Alessandra Sutti

Fast responsive and morphologically robust thermo-responsive hydrogel nanofibres from poly(N-isopropylacrylamide) and POSS crosslinker

Stable thermo-responsive hydrogel nanofibres have been prepared by electrospinning of commercial poly(N-isopropylacrylamide) (PNIPAM) in the presence of a polyhedral oligomeric silsesquioxane (POSS) possessing eight epoxide groups and of an organic-base catalyst, followed by a heat curing treatment. The nanofibres showed excellent hydrogel characteristics with fast swelling and de-swelling responses triggered by temperature changes. They were also morphologically robust as their physical integrity was preserved upon repeated hydration/dehydration cycles and exposure to solvents.

Electrospinning of nanofibres with parallel line surface texture for improvement of nerve cell growth

Nanofibres having a parallel line surface texture were electrospun from cellulose acetate butyrate solutions using a solvent mixture of acetone and N,N′-dimethylacetamide. The formation mechanism of the unusual surface feature was explored and attributed to the formation of voids on the jet surface at the early stage of electrospinning and subsequent elongation and solidification of the voids into a line surface structure. The fast evaporation of a highly volatile solvent, acetone, from the polymer solution was found to play a key role in the formation of surface voids, while the high viscosity of the residual solution after the solvent evaporation ensured the line surface to be maintained after the solidification. Based on this principle, nanofibres having a similar surface texture were also electrospun successfully from other polymers, such as cellulose acetate, polyvinylidene fluoride, poly(methyl methacrylate), polystyrene and poly(vinylidene fluoride-co-hexafluoropropene), either from the same or from different solvent systems. Polarized Fourier transform infrared spectroscopy was used to measure the polymer molecular orientation within nanofibres. Schwann cells were grown on both aligned and randomly oriented nanofibre mats. The parallel line surface texture assisted in the growth of Schwann cells especially at the early stage of cell culture regardless of the fibre orientation. In contrast, the molecular orientation within nanofibres showed little impact on the cell growth.

Phase transition of poly(N-isopropylacrylamide) in aqueous protic ionic liquids: kosmotropic versus chaotropic anions and their interaction with water.

We have investigated the influence of a series of triethylammonium-based protic ionic liquid-water solutions on the lower critical solution temperature (LCST) of poly(N-isopropylacrylamide) (PNIPAM). We find that kosmotropic anions lower the LCST of PNIPAM more dramatically when compared with chaotropic anions. In addition, we have probed the solvent properties of the hydrated protic ionic liquid solutions using (1)H NMR, polarity measurements, and solvatochromic analysis of the Kamlet-Taft parameters, β and π*. We find that the hydrogen bond character--more specifically, the interactions between water and pIL--is the dominant parameter responsible for lowering the LCST of PNIPAM. We have added choline dihydrogen phosphate (choline dhp) into this study on the basis of positive results from previously reported protein folding studies using this ionic liquid.

Biofunctionalization of 3D nylon 6,6 scaffolds using a two-step surface modification

Nylon is a relatively inert polymer. The ability to easily functionalize nylon with biomolecules will improve the utilization of nylon in biological systems. A potential use of the biofunctionalized nylon scaffolds is in devices for cell therapeutics that can specifically select cells present in small numbers, such as hematopoietic stem cells. This study developed a versatile and simple two-step technique combining oxygen plasma treatment with wet silanization to graft biomolecules onto nylon 6,6 3D porous scaffolds. Scaffolds that were exposed to oxygen plasma exhibited up to 13-fold increase in silane attachment ((3-mercaptopropyl)trimethoxysilane/(3-aminopropyl)trimethoxysilane) compared to untreated scaffolds. To address the limitation of nondestructive characterization of the surface chemistry of 3D scaffolds, fluorescent CdSe/ZnS nanoparticles were used as a reporting tool for -NH2 functionalized surfaces. Scaffolds that were covalently bound with neutravidin protein remained stable in phosphate buffered saline up to four months. Functionality of the neutravidin-grafted scaffolds was demonstrated by the specific binding of CD4 cells to the scaffold via CD4-specific antibody. Ultimately, these neutravidin-functionalized 3D nylon scaffolds could be easily customized on demand utilizing a plethora of biotinylated biomolecules (antibodies, enzymes and proteins) to select for specific cell of interest. This technique can be extended to other applications, including the enhancement of cell-scaffold interactions.

Bending and abrasion fatigue of common suture materials used in arthroscopic and open orthopedic surgery

In orthopedic surgery, the reattachment of tendon to bone requires suture materials that have stable and durable properties to allow time for healing at the tendon–bone interface. The suture, not rigidly restrained within the anchor eyelet, is free to move during surgery and potentially after surgery with limb motion. During such movement, the suture is subjected to bending and frictional forces that can lead to fatigue‐induced failure. We investigated some common contemporary commercial number‐two‐grade suture materials and evaluated their resistance to bending abrasion fatigue and the consequent failure. Sutures were oscillated over a stainless steel wire at low frequency under load. Number of abrasion cycles to failure, changes in suture morphology, and fatigue‐failure method was recorded for each material. Suture structure had a significant effect on abrasion resistance, with braided sutures containing large numbers of fine high tenacity core filaments performing15–20 times better than other braided suture structures. Ultra high molecular weight polyethylene (UHMWPE) core filaments resisted bending abrasion failure better than other core materials due to the load spreading and abrasion resistance of these filaments. Sutures with UHMWPE cores also had high resistance to tensile failure. Limited correlation was observed between tensile strength and abrasion resistance.

