Oliver Graudejus

Flexible and stretchable micro-electrodes for in vitro and in vivo neural interfaces

Microelectrode arrays (MEAs) are designed to monitor and/or stimulate extracellularly neuronal activity. However, the biomechanical and structural mismatch between current MEAs and neural tissues remains a challenge for neural interfaces. This article describes a material strategy to prepare neural electrodes with improved mechanical compliance that relies on thin metal film electrodes embedded in polymeric substrates. The electrode impedance of micro-electrodes on polymer is comparable to that of MEA on glass substrates. Furthermore, MEAs on plastic can be flexed and rolled offering improved structural interface with brain and nerves in vivo. MEAs on elastomer can be stretched reversibly and provide in vitro unique platforms to simultaneously investigate the electrophysiological of neural cells and tissues to mechanical stimulation. Adding mechanical compliance to MEAs is a promising vehicle for robust and reliable neural interfaces.

Controlling the Morphology of Gold Films on Poly(dimethylsiloxane)

Gold films on poly(dimethylsiloxane) (PDMS) have applications in stretchable electronics, tunable diffraction gratings, soft lithography and as neural interfaces. The electrical and optical properties of these films depend critically on the morphology of the gold. Therefore, we examine qualitatively and quantitatively the factors that affect the morphology of the gold film. Three morphologies can be produced controllably: microcracked, buckled, and smooth. Which morphology a gold film will adopt depends on the film stress and the growth mode of the film. The factors that affect the film stress and growth mode, and thus the morphology, are as follows: deposition temperature, film thickness, elastic modulus, adhesion layer thickness, surface properties of the PDMS, and mechanical prestrain applied during deposition. We discuss how the different components of the film stress and growth mode of the film affect the morphology.

Monitoring hippocampus electrical activity in vitro on an elastically deformable microelectrode array.

Interfacing electronics and recording electrophysiological activity in mechanically active biological tissues is challenging. This challenge extends to recording neural function of brain tissue in the setting of traumatic brain injury (TBI), which is caused by rapid (within hundreds of milliseconds) and large (greater than 5% strain) brain deformation. Interfacing electrodes must be biocompatible on multiple levels and should deform with the tissue to prevent additional mechanical damage. We describe an elastically stretchable microelectrode array (SMEA) that is capable of undergoing large, biaxial, 2-D stretch while remaining functional. The new SMEA consists of elastically stretchable thin metal films on a silicone membrane. It can stimulate and detect electrical activity from cultured brain tissue (hippocampal slices), before, during, and after large biaxial deformation. We have incorporated the SMEA into a well-characterized in vitro TBI research platform, which reproduces the biomechanics of TBI by stretching the SMEA and the adherent brain slice culture. Mechanical injury parameters, such as strain and strain rate, can be precisely controlled to generate specific levels of damage. The SMEA allowed for quantification of neuronal function both before and after injury, without breaking culture sterility or repositioning the electrodes for the injury event, thus enabling serial and long-term measurements. We report tests of the SMEA and an initial application to study the effect of mechanical stimuli on neuron function, which could be employed as a high-content, drug-screening platform for TBI.

Characterization of an Elastically Stretchable Microelectrode Array and Its Application to Neural Field Potential Recordings

Elastically stretchable microelectrode arrays (SMEAs) were fabricated, and their functionality was tested by recording field potentials from neural tissue. The SMEA includes 11 microelectrodes, each with a recording area of 100 × 200 μm and a reference electrode. The microelectrodes were fabricated by depositing and patterning thin-film gold conductors on the elastomeric substrate poly(dimethylsiloxane). A photopatternable silicone was used to encapsulate the microelectrodes and pattern vias for electrical contact. The recording sites of the microelectrodes were electroplated with platinum black to reduce the impedance of the electrode/electrolyte interface. Spontaneous and stimulus-evoked activity was recorded from hippocampal slices placed on an array that was biaxially stretched up to 13.3%. No appreciable difference in microelectrode properties was detected before and after stretching, demonstrating that the microelectrodes can be stretched reversibly.

The Effects of a Female Role Model on Academic Performance and Persistence of Women in STEM Courses

ABSTRACT Women are more likely to leave science, technology, engineering, and mathematics compared to men, in part because they lack similar role models such as peers, teaching assistants, and instructors. We examined the effect of a brief, scalable online intervention that consisted of a letter from a female role model who normalized concerns about belonging, presented time spent on academics as an investment, and exemplified overcoming challenges on academic performance and persistence. The intervention was implemented in introductory psychology (Study 1, N = 258) and chemistry (Study 2, N = 68) courses. Relative to the control group, the intervention group had higher grades and lower failing and withdrawal rates.

