An arched micro-injector (ARCMI) for innocuous subretinal injection

Correlation between subretinal tissue plasminogen activator and air injection rates with pressure in a retina mimicking model

By investigating the correlation between the injection rate and pressure of subretinal tissue plasminogen activator (tPA) and air using a standard Viscous Fluid Control (VFC) system with a 38-gauge cannula, we aimed to establish guidelines for stable injections. We fabricated a retina mimicking model (RMM) with 0.25% agarose solution and an aluminum plate, and substituted submacular hemorrhage (SMH) and tPA with blood-mimicking fluid (BMF) and balanced salt solution (BSS), respectively. The diameter of the pre-bleb mimicking SMH in RMM was 1.30 ± 0.16 cm, increasing to 1.98 ± 0.24 cm and 1.83 ± 0.22 cm after bleb propagation with BSS and air, respectively. BSS injection rates were 2.86 ± 0.04 µl/sec, 6.74 ± 0.48 µl/sec and 8.55 ± 0.16 µl/sec at 8, 12, and 16 psi, respectively. Air injection rates were 37.98 ± 3.11 µl/sec, 79.01 ± 5.13 µl/sec and 156.06 ± 13.72 µl/sec at 2, 3 and 4 psi, respectively. By experimenting with different pressures in the RMM, we found 12 psi to be the minimum for proper BSS injection and 2 psi for air. These findings provide crucial parameters for safer surgery to prevent irreversible damage.

Biomechanical considerations for optimising subretinal injections

Subretinal injection is the preferred delivery technique for various novel ocular therapies and is widely used because of its precision and efficient delivery of gene and cell therapies; however, choosing an injection point and defining delivery parameters to target a specified retinal location and area is an inexact science. We provide an overview of the key factors that play important roles during subretinal injections to refine the technique, enhance patient outcomes, and minimise risks. We describe the role of anatomical and physical variables that affect subretinal bleb propagation and shape and their impact on retinal integrity. We highlight the risks associated with subretinal injections and consider strategies to mitigate reflux and retinal trauma. Finally, we explore the emerging field of robotic assistance in improving intraocular manouvrability and precision to facilitate the injection procedure.

Self-Plugging Microneedle (SPM) for Intravitreal Drug Delivery

Intravitreal injection (IVI) is a common technology which is used to treat ophthalmic diseases inside eyeballs by delivering various drugs into the vitreous cavity using hypodermic needles. However, in some cases, there are possible side effects such as ocular tissue damage due to repeated injection or eyeball infection through the hole created during the needle retraction process. The best scenario of IVI is a one-time injection of drugs without needle retraction, keeping the system of the eyeball closed. Microneedles (MNs) have been applied to ocular tissues over 10 years, and no serious side effects on ocular tissue due to MN injection have been reported. Therefore, a self-plugging MN (SPM) is developed to perform intraocular drug delivery and to seal the scleral puncture simultaneously. The SPMs are fabricated by a thermal drawing process and then coated with a polymeric carrier of drugs and a hydrogel-based scleral plugging component. Each coated functional layer is characterized and demonstrated by in vitro and ex vivo experiments. Finally, in vivo tests using a porcine model confirms prompt sealing of SPM and sustained intraocular drug delivery.

Oblique injection depth correction by a two parallel OCT sensor guided handheld SMART injector

We present a SMART injector with two parallel common-path optical coherence tomography fibers to enable angle measurements and injection depth corrections for oblique subretinal injection. The two optical fibers are attached to opposite sides of a 33 G needle with known offsets and designed to pass through a 23 G trocar that has an inner diameter of 0.65 mm. By attaching a SMART system to a rotational stage, the measured angles are calibrated for minimal error from reference angles. A commercial eye model was used to evaluate the control performance, and injection experiments were performed on a phantom made of agarose gel and a porcine eye.

