Chris Sammon

A FTIR-ATR study of liquid diffusion processes in PET films: comparison of water with simple alcohols

An in-situ FTIR-ATR method for simultaneously obtaining both kinetic and structural information during liquid sorption into polymers was presented. The kinetics and diffusion profile of the sorption of liquid water and liquid methanol into poly(ethylene terephthalate) (PET) were compared and contrasted. The diffusion of water into PET was shown to follow Fickian kinetics, without significant swelling and the calculated diffusion coefficients (D) varied between 8.57 and 0.52 x 10(-9) cm(2) s(-1) for a crystallinity range of 4-25%. The D values decreased non-linearly with the increase in crystallinity. The average spherulitic crystal size was thought to play a significant role in determining the rate of water sorption. Conversely, the sorption of liquid methanol was accompanied by significant swelling and crystallisation and hence showed non-Fickian or anomalous kinetics. The sorption data were fitted to a dual sorption model which indicated that the rate of diffusion of liquid methanol was faster than that of liquid water, probably due to the accompanying swelling. Increasing the level of crystallinity was shown to decrease the capacity for the polymer to swell and reduced the calculated diffusion coefficients

Complexes of heterocyclic thiones and Group 12 metals: Part four. Preparation and characterisation of 1:1 complexes of mercury(II) halides with 1,3-thiazolidine-2-thione and 1,3-benzothiazoline-2-thione. Crystal structure of the discrete trans dimer [(μ-dibromo)bis(trans{(bromo)(1,3-thiazolidine-2-thione)}mercury(II))]

Abstract The addition of 1,3-thiazolidine-2-thione (tzdSH) or 1,3-benzothiazoline-2-thione (bztzSH) to mercury(II) halides in equimolar quantities in ethanolic solutions resulted in the formation of the 1:1 complexes LHgX2 (L=tzdSH, bztzSH; X=Cl, Br, I) which were characterised by elemental analysis. Spectroscopic evidence confirmed the exocyclic sulphur to be the donor atom in the thione form of the ligand and that the complexes were halogen bridged dimers. The X-ray structure of [(tzdSH)HgBr2]2 shows the molecule to be a centrosymmetric double halogen bridged dimer with distorted tetrahedral coordination geometry for Hg; secondary Hg⋯Br interactions link the molecules together into chains, and there are intramolecular N–H⋯Br hydrogen bonds between the heterocyclic ligands and the bridging bromides.

Monitoring the Thermal Gelation of Cellulose Ethers in situ Using Attenuated Total Reflectance Fourier Transform Infrared Spectroscopy

In this work attenuated total reflection Fourier transform infrared (ATR-FTIR) spectroscopy was used to probe the thermal gelation behavior of aqueous solutions of hydroxypropyl methylcellulose (HPMC), specifically thermal gelation and accompanying precipitation. Cloud point measurements are usually evaluated through turbidity in dilute solutions but the method cannot readily be applied to more concentrated or highly viscous solutions. From the ATR-FTIR data, intensity changes of the v(CO) band marked the onset of gelation and information about the temperature of gelation and the effect of the gel structure on the water hydrogen bonding network was elucidated. Changes in the relative intensities of bands associated with the methoxyl groups and hydrogen-bond-forming secondary alcohol groups indicated that hydrophobic polymer chain interactions were involved in the gelation process. The dominance of inter-molecular H bonding over intra-molecular H bonding within the cellulose ether in solution was also observed. The ATR-FTIR data was in good agreement with measurements of turbidity conducted on the same systems. The work indicates significant potential for the use of ATR-FTIR for the investigation of gelation and cloud point measurements in viscous cellulosic formulations.

