Biomedical Grade Research Articles

Wear Resistant Nanocomposites Based on Biomedical Grade UHMWPE Paraffin Oil and Carbon Nano-Filler: Preliminary Biocompatibility and Antibacterial Activity Investigation.

In the present paper, we investigate the effectiveness of nanocomposites (composed of ultra-high molecular weight polyethylene (UHMWPE) mixed with carbon nano-filler (CNF) and medical grade paraffin oil (PO), from the biological point of view. Wear measurements were carried out without (air) and with lubricant (distilled water, natural, and artificial lubricant), and antibacterial activity and cytotoxicity were evaluated. The results highlighted that the presence of CNF is important in the nanocomposite formulation because it reduces the wear rate and prevents oxidative degradation during its processing. An amount of 1.0 wt % of CNF is best because it reaches the optimal distribution within the polymeric matrix, resulting in the best wear resistant, bio-active, and anti-bacterial nanocomposite among all investigated samples.

Studies of combined NO-eluting/CD47-modified polyurethane surfaces for synergistic enhancement of biocompatibility

The blood compatibility of various intravascular (IV) devices (e.g., catheters, sensors, etc.) is compromised by activation of platelets that can cause thrombus formation and device failure. Such devices also carry a high risk of microbial infection. Recently, nitric oxide (NO) releasing polymers/devices have been proposed to reduce these clinical problems. CD47, a ubiquitously expressed transmembrane protein with proven anti-inflammation/anti-platelet properties when immobilized on polymeric surfaces, is a good candidate to complement NO release in both effectiveness and longevity. In this work, we successfully appended CD47 peptides (pepCD47) to the surface of biomedical grade polyurethane (PU) copolymers. SIRPα binding and THP-1 cell attachment experiments strongly suggested that the pepCD47 retains its biological properties when bound to PU films. In spite of the potentially high reactivity of NO toward various amino acid residues in CD47, the efficacy of surface-immobilized pepCD47 to prevent inflammatory cell attachment was not inhibited after being subjected to a high flux of NO for three days, demonstrating excellent compatibility of the two species. We further constructed a CD47 surface immobilized silicone tubing filled with NO releasing S-nitrosoglutathione/ascorbic acid (GSNO/AA) solution for synergistic biocompatibility evaluation. Via an ex vivo Chandler loop model, we demonstrate for the first time that NO release and CD47 modification could function synergistically at the blood/material interface and produce greatly enhanced anti-inflammatory/anti-platelet effects. This concept should be readily implementable to create a new generation of thromboresistant/antimicrobial implantable devices.

Surface Modifications Induced in UHMWPE Based Nanocomposites during the Ageing in Simulated Synovial Fluid

AbstractSimulated synovial fluid (SSF) is a fluid that approximates the biological environment of a human joint because it is based on hyaluronic acid. The soaking of biomedical grade ultra high molecular weight polyethylene (UHMWPE) in SSF for longer periods results in ageing of the polymer, hardening the surface, and improving the surface roughness and wettability. This is because SSF progressively penetrates inside the polymer inducing oxidative degradation. Nanocomposite of UHMWPE reinforced with carbon nanofiller (CF) exhibits a higher resistance to the degradation of SSF compared to the control sample (pure UHMWPE).CNF, homogeneously distributed in the polymeric matrix, closes the pores among the grain boundaries of UHMWPE matrix, hindering the SSF insertion within it and its degrading action.

Finite element simulation of orthogonal machining of biomedical grade Co–Cr–Mo alloy

Cobalt–chromium–molybdenum (Co–Cr–Mo) alloys are used extensively within the biomedical industry for hip, knee and shoulder prostheses. These components are manufactured using a range of different processes which includes machining. However, material properties such as high hardness, high wear resistance and strain rate hardening classifies these alloys as difficult to cut materials. Finite Element (FE) Modelling of machining processes can reduce the number of machining tests required for optimisation. The aim of the present work was to develop a FE model that can predict the orthogonal forces during the machining of biomedical grade Co–Cr–Mo alloy. To achieve this, it was necessary to develop the constitutive material model for this alloy. A modified Zerilli–Armstrong model was found to have the greatest predication capability compared to a modified Johnson–Cook and a strain compensated Arrhenius-type model. An orthogonal cutting finite element model was developed using Deform 3D over a range of different feed rates and cutting speeds. The model predicted the cutting forces to a high degree of accuracy (less than 5% error) over a range of different feed rates at low cutting speeds.

