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In this work, we report on the implementation of a closed-loop liquid-loaded resonant mass sensor as a test vehicle for the realization of highly sensitive miniaturized biomarker assays. Using thin-film piezoelectric-on-silicon (TPoS) contour-mode disc resonators that are specifically designed and optimized for liquid-phase operation, a liquid-loaded low power (~1.6 mW) oscillator at ~17 MHz is demonstrated with a single transistor. By proper placement of the electrodes and the supporting tethers, a high liquid-loaded quality factor (~380) and a low insertion loss (~19 dB) are concurrently achieved which enable the accurate frequency tracking of the potential mass microbalance. The frequency shifts due to the liquid-loading and the preliminary characterized frequency stability of the oscillator imply a minimum mass detection resolution in the picograms range. [2020-0177]

We demonstrate a new fabrication technology to realize “intelligent”, transdermal, minimally invasive microneedle array ( i $\mu $ NA) by crosslinking a hydrogel, Polyethylene Glycol Diacrylate (PEGDA) by photo-polymerization using Digital Light Processing (DLP) based 3D printing. The photo-polymerization conditions have been optimized so that the mutually exclusive requirements of excellent mechanical strength while retaining hydrogel properties of PEGDA are met which would allow swelling/delivery of therapeutic cargo of diclofenac sodium via diffusion. An array having 100 microneedles arranged in a $10\times 10$ array was successfully 3D printed which efficiently penetrated human skin during ex vivo characterization. In vitro drug release studies demonstrated that the PEGDA based i $\mu $ NA behaves as a stimuli responsive device showing distinct release characteristics from external stimuli such as temperature and pH. [2020-0133]

3D printing involves the use of photopolymerizable resins, which are toxic and typically have incompatible properties with materials such as polystyrene (PS), which present limitations for biomedical applications. We present a method to dramatically improve the poor adhesion between the PS insulative layer on 3D printed Microelectrode Array (MEA) substrates by functionalizing the resin surface with polydopamine (PDA), a mussel-inspired surface chemistry derivative. A commercial 3D printing prepolymer resin, FormLabs Clear (FLC), was printed using a digital light processing (DLP) printer and then surface functionalized with PDA by alkali-induced aqueous immersion deposition and self-polymerization. It was observed that the adhesion of the PS to FLC was improved due to the precision emanating from the DLP method and further improved after the functionalization of DLP printed substrates with PDA at 1, 12, and 24 h time intervals. The adhesion of PS was evaluated through scotch tape peel testing and instron measurements of planar substrates and incubation testing with qualitative analysis of printed culture wells. The composition and topology of the samples were studied to understand how the properties of the surface change after PDA functionalization and how this contributes to the overall improvement in PS adhesion. Furthermore, the surface energies at each PDA deposition time were calculated from contact angle studies as it related to adhesion. Finally, biocompatibility assays of the newly modified surfaces were performed using mouse cardiac cells (HL-1) to demonstrate the biocompatibility of the PDA functionalization process. PDA surface functionalization of 3D DLP printed FLC resin resulted in a dramatic improvement of thin film PS adhesion and proved to be a biocompatible solution for improving additive manufacturing processes to realize biosensors such as

We demonstrate new fabrication technologies for 3D microelectrode platforms, fully realized for several 3D multi-functional biosystems. The microfabrication technology involves 3D metallized microtowers realized by 3D printing, metal evaporation, and coarse biocompatible lamination to insulate the traces. Electrospun 3D nanofiber scaffolds (NFSs) are coupled to the microelectrodes to provide additional functionality. The scaffolds were formed via electrospinning two types of nanofibers: ~200-500 nm PET, a hydrophobic polymer, and ~100 nm PVA/PAA, a hydrophilic co-polymer. PVA/PAA nanofibers had consistent diameters without beading and were used in subsequent experiments. Impedance measurements before, 651.3 $\text{k}\Omega $ , and after, 659.4 $\text{k}\Omega $ , deposition of PVA/PAA remains unchanged, indicating enhanced functionality without interfering with the electrical characteristics of the 3D MEAs. Silver nanoparticles (Ag NP) were embedded as model drug compounds in the PVA/PAA-NFS to demonstrate the potential of the 3D MEA as a biosensor and drug delivery system. TEM and antimicrobial studies demonstrated ~5-15 nm Ag NP within the PVA/PAA-NFS, which was potent to Acinetobacter baumannii and Escherichia coli. Fine 3D insulation atop the microtowers is achieved using a drop-casted/spin-coated 3D layer of Polystyrene (PS), which is laser micromachined to realize $50\times 50\,\,\mu \text{m}^{{2}}\,\,3\text{D}$ microelectrodes with impedance properties similar to other reported approaches. [2019-0043]

