Glass Polyalkenoate Cements Designed for Cranioplasty Applications: An Evaluation of Their Physical and Mechanical Properties

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 a series of aluminum-free GPCs constructed from silicate (SiO2), calcium (CaO), zinc (ZnO) and sodium (Na2O)-containing glasses mixed with poly-acrylic acid (PAA) and to evaluate the potential of these cements for cranioplasty applications. Three glasses were formulated based on the SiO2-CaO-ZnO-Na2O parent glass (KBT01) with 0.03 mol % (KBT02) and 0.06 mol % (KBT03) germanium (GeO2) substituted for ZnO. Each glass was then mixed with 50 wt % of a patented SiO2-CaO-ZnO-strontium (SrO) glass composition and the resultant mixtures were subsequently reacted with aqueous PAA (50 wt % addition) to produce three GPCs. The incorporation of Ge in the glass phase was found to result in decreased working (142 s to 112 s) and setting (807 s to 448 s) times for the cements manufactured from them, likely due to the increase in crosslink formation between the Ge-containing glasses and the PAA. Compressive (σc) and biaxial flexural (σf) strengths of the cements were examined at 1, 7 and 30 days post mixing and were found to increase with both maturation and Ge content. The bonding strength of a titanium cylinder (Ti) attached to bone by the cements increased from 0.2 MPa, when placed, to 0.6 MPa, after 14 days maturation. The results of this research indicate that Germano-Silicate based GPCs have suitable handling and mechanical properties for cranioplasty fixation.

An Injectable Glass Polyalkenoate Cement Engineered for Fracture Fixation and Stabilization

“…The network connectivity for KT1, KT2 and KT3 was calculated to be 2, 2.2 and 2.4, respectively [ 24 ], as increasing the amount of GeO increased network connectivity. XRD confirmed that no crystalline phases were present within the glasses ( Figure 4 ).…”

“…In this study, in addition to maturation, strengths also increased with Ge content. Ge is a 4+ valency ion; thus, it will bond and increase the network connectivity (NC) of the cement [ 24 ]. Hill et al [ 38 ] described the entanglement of polyanion chains during GPC setting and how they limit lateral movement, while interactions with neighboring chains limit longitudinal movement.…”

“…Three glass compositions, KT1, KT2 and KT3, were formulated. The control, KT1, was a SiO 2 (0.50) + CaO (0.10) + ZnO (0.30) + Na 2 O (0.10) glass; KT2 and KT3 contain incremental additions of Ge added at the expense of Zn ( Table 1 ) [ 24 ].…”

“…The network connectivity of the glasses was calculated using Equation (1) [ 25 ] where SiO 2 and GeO 2 were considered to act as network formers and CaO, ZnO and Na 2 O as network modifiers [ 24 ]. where NC = Network Connectivity, BO = Bridging Oxygens, NBO = Non-Bridging Oxygens.…”

“…Germanium (Ge) has been incorporated into the glass as it adopts the role of a network former and is theoretically able to isomorphically replace Si in the network [ 23 ]. The work contained herein expands partly on the authors’ earlier work [ 24 ], by further investigating the applicability of germano-silicate glasses as the glass component in an injectable GPC for fracture fixation whilst also evaluating the suitability of these materials as carriers for biologics; in this case, bovine serum albumin (BSA), an analogue for bone morphogenetic protein-2.…”