Design of Laser Activated Antimicrobial Porous Tricalcium Phosphate-Hydroxyapatite Scaffolds for Orthopedic Applications.

The field of bone tissue engineering is steadily being improved by novel experimental approaches. Nevertheless, microbial adhesion after scaffold implantation remains a limitation that could lead to the impairment of the regeneration process, or scaffold rejection. The present study introduces a methodology that employs laser-based strategies for the development of antimicrobial interfaces on tricalcium phosphate-hydroxyapatite (TCP-HA) scaffolds. The outer surfaces of the ceramic scaffolds with inner porosity were structured using a femtosecond laser (λ = 800 nm; τ = 70 fs) for developing micropatterns and altering local surface roughness. The pulsed laser deposition of ZnO was used for the subsequent functionalization of both laser-structured and unmodified surfaces. The impact of the fs irradiation was investigated by Raman spectroscopy and X-ray diffraction. The effects of the ZnO-layered ceramic surfaces on initial bacterial adherence were assessed by culturing Staphylococcus aureus on both functionalized and non-functionalized scaffolds. Bacterial metabolic activity and morphology were monitored via the Resazurin assay and microscopic approaches. The presence of ZnO evidently decreased the metabolic activity of bacteria and led to impaired cell morphology. The results from this study have led to the conclusion that the combination of fs laser-structured surface topography and ZnO could yield a potential antimicrobial interface for implants in bone tissue engineering.

Improvement of Metal-Doped ß-TCP Scaffolds for Active Bone Substitutes via Ultra-Short Laser Structuring.

Various efforts have been made to develop antibacterial biomaterials capable of also sustaining bone remodulation to be used as bone substitutes and reduce patient infection rates and related costs. In this work, beta-tricalcium phosphate (ß-TCP) was chosen due to its known biocompatibility and use as a bone substitute. Metal dopants were incorporated into the crystal structure of the ß-TCP, and disks were produced from this material. Magnesium and strontium, as well as copper and silver, were chosen as dopants to improve the osteogenic and antibacterial properties, respectively. The surface of the ß-TCP samples was further modified using a femtosecond laser system. Grid and line patterns were produced on the plates' surface via laser ablation, creating grooves with depths lower than 20 µm and widths between 20 and 40 µm. Raman and FTIR analysis confirmed that laser ablation did not result in the degradation or phase change of the materials, making it suitable for surface patterning. Laser ablation resulted in increased hydrophilicity of the materials, as the control samples (non-ablated samples) have WCA values ranging from 70° to 93° and become, upon laser ablation, superwicking surfaces. Confocal measurements show an increase in specific surface area of 50% to 200% compared to the control. Overall, the results indicate the potential of laser ablation to improve the surface characteristics of ß-TCP, which may lead to an improvement in the antibacterial and osteogenic properties of the produced materials.

Bone-like ceramic scaffolds designed with bioinspired porosity induce a different stem cell response.

Biomaterial science increasingly seeks more biomimetic scaffolds that functionally augment the native bone tissue. In this paper, a new concept of a structural scaffold design is presented where the physiological multi-scale architecture is fully incorporated in a single-scaffold solution. Hydroxyapatite (HA) and ß-tricalcium phosphate (ß-TCP) bioceramic scaffolds with different bioinspired porosity, mimicking the spongy and cortical bone tissue, were studied. In vitro experiments, looking at the mesenchymal stem cells behaviour, were conducted in a perfusion bioreactor that mimics the physiological conditions in terms of interstitial fluid flow and associated induced shear stress. All the biomaterials enhanced cell adhesion and cell viability. Cortical bone scaffolds, with an aligned architecture, induced an overexpression of several late stage genes involved in the process of osteogenic differentiation compared to the spongy bone scaffolds. This study reveals the exciting prospect of bioinspired porous designed ceramic scaffolds that combines both cortical and cancellous bone in a single ceramic bone graft. It is prospected that dual core shell scaffold could significantly modulate osteogenic processes, once implanted in patients, rapidly forming mature bone tissue at the tissue interface, followed by subsequent bone maturation in the inner spongy structure.

