Microneedles
Although the concept of microneedling was first introduced in the 1970s, its popularity has surged due to its effectiveness in drug delivery and its cosmetic benefits.
Alongside with materials, a variety of MNs types (solid, hollow, coated, hydrogel) has also been developed to possess different functions.
The microneedles range in size, shape, and function but are all used as an alternative to other delivery methods like the conventional hypodermic needle or other injection apparatus.
Stimuli-responsive microneedles are advanced devices that respond to environmental triggers such as temperature, pH, or light to release therapeutic agents.
[9] The concept of microneedles was first derived from the use of large hypodermic needles in the 1970s,[10] but it only became prominent in the 1990s as microfabrication manufacturing technology developed.
[10] Later, the concept of MNs finally came into experimentation in 1994 when Orentreich discovered the insertion of tri-beveled needles to the skin could possibly stimulates the release of fibrous strand.
[13] Subsequent research into microneedle drug delivery has explored the medical and cosmetic applications of this technology through its design.
The selection of materials for formation of MNs greatly depends on the strength of skin penetration, manufacturing method, and rate of drug release.
[19] On the contrary, MNs made of metals like stainless steel, titanium, and aluminum, are non-toxic and possess strong mechanical properties to penetrate the skin without breakage.
[12] Since the delivery of the drug depends on the flow rate of the microneedle, this type of array could become clogged by excessive swelling or flawed design.
Pharmaceutical companies and researchers have begun to study and implement polymers such as Fibroin, a silk-based protein that can be molded into structures like microneedles and dissolved once in the body.
[21][25] This material draws water from interstitial fluid in the stratum corneum and results in polymer swelling and release of drug.
[21] However, these routes have limited therapeutic effects because stratum corneum serves as a barrier that reduces the entry of drug molecules into the systemic circulation and target tissues.
The micropores facilitate the absorption of large molecules, like calcein and insulin, by 4 times via in-vitro skin models.
[11] In addition, MNs' direct drug delivery to systemic circulation avoided the first-pass effect in the liver.
However, current tissue fluid extraction methods are pain-inducing, and it may take up to hours or days for samples to be analyzed in medical laboratories.
MNs allow penetration through the epidermis but not long enough to compress nerves in deeper layers, and thus, they are minimally invasive and almost painless.
[31] The repetitive penetration through the stratum corneum forms micropores, and these physical traumas to the skin sequentially stimulate the wound-healing cascade and expression of collagen and elastin in the dermis.
[31] By making use of the human natural regeneration properties, microneedling could be used alone to treat scars, wrinkles, and skin rejuvenation, or in combination therapy with topical tretinoin and vitamin C for enhanced effect.
Dermarollers are hand-held rollers equipped with a total of 192 solid steel micro-sized needles arranged into 24 arrays, lengths ranging from 0.5-1.5mm.
In addition to improving psychological and emotional comfort, microneedles have been shown to be substantially less painful than conventional injections.
One of the biggest drawbacks of traditional needles is the hazardous waste that they produce, making disposal a serious concern for doctors and hospitals.
For patients who require regular administration of medication at home, disposal can become an environmental concern is needles are placed in the trash.
Microneedles only damage the skin to a depth of 10-15μm, making it difficult for bacteria to enter the bloodstream and giving the body a smaller wound to repair.
Although there is a lower risk of infection associated with microneedles, the arrays are more fragile than a typical hypodermic needle due to their small size and thus have a chance of breaking off and remaining in the skin.
There is a limited amount of literature available on the subject of microneedle drug delivery, as current research is still exploring how to make effective needles.
[35] Apart from procedural pain, some common post-treatment adverse events (AEs) of MNs include temporary discomfort, erythema (skin redness), and edema.
[11][36] However, most of the adverse side effects are not long-lasting and could be resolved spontaneously within 24 hours after the treatment, making MNs a rather safe tool.
[36][37] Photoprotection and minimal exposure to chemicals irritants are often advised for an effective recovery and lowered chance of skin inflammation.
