| 1. |
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| 2. |
- Bang, Le T., et al.
(författare)
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Synthesis and assessment of metallic ion migration through a novel calcium carbonate coating for biomedical implants
- 2020
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Ingår i: Journal of Biomedical Materials Research. Part B - Applied biomaterials. - : Wiley. - 1552-4973 .- 1552-4981. ; 108:2, s. 429-438
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Tidskriftsartikel (refereegranskat)abstract
- Titanium (Ti) implants are commonly regarded as well accepted by the body. However, metal ion release is still a cause for concern. A small decrease in pH, which can be caused by inflammation, may produce a large increase in the corrosion rate of Ti implants. Coating the alloy with a buffer layer could have a significant protective effect. In this study, a calcium carbonate coating was developed on commercially pure Ti and a Ti-6Al-4V alloy through a hydrothermal treatment of previously NaOH-treated surfaces in calcium-citric acid chelate complexes. The results showed that a superstructured calcite coating layer formed on the Ti substrate after treatment at 170 degrees C for 3 hr. The coating was approx. 1 mu m thick and covered the substrate surface uniformly. When prolonging the hydrothermal treatment from 5 hr to 24 hr, the rhombohedral structure of calcite was observed in addition to the superstructure of calcite. Dissolution test results showed no significant differences in solution pH between the coated- and un-coated samples. However, the CaCO3 coating reduced by approx. 2-5 times the Ti and V ion release from the substrate as compared to the uncoated material, at pH 4. CaCO3 and hydroxyapatite (HA) coatings gave nonsignificant effects at neutral pH although the HA coating showed a trend for better results at the longer time points. The reduction in metal ion release from the substrate and the buffering ability of the CaCO3 coating encourage further studies on this coating for clinical applications.
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| 3. |
- Corrêa Filho, Luimar N., 1985-
(författare)
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Functional properties of silicon nitride based materials for joint applications
- 2020
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Total hip and total knee replacements are generally successful procedures for patients suffering with pain due to bone fracture or diseases affecting the joints. However, the materials that are commonly used still have limitations. In particular, corrosion products and wear debris may give rise to negative body reactions.In this thesis, silicon nitride based materials were investigated for use in joint implants, namely as a coating for e.g. femoral heads and the metallic modular taper junction in hip implants, as well as a bulk bioceramic for joint applications. One of the main advantages of these materials is the potential to dissolve slowly in aqueous solutions, releasing only biocompatible ions.To understand the mechanical and wear properties of these materials, thin film coatings were deposited using magnetron-based techniques onto Si wafers and a CoCrMo alloy, the latter frequently used in biomedical implants. Coatings up to 8.8 µm thick were deposited on 2D flat discs as well as full 3D implant heads, following a CrN interlayer for improved adhesion. The chemical composition, microstructure, surface roughness, adhesion, wear resistance, and dissolution properties of the coatings were evaluated as a function of substrate rotation, bias voltage, target power as well as the addition of different elements.Results show that it is possible to produce coatings with mechanical properties and a wear performance similar to bulk ceramics and other ceramic coatings already evaluated in vivo. It was evident that a high coating density is needed, to avoid premature failure in an in vivo environment. The coating density, and stability over time in solution, was found to increase when a higher target power and process heating were used.New bulk silicon nitride materials containing only biocompatible additives, were evaluated for potential use in joint applications by wear tests for the first time, showing very low wear rates of the counter material.Silicon nitride coatings and bulk materials tested in this work showed promising results for further investigation and a basis for future application in joint bearings.
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| 4. |
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| 5. |
- Filho, Luimar Correa, et al.
