Design and Fabrication of Piezoelectric Sensors and Actuators for Characterization of Soft Materials

The research presented in this dissertation supports the overall goal of creating piezoelectric measurement technology for the analysis and characterization of soft materials that serve as feedstocks (inputs) and products (outputs) of emerging biomanufacturing processes, including cell and additive biomanufacturing processes. The first objective was to define measurement challenges associated with real-time monitoring of material compositional profiles using biosensors in practical biomanufacturing and bioprocessing formats, as insight into a material's composition (i.e., concentration of a given biologic within a material or product) provides molecular-scale insight into processes and product quality. The second objective was to design, fabricate, and characterize continuous flow cell separation technology based on 3D printed self-exciting and -sensing millimeter-scale piezoelectric transducers and microfluidic networks for separation and characterization of expanded therapeutic cells. The third objective was to establish a sensor-based characterization approach for viscoelastic properties of hydrogels and gelation processes using high-order modes of piezoelectric-excited millimeter cantilever (PEMC) sensors and understand the influence of cantilever mode number on critical sensor characteristics, including sensitivity, dynamic range, and limit of detection. The first objective was addressed through a comprehensive review of recent progress in electrochemical and hybrid biosensors, which included discussions of measurement formats, sensor performance, and measurement challenges associated with use in practical bioprocessing environments. This critical review revealed that cost, disposability, form factor, complex measurement matrices, multiplexing, and sensor regeneration/reusability are among the most pressing challenges that require solutions through advancement of sensor design and manufacturing approaches before biosensors can facilitate high-confidence long-term continuous bioprocess monitoring. The second objective was addressed by creating a microextrusion-based additive manufacturing approach for fabrication of piezoelectric-based MEMS devices that enabled integration of 3D configurations of piezoelectric transducers and microfluidic networks in a one-pot manufacturing process. The devices contained orthogonal out-of-plane piezoelectric sensors and actuators and generated tunable bulk acoustic waves (BAWs) capable of size-selective manipulation, trapping, and separation of suspended particles in droplets and microchannels. This work suggests that additive manufacturing potentially provides new opportunities for the fabrication of sensor-integrated microfluidic platforms for cell culture analysis. The third objective was addressed through resonant frequency tracking of low- and high-order modes in dynamic-mode cantilevers to enable the real-time characterization of hydrogel viscoelastic properties and continuous monitoring of sol-gel phase transitions over a wide dynamic range using practically relevant hydrogel systems used commonly in additive biomanufacturing. This work suggests that high-order modes of PEMC sensors facilitate characterization of hydrogel viscoelastic properties and gelation processes with improved dynamic range and limit of detection that can complement the performance of low-order modes. Through this research, new approaches for sensor-based characterization of soft material composition and mechanical properties using millimeter-scale piezoelectric devices are presented as solutions for current challenges in biomanufacturing and biosensing to advance capability in real-time sensing of quality attributes among biomanufactured products.