Abstract
Phosphoserine-modified cements (PMCs) are a family of wet-field tissue adhesives that bond strongly to bone and biomaterials. The present study evaluated variations in the adhesive strength using a scatter plot, failure mode, and a regression analysis of eleven factors. All single-factor, continuous-variable correlations were poor (R2 < 0.25). The linear regression model explained 31.6% of variation in adhesive strength (R2 = 0.316 p < 0.001), with bond thickness predicting an 8.5% reduction in strength per 100 μm increase. Interestingly, PMC adhesive strength was insensitive to surface roughness (Sa 1.27–2.17 μm) and the unevenness (skew) of the adhesive bond (p > 0.167, 0.171, ANOVA). Bone glued in conditions mimicking the operating theatre (e.g., the rapid fixation and minimal fixation force in fluids) produced comparable adhesive strength in laboratory conditions (2.44 vs. 1.96 MPa, p > 0.986). The failure mode correlated strongly with the adhesive strength; low strength PMCs (<1 MPa) failed cohesively, while high strength (>2 MPa) PMCs failed adhesively. Failure occurred at the interface between the amorphous surface layer and the PMC bulk. PMC bonding is sufficient for clinical application, allowing for a wide tolerance in performance conditions while maintaining a minimal bond strength of 1.5–2 MPa to cortical bone and metal surfaces.
Highlights
A number of adhesives have been proposed for tissue reconstruction
Preliminary testing identified a number of factors, and covariates, that could contribute to the adhesive strength after curing for 24 h (Table 1)
The purpose of this study was (a) to identify which factors contribute to adhesive strength in Phosphoserine-modified cements (PMCs), and (b) to bridge disparate test conditions, thereby allowing for comparisons/predictions on how PMC formulations behave in both the laboratory and the clinic
Summary
A number of adhesives have been proposed for tissue reconstruction. Aside from non-degradable adhesives [1], most biocompatible and biodegradable tissue adhesives utilize crosslinking mechanisms inspired by natural (marine) adhesives. The most common approach to creating adhesion is to incorporate a modified amino acid, L-DOPA (e.g., as a pendant group, onto a polymer) [2,3]. Strong adhesion has been created in biomaterials that are not adhesive (bioceramics) by incorporating a modified amino acid (phosphoserine) [8,9,10]. PMCs are suited for hard tissue applications, with a stronger compressive and (adhesive) shear strength than human cancellous bone [10,16], because they remodel into bone in vivo [10,12,13,14]. Prior in vivo studies have demonstrated that PMCs are safe (no adverse reactions) and readily remodel into bone [8,12,13,14]. The focus of the present study was the physical (e.g., bond strength), rather than biological properties of PMCs
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