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A water stable nanocellulose film was prepared and used as a template for functional membrane material. A simple method to considerably improve water stability of 2,2,6,6-tetramethylpiperidin-1-yl)oxy (TEMPO) oxidized cellulosic nanofibril films was applied. The method involved the use of a 10-25% of poly(vinyl alcohol) (PVA) as bridging agent in films, which were prepared by solvent casting without additional post-treatments. The influence of amount and degree of hydrolysis of PVA on mechanical properties of wet films was studied. Due to numerous functional groups on the surface of the water stable, porous film, it could be used as a template for functional membrane materials with respect to ion capturing. Further functionalization of the film surface could be done by grafting thermoresponsive poly(N-isopropylacrylamide) (PNIPAM) to pursue improved control over hydrophilicity of the surface for antifouling purposes.

The desire to reduce overall weight in devices is a key driver for perpetual material development; the ability to combine composites with energy storage functions/capabilities which simultaneously provide structural integrity has the potential to supersede monofunctional components. To achieve this ambition, the multifunctional structure must perform both mechanical and energy storage functions sufficiently, but often there is a trade off in performance which is a significant challenge to overcome. Carbon aerogels have been shown to contribute positively to (electro-chemical double layer) capacitive performance due to an increased surface area in multifunctional carbon fiber based composite electrodes, but have also been shown to reduce mechanical properties; the addition of nanoscale reinforcers, such as carbon nanotubes, graphene or alike, with their superlative electrical and mechanical properties are proposed to address these concerns and create a truly hierarchical structure suitable for structural power applications.

Pre-cut unidirectional carbon fibre prepreg composites, with an overlapped finger-joint architecture, were modified through the addition of polyethersulfone (PES) interleaves. The properties arising from these finger-jointed configurations were strongly dependent on the interply overlap region. When the tough thermoplastic interleaves spanned only the central portion of the overlap, a crack arresting failure mechanism was observed in tension. A pronounced plateau region or pseudo-ductile response was shown in conjunction with a strain hardening response after crack arrest. The local strain-to-failure of PES interleaved samples was ~3.2%, an increase of 85% compared to the pre-cut baseline (strain-to-failure 1.6%, pre-cut specimens without interleaves).

A simple, reproducible, already introduced grafting method of methacrylic monomers onto carbon fibers is applied to cyanobiphenyl containing liquid crystalline (lc) monomers. The development of lc phases is faster and more uniform in the presence of carbon fibers. Applying a voltage to the grafted carbon fibers, causes phase transitions of the liquid crystals. By varying spacer length of the grafted lc polymers the physico-chemical properties, e. g. wetting and electrokinetic behavior (zeta-potential) are significantly influenced.

Tissue engineering scaffolds are 3D constructs that simulate the growth environment in vivo. The present work aims to address the question of whether thin films, i.e., flat surfaces, are a suitable model for more complex 3D structures? With this in mind a complete study of the morphology and surface chemistry of poly(D,Llactide) (PDLLA) substrates, fabricated into two different structures, is presented. The polymer structures studied include a 3D, porous, foam-like scaffold prepared by the thermally induced phase separation (TIPS) method and flat polymer thin films made by solvent casting. Based on the maximum bubble point test, a new method to assess the wettability of wet pore wall surfaces inside highly porous 3D structures was developed and tested. The maximum pore diameter determined using the maximum bubble point test for the total wetting liquids was confirmed through image analysis of scanning electron micrographs. The method allows the determination of the contact angle between the wet pore wall and a contacting liquid. The captive bubble method was employed to characterise the wettability of flat polymer films in contact with water. Both structures were further characterised using zeta- (ζ-) potential measurements to assess the surface chemistry of the polymer. The results demonstrate that PDLLA contains acidic functional groups and is hydrophobic. In order to evaluate the sensitivity of the test methods, the polymer surfaces were modified by protein adsorption using fibronectin and collagen. ζ-Potential and wettability measurements show that proteins indeed adsorb on virgin PDLLA surfaces. Protein adsorption causes the wettability of the PDLLA for water to improve. Our results strongly indicate that flat surfaces are not a suitable model for surfaces in complex 3D structures such as highly porous tissue engineering scaffolds. Such scaffolds must be characterised as a 3D system.

Hybrid sol–gel inorganic–organic fibres offer great potential in tissue engineering and regenerative medicine. A significant challenge is to process them using scalable technologies into useful scaffolds that provide control over fibre diameter, morphology, mechanical properties, ion release, degradation and cell response. In this work we develop formulations that are amenable to processing via solution blow spinning (SBS), a rapid technique using simple equipment to spray nano-/micro-fibres without any electric fields. The technique is extended to produce porous class I and II hybrid fibres using cryogenic SBS, with formulations developed based on tetraethyl orthosilicate/gelatin that are relatively facile to lyophilise. The formulations developed here take advantage of the reversible thermally activated conformation change of gelatin in aqueous solutions from random coil to triple helix to enable viscosity tuning and therefore fibre spinning. Gelatin is functionalised with (3-glycidyloxypropyl)trimethoxysilane to produce class II hybrids which exhibit controllable time- and temperature-dependent viscosity profiles which can be tuned for spinning into highly porous fibres.