Safety of Same-Eye Subretinal Sequential Readministration of AAV2-hRPE65v2 in Non-human Primates

We have demonstrated safe and effective subretinal readministration of recombinant adeno-associated virus serotype (rAAV) to the contralateral eye in large animals and humans even in the setting of preexisting neutralizing antibodies (NAbs). Readministration of AAV to the same retina may be desirable in order to treat additional areas of the retina not targeted initially or to boost transgene expression levels at a later time point. To better understand the immune and structural consequences of subretinal rAAV readministration to the same eye, we administered bilateral subretinal injections of rAAV2-hRPE65v2 to three unaffected non-human primates (NHPs) and repeated the injections in those same eyes 2 months later. Ophthalmic exams and retinal imaging were performed after the first and second injections. Peripheral blood monocytes, serum, and intraocular fluids were collected at baseline and post-injection time points to characterize the cellular and humoral immune responses. Histopathologic and immunohistochemical studies were carried out on the treated retinas. Ipsilateral readministration of AAV2-hRPE65v2 in NHPs did not threaten the ocular or systemic health through the time span of the study. The repeat injections were immunologically and structurally well tolerated, even in the setting of preexisting serum NAbs. Localized structural abnormalities confined to the outer retina and retinal pigmented epithelium (RPE) after readministration of the treatment do not differ from those observed after single or contralateral administration of an AAV carrying a non-therapeutic transgene in NHPs and were not observed in a patient treated with the nearly identical, FDA-approved, AAV2-hRPE65v2 vector (voretigene neparvovec-rzyl), suggesting NHP-specific abnormalities.

Microneedles for vaccine delivery: challenges and future perspectives

Vaccine delivery to the skin using conventional needles is associated with needle-stick injuries and needle-phobia, which are all major obstacles to vaccination. The development of microneedles has enabled to overcome these limitations and as a result viral, DNA and bacterial vaccines have been studied for the delivery into the skin. Research has shown the superiority of microneedle vaccination over conventional needles in terms of immunogenicity, vaccine stability and dose-sparing abilities in animals and humans. Additional research on improving vaccine stability and delivering vaccines to other areas of the body besides the skin is ongoing as well. Thus, this review paper describes current advances in microneedles as a delivery system for vaccines as well as future perspectives for this research field.

Minimally invasive curved-micro-drainer (CMD) capable of innocuous drainage of subretinal fluid for the treatment of retinal detachment

Retinal detachment is a serious vision threatening disease. Current consensus for the treatment of retinal detachment is to reattach the retina onto the choroid layer by drainage of accumulated subretinal fluid. Although several surgical methods have been developed, no satisfactory visual outcome has been obtained without surgical complications such as unintended puncture and hemorrhage of the retina and choroid tissue. In this study, we developed a novel Curved-Micro-Drainer (CMD) for the innocuous drainage of subretinal fluid. It is a curved structure with a 15° beveled tip that is 5 mm in length, with an 80 μm inner diameter and a 100 μm outer diameter. This high inner-to-outer diameter ratio of CMD with a 100 μm outer diameter allows efficient drainage of highly viscous subretinal fluid in a minimally invasive manner. In addition, the curved structure precisely matches the spherical ocular structure, which facilitates the CMD insertion into the subretinal space without choroid tissue damage. We demonstrate that the optimized CMD allows for the innocuous drainage of the viscous subretinal fluid from the porcine eye, whereas the traditional hypodermic needle (31-gauge) induces severe retinal and choroid damage. CMD can overcome a critical safety issue and is a potential alternative to conventional surgical interventions for the innocuous drainage of subretinal fluid.

One-touch-activated blood multidiagnostic system using a minimally invasive hollow microneedle integrated with a paper-based sensor

The development of real-time innocuous blood diagnosis has been a long-standing goal in healthcare; an improved, miniature, all-in-one point-of-care testing (POCT) system with low cost and simplified operation is highly desired. Here, we present a one-touch-activated blood multidiagnostic system (OBMS) involving the synergistic integration of a hollow microneedle and paper-based sensor, providing a number of unique characteristics for simplifying the design of microsystems and enhancing user performance. In this OBMS, all functions of blood collection, serum separation, and detection were sequentially automated in one single device that only required one-touch activation by finger-power without additional operations. For the first time, we successfully demonstrated the operation of this system in vivo in glucose and cholesterol diagnosis, showing a great possibility for human clinical application and commercialization. Additionally, this novel system offers a new approach for the use of microneedles and paper sensors as promising intelligent elements in future real-time healthcare monitoring devices.