Tribocorrosion response of duplex layered CoCrMoC/CrN and CrN/CoCrMoC coatings on implant grade 316LVM stainless steel

The objective of this work was to improve the tribocorrosion performance of biomedical grade 316LVM stainless steel via the application of duplex layered coatings. Two different PVD coatings were deposited via magnetron sputtering: (1) an underlying CoCrMo carbon S-phase layer followed by an outermost CrN layer designated as CrN/S and; (2) an underlying CrN layer followed by an outermost CoCrMo carbon S-phase designated as S/CrN. Tribocorrosion of the coated and uncoated 316LVM was studied against an alumina ball which was made to slide in a reciprocation motion in Ringer's solution. The contributions of wear, corrosion and their synergy were elucidated by performing tests under open circuit, cathodic and anodic potential conditions. The resultant wear scars were analysed via SEM, EDS, optical microscopy and contact profilometry. Both coatings displayed superior tribocorrosion response to AISI 316LVM with CrN/S exhibiting the best performance. CrN/S displayed lowest coefficient of friction under all electrochemical conditions (~0.10–0.15) and a material loss under anodic condition with a 93% decrease when compared to 316LVM. The CrN/S scars exhibited a smooth morphology under all test conditions in contrast with the other two test materials which displayed shearing marks oriented along the sliding direction under OCP and anodic conditions. By considering the resultant scar morphologies, a hypothesis is being proposed to explain the tribocorrosion degradation mechanisms encountered.

Electrochemically reduced graphene oxide on CoCr biomedical alloy: Characterization, macrophage biocompatibility and hemocompatibility in rats with graphene and graphene oxide.

Electrochemically reduced graphene oxide (ErGO) films on a biomedical grade CoCr alloy have been generated and characterized in order to study their possible application for use on joint prostheses. The electrodeposition process was performed by cyclic voltammetry. The characterization of the ErGO films on CoCr alloys by XPS revealed sp2 bonding and the presence of CO and CO residual groups in the graphene network. Biocompatibility studies were performed with mouse macrophages J774A.1 cell cultures measured by the ratio between lactate dehydrogenase and mitochondrial activities. An enhancement in the biocompatibility of the CoCr with the ErGO films was obtained, a result that became more evident as exposure time increased. Macrophages on the CoCr with the ErGO were well-distributed and conserved the characteristic cell shape. In addition, vimentin expression was unaltered in comparison with the control, results that indicated an improvement in the CoCr biocompatibility with the ErGO on the material surface. The in vivo response of graphene and graphene oxide was assessed by intraperitoneal injection in wistar rats. Red blood cells are one of the primary interaction sites so hemocompatibility tests were carried out. Rats inoculated with graphene and graphene oxide showed red blood cells of smaller size with a high content in hemoglobin.

3D-additive deposition of an antibacterial and osteogenic silicon nitride coating on orthopaedic titanium substrate

A 3D-additive manufacturing approach produced a dense Si3N4 ceramic coating on a biomedical grade commercially pure titanium (cp-Ti) substrate by an automatic laser-sintering procedure. Si3N4 coatings could be prepared with thicknesses from the single to the tens of microns. A coating thickness, t = 15 ± 5 μm, was selected for this study, based on projections of homogeneity and scratching resistance. The Si3N4 coating met the 20 N threshold required for biomaterial applications, according to the standard scratch testing (ASTM C1624-05). The Si3N4 coating imparted both the antibacterial and osteogenic properties of bulk Si3N4 to the cp-Ti substrate. Both properties were comparable to those previously described for bulk Si3N4 biomedical implants. The newly developed Si3N4-coating was applied to commercially available Ti-alloy acetabular shells for total hip arthroplasty. A “glowing” test based on luciferase gene transformation was applied to visualize the colonization of gram-negative Escherichia coli on Si3N4-coated and uncoated Ti-alloy acetabular shells. The results showed that the coating technology conferred resistance to Staphylococcus epidermidis and Escherichia coli adhesion onto the bulk acetabular sockets.