(författare)
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The Effect of Coating Density on Functional Properties of SiNx Coated Implants
- 2019
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Ingår i: Materials. - : MDPI AG. - 1996-1944. ; 12:20
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Tidskriftsartikel (refereegranskat)abstract
- Ceramic coatings may be applied onto metallic components of joint replacements for improved wear and corrosion resistance as well as enhanced biocompatibility, especially for metal-sensitive patients. Silicon nitride (SiNx) coatings have recently been developed for this purpose. To achieve a high coating density, necessary to secure a long-term performance, is however challenging, especially for sputter deposited SiNx coatings, since these coatings are insulating. This study investigates the time-dependent performance of sputter-deposited SiNx based coatings for joint applications. SiNx coatings with a thickness in the range of 4.3–6.0 µm were deposited by reactive high power impulse magnetron sputtering onto flat discs as well as hip heads made of CoCrMo. SiNx compositional analysis by X-ray photoelectron spectroscopy showed N/Si ratios between 0.8 and 1.0. Immersion of the flat disks in fetal bovine serum solution over time as well as short-term wear tests against ultra-high molecular weight polyethylene (UHMWPE) discs showed that a high coating density is required to inhibit tribocorrosion. Coatings that performed best in terms of chemical stability were deposited using a higher target power and process heating.
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| 6. |
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| 7. |
- Filho, Luimar, et al.
(författare)
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The effect of N, C, Cr, and Nb content on silicon nitride coatings for joint applications
- 2020
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Ingår i: Materials. - : MDPI AG. - 1996-1944. ; 13:8
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Tidskriftsartikel (refereegranskat)abstract
- Ceramic coatings are an alternative to achieve or maintain a high wear resistance of metallic surfaces, and simultaneously allow for a reduction in metal ion release. Silicon nitride based (SiNx) coatings deposited by high power impulse magnetron sputtering (HiPIMS) have shown potential for use in joint implants seen from an improved chemical stability in combination with a good adhesion. The aim of this study was to investigate the effect of N, C, Cr and Nb content on the tribocorrosive performance of 3.7 to 8.8 µm thick SiNx coatings deposited by HiPIMS onto CoCrMo discs to improve the mechanical properties and/or chemical stability of SiNx .Coating composition was evaluated by X-ray photoelectron spectroscopy (XPS) and the surface roughness by Vertical Scanning Interferometry (VSI). Hardness and Young’s modulus were investigated by nanoindentation and coating adhesion was measured by scratch tests. Multidirectional wear tests against UHMWPE pins were performed for 2 million cycles in bovine serum solution (25%) at 37°C, at an estimated contact pressure of 2.1 MPa.Coatings with a relatively low hardness tended to fail earlier in the wear test, due to chemical reactions and eventually dissolution, accelerated by the tribological contact. In fact, while no definite correlation could be observed between coating composition (N: 42.6-55.5 at%, C: 0-25.7 at%, Cr: 0 or 12.8 at%, and Nb: 0-24.5 at%) and wear performance, it was apparent that high-purity and/or -density coatings (i.e. low oxygen content and high nitrogen content) were desirable to prevent coating and/or counter surface wear. Coatings deposited with a higher energy fulfilled the target profile in terms of low surface roughness (Ra<20nm), adequate adhesion (Lc2>30N), chemical stability over time in the tribocorrosive environment, as well as low polymer wear, presenting potential for a future application in joint bearings.
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| 8. |
- Filho, Luimar, et al.
(författare)
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Towards Functional Silicon Nitride Coatings for Joint Replacements
- 2019
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Ingår i: Coatings. - : MDPI AG. - 2079-6412. ; 9:2
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Tidskriftsartikel (refereegranskat)abstract
- Silicon nitride (SiNx) coatings are currently under investigation as bearing surfaces for joint implants, due to their low wear rate and the good biocompatibility of both coatings and their potential wear debris. The aim of this study was to move further towards functional SiNx coatings by evaluating coatings deposited onto CoCrMo surfaces with a CrN interlayer, using different bias voltages and substrate rotations. Reactive direct current magnetron sputtering was used to coat CoCrMo discs with a CrN interlayer, followed by a SiNx top layer, which was deposited by reactive high-power impulse magnetron sputtering. The interlayer was deposited using negative bias voltages ranging between 100 and 900 V, and 1-fold or 3-fold substrate rotation. Scanning electron microscopy showed a dependence of coating morphology on substrate rotation. The N/Si ratio ranged from 1.10 to 1.25, as evaluated by X-ray photoelectron spectroscopy. Vertical scanning interferometry revealed that the coated, unpolished samples had a low average surface roughness between 16 and 33 nm. Rockwell indentations showed improved coating adhesion when a low bias voltage of 100 V was used to deposit the CrN interlayer. Wear tests performed in a reciprocating manner against Si3N4 balls showed specific wear rates lower than, or similar to that of CoCrMo. The study suggests that low negative bias voltages may contribute to a better performance of SiNx coatings in terms of adhesion. The low wear rates found in the current study support further development of silicon nitride-based coatings towards clinical application.
