Adsorption of Zirconyl Salts and Their Acids on Hydroxyapatite: Use of the Salts as Coupling Agents to Dental Polymer Composites

Abstract

Zirconyl methacrylate (I) and zirconyl-2-ethylhexanoate (II) were synthesized, and their adsorption isotherms from solutions onto synthetic hydroxyapatite were studied. The isotherms of methacrylic and 2-ethylhexanoic acids were also determined from the same solvents. The adsorption of I was irreversible from methylene chloride, and that of II was irreversible from cyclohexane. The adsorption in both cases was constant from solutions above a certain concentration, and exhaustive below this threshold concentration. Both compounds rendered the dried apatite powder extremely hydrophobic; however, the adsorbate was slowly washed off by excess water. The configuration of the adsorbate molecules, deduced from the maximum adsorption and other adsorption characteristics of the two compounds, indicated that: (i) in both cases the adsorbate may be held to the surface by concerted hydrogen bonding of the carboxylate and zirconyl oxygen atoms; and (ii) the hydrocarbon moieties in both adsorbates expose themselves toward the solution, thereby making the dried surface hydrophobic. The adsorptive behavior of the respective acids was similar to that of the salts. Polymer, filled with synthetic hydroxyapatite covered with irreversibly adsorbed I, had a diametral tensile strength about 50% greater than that of the polymer filled with untreated apatite. The strength of the composite was not affected by treatment of the apatite with II or with the acids.

Calcium orthophosphate-based biocomposites and hybrid biomaterials

“…Therefore, polymers with functional groups pendant to the polymer backbone, which can act as sites for bridging to calcium orthophosphates, are more promising in this respect [49]. Besides, the surface of calcium orthophosphates might be modified as well [116,416,417,552,914,915]. In order to improve the situation, various supplementary reagents are applied.…”

“…Other researchers used glutaraldehyde as a crosslinked reagent in various calcium orthophosphate-based biocomposites [388,392,500,502,503,520,525,585,621,646,649,917]. The interfacial bonding between calcium orthophosphates and other components might be induced by using various coupling agents and surface modifiers, such as silanes [192,234,337,540,[918][919][920][921][922][923], zirconates [225,337,339,914,924], titanates [225,337,924], phosphoric acid [543], alkaline pretreatment [722,725], polyacids [115,116,234], and other chemicals. Besides, some polymers might be grafted onto the surface of calcium orthophosphates [552].…”

Biocomposites and hybrid biomaterials based on calcium orthophosphates

“…1133 Other researchers used glutaraldehyde as a cross-linked reag ent. 470,474,598,600,601,619,624,699,736,778,781,1141 Alternatively, the interfacial bonding among calcium orthophosphates and other components might be induced by silanes, 242,268,269,293,406,640,[1142][1143][1144][1145] zirconates, 282,406,408,1146,1147 titanates, 282,406,1146 phosphoric acid, 643 alkaline pretreatment, 877,880 polyacids 143,144,293 and some other chemicals. Furthermore, some polymers might be grafted onto the surface of calcium orthophosphate particles.…”

“…179 In addition to the aforementioned, the surface of calcium orthophosphates might be modified as well. 144,509,510,656,[1147][1148][1149][1150][1151][1152][1153][1154] An interesting approach for HA surface modification was described by Lee et al 1154 First, in situ synthesis of surface thiol-functionalized HA (HA-SH) was realized by adding 3-mercaptopropionic acid during hydrothermal synthesis of HA (Fig. 10A).…”

“…1154 Other examples might be found in the literature. 144,509,510,656,[1147][1148][1149][1150][1151][1152][1153] In general, the purpose of surface modifying is not only to guarantee the even distribution of calcium orthophosphate particles at a high loading level in the matrix, but also to prevent or delay the debonding process of calcium orthophosphate particles from the matrix. Obviously, all surface modifiers must satisfy several biomedical requirements, such as no toxicity, good biocompatibility and no changes in the biological or physicochemical properties of the fillers.…”