Biofilm inhibitory coatings formulated from glass polyalkenoate cement chemistry: an evaluation of their adhesive nature

Abstract

Glass polyalkenoate cements (GPCs), are formed by the reaction between an ion-leachable glass and an aqueous solution of polyacrylic acid (PAA) [1]. GPCs may also be formed from a combination of polyalkenoaic acids and various fillers such as those based on the use of additional fillers like N,N0-methylenebisacrylamide to increase their strength and toughness [2]. These materials can be formulated to be anticariostatic [3] by the inclusion of fluoride in the glass phase of GPCs which subsequently releases beneficial amounts of the F ion into the oral environment [4, 5]. Commercially available GPCs are all based on calcium alumino silicate glass chemistry [6]. Aluminium is present in the glass because it can isomorphically replace the SiO4 tetrahedra within the glass structure. This causes a local charge imbalance within the structure, resulting in the acid degradability of the glass [7]. More importantly, aluminium is essential for the mechanical integrity of the cement as the ions undergo cement forming [8]. However, the presence of aluminium retards the medical and surgical applications of such cements as aluminium ions (Al) released in vivo can cause demineralisation of the bone [9] and has been implicated in the pathogenesis of degenerative brain diseases including Parkinson’s and Alzheimer’s disease [10, 11]. The authors have developed GPCs based on calcium zinc silicate, rather than calcium alumino silicate glasses [3, 12–14], where the zinc ion (Zn) replaces Al, as it can act as a network modifying oxide in the glass phase [9, 15]. A serendipitous effect of developing zinc-based GPCs was that these cements have antimicrobial ability [3] as the release of zinc ions inhibits bacterial growth. The silver ion (Ag) also has an acknowledged antibacterial effect [16, 17] and the authors have recently developed coatings based on silver/zinc-based GPCs which have proven bactericidal efficacy against S. aureus and P. aeruginosa, common aetiological agents of hospital-acquired infections [18]. In that study, the authors also reported that these GPC coatings adhere to Ti6Al4V titanium alloy. Conventional GPCs are inherently capable of chemically bonding to metal substrates [19] with the assistance of the oxide layer which forms on the alloy surface [20]. However, the authors have not yet reported on the extent of this bonding between these silver/zinc-based GPC coatings and metal. There have been previous studies to create novel testing modalities to evaluate the bond strength of luting cements some of which have been previously reported by the authors [21]. One in-house study involved sandwiching the GPC between hydroxyapatite (HA, a material comparable to the mineral phase of bone) and hardened steel discs [21]. However, the possible applications of these silver/zinc-based GPC coatings include a range of clinical applications where biofilms can proliferate, such as on hard surfaces (surgical stainless steel) [22] and flexible surfaces (tubing for catheters and aspirators) [23], and so the objective of this study is to modify the conventional T-peel test [24], historically employed to determine resistance of a bonded assembly of two adherents when at least one adherent is flexible [24], to quantify the bond between tape and a surgical metal substrate bonded by a luting GPC. There are two types of peel A. Coughlan M. R. Towler (&) Clinical Materials Unit, Materials and Surface Science Institute, University of Limerick, National Technological Park, Limerick, Ireland e-mail: Mark.Towler@ul.ie