We present a nontraditional fabrication technique for the realization of three-dimensional (3D) microelectrode arrays (MEAs) capable of interfacing with 3D cellular networks in vitro. The technology uses cost-effective makerspace microfabrication techniques to fabricate the 3D MEAs with 3D printed base structures with the metallization of the microtowers and conductive traces being performed by stencil mask evaporation techniques. A biocompatible lamination layer insulates the traces for realization of 3D microtower MEAs (250 μm base diameter, 400 μm height). The process has additionally been extended to realize smaller electrodes (30 μm × 30 μm) at a height of 400 μm atop the 3D microtower using laser micromachining of an additional silicon dioxide (SiO2) insulation layer. A 3D microengineered, nerve-on-a-chip in vitro model for recording and stimulating electrical activity of dorsal root ganglion (DRG) cells has further been integrated with the 3D MEA. We have characterized the 3D electrodes for electrical, chemical, electrochemical, biological, and chip hydration stability performance metrics. A decrease in impedance from 1.8 kΩ to 670 Ω for the microtower electrodes and 55 to 39 kΩ for the 30 μm × 30 μm microelectrodes can be observed for an electrophysiologically relevant frequency of 1 kHz upon platinum electroless plating. Biocompatibility assays on the components of the system resulted in a large range (∼3%-70% live cells), depending on the components. Fourier-transform infrared (FTIR) spectra of the resin material start to reveal possible compositional clues for the resin, and the hydration stability is demonstrated in in-vitro-like conditions for 30 days. The fabricated 3D MEAs are rapidly produced with minimal usage of a cleanroom and are fully functional for electrical interrogation of the 3D organ-on-a-chip models for high-throughput of pharmaceutical screening and toxicity testing of compounds in vitro.

We have developed a novel microfabrication and assembly strategy for the realization of 3D Microelectrode Arrays (3D MEAs) which allows for simultaneous optical and electrical probing of a Nerve-on-a-Chip® construct. Specific microfabrication and assembly process innovations include "edge-wrapped" metal interconnects and custom Digital Light Processing (DLP) 3D printed transition rigs respectively. A Nerve-on-a-Chip® construct consisting of primary rat Dorsal Root Ganglion (DRG) cells are further seeded and grown atop the 3D MEA for 28 Days in vitro (DIV). Herein, we present results of the fabrication technology including AFM profilometry of interconnects, in addition to Impedance Spectroscopy, Root Mean Square (RMS) noise characterization, mechanical stability of the MEAs and long-term culture viability of the integrated tissue chip (Nerve-on-a-Chip® construct on the 3D MEAs) with fluorescence imaging.

Microelectrode Arrays are established platforms for biosensing applications; however, limitations in electrode impedance and cell-electrode coupling still exist. In this paper, the SNR of $25~\mu \text{m}$ diameter gold (Au) microelectrodes was improved by decreasing the impedance with precision electrodeposition. SEM determined that N-P Pt. microelectrodes had nano-porous structures that filled the insulation cylinders. EIS, CV, and RMS noise measurements concluded that the optimized electrodeposition of N-P Pt. led to a lowered impedance of $18.36~\text {k}\Omega \pm 2.6~\text {k}\Omega $ at 1 kHz, a larger double layer capacitance of 73 nF, and lowered RMS noise of $2.08 \pm 0.16~\mu \text{V}$ as compared to the values for Au of $159~\text {k}\Omega \pm 28~\text {k}\Omega $ at 1 kHz, 17nF, and $3.14 \pm 0.42~\mu \text{V}$ , respectively. Human motoneurons and human cardiomyocytes were cultured on N-P Pt. devices to assess their biocompatibility and signal quality. In order to improve the cell-electrode coupling, a precision plating technique was used. Both cell types were electrically active on devices for up to 10 weeks, demonstrated improved SNR, and expected responses to precision chemical and electrical stimulation. The modification of Au microelectrodes with nanomaterials in combination with precision culturing of human cell types provides cost effective, highly sensitive, well coupled and relevant biosensing platforms for medical and pharmaceutical research. [2018-0187]

