Viscoplastic fracture transition of a biopolymer gel.

Physical gels are swollen polymer networks consisting of transient crosslink junctions associated with hydrogen or ionic bonds. Unlike covalently crosslinked gels, these physical crosslinks are reversible thus enabling these materials to display highly tunable and dynamic mechanical properties. In this work, we study the polymer composition effects on the fracture behavior of a gelatin gel, which is a thermoreversible biopolymer gel consisting of denatured collagen chains bridging physical network junctions formed from triple helices. Below the critical volume fraction for chain entanglement, which we confirm via neutron scattering measurements, we find that the fracture behavior is consistent with a viscoplastic type process characterized by hydrodynamic friction of individual polymer chains through the polymer mesh to show that the enhancement in fracture scales inversely with the squared of the mesh size of the gelatin gel network. Above this critical volume fraction, the fracture process can be described by the Lake-Thomas theory that considers fracture as a chain scission process due to chain entanglements.

Comparative studies of hyaluronan in marketed ophthalmic products.

PURPOSE: Research has indicated that there is a correlation between the molecular weight of hyaluronan or hyaluronic acid (HA) and its biocompatibility/biological functions with high molecular weight HA showing many biological benefits. The purpose of this research was to characterize and compare the molecular weights, molecular weight distributions, and concentrations of HA present in a series of commercially available HA-containing ophthalmic products. METHODS: On-line size-exclusion chromatography with triple detection (SEC-TD) was used to determine the molecular weights and concentration of HA in commercially available products, including marketed contact lens multipurpose solutions and contact lens packaging solutions. Eleven commercially available HA-containing ophthalmic products were characterized by SEC-TD. RESULTS: The weight-average molecular weights of the products tested ranged from 155,000 Daltons (Da) to 1,400,000 Da, the number-average molecular weight of the products ranged from 99,000 to 927,000 Da, and the concentration of HA ranged from 0.003 to 0.15%. CONCLUSIONS: A wide range of HA molecular weights and concentrations were found in the 11 ophthalmic products characterized in the present study. This study is the first reported to characterize HA molecular weights and concentrations in various marketed HA-containing ophthalmic products. Future investigation of the effect of low molecular weight HA on eye is required.

Prevention and removal of lipid deposits by lens care solutions and rubbing.

PURPOSE: Despite the prevalence of silicone hydrogel (SiHy) contact lenses, there are relatively few studies that evaluate the efficacy of multipurpose lens care solutions (MPSs) in reducing lipid deposition on these lenses and the effect of rubbing on the removal. Therefore, we used an in vitro soaking and rubbing model to compare the effectiveness of borate buffered saline (BBS) and two commercial MPSs, PureMoist and Biotrue, in preventing sorption of representative polar and nonpolar lipids. METHODS: Radiolabeled cholesterol (CH) and dipalmitoylphosphatidylcholine (DPPC) were sorbed on two SiHy lenses (senofilcon A and balafilcon A) from an artificial tear fluid. Deposition and removal were evaluated by quantitative solvent extraction and scintillation counting. RESULTS: The efficiencies of the MPSs in reducing lipid deposition are somewhat dependent on lens material. Both DPPC and CH sorption on senofilcon A are greater when lenses are preconditioned in BBS compared with preconditioning in either MPS (p < 0.05). However, neither MPS affects lipid sorption on balafilcon A lenses (p > 0.05). As for removal of presorbed lipids, neither PureMoist, Biotrue, nor BBS removed CH in the absence of rubbing. When a simulated rubbing protocol was used, minimal but detectible CH was removed (p < 0.05) from senofilcon A and balafilcon A lenses (likely only from the lens surface). These commercial solutions were not substantially better than BBS in removing DPPC, with or without rubbing (p > 0.05). CONCLUSIONS: These data suggest that MPSs do not appreciably alter lipid sorption. Rubbing lenses removes a small amount of sorbed lipids. Yet, we recommend that MPSs be used as they may disinfect SiHy lenses and may clean their surfaces of large particles.

Toxic anterior segment syndrome and possible association with ointment in the anterior chamber following cataract surgery.