Effect of nitrogen plasma treatment on the crystallinity and self-bonding of polyetheretherketone (PEEK) for biomedical applications.

Polyetheretherketone (PEEK) is a thermoplastic material with outstanding properties and high potential for biomedical applications, including hermetic encapsulation of active implantable devices. Different biomedical grade PEEK films with initial degree of crystallinity ranging from 8% to 32% (with or without mineral filling) were inspected. PEEK surfaces were treated with nitrogen RF plasma and the effects on materials crystallinity and self‐bonding were evaluated. In particular, the relationship between auto‐adhesive properties and crystalline content of PEEK before and after plasma treatment was examined.PEEK samples showed different bonding strength depending on their degree of crystallinity, with higher self‐bonding performance of mineral‐filled semi‐crystalline films. XRD did not show any modification of the PEEK microstructure as a result of plasma treatment, excluding a significant influence of crystallinity on the self‐bonding mechanisms. Nevertheless, plasma surface treatment successfully improved the self‐bonding strength of all the PEEK films tested, with larger increase in the case of semi‐crystalline unfilled materials. This could be interpreted to the increase in chain mobility that led to interfacial interpenetration of the amorphous phase.

Strong Adhesives from Corn Protein and Tannic Acid

AbstractModern society is in great need of environmentally sustainable and low‐cost alternatives to some petroleum derived adhesives. To allow recycling and avoid pollution, adhesives for single use products including packaging are of particular interest. Potential candidates for such applications are the adhesive formulations of corn zein protein and tannic acid presented here. High strength adhesive bonding is found when the formulations are optimized with regard to composition, pH, and curing temperature. Bonding is tested on aluminum substrates using lap shear configurations. Adhesion strengths exceed the minimal bonding of zein‐only controls. Maximum adhesion for zein and tannic acid is as strong as commercial Super Glue when measured under similar conditions. The system forms nanometer and micrometer sized pores throughout the bulk adhesive. A low amount of tannic acid and neutral pH of the strongest adhesive make the corn zein–tannic acid system potentially appealing for cost efficient adhesives used in packaging, cosmetics, and other single use applications where biomedical grade purity is not required.

The influence of protein concentration, temperature and cathodic polarization on the surface status of CoCrMo biomedical grade alloys

CoCrMo alloys have been widely used in hip replacements. On the one hand they have exhibited excellent long-term survival rates, but recently high failure rates have been observed, associated with adverse local tissue reactions. It is still a puzzle why CoCrMo alloys sometimes work very well, while at the other times the failure rate is unacceptably high. The current work aims to investigate the influence of protein adsorption on the oxide layer properties and consequently on corrosion behaviour of CoCrMo biomedical grade alloys in different surface and media conditions. Electrochemical Impedance Spectroscopy (EIS), SEM and AFM were employed to characterise the surfaces. TEM was also used to reveal the subsurface chemical composition. The results showed a significant drop in the resistance of the oxide layer on the surfaces after some cathodic potential polarization. It was also shown that higher protein content and temperature reduced the oxide layer/metal surface interface resistivity. EDX quantitative chemical composition spot analysis of the subsurface after cathodic polarization showed a depletion of chromium in the outermost layer. AFM imaging and peak-force quantitative nanomechanical mapping QNM revealed lower adhesion forces for a relatively thick proteinaceous adsorbed layer on the surface after high cathodic polarization in particular at 50 °C.

