Standardized methodology for in vitro assessment of bone-to-bone adhesion strength

Advancement of adhesives technology has been limited in orthopedics, which still has a striking reliance on metal hardware to help facilitate fracture healing. Despite an obvious clinical need, bone adhesives are not currently available on the market. Testing the bone adhesion strength and other aspects of the adhesive performance is extremely complex. This paper presents standardized methodology for in vitro assessment of bone-to-bone adhesion strength. Two test configurations (lap shear and butt joint) were used to comparatively assess the adhesion strength of four commercially available adhesive material, poly(methyl methacrylate) cement (CMW), glass-ionomer cement (FUJI), dimethacrylate resin (SB) and cyanoacrylate resin (VB), which were allowed to set under two environmental conditions (air and water). Under dry conditions, both test configurations generally yielded similar measurements of adhesion strength, which was around 1.1, 2.8 and 9.1 MPa for CMW, FUJI and VB, respectively. The dry adhesion strength for SB measured using the butt configuration (2.5 MPa) was 43.2% higher compared to that measured using lap shear (1.4 MPa). In a wet environment, the measured adhesion strength generally decreased and was dependent on the test configuration used. The failure mode of the samples adhered using CMW was adhesive, while that using FUJI, SB and VB was a combination of both adhesive and cohesive, independent of the test configuration and the setting condition. This proposed methodology is comparable to ASTM standards and can be used to study the effect of different biomaterial formulations as well as test parameters on the bone-to-bone adhesion strength, in a reproducible manner.