3D printed bioabsorbable composite scaffolds of poly (lactic acid)-tricalcium phosphate-ceria with osteogenic property for bone regeneration.

The fabrication of customized implants by additive manufacturing has allowed continued development of the personalized medicine field. Herein, a 3D-printed bioabsorbable poly (lactic acid) (PLA)- ß-tricalcium phosphate (TCP) (10 wt %) composite has been modified with CeO2 nanoparticles (CeNPs) (1, 5 and 10 wt %) for bone repair. The filaments were prepared by melt extrusion and used to print porous scaffolds. The nanocomposite scaffolds possessed precise structure with fine print resolution, a homogenous distribution of TCP and CeNP components, and mechanical properties appropriate for bone tissue engineering applications. Cell proliferation assays using osteoblast cultures confirmed the cytocompatibility of the composites. In addition, the presence of CeNPs enhanced the proliferation and differentiation of mesenchymal stem cells; thereby, increasing alkaline phosphatase (ALP) activity, calcium deposition and bone-related gene expression. Results from this study have shown that the 3D printed PLA-TCP-10%CeO2 composite scaffold could be used as an alternative polymeric implant for bone tissue engineering applications: avoiding additional/revision surgeries and accelerating the regenerative process.

Effect of Silicon Dioxide and Magnesium Oxide on the Printability, Degradability, Mechanical Strength and Bioactivity of 3D Printed Poly (Lactic Acid)-Tricalcium Phosphate Composite Scaffolds.

BACKGROUND: Poly (lactic acid) (PLA) is a biodegradable polyester that has been exploited for a variety of biomedical applications, including tissue engineering. The incorporation of ß-tricalcium phosphate (TCP) into PLA has imparted bioactivity to the polymeric matrix. METHODS: We have modified a 90%PLA-10%TCP composite with SiO2 and MgO (1, 5 and 10 wt%), separately, to further enhance the material bioactivity. Filaments were prepared by extrusion, and scaffolds were fabricated using 3D printing technology associated with fused filament fabrication. RESULTS: The PLA-TCP-SiO2 composites presented similar structural, thermal, and rheological properties to control PLA and PLA-TCP. In contrast, the PLA-TCP-MgO composites displayed absence of crystallinity, lower polymeric molecular weight, accelerated degradation ratio, and decreased viscosity within the 3D printing shear rate range. SiO2 and MgO particles were homogeneously dispersed within the PLA and their incorporation increased the roughness and protein adsorption of the scaffold, compared to a PLA-TCP scaffold. This favorable surface modification promoted cell proliferation, suggesting that SiO2 and MgO may have potential for enhancing the bio-integration of scaffolds in tissue engineering applications. However, high loads of MgO accelerated the polymeric degradation, leading to an acid environment that imparted the composite biocompatibility. The presence of SiO2 stimulated mesenchymal stem cells differentiation towards osteoblast; enhancing extracellular matrix mineralization, alkaline phosphatase (ALP) activity, and bone-related genes expression. CONCLUSION: The PLA-10%TCP-10%SiO2 composite presented the most promising results, especially for bone tissue regeneration, due to its intense osteogenic behavior. PLA-10%TCP-10%SiO2 could be used as an alternative implant for bone tissue engineering application.

Hydroxyapatite and ß-TCP modified PMMA-TiO2 and PMMA-ZrO2 coatings for bioactive corrosion protection of Ti6Al4V implants.

Organic-inorganic hybrid coatings deposited on different types of metallic alloys have shown outstanding anticorrosive performance. The incorporation of osteoconductive additives such as hydroxyapatite (HA) and ß-tricalcium phosphate (ß-TCP) into organic-inorganic hybrid coatings is promising to improve the osseointegration and corrosion resistance of Ti6Al4V alloys, which are the most widely used metallic orthopedic and dental implant materials today. Therefore, this study evaluated the capability of poly(methyl methacrylate) (PMMA)-TiO2 and PMMA-ZrO2 hybrid coatings modified with HA and ß-TCP to act as bioactive and corrosion protection coatings for Ti6Al4V alloys. In terms of cell growth and mineralization, osteoblast viability, Ca+2 deposition and alkaline phosphatase assays revealed a significant improvement for the HA and ß-TCP modified coatings, compared to the bare alloy. This can be explained by an increase in nanoscale roughness and associated higher surface free energy, which lead to enhanced protein adsorption to promote osteoblast attachment and functions on the coatings. The effect of HA and ß-TCP additives on the anticorrosive efficiency was studied by electrochemical impedance spectroscopy (EIS) in a simulated body fluid (SBF) solution. The coatings presented a low-frequency impedance modulus of up to 430 GΩ cm2, 5 decades higher than the bare Ti6Al4V alloy. These findings provide clear evidence of the beneficial role of HA and ß-TCP modified hybrid coatings, improving both the biocompatibility and corrosion resistance of the Ti6Al4V alloy.

Dual Role of Lithium on the Structure and Self-Healing Ability of PMMA-Silica Coatings on AA7075 Alloy.

