Biocompatible Monomers and Photopolymers

One major research field of the Griesser group deals with the development of new biocompatible resins based on Thiol-X chemistry for additive manufacturing technologies. In the last years, particularly, the thiol-yne reaction has been investigated for the 3D printing of biocompatible medical devices (e.g. clear aligners, stents and bone screws; see pictures below) by means of stereolithography. This system is characterized by a high monomer conversion (> 98%), which greatly reduces the migration of monomer residues. Significant advantages of this reaction compared to the polymerization of acrylate and methacrylate monomers are the biocompatibility of alkyne monomers, the high polymerization rate as well as the comparably high impact strength of the formed photopolymers.

3D printed medical devices:

Stretchable Optics and Electronics

The development of stretchable optics and electronics paves the way towards an easy integration of multifunctional devices in clothing, three-dimensional surfaces of machines, human skin or polymeric materials. The research of the Griesser groups deals with the development of UV-curable inks, resins and pastes for the realization of stretchable waveguides and conductors by means of ink-jet or screen printing. 

Based on this technology, electrodes as well as strain and pressure sensors are developed that can easily be structured and applied on large areas. In particular, ink-jet printing in combination with screen printing enables highly efficient and large area fabrication of stretchable sensor arrays on unconventional substrates such as textiles or polymer foils. 

Ink-jet printed stretchable waveguides on PDMS substrates

Photosensitive Materials for Organic Electronics

One main research topic of the Griesser Group is the investigation and development of photoreactive materials for organic electronic devices. We explore photosensitive interfacial layers in organic transistors and light emitting diodes allowing a selective modulation of the device parameters by means of UV-light. This approach has already been applied for the selective modulation of the charge charier mobility as well as the threshold voltage of Organic Thin Film Transistors.

Tuning of OTFT device parameter by photosensitive interfacial layers

Low-migration Photoinitiators

Beside the well-documented toxicity of commonly used acrylates, also the migration of the applied photoinitiators is a non-neglectable topic. In order to overcome this limitation, the Griesser group focuses on the development of low-migration photoinitiators. One concept, which is evaluated in this context, is to derivatize commericially available photoinitiators with alkyne groups that are capable of undergoing a copolymerization reaction in thiol based formulations. Moreover, oligomeric photoinitiators are synthesized and investigated with the aim to facilitate high water-solubility together with improved migration stability. Such photoinitiators can be applied in water-borne UV-curable inks which provide several benefits compared to classical acrylate based systems, e.g. low odor, no VOCs etc.

Surface and Nanoscience

A key research topic of the Griesser Group is the micro and nanostructuring of surfaces and materials by means of photolithographic tools such as Two Photon Absoption (TPAL), Extreme UV (EUVL), UV Interference (UVIL) and Scanning Nearfield Lithography (SNL), which is mainly performed in close collaboration with external partners such as Prof. Graham Leggett (University of Sheffield, GB), Dr. Volker Schmidt (Joanneum Research Weiz, AUT) and Dr. Celestino Padeste (Paul Scherrer Institute Villigen, CH).

Examples include the nanopatterning of metal sulfides by means of EUVL. This approach provides new pathways to fabricate highly ordered structured metal sul?de layers with periodicities far below 100 nm for potential application in hybrid solar cells.

AFM and SEM images of copper indium sulfide column structures with a periodicity of 141 nm

Moreover, a versatile method for efficient photopatterning of polysaccharide thin films was demonstrated using the example of cellulose, the most abundant biopolymer on earth. Depending on the conditions of development (organic solvent or enzymatic treatment) either negative- or positive-type cellulose structures could be obtained, offering lateral resolutions down to the sub-µm range by means of TPAL.

 
AFM micrograph and line profile of photopatterned (via TPAL) cellulose films

The Griesser group also focusses on the micro and nanopatterning of SAMs by means of photolithography, which is used (1) to tailor and improve the properties of surfaces and (2) to realize functional nanostructures such as protein nanopatterns. Scanning Probe techniques (in close collaboration with Prof. Christian Teichert) are routinely used for the morphological characterization of patterned films.

Friction force images of photo patterned (via SNL) Self Assembled Monolayer