Response of human alveolar bone-derived cells to a novel poly(vinylidene fluoride-trifluoroethylene)/barium titanate membrane

Mesenchymal Stem Cells Combined with a P(VDF-TrFE)/BaTiO3 Scaffold and Photobiomodulation Therapy Enhance Bone Repair in Rat Calvarial Defects

BACKGROUND

Tissue engineering and cell therapy have been the focus of investigations on how to treat challenging bone defects. This study aimed to produce and characterize a P(VDF-TrFE)/BaTiO₃ scaffold and evaluate the effect of mesenchymal stem cells (MSCs) combined with this scaffold and photobiomodulation (PBM) on bone repair.

METHODS AND RESULTS

P(VDF-TrFE)/BaTiO₃ was synthesized using an electrospinning technique and presented physical and chemical properties suitable for bone tissue engineering. This scaffold was implanted in rat calvarial defects (unilateral, 5 mm in diameter) and, 2 weeks post-implantation, MSCs were locally injected into these defects (n = 12/group). Photobiomodulation was then applied immediately, and again 48 and 96 h post-injection. The μCT and histological analyses showed an increment in bone formation, which exhibited a positive correlation with the treatments combined with the scaffold, with MSCs and PBM inducing more bone repair, followed by the scaffold combined with PBM, the scaffold combined with MSCs, and finally the scaffold alone (ANOVA, p ≤ 0.05).

CONCLUSIONS

The P(VDF-TrFE)/BaTiO₃ scaffold acted synergistically with MSCs and PBM to induce bone repair in rat calvarial defects. These findings emphasize the need to combine a range of techniques to regenerate large bone defects and provide avenues for further investigations on innovative tissue engineering approaches.

Multi-Parametric Exploration of a Selection of Piezoceramic Materials for Bone Graft Substitute Applications

This work was devoted to the first multi-parametric unitary comparative analysis of a selection of sintered piezoceramic materials synthesised by solid-state reactions, aiming to delineate the most promising biocompatible piezoelectric material, to be further implemented into macro-porous ceramic scaffolds fabricated by 3D printing technologies. The piezoceramics under scrutiny were: KNbO₃, LiNbO₃, LiTaO₃, BaTiO₃, Zr-doped BaTiO₃, and the (Ba_0.85Ca_0.15)(Ti_0.9Zr_0.1)O₃ solid solution (BCTZ). The XRD analysis revealed the high crystallinity of all sintered ceramics, while the best densification was achieved for the BaTiO₃-based materials via conventional sintering. Conjunctively, BCTZ yielded the best combination of functional properties-piezoelectric response (in terms of longitudinal piezoelectric constant and planar electromechanical coupling factor) and mechanical and in vitro osteoblast cell compatibility. The selected piezoceramic was further used as a base material for the robocasting fabrication of 3D macro-porous scaffolds (porosity of ~50%), which yielded a promising compressive strength of ~20 MPa (higher than that of trabecular bone), excellent cell colonization capability, and noteworthy cytocompatibility in osteoblast cell cultures, analogous to the biological control. Thereby, good prospects for the possible development of a new generation of synthetic bone graft substitutes endowed with the piezoelectric effect as a stimulus for the enhancement of osteogenic capacity were settled.

Analytical modeling of the evaporation of sessile drop linear arrays

An analytical model for predicting the competitive evaporation of two and three sessile drops is proposed, based on an analytical solution, in terms of Mehler functions, of the steady species and energy conservation equations for the gaseous phase. The assessment through a comparison with accurate numerical solutions of the species conservation equations is reported in order to quantify the accuracy of the analytical solution. The model is validated against three available sets of experiments on two and three sessile drops on a line array. The decrease of the evaporation rate caused by the vicinity of sessile drops is reported in terms of a screening coefficient given by a relatively simple analytical expression. The influence of wall wettability on the evaporation of pairs of sessile drops is analyzed, and a parameter is proposed to quantify the effect of geometry in a unified way.