Friction and wear performance evaluation of UHMWPE using Taguchi based grey approach: A study on the influence of load and bio-serum lubrication

The friction and wear behavior of biomedical implant materials is a subject of interest to tribologists. It stems from the fact that friction & wear are the key factors affecting the life of artificial replacement joints. This study investigates the tribological performance of UHMWPE against Biomedical grade 316 L stainless steel and TiAl6V4under different bio serum lubrications. The selected materials are commonly used for total joint replacement and form a tribo pair in contact. The friction and wear tests were performed on a pin on disc tribo-meter at normal body temperature of 37 °C. The design of experiment approach based on Taguchi methodology was used for experimentation planning and Taguchi's L18 orthogonal array was used based on the levels of the control factors viz., counter-face material, bio lubrication and load. Further, Taguchi and grey based approaches were used for optimization of the friction and wear processes with respect to the control factors. Furthermore, ANOVA technique was used to study the effect of selected process parameters on the tribological performance of UHMWPE. It is perceived that the load is the most important parameter that affects both average friction coefficient and specific wear rate. Grey relational analysis revealed that using Ti6Al4V Counterface material with human serum and 52 N normal load gives the optimum tribological performance for UHWMPE. The worn surfaces of UHWMPE were examined using scanning electron microscopy to reveal the wear mechanisms.

Reprint of “Effect of substrate bias on biocompatibility of amorphous carbon coatings deposited on Ti6Al4V by PECVD”

Long service life of implants is of high importance to patients. This study deposited amorphous carbon (a-C) coatings on biomedical grade Ti6Al4V substrate using plasma-enhanced chemical vapor deposition (PECVD). The effect of substrate bias power on microstructure and corrosion of the coatings is investigated and compared with the bare Ti6Al4V substrate. The experimental results show that the substrate bias power of 30 W leads to amorphous carbon in microstructure. With increased bias nanocrystalline graphite appears. All coated samples have significant improvements in corrosion resistivity as compared to Ti6Al4V alone. The sample deposited at bias power of 30 W with a thickness of 150 nm demonstrated the lowest corrosion current of 6.47 nA/cm2 and the lowest corrosion rate of 8.05 nm/year, which can postpone the corrosion of the Ti6Al4V substrate for at least 18 years. From the in-vitro cell culture studies, the best sample also registered the higher cell viability and biocompatibility as compared to bare Ti6Al4V, thus could be helpful in promoting healing.

An Experimental Study on Micro-Milling of a Medical Grade Co-Cr-Mo Alloy Produced by Selective Laser Melting.

Cobalt-chromium-molybdenum (Co-Cr-Mo) alloys are very promising materials, in particular, in the biomedical field where their unique properties of biocompatibility and wear resistance can be exploited for surgery applications, prostheses, and many other medical devices. While Additive Manufacturing is a key technology in this field, micro-milling can be used for the creation of micro-scale details on the printed parts, not obtainable with Additive Manufacturing techniques. In particular, there is a lack of scientific research in the field of the fundamental material removal mechanisms involving micro-milling of Co-Cr-Mo alloys. Therefore, this paper presents a micro-milling characterization of Co-Cr-Mo samples produced by Additive Manufacturing with the Selective Laser Melting (SLM) technique. In particular, microchannels with different depths were made in order to evaluate the material behavior, including the chip formation mechanism, in micro-milling. In addition, the resulting surface roughness (Ra and Sa) and hardness were analyzed. Finally, the cutting forces were acquired and analyzed in order to ascertain the minimum uncut chip thickness for the material. The results of the characterization studies can be used as a basis for the identification of a machining window for micro-milling of biomedical grade cobalt-chromium-molybdenum (Co-Cr-Mo) alloys.