Complexes of heterocyclic thiones and Group 12 metals Part 5. Reactions of 1,3-thiazolidine-2-thione and benzo-1,3-thiazoline-2-thione with mercury(II) halides in a 2 : 1 ratio. Crystal structures of bis(1,3-thiazolidine-2-thione) mercury(II) bromide and bis(benzo-1,3-thiazolinato)mercury(II)

Reactions of mercury(II) halides with 1,3-thiazolidine-2-thione (tzdSH) and benzo-1,3-thiazoline-2-thione (bztzSH) in aqueous ethanol produced the 1:2 complexes with the former ligand but, due to steric effects, only the previously described 1: 1 complexes of the latter were isolated. Vibrational and C-13 NMR spectral studies indicate eta (1)-thione donation by the heterocyclic ligand and this has been confirmed by the crystal structure determination of (tzdSH)(2)HgBr2. The structure consists of pseudotetrahedral mercury (II) with longer C-S and shorter C-N bonds than in the free ligand and with the Br-Hg-Br angle being similar to 20 degrees smaller than the largest angle, S-Hg-S, around mercury due to deformation by inter- and intra-molecular interactions. The heterocyclic ligands are unsymmetrical round mercury relative to the two bromines. Reaction of the two thiones with mercury(II) acetate in ethanol in the presence of triethylamine results in deprotonation with the formation of the corresponding thionates. The former produced insoluble (tzdS)(2)Hg while the latter formed plate-like (bztzS)(2)Hg whose crystal structure showed linearity around mercury with digonal coordination via the thionate sulphur. The small Hg-S-C angle and (HgN)-N-... separation are indicative of a weak interaction between mercury and the nitrogen of the thioamide double bond

FTIR–ATR studies of diffusion and perturbation of water in polyelectrolyte thin films. Part 4. Diffusion, perturbation and swelling processes for ionic solutions in SPEES/PES membranes

We report diffusion rates and equilibrium concentrations of water in a polyelectrolyte SPEES/PES film using ATR/FTIR spectroscopy. The data for water obtained by fitting spectral intensities to a dual mode diffusion model in the presence of different counter ions (at 0.2 mol dm(-3)) follow the order Li+ > Cs+ > Na+ > Ca2+ > K+. Diffusion is progressively slower for higher concentrations of NaCl (0.2-0.85 mol dm(-3)) and the NO3- counter anion leads to a faster diffusion rate than for Cl- at the same concentration. Both water uptake and diffusion rates are broadly consistent with expectations based on the differential degrees of swelling, caused by changes in the SO3-/SO3- interpolymer chain repulsive forces leading to a decrease in volume diffusion compared with the value for pure water. Direct spectral measurements of the degree of swelling confirm that the process does occur, although the order of the swelling amounts does not map directly onto that of the diffusion rates. This is probably because the interfacial dissociation processes are hydration dependent

ATR-FTIR study of the diffusion and interaction of water and electrolyte solutions in polymeric membranes

We present a comparative review of the most up to date ATR-FTIR measurements of water diffusion into three polymers, PET, PVC and SPEES-PES. New data on the diffusion of water from electrolyte solutions into SPEES-PES have been added and we discuss reasons for changes in transport coefficient due to ionic screening of interchain repulsions. Finally, we point out, and attempt to interpret, the differences in perturbation of the water IR bands in the three different polymer types. Some suggestions for further elucidation of the effect have been made.

Nucleus pulposus phenotypic markers to determine stem cell differentiation : fact or fiction?

Progress in mesenchymal stem cell (MSC) based therapies for nucleus pulposus (NP) regeneration are hampered by a lack of understanding and consensus of the normal NP cell phenotype. Despite the recent consensus paper on NP markers, there is still a need to further validate proposed markers. This study aimed to determine whether an NP phenotypic profile could be identified within a large population of mature NP samples. qRT-PCR was conducted to assess mRNA expression of 13 genes within human non-degenerate articular chondrocytes (AC) (n=10) and NP cells extracted from patients across a spectrum of histological degeneration grades (n=71). qRT-PCR results were used to select NP marker candidates for protein expression analysis. Differential expression at mRNA between AC and non-degenerate NP cells was only observed for Paired Box Protein 1 (PAX1) and Forkhead box F1 (FOXF1). In contrast no other previously suggested markers displayed differential expression between non-degenerate NP and AC at mRNA level. PAX1 and FOXF1 protein expression was significantly higher in the NP compared to annulus fibrosus (AF), cartilaginous endplate (CEP) and AC. In contrast Laminin-5 (LAM-332), Keratin-19 (KRT-19) and Hypoxia Inducible Factor 1 alpha (HIF1α) showed no differential expression in NP cells compared with AC cells. A marker which exclusively differentiates NP cells from AF and AC cells remains to be identified, raising the question: is the NP a heterogeneous population of cells? Or does the natural biological variation during IVD development, degeneration state and even the life cycle of cells make finding one definitive marker impossible?