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| 9. |
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| 10. |
- Filho, Luimar, et al.
(författare)
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Wear performance of a new biocompatible silicon nitride for biomedical applications
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- Ceramics are used in bearings of joint implants due to their high wear resistance and biocompatibility. Silicon nitride (Si3N4) is a biomaterial with bacteriostatic properties, high wear resistance, it shows slow dissolution in aqueous environments and contains mainly biocompatible ions. In this work sintering additives SrO, MgO and SiO2 were used in order to gain improvement in biocompatibility, over the commonly used Al2O3 and Y2O3. This substitution may however have a substantial effect on the wear properties of the material, and the aim of the study was to evaluate these properties in a relevant setting. Si3N4 was sintered by spark plasma sintering in the shape of discs for later grinding and polishing. The wear resistance was evaluated by multidirectional pin-on-disc wear tests against ultra-high molecular weight polyethylene pins. Tests were performed in bovine serum solution at 37 °C for 2 million cycles. The surface roughness of the materials was measured by an optical surface profiler, phase composition by X-ray diffraction, surface morphology by scanning electron microscopy, and the pH of the wear lubricant was measured at intervals of half a million cycles. The surface roughness of the ceramic discs and UHMWPE pins was in accordance with the biomedical standard, and the XRD measurements and SEM images showed the presence of α- and β-phase silicon nitride. The multidirectional wear tests showed a low wear factor and a comparable coefficient of friction to previous work, showing promise for application in joint implants. No difference between the material groups could be found in terms of UHMWPE pin wear. However, the dissolution of the materials over time may be a concern for biotribological applications.
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| 11. |
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| 12. |
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| 13. |
- Kootala, Sujit, et al.
(författare)
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Reinforcing Mucus Barrier Properties with Low Molar Mass Chitosans
- 2018
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Ingår i: Biomacromolecules. - : American Chemical Society (ACS). - 1525-7797 .- 1526-4602. ; 19:3, s. 872-882
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Tidskriftsartikel (refereegranskat)abstract
- The mucus gel covers the wet epithelia that forms the inner lining of the body. It constitutes our first line of defense protecting the body from infections and other deleterious molecules. Failure of the mucus barrier can lead to the inflammation of the mucosa such as in inflammatory bowel diseases. Unfortunately, there are no effective strategies that reinforce the mucus barrier properties to recover or enhance its ability to protect the epithelium. Herein, we describe a mucus engineering approach that addresses this issue where we physically cross-link the mucus gel with low molar mass chitosan variants to reinforce its barrier functions. We tested the effect of these chitosans on mucus using in-lab purified porcine gastric mucins, which mimic the native properties of mucus, and on mucus-secreting HT29-MTX epithelial cell cultures. We found that the lowest molar mass chitosan variant (degree of polymerization of 8) diffuses deep into the mucus gels while physically cross-linking the mucin polymers, whereas the higher molar mass chitosan variants (degree of polymerization of 52 and 100) interact only superficially. The complexation resulted in a tighter mucin polymer mesh that slowed the diffusion of dextran polymers and of the cholera toxin B subunit protein through the mucus gels. These results uncover a new use for low molar mass mucoadhesive polymers such as chitosans as noncytotoxic mucosal barrier enhancers that could be valuable in the prevention and treatment of mucosal diseases.
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| 14. |
- López, Alejandro, 1983-, et al.
(författare)
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Morphology and adhesion of silicon nitride coatings upon soaking in fetal bovine serum
- 2018
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Ingår i: 15th International Symposium on Computer Methods in Biomechanics and Biomedical Engineering and 3rd Conference on Imaging and Visualization, Lisbon, March 26-29, 2018.