Encapsulating drugs in functional nanoparticles provides controlled and targeted release of drugs. In this study, a general approach for encapsulating hydrophobic drugs in polyelectrolyte nanoparticles was developed for a controlled drug release. Gemcitabine (GEM), an anticancer drug for pancreatic ductal adenocarcinoma (PDAC), was used as a model drug to produce poly(acrylic acid) (PAA)-GEM conjugate nanoparticles to achieve a controlled release of GEM in cells. The PAA-GEM conjugate nanoparticles were fabricated by coupling GEM onto PAA through the formation of amide bonds. The hydrophobic interactions of GEM molecules induced the formation of the nanoparticles with the GEM core and PAA shell. Fabrication conditions such as the PAA/GEM ratio and pH were optimized to achieve high structure stability and drug loading efficiency. The size and surface charge of the nanoparticles were characterized by transmission electron microscopy (TEM), dynamic light scattering (DLS) and zeta potential measurement. The optimized PAA-GEM nanoparticles had a size around 12 nm, 30 nm and 60 nm in dry state, water, and phosphate buffered saline (PBS), respectively. The encapsulation efficiency was 29.29 ± 1.7%, and the loading capacity was 9.44 ± 0.46%. Less than 7% GEM was released from the PAA-GEM nanoparticles after 96 hour incubation in phosphate buffered saline. The cytotoxic efficacy of the PAA-GEM nanoparticles in cancer cells was investigated through viability studies of PANC-1, a human pancreatic cancer cell line. It was found that the PAA-GEM nanoparticles had more than a 48 hour delay of releasing GEM and had the same cytotoxic efficacy in PANC-1 cells as free GEM. The uptake of the PAA-GEM nanoparticles by PANC-1 cells was investigated using PAA-GEM labeled by rhodamine G6. Fluorescence and bright field overlay images indicated that the PAA-GEM nanoparticles were taken up by PANC-1 cells within 2 hours. It is believed that the PAA-GEM nanoparticles were decomposed in PANC-1 cells and GEM was released from the nanoparticles.

In this article, the microfluidic channels that deliver liquid to a microscale thin-film piezoelectric-on-silicon (TPoS) gravimetric resonant sensor are incorporated into the backside of the silicon-on-insulator (SOI) wafer on which the resonator is fabricated. Specifically, a microwell is embedded at the bottom of the disk -shaped TPoS resonator, while a very thin layer of parylene covering the backside of the resonator and the microwell forms an isolation layer between the liquid and the top device-layer features. In this way, the liquid is in contact with the backside of the resonator, while the device-defining trenches and the electrical connections to the resonator stay clear, thus mitigating the acoustic energy loss and undesirable feedthroughs. The impact of the parylene layer thickness on a few symmetric ( ${S}$ ) and antisymmetric ( ${A}$ ) Lamb wave modes of the resonator is experimentally studied, and the performance of such modes in the liquid is characterized by filling the microwells through a PDMS-based microfluidic channel. The parylene layer, while marginally affecting the resonator in the air, is found to substantially enhance its performance in the liquid media. Strong resonance peaks with high quality factors ( ${Q}$ ) are observed for the ${S}$ modes, among which ${Q}$ values above 400 are recorded for a specific mode named ${S}$ ( 4 , 2 ) (among the highest ever reported). This article can potentially facilitate the realization of highly stable and sensitive resonant mass sensors (i.e., microbalance) for real-time applications. Additionally, the effect of the acoustic energy radiation in the form of evanescent shear and longitudinal waves in liquid on the ${Q}$ and resonance frequency of the disk resonators is experimentally validated.

Aerogels are one of the most interesting materials of the 21st century owing to their high porosity, low density, and large available surface area. Historically, aerogels have been used for highly efficient insulation and niche applications, such as interstellar particle capture. Recently, aerogels have made their way into the composite universe. By coupling nanomaterial with a variety of matrix materials, lightweight, high-performance composite aerogels have been developed for applications ranging from lithium-ion batteries to tissue engineering materials. In this paper, the current status of aerogel composites based on nanomaterials is reviewed and their application in environmental remediation, energy storage, controlled drug delivery, tissue engineering, and biosensing are discussed.

