Study On Mechanical Activation Strengthened Ultrahigh Molecular Weight Polyethelene Loaded With Alendronate Sodium

UHMWPE loaded with ALN,as a new orthopeadic biomaterial for joint replacements,has a wide variety of potential.UHMWPE has been used as the liner of AHJ over 50 years.However,the aseptic loosening of AHJ,which eventually leads to its failure,is found to be the most common result of wear debris,particularly,UHMWPE wear debris.To prolong the service life of AHJ,our research group was committed to reduce the generation of wear debris by loading ALN to UHMWPE.However,poor mechanical and tribological properties of UHMWPE-ALN are still obstacle for further application.It is hypothesized that the increasing of molecular connectivity between polymer particles reduces the fusion defects by mechanical activation,and consequently,improves the mechanical properties and wear resistance of UHMWPE.The purpose of this study was to investigate the effect and mechanism of mechanical activation on mechanical,tribological and drug release properties of ALN-loaded UHMWPE.The main contents and results of this study are shown as below;(1)The mechanical and tribological properties of untreated,dry ball milled and wet ball milled UHMWPE-ALN were investigated.The results of tensile test and small punch test showed that dry ball milling significantly increased the Young's modulus and tensile strength of UHMWPE-ALN,and significantly increased the Young's modulus,tensile strength and elongation at break of UHMWPE-ALN-F68.While it showed that wet ball milling significantly increased the Young's modulus and work-to-failure of UHMWPE-ALN,and significantly increased the Young's modulus,yield strength,tensile strength,elongation at break and work-to-failure of UHMWPE-ALN-F68.The results of contact angle test showed that both dry ball milling and wet ball milling increased the contact angle of UHMWPE-ALN and UHMWPE-ALN-F68 to water and 25 vol%calf serum.There is no significant difference between the contact angle of UHMWPE-ALN and UHMWPE-ALN-F68 to water and 25 vol%calf serum.The results of XRD showed that both dry and wet ball milling didn't affect the crystal parameter of UHMWPE-ALN and UHMWPE-ALN-F68.(2)Tensile test,small punch test and reciprocating sliding wear test were applied to characterize the mechanical and tribological properties of UHMWPE-ALN-ma.SEM,EDS and FTIR were employed to characterize UHMWPE-ALN-ma.Tensile test and small punch test showed that Young's modulus,tensile strength and WTF of UHMWPE-ALN-ma increased significantly compared to those of UHMWPE-ALN.The friction coefficients and wear factors of UHMWPE-ALN-ma both decreased significantly compared to those of UHMWPE-ALN.Mechanical activation obviously reduced type 1(void)and type 2(the disconnected and dislocated machining marks)fusion defects of UHMWPE-ALN-ma,which were revealed by SEM images of freeze fracture surfaces after etching and lateral surfaces of specimens after extension to fracture,respectively.It was attributed to peeled-off layers and chain scission of molecular chains of UHMWPE particles after mechanical activation,which were revealed by SEM images and FTIR spectra of UHMWPE-ALN-ma and UHMWPE-ALN,respectively.Moreover,EDS spectra revealed the more homogeneous distribution of ALN in UHMWPE-ALN-ma compared to that of UHMWPE-ALN.The present results showed that mechanical activation was a potential strategy to improve mechanical and tribological properties of UHMWPE-ALN-ma as an orthopeadic biomaterial for joint replacements.(3)Drug release properties of UHMWPE-ALN-ma and UHMWPE-ALN were investigated after friction and wear test for 10 days in 25 vol%calf serum.Lubricants of each day in the period of friction and wear test were taken out to determination the quantity of ALN released from UHMWPE-ALN-ma and UHMWPE-ALN under friction condition.The chromogenic reaction of ninhydrin and ALN was employed to determinate the concentration of ALN in the lubricants.The results showed that mechanical activation decreased the concentration of ALN released from UHMWPE-ALN and decreased the cumulative mass of ALN release.Besides,mechanical activation made the release velocity of ALN more uniform due to the uniform dispersion of ALN in UHMWPE-ALN.The drug release velocity of ALN from UHMWPE-ALN-ma and UHMWPE-ALN could be positive correlation to the degree of wear.