Liquid Crystal Membranes for Serum-Compatible Diabetes Management-Assisting Subcutaneously Implanted Amperometric Glucose Sensors
作者:Pawel Rowinski、Magdalena Rowinska、Adam Heller
DOI:10.1021/ac702151u
日期:2008.3.1
Membranes formed of thermodynamically stable cubic phase lyotropic liquid crystals (LLCs) could replace the presently used polymeric membranes, applied to reduce the flux of glucose in semicontinuous, subcutaneously implanted, user-replaced, miniature, amperometric glucose sensors, assisting in the management of diabetes. LLC-forming amphiphilic compounds set and toughen spontaneously after mixing with water, without undergoing chemical change. When applied by doctor-blading, they form membranes having three-dimensionally interconnected water channels of uniform diameter, with reproducible glucose transport-characteristics. We find that the best studied cubic phase LLCs, which are formed of monoolein and water, are not useful in their intended application because they are hydrolyzed by serum lipases. Those formed of phytantriol, a liquid at ambient temperature, and water, are not hydrolyzed but change their shape and size in a dehydration and rehydration cycle. Because glucose sensors are sterilized and stored in a sealed package in a dry atmosphere, drying and rehydration must not change the transport characteristics. A third, novel, LLC-forming, amphiphile 1-O-β-(3,7,11,15-tetramethylhexadecyl)-d-ribopyranoside, I, was synthesized, and its phase diagram was tailored by adding Vitamin E acetate, to form a cubic phase. The phase was stable through the 20 °C−90 °C temperature range in excess of water and had the desired glucose-transport characteristics. A preferred LLC, II, was formed of water and I containing 7 wt % of Vitamin E acetate. When II was applied to a wired glucose oxidase bioelectrocatalyst, sensors of reproducible glucose-sensitivity were formed. At a 0.1 mm thickness of II, the membrane reduced the glucose flux 5-fold and increased the 90% response-time by less than 2 min. The membrane was mechanically rugged, withstanding the ∼1 N m-2 maximal shear stress at 5 mm diameter electrodes rotating at 4000 rpm. The activation energy for glucose permeation through II was reduced to 15.6 kJ/mol, making the sensors's current less temperature-dependent than that of the polymeric-membrane overcoated implantable glucose sensors.
由热力学稳定的立方相液晶(LLCs)形成的膜可以替代目前用于减少在半连续皮下植入、用户可更换的微型安培式葡萄糖传感器中葡萄糖通量的聚合物膜,从而帮助糖尿病管理。形成LLC的两亲化合物在与水混合后自发凝聚并变得坚韧,而不经历化学变化。通过刮涂法应用后,它们形成具有均匀直径的三维互联水通道的膜,具有可重复的葡萄糖传输特性。我们发现,最常研究的由单油酸酯和水形成的立方相LLC在预期应用中并不实用,因为它们会被血清脂肪酶水解。而由在常温下为液态的植物三醇和水形成的LLC则不会被水解,但在脱水和再水化过程中会改变形状和大小。由于葡萄糖传感器在密封包装中以干燥气氛进行消毒和存储,因此干燥和再水化不得改变传输特性。合成了一种新的LLC形成两亲化合物1-O-β-(3,7,11,15-四甲基十六烷基)-d-核糖吡喃苷I,并通过添加维生素E醋酸盐来调整其相图,以形成立方相。该相在20 °C到90 °C的温度范围内在水的过量下保持稳定,并具有所需的葡萄糖传输特性。优选的LLC II由水和含有7 wt%维生素E醋酸盐的I形成。当II应用于有线葡萄糖氧化酶生物电催化剂时,形成了具有可重复葡萄糖灵敏度的传感器。在II的厚度为0.1 mm时,该膜使葡萄糖通量减少了5倍,并且90%响应时间增加不到2分钟。该膜机械坚固,能够承受约1 N m-2的最大剪切应力,在直径5 mm、旋转速度为4000 rpm的电极上。葡萄糖通过II的渗透活化能降低至15.6 kJ/mol,使传感器的电流对温度的依赖性低于覆盖聚合物膜的可植入葡萄糖传感器。