PURPOSE: To report clinical and laboratory findings of 8 cases of toxic anterior segment syndrome (TASS) related to an oily substance in the anterior chamber of patients following cataract surgery with intraocular lens (IOL) implantation. SETTING: John Moran Eye Center, University of Utah, Salt Lake City, Utah, USA. METHODS: Eight patients had uneventful phacoemulsification by the same surgeon via clear corneal incisions with implantation of the same 3-piece silicone IOL design. Postoperative medications included antibiotic/steroid ointment and pilocarpine gel; each eye was firmly patched at the end of the procedure. On the first postoperative day, some patients presented with diffuse corneal edema, increased intraocular pressure, and an oily film-like material within the anterior chamber coating the corneal endothelium. The others presented with an oily bubble floating inside the anterior chamber, which was later seen coating the IOL. Additional surgical procedures required included penetrating keratoplasty, IOL explantation, and trabeculectomy. Two corneal buttons were analyzed histopathologically. Two explanted IOLs had gross and light microscopic analyses (as well as surface analyses of 1 of them), and 4 other explanted IOLs had gas chromatography-mass spectrometry. RESULTS: Pathological examination of the corneas showed variable thinning of the epithelium with edema. The stroma was diffusely thickened and the endothelial cell layer was absent. Evaluation of the explanted IOLs confirmed the presence of an oily substance coating large areas of their anterior and posterior optic surfaces. Gas chromatography-mass spectrometry of the lens extracts identified a mixed chain hydrocarbon compound that was also found in the gas chromatography-mass spectrometry analyses of the ointment used postoperatively. CONCLUSIONS: The results indicate that the ointment gained access to the eye, causing the postoperative complications described. These cases highlight the importance of appropriate wound construction and integrity, as well as the risks of tight eye patching following placement of ointment.

Detailed characterization of cationic hydroxyethylcellulose derivatives using aqueous size-exclusion chromatography with on-line triple detection.

A more complete understanding of polymeric, cationic cellulose derivatives, including polyquaterium-10 (Polymer JR), has become increasingly important in the eye care industry as thorough characterization of raw materials helps promote product quality and process control. Often such detailed information requires utilization of a combination of analytical techniques. In this work three Polymer JR samples with different viscosities were characterized using aqueous size exclusion chromatography (SEC) with a light scattering detector, a differential viscometer, and a differential refractometer (triple detection). Detailed molecular information such as absolute molecular weights, molecular weight distributions, intrinsic viscosities, and molecular conformations were obtained. One major challenge of analyzing cationic polymers is abnormal size exclusion separation, which could be caused by the ionic interaction between sample molecules and the column packing material. A selection of mobile phases varying in pH, buffer, organic solvent content, and molar concentration of salts was employed to evaluate the correlation of obtained molecular weight values and mobile phase composition. Universal calibration concept was used to examine the abnormal size exclusion separation phenomenon of Polymer JR samples when using different mobile phases. It was observed that the abnormal size exclusion was dependent on both the separation conditions and molecular weights of the samples. Despite the changes in separation parameters and uncharacteristic polymeric structure compared to conventional SEC samples, the use of aqueous SEC with triple detection provided reproducible and valuable molecular information of Polymer JR samples with low to medium molecular weights. By using a combination of high buffer content and adding organic solvent, the abnormal exclusion separation of high molecular weigh Polymer JR could be considerably reduced.

Effects of Polyhexamethylene Biguanide and Polyquaternium-1 on Phospholipid Bilayer Structure and Dynamics.

Multipurpose solutions (MPS) are a single solution that functions to simultaneously rinse, disinfect, clean, and store soft contact lenses. Several commercial MPS products contain polyhexamethylene biguanide (PHMB) and/or polyquaternium-1 (PQ-1) as antimicrobial agents. In this paper we have created an in vitro small unilamellar vesicle (SUV) model of the corneal epithelial surface, and we have assessed the interactions of PHMB and PQ-1 with several model biomembranes by using fluorescence spectroscopy, dynamic light scattering (DLS), and liquid chromatography-mass spectrometry (LC-MS). Steady-state and time-resolved fluorescence were used to assess the membrane acyl chain and polar headgroup region local microenvironment as a function of added PHMB or PQ-1. DLS was used to detect and quantify SUV aggregation induced by PHMB and PQ-1. LC-MS was used to determine the liposomal composition from any precipitated materials in comparison to the as-prepared SUVs. The results are consistent with PHMB adsorbing onto and PQ-1 intercalating into the biomembrane structure. The differences between the two interaction mechanisms have substantial impacts on the biomembrane dynamics and stability.

Comparative studies of poly(dimethyl siloxanes) using automated GPC-MALDI-TOF MS and on-line GPC-ESI-TOF MS.

