Structural changes of UHMWPE after e-beam irradiation and thermal treatment

The Impacts of the Sterilization Method and the Electrospinning Conditions of Nanofibrous Biodegradable Layers on Their Degradation and Hemocompatibility Behavior

The use of electrospun polymeric biodegradable materials for medical applications is becoming increasingly widespread. One of the most important parameters regarding the functionality of nanofiber scaffolds during implantation and the subsequent regeneration of damaged tissues concerns their stability and degradation behavior, both of which are influenced by a wide range of factors (the properties of the polymer and the polymer solution, the technological processing approach, the sterilization method, etc.). This study monitored the degradation of nanofibrous materials fabricated from degradable polyesters as a result of the sterilization method applied (ethylene oxide and gamma irradiation) and the solvent system used to prepare the spun polymer solution. Aliphatic polyesters PCL and PLCL were chosen for this study and selected with respect to the applicability and handling in the surgical setting of these nanofibrous materials for vascular bandaging. The results revealed that the choice of solvent system exerts a significant impact on degradation during sterilization, especially at higher gamma irradiation values. The subsequent enzyme-catalyzed degradation of the materials following sterilization indicated that the choice of the sterilization method influenced the degradation behavior of the materials. Whereas wave-like degradation was evident concerning ethylene oxide sterilization, no such behavior was observed following gamma-irradiation sterilization. With concern for some of the tested materials, the results also indicated the potential for influencing the development of degradation within the bulk versus degradation from the surface of the material. Both the sterilization method and the choice of the spinning solvent system were found to impact degradation, which was observed to be most accelerated in the case of PLCL (L-lactide-co-caprolactone copolymer) electrospun from organic acids and subsequently sterilized using gamma irradiation. Since we planned to use these materials in cardiovascular applications, it was decided that their hemocompatibility would also be tested. The results of these tests revealed that changes in the structures of the materials initiated by sterilization may exert thrombogenic and anticoagulant impacts. Moreover, the microscopic analysis suggested that the solvent system used in the preparation of the materials potentially affects the behavior of erythrocytes; however, no indication of the occurrence of hemolysis was detected.

Screening the Efficacy of a Microbial Consortium of Bacteria and Fungi Isolated from Different Environmental Samples for the Degradation of LDPE/TPS Films

In this study, a screening of the efficacy of a microbial consortium of bacteria and fungi isolated from activated sludge, river sediment, and compost for the degradation of LDPE/TPS was performed. According to the morphological and biochemical characterization, eight bacteria, Bacillus sonorensis, Bacillus subtilis, Lysinibacillus massiliensis, Bacillus licheniformis, Bacillus indicus, Bacillus megaterium, Bacillus cereus, and Pseudomonas alcaligenes, five molds, Aspergillus sp. 1, Aspergillus sp. 2, Trichoderma sp., Rhizopus sp., Penicillium sp., and Alternaria sp., and a yeast, Candida parapsilosis, were identified. The first experiment E1 was inoculated with microorganisms isolated from activated sludge and river sediment, and E2 with microorganisms isolated from compost. In both experiments, different types of polymeric materials, low density polyethylene (E1-1 and E2-1), thermoplastic starch (E1-2 and E2-2), low density polyethylene + thermoplastic starch (E1-3 and E2-3), low density polyethylene + thermoplastic starch + styrene-ethylene-styrene (E1-4 and E2-4) were added. The obtained results, weight loss, SEM, and FTIR analysis showed that the microorganisms in both experiments were able to degrade polymeric materials. The mixed culture of microorganisms in experiments E1-2 and E2-2 completely degraded TPS (thermoplastic starch). The percent weight losses of LDPE, LDPE+20% TPS, and LDPE+20% TPS+SEBS in experiment E1 were 3.3184%, 14.1152%, and 16.0062% and in experiment E2 were 3.9625%, 20.4520% and 21.9277%, respectively. SEM microscopy shows that the samples with a LDPE matrix exhibited moderate surface degradation and negligible oxidative degradation under the given conditions. FTIR/ATR data demonstrate that degradation was more intense in E2 than in E1.

