Adsorption of albumin and sodium hyaluronate on UHMWPE: a QCM-D and AFM study

Quartz Crystal Microbalance Application and In Silico Studies to Characterize the Interaction of Bovine Serum Albumin with Plasma Polymerized Pyrrole Surfaces: Implications for the Development of Biomaterials

Plasma polymerized pyrrole/iodine (PPPy/I) microparticles and bovine serum albumin (BSA) protein have shown interesting results in experimental models for the treatment of traumatic spinal cord injury. By studying the interaction between BSA and PPPy/I by a quartz crystal microbalance (QCM) and docking, we obtained important results to elucidate possible cellular interactions and promote the use of these polymers as biomaterials. These measurements were also used to characterize the adsorption process using an equilibrium constant. In addition, atomic force microscopy (AFM) was used to obtain images of the QCM surface sensors before and after BSA adsorption. Furthermore, we carried out molecular dynamics simulations and molecular docking to characterize the molecular recognition between BSA and the previously reported PPPy/I structure. For this study, we used two combinatorial models that have not been tested. Thus, we could determine the electrostatic (ΔGele) and nonelectrostatic (ΔGnonelec) components of the free binding energy (ΔGb). We demonstrated that BSA is adsorbed on PPPy/I with an adsorption constant of K = 24.35 μ-1 indicating high affinity. This observation combined with molecular docking and binding free energy calculations showed that the interaction between BSA and both combinatorial models of the PPPy structure is spontaneous.

Interaction Mechanisms and Predictions of the Biofouling of Polymer Films: A Combined Atomic Force Microscopy and Quartz Crystal Microbalance with Dissipation Monitoring Study

Biofouling of polymeric membranes is a severe problem in water desalination and treatment applications. A fundamental understanding of biofouling mechanisms is necessary to control biofouling and develop more efficient mitigation strategies. To shed light on the type of forces that govern the interactions between biofoulants and membranes, biofoulant-coated colloidal AFM probes were employed to investigate the biofouling mechanisms of two model biofoulants, BSA and HA, toward an array of polymer films commonly used in membrane synthesis, which included CA, PVC, PVDF, and PS. These experiments were combined with quartz crystal microbalance with dissipation monitoring (QCM-D) measurements. The Derjaguin, Landau, Verwey, and Overbeek (DLVO) and the extended-DLVO (XDLVO) theoretical models were applied to decouple the overall adhesion interactions between the biofoulants and the polymer films into their component interactions, i.e., electrostatic (El), Lifshitz-van der Waals (LW), and Lewis acid-base (AB) interactions. The XDLVO model was found to predict better the AFM colloidal probe adhesion data and the QCM-D adsorption behavior of BSA onto the polymer films than the DLVO model. The ranking of the polymer films' adhesion strengths and adsorption quantities was inversely proportional to their γ^- values. Higher normalized adhesion forces were quantified for the BSA-coated colloidal probes with the polymer films than the HA-coated colloidal probes. Similarly, in QCM-D measurements, BSA was found to cause larger adsorption mass shifts, faster adsorption rates, and more condensed fouling layers than HA. A linear correlation (R² = 0.96) was obtained between the adsorption standard free energy changes (ΔG_ads^°) estimated for BSA from the equilibrium QCM-D adsorption experiments and the AFM normalized adhesion energies (W_AFM/R) estimated for BSA from the AFM colloidal probe measurements. Eventually, an indirect approach was presented to calculate the surface energy components of biofoulants characterized by high porosities from Hansen dissolution tests to perform the DLVO/XDLVO analyses.

