Responsive hydrogel sensor for monitoring antibody production

Precise control over the biomanufacturing process is crucial for maximizing yield and quality of monoclonal antibodies (mAbs); however, the industry does not have sensors capable of continuously monitoring either mAb yield or quality. Consequently, this production is plagued with poor quality control, reduced productivity, and increased costs. To develop such a sensor, we investigated the use of aptamers selective to human immunoglobulin G (IgG, sub-type of mAbs). First, we investigated the physiochemical properties of six different aptamers that bind to two distinct regions of the protein as well as tested their the binding affinity to human IgG, before and after standard sterilization procedures (autocalve and gamma irradation), using surface plasmon resonance (SPR, Figure 1). Chemical modification procedures were developed for immobilization of the aptamers onto a biotin capture sensor chip for use in SPR. Based on these results, two aptamers were selected which bind to separate regions of IgG, which have optimal physiochemical properties and have strong binding affinity to IgG. Similarly, the aptamers were modified to covalently bond and incorporate into a hydrogel network creating an IgG-sensitive hydrogel. In the presence of IgG in solution, both immobilized aptamers bind to the IgG molecule and form a new crosslink which subsequently causes shrinking (volume reduction) of the hydrogel [1]. This change in volume is monitored using our patent-pending magnetic transduction technique [2]. The degree of hydrogel shrinkage is measured using a magnetometer chip and fixing a permanent magnet to the hydrogel surface. An electronic reader with the magnetometer transduces the hydrogel response into an electrical signal. Response tests using this setup were performed in four different complex environments including industrial cell culture medium. The results show that this IgG-sensitive hydrogel is stable to autoclave and gamma irradition and responds to increasing and decreasing concentrations of IgG in various solutions (Figure 2). The magnitude of hydrogel response is used to correlate the change in IgG concentraion. Please click Additional Files below to see the full abstract

Study of accuracy and selectivity of a hydrogel-based sensor array by Design of Experiments (DOE)

Reliable continuous sensors are salient to achieving advanced Process Analytical Technologies in the bioproduction industry. Sensors provide information on key parameters in a bioreactor such as physical variables (temperature, pressure, speed of stirrer), chemical variables (pH, pO2, pCO2, nutrients, metabolites), and biological variables (biomass, cell metabolism).1-2 Simultaneously, chemometric analysis using multivariate data analysis, bioprocess modeling, and design of experiments (DOE) have become important in developing advanced biosensors because of the need to clean the complex raw data from biosensors to provide repeatable, robust, and reliable information.3-4 In this work, the first step of the chemometric analysis process, DOE was performed with a prototype biosensor developed to simultaneously monitor glucose, lactate, pH, and osmolarity to understand the accuracy and selectivity of this sensor. Please click Additional Files below to see the full abstract

Growth and characterization of TiO2 nanotubes from sputtered Ti film on Si substrate

In this paper, we present the synthesis of self-organized TiO(2) nanotube arrays formed by anodization of thin Ti film deposited on Si wafers by direct current (D.C.) sputtering. Organic electrolyte was used to demonstrate the growth of stable nanotubes at room temperature with voltages varying from 10 to 60 V (D.C.). The tubes were about 1.4 times longer than the thickness of the sputtered Ti film, showing little undesired dissolution of the metal in the electrolyte during anodization. By varying the thickness of the deposited Ti film, the length of the nanotubes could be controlled precisely irrespective of longer anodization time and/or anodization voltage. Scanning electron microscopy, atomic force microscopy, diffuse-reflectance UV–vis spectroscopy, and X-ray diffraction were used to characterize the thin film nanotubes. The tubes exhibited good adhesion to the wafer and did not peel off after annealing in air at 350 °C to form anatase TiO(2). With TiO(2) nanotubes on planar/stable Si substrates, one can envision their integration with the current micro-fabrication technique large-scale fabrication of TiO(2) nanotube-based devices