Thermo-responsive Hercosett/Poly(N-isopropylacrylamide) films: a new, fast, optically responsive coating

Poly(N-isopropylacrylamide) (PNIPAM) is a common thermo-responsive, water-soluble polymer, while Hercosett is a cationic resin commonly employed in the paper industry. In this paper, Hercosett™ and poly(N-isopropylacrylamide) (PNIPAM) nanoparticles were used to prepare composite films that show thermo-responsive behavior and swelling-shrinking properties in water. First, size-controlled PNIPAM hydrogel nanoparticles were synthesized. These were then embedded within a matrix of the cationic resin Kymene 577H by film casting. The distribution of nanoparticles in the resin film was investigated. The thermo-responsive properties of the as-synthesized PNIPAM hydrogel nanoparticles and of the composite films were characterized together with the repeatability of the swelling-shrinking cycles. The presence of nanoparticles endowed the film with highly enhanced water retention (in comparison with resin-only films) and, most importantly, thermo-responsiveness. A very fast optical and morphological response was in fact observed. Due to the dual (optical and morphological) response, this new system is suitable for applications in optical or morphological actuation and gating.

Rapid Bayesian optimisation for synthesis of short polymer fiber materials.

The discovery of processes for the synthesis of new materials involves many decisions about process design, operation, and material properties. Experimentation is crucial but as complexity increases, exploration of variables can become impractical using traditional combinatorial approaches. We describe an iterative method which uses machine learning to optimise process development, incorporating multiple qualitative and quantitative objectives. We demonstrate the method with a novel fluid processing platform for synthesis of short polymer fibers, and show how the synthesis process can be efficiently directed to achieve material and process objectives.

Metal ion type significantly affects the morphology but not the activity of lipase–metal–phosphate nanoflowers

Enzyme–metal-ion–phosphate nanoflowers are high-surface area materials which are known to show higher activity than the constituting protein. Although the synthesis of hybrid nanoflowers has been demonstrated with a variety of proteins and reaction conditions, only di-valent metal ions have been tested to date. We expand on previous findings by testing a range of metal ions of different valence in co-presence with lipase from Burkholderia cepacia: Ag(I), Fe(II), Cu(II), Au(III). All metal ions produced colour precipitates, although the type of metal caused different precipitate morphologies under comparable reaction conditions: from nanoflowers to forests of nano-plates and crystal-like precipitates. In contrast, the type of metal ion did not appear to significantly affect the products specific enzyme activity, which remained greater than that of free lipase. This indicates that the type of metal ion and the macroscopic arrangement of the petals play a secondary role to that of the co-presence of the metal and phosphate ions in determining lipase nanoflower activity. The demonstrated ability to produce metal–phosphate-protein nanoflowers with a selection of different metals also opens the way to producing a wider range of functional, nanostructured, materials.

Temperature-Responsive Self-Assemblies of ‘Kinked' Amphiphiles

The synthesis of novel norbornane-based amphiphiles and the thermal response of their corresponding colloids is presented. It was found that the hydrodynamic diameter (DH) expansion or contraction of 1–4 in response to increasing temperature was governed by the length of the hydrophobic region possessed by the amphiphile (a 12 or 16 carbon chain). These data were used as a starting point to extend into an active tumour targeting system whereby two amphiphiles were modified to incorporate the oestrogen receptor antagonist Tamoxifen at the polar head group. This was achieved by a triazole moiety while both the C12 (18) or C16 (19) hydrophobic chains were incorporated as the hydrophobic region in an attempt to retain the response to thermal stimuli observed in our preliminary findings. These functionalised novel amphiphiles possessed critical aggregation concentration values of 510 and 19 µM, while aqueous self-assemblies of 56 and 106 nm for 18 and 19 were observed. Imaging by cryogenic transmission electron microscopy showed 18 to possess liposomal morphology, while 19, bearing a C16 hydrophobic portion, formed non-defined amorphous aggregates. Finally, the response to temperature of these assemblies was investigated with only the C12 variant 18 displaying a temperature response in the 5–55°C thermal window investigated.

Nano-capsules of amphiphilic poly(ethylene glycol)-block-poly(bisphenol A carbonate) copolymers via thermodynamic entrapment

The synthesis of amphiphilic poly(ethylene glycol)-block-poly(bisphenol A carbonate) (PEG-b-PC) block copolymer is presented here using a simple bio-chemistry coupling reaction between poly(bisphenol A carbonate) (PC) with a monomethylether poly(ethylene glycol) (mPEG-OH) block, mediated by dicyclohexylcarbodiimide/4-dimethylaminopyridine. This method inherently allows great flexibility in the choice of starting materials as well as easy product purification only requiring phase separation and water washing. Collective data from Fourier transform infrared spectroscopy (FTIR), nuclear magnetic resonance spectroscopy (NMR) and modulated dynamic scanning calorimetry (MDSC) confirmed the successful attachment of the poly(ethylene glycol) (mPEG-OH) and poly(bisphenol A carbonate) (PC) blocks. The preparation of nano-capsules was carried out by sudden addition of water to PEG-b-PC copolymers dispersed in THF, resulting in the controlled precipitation (i.e. thermodynamic entrapment) of the copolymer. Nano-capsules as small as 85 nm ± 30 nm were produced using this simple and fast methodology. We also demonstrate that encapsulating a water-insoluble bisphenol A diglycidyl ether (DGEBA) epoxy resin is possible highlighting the potential use of these capsules as a chemical delivery system.