Mechanical properties of single alginate microspheres determined by microcompression and finite element modelling
Mechanical properties of single alginate microspheres determined by microcompression and finite element modelling
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DOI：
10.1016/j.ces.2008.10.050
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发表时间：
2009-03-01
影响因子：
4.7
通讯作者：
Zhang, Z.
中科院分区：
文献类型：
--
作者：
Nguyen, V. B.;Wang, C. X.;Zhang, Z.
海藻酸钙微球作为药物释放系统的载体、生物催化剂等生物材料的包埋体以及组织工程中的基质已被广泛研究。了解这种微球的机械性能是至关重要的，因为它们在加工和最终应用过程中可能会受到机械力的影响。为了表征其力学性能，可以将微球压缩在两个平面之间，并将理论模型应用于力-位移和力-时间数据，以提取力学性能参数。在以前的工作中，单个海藻酸钙微球被压缩，然后保持恒定变形，并测量施加在其上的力。结果表明，力随着变形的增加而增大，并且在保持过程中有明显的力松弛。在这项工作中，通过有限元分析模拟了单个(102微米)海藻酸钙微球的压缩和保持对应的力-位移/时间数据。由于力松弛可能是由失水或微球粘弹性引起的，因此首先使用多孔弹性材料模型来评估在保持过程中微球固体基质失水的潜在影响。通过图像分析，确定了微球在压缩和松弛过程中的体积损失。假设体积的所有变化都是由于失水引起的，并假设海藻酸盐渗透率的文献值，孔弹性材料模型表明失水对松弛过程中的力行为的影响很小，可以忽略不计。这使得可压缩、各向同性和均匀的线性粘弹性材料模型可以根据实验松弛数据进行评估，以获得微球的粘弹性参数。具有两个松弛时间的粘弹性材料模型对压缩和松弛都有很好的模拟能力。瞬时弹性模数为490kPa，长期弹性模数为68.6kpa，松弛时间为0.013和0.085 S。通过有限元模拟得到了压缩微球的接触半径、中心侧向伸长量等变形参数，并与实验数据进行了比较，结果表明该模型具有较好的一致性，至少对被测微球是有效的。(C)2008爱思唯尔有限公司。保留所有权利。
Calcium alginate microspheres have been studied extensively as carriers in drug delivery systems, for encapsulation of biological materials such as biocatalysts, and as matrices in tissue engineering. Understanding the mechanical properties of such microspheres is essential because they may be exposed to mechanical forces during processing and in end applications. In order to characterise their mechanical properties, microspheres may be compressed between two flat surfaces, and a theoretical model applied to the force-displacement and force-time data to extract mechanical property parameters. In previous work, single calcium alginate microspheres were compressed and then held at constant deformation, and the force being imposed on them was measured. It was found that the force increased with deformation, as expected, and that there was significant force relaxation during holding. In this work, force versus displacement/time data corresponding to compression and holding of a single (102 mu m) calcium alginate microsphere were modelled by finite element analysis. Since the force relaxation might be due to water loss or microsphere viscoelasticity, a poroelastic material model was first used to assess the potential effect of water loss from the microsphere solid matrix during holding. Using image analysis, the volume loss during compression and relaxation of the microsphere was determined. Assuming all the change in volume was due to water loss, and assuming a literature value of alginate permeability, the poroelastic material model showed that the effect of water loss on the force behaviour was small enough during relaxation that it might be neglected. This allowed a compressible, isotropic and homogeneous linear viscoelastic material model to be evaluated against experimental relaxation data to obtain viscoelastic property parameters of the microsphere. A viscoelastic material model with two relaxation times showed excellent capability in modelling both compression and relaxation. The instantaneous elastic modulus, long-term elastic modulus and the two relaxation times were found to be 490, 68.6 kPa, and 0.013 and 0.085 s, respectively. Deformation parameters of the compressed microsphere such as the contact radius and central lateral extension were also obtained from finite element modelling, and were compared with experimental data, showing good agreement and confirming the validity of the model at least for the microsphere under test. (C) 2008 Elsevier Ltd. All rights reserved.