Marc in het Panhuis

Self-healing hydrogels

Over the past few years, there has been a great deal of interest in the development of hydrogel materials with tunable structural, mechanical, and rheological properties, which exhibit rapid and autonomous self-healing and self-recovery for utilization in a broad range of applications, from soft robotics to tissue engineering. However, self-healing hydrogels generally either possess mechanically robust or rapid self-healing properties but not both. Hence, the development of a mechanically robust hydrogel material with autonomous self-healing on the time scale of seconds is yet to be fully realized. Here, the current advances in the development of autonomous self-healing hydrogels are reviewed. Specifically, methods to test self-healing efficiencies and recoveries, mechanisms of autonomous self-healing, and mechanically robust hydrogels are presented. The trends indicate that hydrogels that self-heal better also achieve self-healing faster, as compared to gels that only partially self-heal. Recommendations to guide future development of self-healing hydrogels are offered and the potential relevance of self-healing hydrogels to the exciting research areas of 3D/4D printing, soft robotics, and assisted health technologies is highlighted.

Biofabrication: an overview of the approaches used for printing of living cells

The development of cell printing is vital for establishing biofabrication approaches as clinically relevant tools. Achieving this requires bio-inks which must not only be easily printable, but also allow controllable and reproducible printing of cells. This review outlines the general principles and current progress and compares the advantages and challenges for the most widely used biofabrication techniques for printing cells: extrusion, laser, microvalve, inkjet and tissue fragment printing. It is expected that significant advances in cell printing will result from synergistic combinations of these techniques and lead to optimised resolution, throughput and the overall complexity of printed constructs.

Bio-ink for on-demand printing of living cells

Drop-on-demand bioprinting allows the controlled placement of living cells, and will benefit research in the fields of tissue engineering, drug screening and toxicology. We show that a bio-ink based on a novel microgel suspension in a surfactant-containing tissue culture medium can be used to reproducibly print several different cell types, from two different commercially available drop-on-demand printing systems, over long printing periods. The bio-ink maintains a stable cell suspension, preventing the settling and aggregation of cells that usually impedes cell printing, whilst meeting the stringent fluid property requirements needed to enable printing even from many-nozzle commercial inkjet print heads. This innovation in printing technology may pave the way for the biofabrication of multi-cellular structures and functional tissue.

Recovery from applied strain in interpenetrating polymer network hydrogels with ionic and covalent cross-links

We have prepared an interpenetrating polymer network hydrogel based on the simultaneous formation of two polymer networks, gellan gum and poly(acrylamide). The gellan gum network is ionically cross-linked, while poly(acrylamide) network is covalently cross-linked. These gels can recover 53 ± 4% of the hysteresis of the first compressive cycle and 90 ± 9% of subsequent cycles.

Fabrication of Polyaniline-Based Gas Sensors Using Piezoelectric Inkjet and Screen Printing for the Detection of Hydrogen Sulfide

This work describes a fully printable polyaniline-copper (II) chloride sensor for the detection of hydrogen sulfide gas. The sensing device is composed of screen printed silver interdigitated electrode (IDE) on a flexible PET substrate with inkjet printed layers of polyaniline and copper (II) chloride. The sensor is employed as a chemiresistor with changes in measured current being correlated with concentration. On exposure to hydrogen sulfide, 2.5 ppmv (parts per million by volume) is clearly detectable with a linear relationship between measured current and concentration over the 10-100 ppmv region. The detection mechanism is discussed with respect to the hydrogen sulfide response, the choice of electrode materials in addition to UV-vis and surface enhanced Raman spectroscopy (SERS) characterization.

3D printing of transparent and conductive heterogeneous hydrogel-elastomer systems

A hydrogel-dielectric-elastomer system, polyacrylamide and poly(dimethylsiloxane) (PDMS), is adapted for extrusion printing for integrated device fabrication. A lithium-chloride-containing hydrogel printing ink is developed and printed onto treated PDMS with no visible signs of delamination and geometrically scaling resistance under moderate uniaxial tension and fatigue. A variety of designs are demonstrated, including a resistive strain gauge and an ionic cable.

Inkjet deposition and characterization of transparent conducting electroactive polyaniline composite films with a high carbon nanotube loading fraction

We report the synthesis and inkjet processing of water dispersable polyaniline composite materials with a high carbon nanotube loading fraction. Printed films displayed good optical transparency, sheet resistance and electrochromic behaviour, allowing switching between yellow, green and blue.

Conducting bio-materials based on gellan gum hydrogels

Hydrogels, a class of highly hydrated polymer materials, are emerging as a viable bio-material for tissue engineering applications due to their bio-degradability, process-ability, and similarity with the natural extra-cellular matrix. Here, we report on gellan gum hydrogels and demonstrate that the gelation temperature can be tailored to be physiologically relevant. Furthermore, we demonstrate the biocompatibility of these hydrogels and show that cell behaviour is influenced by gel modulus and the incorporation of surface topographical features. Carbon nanotubes were incorporated into hydrogels as conducting fillers to achieve an electrically conducting hydrogel for the future purpose of electrical cell stimulation. Percolation studies revealed that a carbon nanotube concentration of 1.3% by weight is required to achieve electrical conduction through the hydrogel.

Imaging of Human Lens Lipids by Desorption Electrospray Ionization Mass Spectrometry

The lipid composition of the human lens is distinct from most other tissues in that it is high in dihydrosphingomyelin and the most abundant glycerophospholipids in the lens are unusual 1-O-alkyl-ether linked phosphatidylethanolamines and phosphatidylserines. In this study, desorption electrospray ionization (DESI) mass spectrometry-imaging was used to determine the distribution of these lipids in the human lens along with other lipids including, ceramides, ceramide-1-phosphates, and lyso 1-O-alkyl ethers. To achieve this, 25 μm lens slices were mounted onto glass slides and analyzed using a linear ion-trap mass spectrometer equipped with a custom-built, 2-D automated DESI source. In contrast to other tissues that have been previously analyzed by DESI, the presence of a strong acid in the spray solvent was required to desorb lipids directly from lens tissue. Distinctive distributions were observed for [M + H]+ ions arising from each lipid class. Of particular interest were ionized 1-O-alkyl phosphatidylethanolamines and phosphatidylserines, PE (18:1e/18:1), and PS (18:1e/18:1), which were found in a thin ring in the outermost region of the lens. This distribution was confirmed by quantitative analysis of lenses that were sectioned into four distinct regions (outer, barrier, inner, and core), extracted and analyzed by electrospray ionization tandem mass spectrometry. DESI-imaging also revealed a complementary distribution for the structurally-related lyso 1-O-alkyl phosphatidylethanolamine, LPE (18:1e), which was localized closer to the centre of the lens. The data obtained in this study indicate that DESI-imaging is a powerful tool for determining the spatial distribution of human lens lipids.

Inkjet printed water sensitive transparent films from natural gum–carbon nanotube composites

We have fabricated novel water sensitive transparent films on flexible substrates by inkjet printing of aqueous based inks of single- and multi-walled carbon nanotubes dispersed with ultra low concentrations of the biopolymers gellan and xanthan gum.