the matrix demonstrated higher bioactivity, boosting the metabolic activity of fibroblasts, myoblasts, and chondrocytes and enhancing the osteogenic and myogenic differentiation. These findings demonstrated the potential of these nanocomposite matrices for regenerative medicine applications, such as tissue engineering.