A fully organic retinal prosthesis restores vision in a rat model of degenerative blindness

The degeneration of photoreceptors in the retina is one of the major causes of adult blindness in humans. Unfortunately, no effective clinical treatments exist for the majority of retinal degenerative disorders. Here we report on the fabrication and functional validation of a fully organic prosthesis for long-term in vivo subretinal implantation in the eye of Royal College of Surgeons rats, a widely recognized model of retinitis pigmentosa. Electrophysiological and behavioural analyses reveal a prosthesis-dependent recovery of light sensitivity and visual acuity that persists up to 6–10 months after surgery. The rescue of the visual function is accompanied by an increase in the basal metabolic activity of the primary visual cortex, as demonstrated by positron emission tomography imaging. Our results highlight the possibility of developing a new generation of fully organic, highly biocompatible and functionally autonomous photovoltaic prostheses for subretinal implants to treat degenerative blindness.

Soft Three-dimensional self-opening intraneural peripheral interface for optic nerve stimulation

Marta Jole Ildelfonsa Airaghi Leccardi, Eleonora Borda, Diego Ghezzi

Retinitis Pigmentosa and age-related macular degeneration are two of the principal causes of blindness in industrialized countries, for which there is still no established prevention, treatment or cure. In the past decade, retinal prostheses emerged as promising technology to restore vision1. On the contrary, optic nerve stimulation has been proposed as an attractive alternative to retinal prostheses, by acting directly on the axons of the ganglion cells2. Our research group is currently testing a self-opening intraneural electrode array for optic nerve stimulation (OpticSELINE)2. The implant consists of a flexible polyimide-based structure embedding gold interconnects and active sites. Although polyimide provides flexibility to the device, the use of a softer and stretchy material would greatly help in the integration of the array inside the nerve tissue. A commonly used material to fabricate soft neural interfaces is polydimethylsiloxane (PDMS); however, it presents challenging steps in the microfabrication process, especially for the encapsulation of the active sites. On the other hand, off-Stochiometric-Thiol-Ene Epoxy polymers (OSTE+)3 represent a promising replacement for the polyimide structure thanks to their tunable mechanical properties. In fact, by adjusting the stoichiometry of the constituting monomers, the Young’s modulus of OSTE+ can be decreased down to a few MPa at physiological temperature4. The preparation of OSTE+ consists of two curing steps3 in which (1) thiol-ene photopolymerization allows to pattern the polymer surface and remove the non- polymerized areas before (2) thermal curing. Thus, it is possible to encapsulate the electrode array simply using photolithographic techniques. Furthermore, the off-stoichiometric formulation introduces an excess of reactive thiol groups in the bulk and on the surface3. In this way, OSTE+ can covalently bind to other surfaces without the use of bonding strategies such as plasma activation. Therefore, the versatility of OSTE+ makes it a promising alternative to PDMS. Taking advantage of these properties, we used direct writing photolithography to fabricate implantable multielectrode arrays in OSTE+ (Figure 1). The functional characteristics of the array have been tested by electrochemical characterization. In conclusion, the introduction of OSTE+ in the OpticSELINE aims at minimizing the mechanical mismatch between the electrode array and the optic nerve. This technology has the potential to allow stable and selective stimulation (or recording) of the optic nerve during chronic implantations. The advancement will improve the use of the OpticSELINE as visual prosthesis for blind patients and as tool to further investigate the effect of the electrical stimulation in the visual system.

2018

In vivo evaluation of gene editing and prosthetic strategies to restore vision in small and large animal models of retinal degeneration