Microelectrode Array (MEA) devices are well established platforms for biosensing applications, however, limitations in electrode materials and cell coupling to electrodes still exist. Signal-to-noise ratio (SNR), a fabrication limitation, can be improved by reducing the impedance of the microelectrodes without increasing their physical size using conductive nanomaterials. Platinum is a well-studied conductive material that has been determined to be compatible with MEA devices, contains high electronic conductivity, is non-toxic to cells and has excellent catalytic activity. Nano-porous platinum, as compared to pure platinum, has larger surface area enabled by nano-scale definition, and as a result can lower the impedance of microelectrodes. Therefore, in this study nano-porous platinum was electroplated onto thin film gold electrodes to increase SNR in a single-well MEA device. Numerous commercial and research grade MEAs are available and have been subject to for various applications such as disease modeling and pharmaceutical screening. Although high densities of cells can increase the probability of cell-electrode coupling, only signals near electrodes will be detected. Our approach introduces a method of precise patterning of cells on electrodes to increase the probability of cell-electrode coupling and reducing inaccuracies and expenses associated with cell plating. The single-well MEA glass die was designed and fabricated to contain 64 microelectrodes (30 µm diameter with a pitch of 200 µm) and 4 internal on-chip reference electrodes. The MEA glass die fabrication was performed on a 4-inch, 500 µm thick glass wafer. First, metal traces composed of titanium and gold were deposited using lift-off lithography. Subsequently, 5 µm of SU-8 was spin coated and defined as an insulation layer. A separate printed circuit board (PCB) was designed and fabricated to contain 72 contact pads and routing traces. The biocompatible epoxy 353ND was used to package the glass die and PCB in specific orientations determined by alignment markers. Ball bonding with 20 µm diameter gold wire was used to wirebond the glass die to the PCB. A packaging technique was developed that would allow the characterization of key properties of the MEA. This technique involved using copper wire, 100 µm in diameter, and attaching it to the contact pads on the backside of PCBs using a conductive epoxy. Finally, a polystyrene culture well and lid were attached to the MEA using the epoxy, 353ND. Nano-Porous platinum electroplating solution was prepared with a combination of chloroplantinic acid, HCl and lead acetate, all diluted in DI water. Fully packaged devices containing approximately 3 mL of electrolyte were placed within the Axion BioSystems Muse for nano-porous platinum electrodeposition, utilizing the custom Application Specific Integrated Circuit (ASIC) in the system at room temperature. The nano-porous platinum electroplated devices were subsequently characterized using electrical impedance spectroscopy and cyclic voltammetry against the control devices, which contained gold electrodes. The impedance of each device was measured across a scanned frequency range of 10 Hz-100 kHz between the microelectrode, the internal reference electrode and cellular conductive media. The impedance of the nano-porous platinum devices is an order of magnitude lower than the devices with gold electrodes. Cyclic voltammograms were obtained at a scan rate of 20 mV/s in the range from -0.28 to 1.2 V vs. Ag/AgCl. RMS noise comparison between nano-porous platinum electroplated devices and control devices (gold electrodes) was determined using the Muse system and Axion’s Integrated Studio (AxIS) software. Biosensing applications for the devices were explored using electrogenic cells in combination with a precise plating technique. As depicted in Figure 1, cells were positioned in a pattern on and around electrodes to increase the probability of cell-electrode coupling. The electrical response was obtained and analyzed using the Muse system and AxIS software. SNR of action potentials recorded from cells growing on devices enhanced with nano-porous platinum electrodeposition and cells on control devices with gold electrodes were compared. Activity within neuronal networks / beat frequencies of cell patches on electrodes were monitored over the course of 2-3 weeks. The methods explored in this study not only decreases impedance of microelectrodes to increase SNR but also increases cell-electrode coupling by warranting the placement of cells next or on the electrodes by precision patterning. Future studies will aim to optimize electrode sensitivity using novel electrode materials, the porosity of different materials, and characterization using emerging analytical methods. Eventually these devices will provide in vitro systems to monitor both acute and chronic effects of drugs and toxins as well as to perform functional studies under physiological or induced pathophysiological conditions that mimic in vivo damages. Figure 1: Electrogenic cells patterned near nano-porous platinum electrode Figure 1