(Bio)Tribocorrosion in Dental Implants: Principles and Techniques of Investigation

Tribocorrosion is a current and very discussed theme in tribology and medicine for its impact on industrial applications. Currently, the phenomena are mainly oriented to the biological environment and, in particular, to medical devices such as hip prostheses, dental implants, knee joints, etc. The term tribocorrosion underlines the simultaneous action of wear and corrosion in a tribocouple. It has a non-negligible effect on the total loss of contact materials and the potential failure of the bio-couplings. This overview aims to focus firstly on the basic principles of prosthesis tribocorrosion and subsequently to describe the techniques and the analytical models developed to quantify this phenomenon, reporting the most relevant results achieved in the last 20 years, proposed in chronological order, in order to discuss and to depict the future research developments and tendencies. Despite considerable research efforts, from this investigation come many issues worthy of further investigation, such as how to prevent or minimize tribocorrosion in biological tribopairs, the development of a consolidated protocol for tribological experiments in corrosive environments joined with new biomaterials and composites, the possibility to achieve more and more accurate theoretical models, and how to be able to ensure the success of new implant designs by supporting research and development for the management of implant complications. The above issues certainly constitute a scientific challenge for the next years in the fields of tribology and medicine.

Functional Ultra-High Molecular Weight Polyethylene Composites for Ligament Reconstructions and Their Targeted Applications in the Restoration of the Anterior Cruciate Ligament

The selection of biomaterials as biomedical implants is a significant challenge. Ultra-high molecular weight polyethylene (UHMWPE) and composites of such kind have been extensively used in medical implants, notably in the bearings of the hip, knee, and other joint prostheses, owing to its biocompatibility and high wear resistance. For the Anterior Cruciate Ligament (ACL) graft, synthetic UHMWPE is an ideal candidate due to its biocompatibility and extremely high tensile strength. However, significant problems are observed in UHMWPE based implants, such as wear debris and oxidative degradation. To resolve the issue of wear and to enhance the life of UHMWPE as an implant, in recent years, this field has witnessed numerous innovative methodologies such as biofunctionalization or high temperature melting of UHMWPE to enhance its toughness and strength. The surface functionalization/modification/treatment of UHMWPE is very challenging as it requires optimizing many variables, such as surface tension and wettability, active functional groups on the surface, irradiation, and protein immobilization to successfully improve the mechanical properties of UHMWPE and reduce or eliminate the wear or osteolysis of the UHMWPE implant. Despite these difficulties, several surface roughening, functionalization, and irradiation processing technologies have been developed and applied in the recent past. The basic research and direct industrial applications of such material improvement technology are very significant, as evidenced by the significant number of published papers and patents. However, the available literature on research methodology and techniques related to material property enhancement and protection from wear of UHMWPE is disseminated, and there is a lack of a comprehensive source for the research community to access information on the subject matter. Here we provide an overview of recent developments and core challenges in the surface modification/functionalization/irradiation of UHMWPE and apply these findings to the case study of UHMWPE for ACL repair.

Effect of albumin, urea, lysozyme and mucin on the triboactivity of Ti6Al4V/zirconia pair used in dental implants

The titanium implant/zirconia abutment interface can suffer failure upon mechanical and biological issues, ultimately leading to the loss of the artificial tooth. The study of the effect of the organic compounds present in saliva on the tribological behavior of these systems is of utmost importance to understand the failure mechanisms and better mimic the in vivo conditions. The aim of the present work is to evaluate the effect of the addition of albumin, urea, lysozyme and mucin to artificial saliva, on the triboactivity of Ti6Al4V/zirconia pair commonly used in dental implants and then, compare the results with those obtained with human saliva. The solutions' viscosity was measured and the adsorption of the different biomolecules to both Ti6Al4V and zirconia was accessed. Tribological tests were performed using Ti6Al4V balls sliding on zirconia plates inside of a corrosion cell. Friction and wear coefficients were determined, and the open circuit potential (OCP) was monitored during the tests. Also, the wear mechanisms were identified. The presence of mucin in the artificial lubricant led to the lowest wear coefficients. The main wear mechanism was abrasion, independently of the used lubricant. Adhesive wear was observed for the systems without mucin. Tribocorrosion activity and wear coefficient were lower in the presence of mucin. None of the studied artificial lubricants mimicked the effect of human saliva (HS) on the tribological behavior of the studied pair since this lubricant led to the lowest friction coefficient and highest corrosion activity.