Nanocrystallisation of Nickel Free High Nitrogen Austenitic Stainless Steel through Ultrasonic Shot Peening

Ultrasonic Shot Peening (USP) - a novel route of surface modification was employed on biomedical grade Nickel free high nitrogen stainless steel (18Cr-21Mn-0.65N-balance Fe) to obtain a surface nanostructure without changing its chemical composition and microstructural phase transformation. Hardened steel shots of diameter 2 mm and 3mm were repeatedly impacted on the specimen surface at a constant frequency of 20KHz for 2 and 8 minutes duration. Coarse surface grains of size 36±6µm transformed into nanocrystalline grains of size 13-18 nm. The deformed layer resulted by USP treatment increased with increase in shot diameter and duration of USP. The microstructure was characterized by using optical microscope, SEM, XRD and TEM technique. The hardness and roughness of the treated surface was also found to be strongly dependent on the USP process parameters.

Characterization of gradient properties generated by SMAT for a biomedical grade 316L stainless steel

Gradient microstructure generated by surface mechanical attrition treatment (SMAT) has beneficial effects for treated mechanical components, such as improved fatigue behaviour and tensile yield stress. Little effort has been devoted to characterize the local properties of each region in the gradient microstructure generated by SMAT. In this paper, the gradient microstructure was first highlighted by microscopic observation using Electron Back-Scatter Diffraction (EBSD). Nanoindentation was used to characterize the loading-unloading behaviour at different depths beneath the treated surface. All the indentation patterns were observed using Atomic Force Microscopy (AFM) and a pile-up phenomenon was detected. The nanoindentation results were analysed taking into account this pile-up effect on the dimension of the imprints. The results reveal that grain refinement plays a dominant role on the hardness values, while the effect of residual stress is less significant. In addition, correcting the indentation contact area appears to be necessary in the near surface region which is strongly affected by SMAT.

Surface Characterization, Antimicrobial Effectiveness, and Human Cell Response for a Biomedical Grade Polyurethane Blended with a Mixed Soft Block PTMO-Quat/PEG Copolyoxetane Polyurethane.

Infection is a serious medical complication associated with health care environments. Despite advances, the 5-10% incidence of infections for hospital patients is well documented. Sources of pathogenic organisms include medical devices such as catheters and endotracheal tubes. Offering guidance for curbing the spread of such infections, a model antimicrobial coating is described herein that kills bacteria on contact but is compatible with human cells. To achieve these characteristics, a novel blend of a conventional biomedical grade polyurethane (Tecoflex) with mixed soft block polyurethane is described. The functional polyurethane (UP-C12-50-T) has a copolyoxetane soft block P-C12-50 with quaternary ammonium (C12) and PEG-like side chains and a conventional poly(tetramethylene oxide) (PTMO, T) soft block. DSC and DMA data point to limited miscibility of UP-C12-50-T with Tecoflex. The blend of Tecoflex with 10 wt % UP-C12-50-T designated UP-C12-50-T-10 radically changed surface properties. Evidence for surface concentration of the P-C12-50 soft block was obtained by atomic force microscopy (AFM), dynamic contact angles (DCAs), zeta potentials (ζ), and X-ray photoelectron spectroscopy (XPS). The antimicrobial effectiveness of the blend coatings was established by the ASTM E2149 "shake flask" test for challenges of E. coli and a methicillin resistant strain of S. epidermidis. Cytocompatibility was demonstrated with an in vitro test designed for direct contact (ISO 10993-5). Growth of human mesenchymal stem cells (MSCs) beside and under UP-C12-50-T-10 indicated remarkable biocompatibility for a composition that is also strongly antimicrobial. Overall, the results point to a model coating with a level of P-C12-50 that combines high antimicrobial effectiveness and low toxicity to human cells.

Novel laser surface texturing for improved primary stability of titanium implants

Recently, the production of well-defined patterned surfaces with random or regular micro and nano-features has brought new opportunities for research and development in the field of tissue engineering and regenerative medicine. Among advanced micro and nano processing technologies, laser surface texturing (LST) stands out due to its simplicity, flexibility, precision, reproducibility and relatively low cost. This work studies the development of patterned surfaces controlled by of LST into biomedical grade V titanium, Ti–6Al–4V–alloy. We present different cross-hatched micropatterns followed by the characterisation of surface morphology and topography. Structural integrity of the produced patterns is evaluated by friction tests against bone, mimicking the insertion of an implant. Wettability is studied as it is crucial for protein adsorption and cell adhesion. The results show that the surface topography obtained using different patterning plans influences the wetting behaviour and the coefficient of friction against bone.