Core-shell fibrous membranes of PVDF-Ba0.9Ca0.1TiO3/PVA with osteogenic and piezoelectric properties for bone regeneration

The goal of this research was to promote the bioactivity and osteogenic characteristics of polyvinylidene fluoride(PVDF) fibrous membrane, while preserving its piezoelectric property for bone regeneration. In this regard, core-shell fibrous membrane of PVDF-Ba_0.9Ca_0.1TiO₃/polyvinyl alcohol(PVA) was developed via emulsion electrospinning approach. While PVA was in the outer layer of fibers with thickness of 53 ± 18 nm, the Ba_0.9Ca_0.1TiO₃ nanoparticles was uniformly dispersed in the PVDF core. The formation of PVA shell resulted in significant improvement of its hydrophilicity (3 times) and degradation rate, while piezoelectricity did noticeably modulate. In addition, incorporation of Ba_0.9Ca_0.1TiO₃ nanopowder remarkably improved bioactivity, protein adsorption and mechanical properties of PVDF/PVA fibrous membranes. Finally, the osteogenic differentiation of mesenchymal stem cells on the nanocomposite fibrous membranes, in the absence of osteogenic supplements, was also observed. Overall, the results confirmed the promising potential of PVDF-Ba_0.9Ca_0.1TiO₃/PVA fibrous membrane containing 1-2 wt% nanopowder for bone regeneration.

Effect of stem cells combined with a polymer/ceramic membrane on osteoporotic bone repair

Cell therapy associated with guided bone regeneration (GBR) can be used to treat bone defects under challenging conditions such as osteoporosis. This study aimed to evaluate the effect of mesenchymal stem cells (MSCs) in combination with a poly(vinylidene-trifluoroethylene)/barium titanate (PVDF-TrFE/BT) membrane on bone repair in osteoporotic rats. Osteoporosis was induced in female rats by bilateral removal of the ovaries (OVX) or sham surgery (SHAM), and the osteoporotic condition was characterized after 5 months by microtomographic and morphometric analyses. Calvarial defects were created in osteoporotic rats that immediately received the PVDF-TrFE/BT membrane. After 2 weeks, bone marrow-derived MSCs from healthy rats, characterized by the expression of surface markers using flow cytometry, or phosphate-buffered saline (PBS) (Control) were injected into the defects and bone formation was evaluated 4 weeks post-injection by microtomographic, morphometric, and histological analyses. A reduction in the amount of bone tissue in the femurs of OVX compared with SHAM rats confirmed the osteoporotic condition of the experimental model. More bone formation was observed when the defects were injected with MSCs compared to that with PBS. The modification that we are proposing in this study for the classical GBR approach where cells are locally injected after a membrane implantation may be a promising therapeutic strategy to increase bone formation under osteoporotic condition.

Lycopene influences osteoblast functional activity and prevents femur bone loss in female rats submitted to an experimental model of osteoporosis

Antioxidant properties of several nutrients may influence bone metabolism, affording protection against damaging effects caused by oxidative stress. Thus, we hypothesized that lycopene may benefit bone tissue metabolism and functional activity of osteoblastic cells from bone marrow of osteoporotic female rats. Wistar rats were ovariectomized and paired with sham animals. In vitro evaluations were performed after 60 days of surgery, when cells were cultured in osteogenic medium and divided in control (C), ovariectomized (OVX) and ovariectomized + 1 μmol/L lycopene (OVXL) groups. Besides, in vivo studies were carried out to evaluate femur bone remodeling by histological and histomorphometric analyses after daily intake of 10 mg/kg of lycopene for 30 and 60 days after ovariectomy. Cell proliferation was significantly higher in OVX and OVXL groups after 10 days of culture. Alkaline phosphatase activity (ALP) was higher in OVXL group in later periods of cell culture, whereas its in situ detection was higher for this group in all experimental periods; nevertheless, mineralization did not show significant differences among the groups. There was a significant upregulation of genes Sp7, Runx2 and Bsp after 3 days and genes Runx2 and Bglap after 10 days from OVXL when compared to OVX. In vivo results demonstrated that daily intake of 10 mg/kg of lycopene for 60 days decreased bone loss in femur epiphysis in ovariectomized rats by maintaining trabecular bone similar to controls. Data obtained suggest that lycopene might benefit the functional activity of osteoblastic cells from ovariectomized rats, as well as avoid further bone resorption.

