A novel combination of thermal bonding and inmold assembly technology was created to produce microfluidic chips out of polymethylmethacrylate (PMMA), which is named "in-mold bonding technology". In-mold bonding experiments of microfluidic chips were carried out to investigate the influences of bonding process parameters on the deformation and bonding strength of microchannels. The results show that bonding temperature has the greatest impact on the deformation of microchannels, while bonding pressure and bonding time have more influence on deformation in height than in top width. Considering the bonding strength, the bonding temperature and the bonding pressure have more impact than the bonding time. The time is crucial for the sealing of the chips. By setting the bonding parameters reasonably, the microchannel deformation is < 10%, while the bonding strength of the chips is 350 kPa. The production cycle of the chip is reduced to < 5 min.

Microfluidic chips have been widely applied in biochemical analysis, DNA sequencing, and disease diagnosis due to their advantages of miniaturization, low consumption, rapid analysis, and automation. Injection molded microfluidic chips have attracted great attention because of their short processing time, low cost, and mass production. The microchannel is the critical element of a microfluidic chip, and thus the microchannel replicability directly affects the performance of the microfluidic chip. In the current paper, a new method is proposed to evaluate the replicability of the microchannel profile via the root mean square value of the actual profile curve and the ideal profile curve of the microchannel. To investigate the effects of injection molding parameters (i.e., mold temperature, melting temperature, holding pressure, holding time, and injection rate) on microchannel replicability, a series of single-factor experiments were carried out. The results showed that, within the investigated experimental range, the increase of mold temperature, melt temperature, holding pressure, holding time, and injection rate could improve microchannel replicability accuracy. Specifically, the microchannels along the flow direction of the polymer melt were significantly affected by the mold temperature and melt temperature. Moreover, the replicability of the microchannel was influenced by the distance from the injection gate. The effect of microchannel replication on electrophoresis was demonstrated by a protein electrophoresis experiment.

Abstract Generally, the strength at the weld line of the injection molded part is very weak. The heat transfer coefficient (HTC) between the polymer melt and the mold cavity surface was analyzed to solve this problem. The surface roughness of the mold cavity and the material of the mold insert were changed to adjust the interface environment between the polymer melt and the mold cavity surface. HTC was obtained by combing the experimental measurement with the theoretical calculation. In the current study, the influence of HTC on the tensile strength of the weld line of the molded specimen was investigated. The results show that the weld line strength of the molded specimen increases with the decrease in HTC between the polymer and the mold cavity surface. Meanwhile, the decrease in the surface roughness of the mold cavity or replacing the mold material with lower thermal conductivity can reduce the value of the HTC between the polymer and the mold effectively and can delay the cooling rate of the hot polymer melt. This provides a new idea to solve thin-wall injection molding weld line defects.