Effectiveness of Screw Surface Coating on the Stability of Zirconia Abutments After Cyclic Loading

Purpose: Different surface treatments have been developed in attempts to prevent the loosening of abutment screws. The aim of the current study was to compare the effectiveness of titanium alloy screws with tungsten-doped diamond-like carbon (W-DLC) coating and uncoated screws in providing stability to zirconia (ZrO2) ceramic abutments after cyclic loading. Materials and Methods: Twenty prefabricated ZrO2 ceramic abutments on their respective external-hex implants were divided into two groups of equal size according to the type of screw used: uncoated titanium alloy screw (Ti) or titanium alloy screw with W-DLC coating (W-DLC/Ti). The removal torque value (preload) of the abutment screw was measured before and after loading. Cyclic loading between 11 and 211 N was applied at an angle of 30 degrees to the long axis of the implants at a frequency of 15 Hz. A target of 0.5 x 10(6) cycles was defined. Group means were calculated and compared using analysis of variance and the F test (alpha=.05). Results: Before cyclic loading, the preload for Ti screws was significantly higher than that for W-DLC/Ti screws (P=.021). After cyclic loading, there was no significant difference between them (P=.499). Conclusions: Under the studied conditions, it can be concluded that, after cyclic loading, both abutment screws presented a significant reduction in the mean retained preload and similar effectiveness in maintaining preload. INT J ORAL MAXILLOFAC IMPLANTS 2012;27:1061-1067

Surface coating deterioration studies

This project is concerned with the deterioration of surface coatings as a result of weathering and exposure to a pollutant gas (in this case nitric oxide). Poly(vinyl chloride) (PVC) plastisol surface coatings have been exposed to natural and artificial weathering and a comparison of the effects of these two types of weathering has been made by use of various analytical techniques. These techniques have each been assessed as to their value in providing information regarding changes taking place in the coatings during ageing, and include, goniophotometry, micro-penetrometry, surface energy measurements, weight loss measurements, thermal analysis and scanning electron microscopy. The results of each of these studies have then been combined to show the changes undergone by PVC plastisol surface coatings during ageing and to show the effects which additives to the coatings have on their behaviour and in particular the effects of plasticiser, pigment and uv and thermal stabilisers. Finally a preliminary study of the interaction between five commercial polymers and nitric oxide has been carried out, the polymers being polypropylene, cellulose acetate butyrate, polystyrene, polyethylene terephthalate and polycarbonate. Each of the samples was examined using infra-red spectroscopy in the transmission mode.

Inorganic-organic hybrid polymers: Solution-processible coating materials for defined surface functionalization

