On the Potential of Bulk Metallic Glasses for Dental Implantology: Case Study on Ti40Zr10Cu36Pd14.

Ti40Zr10Cu36Pd14 Bulk Metallic Glass (BMG) appears very attractive for future biomedical applications thanks to its high glass forming ability, the absence of toxic elements such as Ni, Al or Be and its good mechanical properties. For the first time, a complete and exhaustive characterization of a unique batch of this glassy alloy was performed, together with ISO standard mechanical tests on machined implant-abutment assemblies. The results were compared to the benchmark Ti-6Al-4V ELI (Extra-Low-Interstitial) to assess its potential in dental implantology. The thermal stability, corrosion and sterilization resistance, cytocompatibility and mechanical properties were measured on samples with a simple geometry, but also on implant-abutment assemblies' prototypes. Results show that the glassy alloy exhibits a quite high thermal stability, with a temperature range of 38 °C between the glass transition and crystallization, a compressive strength of 2 GPa, a certain plastic deformation (0.7%), a hardness of 5.5 GPa and a toughness of 56 MPa.√m. Moreover, the alloy shows a relatively lower Young's modulus (96 GPa) than the Ti-6Al-4V alloy (110-115 GPa), which is beneficial to limit bone stress shielding. The BMG shows a satisfactory cytocompatibility, a high resistance to sterilization and a good corrosion resistance (corrosion potential of -0.07 V/SCE and corrosion current density of 6.0 nA/cm²), which may ensure its use as a biomaterial. Tests on dental implants reveal a load to failure 1.5-times higher than that of Ti-6Al-4V and a comparable fatigue limit. Moreover, implants could be machined and sandblasted by methods usually conducted for titanium implants, without significant degradation of their amorphous nature. All these properties place this metallic glass among a promising class of materials for mechanically-challenging applications such as dental implants.

Effect of nanoclay addition on physical, chemical, optical and biological properties of experimental dental resin composites.

OBJECTIVE: To prepare organically modified montmorillonite (OM MMT) and assess mechanical, physical, chemical and biological effects of its introduction into resin-composites. METHODS: Natural MMT clay was modified by a methacrylate functionalized quaternary ammonium intercalating agent. Interlayer distance was measured by X-ray diffraction. Dental composites were then prepared with x=0, 1, 2.5, 5 or 7.5wt.% of OM MMT, (75-x) wt.% of silanated barium glass and 25wt.% of methacrylate based matrix). Relative weight loss was measured and the effect of the substitution on mechanical properties was studied by dynamic mechanical analysis and hardness tests. Properties of resin composites were evaluated in terms of water sorption, light transmittance, biological tests and by high-performance liquid chromatography (HPLC). RESULTS: Resin based composites with well-dispersed organically modified MMT were successfully prepared. There were no significant weight loss differences shown by TGA within all samples. The DMA analysis showed that the introduction of clays have a beneficial effect in increasing the storage and elastic modulus of composites. Clay presence was shown to interfere with the blue light transmittance, affecting Vickers hardness and water sorption levels. The amount of released monomers measured from extracts was below expected levels for this type of materials and biological tests show satisfactory cell compatibility. SIGNIFICANCE: This paper reports the successful functionalization of MMT by a methacrylate group and further incorporation in experimental dental composites. Physical and biological results show a potential interest to the application of nanoclays into dental resin composites.

Direct silanization of zirconia for increased biointegration.

High-performance bioinert ceramics such as zirconia have been used for biomedical devices since the early seventies. In order to promote osseointegration, the historical solution has been to increase the specific surface of the implant through roughness. Nevertheless these treatments on ceramics may create defects at the surface, exposing the material to higher chances of early failure. In zirconia, such treatments may also affect the stability of the surface. More recently, the interest of improving osseointegration of implants has moved the research focus towards the actual chemistry of the surface. Inspired by this, we have adapted the current knowledge and techniques of silica functionalization and applied it to successfully introduce 3-aminopropyldimethylethoxy silane (APDMES) directly on the surface of zirconia (3Y-TZP). We used plasma of oxygen to clean the surface and promote hydroxylation of the surface to increase silane density. The samples were extensively characterized by means of X-ray photoelectron spectroscopy (XPS) and contact angle, mechanically tested and its cytotoxicity was evaluated through cell adhesion and proliferation tests. Additionally, aging was studied to discard negative effects of the treatment on the stability of the tetragonal phase. No adverse effect was found on the mechanical response of treated samples. In addition, plasma-treated samples exhibited an unexpectedly higher resistance to aging. Finally, silane density was 35% lower than the one reported in literature for silica. However cells displayed a qualitatively higher spreading in opposition to the rounder appearance of cells on untreated zirconia. These results lay the foundations for the next generation of zirconia implants with biologically friendlier surfaces. STATEMENT OF SIGNIFICANCE: The use of zirconia-based ceramics in biomedical devices is broad and well accepted, especially in dental implants. However, they do not bond naturally to bone, therefore to ensure fixation surgeons typically rely on roughness at different scales, or on cements. Alternatively in this work we present a new perspective of surface modification through chemistry to enhance the interaction between surface and biological environment, without the downsides of roughness. This surface treatment is proposed for zirconia, which allowed a direct silanization of its surface and a higher cell attachment. The results of this research may open the possibility for the next generation of bioinert ceramic implants with more advanced tailored surfaces for increased osseointegration.