Vibrational spectroscopic studies of the dynamics and perturbation of water in polymeric films

Abstract This paper reviews the current state of knowledge of how the dynamics and interactions of water are altered on sorption into a polymer. In particular, the role of infrared and Raman spectroscopies is examined, based on work in our group (and in other laboratories). Key questions as to the relevance of water-water and water-polymer interactions for the determination of the dynamic properties of ‘bound’ water are defined and addressed. It is concluded that water ‘confined’ to polymeric voids (or defects) is motionally hindered by strong water-polymer intermolecular forces. However, water-water interactions are loosened, the water network is ‘broken’ (to a degree which depends on the hydration level) and several water ‘types’ may be distinguished, depending on the time scale of the particular experiment. A non-uniform distribution of motional correlations in space and time is inferred, as maybe expected for such a heterogeneous material.

Thermally triggered injectable hydrogel, which induces mesenchymal stem cell differentiation to nucleus pulposus cells: Potential for regeneration of the intervertebral disc

There is an urgent need for new therapeutic options for low back pain, which target degeneration of the intervertebral disc (IVD). Here, we investigated a pNIPAM hydrogel system, which is liquid at 39°C ex vivo, where following injection into the IVD, body temperature triggers gelation. The combined effects of hypoxia (5% O2) and the structural environment of the hydrogel delivery system on the differentiation of human mesenchymal stem cells (hMSCs), towards an NP cell phenotype was investigated. hMSCs were incorporated into the liquid hydrogel, the mixture solidified and cultured for up to 6weeks under 21% O2 or 5% O2 where viability was maintained. Immunohistochemistry revealed significant increases in NP matrix components: aggrecan; collagen type II and chondroitin sulphate after culture for 1week in 5% O2, accompanied by increased matrix staining for proteoglycans and collagen, observed histologically. NP markers HIF1α, PAX1 and FOXF1 were also significantly increased where hMSC were incorporated into hydrogels with accelerated expression observed when cultured in 5% O2. hMSCs cultured under hypoxic conditions, which mimic the native disc microenvironment, accelerate differentiation of hMSCs within the hydrogel system, towards the NP phenotype without the need for chondrogenic inducing medium or additional growth factors, thus simplifying the treatment strategy for the repair of IVD degeneration.

Polyurethane scaffold with in situ swelling capacity for nucleus pulposus replacement

Nucleus pulposus (NP) replacement offers a minimally invasive alternative to spinal fusion or total disc replacement for the treatment of intervertebral disc (IVD) degeneration. This study aimed to develop a cytocompatible NP replacement material, which is feasible for non-invasive delivery and tunable design, and allows immediate mechanical restoration of the IVD. A bi-phasic polyurethane scaffold was fabricated consisting of a core material with rapid swelling property and a flexible electrospun envelope. The scaffold was assessed in a bovine whole IVD organ culture model under dynamic load for 14 days. Nucleotomy was achieved by incision through the endplate without damaging the annulus fibrosus. After implantation of the scaffold and in situ swelling, the dynamic compressive stiffness and disc height were restored immediately. The scaffold also showed favorable cytocompatibility for native disc cells. Implantation of the scaffold in a partially nucleotomized IVD down-regulated catabolic gene expression, increased proteoglycan and type II collagen intensity and decreased type I collagen intensity in remaining NP tissue, indicating potential to retard degeneration and preserve the IVD cell phenotype. The scaffold can be delivered in a minimally invasive manner, and the geometry of the scaffold post-hydration is tunable by adjusting the core material, which allows individualized design.