A new class of inorganic-organic hybrid polymers could successfully been prepared by the combination of different polymerization techniques. The access to a broad range of organic polymers incorporated into the hybrid polymer was realized using two independent approaches.rnIn the first approach a functional poly(silsesquioxane) (PSSQ) network was pre-formed, which was capable to initiate a controlled radical polymerization to graft organic vinyl-type monomers from the PSSQ precursor. As controlled radical polymerization techniques atom transfer radical polymerization (ATRP), as well as reversible addition fragmentation chain transfer (RAFT) polymerization could be used after defined tuning of the PSSQ precursor either toward a PSSQ macro-initiator or to a PSSQ macro-chain-transfer-agent. The polymerization pathway, consisting of polycondensation of trialkoxy-silanes followed by grafting-from polymerization of different monomers, allowed synthesis of various functional hybrid polymers. A controlled synthesis of the PSSQ precursors could successfully be performed using a microreactor setup; the molecular weight could be adjusted easily while the polydispersity index could be decreased well below 2.rnThe second approach aimed to incorporate differently derived organic polymers. As examples, polycarbonate and poly(ethylene glycol) were end-group-modified using trialkoxysilanes. After end-group-functionalization these organic polymers could be incorporated into a PSSQ network.rnThese different hybrid polymers showed extraordinary coating abilities. All polymers could be processed from solution by spin-coating or dip-coating. The high amount of reactive silanol moieties in the PSSQ part could be cross-linked after application by annealing at 130° for 1h. Not only cross-linking of the whole film was achieved, which resulted in mechanical interlocking with the substrate, also chemical bonds to metal or metal oxide surfaces were formed. All coating materials showed high stability and adhesion onto various underlying materials, reaching from metals (like steel or gold) and metal oxides (like glass) to plastics (like polycarbonate or polytetrafluoroethylene).rnAs the material and the synthetic pathway were very tolerant toward different functionalities, various functional monomers could be incorporated in the final coating material. The incorporation of N-isopropylacrylamide yielded in temperature-responsive surface coatings, whereas the incorporation of redox-active monomers allowed the preparation of semi-conductive coatings, capable to produce smooth hole-injection layers on transparent conductive electrodes used in optoelectronic devices.rnThe range of possible applications could be increased tremendously by incorporation of reactive monomers, capable to undergo fast and quantitative conversions by polymer-analogous reactions. For example, grafting active esters from a PSSQ precursor yielded a reactive surface coating after application onto numerous substrates. Just by dipping the coated substrate into a solution of a functionalized amine, the desired function could be immobilized at the interface as well as throughout the whole film. The obtained reactive surface coatings could be used as basis for different functional coatings for various applications. The conversion with specifically tuned amines yielded in surfaces with adjustable wetting behaviors, switchable wetting behaviors or as recognition element for surface-oriented bio-analytical devices. The combination of hybrid materials with orthogonal reactivities allowed for the first time the preparation of multi-reactive surfaces which could be functionalized sequentially with defined fractions of different groups at the interface. rnThe introduced concept to synthesis functional hybrid polymers unifies the main requirements on an ideal coating material. Strong adhesion on a wide range of underlying materials was achieved by secondary condensation of the PSSQ part, whereas the organic part allowed incorporation of various functionalities. Thus, a flexible platform to create functional and reactive surface coatings was achieved, which could be applied to different substrates. rn

Development of novel surface coatings based on acrylic copolymers

The present study describes the preparation of Vinyl acetate-Butyl acrylate copolymer lattices of varying compositions and solid contents by semicontinuous emulsion polymerization method. This copolymer lattices were used as binder to develop a new surface coating formulation. The properties of this surface coating were improved by using nano TiO2 colloidal sol as a pigment. Antimicrobial activity of surface coatings was improved by the addition of carboxymethyl chitosan as biocide. Uniformly dispersed tyre crumb was used to give a mat finish to the coating. The mechanical properties adhesive properties, thermal properties etc. of the coatings are presented in thesis.

Oxide surface modification: Synthesis and characterization of zirconia-coated alumina

Four aluminas were used as Supports for impregnation with a zirconium oxide with the aim to achieve a coating, without phase separation, between Support and modifier. The Supports were impregnated with different concentrations Of zirconium aqueous resin, obtained through the polymeric precursor method. After impregnation the samples were calcined and then characterized by XRD, which led to identification of crystalline zirconia in different concentrations from each support used. Using a simple geometric model the maximum amount Of Surface modifier Oxide required for the complete coating of a support with a layer of unit cells was estimated. According to this estimate, only the support should be identified below the limit proposed and crystalline zirconium oxide Should be identified above this limit when a complete coating is reached. The results obtained From XRD agree with the estimated values and to confirm the coating, the samples were also characterized by EDS/STEM, HRTEM, XPS, and XAS. The results showed that the zirconium oxide oil the Surface of alumina Support reached the coating in the limit of 15 Zr nm(-2), without the formation of the ZrO(2) phase. (c) 2009 Elsevier Inc. All rights reserved.

