Fabrication of Radio-Opaque and Macroporous Injectable Calcium Phosphate Cement.

The aim of this work was the development of injectable radio-opaque and macroporous calcium phosphate cement (CPC) to be used as a bone substitute for the treatment of pathologic vertebral fractures. A CPC was first rendered radio-opaque by the incorporation of zirconium dioxide (ZrO2). In order to create macroporosity, poly lactic-co-glycolic acid (PLGA) microspheres around 100 µm were homogeneously incorporated into the CPC as observed by scanning electron microscopy. Physicochemical analyses by X-ray diffraction and Fourier transform infrared spectroscopy confirmed the brushite phase of the cement. The mechanical properties of the CPC/PLGA cement containing 30% PLGA (wt/wt) were characterized by a compressive strength of 2 MPa and a Young's modulus of 1 GPa. The CPC/PLGA exhibited initial and final setting times of 7 and 12 min, respectively. Although the incorporation of PLGA microspheres increased the force necessary to inject the cement and decreased the percentage of injected mass as a function of time, the CPC/PLGA appeared fully injectable at 4 min. Moreover, in comparison with CPC, CPC/PLGA showed a full degradation in 6 weeks (with 100% mass loss), and this was associated with an acidification of the medium containing the CPC/PLGA sample (pH of 3.5 after 6 weeks). A cell viability test validated CPC/PLGA biocompatibility, and in vivo analyses using a bone defect assay in the caudal vertebrae of Wistar rats showed the good opacity of the CPC through the tail and a significant increased degradation of the CPC/PLGA cement a month after implantation. In conclusion, this injectable CPC scaffold appears to be an interesting material for bone substitution.

Fabrication of 3D printed antimicrobial polycaprolactone scaffolds for tissue engineering applications.

Synthetic polymers are widely employed for bone tissue engineering due to their tunable physical properties and biocompatibility. Inherently, most of these polymers display poor antimicrobial properties. Infection at the site of implantation is a major cause for failure or delay in bone healing process and the development of antimicrobial polymers is highly desired. In this study, silver nanoparticles (AgNps) were synthesized in polycaprolactone (PCL) solution by in-situ reduction and further extruded into PCL/AgNps filaments. Customized 3D structures were fabricated using the PCL/AgNps filaments through 3D printing technique. As demonstrated by scanning electron microscopy, the 3D printed scaffolds exhibited interconnected porous structures. Furthermore, X-ray photoelectron spectroscopy analysis revealed the reduction of silver ions. Transmission electron microscopy along with energy-dispersive X-ray spectroscopy analysis confirmed the formation of silver nanoparticles throughout the PCL matrix. In vitro enzymatic degradation studies showed that the PCL/AgNps scaffolds displayed 80% degradation in 20 days. The scaffolds were cytocompatible, as assessed using hFOB cells and their antibacterial activity was demonstrated on Escherichia coli. Due to their interconnected porous structure, mechanical and antibacterial properties, these cytocompatible multifunctional 3D printed PCL/AgNps scaffolds appear highly suitable for bone tissue engineering.

Investigation of polymer-derived Si-(B)-C-N ceramic/reduced graphene oxide composite systems as active catalysts towards the hydrogen evolution reaction.

Hydrogen Evolution Reaction (HER) is an attractive technology for chemical conversion of energy. Replacement of platinum with inexpensive and stable electrocatalysts remains a major bottleneck hampering large-scale hydrogen production by using clean and renewable energy sources. Here, we report electrocatalytically active and ultra-stable Polymer-Derived Ceramics towards HER. We successfully prepared ultrathin silicon and carbon (Si-C) based ceramic systems supported on electrically conducting 2D reduced graphene oxide (rGO) nanosheets with promising HER activity by varying the nature and the composition of the ceramic with the inclusion of nitrogen, boron and oxygen. Our results suggest that oxygen-enriched Si-B-C-N/rGO composites (O-SiBCN/rGO) display the strongest catalytic activity leading to an onset potential and a Tafel slope of - 340 mV and ~ 120 mV dec-1 respectively. O-SiBCN/rGO electrodes display stability over 170 h with minimal increase of 14% of the overpotential compared to ~ 1700% for commercial platinum nanoparticles. Our study provides new insights on the performance of ceramics as affordable and robust HER catalysts calling for further exploration of the electrocatalytic activity of such unconventional materials.

Development of new biocompatible 3D printed graphene oxide-based scaffolds.

The aim of this work was to develop a bioresorbable, biodegradable and biocompatible synthetic polymer with good mechanical properties for bone tissue engineering applications. Polylactic acid (PLA) scaffolds were generated by 3D printing using the fused deposition modelling method, and reinforced by incorporation of graphene oxide (GO). Morphological analysis by scanning electron microscopy indicated that the scaffold average pore size was between 400 and 500 µm. Topography imaging revealed a rougher surface upon GO incorporation (Sa = 5.8 µm for PLA scaffolds, and of 9.9 µm for PLA scaffolds with 0.2% GO), and contact angle measurements showed a transition from a hydrophobic surface (pure PLA scaffolds) to a hydrophilic surface after GO incorporation. PLA thermomechanical properties were enhanced by GO incorporation, as shown by the 70 °C increase of the degradation peak (thermal gravimetric analysis). However, GO incorporation did not change significantly the melting point assessed by differential scanning calorimetry. Physicochemical analyses by X-ray diffraction and Raman spectroscopy confirmed the filler presence. Tensile testing demonstrated that the mechanical properties were improved upon GO incorporation (30% increase of the Young's modulus with 0.3% GO). Cell viability, attachment, proliferation and differentiation assays using MG-63 osteosarcoma cells showed that PLA/GO scaffolds were biocompatible and that they promoted cell proliferation and mineralization more efficiently than pure PLA scaffolds. In conclusion, this new 3D printed nanocomposite is a promising scaffold with adequate mechanical properties and cytocompatibility which may allow bone formation.