Biomimetic piezoelectric nanocomposite membranes synergistically enhance osteogenesis of deproteinized bovine bone grafts

Purpose: The combination of a bone graft with a barrier membrane is the classic method for guided bone regeneration (GBR) treatment. However, the insufficient osteoinductivity of currently-available barrier membranes and the consequent limited bone regeneration often inhibit the efficacy of bone repair. In this study, we utilized the piezoelectric properties of biomaterials to enhance the osteoinductivity of barrier membranes. Methods: A flexible nanocomposite membrane mimicking the piezoelectric properties of natural bone was utilized as the barrier membrane. Its therapeutic efficacy in repairing critical-sized rabbit mandible defects in combination with xenogenic grafts of deproteinized bovine bone (DBB) was explored. The nanocomposite membranes were fabricated with a homogeneous distribution of piezoelectric BaTiO₃ nanoparticles (BTO NPs) embedded within a poly(vinylidene fluoridetrifluoroethylene) (P(VDF-TrFE)) matrix. Results: The piezoelectric coefficient of the polarized nanocomposite membranes was close to that of human bone. The piezoelectric coefficient of the polarized nanocomposite membranes was highly stable, with more than 90% of the original piezoelectric coefficient (d₃₃) remaining up to 28 days after immersion in culture medium. Compared with commercially-available polytetrafluoroethylene (PTFE) membranes, the polarized BTO/P(VDF-TrFE) nanocomposite membranes exhibited higher osteoinductivity (assessed by immunofluorescence staining for runt-related transcription factor 2 (RUNX-2) expression) and induced significantly earlier neovascularization and complete mature bone-structure formation within the rabbit mandible critical-sized defects after implantation with DBB Bio-Oss® granules. Conclusion: Our findings thus demonstrated that the piezoelectric BTO/P(VDF-TrFE) nanocomposite membranes might be suitable for enhancing the clinical efficacy of GBR.

Potential of Osteoblastic Cells Derived from Bone Marrow and Adipose Tissue Associated with a Polymer/Ceramic Composite to Repair Bone Tissue

One of the tissue engineering strategies to promote bone regeneration is the association of cells and biomaterials. In this context, the aim of this study was to evaluate if cell source, either from bone marrow or adipose tissue, affects bone repair induced by osteoblastic cells associated with a membrane of poly(vinylidene-trifluoroethylene)/barium titanate (PVDF-TrFE/BT). Mesenchymal stem cells (MSC) were isolated from rat bone marrow and adipose tissue and characterized by detection of several surface markers. Also, both cell populations were cultured under osteogenic conditions and it was observed that MSC from bone marrow were more osteogenic than MSC from adipose tissue. The bone repair was evaluated in rat calvarial defects implanted with PVDF-TrFE/BT membrane and locally injected with (1) osteoblastic cells differentiated from MSC from bone marrow, (2) osteoblastic cells differentiated from MSC from adipose tissue or (3) phosphate-buffered saline. Luciferase-expressing osteoblastic cells derived from bone marrow and adipose tissue were detected in bone defects after cell injection during 25 days without difference in luciferin signal between cells from both sources. Corroborating the in vitro findings, osteoblastic cells from bone marrow combined with the PVDF-TrFE/BT membrane increased the bone formation, whereas osteoblastic cells from adipose tissue did not enhance the bone repair induced by the membrane itself. Based on these findings, it is possible to conclude that, by combining a membrane with cells in this rat model, cell source matters and that bone marrow could be a more suitable source of cells for therapies to engineer bone.