Osseointegration of implants with dendrimers surface characteristics installed conventionally or with Piezosurgery®. A comparative study in the dog

Aim: The first aim of the present experiment was to compare bone healing at implants installed in recipient sites prepared with conventional drills or a piezoelectric device. The second aim was to compare implant osseointegration onto surfaces with and without dendrimers coatings. Material and Methods: Six Beagles dogs were used in this study. Five implants with two different surfaces, three with a ZirTi® surface (zirconia sand blasted, acid etched), and two with a ZirTi®-modified surface with dendrimers of phosphoserine and polylysine were installed in the right side of the mandible. In the most anterior region (P2, P3), two recipient sites were prepared with drills, and one implant ZirTi® surface and one coated with dendrimers implants were installed at random. In the posterior region (P4 and M1), three recipient sites were randomly prepared: two sites with a Piezosurgery® instrument and one site with drill and two ZirTi® surface and one coated with dendrimers implants installed. Three months after the surgery, the animals were sacrificed for histological analysis. Results: No complications occurred during the healing period. Three implants were found not integrated and were excluded from analysis. However, n = 6 was obtained. The distance IS-B at the buccal aspect was 2.2 ± 0.8 and 1.8 ± 0.5 mm, while IS-C was 1.5 ± 0.9 and 1.4 ± 0.6 mm at the Piezosurgery® and drill groups, respectively. Similar values were obtained between the dendrimers-coated and ZirTi® surface implants. The BIC% values were higher at the drill (72%) compared to the Piezosurgery® (67%) sites. The BIC% were also found to be higher at the ZirTi® (74%) compared to the dendrimers-coated (65%) implants, the difference being statistically significant. Conclusion: This study has revealed that oral implants may osseointegrate equally well irrespective of whether their bed was prepared utilizing conventional drills with abundant cooling or Piezosurgery®. Moreover, the surface coating of implants with dendrimers phosphoserine and polylysine did not improve osseointegration. © 2012 John Wiley & Sons A/S.

Oxide surface modification: Synthesis and characterization of zirconia-coated alumina

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Safety by design: production of engineering surface modified nanomaterials

This PhD thesis focused on nanomaterial (NM) engineering for occupational health and safety, in the frame of the EU project “Safe Nano Worker Exposure Scenarios (SANOWORK)”. Following a safety by design approach, surface engineering (surface coating, purification process, colloidal force control, wet milling, film coating deposition and granulation) were proposed as risk remediation strategies (RRS) to decrease toxicity and emission potential of NMs within real processing lines. In the first case investigated, the PlasmaChem ZrO2 manufacturing, the colloidal force control applied to the washing of synthesis rector, allowed to reduce ZrO2 contamination in wastewater, performing an efficient recycling procedure of ZrO2 recovered. Furthermore, ZrO2 NM was investigated in the ceramic process owned by CNR-ISTEC and GEA-Niro; the spray drying and freeze drying techniques were employed decreasing NM emissivity, but maintaining a reactive surface in dried NM. Considering the handling operation of nanofibers (NFs) obtained through Elmarco electrospinning procedure, the film coating deposition was applied on polyamide non-woven to avoid free fiber release. For TiO2 NF the wet milling was applied to reduce and homogenize the aspect ratio, leading to a significant mitigation of fiber toxicity. In the Colorobbia spray coating line, Ag and TiO2 nanosols, employed to transfer respectively antibacterial or depolluting properties to different substrates, were investigated. Ag was subjected to surface coating and purification, decreasing NM toxicity. TiO2 was modified by surface coating, spray drying and blending with colloidal SiO2, improving its technological performance. In the extrusion of polymeric matrix charged with carbon nanotube (CNTs) owned by Leitat, the CNTs used as filler were granulated by spray drying and freeze spray drying techniques, allowing to reduce their exposure potential. Engineered NMs tested by biologists were further investigated in relevant biological conditions, to improve the knowledge of structure/toxicity mechanisms and obtain new insights for the design of safest NMs.

Quantum dot cytotoxicity in vitro: An investigation into the cytotoxic effects of a series of different surface chemistries and their core/shell materials

Abstract The aim of this study was to assess the effects of a series of different surface coated quantum dots (QDs) (organic, carboxylated [COOH] and amino [NH(2)] polytethylene glycol [PEG]) on J774.A1 macrophage cell viability and to further determine which part of the QDs cause such toxicity. Cytotoxic examination (MTT assay and LDH release) showed organic QDs to induce significant cytotoxicity up to 48 h, even at a low particle concentration (20 nM), whilst both COOH and NH(2) (PEG) QDs caused reduced cell viability and cell membrane permeability after 24 and 48 h exposure at 80 nM. Subsequent analysis of the elements that constitute the QD core, core/shell and (organic QD) surface coating showed that the surface coating drives QD toxicity. Elemental analysis (ICP-AES) after 48 h, however, also observed a release of Cd from organic QDs. In conclusion, both the specific surface coating and core material can have a significant impact on QD toxicity.

