A thermogelling organic-inorganic hybrid hydrogel with excellent printability, shape fidelity and cytocompatibility for 3D bioprinting

Assessment of the viability and mechanoresponsiveness of hMSC-TERT printed with bioinert, thermoresponsive hydrogels

During three-dimensional (3D) bioprinting, the integration of living cells into hydrogel matrices results in complex biophysicochemical interactions between viscosity, shear stress, and temperature, critically influencing the structural and functional integrity of the resulting constructs. This study delves into the short-term biological ramifications of 3D extrusion printing of telomerase-immortalized human mesenchymal stromal cells (hMSC-TERT) embedded in bioinert hydrogels. Pluronic F127 and custom-synthesized poly(2-methyl-2-oxazoline)-block-poly(2-n-propyl-2-oxazine) (POx/POzi) are synthetic, block copolymers that create shear-thinning, physically crosslinked hydrogels that were used for this study. The rheological properties of the cell-free hydrogels and cell-laden bioinks were examined, revealing that they exhibited comparable behavior. Contrary to the original hypotheses, a key finding of this research is the reduction in cell viability (up to 50%) within 24 h post-printing, a trend consistently observed across varying initial conditions. The relative expression levels of the mechanoresponsive genes FOS and PTGS2 were increased, partly due to the suspension and incubation of the cells in both hydrogels. Only FOS was significantly upregulated in some cases because of the printing process after 2 and 4 h of incubation. These insights highlight the potential of using POx/POzi hydrogel as a matrix in 3D bioprinting, particularly for depositing hMSC-TERT into structures with vasculature-mimicking scaffolds or scaffolds designed for bone regeneration.

Synthesis and characterization of a new bio-inspired low molecular weight inorganic-organic hybrid resin with tunable properties and multifunctionality for in situ polymerization

Synthesis and characterization of a new bio-inspired low molecular weight inorganic-organic hybrid polymer with tunable properties and multifunctionality for in situ polymerization and cross linking. The hybrid bioactive polymer was synthesized through modified sol-gel method using 3- trimethoxy silyl propyl methacrylate as the precursor. The new polymer was characterized using Proton Nuclear Magnetic Resonance (1H-NMR), Carbon-13 Nuclear Magnetic Resonance Spectroscopy (13C- NMR), Atomic Force Microscopy (AFM), Transmission Electron Microscopy (TEM) for confirming the existence of inorganic as well as organic entities in the material. The volumetric shrinkage and bioactivity of the newly synthesized polymer was analyzed using Micro Computed Tomography (µ-CT) and Scanning Electron Microscopy (SEM). The excellent bioactivity with low polymerization shrinkage compared to the conventional resin used in biomedical applications, makes the new bio-inspired inorganic-organic hybrid bioactive polymer a potential resin matrix for the development of dental composites, bone cements and for coating applications.

Advanced optical assessment and modeling of extrusion bioprinting

In the context of tissue engineering, biofabrication techniques are employed to process cells in hydrogel-based matrices, known as bioinks, into complex 3D structures. The aim is the production of functional tissue models or even entire organs. The regenerative production of biological tissues adheres to a multitude of criteria that ultimately determine the maturation of a functional tissue. These criteria are of biological nature, such as the biomimetic spatial positioning of different cell types within a physiologically and mechanically suitable matrix, which enables tissue maturation. Furthermore, the processing, a combination of technical procedures and biological materials, has proven highly challenging since cells are sensitive to stress, for example from shear and tensile forces, which may affect their vitality. On the other hand, high resolutions are pursued to create optimal conditions for subsequent tissue maturation. From an analytical perspective, it is prudent to first investigate the printing behavior of bioinks before undertaking complex biological tests. According to our findings, conventional shear rheological tests are insufficient to fully characterize the printing behavior of a bioink. For this reason, we have developed optical methods that, complementarily to the already developed tests, allow for quantification of printing quality and further viscoelastic modeling of bioinks.

Thermoresponsive Alginate-Graft-pNIPAM/Methyl Cellulose 3D-Printed Scaffolds Promote Osteogenesis In Vitro

In this work, a sodium alginate-based copolymer grafted by thermoresponsive poly(N-isopropylacrylamide) (PNIPAM) chains was used as gelator (Alg-g-PNIPAM) in combination with methylcellulose (MC). It was found that the mechanical properties of the resulting gel could be enhanced by the addition of MC and calcium ions (Ca2+). The proposed network is formed via a dual crosslinking mechanism including ionic interactions among Ca2+ and carboxyl groups and secondary hydrophobic associations of PNIPAM chains. MC was found to further reinforce the dynamic moduli of the resulting gels (i.e., a storage modulus of ca. 1500 Pa at physiological body and post-printing temperature), rendering them suitable for 3D printing in biomedical applications. The polymer networks were stable and retained their printed fidelity with minimum erosion as low as 6% for up to seven days. Furthermore, adhered pre-osteoblastic cells on Alg-g-PNIPAM/MC printed scaffolds presented 80% viability compared to tissue culture polystyrene control, and more importantly, they promoted the osteogenic potential, as indicated by the increased alkaline phosphatase activity, calcium, and collagen production relative to the Alg-g-PNIPAM control scaffolds. Specifically, ALP activity and collagen secreted by cells were significantly enhanced in Alg-g-PNIPAM/MC scaffolds compared to the Alg-g-PNIPAM counterparts, demonstrating their potential in bone tissue engineering.

Immuno-activated mesenchymal stem cell living electrospun nanofibers for promoting diabetic wound repair

Diabetic wound is the leading cause of non-traumatic amputations in which oxidative stress and chronic inflammation are main factors affecting wound healing. Although mesenchymal stem cells (MSCs) as living materials can promote skin regeneration, they are still vulnerable to oxidative stress which limits their clinical applications. Herein, we have prepared (polylactic-co-glycolic acid) (PLGA) nanofibers electrospun with LPS/IFN-γ activated macrophage cell membrane. After defining physicochemical properties of the nanofibers modified by LPS/IFN-γ activated mouse RAW264.7 cell derived membrane (RCM-fibers), we demonstrated that the RCM-fibers improved BMMSC proliferation and keratinocyte migration upon oxidative stress in vitro. Moreover, bone marrow derived MSCs (BMMSCs)-loaded RCM-fibers (RCM-fiber-BMMSCs) accelerated wound closure accompanied by rapid re-epithelialization, collagen remodeling, antioxidant stress and angiogenesis in experimental diabetic wound healing in vivo. Transcriptome analysis revealed the upregulation of genes related to wound healing in BMMSCs when co-cultured with the RCM-fibers. Enhanced healing capacity of RCM-fiber-BMMSCs living material was partially mediated through CD200-CD200R interaction. Similarly, LPS/IFN-γ activated THP-1 cell membrane coated nanofibers (TCM-fibers) exhibited similar improvement of human BMMSCs (hBMMSCs) on diabetic wound healing in vivo. Our results thus demonstrate that LPS/IFN-γ activated macrophage cell membrane-modified nanofibers can in situ immunostimulate the biofunctions of BMMSCs, making this novel living material promising in wound repair of human diabetes.