Abstract
Introduction
According to American Joint Replacement Registry, particle mediated osteolysis represents 13 % of the knee revision surgeries performed in the United States. The comprehension of mechanical and wear properties of materials envisioned for TJR is a key step in product development. Furthermore, the maintenance of UHMWPE mechanical properties after material modification is an important aspect of material success. Initial studies conducted by our research group demonstrated that the incorporation of ibuprofen in UHMWPE had a minor impact on UHMWPE physicochemical and mechanical properties. Drug release was also evaluated and resulted in an interesting profile as a material to be used as an anti-inflammatory system. Therefore, the present study investigated the effect of drug release on the mechanical and biological properties of ibuprofen-loaded UHMWPE.
Experimental
UHMWPE resin GUR 1020 from Ticona was for sample preparation. Samples with drug concentrations of 3% and 5% wt were consolidated as well as samples without anti-inflammatory addition through compression molding at 150 °C and 5 MPa for 15 minutes. Mechanical properties were evaluated via the tensile strength experiment (ASTM D638) and dynamic mechanic tests. Wear resistance was measured using the pin on disc (POD) apparatus. Finally, cytotoxicity analysis was conducted based on ISO 10993–5.
Results
Dynamic-mechanic analysis demonstrated no difference in flexion modulus and stress for all materials (Table 1). No difference was also verified during cyclical loading experiments (Table 1), which indicates that the drug concentration added to material composition did not affect these properties. POD experiments were proposed to evaluate wear resistance of ibuprofen-loaded UHMWPE samples considering the combination of materials similar to those employed in TJR. Results from POD tests are presented in Table 1. Volumetric wear was close to zero for all samples after 200 thousand cycles.
Comprehension of the effect of drug release on mechanical properties is essential to estimate how the material will behave after implantation. Therefore, mechanical properties were assessed after 30 days of ibuprofen release and the results were compared with those obtained in samples as prepared (Table 2). Initial results demonstrated a decrease in elastic modulus in samples prepared with ibuprofen. However, no difference was verified between UHMWPE, UHMWPE 3% IBU and UHMWPE 5% IBU after ibuprofen release. Finally, cell viability of UHMWPE 3% IBU and UHMWPE 5% was found to be superior to 100% (Figure 1). Therefore, both materials can be considered nontoxic.
Conclusions
Ibuprofen-loaded UHMWPE did not demonstrate a significant influence on the mechanical and biological behavior of UHMWPE. Dynamic-mechanical tests demonstrated constancy for all samples under analysis. Wear testing resulted in gravimetric wear close to zero, for all tested materials. Mechanical properties conducted after 30 days of ibuprofen release also had a positive outcome. Although presenting a difference in modulus prior and after release tests, modulus and tensile yield stress remained inside acceptable range indicated to UHMWPE used in orthopedic implants. Furthermore, after drug elution UHMWPE 3% IBU and UHMWPE 5% IBU recovered original UHMWPE properties. Cytotoxicity assessment was performed and both ibuprofen-based formulations were considered nontoxic according to ISO 10993–5.
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