Assessing behaviour of osteoblastic cells in dynamic culture conditions using titanium-doped phosphate glass microcarriers

Zinc phosphate glass microspheres promoted mineralization and expression of BMP2 in MC3T3-E1 cells

Degradable phosphate glasses have shown favorable properties for tissue engineering. By changing the composition of the glasses, the degradation rate, and ion release are controllable. Zinc oxide can function as a glass network modifier and has been shown to play a positive role in bone formation. Also, phosphate glasses can easily be processed into microspheres, which can be used as microcarriers. This study aims to develop zinc phosphate glasses microspheres and explore the optimized size and composition for applications in bone tissue engineering. Zinc-titanium-calcium-sodium phosphate glasses with 0, 1, 3, 5, or 10 mol % zinc oxide were prepared and processed into microspheres. The smaller microspheres ranged in size from 50 to 106 μm, while the larger ones ranged from 106 to 150 μm. The characteristics of glasses were examined. The osteoblastic cell line MC3T3-E1 was cultured on the surface of microspheres and the cell viability was examined. To evaluate osteogenic differentiation, Alizarin Red S staining, quantitative reverse transcription polymerase chain reaction, and western blot analysis were performed after 14 days. Different sizes of zinc phosphate glass microspheres were successfully made. The glass microspheres with <10 mol % zinc oxide were able to support the adhesion and proliferation of MC3T3-E1 cell lines. The relative gene expression of BMP2 was significantly upregulated in the smaller glass microspheres containing 3 mol % zinc oxide (26-fold, p < .001) and both sizes of microspheres containing 5 mol % zinc oxide (smaller: 27-fold, p < .001; larger: 35-fold, p < .001). Additionally, cluster formation was observed in glass microspheres after 14 days, and the mineralization of MC3T3-E1 cell lines was promoted. Based on these findings, the glass microspheres containing 3-5 mol % of zinc oxide can promote osteogenic differentiation for MC3T3-E1 cells.

Improving product quality and productivity of an antibody-based biotherapeutic using inverted frustoconical shaking bioreactors

The Chinese hamster ovarian (CHO) cells serve as a common choice in biopharmaceutical production, traditionally cultivated in stirred tank bioreactors (STRs). Nevertheless, the pursuit of improved protein quality and production output for commercial purposes demand exploration into new bioreactor types. In this context, inverted frustoconical shaking bioreactors (IFSB) present unique physical properties distinct from STRs. This study aims to compare the production processes of an antibody-based biotherapeutic in both bioreactor types, to enhance production flexibility. The findings indicate that, when compared to STRs, IFSB demonstrates the capability to produce an antibody-based biotherapeutic with either comparable or enhanced bioprocess performance and product quality. IFSB reduces shear damage to cells, enhances viable cell density (VCD), and improves cell state at a 5-L scale. Consequently, this leads to increased protein expression (3.70 g/L vs 2.56 g/L) and improved protein quality, as evidenced by a reduction in acidic variants from 27.0% to 21.5%. Scaling up the culture utilizing the Froude constant and superficial gas velocity ensures stable operation, effective mixing, and gas transfer. The IFSB maintains a high VCD and cell viability at both 50-L and 500-L scales. Product expression levels range from 3.0 to 3.6 g/L, accompanied by an improved acidic variants attribute of 20.6%-22.7%. The IFSB exhibits superior productivity and product quality, underscoring its potential for incorporation into the manufacturing process for antibody-based biotherapeutics. These results establish the foundation for IFSB to become a viable option in producing antibody-based biotherapeutics for clinical and manufacturing applications.

Intrinsically fluorescent bioactive glass-poly(ester amide) hybrid microparticles for dual drug delivery and bone repair