In this work, structural and active corrosion inhibition effects induced by lithium ion addition in organic-inorganic coatings based on poly(methyl methacrylate) (PMMA)-silica sol-gel coatings have been investigated. The addition of increasing amounts of lithium carbonate (0, 500, 1000, and 2000 ppm), yielded homogeneous hybrid coatings with increased connectivity of nanometric silica cross-link nodes, covalently linked to the PMMA matrix, and improved adhesion to the aluminum substrate (AA7075). Electrochemical impedance spectroscopy (EIS), performed in 3.5% NaCl aqueous solution, showed that the improved structural properties of coatings with higher lithium loadings result in an increased corrosion resistance, with an impedance modulus up to 50 GΩ cm2, and revealed that the lithium induced self-healing ability significantly improves their durability. Time-of-flight secondary ion mass spectrometry (ToF-SIMS) and X-ray photoelectron spectroscopy (XPS) suggest that the regeneration process occurs by means of lithium ions leaching from the adjacent coating toward the corrosion spot, which is restored by a protective layer of precipitated Li rich aluminum hydroxide species. An analogue mechanism has been proposed for artificially scratched coatings presenting an increase of the impedance modulus after salt spray test compared to the lithium free coating. These results evidence the active role of lithium ions in improving the passive barrier of the PMMA-silica coating and in providing through the self-restoring ability a significantly extended service life of AA7075 alloy exposed to saline environment.

Structure and properties of epoxy-siloxane-silica nanocomposite coatings for corrosion protection.

HYPOTHESIS: The fraction of the silica/siloxane phase is a crucial parameter, which determines the structure and thus the properties of epoxy-siloxane-silica hybrid coatings. A careful adjustment of the colloidal precursor formulation allows tuning the nanostructure towards a highly condensed and cross-linked hybrid nanocomposite, suitable as an efficient anticorrosive coating. EXPERIMENTS: Novel epoxy-siloxane-silica hybrids have been prepared through the curing reaction of poly(bisphenol A-co-epichlorohydrin) (DGEBA) with diethyltriamine (DETA) and (3-glycidoxypropyl)methyltriethoxysilane (GPTMS), followed by hydrolytic condensation of tetraethoxysilane (TEOS) and GPTMS. At a constant proportion of the organic phase, the effects of the varying molar proportions of siloxane (GPTMS) and silica (TEOS) on the film properties have been investigated. FINDINGS: A detailed structural analysis suggests for intermediate TEOS to GPTMS ratios a structure of highly condensed silica-siloxane domains covalently bonded to the embedding epoxy phase. The homogeneous distribution of the quasi-spherical sub-nonmetric silica-siloxane nodes is in agreement with low surface roughness (<5 nm), observed by atomic force microscopy. This dense nanostructure results in high thermal stability (>300 °C), strong adhesion to steel substrate and excellent barrier property in saline solution, with corrosion resistance in the GΩ cm2 range.

A Comparative Study on Graphene Oxide and Carbon Nanotube Reinforcement of PMMA-Siloxane-Silica Anticorrosive Coatings.

Carbon nanotubes (CNTs) and graphene oxide (GO) have been used to reinforce PMMA-siloxane-silica nanocomposites considered to be promising candidates for environmentally compliant anticorrosive coatings. The organic-inorganic hybrids were prepared by benzoyl peroxide (BPO)-induced polymerization of methyl methacrylate (MMA) covalently bonded through 3-(trimethoxysilyl)propyl methacrylate (MPTS) to silica domains formed by hydrolytic condensation of tetraethoxysilane (TEOS). Single-walled carbon nanotubes and graphene oxide nanosheets were dispersed by surfactant addition and in a water/ethanol solution, respectively. These were added to PMMA-siloxane-silica hybrids at a carbon (CNT or GO) to silicon (TEOS and MPTS) molar ratio of 0.05% in two different matrices, both prepared at BPO/MMA molar ratios of 0.01 and 0.05. Atomic force microscopy and scanning electron microscopy showed very smooth, homogeneous, and defect-free surfaces of approximately 3-7 µm thick coatings deposited onto A1020 carbon steel by dip coating. Mechanical testing and thermogravimetric analysis confirmed that both additives CNT and GO improved the scratch resistance, adhesion, wear resistance, and thermal stability of PMMA-siloxane-silica coatings. Results of electrochemical impedance spectroscopy in 3.5% NaCl solution, discussed in terms of equivalent circuits, showed that the reinforced hybrid coatings act as a very efficient anticorrosive barrier with an impedance modulus up to 1 GΩ cm(2), approximately 5 orders of magnitude higher than that of bare carbon steel. In the case of GO addition, the high corrosion resistance was maintained for more than 6 months in saline medium. These results suggest that both carbon nanostructures can be used as structural reinforcement agents, improving the thermal and mechanical resistance of high performance anticorrosive PMMA-siloxane-silica coatings and thus extending their application range to abrasive environments.