Effect of build orientation on the manufacturing process and the properties of stereolithographic dental ceramics for crown frameworks.

STATEMENT OF PROBLEM: Stereolithography (SLA) ceramic crown frameworks are suitable for clinical use, but the impact of SLA build orientation has not been identified. PURPOSE: The purpose of this in vitro study was to investigate the effect of 3 build orientations on the physical and mechanical properties and the microstructure of SLA alumina dental ceramics. MATERIAL AND METHODS: The physical and mechanical properties and microstructures of 3 different oriented SLA alumina ceramics (ZX, ZY, and XY) were evaluated by visual observation, hydrostatic weighing (n=10/group), Weibull analyses (n=30/group), scanning electron microscopy, 3-point flexural strength (n=30/group), fracture toughness (indentation, single-edge-V-notched-beam) (n=4/group), and Vickers hardness (n=15/group) testing. The hydrostatic weighing, 3-point flexural strength, fracture toughness, and Vickers hardness testing data were statistically analyzed (α=.05). RESULTS: The minimum resting period of slurries between the polymerization of 2 layers was shorter for the ZY- and ZX-oriented specimens and increased with the layer surface. The density and Vickers hardness of the SLA-manufactured specimens were similar for all groups (P>.05). The 95% confidence intervals of the Weibull moduli of the ZX- and ZY-oriented specimens were higher than that of the XY-oriented specimens, with no overlap fraction. The ZY-oriented specimens displayed significantly higher 3-point flexural strength (P<.05) and fracture toughness as evaluated by the single-edge-V-notched-beam method than the ZX-oriented specimens (P<.05). They also displayed significantly higher 3-point flexural strength than the XY-oriented specimens (P<.05). The microstructural analysis showed that the texturing was heterogeneous and that the major axis of the large grains of alumina ran parallel to the orientation of the layers. CONCLUSIONS: The ZY orientation produced a reliable dental ceramic by SLA, with the shortest general manufacturing time and the highest mechanical strength when the layers were perpendicular to the test load surface.

Micropatterning of beta tricalcium phosphate bioceramic surfaces, by femtosecond laser, for bone marrow stem cells behavior assessment.

The bioactivity of synthetic bone implants is highly impacted by their surface topography, especially by the presence of micro-patterns likely to generate cells growth guidance. In this study, laser machining technology was employed in order to produce controlled regular micro-patterns on dense calcium phosphate surfaces, without any contamination. The choice of the source was directed towards a femtosecond pulsed laser in order to limit the thermal impact of such a process and thus to avoid the unwanted phase transformations potentially induced by the temperature elevation. Beta tricalcium phosphate substrates with perfectly controlled micro-patterning and without any secondary phase were obtained by optimization of the process parameters (laser power, scanning speed, pulse frequency). The microstructural characteristics were investigated by microscopy (optical, confocal, scanning electron) and the phase identification was performed by X-ray diffraction. This work allowed highlighting the effects of the process parameters on the patterning. The high benefits of the laser treatment on wettability were shown by contact angle assays. Finally, the influence of surface micro-patterning on cell behavior was highlighted in vitro. This technique seems to provide an interesting alternative to conventional surface treatments of calcium phosphates.

Crosslinking chemistry of poly(vinylmethyl-co-methyl)silazanes toward low-temperature formable preceramic polymers as precursors of functional aluminium-modified Si-C-N ceramics.