The bone extracellular matrix (ECM) is a composite scaffold having inorganic hydroxyapatite and organic collagen fibers. Synthetic bone repair scaffolds that mimic the chemical composition of the native ECM and capable of delivering therapeutics are beneficial. In this study, we prepared intrinsically fluorescent organic-inorganic hybrid microparticle biomaterials by sol-gel process. Unlike the conventional Stöber process which requires an alkaline condition for microparticle formation, an acidic condition in the presence of a biodegradable poly(ester amide) (PEA) polymer was used to prepare silica and tertiary bioactive glass hybrids. During their preparation, one or two model drugs were loaded in the microparticles. Our results showed that a gelation temperature between 40 °C-60 °C and the inclusion of PEA were critical for microparticle formation. Unexpectedly, the hybrid microparticles were fluorescent with tunable emission by changing the excitation wavelengths ranging from 300 to 565 nm for potential multiplex imaging. Gene expression studies showed that the hybrid materials induce osteogenic differentiation of 10T1/2 cells without adding exogenous biochemical factors. The bioactivity of the inorganic phase and the dual drug release from homogenous, biodegradable, biocompatible, osteoinductive, and intrinsically fluorescent microparticles may offer a unique platform for bone regeneration and therapy.

Copper-containing bioactive glasses and glass-ceramics: From tissue regeneration to cancer therapeutic strategies

Copper is one of the most used therapeutic metallic elements in biomedicine, ranging from antibacterial approaches to cancer theranostics. This element could be easily incorporated into different types of biomaterials; specifically, copper-doped bioactive glasses (BGs) provide great opportunities for biomedical engineers and clinicians as regards their excellent biocompatibility and regenerative potential. Although copper-incorporated BGs are mostly used in bone tissue engineering, accelerated soft tissue healing is achievable, too, with interesting potentials in wound treatment and skin repair. Copper can modulate the physico-chemical properties of BGs (e.g., reactivity with bio-fluids) and improve their therapeutic potential. Improving cell proliferation, promoting angiogenesis, reducing or even prohibiting bacterial growth are counted as prominent biological features of copper-doped BGs. Recent studies have also suggested the suitability of copper-doped BGs in cancer photothermal therapy (PTT). However, more research is needed to determine the extent to which copper-doped BGs are actually applicable for tissue engineering and regenerative medicine strategies in the clinic. Moreover, copper-doped BGs in combination with polymers may be considered in the future to produce relatively soft, pliable composites and printable inks for use in biofabrication.

Pre-Seeding of Simple Electrospun Scaffolds with a Combination of Endothelial Cells and Fibroblasts Strongly Promotes Angiogenesis

BACKGROUND

Introduction of pro-angiogenic cells into tissue-engineered (TE) constructs (prevascularisation) is a promising approach to overcome delayed neovascularisation of such constructs post-implantation. Accordingly, in this study, we examined the contribution of human dermal microvascular endothelial cells (HDMECs) and human dermal fibroblasts (HDFs) alone and in combination on the formation of new blood vessels in ex-ovo chick chorioallantoic membrane (CAM) assay.

METHODS

Poly-3-hydroxybutyrate-co-3-hydroxyvalerate (PHBV) and polycaprolactone (PCL) were first examined in terms of their physical, mechanical, and biological performances. The effect of gelatin coating and co-culture conditions on enhancing endothelial cell viability and growth was then investigated. Finally, the angiogenic potential of HDMECs and HDFs were assessed macroscopically and histologically after seeding on simple electrospun PHBV scaffolds either in isolation or in indirect co-culture using an ex-ovo CAM assay.

RESULTS

The results demonstrated that PHBV was slightly more favourable than PCL for HDMECs in terms of cell metabolic activity. The gelatin coating of PHBV scaffolds and co-culture of HDMECs with HDFs both showed a positive impact on HDMECs viability and growth. Both cell types induced angiogenesis over 7 days in the CAM assay either in isolation or in co-culture. The introduction of HDMECs to the scaffolds resulted in the production of more blood vessels in the area of implantation than the introduction of HDFs, but the co-culture of HDMECs and HDFs gave the most significant angiogenic activity.

CONCLUSION

Our findings showed that the in vitro prevascularisation of TE constructs with HDMECs and HDFs alone or in co-culture promotes angiogenesis in implantable TE constructs.