Resorcinol-formaldehyde based aerogel precursors were infused into structural carbon fibre weaves, then gelled and carbonised to generate a continuous monolithic matrix network. This hierarchical carbon preform was subsequently infused with polymeric resins, both multifunctional and structural, to produce dense composites. The resulting hierarchical composites have a nanoscale reinforcement in the matrix at up to an order of magnitude higher loadings than typically available by other techniques. Compression, tension, ±45° shear and short beam tests demonstrate the potential of such matrix systems to address matrix dominated failures. However, for the best structural performance it will be necessary to re-optimise the fibre-matrix interface, which is degraded by the current processing regime.

Results of grafting reactions of a liquid crystalline (lc) monomer ontocarbon fiber surfaces are presented and compared with results of noncovalently bondedlc polymer, which is proved reproducible by scanning electron microscopy. Electro-optical investigations under a polarizing microscope hints of the possibility of changinglc polymer and lc low molecular mass matrix molecules properties by applying a certainvoltage to the carbon fibers. Wetting and electrokinetic measurements were performedand correlated with grafting reaction parameters. Those investigations revealed anearly complete coverage of the carbon fiber surfaces by lc polymers. These measure-ments are suitable to characterize carbon fibers modified by grafted or coated polymers. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 71: 1893–1904, 1999 Key words: grafting reaction; carbon fiber; liquid crystalline monomer and polymer;contact angle; zeta-potential INTRODUCTION As described in part I of this article, 1 grafting ofmethacrylic acid onto carbon fibers can be easilyachieved by radically initiated bulk polymeriza-tion. The influences on modification prior to graft-ing and the influences on the amount of initiatorto the behavior of the resulting surfaces werestudied.Besides non-lc monomers and polymers, lc ma-terial was also grafted onto carbon fibers. Thiswas accomplished by 1,3-dicyclohexylcarbodiim-ide-activated esterification of acidic surfacegroups present on the carbon fiber with lc mono-mers and polymers.

This thesis reports and discusses the development of several multifunctional biopolymers to be used in a cleaner approach for producing high porosity macroporous polymers by high internal phase emulsion (HIPE) templating for application as tissue engineering scaffolds. The aim is to identify and create biocompatible polymers that can self-stabilize HIPEs, be self-crosslinkable and also act simultaneously as the matrix for the macroporous polymers after emulsification, solidification and removal of the templating phase and aqueous solvent for the polymers. Firstly, the design of a self-emulsifying biopolymer was carried out using a chitosan based biopolymer grafted with thermoresponsive poly(N-isopropylacrylamide) (PNIPAM) and oligolysine (CSNLYS). Self-emulsification of HIPEs was found to be successful using this copolymer. The HIPEs could be solidified by raising the temperature above the lower critical solution temperature (LCST) of the PNIPAM component to 40°C. In addition, it was found that by changing the degree of polymerization of the grafted oligolysine, HIPEs with very different emulsion droplet sizes resulted, ranging from microemulsions with average droplet sizes of 0.13 µm, to macroemulsions with average droplet sizes of 10.5 µm. Polymerized (high internal phase macroemulsion) (polyHIPE) and polymerized (high internal phase 7 microemulsion) (polyHIPME) were formed by removing the liquid templating phases resulting in closed celled high porosity foams. Chitosan-graft-poly(N-isopropylacrylamide)-graft-oligoproline (CSN-PRO) and chitosan-graft-poly(N-isopropylacrylamide)-graft-oligo(glutamic acid) (CSN-GLU) were synthesized next to produce self-stabilized HIPE. CSN-PRO was found to be able to stabilize HIPE but not CSN-GLU, forming closed pores with pore sizes ranging from 32 µm to 71 µm. Upon addition of a low concentration of the surfactant PEG(20)sorbitan monolaurate, and varying the polymer concentration and internal phase volume ratio, different polyHIPEs with pore size of up to 143 µm, porosities of up to 99%, surface areas >300 m 2 /g and controlled pore interconnectivity can be formed. The CSN-PRO stabilized polyHIPEs are able to retain their thermoresponsiveness and remain intact when immersed into water at physiological temperature but dissolve below their LCST, which is useful in applications such as drug delivery and for tissue engineering scaffolds. Murine embryonic stem cells which are nonanchorage dependent were seeded to assess biocompatibility and were found to be able to survive and enter the pores of the poly(CSN-PRO)HIPE hydrogel. To produce scaffolds suitable for the attachment of anchorage dependent cells, a polypeptide, gelatin was used to create the self-emulsifying copolymer gelatin-graft-PNIPAM (GN). It was found GN does self-stabilize HIPEs. Upon solidification of the HIPEs and the removal of the templating oil phase and water from the aqueous phase highly porous and interconnected tissue 8 engineering scaffold resulted without the use of any additional surfactant. Poly(GN)HIPEs can be formed by two different solidification mechanisms as conferred by the components of GN, gelatin and PNIPAM. By inheriting the temperature sensitivity of these two components, GNHIPEs can be solidified at either 4°C due to the gelatin component or 40°C due to the PNIPAM component. The physical properties of the resultant self-stabilized poly(GN)HIPEs can be controlled by varying the aqueous phase, emulsion phase volume ratio and solidification temperature. Because of the inherent temperature sensitivity, poly(GN)HIPE hydrogels are able to response rapidly to changes in temperature during the initial cell culturing period. Fibroblast cells seeded into the scaffold were seen to thrive, spread and proliferate in a culture period of 10 days, with a maximum depth of penetration of 360 µm. The cell-laden poly(GN)HIPE scaffold was shown to be injectable through a syringe without harming the encapsulated cells. This system provides a new strategy for the easy fabrication of safe and injectable biocompatible scaffolds for tissue engineering. Open Access