Boron Nitride Based Nanobiocomposites: Design by 3D Printing for Bone Tissue Engineering.

Here, we produced a synthetic polymer having adequate biocompatibility, biodegradability, and bioresorbability, as well as mechanical properties for applications in bone tissue engineering. We used the fused deposition modeling (FDM) based 3D printing approach in order to produce biomimetic biodegradable scaffolds made of polylactic acid (PLA). We strengthened these scaffolds by addition of exfoliated boron nitride (EBN) as filler. We demonstrated the presence of EBN by physicochemical analysis using Raman spectroscopy and X-ray diffraction (XRD). Using differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA), we found that EBN incorporation did not influence the transition temperature, but reduced the polymer crystallinity. Scanning electron microscopy for morphology evaluation showed a mean scaffold pore size of 500 µm. EBN incorporation did not affect the scaffold mechanical properties (tensile test), but modified the surface roughness. Moreover, contact angle quantification indicated that the surface of PLA/EBN scaffolds was hydrophilic and that of PLA scaffolds hydrophobic. Finally, the results of the cytotoxicity, cell attachment, and proliferation experiments using MG-63 and MC3T3 cells indicated that PLA scaffolds filled with EBN were nontoxic and compatible with osteoblastic cells and also promoted the scaffold mineralization by MG-63 cells. Altogether, our results suggest that this 3D printed nanocomposite scaffold is suitable for tissue engineering.

Efficient nanoparticles removal and bactericidal action of electrospun nanofibers membranes for air filtration.

Human exposure to air pollution and especially to nanoparticles is increasing due to the combustion of carbon-based energy vectors. Fibrous filters are among the various types of equipment potentially able to remove particles from the air. Nanofibers are highly effective in this area; however, their utilization is still a challenge due to the lack of studies taking into account both nanoparticle collection efficiency and antibacterial effect. The aim of this work is to produce and evaluate novel silver/polyacrylonitrile (Ag/PAN) electrospun fibers deposited on a nonwoven substrate to be used as air filters to remove nanoparticles from the air and also showing antibacterial activity. In order to determine the optimum manufacturing conditions, the effects of several electrospinning process parameters were analyzed such as solution concentration, collector to needle distance, flow rate, voltage, and duration. Ag/PAN nanofibers were characterized by X-ray diffraction (XRD), Transmission Electron Microscopy (TEM), Fourier Transform Infra-Red spectroscopy (FTIR), Energy-dispersive X-ray spectroscopy (EDX), X-ray photoelectron spectroscopy (XPS), and Scanning Electron Microscopy (SEM). In addition, filtration performances were determined by measuring the pressure drop and collection efficiency of sodium chloride (NaCl) aerosol particles (9 to 300 nm diameters) using Scanning Mobility Particle Sizers (SMPS). Filters with high filtration efficiency (≈100%) and high-quality factor (≈0.05 Pa-1) were obtained even adding different concentrations of Ag nanoparticles (AgNPs) to PAN nanofibers. The resultant Ag/PAN nanofibers showed excellent antibacterial activity against 104 CFU/mL E. coli bacteria.

A 3D finite element model for hyperthermia injury of blood-perfused skin.

The objective of this study is to propose a numerical model of thermal damage to the skin. This model simulates the propagation of a burn and suggests treatments to prevent it from spreading. In order to achieve this goal, we developed a 3D multi-layer finite element model of the skin coupled with a model presenting hyperthermic damage. The numerical model of the skin takes account of not only the thermal properties of various layers, but also blood perfusion and veins. The model of thermal damage is based on the Arrhenius' law. We tested two various quick intervention treatments so as to prevent the burn from spreading. The first treatment consists of cooling the burned zone with a flow of cool water at 10°C, whereas the second solution simulates the apposition of ice on the burn. The results show that, according to the severity of the burn, the second treatment seems to be the most appropriate. Moreover, our model opens interesting prospects in the analysis of hyperthermic damage.

Influence of gravity on the skin thermal behavior: experimental study using dynamic infrared thermography.

BACKGROUND/AIM: To better understand the thermomechanical behavior of the skin and its direct environment, we present an experimental study using dynamic infrared thermography. This experimental study aims to highlight quantitatively some effects of blood flow on the heat diffusion. METHODS: The originality of this research was to change the blood flow by using effects of gravity and to quantify the temperature changes. The experimental step consists of putting a cylindrical steel bar cooled or warmed on the skin of a human forearm and to measure the change of the temperature using an infrared camera. Measures have been recorded for different positions of the forearm. RESULT AND CONCLUSION: We noted very clearly the influence of blood circulation in the veins on the diffusion of the temperature. The return to thermal balance is faster when the arm is in a horizontal position. Moreover, a comparative study of experimental cooling and warming showed a symmetrical thermal behavior for the skin under this type of thermal solicitations. This work provided to build a database that can be used for the validation of predictive thermal models of human skin.