European Database of Explanted UHMWPE Liners from Total Joint Replacements: Correlations among Polymer Modifications, Structure, Oxidation, Mechanical Properties and Lifetime In Vivo

This contribution lays the foundation for the European database of explanted UHMWPE liners from total joint replacements. Three EU countries (Czech Republic, Italy and Spain) have joined their datasets containing anonymized patient data (such as age and BMI), manufacturer data (such as information on UHMWPE crosslinking, thermal treatment and sterilization), orthopedic evaluation (such as total duration of the implant in vivo and reasons for its revision) and material characterization (such as oxidative degradation and micromechanical properties). The joined database contains more than 500 entries, exhibiting gradual growth, and it is beginning to show interesting trends, which are discussed in our contribution, including (i) strong correlations between UHMWPE oxidative degradation, degree of crystallinity and microhardness; (ii) statistically significant differences between UHMWPE liners with different types of sterilization; (iii) realistic correlations between the extent of oxidative degradation and the observed reasons for total joint replacement failures. Our final objective and task for the future is to continuously expand the database, involving researchers from other European countries, in order to create a robust tool that will contribute to the better understanding of structure-properties-performance relationships in the field of arthroplasty implants.

Discussion of Orientation and Performance of Crosslinked Ultrahigh-Molecular-Weight Polyethylene Used for Artificial Joints

Previously, the orientation structure of ultrahigh-molecular-weight polyethylene (UHMWPE) for artificial joints was considered to be unchanged after irradiation crosslinking. Therefore, much of the research related to the long-term failure of artificial joints has focused on material improvements. In this study, ultrasmall-angle X-ray scattering (USAXS) and the small/wide-angle X-ray scattering (SAXS-WAXS) combined technique reveal that the orientation structures of UHMWPE materials at all scales (nanoscale to microscale) are responsible for the long-term failure of artificial joints. To further illustrate the formation of these hierarchical oriented structures, a simple model is presented. In this model, first, the migration of free radicals plays a vital role, and the different steric hindrances in different directions directly lead to uneven migration behavior of free radicals. Second, the uneven migration of free radicals contributes to an inhomogeneous concentration of free radicals, thus resulting in observable crosslinking nonuniformities. Finally, all the hierarchical structural nonuniformities promote long-term failure of artificial joints after long-term wear.

Morphological Transformation in Polymer Composite Materials Filled with Carbon Nanoparticles: Part 1.—SEM and XRD Investigations

HDPE-based nanocomposite fibers have been extruded from a melt and drawn up to draw ratio DR = 8. Two kinds of carbon nanodiscs (original ones and those exposed to additional annealing) have been used as fillers. Obtained nanocomposite fibers have been investigated with the help of different experimental methods: rheology, SEM and WAXS. It has been demonstrated that the annealed carbon nanodiscs possess a nucleation ability that finally leads to strong transformation of the material morphology.

Electron beam irradiation treatment of textiles materials: a review

Electron beam irradiation technology has gained more attention as it appears to be a promising economically and environmentally sustainable alternative to traditional wet-chemical processing. It is an advanced approach that is clean, solvent-free, time-saving, and ecologically benign with acceptable handling and operation properties. This review provides a study of the latest literature on the technology of electron beam irradiation surface modification of textile. Considerable emphasis is also placed on the most novel applications of electron beam irradiation such as the functionalization of textile materials, which leads to the development of alternative sustainable techniques or revolutionary advanced materials soon.