In this study we compare on-line gel permeation chromatography (GPC) electrospray ionization (ESI) time-of-flight (TOF) mass spectrometry (MS) to automated GPC matrix assisted laser desorption ionization (MALDI) TOF MS for poly (dimethylsiloxane) (PDMS) analysis. Average mass values for a hydroxyl-terminated PDMS (OH-PDMS) sample were obtained and compared to traditional GPC that was calibrated with narrow polystyrene standards, by direct ESI and MALDI MS analysis, by a summation of mass spectra of all GPC fractions, and also by the recalibration method determined by both mass spectrometric methods. Quantitatively, the difference noted here between these hyphenated techniques is that GPC-ESI-TOF MS effectively reports the low-mass oligomers and underestimates the high-mass oligomers, while GPC-MALDI-TOF MS effectively reports the high-mass oligomers and underestimates the low-mass oligomers. In the GPC-ESI-TOF MS experiments, ion current suppression was observed in the high molecular weight region. The suppression effect was confirmed by repeatable sample runs and by injecting different PDMS samples. Higher chromatographic resolution was observed for GPC-ESI-TOF MS compared to GPC-MALDI-TOF MS. In fact, truly mono-disperse oligomers were observed in the low molecular weight range from GPC-ESI MS experiments.

Detailed analysis of alpha,omega-bis(4-hydroxybutyl) poly(dimethylsiloxane) using GPC-MALDI TOF mass spectrometry.

In this study the prepolymer alpha,omega-bis(4-hydroxybutyl) poly(dimethylsiloxane), used in the formulation of oxygen permeable films, is evaluated by gel permeation chromatography (GPC) combined with matrix assisted laser desorption ionization (MALDI) time of flight (TOF) mass spectrometry (MS). Two unexpected mass distributions are observed in the mass spectra. Reaction schemes for the formation of these distributions are proposed. A solution phase trimethylsilane end group modification was performed on the prepolymer to determine whether the unexpected mass distributions occur as impurities from synthesis or as artifacts from the MS process. Evaluation of the TMS modified prepolymer indicates the unexpected mass distributions indeed occur as impurities from the synthetic procedure. Average molecular weight values are determined by traditional GPC, direct MALDI-TOF MS, and GPC-MALDI-TOF MS methods and the results are compared.

Characterization of implant device materials using size-exclusion chromatography with mass spectrometry and with triple detection.

A more complete understanding of the raw materials used for making implant device materials becomes increasingly important in the medical device industry. Often such detailed information requires utilization of a combination of analytical techniques. In this work, we characterize a poly(dimethyl siloxane) (PDMS) material using on-line size exclusion chromatography (SEC) with electrospray ionization (ESI) and matrix assisted laser desorption ionization (MALDI) mass spectrometry (MS) techniques. Here, we obtain detailed molecular compositional information such as repeat units, end group chemistry, and identification of impurities in both the high and low mass range. SEC with light scattering, viscosity, and refractive index detection (triple detection) is used to obtain information on a small quantity of high mass impurity that was undetected by both SEC-ESI and MALDI MS techniques. SEC with triple detection measures absolute molecular weights and molecular weight distributions. We compare average molecular weight values of the implantable device polymer obtained by SEC with triple detection, SEC-ESI, and SEC-MALDI MS techniques.

Detailed characterization of hyaluronan using aqueous size exclusion chromatography with triple detection and multiangle light scattering detection.

Hyaluronan (HA) has attracted great interest and attention from ophthalmic surgical and eye care companies owing to its unique properties. A more complete understanding of HA biopolymers has, therefore, become increasingly critical as thorough characterization of raw materials helps promote product quality and process control. Often, such detailed information requires the use of a combination of analytical techniques. In this study, we compared size exclusion chromatography (SEC) with online multiangle light scattering (SEC-MALS) and SEC with triple detection (SEC-TD) experiments for HA analysis. Three lots of commercially available eye drop grade HA were characterized by SEC-MALS and SEC-TD. The absolute molecular weight averages, molecular weight distribution, radius of gyration, and solution conformation of the three HA lots were determined and compared by the two techniques. In addition, the intrinsic viscosity and intrinsic viscosity distribution were measured by SEC-TD.

A preservative-and-fluorescein interaction model for benign multipurpose solution-associated transient corneal hyperfluorescence.

PURPOSE: Multipurpose contact lens solution (MPS)/preservative-associated transient corneal hyperfluorescence has been suggested to represent corneal injury. To determine the validity of this assumption, the molecular-level interactions of common disinfectants in soft contact lens MPS and the corneal epithelium using an in vitro model were assessed. METHODS: A liposome-based model of the corneal epithelial surface was developed and used to assess the interactions of polyhexamethylene biguanide (PHMB), polyquaternium-1 (PQ-1), and fluorescein with membrane components and the effects of PHMB and PQ-1 on membrane integrity. The fluorescence anisotropy (a measure of interactions between molecules) was determined. Liposome integrity was assessed by measuring the liposome melting point temperature. RESULTS: Free fluorescein did not associate with the liposome (P>0.4). Both fluorescein-tagged PHMB and PQ-1 associated with liposomes (P<0.002 and P≤0.01, respectively); however, only PHMB induced free fluorescein association with membrane components. At physiological temperature, no significant shift in the melting point temperature was observed when liposomes were exposed to PHMB from 0 to 100 ppm (P>0.05). In contrast, exposure of >7 ppm PQ-1 disrupted the liposomes. CONCLUSIONS: Based on this study, PHMB-to-liposome bilayer interaction is nondestructive, even at concentrations 100 times higher than found in commercially available MPS products. In contrast, PQ-1-to-liposome bilayer interaction led to liposome disruption. This study presents molecular-level evidence to support that preservative-associated transient corneal hyperfluorescence is a benign transient phenomenon and its evaluation clinically may be an ambiguous strategy for determining biocompatibility and cell surface integrity.