A compact integrated device for spatially selective optogenetic neural stimulation based on the Utah Optrode Array

Optogenetics is a powerful tool for neural control, but controlled light delivery beyond the superficial structures of the brain remains a challenge. For this, we have developed an optrode array, which can be used for optogenetic stimulation of the deep layers of the cortex. The device consists of a 10×10 array of penetrating optical waveguides, which are predefined using BOROFLOAT® wafer dicing. A wet etch step is then used to achieve the desired final optrode dimensions, followed by heat treatment to smoothen the edges and the surface. The major challenge that we have addressed is delivering light through individual waveguides in a controlled and efficient fashion. Simply coupling the waveguides in the optrode array to a separately-fabricated μLED array leads to low coupling efficiency and significant light scattering in the optrode backplane and crosstalk to adjacent optrodes due to the large mismatch between the μLED and waveguide numerical aperture and the working distance between them. We mitigate stray light by reducing the thickness of the glass backplane and adding a silicon interposer layer with optical vias connecting the μLEDs to the optrodes. The interposer additionally provides mechanical stability required by very thin backplanes, while restricting the unwanted spread of light. Initial testing of light output from the optrodes confirms intensity levels sufficient for optogenetic neural activation. These results pave the way for future work, which will focus on optimization of light coupling and adding recording electrodes to each optrode shank to create a bidirectional optoelectronic interface

Multisite microLED optrode array for neural interfacing

We present an electrically addressable optrode array capable of delivering light to 181 sites in the brain, each providing sufficient light to optogenetically excite thousands of neurons in vivo, developed with the aim to allow behavioral studies in large mammals. The device is a glass microneedle array directly integrated with a custom fabricated microLED device, which delivers light to 100 needle tips and 81 interstitial surface sites, giving two-level optogenetic excitation of neurons in vivo. Light delivery and thermal properties are evaluated, with the device capable of peak irradiances >80  mW  /  mm2 per needle site. The device consists of an array of 181 80  μm  ×  80  μm2 microLEDs, fabricated on a 150-μm-thick GaN-on-sapphire wafer, coupled to a glass needle array on a 150-μm thick backplane. A pinhole layer is patterned on the sapphire side of the microLED array to reduce stray light. Future designs are explored through optical and thermal modeling and benchmarked against the current device

An Improved Design for Chemomechanical Sensors: A Piezoresistive Pressure Sensor with a Mechanical Boss

Stimuli-responsive hydrogels can be used to convert miniature pressure sensors into novel chemomechanical sensors via confinement of the hydrogel sample between a porous membrane and a piezoresistive diaphragm. Chemomechanical sensors could prove beneficial in a variety of applications, including continuous monitoring of bioreactors and biomedical systems. In this study, one hydrogel composition with a high sensitivity to changes in pH was tested in two different chemomechanical sensors in order to compare the data obtained from each sensor design. In the first and older chemomechanical sensor design, a prefabricated hydrogel sample is loaded into the sensor chamber using a screw-on cap. In the newer sensor design, a thinner hydrogel is synthesized in situ and is held in place by a silicon boss that is mechanically connected to a piezoresistive diaphragm. The newer design results in a decreased chemomechanical sensor response time (by 60 times), and maintains a high sensitivity to changes in environmental stimuli

Long term in vitro stability of fully integrated wireless neural interfaces based on Utah slant electrode array

We herein report in vitro functional stability and recording longevity of a fully integrated wireless neural inteace (INI). The INI uses biocompatible Parylene-C as an encapsulation layer, and was immersed in phosphate buffered saline (PBS) for a period of over 150 days. The full functionality (wireless radio-frequency power, command, and signal transmission) and the ability of INI to record artificial action potentials even after 150 days of PBS soaking without any change in signal∕noise amplitude constitutes a major milestone in long term stability, and evaluate the encapsulation reliability, functional stability, and potential usefulness for future chronic implants