Design and evaluation of an additive-manufactured microfluidic device for observing initial biofilm attachment on copper surfaces

Abstract

The growing interest in microfluidic devices has highlighted the need for improved manufacturing methods that overcome the limitations of traditional methods. One challenge is integrating copper and other metal surfaces into microchannels, as achieving strong and stable bonding is complex. Reliable bonding requires thorough control over surface and bonding quality. This study presents an alternative fabrication approach using double-sided pressure-sensitive adhesive (PSA) tape. Traditional methods are often expensive, time-consuming, and complex, whereas this approach enables the integration of copper surfaces while maintaining cost-effectiveness, repeatability, optical transparency, and compatibility with confocal laser scanning microscopy (CLSM to facilitate bacterial adhesion observation. A straight 80 micron-thick microchannel was selected as the optimal design among three designs for biofilm studies. The impact of flow rate, surface roughness, hydrophobicity, and salt concentration on bonding quality was examined. COMSOL Multiphysics® was used to visualize flow profiles and shear stress distributions across the channel geometry. We developed a low-cost microfluidic device using PSA tape, designed to support the observation of bacterial attachment under controlled conditions. Although biofilm formation was not the main focus, the device is CLSM-compatible and shows potential for future biofilm studies. Additionally, Saffman-Taylor fingering was used as an assessment tool to validate bonding quality. Experimental tests examined how salt concentration, flow rate, and surface finish influenced instability patterns. The fabricated device was tested under controlled flow conditions with Pseudomonas fluorescens N2E2 to evaluate bacterial adhesion. The PSA copper microfluidic device was optimized to have smoother surfaces, reduced STF, and negligible leakage. Contact angle measurements confirmed that smoother surfaces became more hydrophobic, which may impact cell behavior. Higher flow rates and increased salt concentration promote instability, reinforcing the role of viscosity in fluid behavior. However, cell adhesion was not observed on the metal surface. Instead, cells adhered to the cover glass, suggesting that device orientation and gravitational forces played a role. Moreover, since the surface preference of the bacterial strain remains unclear, future work should include testing alternative bacterial strains. Overall, this study demonstrates a reproducible, low-cost fabrication method that supports biological integration and provides an optically transparent platform compatible with CLSM for high-resolution microscopy.