Germanium glass polyalkenoate cements for cranioplasty fixation

Abstract

Glass polyalkenoate cements (GPCs) have potential for skeletal cementation. Unfortunately, commercial GPCs all contain and subsequently release aluminum ions, which have been implicated in degenerative brain disease. The purpose of this research was to create aluminum free GPCs constructed from silicate (SiO2)-calcium (CaO)-zinc (ZnO), glasses mixed with polyacrylic acid (PAA200) in order to evaluate the potential of these novel GPCs for attaching titanium miniplates directly to the skull, a clinical procedure known as cranioplasty. Three glasses were formulated: KBT01 SiO2-CaO-ZnO-sodium (Na2O) glass, KBT02 SiO2-CaO-ZnO-Na2Ogermanium (GeO2), with a 0.03 mol% GeO2 substitution for ZnO and KBT03 SiO2-CaO-ZnONa2O- GeO2, with a 0.06 mol% GeO2 substitution for ZnO in glass structure. X-ray diffraction (XRD) and particle size analysis (PSA) confirmed that all glasses were completely amorphous with similar mean particle sizes. Each glass in the series was mixed with 50 wt% a patented SiO2- CaO-ZnO-strontium (SrO) glass composition, BT101, and subsequently mixed with PAA200 at 50 wt% addition to produce a series of cements. The addition of Ge to the glass series resulted in decreased working times (~142 s to 112 s) and setting times (~807 to 448 s) for the cements manufactured from them. This was due to the increase in crosslink formation during the setting reaction between the Ge-containing glasses and the PAA200. Regarding ion release, Atomic Absorption Spectroscopy (AAS) determined Zn2+ ion release to be 9.56, 8.02 and 5.83 ppm after 30 days for KBT01, KBT02 and KBT03 cements respectively. Germanium ions were not released from the KBT01 cement since the glasses it was formulated from did not contain Ge4+. KBT02 and KBT03 cements released 1.23 ppm and 1.94 ppm of Ge4+ ions after 30 days. The mechanical properties (compressive ~ σc, and biaxial flexural strength ~ σf) of the resulting cements were of the resulting cements were examined over three time modalities, 1, 7 and 30 days. σc of the cements ranged from ~27- 56 MPa, while σf ranged from ~17-33 MPa. Both strength modalities increased with maturation and increasing Ge content, as Ge may facilitate improved chemical bonding between the COO- groups, thus creating stronger cements in KBT02 and KBT03. The bond strength of the titanium cylinder (Ti) to the bone that it was attached to by the cements increased from ~0.23MPA to 0.63 MPa respectively from placement up to 14 days maturation. Failure of these constructs occurred at the interface between the Ti cylinder and the cement. The results of this research indicate that, due to their novel composition, Ge-based GPCs have suitable handling properties, strengths and adhesiveness for potential in cranioplasty fixation.