Graphical abstract

Comparison of macro-, micro- and nanomechanical properties of clinically-relevant UHMWPE formulations

We characterized a set of eleven clinically relevant formulations of UHMWPE for total joint replacements. Although their molecular and supermolecular structure were quite similar as evidenced by IR, DSC and SAXS measurements, there were slight differences in their crystallinity (DSC crystallinity ranging from 52 to 61%), which were connected with processing conditions, such as the total radiation dose, thermal treatment and/or addition of biocompatible stabilizers. Mechanical properties were assessed at all length scales, using macroscale compression testing, non-instrumented and instrumented microindentation hardness testing (at loading forces ~500 mN), and nanoindentation hardness testing measured at both higher and lower loading (~4 mN and ~0.6 mN, respectively). In agreement with theoretical predictions, we found linear correlations between UHMWPE crystallinity and its stiffness-related properties (elastic moduli, yield stress, and hardness) at all length scales (macro-, micro- and nanoscale). Detailed statistical evaluation of our dataset showed that the accuracy and precision of the applied methods decreased in the following order: non-instrumented microindentation ≥ instrumented microindentation ≥ macromechanical properties ≥ nanoindentation measured at higher loading forces ≫ nanoindentation measured at lower loading forces. The results confirm that microindentation and nanoindentation at sufficiently high loading forces are reliable methods, suitable for UHMWPE characterization.

Structure, processing and performance of ultra-high molecular weight polyethylene (IUPAC Technical Report). Part 2: crystallinity and supra molecular structure

Test methods including OM, SEM, TEM, DSC, SAXS, WAXS, and IR were used to characterise supra-molecular structure in three batches of polyethylene (PE), which had weight-average relative molar masses M ¯ w   ${\overline{M}}_{\text{w}}$ of approximately 0.6 × 106, 5 × 106, and 9 × 106. They were applied to compression mouldings made by the polymer manufacturer. Electron microscopy showed that powders formed in the polymerization reactor consisted of irregularly shaped grains between 50 and 250 μm in diameter. Higher magnification revealed that each grain was an aggregate, composed of particles between 0.4 and 0.8 μm in diameter, which were connected by long, thin fibrils. In compression mouldings, lamellar thicknesses ranged from 7 to 23 nm. Crystallinity varied between 70 and 75 % in reactor powder, but was lower in compression mouldings. Melting peak temperatures ranged from 138 to 145 °C, depending on processing history. DMTA showed that the glass transition temperature θ g was −120 °C for all three grades of polyethylene. IR spectroscopy found negligibly small levels of oxidation and thermal degradation in mouldings. Optical microscopy revealed the presence of visible fusion defects at grain boundaries. It is concluded that relatively weak defects can be characterized using optical microscopy, but there is a need for improved methods that can detect less obvious fusion defects.

A novel method to eliminate the influence of absorbed lipids on the characterization of ultra-high molecular weight polyethylene using Fourier-transform infrared spectroscopy

BACKGROUND

Fourier-transform infrared spectroscopy (FTIR) is one of the standard methods to analyze ultra-high molecular weight polyethylene (UHMWPE) in orthopedic implants. For retrieved components, lipid extraction using an organic solvent prior to the measurement is necessary to eliminate the influence of lipids absorbed in vivo. However, its influence on the measurement has not been substantially investigated.

OBJECTIVE

To investigate the influence of lipid extraction on the FTIR analysis of UHMWPE and to develop a novel method to obtain reliable results without inconvenient lipid extraction.

METHODS

FTIR analysis was repeatedly performed on UHMWPE specimens from retrieved components before and after lipid extraction under various conditions. A method to calculate the extent of influence of the absorbed lipids from the FTIR spectra was developed using a peak separation technique.

RESULTS

An elevated temperature was necessary for lipid extraction; however, it had the potential to influence the results if the conditions were not properly controlled. The results obtained using the peak separation technique coincided with those obtained after lipid extraction.

CONCLUSION

The use of the peak separation technique enables the efficient acquisition of reliable results without the need for lipid extraction.

