Human eye-inspired soft optoelectronic device using high-density MoS2-graphene curved image sensor array

Abstract

Soft bioelectronic devices provide new opportunities for next-generation implantable devices owing to their soft mechanical nature that leads to minimal tissue damages and immune responses. However, a soft form of the implantable optoelectronic device for optical sensing and retinal stimulation has not been developed yet because of the bulkiness and rigidity of conventional imaging modules and their composing materials. Here, we describe a high-density and hemispherically curved image sensor array that leverages the atomically thin MoS₂-graphene heterostructure and strain-releasing device designs. The hemispherically curved image sensor array exhibits infrared blindness and successfully acquires pixelated optical signals. We corroborate the validity of the proposed soft materials and ultrathin device designs through theoretical modeling and finite element analysis. Then, we propose the ultrathin hemispherically curved image sensor array as a promising imaging element in the soft retinal implant. The CurvIS array is applied as a human eye-inspired soft implantable optoelectronic device that can detect optical signals and apply programmed electrical stimulation to optic nerves with minimum mechanical side effects to the retina.

Fig. 1

High-density curved image sensor array based on the MoS₂-graphene heterostructure. a Schematic illustration of the high-density CurvIS array based on the MoS₂-graphene heterostructure. b Optical camera image of the high-density CurvIS array. Inset shows the image (i.e., university logo) captured by the CurvIS array. c Schematic illustration of the device design. Inset shows an optical microscope image of a single phototransistor. d Cross-sectional transmission electron microscope image of the MoS₂-graphene phototransistor (left) and the magnified image of the MoS₂-graphene heterostructure (right). e Optical (left) and magnified scanning electron microscope (right) image of the high-density CurvIS array on the concave hemisphere

Fig. 2

Theoretical analysis of the induced strain on the device array conformed to a hemispherical dome. a Schematic illustration showing the approximation used in the analysis. The truncated and untruncated films are approximated as circular films of radius 3.5 mm (R _fs) and 9.3 mm (R _fl), respectively. b,c Radial b and hoop c strain distributions in the two films. d,e Radial d and hoop e strain plotted as a function of the radial coordinate r. Highlighted zones indicate tolerable strain levels. f Maximum tensile radial strain (left) and tensile hoop strain (right) of films with different radii

Fig. 3

Device characterization and imaging using the curved image sensor array. a The optical camera image of the phototransistor array with a truncated icosahedron design on a planar substrate. Inset shows a schematic illustration of the device structure. b Transfer curves of the phototransistor under different light (515 nm) intensities. c Normalized photocurrent change under different light intensities. d Photoresponsivity of the MoS₂-graphene phototransistor compared to the silicon photodetector with the same thickness. e Normalized photocurrent change under IR illumination (850 nm) of different light intensities. Inset shows the light absorbance of MoS₂ and silicon. f Sigma-shaped image captured by the CurvIS array. g The same image with Fig. 3f but captured under IR illumination. Inset images are acquired by a commercial silicon photodetector array with (left) and without (right) an IR filter under IR illumination

Fig. 4

Human eye-inspired soft optoelectronic device. a Schematic illustration showing the ocular structure of human. b Schematic illustration showing the ocular structure with the soft optoelectronic device. c Micro CT image (left) and magnified image (right) showing deformation of (i) the bare eye model, attached by (ii) the soft optoelectronic device, (iii) a flexible film device, and (iv) wafer-based electronics. d Induced Stress by three different implanted devices. e The H&E stain histology of the normal retina and the retina implanted with the soft optoelectronic device. f FEA results of the maximum principal strain in eye model (i) without any device, (ii) with the soft optoelectronic device, (iii) with a flexible film device, and (iv) with wafer-based electronics

Fig. 5

Finite element analysis of the soft optoelectronic device and the eye model. a Maximum in-plane principle strain distribution in the soft optoelectronic device (top) and the circular device (bottom). b The reddish out-of-contact part of the soft optoelectronic device (top) and the circular device (bottom). c Maximum in-plane principle strain distribution in the eye models attached by the soft optoelectronic device (top) and the circular device (bottom). d Deformed shape of the eye model attached by the soft optoelectronic device (top) and the circular device (bottom) obtained by the FEA

Fig. 6

Soft flexible printed circuit board that integrates the CurvIS array with UNE. a Schematic drawing of the electronics for detecting the external light (bottom) and for applying the stimulation (top). b Optical camera image of the CurvIS array and the UNE on the eye model, which are connected by the soft FPCB. c Magnified optical camera image of the vertically stacked the CurvIS array and the UNE. d Schematic illustration of the phototransistor (bottom) and the stimulation electrode (top) stacked together and connected via the soft FPCB. e Optical camera image of the soft FPCB. f, g Optical camera image of the soft FPCB under poking f and bending g. h, i Generated electrical pulses at three different pixels by responding the light on/off h, and magnified electrical pulse i

Fig. 7

Retinal stimulation by the soft optoelectronic device. a Schematic drawing of the experimental setup for stimulating the retina (left) and for recording neural signals from the visual cortex (right). b, c Measurement of elicited spikes b and LFP changes c in the visual cortex by optical stimulation. d, e Measurement of elicited spikes d and LFP changes e in the visual cortex by electrical stimulation