AMD: Safer self-sealing micro-needles

Precisely, this new self-sealing microneedle was developed

to inject therapeutic products into the eyes,

to the retina, while preventing possible complications at the injection site. Coated with a therapeutic drug released upon insertion into the eyeball, the microneedle can also be equipped with a special hydrogel that simultaneously seals the insertion site. Different needle lengths are possible, so that therapeutic agents can be precisely targeted and dispersed to retinal tissues or other areas of the eyeball.

Avoid side effects related to eye injections

Lead author Dr. Ali Khademhosseini recalls the challenges of retinal drug delivery: the retina is a thin layer of cells that make up the inner lining of the back of the eyeball. It enables vision by receiving light and converting it into signals which, transmitted to the brain, are then interpreted as images. As vital as it is for clear and sharp vision, the retina and its critical central part, the macula, are also the regions most vulnerable to different types of damage related to age, genetics, disease and to other risk factors. This damage can cause symptoms ranging from distorted or severely impaired vision to complete blindness: thus, age-related macular degeneration (AMD) is the leading cause of irreversible vision loss in adults over 60, and diabetic retinopathy is the leading cause of blindness in adults aged 20-74.

Some forms of retinopathy can be treated by injecting drugs into the eyeball using syringes and hypodermic needles. In this procedure, the injected drugs diffuse through the fluid in the eyeball to reach the damaged site. In many cases, multiple injections are needed over an extended period to preserve vision.

These treatments are a painful ordeal for the patients,

and carry a risk of bacterial infection at the needle removal site. Additionally, any floating tumor cells in diseased eyes could escape and migrate to other sites.

Attempts at implantable needles have been conducted, however, mechanical difficulties and navigation through the viscous fluid in the eyeball do not allow precise needle placement and carry an additional risk of retinal damage. Other approaches such as polymer plugs aimed at closing the holes left by the hypodermic needles, but these approaches require an additional gesture, after the injection. Since then, different types of microneedles, both in singular or patch form, have been shown to be effective in delivering drugs to different sites of the eye, with minimal puncture size and targeted drug delivery of optimal way.

The study: the team drew inspiration from these latest technologies to develop its new self-sealing micro-needle for ocular injection treatments. The culmination of the research consists of biodegradable, ultra-fine and hyper-sharp tip micro-needles of various lengths. This versatility in needle length allows for more controlled placement within the eyeball and more precise delivery of medication to the site of injury; the thinness of the needles minimizes the size of the incision in the eyeball. The pointed end of the needle can be covered by dipping the therapeutic drug, the needle releasing the drug upon insertion into the eyeball; Finally, at the blunt end of the micro-needle is attached an optimized hydrogel plug which can swell after injection of the needle and seal the insertion hole.

First proofs of concept, in vitro, ex vivo and in vivo: microneedles have been tested for strength, drug delivery and sealing system effectiveness. Early in vitro tests using the drug-loaded microneedles demonstrated near-complete drug delivery over a 24-hour period; similar experiments using ocular fluids from animal models demonstrate the correct delivery of the drug over a suitable distance: the distance of distribution of the drug -here a dye- from the insertion site proves to be directly proportional to the length of the needle, which suggests a great capacity for control via the choice of the length of the needle.

Final in vivo tests in animal models confirm proper, targeted, occluded administration with no leakage of ocular fluid, deep penetration into retinal tissues, no signs of inflammation or tissue breakdown at the injection site.

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