Crosslinking chemistry of a liquid poly(vinylmethyl-co-methyl)silazane with an alane hydride-based complex according to Si : Al ratios varying from 5 to 2.5 has been investigated in detail through the characterization of the as-obtained polymers using solid-state NMR, FT-IR and elemental analyses. This reaction allows tailoring the chemical and physical properties of the neat liquid polysilazane while extending its processability to lead to a series of low-temperature formable aluminium-modified polysilazanes. Structural models have been established based on solid-state NMR spectroscopy. Then, pyrolysis under nitrogen occurring the conversion of polymers into ceramics has been studied by coupling TG experiments with FTIR of pyrolysis intermediates. Pyrolysis at 1000 °C leads to X-ray amorphous Al-modified silicon carbonitride materials with higher ceramic yields compared to the materials obtained from the neat polysilazane. However, the increase of the ceramic yield is minimized with the decrease of the Si : Al ratio from 5 to 2.5 in the as-obtained polymers. This is due to the introduction of -NR3 (R = CH3 and C2H5) units as side groups during the polymer synthesis which are released in the low temperature regime of the pyrolysis. The structural evolution of the amorphous network of ceramics has been studied by annealing up to 1800 °C though X-ray diffraction and Raman spectroscopy. Such studies point out that samples remain amorphous even after annealing at 1400 °C (low Si : Al ratio) and 1600 °C (high Si : Al ratio) before forming Si3N4/SiC/AlN and AlN/SiC/C composites after annealing at 1800 °C depending on the Si : Al ratio fixed in the early stage of the process. Dense pieces could be prepared from these low-temperature formable polymers. The latter, especially those containing a certain portion of -NR3 (R = CH3 and C2H5) units acting as plasticizing groups during the process, display appropriate requirements for pressing at low temperature forming dense pieces with hardness and Young's modulus as high as 21.7 GPa and 192.7 GPa, respectively.

Mechanical properties, structure, bioactivity and cytotoxicity of bioactive Na-Ca-Si-P-O-(N) glasses.

Bioactive glasses are able to bond to bone through formation of carbonated hydroxyapatite in body fluids. However, because of their poor strength their use is restricted to non-load-bearing applications. The effects of nitrogen addition on the physical and mechanical properties and structure of bioactive oxynitride glasses in the system Na-Ca-Si-P-O-N have been studied. Glasses with compositions (mol.%): 29Na2O-13.5CaO-2.5P2O5-(55 -3x)SiO2-xSi3N4 (x is the no. of moles of Si3N4) were synthesised with up to 1.5 at% P and 4.1 at% N. A novel 3-step process was used for addition of P and N and this proved successful in minimising weight losses and producing homogeneous glasses with such high SiO2 contents. The substitution of 4.12 at% N for oxygen results in linear increases in density (1.6%), glass transition temperature (6%), hardness (18%) and Young's modulus (74%). Vickers Indentation Fracture (VIF) resistance (Kifr) was calculated from various relationships depending on the load, indent diagonal, crack lengths and Young's modulus to hardness (E/H) ratio. Firstly, Meyer's index n is calculated from the slope of the logarithmic plot of load versus indent diagonal. Then by comparing the experimental slopes of the logarithmic plots of crack lengths versus load it is concluded that the cracking mode is Radial Median type. The substitution of 4.12 at% N for oxygen results in an increase in Kifr of 40%. These increases in properties are consistent with the incorporation of N into the glass structure in three-fold coordination with silicon which results in extra cross-linking of the glass network. The structure of these bioactive oxynitride glasses was investigated by solid state nuclear magnetic resonance (MAS NMR) of 31P and 29Si. The structure reveals that all the N atoms are bonded to Si atoms with the formation of SiO3N, SiO2N2 and Q4 structural units with extra bridging anions at the expense of Q3 units. The bioactivity of the glasses has been evaluated by soaking them in simulated body fluid (SBF) and results confirm that all these oxynitride glasses are bioactive. Cytotoxicity tests based on different concentrations of these bioactive glass powders in a cell growth environment have also shown that they are not cytotoxic.

Effect of nitrogen and fluorine on mechanical properties and bioactivity in two series of bioactive glasses.