In vitro and in vivo evaluation of a polylactic acid-bioactive glass composite for bone fixation devices.

Poly(lactic acid) is nowadays among the most used bioabsorbable materials for medical devices. To promote bone growth on the material surface and increase the degradation rate of the polymer, research is currently focused on organic-inorganic composites by adding a bioactive mineral to the polymer matrix. The purpose of this study was to investigate the ability of a poly(L,DL-lactide)-Bioglass® (P(L,DL)LA-Bioglass(®) 45S5) composite to be used as a bone fixation device. In vitro cell viability testing of P(l,dl)LA based composites containing different amounts of Bioglass(®) 45S5 particles was investigated. According to the degradation rate of the P(L,DL)LA matrix and the cytocompatibility experiments, the composite with 30 wt % of Bioglass® particles seemed to be the best candidate for further investigation. To study its behavior after immersion in simulated physiological conditions, the degradation of the composite was analyzed by measuring its weight loss and mechanical properties and by proceeding with X-ray tomography. We demonstrated that the presence of the bioactive glass significantly accelerated the in vitro degradation of the polymer. A preliminary in vivo investigation on rabbits shows that the addition of 30 wt % of Bioglass(®) in the P(L,DL)LA matrix seems to trigger bone osseointegration especially during the first month of implantation. This composite has thus strong potential interest for health applications.

Mitochondrial expression of arginase II in male and female rat inner medullary collecting ducts.

Microdissected rat proximal straight tubules (PST) and inner medullary collecting ducts (IMCD) highly produce urea from l-arginine, supporting the expression of the mitochondrial arginase II. However, IMCD contain a very low density of mitochondria compared with PST. Recently, arginase II has been localized by immunohistochemistry in rat PST but not IMCD. This study was designed to verify whether rat IMCD express arginase II and to identify its subcellular localization. We developed an antibody raised against arginase II that allowed the detection of a band of 38 kDa corresponding to arginase II on immunoblots. In male and female rat kidneys, Western blot analyses revealed that arginase II was highly expressed in the inner medulla (IM), the outer stripe of the outer medulla (osOM), and the deep cortex. Immunocytochemistry demonstrated that arginase II was homogeneously expressed in IMCD. Proteins of the cytosolic and mitochondrial fractions extracted from osOM and IM and analyzed by Western blot showed that 86% of arginase II was associated with mitochondria. The molecular weight of arginase II was similar in the cytosolic and mitochondrial fractions. Immunoelectron microscopy confirmed the presence of arginase II in the mitochondria of IMCD. In conclusion, arginase II is expressed in mitochondria of male and female rat IMCD.

Localization and differential expression of arginase II in the kidney of male and female mice.

Arginase II (AII) has been almost exclusively studied in male mammalian kidneys. Our investigations were conducted to localize AII gene expression in the female mouse kidney, and to analyze the differential expression of AII gene at the transcriptional and translational levels in the kidneys of female and male mice. Total RNAs and soluble proteins extracted from renal zones and whole kidneys were analyzed by Northern and Western blots, respectively. Mitochondrial and cytosolic proteins were analyzed by Western blot. L-[guanidino-14C]arginine hydrolysis by AII was detected in microdissected tubules and the 14CO2 released from [14C]urea hydrolysis was quantified. The results of these experiments showed that: (1) both AII mRNA and protein were highly expressed in the deep cortex and the outer stripe of the outer medulla, (2) urea was produced mainly in the proximal straight tubules (PST), (3) the 38-kDa AII protein was more abundant in the mitochondria than the cytosol, and (4) the renal content of AII mRNA and protein was about three-fold higher in female than in male mice. In conclusion, in both genders, AII gene expression is restricted to the PST and localized into mitochondria. AII gene is differentially expressed in the kidney of female and male mice since higher levels of AII mRNA, protein and activity were observed in the kidneys of the former than those of the latter. Renal AII gene expression was gender-dependent in mice but not in rats. Finally, in the PST of females, L-arginine-derived ornithine may be a precursor for the renal production of L -glutamate and L-glutamine because high levels of AII, ornithine aminotransferase and glutamine synthetase are expressed in this nephron segment.