Nanostructured Coating for Biomaterial Lubrication through Biomacromolecular Recruitment

Biomaterials employed in the articular joint cavity, such as polycarbonate urethane (PCU) for meniscus replacement, lack of lubrication ability, leading to pain and tissue degradation. We present a nanostructured adhesive coating based on dopamine-modified hyaluronan (HADN) and poly-lysine (PLL), which can reestablish boundary lubrication between the cartilage and biomaterial. Lubrication restoration takes place without the need of exogenous lubricious molecules but through a novel strategy of recruitment of native lubricious molecules present in the surrounding milieu. The biomimetic adhesive coating PLL-HADN (78 nm thickness) shows a high adhesive strength (0.51 MPa) to PCU and a high synovial fluid responsiveness. The quartz crystal microbalance with dissipation monitoring shows the formation of a thick and softer layer when these coatings are brought in contact with the synovial fluid. X-ray photoelectron spectroscopy and ConA-Alexa staining show clear signs of lubricious protein (PRG4) recruitment on the PLL-HADN surface. Effective recruitment of a lubricious protein by PLL-HADN caused it to dissipate only one-third of the frictional energy as compared to bare PCU when rubbed against the cartilage. Histology shows that this reduction makes the PLL-HADN highly chondroprotective, whereas PLL-HA coatings still show signs of cartilage wear. Shear forces in the range of 0.07-0.1 N were able to remove ∼80% of the PRG4 from the PCU-PLL-HA but only 27% from the PCU-PLL-HADN. Thus, in this study, we have shown that surface recruitment and strong adsorption of biomacromolecules from the surrounding milieu is an effective biomaterial lubrication strategy. This opens up new possibilities for lubrication system reconstruction for medical devices.

Role of protein adsorption in the bio corrosion of metallic implants - A review

Implants are exposed to a complex physiological environment that contains various organic compounds, especially proteins. The adsorption of proteins has an immense influence on the corrosion, biocompatibility and wear properties of implantable metals. Proteins engage in multiple processes that could potentially inhibit or promote metal degradation, depending on the type of proteins, their concentration and the properties of the implant material. In the bio corrosion process, proteins are denatured and transform into a film on the metal surface, inhibiting corrosion. This film is found on many retrieved artificial joints, especially on worn areas, and can protect the passive film from scrapping due to its lubricating effect, thus decreasing tribocorroion. On the other hand, the interactions of metal ions with proteins (and amino acids) create colloidal organometallic complexes. Transport of the complex compounds away from the interface increases dissolution rates; thus, it accelerates the corrosion of metallic implants. The influence of protein adsorption on the corrosion behaviour of metallic biomaterials is presented in this review. Biocompatible metals that are favourably used as implants such as stainless steel, Co-Cr alloys, Ti alloys and biodegradable Mg and Fe alloys are specifically addressed. We have highlighted the adsorption phenomenon of protein on metallic implants, the interaction of proteins with metallic implants and the role of protein adsorption on implant biocorrosion behaviour as well as their wear resistance.

Estimation of the free energy of adsorption of a polypeptide on amorphous SiO2 from molecular dynamics simulations and force spectroscopy experiments

Estimating the free energy of adsorption of materials-binding peptides is fundamental to quantify their interactions across bio/inorganic interfaces, but is difficult to achieve both experimentally and theoretically. We employ a combination of molecular dynamics (MD) simulations and dynamical force-spectroscopy experiments based on atomic force microscopy (AFM) to estimate the free energy of adsorption ΔGads of a (GCRL) tetrapeptide on amorphous SiO2 in pure water. The results of both equilibrium, advanced sampling MD and non-equilibrium, steered MD are compared with those of two different approaches used to extract ΔGads from the dependence of experimentally measured adhesion forces on the applied AFM loading rates. In order to obtain unambiguous peak forces and bond loading rates from steered MD trajectories, we have developed a novel numerical protocol based on a piecewise-harmonic fit of the adhesion work profile along each trajectory. The interpretation of the experiments has required a thorough quantitative characterization of the elastic properties of polyethylene glycol linker molecules used to tether (GCRL)15 polypeptides to AFM cantilevers, and of the polypeptide itself. All obtained ΔGads values fall within a relatively narrow window between -5 and -9 kcal mol(-1), but can be associated with large relative error bars of more than 50%. Among the different approaches compared, Replica Exchange with Solute Tempering simulations augmented with MetaDynamics (RESTMetaD) and fitting of dynamic force spectroscopy experiments with the model of Friddle and De Yoreo lead to the most reliable ΔGads estimates.