Comparison of biolimus eluted from an erodible stent coating with bare metal stents in acute ST-elevation myocardial infarction (COMFORTABLE AMI trial): rationale and design

Compared with bare metal stents (BMS), early generation drug-eluting stents (DES) reduce the risk of revascularisation in patients with ST-elevation myocardial infarction (STEMI) at the expense of an increased risk of very late stent thrombosis (ST). Durable polymer coatings for controlled drug release have been identified as a potential trigger for these late adverse events and this has led to the development of newer generation DES with durable and biodegradable polymer surface coatings with improved biocompatibility. In a recent all-comers trial, biolimus-eluting stents with a biodegradable polymer surface coating were found to reduce the risk of very late ST by 80% compared with sirolimus-eluting stents with durable polymer, which also translated into a lower risk of cardiac death and myocardial infarction (MI) beyond one year.

The impact of different nanoparticle surface chemistry and size on uptake and toxicity in a murine macrophage cell line

This study investigated the uptake, kinetics and cellular distribution of different surface coated quantum dots (QDs) before relating this to their toxicity. J774.A1 cells were treated with organic, COOH and NH2 (PEG) surface coated QDs (40 nM). Model 20 nm and 200 nm COOH-modified coated polystyrene beads (PBs) were also examined (50 microg ml(-1)). The potential for uptake of QDs was examined by both fixed and live cell confocal microscopy as well as by flow cytometry over 2 h. Both the COOH 20 nm and 200 nm PBs were clearly and rapidly taken up by the J774.A1 cells, with uptake of 20 nm PBs being relatively quicker and more extensive. Similarly, COOH QDs were clearly taken up by the macrophages. Uptake of NH2 (PEG) QDs was not detectable by live cell imaging however, was observed following 3D reconstruction of fixed cells, as well as by flow cytometry. Cells treated with organic QDs, monitored by live cell imaging, showed only a small amount of uptake in a relatively small number of cells. This uptake was insufficient to be detected by flow cytometry. Imaging of fixed cells was not possible due to a loss in cell integrity related to cytotoxicity. A significant reduction (p<0.05) in the fluorescent intensity in a cell-free environment was found with organic QDs, NH2 (PEG) QDs, 20 nm and 200 nm PBs at pH 4.0 (indicative of an endosome) after 2 h, suggesting reduced stability. No evidence of exocytosis was found over 2 h. These findings confirm that surface coating has a significant influence on the mode of NP interaction with cells, as well as the subsequent consequences of that interaction.

Titanium and hydroxyapatite coating of polyetheretherketone and carbon fiber-reinforced polyetheretherketone: A pilot study in sheep

Purpose: The purpose of this study was to evaluate the bone formation capability of polyetheretherketone (PEEK) and carbon fiber-reinforced PEEK (CFR-PEEK) implants coated with different titanium and hydroxyapatite plasma-sprayed layers after 2 and 12 weeks. Methods: In six sheep 108 implants were placed in the pelvis. Altogether six different surface modifications were tested. After 2 and 12 weeks, n = 3 implants per group were examined histologically and n = 6 implants per group were tested by a pull-out test. Results: Biomechanically (p = 0.001) as well as histologically (p > 0.05) surface coating of PEEK/CFR-PEEK led to an increase of osseointegration from 2 to 12 weeks. After 12 weeks, coated implants demonstrated significant (p < 0.001) higher pull-out values in comparison to uncoated implants. Overall, the double coating (titanium bond layer and hydroxyapatite top layer) showed the most favorable results after 2 and 12 weeks. Conclusions: Plasma-sprayed titanium and hydroxyapatite coatings on PEEK or CFR-PEEK demonstrated a significant improvement of osseointegration.

