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Biomedical subjects

M Geoghegan

Publications and source records attributed to M Geoghegan.

12 recordsLinked to original sources
PubMed2005

Block copolymer adsorption from a homopolymer melt to an amine-terminated surface.

Using neutron reflectometry, the adsorption of diblock copolymers from a neutral polystyrene (PS) matrix is studied as a function of substrate type and non-adsorbing block degree of polymerization. The block copolymer is poly(deutero styrene)-block-poly(methyl methacrylate) and the substrates are silicon oxide, SiO(x), and SiO(x) functionalized with (3-aminopropyl)triethoxysilane (APTES). We have determined the equilibrium volume fraction-depth profiles for such films, and compared them with volume fraction profiles generated by self-consistent mean-field (SCMF) theory and find good agreement between the experimental and theoretical data. SCMF calculations show that the segmental interaction energy between PS matrix chains and APTES is two orders of magnitude stronger than that between PS and SiO(x).

Journal Article↗
PubMed2005

Responsive brushes and gels as components of soft nanotechnology.

Progress in the development of generic molecular devices based on responsive polymers is discussed. Characterisation of specially synthesised polyelectrolyte gels, "grafted from" brushes and triblock copolymers is reported. A Landolt pH-oscillator, based on bromate/ sulfite/ferrocyanide, with a room temperature period of 20 min and a range of 3.1 < pH < 7.0, has been used to drive periodic oscillations in volume in a pH responsive hydrogel. The gel is coupled to the reaction and changes volume by a factor of at least 6. A continuously stirred, constant volume, tank reactor was set-up on an optical microscope and the reaction pH and gel size monitored. The cyclic force generation of this system has been measured directly in a modified JKR experiment. The responsive nature of polyelectrolyte brushes, grown by surface initiated ATRP, have been characterised by scanning force microscopy, neutron reflectometry and single molecule force measurements. Triblock copolymers, based on hydrophobic end-blocks and either polyacid or polybase mid-block, have been used to produce polymer gels where the deformation of the molecules can be followed directly by SAXS and a correlation between molecular shape change and macroscopic deformation has been established. The three systems studied allow both the macroscopic and a molecular response to be investigated independently for the crosslinked gels and the brushes. The triblock copolymers demonstrate that the individual response of the polyelectrolyte molecules scale-up to give the macroscopic response of the system in an oscillating chemical reaction.

Journal Article↗
PubMed2001

Thermodynamic suppression of Brownian motion.

We have used helium-3 nuclear reaction analysis to measure the Brownian motion (intradiffusion coefficient) of polystyrene in a partially miscible blend with poly(alpha-methylstyrene). In the one-phase region, when the correlation length is close to the polystyrene chain size, the intradiffusion coefficient falls to half of its thermal value. For larger and smaller values of the correlation length, diffusion is normal. These results show that the correlation length of a polymer blend constrains polymer diffusion, as suggested from previous neutron scattering measurements, and mean-field theory.

Journal Article↗
PubMed2000

Wetting in a phase separating polymer blend film: quench depth dependence

We have used 3He nuclear reaction analysis to measure the growth of the wetting layer as a function of immiscibility (quench depth) in blends of deuterated polystyrene and poly(alpha-methylstyrene) undergoing surface-directed spinodal decomposition. We are able to identify three different laws for the surface layer growth with time t. For the deepest quenches, the forces driving phase separation dominate (high thermal noise) and the surface layer grows with a t(1/3) coarsening behavior. For shallower quenches, a logarithmic behavior is observed, indicative of a low noise system. The crossover from logarithmic growth to t(1/3) behavior is close to where a wetting transition should occur. We also discuss the possibility of a "plating transition" extending complete wetting to deeper quenches by comparing the surface field with thermal noise. For the shallowest quench, a critical blend exhibits a t(1/2) behavior. We believe this surface layer growth is driven by the curvature of domains at the surface and shows how the wetting layer forms in the absence of thermal noise. This suggestion is reinforced by a slower growth at later times, indicating that the surface domains have coalesced. Atomic force microscopy measurements in each of the different regimes further support the above. The surface in the region of t(1/3) growth is initially somewhat rougher than that in the regime of logarithmic growth, indicating the existence of droplets at the surface.

Journal Article↗
PubMed1994

Non-anticoagulation in atrial fibrillation.

Atrial fibrillation (AF) is an important risk factor for stroke and anticoagulation is now indicated in many patients at increased risk. Studies however have shown that many patients at risk are not anticoagulated for reasons that are not well explored. We identified prospectively the reasons for non-anticoagulation in patients with AF in 94 consecutive hospital patients with cardiac or cerebrovascular disease who had AF. Patients with intermittent or lone AF and < 60 years were excluded n = 16. The remaining group had a mean age of 76 +/- 7 years with a mental test score of 7.4 +/- 2 (normal 10), 31 lived alone and they lived an average of 14 +/- 11 miles from the hospital laboratory. The reasons for non-anticoagulation overlapped and were: medical in 29: cognitive impairment/compliance in 32: and monitoring problems in 50. Anticoagulation for AF in the elderly is a complex enterprise which must take into account social and cognitive as well as medical issues.

Aged↗
PubMed1994

Prevalence and forms of neuropathic morbidity in 800 diabetics.

We prospectively determined the prevalence of morbidity from the various forms of diabetic neuropathy over one year in a population of 800 patients with diabetes mellitus (336 type 1, 464 type 2 DM). Symptoms documented were: pain/paraesthesia in the feet, loss of feeling and the restless legs syndrome. We also documented the prevalence of: neuropathic ulcers, amyotrophy, foot drop, and oculomotor palsy. Autonomic symptoms documented were: impotence, postural hypotension and diarrhoea. The only symptoms reported by 100 non-diabetic control subjects were: loss of feeling in 2% and restless legs syndrome in 7%. In the diabetics; pain/paraesthesia was present in 13%, feeling loss in 7% and neuropathic ulcers in 2%. The prevalence of Diabetic amyotrophy (proximal femoral neuropathy) was 0.8%, oculomotor palsy 0.1% and peroneal nerve palsy 0.1%. Erectile impotence was present in 20%, symptomatic postural hypotension in 1% and diabetic diarrhoea in 1%. Overall; 22.9% of the population was afflicted by one or more problems resulting from neuropathy. Neuropathy was associated with older age (p < 0.001), and serious retinopathy (p < 0.001) in both groups of diabetics and with duration of diabetes, proteinuria (p < 0.02), hypertension (p < 0.01) and ischaemic heart disease (p < 0.02) in type 1 diabetics.

Adult↗
PubMed1987

Incidence, risk factors, and morphology in operating microscope light retinopathy.

A review of 135 consecutive cataract operations identified ten cases (7.4%) of operating microscope light retinopathy. Ophthalmoscopically, these light retinopathy lesions appeared as a focal pigment epithelial change with varying degrees of pigment clumping in the center. Fluorescein angiography accentuated the lesion by demonstrating a sharply demarcated transmission defect, occasionally with multiple satellite lesions. The shape of the lesion matched the shape of the illuminating source of the particular operating microscope used during the surgery. The most significant risk factor associated with the production of these light retinopathy lesions was prolonged operating time. Mean total operating time for the ten patients with light retinopathy was 51 minutes longer than for those without (P less than .0001). Other significant associated factors were the presence of diabetes mellitus (P less than .03), younger age (P less than .05), and the use of hydrochlorothiazide (P less than .04).

Cataract Extraction↗