A Study on the preparation of polymeric microspheres using microfluidic devices

使用微流控装置可以制备直径为10-100 μm的单分散聚合物微球。本论文的主要研究内容包括：（a）微流控通道的制备：（B）微滴和聚合物颗粒的制备：通过机械加工（端铣刀、金刚石工具超精密切削、砂轮等）在聚合物或玻璃基底上制备出截面尺寸为10-100 μm的微通道，激光加工（受激准分子激光）或光刻技术（各向同性湿法蚀刻、各向异性干法蚀刻）。采用干法刻蚀技术制备的玻璃微通道具有精确的尺寸和较高的纵横比，采用不同几何形状（T型、交叉型、流动聚焦型）的微流体通道进行液滴形成实验。通道表面的润湿问题被发现是非常重要的液滴破碎的条件，亲水性玻璃微通道被发现是适合于O/W乳液的制备，这是必要的生产聚合物微球。通过改变待分散相和连续相的流动条件，可以使液滴尺寸发生较大变化。所得单体液滴的最小粒径约为15 μm，多分散性小于5%。此外，生产效率可以通过在芯片上集成多个通道而倍增。通过光引发或热引发聚合，可得到粒径为15-100 μm、CV小于5%的聚合物粒子。

Monodisperese polymeric microspheres having 10-100 μm diameter can be prepared using microfluidic devices. Main parts of our research include the followings : (a) fabrication of microfluidic channels for the droplet formation ; (b) preparation of droplets and polymeric particles.Microchannels with cross-sectional dimensions of 10-100 μm were fabricated on polymer or glass substrate by mechanical machining (endmill, ultra-precision cutting using diamond tools, mounted wheels, etc.), laser machining (excimer laser) or lithographical techniques (isotropic wet etching, anisotropic dry etching). Glass channels fabricated by dry etching could have accurate dimensions and higher aspect ratio.Microfluidic channels having various geometries (T-junction, cross-junction, flow-focusing junction) were used for droplet formation experiments. The wetting issue of the channel surface was found to be very important for the condition of droplet breakup, and hydrophilic glass microchannels were found to be suitable for the preparation of O/W emulsions, which is necessary for the production of polymeric microspheres. Droplet size could be varied widely by changing flow conditions of to-be-dispersed phase and continuous phase. The minimum diameter of monomer droplets we achieved was about 15 μm and the polydispersity was under 5%. Further, the production efficiency could be mulitplied by integrating multiple channels on a chip. 15-100 μm polymeric particles with CV less than 5% could be obtained by subsequent photo-induced or heat-induced polymerization.