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.

Keywords: biaxial flexural strength; compressive strength; cranioplasty fixation; germanium; glass polyalkenoate cemets; ovis aries bone; tensile strength; titanium miniplate.

Figure 1

(A) displays the Ti Cylinder; (B) shows the thread in the center. (A) and (B) illustrate the materials used in the construction of the test rig; (C) displays a layer of one of the GPCs; (D) shows the Ti and bone samples used; (E) is the anchor that is screwed into the threaded center of the Ti cylinder. (a) The Ti cylinder with a layer of cement attached to the center of the Ti and bone samples, then stored in water for 1, 7 and 14 days; (b) After storage, the anchor was screwed into the Ti cylinder prior to testing.

Figure 2

Bond Strength Test. (a) The start of the test; (b) The bone samples hit equally flat on the X points for both sides, the construct is elevated at 1 mm/ min then the tensile bonding test begins and continues upwards until the failure occurs.

Figure 3

XRD patterns of the formulated glasses (KBT) series.

Figure 4

SEM micrographs. (a) KBT01; (b) KBT02; (c) KBT03.

Figure 5

(a) Working times of the cement series; (b) Net setting times of the cement series. Stars and bars show statistical significance (p < 0.05).

Figure 6

Compressive strengths for the cement series over 1, 7 and 30 days maturation. Stars and bars show statistical significant difference (p < 0.05).

Figure 7

Biaxial flexural strengths for the cement series over 1, 7 and 30 days maturation. Stars and bars show statistical significant difference (p < 0.05).

Figure 8

Tensile strength measurements for the bond strength tested over 1, 7, and 14 days.

Figure 9

Cement/ovis aries bone constructs after: (a) 0 and 1 day maturation; (b) 7 days maturation; (c) 14 days maturation.

Figure 10

Ion release profiles for the cement series over 1, 7 and 30 days.

Figure 11

(a) Radiograph image of the cement sample and SP3 standard; (b) Comparison of the radiopacity of the cements.

Figure 12

Setting time and compressive strength of aluminum-free GPCs reported in the literature. the blue frame denotes the results of this paper.