Synthetic polymers for Microneedle synthesis: From Then to Now

Considering microneedles (MNs) as transdermal drug delivery tools is driven by some crucial factors among which easy handling, simple administration and better patient compliance are primary. Achievable tailored microneedle production allowing encapsulation of range of pharmaceuticals and biomolecules as well as their performance as diagnostic tools emphasized how important it is to derive these products for practice. Initially, biopolymeric microneedles attained much attention being safer, biodegradable, and biocompatible (detailed somewhere else; Koyani 2019), however additional properties such as better mechanical strength, elasticity and hence the flexibility of synthetic polymers found more promising for commercializing the product. Moreover, they assisted to circumvent the limitations of former as well. This review is the brief overview of all the efforts (as per knowledge) and advancement (until 2019) aimed for designing and developing synthetic polymer-based microneedles (SPMNs) to deliver desired pharmaceutical products. It also highlights critical achievements, challenges, and future perspectives of synthetic polymers in microneedle world. Conclusively, it illustrates the journey from first report to current stand of synthetic polymeric microneedles and hence, entitled from then to now. Continue on synthetic polymers for micro needle synthesis

Keywords Microneedles, Synthetic polymers, PVP, PVA, PLGA, PCL

Polyvinylpyrrolidone (PVP), also commonly called polyvidone or povidone, is a water-soluble polymer made from the monomer N-vinylpyrrolidone. PVP was used as a plasma volume expander for trauma victims after the 1950s. It is not preferred as volume expander due to its ability to provoke histamine release and also interfere with blood grouping. It is used as a binder in many pharmaceutical tablets;[2] it simply passes through the body when taken orally. (However, autopsies have found that crospovidone (PVPP) contributes to pulmonary vascular injury in substance abusers who have injected pharmaceutical tablets intended for oral consumption. (Source: Wikipedia)

Poly(vinyl alcohol) (PVOH, PVA, or PVAl) is a water-soluble synthetic polymer. It has the idealized formula [CH2CH(OH)]n. It is used in papermaking, textile warp sizing, as a thickener and emulsion stabilizer in PVAc adhesive formulations and a variety of coatings. It is colourless (white) and odorless. It is commonly supplied as beads or as solutions in water. PVA is used in a variety of medical applications because of its biocompatibility, low tendency for protein adhesion, and low toxicity. (Soucre,  Wikipedia)

PLGA, PLG, or poly(lactic-co-glycolic acid) is a copolymer which is used in a host of Food and Drug Administration (FDA) approved therapeutic devices, owing to its biodegradability and biocompatibility. PLGA is synthesized by means of ring-opening co-polymerization of two different monomers, the cyclic dimers (1,4-dioxane-2,5-diones) of glycolic acid and lactic acid. Polymers can be synthesized as either random or block copolymers thereby imparting additional polymer properties. Common catalysts used in the preparation of this polymer include tin(II) 2-ethylhexanoate, tin(II) alkoxides, or aluminum isopropoxide. During polymerization, successive monomeric units (of glycolic or lactic acid) are linked together in PLGA by ester linkages, thus yielding a linear, aliphatic polyester as a product. (Source: Wikipedia)

Polycaprolactone (PCL) is a biodegradable polyester with a low melting point of around 60 °C and a glass transition temperature of about −60 °C. The most common use of polycaprolactone is in the production of speciality polyurethanes. Polycaprolactones impart good resistance to water, oil, solvent and chlorine to the polyurethane produced. This polymer is often used as an additive for resins to improve their processing characteristics and their end use properties (e.g., impact resistance). Being compatible with a range of other materials, PCL can be mixed with starch to lower its cost and increase biodegradability or it can be added as a polymeric plasticizer to polyvinyl chloride (PVC). Polycaprolactone is also used for splinting, modeling, and as a feedstock for prototyping systems such as fused filament fabrication 3D printers. (Source: Wikipedia)