The Performance Characteristics of a Surface-Modified Cutting Tool

In the past, many papers have been presented which show that the coating of cutting tools often yields decreased wear rates and reduced coefficients of friction. Although different theories are proposed, covering areas such as hardness theory, diffusion barrier theory, thermal barrier theory, and reduced friction theory, most have not dealt with the question of how and why the coating of tool substrates with hard materials such as Titanium Nitride (TiN), Titanium Carbide (TiC) and Aluminium Oxide (Al203) transforms the performance and life of cutting tools. This project discusses the complex interrelationship that encompasses the thermal barrier function and the relatively low sliding friction coefficient of TiN on an undulating tool surface, and presents the result of an investigation into the cutting characteristics and performance of EDMed surface-modified carbide cutting tool inserts. The tool inserts were coated with TiN by the physical vapour deposition (PVD) method. PVD coating is also known as Ion-plating which is the general term of the coating method in which the film is created by attracting ionized metal vapour in this the metal was Titanium and ionized gas onto negatively biased substrate surface. Coating by PVD was chosen because it is done at a temperature of not more than 5000C whereas chemical Vapour Deposition CVD process is done at very high temperature of about 8500C and in two stages of heating up the substrates. The high temperatures involved in CVD affects the strength of the (tool) substrates. In this study, comparative cutting tests using TiN-coated control specimens with no EDM surface structures and TiN-coated EDMed tools with a crater-like surface topography were carried out on mild steel grade EN-3. Various cutting speeds were investigated, up to an increase of 40% of the tool manufacturer’s recommended speed. Fifteen minutes of cutting were carried out for each insert at the speeds investigated. Conventional tool inserts normally have a tool life of approximately 15 minutes of cutting. After every five cuts (passes) microscopic pictures of the tool wear profiles were taken, in order to monitor the progressive wear on the rake face and on the flank of the insert. The power load was monitored for each cut taken using an on-board meter on the CNC machine to establish the amount of power needed for each stage of operation. The spindle drive for the machine is an 11 KW/hr motor. Results obtained confirmed the advantages of cutting at all speeds investigated using EDMed coated inserts, in terms of reduced tool wear and low power loads. Moreover, the surface finish on the workpiece was consistently better for the EDMed inserts. The thesis discusses the relevance of the finite element method in the analysis of metal cutting processes, so that metal machinists can design, manufacture and deliver goods (tools) to the market quickly and on time without going through the hassle of trial and error approach for new products. Improvements in manufacturing technologies require better knowledge of modelling metal cutting processes. Technically the use of computational models has a great value in reducing or even eliminating the number of experiments traditionally used for tool design, process selection, machinability evaluation, and chip breakage investigations. In this work, much interest in theoretical and experimental investigations of metal machining were given special attention. Finite element analysis (FEA) was given priority in this study to predict tool wear and coating deformations during machining. Particular attention was devoted to the complicated mechanisms usually associated with metal cutting, such as interfacial friction; heat generated due to friction and severe strain in the cutting region, and high strain rates. It is therefore concluded that Roughened contact surface comprising of peaks and valleys coated with hard materials (TiN) provide wear-resisting properties as the coatings get entrapped in the valleys and help reduce friction at chip-tool interface. The contributions to knowledge: a. Relates to a wear-resisting surface structure for application in contact surfaces and structures in metal cutting and forming tools with ability to give wear-resisting surface profile. b. Provide technique for designing tool with roughened surface comprising of peaks and valleys covered in conformal coating with a material such as TiN, TiC etc which is wear-resisting structure with surface roughness profile compose of valleys which entrap residual coating material during wear thereby enabling the entrapped coating material to give improved wear resistance. c. Provide knowledge for increased tool life through wear resistance, hardness and chemical stability at high temperatures because of reduced friction at the tool-chip and work-tool interfaces due to tool coating, which leads to reduced heat generation at the cutting zones. d. Establishes that Undulating surface topographies on cutting tips tend to hold coating materials longer in the valleys, thus giving enhanced protection to the tool and the tool can cut faster by 40% and last 60% longer than conventional tools on the markets today.