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Biomedical subjects

Thomas J Millar

Publications and source records attributed to Thomas J Millar.

10 recordsLinked to original sources
PubMed2006

Interactions of poly(tert-butyl acrylate)-poly(styrene) diblock copolymers with lipids at the air-water interface.

Diblock copolymers with hydrophilic poly(tert-butyl acrylate) (PtBA) and hydrophobic poly(styrene) (PS) blocks were synthesized with a view to use them as a surfactant in tear film for increasing the ocular comfort in dry eye syndrome. Interactions of six PtBA-PS copolymers with four important lipids found in the tear film, namely cholesterol, cholesteryl palmitate, dipalmitoyl phosphatidylcholine, and phosphatidylinositol, were studied at the air-water interface using a Langmuir trough. Thermodynamics of mixing of the copolymers and the lipids in the mixed monolayers was determined by calculating excess free energy of mixing. The diblock copolymers showed repulsive interactions with cholesteol and cholesteryl palmitate, near neutral interactions with dipalmitoyl phosphatidylcholine, and attractive interactions with phosphatidylinositol. The lipids interacted with the PS component of the copolymer. The results indicate that a copolymer with a small hydrophilic group and a big hydrophobic group can be a likely candidate for forming stable interactions with the lipids present in the tear film and hence increase the ocular comfort.

Acrylates↗
PubMed2006

Adsorption of lysozyme to phospholipid and meibomian lipid monolayer films.

It is believed that a lipid layer forms the outer layer of the pre-ocular tear film and this layer helps maintain tear film stability by lowering its surface tension. Proteins of the aqueous layer of the tear film (beneath the lipid layer) may also contribute to reducing surface tension by adsorbing to, or penetrating the lipid layer. The purpose of this study was to compare the penetration of lysozyme, a tear protein, into films of meibomian lipids and phospholipids held at different surface pressures to determine if lysozyme were part of the surface layer of the tear film. Films of meibomian lipids or phospholipids were spread onto the surface of a buffered aqueous subphase. Films were compressed to particular pressures and lysozyme was injected into the subphase. Changes in surface pressure were monitored to determine adsorption or penetration of lysozyme into the surface film. Lysozyme penetrated a meibomian lipid film at all pressures tested (max=20 mN/m). It also penetrated phosphatidylglycerol, phosphatidylserine or phosphatidylethanolamine lipid films up to a pressure of 20 mN/m. It was not able to penetrate a phosphatidylcholine film at pressures >or=10 mN/m irrespective of the temperature being at 20 or 37 degrees C. However, it was able to penetrate it at very low pressures (<10 mN/m). Epifluorescence microscopy showed that the protein either adsorbs to or penetrates the lipid layer and the pattern of mixing depended upon the lipid at the surface. These results indicate that lysozyme is present at the surface of the tear film where it contributes to decreasing the surface tension by adsorbing and penetrating the meibomian lipids. Thus it helps to stabilize the tear film.

Adsorption↗
PubMed2006

The surface activity of purified ocular mucin at the air-liquid interface and interactions with meibomian lipids.

PURPOSE: Ocular mucins are thought to contribute to the stability of the tear film by reducing surface tension. The purpose of this study was to compare the effect of different mucins and hyaluronic acid (HA) alone and mixed with meibomian lipids on the surface pressure at an air-liquid interface. METHODS: A Langmuir trough and Wilhelmy balance were used to measure and compare the surface activity of bovine submaxillary gland mucin (BSM), purified BSM, purified bovine ocular mucin and HA, and mixtures of these with meibomian lipids, phosphatidylcholine, and phosphatidylglycerol. Their appearance at the surface of an air-buffer interface was examined using epifluorescence microscopy. RESULTS: Purified ocular mucin had no surface activity even at concentrations that were 100 times more than normally occur in tears. By contrast, commercial BSM caused changes to surface pressure that were concentration dependent. The surface pressure-area profiles showed surface activity with maximum surface pressures of 12.3-22.5 mN/m depending on the concentration. Purified BSM showed no surface activity at low concentrations, whereas higher concentrations reached a maximum surface pressure of 25 mN/m. HA showed no surface activity, at low or high concentrations. Epifluorescence showed that the mucins were located at the air-buffer interface and changed the appearance of lipid films. CONCLUSION: Purified bovine ocular mucin and HA have no surface activity. However, despite having no surface activity in their own right, ocular mucins are likely to be present at the surface of the tear film, where they cause an increase in surface pressure by causing a compression of the lipids (a reorganization of the lipids) and alter the viscoelastic properties at the surface.

Air↗
PubMed2005

The surface pressure dynamics and appearance of mixed monolayers of cholesterol and different sized polystyrenes at an air-water interface.