Bioactive glasses are able to bond to bone through formation of carbonated hydroxyapatite in body fluids, and fluoride-releasing bioactive glasses are of interest for both orthopaedic and, in particular, dental applications for caries inhibition. However, because of their poor strength their use is restricted to non-load-bearing applications. In order to increase their mechanical properties, doping with nitrogen has been performed on two series of bioactive glasses: series (I) was a "bioglass" composition (without P2O5) within the quaternary system SiO2-Na2O-CaO-Si3N4 and series (II) was a simple substitution of CaF2 for CaO in series (I) glasses keeping the Na:Ca ratio constant. The objective of this work was to evaluate the effect of the variation in nitrogen and fluorine content on the properties of these glasses. The density, glass transition temperature, hardness and elastic modulus all increased linearly with nitrogen content which indicates that the incorporation of nitrogen stiffens the glass network because N is mainly in 3-fold coordination with Si atoms. Fluorine addition significantly decreases the thermal property values but the mechanical properties of these glasses remain unchanged with fluorine. The combination of both nitrogen and fluorine in oxyfluoronitride glasses gives better mechanical properties at much lower melting temperatures since fluorine reduces the melting point, allows higher solubility of nitrogen and does not affect the higher mechanical properties arising from incorporation of nitrogen. The characterization of these N and F substituted bioactive glasses using (29)Si MAS NMR has shown that the increase in rigidity of the glass network can be explained by the formation of SiO3N, SiO2N2 tetrahedra and Q(4) units with extra bridging anions at the expense of Q(3) units. Bioactivity of the glasses was investigated in vitro by examining apatite formation on the surface of glasses treated in acellular simulated body fluid (SBF) with ion concentrations similar to those in human blood plasma. Formation of a bioactive apatite layer on the samples treated in SBF was confirmed by grazing incidence X-ray diffraction and scanning electron microscopy (SEM) combined with energy dispersive X-ray spectroscopy (EDS). The crystallinity of this layer decreases with increasing N content suggesting that N may decrease bioactivity slightly.

Development of superhydrophilic and superhydrophobic polyester fabric by growing zinc oxide nanorods.

ZnO nanorods were grown on microfibers of Polyethylene terephthalate (PET) fabric by seeding method to develop hierarchical roughness structure. XRD and XPS analysis show the presence of crystalline ZnO and chemical Zn species at the fiber surface at each stage of the process. Five series of samples with different seed concentrations have been realized, and their surface morphology and topography were characterized by AFM and SEM. Increasing seed concentrations lead to samples with superhydrophilic properties. Not only the water contact angle at fabric surface tends to zero but also the water capillary diffusion inside fabric is faster. Nanostructuration affects the structure inside the fabric, and further experiments with decane liquid have been made to get a better understanding of this effect. To study the superhydrophobicity, nanorods treated samples were modified with octadecyltrimethoxysilane (ODS) by two method; solution deposition and vapor deposition. The superhydrophobicity was characterized by measuring the water contact angle and water sliding angle with 5 µl water droplet. The samples modified with ODS by vapor deposition showed higher water contact angles and low water sliding angle than the ones modified with solution method. The lotus effect has been well correlated with the surface morphology of the nanorods structured fibers. The application of the Cassie-Baxter equation is discussed.

New antibacterial microporous CaP materials loaded with phages for prophylactic treatment in bone surgery.

Hydroxyapatite and beta-tricalcium phosphate (ß-TCP) are materials commonly used in bone repair. The most important problem occurring in bone repair surgery is bacterial infection which is usually overcome by treatment with antibiotics. Currently, emergence of multidrug resistant strains has led to development of alternative treatments such as phage therapy. Phages are bacterial viruses with several advantages over chemotherapy such as specificity of bacterial strain, no side effects and fast response. This study evaluates the possibility of loading hydroxyapatite and ß-tricalcium phosphate ceramics used as bone substitutes with phages and their antibacterial activity against Escherichia coli K12. The majority of phages were retained in dense and microporous HA and ß-TCP samples during at least 6 days suggesting the occurrence of strong interaction between phages and ceramics, which did not prevent bacterial attachment and lysis. This study has shown for the first time that phage loaded ceramics could be used in prophylactic treatments.