Poly(Vinylidene Fluoride-Trifluorethylene)/barium titanate membrane promotes de novo bone formation and may modulate gene expression in osteoporotic rat model

Osteoporosis is a chronic disease that impairs proper bone remodeling. Guided bone regeneration is a surgical technique that improves bone defect in a particular region through new bone formation, using barrier materials (e.g. membranes) to protect the space adjacent to the bone defect. The polytetrafluorethylene membrane is widely used in guided bone regeneration, however, new membranes are being investigated. The purpose of this study was to evaluate the effect of P(VDFTrFE)/BT [poly(vinylidene fluoride-trifluoroethylene)/barium titanate] membrane on in vivo bone formation. Twenty-three Wistar rats were submitted to bilateral ovariectomy. Five animals were subjected to sham surgery. After 150 days, bone defects were created and filled with P(VDF-TrFE)/BT membrane or PTFE membrane (except for the sham and OVX groups). After 4 weeks, the animals were euthanized and calvaria samples were subjected to histomorphometric and computed microtomography analysis (microCT), besides real time polymerase chain reaction (real time PCR) to evaluate gene expression. The histomorphometric analysis showed that the animals that received the P(VDF-TrFE)/BT membrane presented morphometric parameters similar or even better compared to the animals that received the PTFE membrane. The comparison between groups showed that gene expression of RUNX2, BSP, OPN, OSX and RANKL were lower on P(VDF-TrFE)/BT membrane; the gene expression of ALP, OC, RANK and CTSK were similar and the gene expression of OPG, CALCR and MMP9 were higher when compared to PTFE. The results showed that the P(VDF-TrFE)/BT membrane favors bone formation, and therefore, may be considered a promising biomaterial to support bone repair in a situation of osteoporosis.

Participation of MicroRNA-34a and RANKL on bone repair induced by poly(vinylidene-trifluoroethylene)/barium titanate membrane

The poly(vinylidene-trifluoroethylene)/barium titanate (PVDF) membrane enhances in vitro osteoblast differentiation and in vivo bone repair. Here, we hypothesized that this higher bone repair could be also due to bone resorption inhibition mediated by a microRNA (miR)/RANKL circuit. To test our hypothesis, the large-scale miR expression of bone tissue grown on PVDF and polytetrafluoroethylene (PTFE) membranes was evaluated to identify potential RANKL-targeted miRs modulated by PVDF. The animal model used was rat calvarial defects implanted with either PVDF or PTFE. At 4 and 8 weeks, the bone tissue grown on membranes was submitted to a large-scale analysis of miRs by microarray. The expression of miR-34a and some of its targets, including RANKL, were evaluated by real-time polimerase chain reaction and osteoclast activity was detected by tartrate-resistant acid phosphatase (TRAP) staining. Among more than 250 miRs, twelve, including miR-34a, were simultaneously higher expressed (≥2 fold) at 4 and 8 weeks on PVDF. The higher expression of miR-34a was concomitant with a reduced expression of all its evaluated targets, including RANKL. Additionally, more TRAP-positive cells were observed in bone tissue grown on PTFE compared with PVDF in both time points. In conclusion, our results suggest that the higher bone formation induced by PVDF could be, at least in part, triggered by a miR-34a increase and RANKL decrease, which may inhibit osteoclast differentiation and activity, and bone resorption.

Poly(vinylidene-trifluoroethylene)/barium titanate composite for in vivo support of bone formation

In this study, we evaluated the effect of poly(vinylidene fluoride-trifluoroethylene)/barium titanate (P(VDF-TrFE)/BT) membrane on in vivo bone formation. Rat calvarial bone defects were implanted with P(VDF-TrFE)/BT and polytetrafluoroethylene (PTFE) membranes, and at 4 and 8 weeks, histomorphometric and gene expression analyses were performed. A higher amount of bone formation was noticed on P(VDF-TrFE)/BT compared with PTFE. The gene expression of RUNX2, bone sialoprotein, osteocalcin, receptor activator of nuclear factor-kappa B ligand, and osteoprotegerin indicates that P(VDF-TrFE)/BT favored the osteoblast differentiation compared with PTFE. These results evidenced the benefits of using P(VDF-TrFE)/BT to promote new bone formation, which may represent a promising alternative to be employed in guided bone regeneration.