Georgia Tech rebuilds its skin-puncturing STAR particles out of degradable polymers

The design problem is the stratum corneum, the skin's outer layer, which restricts how much of most topically applied drug gets through ^[1]. Microneedle patches solve that on small areas of skin, and the three polymers here have all been used to make them before ^[6]. What a patch cannot do is cover the variable, sometimes large areas that eczema and psoriasis present, and Prausnitz describes the particles filling that gap: "STAR particles provide the power of a microneedle patch to increase skin permeability with the flexibility to apply them over large and variable areas by simply rubbing a gel or cream containing STAR particles on the skin," he said ^[7].

The particles were cut by femtosecond laser micromachining into star shapes with sharp tips and a tapered profile, then tested on pig skin samples ^[8]. Formulation constrained the chemistry. PVA particles dissolve in water, so they were suspended in isopropyl palmitate, a non-aqueous ingredient already common in dermatology, and in that vehicle they punctured skin ^[9]. Cellulose acetate and polylactic acid worked in water formulations ^[10]. All three still punctured after a week of storage, with no visible damage to the particles ^[11].

The drug numbers are the interesting part, and there are three of them. Tacrolimus in isopropyl palmitate with PVA particles rose 1.7-fold at 10 seconds and 3.2-fold at 30 ^[12]. Methotrexate with cellulose acetate particles rose 5.4-fold and 25.2-fold ^[13]. Copper tripeptide-1 with polylactic acid particles rose 12.1-fold and 37-fold ^[14]. Tripling the rub time roughly quintupled the methotrexate effect and tripled the copper tripeptide effect, so the dose-response is steep and not linear in time ^[17].

Read each enhancement factor against its own drug. Methotrexate is used for psoriasis and cannot be delivered topically at all because its skin permeability is so low, so a 25-fold increase starts from close to nothing ^[5]. Tacrolimus already dissolves in non-aqueous solvents, and its 3.2-fold gain is over a control that was already getting drug in ^[4]. The three arms also differ in drug, vehicle and polymer at once, so nothing here separates polymer performance from formulation chemistry.

The honest cost of the switch is in the control. Titania particles in water, run as a comparison, made more pores than any of the polymers, which the researchers attribute to titania's greater hardness ^[15].

The team raises one safety question itself: particles designed to make micropores could end up elsewhere in the body, where the needles could do damage ^[16]. It calls that risk likely small, since the particles need forceful application to work ^[16]. This is excised pig skin and measured intradermal drug concentration ^[8][12].