Egdma

PVA (MW 85,000–124,000, 87–89% hydrolyzed, Aldrich) and Tserkovsky Bengal sodium salt (dye content ~90%, Aldrich) were used in electrospinning for fiber synthesis. The monomer 4VP (95%, Aldrich), the cross-linker EGDMA (98%, Aldrich), and the initiator tertbutyl peroxide (TBPO, 98%, Aldrich) were used without purification. Phosphate-buffered saline (PBS, Aldrich) was utilized for the release studies.

Polymer coatings were prepared on the crystalline indomethacin samples by iCVD of the monomer 2-hydroxyethyl methacrylate (HEMA, purity 97%, Aldrich, Germany) and the cross-linker ethylene glycol dimethacrylate (EGDMA, purity 98%, Aldrich, Germany), using tert-butyl peroxide (TBPO, purity 98%, Aldrich, Germany) as initiator. For all the depositions, the substrate temperature was 28 ± 1 °C, the working pressure was 47 Pa and the filament temperature was 200 ± 5 °C. The TBPO flow rate was set to 0.80 sccm and a Nitrogen patch flow of 3 to 4 sccm was applied. By adjusting the monomer to cross-linker flow ratios, different polymer compositions were achieved (for compositional analysis, please refer to the supplementary information). The p(HEMA-co-EGDMA) polymers are labeled by their cross-linker volume fraction (EGDMA fraction), with 100% denoting the EGDMA homopolymer. For polymer characterization, pristine silicon wafers with a native oxide (Siegert Wafers, Germany) were coated in addition. For all samples, a nominal coating thickness of 200 nm was deposited (monitored in situ by laser interferometry).

The hydrogel-based material presented in this work was based on a tert-polymer PEGDMA-NIPAAm-AA: Poly(Ethylene Glycol DiMethAcrylate-co-N-IsopropylAcrylAmide-co-Acrylic Acid) and was based on previous UV-curable formulations [19 (link)]. This stimulus-responsive hydrogel was sensitive to pH, due to the carboxylic groups of the acrylic acid, and to water, due to the 3D crosslinked structure of the hydrogel. The added thermal initiator was AIBN (Azo(bis)IsoButyroNitrile) in a concentration of 1% w/w, the cross-linker was EGDMA (Ethylene GlycolDiMethAcrylate) in 5% w/w, and the curing reaction accelerating agent was TEMED (N,N,N′,N′-TEtraMethylEthyleneDiamine) in a concentration of 0.5% w/w. The NIPAAm was dissolved in an AA-PEGDMA solution, avoiding the introduction of another solvent. To be suitable for the nanoimprint lithography process, the PEGDMA-NIPAAm-AA required the following ratio for its elements: 10:40:50 [20 (link)]. This formulation was diluted in ethanol at 30% w/w. The materials were all purchased from Sigma–Aldrich (Schnelldorf, Germany) PEGDMA (Mw 550, 98%), AIBN, EGDMA (Mw 198, 98%), and TEMED (Mw 116, 99%) were used without further purification. NIPAAm (Mw 113, 97%) was purified by recrystallization in n-hexane and AA (Mw 72, 99%) was de-inhibited using an ion-exchange resin.

Ethylene glycol dimethacrylate (EGDMA, Aldrich, St. Louis, MI, USA) and methacrylic acid (MAA, Aldrich) were distilled in vacuo over boiling chips prior to polymerization. Benzylfentanyl, acetyl-benzylfentanyl (ABF), and benzoyl-benzylfentanyl (BBF) were synthesized as described herein. Fentanyl was synthesized according to the method in reference [23 (link)]. Heroin, cocaine, methamphetamine, and 2,2-azobisisobutyronitrile (AIBN) were purchased from Sigma-Aldrich and used without further purification. The solvents used were HPLC-grade, obtained from VWR (Radnor, PA, USA), and used without further purification.