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Konferensbidrag (refereegranskat)abstract
- Total hip joint replacements are considered successful in providing patients with close- to-normal lives; however, revision surgeries still represent an individual and socioeconomic burden due to wear and failure of the implants, which occurs at a rate of 3-10% at 10 years. Therefore, eorts are being made to increase the lifespan of articial prostheses. Because of the impossibility to avoid wear debris, functional silicon nitride coatings are being developed due their low wearing, particle solubility and good biological response. However, a compromise needs to be found between coating reactivity and durability.A HIPIMS process was used to sputter a CrN interlayer followed by a SiNx top layer using 1- and 3-fold rotation in an industrial deposition system (CemeCon AG, Würselen, Germany). In order to measure the adhesion of the coatings to the cobalt-chromium-molybdenum substrates a scratch test was used, consisting of generating a scratch with a Rockwell C diamond stylus, at an increasing load from 0 to 100 N, at a displacement rate of 6mm/min. The samples were immersed in 25% fetal bovine serum solution to mimic synovial joint uid and scratched aer 0, 1, 3, 6 weeks periods in this solution. The cross-section of the coatings was assessed through Focused Ion Beam at 30kV for milling and 5kV for secondary electron imaging of the surface.The coatings demonstrated a high nitrogen content, previously shown to be benecial in terms of low dissolution rates. The deposition conditions and coating morphology were found to have an eect on the dissolution rate and thereby also the spallation failure of the coatings. These results are informative for the further development of these coatings into parts of functional 3D implants.
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| 15. |
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| 16. |
- Pettersson, Maria, et al.
(författare)
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Morphology and dissolution rate of wear debris from silicon nitride coatings
- 2016
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Ingår i: ACS Biomaterials Science & Engineering. - : American Chemical Society (ACS). - 2373-9878. ; 2:6, s. 998-1004
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Tidskriftsartikel (refereegranskat)abstract
- Silicon nitride (SiNx) coatings have recentlY been introduced as a potential material for joint implant bearing surfaces, but there is no data on wear debri morphology nor their dissolution rate, something that could play a central role to implant longevity. In this study, wear debris was generated in a ball-on-disc setup in simulated body fluid. After serum digestion the debris was analyzed with scanning electron microscopy and energy-dispersive X-ray spectroscopy. The particle dissolution rate was evaluated using inductively coupled plasma techniques, on model SiNx particlEs. The wear debris from SiNx coatings was found to be round, in the nm range and formed agglomerates in the submicrometer to micrometer range. Model particles dissolved in simulated body fluid at a rate of: c(t) = 39.45[1 - exp(-1.11 X 10(-6) t], where [c(t)] = mg/L and [t] = s. This study can be used as a preliminary prediction of size, shape, and dissolution rate of wear debris from SiNx coatings.
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| 17. |
- Wei, Zheng, 1988-, et al.
(författare)
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Mater release from a biomedical CoCrMo alloy in mixed protein solutions under static and sliding conditions – effects of protein aggregation and metal precipitation
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- Biomedical materials made of cobalt-chromium-molybdenum (CoCrMo) alloys are commonly used in artificial prostheses and dental implants that are exposed to friction and load. The release of Co, Cr, and Mo from these surfaces is governed by physical, chemical, and electrochemical processes. The extent of measured metal release from biomedical CoCrMo alloys into mixed protein solutions may be influenced by protein aggregation and metal precipitation effects. Metal release from, and the surface composition of, a CoCrMo alloy was investigated in physiological relevant solutions (phosphate buffered saline, PBS, with varying concentrations of fibrinogen from bovine plasma and/or bovine serum albumin) at pH 7.3 in static and sliding conditions for time periods between 1 and 24 hours. Cr was strongly enriched in the surface oxide of CoCrMo in all solutions, which corresponded to metal release dominated by Co. PBS and the proteins could induce significant precipitation of metals and protein aggregates, which resulted in strongly underestimated released amounts of Co and Cr, but not Mo, especially under sliding conditions. Protein aggregates were found to precipitate on the surface of CoCrMo under static conditions. The friction coefficient was greater in PBS containing physiologically relevant concentrations of fibrinogen as compared to PBS alone.
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| 18. |
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