Abstract: A microfluidic device capable of performing nondisruptive fluid manipulations in a living host is provided. The microfluidic device may include a combinatorial multiplexer for better scaling of multiple time points and biological signal measurements. The collected samples may be transported, stored and analyzed ex vivo for analytical ease and flexibility, e.g., by a sample analysis assay chip. The microfluidics device may include structure for maintaining fluid equilibrium within the host during the sampling to avoid damage to the host or to the implant.