Synthetic polymers are increasingly being used in situations where they are designed to interact with biological systems. As a result, it is important to investigate the interactions of the polymers with biochemicals. We have used cholesterol, as an example of an important biological surfactant component, to study its interactions with polystyrene. Mixed monolayers of cholesterol and one of two different molecular weight polystyrenes were formed at an air-water interface to investigate their interactions and to determine whether the size of the polystyrene affected the interaction. The pressure-area (pi-A) isocycles of mixed monolayers of cholesterol and polystyrene MW 2700 or polystyrene MW32700 showed that strongest attractive interactions occur at high surface pressures and in polystyrene rich films. The excess area and excess free energy of mixing were most negative at high surface pressures and at high mole fraction of polystyrene. The most stable mixed monolayers were formed with X(PS2700) = 0.9 and X(PS32700) = 0.09. Microscopic observation of the mixed monolayers of cholesterol and polystyrene showed the formation of stable islands in the cholesterol/polystyrene mixtures. These observations, the nature of the inflection points in the isocycles, and the anomalous changes in free energy lead us to conclude that there is a stable rearrangement of polystyrene into compact islands when it is mixed with cholesterol. Any excess cholesterol is excluded from these islands and remains as a separate film surrounding the islands.

Air↗
PubMed2005

Viability analysis of alginate encapsulated micro-organisms using fluorescent stains.

The encapsulation of micro-organisms such as bacteria and fungi in biopolymers is currently being evaluated as delivery systems in many fields. Information about the viability and morphology of the organisms in the microparticle is often required to ascertain the longevity of the systems. A rapid method using fluorescent stains for microbial viability has been validated for organisms within alginate microparticles. Usually viability is assessed by dissolving the microparticles and cell culturing. This new method is advantageous for slow growing or filamentous organisms because these are not quickly or accurately enumerated by plate counts. In addition, the technique also allows the morphology of the organism to be monitored over time.

Alginates↗
PubMed2005

Surface pressure measurements of human tears and individual tear film components indicate that proteins are major contributors to the surface pressure.

PURPOSE: Tear film stability has been associated with a low surface tension (high surface pressure), which has been attributed to a variety of tear film components. In this study, we examined the contribution of various tear proteins, mucin, and meibomian lipids to the surface pressure of human tears. METHODS: A Langmuir trough was used to measure and compare the surface activities of albumin, lipocalin, beta-lactoglobulin, lactoferrin, lysozyme, secretory IgA, mucin, meibomian lipid, and tears. RESULTS: All proteins exhibited surface activity. The surface pressure-area (Pi-A) profiles of most protein films at equilibrium surface pressure (Pieq) were sigmoidal and showed hysteresis between the expansion and compression phases of the cycle. Pieq of most proteins took 4-9 hours to occur. By contrast, the Pi-A profiles for meibomian lipid films were hyperbolic rather than sigmoidal and had little hysteresis, and Pieq was attained within 1 hour. The Pi-A profiles of mucin films showed mostly hyperbolic characteristics with small hysteresis. The Pi-A profiles of films of tears were sigmoidal, showed strong hysteresis, and reached Pieq at about 5 hours. Partitioning of the proteins and whole tears into the subphase also occurred. CONCLUSION: Comparison between the dynamic Pi-A profiles of tears and those of individual tear film components shows that tear film proteins not only are capable of surface activity but also are major contributors to the surface activity of the tear film.

Albumins↗
PubMed2003

Clinical appearance and microscopic analysis of mucin balls associated with contact lens wear.

PURPOSE: The structure of mucin balls collected from silicone hydrogel contact lens wearers was examined to determine their nature. METHODS: Tears containing mucin balls were collected using a capillary tube. These were processed for light microscopic histochemistry, scanning electron microscopy, and electron microscopic elemental analysis. Mucin balls were also observed in vivo using confocal microscopy. RESULTS: Histology showed that the mucin balls were PAS positive, indicating that glycoproteins form a major component. Lipids and bacteria were not detected. Scanning electron microscopy did not show the surface to be smooth but revealed a variation in density across the surface. Elemental analysis was inconclusive. CONCLUSIONS: Mucin balls are likely to be made from collapsed mucin and are unlikely to have been formed as a result of pearling around a silicon, lipid, or bacterial kernel.

Contact Lenses↗
PubMed2003

The effects of novel amphipathic block copolymers on stabilization of the rat tear film.

PURPOSE: To determine whether various novel amphipathic polymers could be used to stabilize the tear film of the rat. The rheologic properties of these polymers were examined to investigate whether particular structural or physical characteristics improve the stability of the tear film. METHODS: Amphipathic polymers or particular phospholipids were mixed with a test solution of tears and saline and applied to the clean, dry corneal surface of a rat. The specular reflection of the tear film was observed at high magnification and recorded. For each of the polymers or lipids, the effects on surface regularity and tear break-up time were compared. After the experiments, histologic sections of the tested eyes were prepared and examined for acute cytotoxic effects on the cornea and ocular conjunctiva. RESULTS: Tear film break-up time was markedly affected by differences in polymer structure. Copolymers consisting of separate hydrophobic and hydrophilic regions appeared to be the best stabilizers. No acute cytotoxic effects were observed in histologic sections of corneas to which the polymers had been applied. CONCLUSIONS: Amphipathic polymers can be designed to increase tear film stability. Increased tear film stability occurred more readily with copolymers, possibly through their interaction with both lipid and aqueous tear components.

Acrylic Resins↗