Phosphate/oxyfluorophosphate glass crystallization and its impact on dissolution and cytotoxicity

The role of fluorine in bioactive glasses is of interest due to the potential of precipitating fluorapatite, a phase with higher chemical resistance than the typical hydroxyapatite precipitated from oxide bioactive glasses. However, the introduction of fluorine in silicate bioactive glasses was found deleterious to the bioactivity of the glass. Here, phosphate glasses with the composition 75NaPO₃-(25-x) CaO-xCaF₂ (in mol%), with x = 0-20 and glass-ceramics were investigated to evaluate their potential as substitutes to the traditional silicate bioactive glass. An increase in CaF₂ substitution for CaO led to an increase in the glass solubility, due to an increase in highly soluble F(M)n species (where M is a cation) and to an increased polymerization of the phosphate network. Structural analysis reveals the formation of FP bonds, in addition to the F(M)n species, in the glass with the higher CaF₂ content. Furthermore, with heat treatment, CaF₂ crystals precipitate within the bulk in the newly developed glass, when x = 20. This bulk crystallization reduces the glass dissolution without compromising the precipitation of a reactive layer at the glass surface. Finally, in vitro cell tests were performed using MC3T3 pre-osteoblastic cells. While the substitution of CaF₂ for CaO led to an increased cytotoxicity, the controlled crystallization of the fluorine containing glasses decreased such cytotoxicity to similar values than traditional bioactive phosphate glass (x0). This study reports on new oxyfluorophosphate glass and glass-ceramics able, not only, to precipitate a Ca-P reactive layer but also to be processed into glass-ceramics with controlled crystal size, density and cellular activity. STATEMENT OF SIGNIFICANCE: Uncontrolled crystallization of bioactive glasses has negative effect on the materials' bioactivity. While in silicate glass the bioactivity is solely reduced, in phosphate glasses it is often completely suppressed. Furthermore, the need for fluorine containing bioactive glasses, not only for use in bone reconstruction but also in toothpaste as emerged. The addition of F in both silicate and phosphate has led to challenges due the lack of Si-F or P-F bonds, generally leading to a decrease in bioactivity. Here, we developed a bioactive invert phosphate glass where up to 20 mol% of CaO was replaced with CaF₂. In the new developed glasses, NMR demonstrated formation of P-F bonds. The content of fluorine was tailored to induce CaF₂ bulk crystallization. Overall an increase in F was associated with an increase network connectivity. In turns it led to an increased dissolution rate which was linked to a higher cytotoxicity. Upon (partial to full) surface crystallization of the F-free glass, the bioactivity (ability to form a reactive layer) was loss and the cytotoxicity again increased due to the rapid dissolution of one crystal phase and of the remaining amorphous phase. On another hand, the controlled bulk precipitation of CaF₂ crystals, in the F-containing glass, was associated with a reduced cytotoxicity. The new oxyfluorophosphate glass-ceramic developed is promising for application in the biomedical field.

Recent advances in the use of microcarriers for cell cultures and their ex vivo and in vivo applications

Microcarriers are 100- to 300-micron support matrices that permit the growth of adherent cells in bioreactor systems. They have a larger surface area to volume ratio in comparison to single cell monolayers, enabling cost-effective cell production and expansion. Microcarriers are composed of a solid matrix that must be separated from expanded cells during downstream processing stages. The detachment method is chosen on the basis of several factors like cell type, microcarrier surface chemistry, cell confluency and degree of aggregation. The development of microcarriers with a range of physiochemical properties permit controlled cell and protein associations that hold utility for novel therapeutics. In this review, we provide an overview of the recent advances in microcarrier cell culture technology. We also discuss its significance as an ex vivo research tool and the therapeutic potential of newly designed microcarrier systems in vivo.

A parameterised mathematical model to elucidate osteoblast cell growth in a phosphate-glass microcarrier culture

Tissue engineering has the potential to augment bone grafting. Employing microcarriers as cell-expansion vehicles is a promising bottom-up bone tissue engineering strategy. Here we propose a collaborative approach between experimental work and mathematical modelling to develop protocols for growing microcarrier-based engineered constructs of clinically relevant size. Experiments in 96-well plates characterise cell growth with the model human cell line MG-63 using four phosphate glass microcarrier materials. Three of the materials are doped with 5 mol% TiO₂ and contain 0%, 2% or 5% CoO, and the fourth material is doped only with 7% TiO₂ (0% CoO). A mathematical model of cell growth is parameterised by finding material-specific growth coefficients through data-fitting against these experiments. The parameterised mathematical model offers more insight into the material performance by comparing culture outcome against clinically relevant criteria: maximising final cell number starting with the lowest cell number in the shortest time frame. Based on this analysis, material 7% TiO₂ is identified as the most promising.