Characterisation of the physical, chemical and mechanical properties of a radiopaque polyethylene

Ultra-high molecular weight polyethylene has a low X-ray attenuation, hence, the performance of the polyethylene implants used for joint replacements cannot be directly investigated using X-ray-based imaging techniques. In this study, the X-ray attenuation of polyethylene was increased by diffusing an FDA-approved oil-based contrast agent (Lipiodol ultra fluid) into the surface of the samples, and the suitability of this novel radiopaque ultra-high molecular weight polyethylene for clinical applications was examined. Different levels of radiopacity were created by controlling the diffusion parameters, and the level of radiopacity was quantified from computed tomography scans and reported in Hounsfield units. The physical, chemical and tensile properties of the radiopaque ultra-high molecular weight polyethylene were examined and compared to untreated and thermally treated controls. The results of this study confirmed that for the samples treated at 115°C or less the diffusion of the contrast agent did not significantly alter the crystallinity (p = 0.7) or melting point (p = 0.4) of the polyethylene. Concomitantly, the tensile properties were not significantly different from the control samples (p > 0.05 for all properties). In conclusion, the radiopaque ultra-high molecular weight polyethylene treated for less than 18 h at a temperature of 115°C or below is a promising candidate for joint replacement applications as it can be identified in a standard X-ray while retaining the tensile properties of clinically used radiolucent ultra-high molecular weight polyethylene.

Influence of Irradiation Temperature on Oxidative and Network Properties of X-Ray Cross-Linked Vitamin E Stabilized UHMWPE for Hip Arthroplasty

Previous studies have shown that increased cross-link density, reduced free radicals, and increased antioxidant grafting resulting from electron-beam irradiation at elevated temperatures improved the wear performance and the oxidative stability of vitamin E blended UHMWPE. The current study explores the impact of elevated irradiation temperature on vitamin E blended UHMWPE using X-ray. We hypothesize that the effects of temperature would be similar to those observed after electron-beam irradiation due to the relatively high dose rate of X-rays. Two X-ray doses of 80 and 100 kGy and two irradiation temperatures, that is, room temperature and 100°C were considered. The reference was Vitelene®, a vitamin E stabilized polyethylene cross-linked with 80 kGy by e-beam at 100°C. Oxidation index and oxidation induction time, as well as cross-link density, gel fraction, and trans-vinylene index, were determined, as the oxidative and network properties are decisive for the long-term implant performance. Gel fraction and oxidation induction time were significantly improved subsequently to warm irradiation in comparison with the material irradiated at room temperature. In conclusion, X-ray irradiation at elevated temperatures resulted in an increase of cross-linking and oxidative resistance of vitamin E stabilized polyethylene comparable to those of e-beam irradiated UHMWPE.

Arrays of Ag and Au Nanoparticles with Terpyridine- and Thiophene-Based Ligands: Morphology and Optical Responses

The assembly of Ag and Au nanoparticles (NPs) into nanoparticulate arrays mediated by terpyridine (tpy), 4'-(2-thienyl)terpyridine (T-tpy), and short α,ω-bis(tpy)oligothiophene ligands has been accomplished at the interface between the Ag or Au NP hydrosol and a solution of the molecular species in dichloromethane. The relationship between the morphology and the optical responses of the arrays has been investigated by advanced methods of TEM (transmission electron microscopy) image analysis and surface plasmon extinction (SPE) spectra. It has been established that the size of islands of closely spaced NPs rather than the average interparticle distance affects the extent of delocalization of the surface plasmon excitations and thus also the SPE spectra. Furthermore, the structure of surface-adsorbate complexes formed in these arrays has been investigated by SERS spectral measurements carried out as a function of the excitation wavelength. Photoinduced charge transfer (CT) transitions from the neutral Ag_s⁰ and Au_s⁰ adsorption sites on metal NPs to antibonding orbitals of the adsorbates have been identified for Ag/tpy, Ag/T-tpy, Au/tpy, and Au/T-tpy nanoparticulate arrays. Although the surface-adsorbate complexes displaying a photoinduced CT are known for Ag NPs, the Au_s⁰ surface complexes with this CT are newly reported. Bis(tpy)oligothiophenes were found to be attached to both Ag and Au NPs via the tpy group(s). The match between the interparticle distances within the NP islands and the lengths of the oligomers molecules indicates that the molecules act as interparticle linkers. In this case, unequivocal spectral marker band evidence of the Ag_s⁰ as well as Au_s⁰ surface complex formation has not been obtained.