Lipid deposition on silicone hydrogel lenses, part I: quantification of oleic Acid, oleic Acid methyl ester, and cholesterol.

PURPOSE: To investigate the sorption of oleic acid, oleic acid methyl ester, and cholesterol on currently marketed silicone hydrogel contact lenses. METHODS: Two liquid chromatography methods were developed and used to analyze lens extracts from continuous-wear and daily-wear modalities from asymptomatic silicone hydrogel contact lens wearers. RESULTS: Of the three probed compounds, cholesterol is the most prevalently sorbed, at levels ranging from below the limit of quantitation (<1.50 microg per lens) to approximately 37.0 microg per lens. Oleic acid and oleic acid methyl ester were found to exist at levels below the limit of quantitation (<1.50 microg per lens). In general, there appears to be no significant difference between the amounts of cholesterol sorbed on the continuous-wear PureVision and daily-wear PureVision lenses evaluated. CONCLUSIONS: The quantities of lipid sorbed to continuous-wear PureVision lenses are significantly different from those previously reported by other authors in a similarly conducted experiment. This difference suggests that any hypothesis of silicone hydrogel lenses based on these previous lipid data should be reconsidered.

Characterization of human tear proteome using multiple proteomic analysis techniques.

Tear proteome profiling may generate useful information for the understanding of the interaction between an eye and its contacting objects, such as a contact lens or a lens implant. This is important for designing improved eye-care devices and maintaining the health of an eye. Proteome profiles of tear fluids may also be used for disease diagnosis and prognosis. However, only a small volume of tear fluid (<5 microL) can be collected in a clinical laboratory under normal operational conditions, which makes proteome profiling a challenge. In this work we apply several proteomic analysis techniques, including gel-based and solution-based approaches with LC-ESI and LC-MALDI MS and MS/MS to gauge the relative merits of producing proteome profiles and to generate as broad a coverage of the tear proteome as possible from this small amount of sample. It is shown that a total of 54 proteins can be confidently identified using less than 5 microL of tear fluid. Of these, 44 proteins can be detected by LC-MALDI MS alone with a consumption of 2 microL of tear fluid. Furthermore, LC-MALDI can be used to determine post-translational modifications (PTMs), such as glycosylation and phosphorylation, without any sample enrichment or treatment. This work represents one of the most extensive proteome profiles (i.e., proteins identified and PTMs characterized) generated from tear fluids using clinically relevant amounts of sample.

Analysis of quartz by FT-IR in air samples of construction dust.

The construction industry is reported to have some of the highest exposures to silica-containing dust. With the designation of crystalline silica as a group I human carcinogen by the International Agency for Research on Cancer (IARC), there exists a need for an analytical method to accurately quantify low levels of quartz. A method is described that uses FT-IR for quartz analysis of personal air samples collected from heavy and highway construction sites using 4-stage personal impactors. Sample filters were ashed and 13-mm or 5-mm pellets were prepared. Absorbance spectra were collected using FT-IR at resolution of 1 cm(-1) and 64 scans per spectrum. Two spectra were collected per sample using the appropriate background spectrum subtraction. Spectral manipulations such as Fourier self-deconvolution and derivatizations were performed to improve quantification. Peak height for quartz was measured at 798 cm(-1) for quantitative analysis. The estimated limit of detection for the 5-mm pellets was 1.3 microg. Recoveries of Min-U-Sil 5 spikes showed an average of > or = 94 percent for the two pellet types. The coefficient of variation of the 5-mm pellet was 9 percent at 6 microg quartz load, and 7 percent at 62 microg load. Interferences from clay, amorphous silica, concrete, calcite, and kaolinite were investigated, these being the more likely sources of interferences in construction environment. Spikes of mixtures of amorphous silica or kaolinite with Min-U-Sil 5 showed both contaminants introduced, on average, a positive error of < 5 microg with average recoveries of 106 percent and 111 percent, respectively. Spikes of mixtures of clay or concrete with Min-U-Sil 5 showed overall average recovery of 100 percent and 90 percent, respectively, after accounting for the presence of quartz in clay and concrete. This method can quantify low levels of quartz with reasonable accuracy in the face of common contaminants found in the construction industry.