Boyd D, Towler M R, Wren A, Clarkin O M
Materials & Surface Science Institute, University of Limerick, National Technological Park, Limerick, Ireland.
J Mater Sci Mater Med. 2008 Apr;19(4):1745-52. doi: 10.1007/s10856-007-3363-4. Epub 2008 Jan 16.
Conventional polymethylmethacrylate (PMMA) cements and more recently Bisphenol-a-glycidyl dimethacrylate (BIS-GMA) composite cements are employed in procedures such as vertebroplasty. Unfortunately, such materials have inherent drawbacks including, a high curing exotherm, the incorporation of toxic components in their formulations, and critically, exhibit a modulus mismatch between cement and bone. The literature suggests that aluminium free, zinc based glass polyalkenoate cements (Zn-GPC) may be suitable alternative materials for consideration in such applications as vertebroplasty. This paper, examines one formulation of Zn-GPC and compares its strengths, modulus, and biocompatibility with three commercially available bone cements, Spineplex, Simplex P and Cortoss. The setting times indicate that the current formulation of Zn-GPC sets in a time unsuitable for clinical deployment. However during setting, the peak exotherm was recorded to be 33 degrees C, the lowest of all cements examined, and well below the threshold level for tissue necrosis to occur. The data obtained from mechanical testing shows the Zn-GPC has strengths of 63 MPa in compression and 30 MPa in biaxial flexure. Importantly these strengths remain stable with maturation; similar long term stability was exhibited by both Spineplex and Simplex P. Conversely, the strengths of Cortoss were observed to rapidly diminish with time, a cause for clinical concern. In addition to strengths, the modulus of each material was determined. Only the Zn-GPC exhibited a modulus similar to vertebral trabecular bone, with all commercial materials exhibiting excessively high moduli. Such data indicates that the use of Zn-GPC may reduce adjacent fractures. The final investigation used the well established simulated body fluid (SBF) method to examine the ability of each material to bond with bone. The results indicate that the Zn-GPC is capable of producing a bone like apatite layer at its surface within 24 h which increased in coverage and density up to 7 days. Conversely, Spineplex, and Simplex P exhibit no apatite layer formation, while Cortoss exhibits only minimal formation of an apatite layer after 7 days incubation in SBF. This paper shows that Zn-GPC, with optimised setting times, are suitable candidate materials for further development as bone cements.
传统的聚甲基丙烯酸甲酯（PMMA）骨水泥以及最近的双酚A - 缩水甘油二甲基丙烯酸酯（BIS - GMA）复合骨水泥被用于椎体成形术等手术中。不幸的是，这类材料存在固有缺陷，包括固化时放热高、配方中含有有毒成分，以及关键的一点，骨水泥与骨之间存在模量不匹配的问题。文献表明，无铝的锌基聚链烯酸酯骨水泥（Zn - GPC）可能是椎体成形术等此类应用中值得考虑的替代材料。本文研究了一种Zn - GPC配方，并将其强度、模量和生物相容性与三种市售骨水泥Spineplex、Simplex P和Cortoss进行了比较。凝固时间表明，当前的Zn - GPC配方凝固时间不适合临床应用。然而在凝固过程中，记录到的最高放热温度为33摄氏度，是所有检测骨水泥中最低的，且远低于组织坏死发生的阈值水平。从力学测试获得的数据表明，Zn - GPC的抗压强度为63 MPa，双轴弯曲强度为30 MPa。重要的是，这些强度会随着材料成熟而保持稳定；Spineplex和Simplex P也表现出类似的长期稳定性。相反，观察到Cortoss的强度会随着时间迅速降低，这引发了临床关注。除了强度，还测定了每种材料的模量。只有Zn - GPC的模量与椎骨小梁骨相似，而所有市售材料的模量都过高。这些数据表明，使用Zn - GPC可能会减少相邻椎体骨折。最后的研究使用了成熟的模拟体液（SBF）方法来检测每种材料与骨结合的能力。结果表明，Zn - GPC能够在24小时内在其表面产生一层类似骨的磷灰石层，该层在覆盖范围和密度上会持续增加直至7天。相反，Spineplex和Simplex P没有形成磷灰石层，而Cortoss在SBF中孵育7天后仅形成了极少量的磷灰石层。本文表明，具有优化凝固时间的Zn - GPC是作为骨水泥进一步开发的合适候选材料。
