Hydrogels represent a class of polymers that mimic the extracellular matrix (ECM) by its ability to absorb water or other water-based biological fluids similar to living tissue. Therefore hydrogels are in the focus of interest in many fields such as tissue engineering, drug delivery, or other biomedical applications.[1, 2] Two-photon polymerization (2PP) offers the possibility to produce hydrogel scaffolds in micro and nano scale resolution. The efficiency of the 2PP process, beside other parameters, depends on the used photoinitiator (PI), its ability to undergo two-photon absorption (2PA) and on the solubility in the polymer solution. Known as the gold standard in biomedical applications, poly(ethylenglycol) (PEG) is one of the most elaborated and well-known material. However, because of its extensive application in medical products, more and more cased are known where PEGylated agents causes anaphylaxis due to anti-PEG antibody reactions. Therefore, is it important to find new polymer classes as a future alternatives. Poly(oxazoline)s provide the desired properties such as biocompatibility and material based stealth effect. Further advantages are commercial availability, safe synthesis in comparision to PEG and the possibility for further functionalization, e.g with growth factors.[3, 4]
Macromonomers based on poly(2-ethyl-2-oxazoline)s (PEtOx) with terminal acrylic end groups were successfully synthesized by cationic ring opening polymerization (CROP). Single acrylated macromomers (PEtOx-AA) with a degree of polymerization (DP) of 10, 15 and 20 were synthesized using methyltosylate (MeTos) as initiator. The bifunctional initiator 1,4-dibromo-2-buten (DBB) was used to synthesize the diacrylated macromonomer (PEtOx-DA) with DP of 10 and 20. PEtOx-DA and PEG-DA were compared in arrays of test structures produced by 2PP using different processing parameters, e.g. laser power and processing speed.
A new watersoluble photoinitiator BTABcP-1 was synthesized via four-step synthesis. Starting with a Vielsmeier-Haack reaction, an aldehyde function was introduced. Then the compound was brominated with NBS, followed by a Heck reaction with acrylic acid to get the precursor for the final aldolcondensation with cyclopentanone. BTABcP-1 shows good solubility in water as well as in polymer solution and its absorption maxima can be found at 382 and 496 nm.