The effect of culture conditions on the bone regeneration potential of osteoblast-laden 3D bioprinted constructs

Systematic development and bioprinting of novel nanostructured multi-material bioinks for bone tissue engineering

A functional bioink with potential in bone tissue engineering must be subjected to critical investigation throughout its intended lifespan. The aim of this study was to develop alginate-gelatin-based (Alg-Gel) multicomponent bioinks systematically and to assess the short- and long-term exposure responses of human bone marrow stromal cells (hBMSCs) printed within these bioinks with and without crosslinking.The first generation of bioinkswas established by incorporating a range of cellulose nanofibrils (CNFs), to evaluate their effect on viscosity, printability and cell viability. Adding CNFs to Alg-Gel solution increased viscosity and printability without compromising cell viability. Inthe second generation of bioinks, the influence of nano-hydroxyapatite (nHA) on the performance of the optimized Alg-Gel-CNF formulation was investigated. The addition of nHA increased the viscosity and improved printability, and an adjustment in alginate concentration improved the stability of the structures in long-term culture. The third generation bioink incorporated RGD-functionalized alginate to support cell attachment and osteogenic differentiation. The optimized bioink composition exhibited improved printability, structural integrity in long-term culture and high hBMSC viability. In addition, the final bioink composition, RGD-Alg-Gel-CNF-nHA, showed osteogenic potential: production of the osteogenic marker proteins (Runx2, OCN), enzyme (ALP), and gene expression (Runx2,OCN). A further aim of the study was to evaluate the osteogenic functionality of cells released from the structures after bioprinting. Cells were printed in two bioinks with different viscosities and incubated at 37 °C in growth medium without additional CaCl2. This caused gelatin to dissolve, releasing the cells to attach to tissue culture plates. The results demonstrated differences in hBMSC osteogenic differentiation. Moreover, the osteogenic differentiation of the released cells was different from that of the embedded cells cultured in 3D. Thus, this systematic investigation into bioink development shows improved results through the generations and sheds light on the biological effects of the bioprinting process.

Effects of Magnesium-Doped Hydroxyapatite Nanoparticles on Bioink Formulation for Bone Tissue Engineering

Bioprinting of nanohydroxyapatite (nHA)-based bioinks has attracted considerable interest in bone tissue engineering. However, the role and relevance of the physicochemical properties of nHA incorporated in a bioink, particularly in terms of its printability and the biological behavior of bioprinted cells, remain largely unexplored. In this study, two bioinspired nHAs with different chemical compositions, crystallinity, and morphologies were synthesized and characterized: a more crystalline, needle-like Mg2+-doped nHA (N-HA) and a more amorphous, rounded Mg2+- and CO32--doped nHA (R-HA). To investigate the effects of the different compositions and morphologies of these nanoparticles on the bioprinting of human bone marrow stromal cells (hBMSCs), gelatin and gelatin methacryloyl (GelMA) were selected as the bioink backbone. The addition of 1% (w/w) of these bioceramic nanoparticles significantly improved the printability of GelMA in terms of extrudability, buildability, and filament spreading. The biological potential of the bioinks was evaluated by examining the hBMSC viability, metabolic activity, and osteogenic differentiation over 21 days. Both nHAs showed high cell viability, with N-HA showing a significant increase in metabolic activity under nonosteogenic conditions and R-HA showing a notable increase with osteogenic stimulation. These results suggest that the two nHAs interact differently with their environment, highlighting the importance of both the chemistry and morphology in bioink performance. In addition, osteogenic differentiation further highlighted how the physicochemical properties of nHAs influence osteogenic markers at both the RNA and protein levels. Clearly, tailoring the physicochemical properties of hydroxyapatite nanoparticles is critical to developing more biomimetic bioinks with great potential for advancing bone bioprinting applications.

Humanized In Vivo Bone Tissue Engineering: In Vitro Preculture Conditions Control the Structural, Cellular, and Matrix Composition of Humanized Bone Organs

Bone tissue engineering (BTE) has long sought to elucidate the key factors controlling human/humanized bone formation for regenerative medicine and disease modeling applications, yet with no definitive answers due to the high number and co-dependency of parameters. This study aims to clarify the relative impacts of in vitro biomimetic 'preculture composition' and 'preculture duration' before in vivo implantation as key criteria for the optimization of BTE design. These parameters are directly related to in vitro osteogenic differentiation (OD) and mineralization and are being investigated across different osteoprogenitor-loaded biomaterials, specifically fibrous calcium phosphate-polycaprolactone (CaP-mPCL) scaffolds and gelatin methacryloyl (GelMA) hydrogels. The results show that OD and mineralization levels prior to implantation, enhanced by a mineralization medium supplement to the osteogenic medium (OM), significantly improve ectopic BTE outcomes, regardless of the biomaterial type. Specifically, preculture conditions are pivotal in achieving more faithful mimicry of human bone structure, cellular and extracellular matrix composition and organization, and provide control over bone marrow composition. This work emphasizes the potential of using biomimetic culture compositions, specifically the addition of a mineralization medium as a cost-effective and straightforward approach to enhance BTE outcomes, facilitating rapid development of bone models with superior quality and resemblance to native bone.

