Search

Bioactive materials, able to induce hydroxyapatite precipitation in contact with body fluids, are of great interest for their bone bonding capacity.. The aim of this paper is to compare bioactive materials with different surface features to verify the mechanisms of action and the relationship with kinetics and type of precipitated hydroxyapatite over time. Four different surface treatments for Ti/Ti6Al4V alloy and a bioactive glass were selected and a different mechanism of bioactivity is supposed for each of them. Apart from the conventional techniques (FESEM, XPS and EDX), less common characterizations (zeta potential measurements on solid surfaces and FTIR chemical imaging) were applied. The results suggest that the OH groups on the surface have several effects: the total number of the OH groups mainly affects hydrophilicity of surfaces, while the isoelectric points, surface charge and ions attraction mainly depend on OH acidic/basic strength. Kinetics of hydroxyapatite precipitation is faster when it involves a mechanism of ion exchange while it is slower when it is due to electrostatic effects. The electrostatic effect cooperates with ion exchange and it speeds up kinetics of hydroxyapatite precipitation. Different bioactive surfaces are able to differently induce precipitation of type A and B of hydroxyapatite, as well as different degrees of crystallinity and carbonation. The bone is made of a ceramic phase (a specific type of hydroxyapatite), a network of collagen fibers and the biological tissue. A strong bond of an orthopedic or dental implant with the bone is achieved by bioactive materials where precipitation and growth of hydroxyapatite occurs on the implant surface starting from the ions in the physiological fluids. Several bioactive materials are already known and used, but their mechanism of action is not completely known and the type of precipitated hydroxyapatite not fully investigated. In this work, bioactive titanium and bioglass surfaces are compared through conventional and innovative methodologies. Different mechanisms of bioactivity are identified, with different kinetics and the materials are able to induce precipitation of different types of hydroxyapatite, with different degree of crystallinity and carbonation. Image, graphical abstract [ABSTRACT FROM AUTHOR]

A glass–ceramic composition has been studied to realise a highly bioactive material, suitable for stimulate the bone regeneration, which has been subjected to a patented ion exchange process with silver ions, to impart antibacterial properties. The obtained material has been characterised by SEM, EDS and XRD analyses, before and after the introduction of Ag+ ions, and has been subjected to mechanical tests. Ag+ release was verified by GF-AAS analysis. The influence of silver on material wettability and bioactivity was evaluated through contact angle measurements and in vitro test on SBF solution. Finally, biocompatibility with osteoblast like cells and antibacterial test on Staphylococcus Aureus, have been realised to demonstrate the effective antimicrobial behaviour and the safety of silver doped glass–ceramic. On the basis of this study, it was evinced that ion exchange technique, optimised on glasses in previous research works, allows the controlled introduction of Ag+ ions and can be transferred on medical devices totally or partially realised with bioactive glass–ceramic. [ABSTRACT FROM AUTHOR]

Plasma spray bioactive glass ceramic coatings on metallic substrates have been characterised and modified by a patented ion exchange process in order to introduce silver ions onto their surface and confer antibacterial properties. Both treated and untreated materials have been analysed by means of SEM, EDS and XRD in order to verify the amount of introduced silver, and also after immersion in simulated body fluid in order to investigate bioactivity. The amount of silver released in simulated body fluid has been quantified by means of graphite furnace atomic adsorption spectrophotometry analysis. Finally cellular and microbiological test have been performed in order to verify material biocompatibility and antibacterial behaviour. [ABSTRACT FROM AUTHOR]

Activation of protein kinase C (PKC) by hyperglycemia is implicated in the pathogenesis of long-term diabetic complications. Monocyte activation and transformation into macrophages is a key step in the atherosclerotic process. Therefore, in this study, we sought to determine 1) the effect of hyperglycemia on monocyte PKC activity and on the distribution of Ca2+-dependent and diacylglycerol-sensitive PKC isoforms; and 2) whether the effects on these parameters are determined by hyperglycemia per se, independent of the diabetic state. The studies were performed in 19 type 2 diabetic patients and 14 control subjects. Plasma glucose concentration was higher and insulin sensitivity lower (both P < 0.01) in diabetic patients than in control subjects. Monocytes from diabetic patients showed similar cytosol PKC activity to those from control subjects but higher membrane PKC activity (78+/-6 vs. 50+/-5 pmol x min(-1) x mg(-1) protein; P < 0.01). A direct correlation was observed between fasting plasma glucose and membrane PKC activity (r2 = 0.4008, P = 0.0001). In contrast, a reciprocal correlation was observed between membrane PKC activity and insulin sensitivity index (r2 = 0.28, P < 0.05). Using immunoblotting analysis, we found that membrane beta2, but not alpha, isoform of PKC was more abundant in monocytes from diabetic patients. In diabetic patients, when euglycemia was acutely induced, membrane PKC activity decreased by approximately 42% and beta2 isoform by approximately 15%. In two normal subjects in whom hyperglycemia was induced, membrane PKC increased from 63 and 57 to 92 and 128.6 pmol x min(-1) x mg(-1) protein, respectively. This increase was associated with an increase in the membrane isoform beta2; alpha isoform was unchanged. We conclude that 1) monocytes express the glucose-sensitive beta2 isoform of PKC; 2) the prevailing plasma glucose acutely regulates the activity of the membrane PKC and the content of membrane PKC beta2 isoform; and 3) this effect appears to be a direct effect of glucose per se, since the phenomenon was observed in normal control subjects when hyperglycemia was induced. Monocyte PKC activation may account for the accelerated atherosclerosis of patients with type 2 diabetes. [ABSTRACT FROM AUTHOR]

