3D printing of surgical staples.

In this work, CAD design and additive manufacturing (3D printing) are used to fabricate surgical staples. The staples were analysed on their mechanical robustness according to ASTM standard F564-17 which involved the in-house design, prototyping and fabrication (using 3D printing) of specialized grips and extension blocks. Our results indicated that staples 3D printed using carbon fibre reinforced nylon 6 (CF-PA6) exhibited a strength value of 37 ± 3 MPa coupled with an implantation-suitable ductility value of 26 ± 4%. The mechanical robustness of CF-PA6 staples subjected to immersion in simulated body fluid resulted in a reduction in stiffness and strength of 40% and 70% over 5 weeks, respectively. The carbon fibre nylon composite staples were able to handle a load of 15 kg and 5 kg prior and following immersion in simulated body fluid, respectively.

Poly(N-isopropylacrylamide) Hydrogel for Diving/Surfacing Device.

Underwater robots and vehicles have received great attention due to their potential applications in remote sensing and search and rescue. A challenge for micro aquatic robots is the lack of small motors needed for three-dimensional locomotion in water. Here, we show a simple diving and surfacing device fabricated from thermo-sensitive poly(N-isopropylacrylamide) or a poly(N-isopropylacrylamide)-containing hydrogel. The poly(N-isopropylacrylamide)-containing device exhibited fast and reversible diving/surfacing cycles in response to changing temperature. Modulation of the interaction between poly(N-isopropylacrylamide) chains and water molecules at temperatures above or below the lower critical solution temperature regulates the gel density through the swelling and de-swelling. The gel surfaced in water when heated and sank when cooled. We further showed reversible diving/surfacing cycles of the device when exposed to electrical and ultrasonic stimuli. Finally, a small electrically heated gel was incorporated into a miniature submarine and used to control the diving depth. These results suggest that the poly(N-isopropylacrylamide)-containing device has good potential for underwater remote-controlled micro aquatic robots.

Programmable enzymatic oxidation of tyrosine-lysine tetrapeptides.

The ability to control the response of self-assembled systems upon exposure to external stimuli has been a long-standing goal of supramolecular chemistry. Short peptides are an attractive platform to realise this objective due to their chemical diversity and modular nature. Here, we synthesise a library of Fmoc-capped tetrapeptides, each containing two tyrosine and two lysine residues and varying in their amino acid sequence. Despite having similar secondary structure, these tetrapeptides form structures which are highly sequence dependent, yielding aggregates, nanofibres or monomers. This in turn highly affects the rate and degree of oxidative polymerisation by the enzyme tyrosinase, with self-assembled nanofibres exhibiting a greater degree of polymerisation. We monitor the formation of tyrosine oxidation products over time, finding that the precipitation of polymers is driven by quinone-based species. This affects the electrochemical properties of the oxidised peptide polymers, as determined through electrical impedance spectroscopy. Finally, intrinsic fluorescence microscale thermophoresis studies confirm that the degree of oxidative polymerisation is highly dependent on tyrosine solvent accessibility and the presence of peptide monomers. The ability to tune the kinetics of enzymatically active substrates and understand their polymerisation pathways on a molecular level is important for the creation of programmable, enzyme responsive biomaterials.

Conducting hydrogels for edible electrodes.

The development of highly swollen, strong, conductive hydrogel materials is necessary for the advancement of edible device research. Using a gellan gum/gelatin ionic-covalent entanglement (ICE) hydrogel, a simple method of producing conductive, edible hydrogels is described. ICE gels containing NaCl or CsCl were developed which exhibited conductivities of 200 ± 20 mS cm-1 and 380 ± 30 mS cm-1, respectively. Furthermore, the potential of food grade products for use as edible electrodes was examined by analysing the electrical properties of alginate-gelatin hydrogels, Vegemite, Marmite, jelly and gold leaf. Lastly, these edible ICE gels were used to demonstrate a capacitive pressure sensor from consumable materials, which displayed a sensitivity of 0.80 ± 0.06 pF kPa-1 for a range of 4-20 kPa. The pressure exerted by the GI tract on its contents is standardly 0.7 kPa to 6.3 kPa. This suggests potential for application in the detection of digestive pressure abnormalities such as intestinal motility disorders.

Effect of heterocyclic capping groups on the self-assembly of a dipeptide hydrogel.

The mechanism and design rules associated with the self-assembly of short peptides into hydrogels is currently not well understood. In this work, four diphenylalanine-based peptides have been synthesised, bearing heterocyclic capping groups which have different degrees of hydrogen bonding potential and nitrogen substitution. For these four peptides, zeta potential and electrical impedance spectroscopy measurements were undertaken to monitor gelation, with the impedance data showing different gelation times for each peptide hydrogel. Through a combination of atomic force microscopy and rheological measurmeents, including dynamic strain and frequency sweeps, and thixotropic tests, the relationship between the mechanism of self-assembly in these hydrogels and their macroscopic behaviour can be established. It is observed that the degree of nitrogen substitution affects the self-assembly mechanisms of the hydrogels and as such, that there is an interplay between branching and bundling self-assembly pathways that are responsible for the final properties of each hydrogel.

Enhanced gelation properties of purified gellan gum.

Gellan gum is a hydrogel-forming polysaccharide when combined with monovalent or divalent cations such as sodium, magnesium, potassium or calcium. Commercially, gellan gums are sold with trace amounts of these cations, which have been proven to affect the gelation and mechanical properties of the resultant hydrogels. A new method based on impedance analysis for determining the gel transition temperature of purified and un-purified gellan gum is presented. The sodium salt form of gellan gum is shown to have lower dissolution and gel transition temperatures.

Films, Buckypapers and Fibers from Clay, Chitosan and Carbon Nanotubes.

The mechanical and electrical characteristics of films, buckypapers and fiber materials from combinations of clay, carbon nanotubes (CNTs) and chitosan are described. The rheological time-dependent characteristics of clay are maintained in clay-carbon nanotube-chitosan composite dispersions. It is demonstrated that the addition of chitosan improves their mechanical characteristics, but decreases electrical conductivity by three-orders of magnitude compared to clay-CNT materials. We show that the electrical response upon exposure to humid atmosphere is influenced by clay-chitosan interactions, i.e., the resistance of clay-CNT materials decreases, whereas that of clay-CNT-chitosan increases.