Thin film PMMA precoating for improved implant bone–cement fixation

Abstract

It has been argued that various specific requirements based on known principles of good adhesion are not being met in the current procedures of formation of the implant-bone cement interface. It has been shown that an annealed thin film PMMA precoating, applied in a low-contact-angle form to surgical alloy surfaces devoid of weak boundary layers, satisfies the majority of the requirements during interface formation. Techniques for the application of the precoating have been developed for SS316LVM, Co-Cr-Mo, and Ti-6A1-4V based on fracture toughness and fatigue tests, and fractography of the interface. Implant surface preparation methods have been established to yield surfaces amenable to adhesive bonding. The composition of the coatings have been studied from the point of view of implant surface wetting, coating roughness and thickness, and interface strength. A biocompatible silane coupling agent (A-174), currently used in orthodontics, has been introduced to provide saline resistant interfaces. The final precoated metal-bone cement interfaces have demonstrated fracture toughnesses in excess of that of bone cement even after prolonged exposure to 37°C physiological saline. Fatigue tests have shown that the fatigue lives (6.5 MPa) of the precoated metal interfaces in saline are at least twice, and in one case several orders of magnitude greater than, that of the uncoated ones even when the latter are tested dry. Fractography of the interfaces show failures that are entirely cohesive in nature. For the UHMWPE (ultrahigh molecular weight polyethylene)-bone cement interface, similar improvement with precoating, however, could not be attained. Finally, the coated metal-bone cement interfaces have been tested as a function of some clinical variables such as cement type, joining time, clinical contamination, and sterilization procedure. Results show that coated metals exhibit a certain level of insensitivity to these variables and retain their performance under all conditions except after particular repeated sterilizations.

The effect of a silane coupling agent on the bond strength of bone cement and cobalt-chrome alloy

“…There was no significant degradation of the silanecoated samples after saline immersion. In addition, the mean failure strengths achieved after silane coating were comparable to the highest strengths achieved by Raab et al and May et al 9,13,17 The primary difference between the current study and the previous studies lies in the surface preparation of the implant surface. Raab et al described an elaborate surface preparation that involved: (1) degreasing the metal specimen in 1N of boiling NaOH for 10 min, (2) rinsing the specimen in H 2 SO 4 for 10 s, (3) passivating it in HNO 3 for 10 min, and (4) ultrasonically rinsing it in distilled water twice for 5 min between each step.…”

“…The increase in failure strength as a result of silane bonding is not surprising and follows a similar trend reported by others. 9,13,17 In a dental application, May et al reported a 48% (16.1 to 23.8 MPa) increase in the push-out strength of silane-coated CoCr bonded to PMMA compared to uncoated samples. 17 Earlier, they reported a 69% (15.7 to 26.3 MPa) increase in push-out strength in grit-blasted specimens with similar surface treatments.…”

“…The model used in the current study was similar to that used by Ahmed et al and Raab et al, and this allowed for a direct comparison between the data from the current study and previous studies. 9,24 A model that mimics the in vivo environment one step further than the previously mentioned push-out models is an in vivo animal model. Barb et al bilater- ally implanted uncoated and PMMA-precoated CoCr femoral prostheses in canine femora for 1, 2, and 6 months.…”

“…13 Similarly, Raab et al, tested silane-coated CoCr samples in shear to failure using a push-out model. 9 Samples were tested 24 h after preparation and after 30 and 60 days of saline solution immersion at 37°C. There was no significant difference in mean push-out strength among any of the treatments (range: 24.8-25.7 MPa), yet each was significantly greater than the mean strength of uncoated specimens (6.9 MPa).…”

Surface roughness of debonded straight-tapered stems in cemented THA reduces subsidence but not cement damage

“…Cementing techniques [16], surface roughness patches [17], textures [18], and pre-coatings [7,[19][20][21] have been considered to create a reliable and endurable fixation. However, as long as the bond between the stem and the cement mantle cannot be secured for the complete lifetime of the implant, not just the bonding strength, but also the fail-safe mechanism against the effects of debonding should be considered.…”