In type 1 diabetic patients, acute loss of metabolic control is associated with increased blood flow, which is believed to favor the development of long-term complications. The mechanisms for inappropriate vasodilation are partially understood, but a role of endothelium-derived nitric oxide (NO) production can be postulated. We assessed, in type 1 diabetic patients, the effect of the acute loss of metabolic control and its restoration on forearm endothelial function in 13 type 1 diabetic patients who were studied under conditions of mild ketosis on two different occasions. In study 1, after basal determination, a rapid amelioration of the metabolic picture was obtained by insulin infusion. In study 2, seven type 1 diabetic patients underwent the same experimental procedure, except that fasting plasma glucose was maintained constant throughout. Basal plasma venous concentrations of nitrites/nitrates (NO2- + NO3-) were determined both before and after intravenous insulin infusion. Endothelium-dependent and -independent vasodilation of the brachial artery was assessed by an intra-arterial infusion of N(G)-monomethyl-L-arginine (L-NMMA) and sodium nitroprusside (SNP), respectively. The same parameters were determined in 13 control subjects at baseline conditions and during a hyperinsulinemic-euglycemic glucose clamp. Baseline forearm blood flow (4.89 +/- 0.86 vs. 3.65 +/- 0.59 ml x (100 ml tissue)(-1) x min(-1)) and NO2- + NO3- concentration (30 +/- 8 vs. 24 +/- 3 micromol/l) were higher in type 1 diabetic patients than in control subjects (P < 0.05). Insulin infusion was associated with lower forearm blood flow and plasma (NO2- + NO3-) concentration (P < 0.05), irrespective of the prevailing glucose levels, as compared with patients under ketotic conditions. The responses to L-NMMA were significantly lower in type 1 diabetic patients during euglycemia and hyperglycemic hyperinsulinemia (-11 +/- 5 and -10 +/- 4%, respectively, of the ratio of the infused arm to the control arm) than in control subjects at baseline (-18 +/- 6%, P < 0.05) and during hyperinsulinemia (-32 +/- 11%, P < 0.01). We conclude that the acute loss of metabolic control is associated with a functional disturbance of the endothelial function characterized by hyperemia and increased NO release during ketosis and blunted NO-mediated vasodilatory response during restoration of metabolic control by intravenous insulin. This functional alteration is unlikely to be explained by hyperglycemia itself. [ABSTRACT FROM AUTHOR]

The aim of the present research is to obtain a multiscale topography (micro- and nano-texture) and a high hydroxylation degree on the surface of a dental implant, in order to get advantages for bone integration. Moreover, a specific protocol for verifying the mechanical resistance to friction during implantation of a modified implant surface was developed. An innovative and patented chemical surface treatment was successfully integrated with a traditional dual acid etching process for dental implants. The result is a multiscale surface topography (a nano-texture overlapped on a micro-porosity), together with a significant increase in the surface hydroxyl groups. The treatment is time and cost effective and it allows getting peculiar surface properties. The treated Ti implants are bioactive (they induce hydroxyapatite precipitation during soaking in simulated body fluid) and they show increased wettability and protein absorption ability, compared to the traditional dual-etched implants. Modified implants do not require particular storage conditions and can be sterilized by conventional techniques. An innovative protocol for the evaluation of the surface resistance to implantation friction was developed and it allowed verifying that both traditional dual-etched and innovative Ti surfaces are able to sustain implantation friction without surface damages. Innovative surfaces with multiscale topography (micro- and nano-texture), high hydroxylation degree and protein adsorption, bioactive and hydrophilic behavior, and high resistance to friction during implantation were developed. An effective method for comparing the resistance to friction of the surfaces of dental implants is proposed. [ABSTRACT FROM AUTHOR]