3D bioprinted small extracellular vesicles from periodontal cells enhance mesenchymal stromal cell function

Recent research indicates that combining 3D bioprinting and small extracellular vesicles (sEVs) offers a promising 'cell-free' regenerative medicine approach for various tissue engineering applications. Nonetheless, the majority of existing research has focused on bioprinting of sEVs sourced from cell lines. There remains a notable gap in research regarding the bioprinting of sEVs derived from primary human periodontal cells and their potential impact on ligamentous and osteogenic differentiation. Here, we investigated the effect of 3D bioprinted periodontal cell sEVs constructs on the differentiation potential of human buccal fat pad-derived mesenchymal stromal cells (hBFP-MSCs). Periodontal cell-derived sEVs were enriched by size exclusion chromatography (SEC) with particle-shaped morphology, and characterized by being smaller than 200 nm in size and CD9/CD63/CD81 positive, from primary human periodontal ligament cells (hPDLCs) and human gingival fibroblasts (hGFs). The sEVs were then 3D bioprinted in 10 % gelatin methacryloyl (GelMA) via microextrusion bioprinting. Release of sEVs from bioprinted constructs was determined by DiO-labelling and confocal imaging, and CD9 ELISA. Attachment and ligament/osteogenic/cementogenic differentiation of hBFP-MSCs was assessed on bioprinted GelMA, without and with sEVs (GelMA/hPDLCs-sEVs and GelMA/hGFs-sEVs), scaffolds. hBFP-MSCs seeded on the bioprinted sEVs constructs spread well with significantly enhanced focal adhesion, mechanotransduction associated gene expression, and ligament and osteogenesis/cementogenesis differentiation markers in GelMA/hPDLCs-sEVs, compared to GelMA/hGFs-sEVs and GelMA groups. A 2-week osteogenic and ligamentous differentiation showed enhanced ALP staining, calcium formation and toluidine blue stained cells in hBFP-MSCs on bioprinted GelMA/hPDLCs-sEVs constructs compared to the other two groups. The proof-of-concept data from this study supports the notion that 3D bioprinted GelMA/hPDLCs-sEVs scaffolds promote cell attachment, as well as ligamentous, osteogenic and cementogenic differentiation, of hBFP-MSCs in vitro.

Additively manufactured porous scaffolds by design for treatment of bone defects

There has been increasing attention to produce porous scaffolds that mimic human bone properties for enhancement of tissue ingrowth, regeneration, and integration. Additive manufacturing (AM) technologies, i.e., three dimensional (3D) printing, have played a substantial role in engineering porous scaffolds for clinical applications owing to their high level of design and fabrication flexibility. To this end, this review article attempts to provide a detailed overview on the main design considerations of porous scaffolds such as permeability, adhesion, vascularisation, and interfacial features and their interplay to affect bone regeneration and osseointegration. Physiology of bone regeneration was initially explained that was followed by analysing the impacts of porosity, pore size, permeability and surface chemistry of porous scaffolds on bone regeneration in defects. Importantly, major 3D printing methods employed for fabrication of porous bone substitutes were also discussed. Advancements of MA technologies have allowed for the production of bone scaffolds with complex geometries in polymers, composites and metals with well-tailored architectural, mechanical, and mass transport features. In this way, a particular attention was devoted to reviewing 3D printed scaffolds with triply periodic minimal surface (TPMS) geometries that mimic the hierarchical structure of human bones. In overall, this review enlighten a design pathway to produce patient-specific 3D-printed bone substitutions with high regeneration and osseointegration capacity for repairing large bone defects.

Investigation of Biomaterial Ink Viscosity Properties and Optimization of the Printing Process Based on Pattern Path Planning

Extruded bioprinting is widely used for the biomanufacturing of personalized, complex tissue structures, which requires biomaterial inks with a certain viscosity to enable printing. However, there is still a lack of discussion on the controllable preparation and printability of biomaterial inks with different viscosities. In this paper, biomaterial inks composed of gelatin, sodium alginate, and methylcellulose were utablesed to investigate the feasibility of adjustment of rheological properties, thereby analyzing the effects of different rheological properties on the printing process. Based on the response surface methodology, the relationship between the material components and the rheological properties of biomaterial inks was discussed, followed by the prediction of the rheological properties of biomaterial inks. The prediction accuracies of the power-law index and consistency coefficient could reach 96% and 79%, respectively. The material group can be used to prepare biomaterial inks with different viscosity properties in a wide range. Latin hypercube sampling and computational fluid dynamics were used to analyze the effects of different rheological properties and extrusion pressure on the flow rate at the nozzle. The relationship between the rheological properties of the biomaterial ink and the flow rate was established, and the simulation results showed that the changes in the rheological properties of the biomaterial ink in the high-viscosity region resulted in slight fluctuations in the flow rate, implying that the printing process for high-viscosity biomaterial inks may have better versatility. In addition, based on the characteristics of biomaterial inks, the printing process was optimized from the planning of the print pattern to improve the location accuracy of the starting point, and the length accuracy of filaments can reach 99%. The effect of the overlap between the fill pattern and outer frame on the print quality was investigated to improve the surface quality of complex structures. Furthermore, low- and high-viscosity biomaterial inks were tested, and various printing protocols were discussed for improving printing efficiency or maintaining cell activity. This study provides feasible printing concepts for a wider range of biomaterials to meet the biological requirements of cell culture and tissue engineering.