A Study on the preparation of polymeric microspheres using microfluidic devices

利用微流控装置可以制备直径为10-100μm的单分散聚合物微球。主要研究内容包括：(A)用于液滴形成的微流体通道的制备；(B)液滴和聚合物颗粒的制备。通过机械加工(端铣刀、使用金刚石工具、安装砂轮等进行超精密切割)、激光加工(准分子激光)或光刻技术(各向同性湿法刻蚀、各向异性干法刻蚀)在聚合物或玻璃衬底上制备横截面尺寸为10-100μm的微通道。干法刻蚀制备的玻璃通道尺寸精确、纵横比高。采用不同几何形状的微流控通道(T形结、交叉结、流聚焦结)进行液滴形成实验。通道表面的润湿问题对液滴的破碎条件非常重要，亲水性玻璃微通道适合制备O/W乳液，而O/W乳液是制备聚合物微球所必需的。通过改变待分散相和连续相的流动条件，可以较大地改变液滴的尺寸。得到的单体液滴最小直径约为15μm，多分散度小于5%。此外，通过在芯片上集成多个通道，可以成倍地提高生产效率。随后的光诱导或热诱导聚合可得到CV值小于5%的15-100μm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.