Paola Vagni

Inherited retinal diseases (IRDs) form a group of diverse disorders that lead to the degeneration of the light-sensing cells of the retina: the photoreceptors. IRDs are among the leading causes of blindness in working-age adults living in industrialized countries and their treatment has been a long-term challenge in medicine. Given the heterogeneity of IRDs in terms of causative genes and symptoms, finding a common therapy is not a real possibility. Conversely, it is important to research as many different approaches as possible so as to have the opportunity to decide which one to use for a specific patient. The outcome of clinical interventions depends in large part on the preclinical research conducted on animal models. As an example of this, this thesis illustrates two preclinical approaches to the treatment of retinal degenerations that lie at the opposite ends of the spectrum of available therapies. The first approach discussed is gene editing. This strategy is most effective during the development of the retina and can be used to correct genetic mutations causing the degeneration of photoreceptors on the progenitor cells. Here, we used a tailored gene editing system based on clustered regularly interspaced short palindromic repeats (CRISPR)/CRISPR-associated protein 9 (Cas9) to prevent photoreceptor death in the retinal degeneration 10 (Rd10) mouse model of retinitis pigmentosa. The construct was delivered in the photoreceptor cells by electroporation and targets the mutated gene, editing its sequence with the help of a DNA repair template. This technique for gene editing has shown promising results in terms of visual function preservation in mice, inspiring further research into viral-free gene editing approaches. On the opposite side of the range of therapeutic options, prosthetic devices are generally used for late-stage retinal degeneration since they bypass the photoreceptor layer and rely on the retinal internal circuits to perform visual stimulation. In this work, I describe a series of experiments performed to test the POLYRETINA photovoltaic epiretinal visual prosthesis, previously developed by our laboratory, in a minipig model of chemically induced retinal degeneration. First, the visual responses were carefully characterized in the animal model before and after the injection of the toxin. Then, preliminary results were obtained using the prosthesis to stimulate the blind retina. Although the experiments are still ongoing, the results are encouraging and demonstrate that we could indeed use a completely photovoltaic prosthesis to restore visual perception in blind patients. In conclusion, this thesis displays preclinical research concerning two ways to restore vision, each adapted to a different stage of retinal degeneration. The overarching goal is to improve as much as possible the outcome of the therapy for the benefit of blind patients. To this end, we need to continue to test all the approaches that have so far shown promising results, such as the ones presented herein, while continuing to develop new ones. This outlook, implemented at the preclinical level, can lead to the best chances of a successful clinical intervention. At the same time, the diagnostic tools need to be perfected and precisely utilized to determine which therapeutic option is best suited for a specific patient.

EPFL2020

Development of a new visual prosthesis for preclinical studies on artificial vision

Marta Jole Ildelfonsa Airaghi Leccardi

The technological evolution in materials science and microengineering favored the production of advanced visual prostheses useful for fighting blindness and to improve patients quality of life. Visual prostheses aim at replacing lost visual functions by artificial (electrical) stimulation of the remaining circuitry with microfabricated electrodes inducing phosphenes appearance in blind people. In particular, for people affected by retinal degenerative diseases such as retinitis pigmentosa and age-related macular degeneration, retinal prostheses offer a valuable treatment option thanks to several advantages: among them, the retinotopic organization, the large surface area available for stimulation, and the straightforward surgical and optical access. The latter becomes very convenient for photovoltaic implants, in which amplified light entering the pupil is exploited as wireless source of power and visual information, allowing the implant to lay free-standing and the placement of a large number of stimulating pixels without the inconvenience of electrical connections. However, although all these advancements, there is nowadays no visual implant suited for artificial vision with both high spatial resolution and large visual field coverage. In this thesis, we developed a photovoltaic and foldable wide-field epiretinal prosthesis with a high density of stimulating pixels (more than 10400 and 18600 pixels with a density of 79 and 141 pixels/mm2, respectively) distributed over a very large surface area, covering 46 deg of visual field, greatly improved with respect to state-of-the-art implants. The large size of the implant imposes two major challenges: the necessity of a good contact between the implant and the retina and of a safe implantation procedure. To address these challenges, the photovoltaic interface is placed on a curved and stretchable substrate, able to be folded, injected into the eye through a small scleral cut, and self-unfold to recover the curvature matching the one of the eyes. Consequently, the rigid pixels were mechanically engineered to withstand the required deformation. We investigated the use of organic optoelectronic materials, such as P3HT:PCBM and PCPDTBT:PCBM, to manufacture photovoltaic pixels able to induce retinal ganglion cells activity upon illumination with short pulses of light. For both systems, light pulses of irradiances within the safety limits allowed the photogeneration of currents and voltages suitable for a stimulation frequency up to 20 Hz with green (565 nm) and near-infrared (730 nm) light, respectively. The conjugated polymer PEDOT:PSS and sputtered Ti (with TiN coating) were used for the anodic and cathodic ends correspondingly, with only the Ti-TiN surface exposed to the electrolytic solution. Ex vivo evaluation with blind mice retinas demonstrated that the photovoltaic pixels could induce, together with direct electrical short-latency stimulation, medium-latency spiking activity of retinal ganglion cells as evidence of prosthetic-induced network-mediated responses. Investigations and optimizations about functional, mechanical, thermal, optical, and stability properties of the prosthesis were carried out in vision of in vivo experiments with blind miniature pigs. Blinded by IAA treatment, the miniature pigs recovered light sensitivity when implanted with the prosthesis. This preliminary result motivates further preclinical inquiries with the prosthesis towards clinical applications.

EPFL2020

Soft Three-dimensional self-opening intraneural peripheral interface for optic nerve stimulation

Marta Jole Ildelfonsa Airaghi Leccardi, Eleonora Borda, Diego Ghezzi

2018

Development of a new visual prosthesis for preclinical studies on artificial vision

Marta Jole Ildelfonsa Airaghi Leccardi

EPFL2020

In vivo evaluation of gene editing and prosthetic strategies to restore vision in small and large animal models of retinal degeneration

Paola Vagni

EPFL2020