Preparation of magnetic metal–organic framework nanocomposites for highly specific separation of histidine-rich proteins

This work reports a novel metal–organic framework (MOF)-based metal affinity platform for the rapid and highly specific separation of histidine-rich proteins using zeolitic imidazolate framework-8 coated magnetic nanocomposites (denoted as Fe₃O₄@ZIF-8).

CR TKA UHMWPE wear tested after artificial aging of the vitamin E treated gliding component by simulating daily patient activities

The wear behaviour of total knee arthroplasty (TKA) is dominated by two wear mechanisms: the abrasive wear and the delamination of the gliding components, where the second is strongly linked to aging processes and stress concentration in the material. The addition of vitamin E to the bulk material is a potential way to reduce the aging processes. This study evaluates the wear behaviour and delamination susceptibility of the gliding components of a vitamin E blended, ultra-high molecular weight polyethylene (UHMWPE) cruciate retaining (CR) total knee arthroplasty. Daily activities such as level walking, ascending and descending stairs, bending of the knee, and sitting and rising from a chair were simulated with a data set received from an instrumented knee prosthesis. After 5 million test cycles no structural failure of the gliding components was observed. The wear rate was with 5.62 ± 0.53 mg/million cycles falling within the limit of previous reports for established wear test methods.

Computational prediction of circular dichroism spectra and quantification of helicity loss upon peptide adsorption on silica

Circular dichroism (CD) spectroscopy is one of the few experimental techniques sensitive to the structural changes that peptides undergo when they adsorb on inorganic material surfaces, a problem of deep significance in medicine, biotechnology, and materials science. Although the theoretical calculation of the CD spectrum of a molecule in a given conformation can be routinely performed, the inverse problem of extracting atomistic structural details from a measured spectrum is not uniquely determined. Especially complicated is the case of oligopeptides, whose folding/unfolding energy landscapes are often very broad and shallow. This means that the CD spectra measured for either dissolved or adsorbed peptides arise from a multitude of different structures, each present with a probability dictated by their relative free-energy variations, according to Boltzmann statistics. Here we present a modeling method based on replica exchange with solute tempering in combination with metadynamics, which allows us to predict both the helicity loss of a small peptide upon interaction with silica colloids in water and to compute the full CD spectra of the adsorbed and dissolved states, in quantitative agreement with experimental measurements. In our method, the CD ellipticity Θ for any given wavelength λ is calculated as an external collective variable by means of reweighting the biased trajectory obtained using the peptide-SiO2 surface distance and the structural helicity as two independent, internal collective variables. Our results also provide support for the often-employed hypothesis that the Θ intensity at λ = 222 nm is linearly correlated with the peptides' fractional helicity.

Calf serum constituent fractions influence polyethylene wear and microbial growth in knee simulator testing

Calf serum lubricants consisting of various polypeptide constituent fractions are routinely used in knee wear simulators as part of the standardized test protocol. Three calf sera (bovine, new-born and alpha) were diluted as per the recommendation of ISO 14243-3 and used in displacement-controlled knee wear simulators to investigate their effects on polyethylene wear. Biochemical analyses included measuring total polypeptide degradation, electrophoretic profiles and low-molecular weight polypeptide concentrations to elucidate their involvement in the wear process. The effects of the various calf sera constituent fractions on microbial growth were also explored. The polyethylene wear rates and the results from the biochemical analyses for the three calf serum lubricants were all found to be statistically significantly different from each other. The lubricant derived from the alpha-calf serum was closest in constituent fractions to human synovial fluid. It also showed the lowest polyethylene wear rate (14.38 ± 0.85 mm3/million cycles) and the lowest amount of polypeptide degradation (7.77 ± 3.87%). Furthermore, the alpha-calf serum lubricant was associated with the least amount of change in the electrophoretic profile, the least change in low-molecular weight polypeptide concentration, and the lowest microbial growth in the presence of sodium azide (a microbial inhibitor conventionally used in implant wear testing). Replacing sodium azide with a broad spectrum antibiotic-antimycotic eradicated the microbial growth. Some speculation was entertained regarding the effect of alpha-calf serum on colloid-mediated boundary lubrication. Based on the results, it was recommended that ISO 14243-3 be modified to include guidelines on calf serum constituent fractions that would favour using alpha-calf serum in order to improve the fidelity of the simulation in knee implant wear testing.

