M. in het Panhuis

An overview of the suitability of hydrogel-forming polymers for extrusion-based 3D-printing

This review evaluates hydrogel-forming polymers that are suitable for soft tissue engineering with a focus on materials that can be fabricated using additive manufacturing (3D-printing). An overview of the specific material requirements for hydrogel-based tissue engineering constructs is presented. This is followed by an explanation of the various hydrogel-forming polymer classes that includes a detailed examination of material properties that are critical for extrusion printing. Specifically, mechanisms for hydrogel formation, degradation, and biological response, activity and compatibility are explored. A discussion of extrusion printing strategies for printable hydrogel-forming polymers is then presented in conjunction with a list of considerations to guide future tissue engineering developments.

Peptide modification of purified gellan gum

Gellan gum (GG) is an anionic polysaccharide with potential as a biopolymer for additive manufacturing (3D-bioprinting) and tissue engineering. Previous studies have shown GG to be highly cytocompatible, but lacking specific attachment sites required for anchorage-dependent cells. In this work, we modify purified-GG polymer with a short peptide containing the arginine-glycine-aspartic acid (RGD) sequence that is known to enhance integrin-mediated cell attachment. Radiolabelling of the peptide was used in optimisation of the conjugation procedure to achieve an overall efficiency of 40%. The purification of divalent cations from commercial GG samples was found to be critical for successful conjugation. Rheological studies revealed that the peptide coupling did not prevent gelation behaviour. C2C12 cells showed improved attachment on the surface of and encapsulated within RGD-GG hydrogels, differentiating to multinucleated myofibers after 5-7 days. PC12 cells showed minimal interactions with both GG and RGD-GG, with formation of cell clusters and impedance of terminal differentiation and neurite extension.

Fabrication of chemical sensors using inkjet printing and application to gas detection

This work describes the fabrication of gas sensors using inkjet printing. Sensors were constructed by building up a film of sensing material, such as polyaniline, from aqueous nanoparticulate dispersions. These films were printed over patterned silver interdigitated array designs for the purposes of conductimetric analysis. Unlike screen printing or lithography, inkjet printing does not require stencils or masks, therefore allowing rapid design and prototyping. For this study, polyaniline and modified polyaniline sensors were inkjet printed and assessed for the purposes of gas sensing applications, specifically hydrogen sulfide monitoring.

Diffusion of vitamin B 12 in gellan gum-carbon nanotube hydrogels

We report on the diffusion of vitamin B<inf>12</inf> through gellan gum-carbon nanotube hydrogels. The addition of carbon nanotubes to gellan gum reduced the vitamin B12 diffusion coefficient from 1.70 × 10⁻⁶ cm²/s to 0.70 × 10⁻⁶ cm²/s.

Inkjet printed conducting gel-carbon nanotube materials

The inkjet printing of CNT-biopolymer composite inks onto solid and gel substrates was investigated. Changing the substrate from glass to gel resulted in an increase in the resistance of printed materials from 9.85 kΩ/cm to 39.42 kΩ/cm.

Hydrogel electrode materials

The fabrication of hydrogel electrode materials via inkjet/extrusion printing, wet-spinning and physical cross-linking will be presented. Electrode characteristics such as conductivity, contact resistance, impedance and electrode connectivity will be discussed in detail.

Extrusion printing conducting gel-carbon nanotube structures upon flexible substrates.

Extrusion printing was investigated as a wet-processing method for fabrication of robust, flexible conducting structures. Layer resistance values of 7 – 8 kΩ/cm were obtained for one printed layer on flexible substrates. Increasing the number of extrusion printed layer significantly improved resistance.