Influence of Corona Structure on Binding of an Ionic Surfactant in Oppositely Charged Amphiphilic Polyelectrolyte Micelles

Interaction of polystyrene-block-poly(methacrylic acid) micelles (PS-PMAA) with cationic surfactant N-dodecylpyridinium chloride (DPCl) in alkaline aqueous solutions was studied by static and dynamic light scattering, SAXS, cryogenic transmission electron microscopy (cryo-TEM), isothermal titration calorimetry (ITC), and time-resolved fluorescence spectroscopy. ITC and fluorescence measurements show that there are two distinct regimes of surfactant binding in the micellar corona (depending on the DPCl content) caused by different interactions of DPCl with PMAA in the inner and outer parts of the corona. The compensation of the negative charge of the micellar corona by DPCl leads to the aggregation of PS-PMAA micelles, and the micelles form colloidal aggregates at a certain critical surfactant concentration. SAXS shows that the aggregates are formed by individual PS-PMAA micelles with intact cores and collapsed coronas interconnected with surfactant micelles by electrostatic interactions. Unlike polyelectrolyte-surfactant complexes formed by free polyelectrolyte chains, the PMAA/DPCl complex with collapsed corona does not contain surfactant micelles.

Quantification of structural changes of UHMWPE components in total joint replacements

Background

At present time the number of implantations of joint replacements as well as their revisions increases. Higher demands are required on the quality and longevity of implants. The aim of this work was to determine the degree of oxidative degradation and the amount of free/residual radicals in selected ultra-high molecular weight polyethylene (UHMWPE) components of the joint replacements and demonstrate that the measured values are closely connected with quality and lifetime of the polymer components.

Methods

We tested both new (4 samples) and explanted (4 samples) UHMWPE polymers for total joint replacements. The samples were characterized by infrared spectroscopy (IR), electron spin resonance (ESR) and microhardness (MH) test. The IR measurements yielded the values of oxidation index and trans-vinylene index. The ESR measurements gave the free radicals concentration.

Results

In the group of new polyethylene components, we found oxidation index values ranging from 0.00-0.03 to 0.24. The trans-vinylene index values ranged from 0.044 to 0.080. The value of free radical concentration was zero in virgin and also in sample of Beznoska Company and non-zero in the other samples. In the group of explanted components, the measured values were associated with their history, micromechanical properties and performance in vivo.

Conclusions

We demonstrated that measuring of oxidative damage may help the orthopaedic surgeon in estimating the quality of UHMWPE replacement component and thus radically to avoid early joint replacement failure due to worse polyethylene quality.

Comparison of one-step and sequentially irradiated ultrahigh-molecular-weight polyethylene for total joint replacements

Structure and properties of several ultrahigh-molecular-weight polyethylenes (UHMWPEs), which were crosslinked either by standard, single-step irradiation or by newer, several-step irradiation (sequential irradiation), were compared. To verify the results, the same characterization was carried out for commercially available UHMWPE liners made of sequentially irradiated polymer (X3™, Stryker, Mahwah, NJ) and one-step irradiated polymer (denoted as PE-IMC, produced by Beznoska, Kladno, Czech Republic). The structure was studied by a number of spectroscopic, diffraction, thermal, and microscopic methods. Mechanical properties were assessed by small-punch, microhardness and, wear testing. Our results suggested that sequential irradiation followed by annealing did not lead to unusual structure at the molecular or supermolecular level. Consequently, all measured mechanical properties, including wear resistance, were comparable with one-step irradiated UHMWPEs.