Neural sensing of electrical activity with stretchable microelectrode arrays

Sensing neural activity within mechanically active tissues poses particular hurdles because most electrodes are much stiffer than biological tissues. As the tissue deforms, the rigid electrodes may damage the surrounding tissue. The problem is exacerbated when sensing neural activity in experimental models of traumatic brain injury (TBI) which is caused by the rapid and large deformation of brain tissue. We have developed a stretchable microelectrode array (SMEA) that can withstand large elastic deformations (> 5% biaxial strain) while continuing to function. The SMEA were fabricated from thin metal conductors patterned on polydimethylsiloxane (PDMS) and encapsulated with a photo-patternable silicone. SMEA were used to record spontaneous activity from brain slice cultures, as well as evoked activity after stimulating through SMEA electrodes. Slices of brain tissue were grown on SMEA in long-term culture and then mechanically injured with our well-characterized in vitro injury model by stretching the SMEA and the adherent culture, which was confirmed by image analysis. Because brain tissue was grown on the substrate-integrated SMEA, post-injury changes in electrophysiological function were normalized to pre-injury function since the SMEA deformed with the tissue and remained in place during mechanical stimulation. The combination of our injury model and SMEA could help elucidate mechanisms responsible for post-traumatic neuronal dysfunction in the quest for TBI therapies. The SMEA may have additional sensing applications in other mechanically active tissues such as peripheral nerve and heart.

Feeling Closer to the Future Self and Doing Better: Temporal Psychological Mechanisms Underlying Academic Performance

This research examined the function of future self-continuity and its potential downstream consequences for academic performance through relations with other temporal psychological factors and self-control. We also addressed the influence of cultural factors by testing whether these relations differed by college generation status. Undergraduate students enrolled at a large public university participated in two studies (Study 1: N = 119, Mage  = 20.55, 56.4% women; Study 2: N = 403, Mage  = 19.83, 58.3% women) in which they completed measures of temporal psychological factors and psychological resources. In Study 2, we also obtained academic records to link responses to academic performance. Future self-continuity predicted subsequent academic performance and was related positively to future focus, negatively to present focus, and positively to self-control. Additionally, the relation between future focus and self-control was stronger for continuing-generation college students than first-generation college students. Future self-continuity plays a pivotal role in academic contexts. Findings suggest that it may have positive downstream consequences on academic achievement by directing attention away from the present and toward the future, which promotes self-control. Further, the strategy of focusing on the future may be effective in promoting self-control only for certain cultural groups.

Advances in encapsulating elastically stretchable microelectrode arrays

Stretchable microelectrode arrays (SMEAs) that are fabricated on the compliant silicone poly dimethyl siloxane (PDMS) have potential applications for research on traumatic brain injury (TBI). Increasing the number of electrodes in the array improves the accuracy in assessing the effects of traumatic injury to cell tissue cultures. The currently available encapsulation process with a photopatternable silicone limits the electrode density on the array. The present research examines four factors in the encapsulation process: exposure dose, scattered and reflected light as well as hard bake time. Careful optimization of these four factors leads to a significant reduction of the minimum feature size of a contact via patterned into the encapsulation layer, thus enabling an increase of the electrode density on the array.

Morphology and Stretchability of Thin Film Metal Conductors on Elastomeric Substrates

Fabrication of biomedical devices and components on soft, elastomeric substrates is a promising step toward mechanically-matched and conformal biological-electrical interfaces. However, while polymeric substrates are extremely deformable, electronic materials typically are not. To explore this convergence of stiff electronic materials and compliant elastomers, we prepare thin film gold conductors on polydimethylsiloxane (PDMS) membranes (Fig. 1), which have Youngs modulus, E ~ 2 MPa. The gold conductors have the property of remaining electrically conducting while stretched uni-axially to 20% strain and more [1]. Varying the fabrication methods affects the initial microstucture and morphology of the metal films, which in turn determine stretchability. To examine this effect, tensile tests are performed to measure electro-mechanical behavior, and scanning electron microscopy is used to observe the morphology of the films. In this study, we compare metal deposition techniques as well as samples of various metal thicknesses, linking resulting film morphologies to stretchability.