Adsorption and reduction of glutathione disulfide on α-Al2O3 nanoparticles: experiments and modeling

Glutathione disulfide (GSSG; γ-GluCysGly disulfide) was used as a physiologically relevant model molecule to investigate the fundamental adsorption mechanisms of polypeptides onto α-alumina nanoparticles. Its adsorption/desorption behavior was studied by enzymatic quantification of the bound GSSG combined with zeta potential measurements of the particles. The adsorption of GSSG to alumina nanoparticles was rapid, was prevented by alkaline pH, was reversed by increasing ionic strength, and followed a nearly ideal Langmuir isotherm with a standard Gibbs adsorption energy of -34.7 kJ/mol. Molecular dynamics simulations suggest that only one of the two glutathionyl moieties contained in GSSG binds stably to the nanoparticle surface. This was confirmed experimentally by the release of GSH from the bound GSSG upon reducing its disulfide bond with dithiothreitol. Our data indicate that electrostatic interactions via the carboxylate groups of one of the two glutathionyl moieties of GSSG are predominantly responsible for the binding of GSSG to the alumina surface. The results and conclusions presented here can provide a base for further experimental and modeling studies on the interactions of biomolecules with ceramic materials.

Commissioning of a displacement-controlled knee wear simulator and exploration of some issues related to the lubricant

A six-station displacement-controlled knee simulator with separately controlled left (L) and right (R) banks (three wear implants per bank) was commissioned for a total of three million cycles (Mc) following ISO 14243-3. A commissioning protocol was applied to compare the polyethylene wear among the six wear stations by exchanging the implants between wear stations. Changes in lubricant characteristics during wear testing, such as polypeptide degradation, low-molecular-weight polypeptide concentration, and possible microbial contamination were also assessed. The total mean wear rate for the implants was 23.60 ± 1.96 mm3/Mc and this was of a similar magnitude to the mean wear rate for the same implant tested under similar conditions by DePuy Orthopaedics Inc. (Warsaw, IN). Repeated run-in wear was observed when the implants were exchanged between wear stations, suggesting that implants should be subjected to the same wear station throughout the duration of a wear test. The total polypeptide degradation for the implants measured 30.53 ± 3.96 per cent; the low-molecular-weight polypeptide concentration of the “used” lubricant for implants (0.131 ± 0.012 g/L) was 3.3 times greater than the mean polypeptide concentration of the fresh, “unused” lubricant (0.039 ± 0.004 g/L). This increase in low-molecular weight polypeptide concentration was suggested to be attributable to protein shear in the articulation of the implant, the circulation of the lubricant, and some proteolytic activity. Sodium azide was ineffective in maintaining a sterile environment for wear testing as a single, highly motile Gram-negative micro-organism was identified in the lubricant from wear tests.

Mass Gain Behaviour of Tibial Polyethylene Inserts during Soak Testing

Fluid adsorption and the associated mass gain behaviour in tibial inserts of total knee replacements was investigated in polyethylene (PE) manufactured from extruded GUR 1050 resin. Repeatedly removing the PE inserts from the soak fluid for gravimetric assessment (including cleaning, desiccation, and weighing) increased the mass gain. Soaking PE inserts for 46 days or 92 days seemed to give about the same mass gain. PE inserts that were soaked at 37 °C gained more mass than PE inserts soaked at room-temperature. Gas-plasma sterilized PE inserts gained less mass than gamma-in-air sterilized PE inserts. No statistically significant differences were detected in mass gain between PE inserts that were of 10 mm and 14 mm thickness. The mass gain of PE inserts was higher in protein-rich soak fluid compared with low-ion distilled water. Prior to knee simulator wear testing, tibial PE inserts should be conditioned in the same medium and under the same test conditions (gravimetric assessment frequency, fluid protein content, and fluid temperature). This approach would help improve the accuracy and precision of the gravimetrically determined PE wear rate during knee simulator wear testing.