Vogelsang C, Wijffels R H, Ostgaard K
Department of Biotechnology, Norwegian University of Science and Technology, N-7491 Trondheim, Norway.
Biotechnol Bioeng. 2000 Nov 5;70(3):247-53. doi: 10.1002/1097-0290(20001105)70:3<247::aid-bit1>3.0.co;2-#.
The mechanical stability of gels applied for entrapment and retention of biocatalysts in bioreactors is of crucial importance for successful scale-up applications. Gel abrasion in agitated reactors will depend on liquid shear, bubble shear, and wall shear, as well as collisions between the gel particles. As a simplified standardized model system, abrasion of gel beads was studied in 1-m-high bubble columns with controlled aeration, and quantified by measuring the loss of gel material into solution. Gel beads were also taken out to measure stress-strain response during controlled compression. More general rheological properties of different gels were studied by applying a variety of regimes of controlled compression of standardized gel cylinders: Gel strength was measured by recording the fracture properties and the Young's modulus. Viscoelastic properties were revealed by recording creep during compression as well as recovery after compression. Oscillation tests up to 1000 cyclic compressions were applied to compare the fatigue of different gels. Results obtained for Ca-alginate gels, gels of chemically modified polyvinyl alcohol with stilbazolium groups (PVA-SbQ) as well as mixed gels of Ca-alginate and PVA-SbQ are compared with previously published data for kappa-carrageenan, agar, and polyethylene glycol (PEG) gels. It is concluded that material fatigue rather than mechanical properties such as stiffness or fracture stress should be considered when selecting a suitable gel material on the basis of abrasion resistance. The very soft and superelastic PVA-SbQ gel showed no significant fatigue in mechanical tests and no abrasion was detected in the standardized model system used. Ca-alginate gels, however, showed severe irreversible changes due to fatigue at oscillating loads and creep at constant load. Due to their similarities with kappa-carrageenan gels in mechanical tests, it is likely that Ca-alginate would also be sensitive to abrasion. Mixed gels of Ca-alginate and PVA-SbQ represent a complex system with intermediate properties, showing significant fatigue and creep, but elastic properties from the PVA-SbQ gel make it less sensitive than the pure Ca-alginate gel.
用于在生物反应器中包埋和保留生物催化剂的凝胶的机械稳定性对于成功扩大应用规模至关重要。搅拌式反应器中的凝胶磨损将取决于液体剪切力、气泡剪切力和壁面剪切力，以及凝胶颗粒之间的碰撞。作为一个简化的标准化模型系统，在1米高的具有可控曝气的鼓泡塔中研究了凝胶珠的磨损，并通过测量进入溶液的凝胶材料损失来进行量化。还取出凝胶珠以测量在可控压缩过程中的应力-应变响应。通过对标准化凝胶圆柱体施加各种可控压缩方式，研究了不同凝胶更一般的流变特性：通过记录断裂特性和杨氏模量来测量凝胶强度。通过记录压缩过程中的蠕变以及压缩后的恢复来揭示粘弹性特性。应用高达1000次循环压缩的振荡试验来比较不同凝胶的疲劳情况。将海藻酸钙凝胶、具有二苯乙烯基联吡啶基团的化学改性聚乙烯醇（PVA-SbQ）凝胶以及海藻酸钙和PVA-SbQ的混合凝胶所获得的结果与先前发表的关于κ-卡拉胶、琼脂和聚乙二醇（PEG）凝胶的数据进行了比较。得出的结论是，在基于耐磨性选择合适的凝胶材料时，应考虑材料疲劳而非诸如刚度或断裂应力等机械性能。非常柔软且超弹性的PVA-SbQ凝胶在机械测试中未显示出明显的疲劳，并且在所使用的标准化模型系统中未检测到磨损。然而，海藻酸钙凝胶在振荡载荷下由于疲劳以及在恒定载荷下的蠕变而表现出严重的不可逆变化。由于它们在机械测试中与κ-卡拉胶凝胶相似，海藻酸钙很可能也对磨损敏感。海藻酸钙和PVA-SbQ的混合凝胶代表了一个具有中间特性的复杂系统，表现出显著的疲劳和蠕变，但来自PVA-SbQ凝胶的弹性特性使其比纯海藻酸钙凝胶更不敏感。