Controlled NO-Release from 3D-Printed Small-Diameter Vascular Grafts Prevents Platelet Activation and Bacterial Infectivity.

Thrombogenicity and bacterial infectiveness are the most common complications for foreign blood contacting surfaces associated with functional failure of small-diameter vascular grafts (SDVGs). In this work, novel bactericidal and nonthrombogenic SDVGs were manufactured via 3D-printing technology, thus producing a controlled nitric oxide (NO) release coating. S-Nitroso-N-acetyl-D-penicillamine (SNAP) was synthesized as an NO-donor, and three biomedical grade composite matrixes of poly(ethylene glycol) (PEG)-SNAP, polycaprolactone (PCL)-SNAP, and PEG-PCL-SNAP were validated for water uptake and NO-release kinetics. To optimize and extend the NO releasing profile, a PCL top-coat (tc) was deposited over the NO-releasing layer. The PEG-PCL-SNAP-tc was selected for biological tests as its NO-release profile was prolonged and well-controlled. Coating the 3D-printed SDVG with PEG-PCL-SNAP-tc resulted in quantitative antibacterial features against both Gram-positive and Gram-negative bacteria and in NO-mediated inhibition of platelet activation and aggregation. Antibacterial and antithrombogenic properties in plasma are expected to be as effective as in PBS, since NO release in plasma was not significantly different from that in PBS. Overall, application of the inexpensive, rapid, and reproducible 3D-printing technology as a custom-based production method, in combination with a well-controlled NO release system, is promising for the production of innovative bactericidal and hemocompatible SDVGs.

Biomedical Grade Stainless Steel Coating of Polycaffeic Acid via Combined Oxidative and Ultraviolet Light-Assisted Polymerization Process for Bioactive Implant Application.

Stainless steel as a biomedical implant material has been studied in various fields and in various forms, such as vascular stents, bone plates, dental screws, and artificial hip and bone material. In this study, we used polycaffeic acid (PCA), a natural phenolic compound, to coat the surface of medical grade stainless steel to provide added potential medicinal effects by virtue of its inherent anti-inflammatory, antiviral, antifibrosis, antithrombosis, and antihypertensive characteristics. We did this via UV irradiation under an alkaline state to solve the cost and time problems of other existing coating methods. The physicochemical properties of the samples were investigated through field emission scanning electron microscopy (FESEM), atomic force microscopy (AFM), contact angle, FTIR, and X-ray photoelectron spectroscopy (XPS). Surface bioactivity using NIH-3T3 cell lines were observed in vitro. We expect that the proposed methodology may contribute to the field of study of implantable metallic devices.

Wear Behavior of Pure Titanium Coated With WC-Co by the Use of Electrospark Deposition Method

Titanium is a highly interesting material in engineering because of its unique combination of high strength to weight ratio, excellent resistance to corrosion, and biocompatibility. However, the material’s low wear resistance, which is its inherent nature, limits its application in highly erosive conditions. In order to enhance the wear resistance of biomedical grade titanium with the help of a WC-Co coating, an electrospark deposition method was used in this work. The goal of this work is to investigate the effect of frequency and current upper limit in the electrospark deposition process on substrate properties. Hardness of the layers was measured by a microhardness tester. In order to study the morphology and microstructure of surface layers, scanning electron microscope was used. Tribological tests were conducted under technically dry friction conditions at a load of 12.5 N by a pin-on-disk tribometer. Titanium was observed in coating and metallurgical bonding between the coating and the substrate. The optimized sample's hardness was about 930 HV 0.1. Results showed that the presence of a carbide layer on the surface of titanium leads to a great enhancement of wear resistance of about 68% in the pin-on-disk test.