Altering the release of tobramycin by incorporating poly(ethylene glycol) into model silicone hydrogel contact lens materials

Abstract

Delivery of drugs from contact lens materials is attractive for a number of reasons. However, the controlled delivery of hydrophilic drugs can be difficult to achieve due to the burst release of drug that is associated with materials of high water content, such as hydrogels. Silicone hydrogels have significant potential for drug delivery due to their increased hydrophobicity and the tortuous nature of the pores, overcoming some of the limitations associated with conventional hydrogel materials. The aim of this study was to examine the potential of model poly(ethylene glycol) (PEG) containing silicone hydrogels for delivery of hydrophilic aminoglycoside antibiotics. It was hypothesized that PEG, a polymer that has seen extensive use in biomedical applications, will provide in addition to hydrophilicity and protein repulsion, a mechanism for controlling the delivery of this hydrophilic antibiotic. PEG was combined with the macromer TRIS to create the model silicone hydrogel materials. The optical and physical properties of the novel TRIS-co-PEG silicone hydrogels exhibited excellent transparency, appropriate refractive index and high transmittance indicating minimal phase separation. Desirable properties such as wettability and protein repulsion were maintained across a wide range of formulations. The water content was found to be highly correlated with the ethylene oxide content. Drug release could be influenced through PEG content and was found to fit Higuchi-like kinetics. Overall, the study demonstrates that incorporation of PEG into a model silicone hydrogel could be used to control the release of a hydrophilic compound. Data suggests this is related to the unique structure and properties of PEG, which alter the types of water found in each formulation and the water content.     

Porosity and biological properties of polyethylene glycol-conjugated collagen materials

Collagen-based materials can be designed for use as scaffolds for connective tissue reconstruction. The goal of the present study was to evaluate the behavior of collagen materials as well as cell and tissue reactions after the conjugation of activated polyethylene glycols (PEGs) with collagen. It is known that proteins conjugated with PEGs exhibit a decrease in their biodegradation rate and their immunogenicity. Different concentrations and molecular weights of activated PEGs (PEG-750 and PEG-5000) were conjugated to collagen materials (films or sponges) which were then investigated by collagenase assay, fibroblast cell culture, and subcutaneous implantation. PEG-conjugated collagen sponge degradation by collagenase was delayed in comparison to untreated sponges. In culture, fibroblasts with a normal morphology reached confluency on PEG-conjugated collagen films. In vivo, the porous structure of non-modified sponges collapsed by day 15 with a few observable fibroblasts between the collagen fibers. In PEG-modified collagen sponges, the porous structure remained stable for 30 days. Cell infiltration was particularly enhanced in PEG-750-conjugated collagen sponges. In conclusion, PEGs conjugated onto collagen sponges stabilize the porous structure without deactivating the biological properties of collagen. These porous composite materials could function as a scaffold to organize tissue ingrowth.     

New Insights on the Self‐Organization of PEG/α‐Cyclodextrin‐Based Polyrotaxanes in Solution: An Experimental and Theoretical Study

Size exclusion chromatography coupled with light scattering (SEC/MALS), dynamic light scattering (DLS), steady‐state and time‐resolved fluorescence, as well as molecular dynamics (MD) simulations are used to study the behavior of several poly(ethylene glycol) (PEG)/α‐cyclodextrins (αCDs) polyrotaxanes (PRs) in solution. The number of CD units in any of the PRs studied is always smaller than that required to saturate the PEG chains. These PRs seem to aggregate in dimethyl sulfoxide (DMSO) solution. The presence of hairpins in the non‐saturated PRs contributes to diminishing their expected large dimensions. Intra‐ and inter­molecular interactions and forces responsible for hairpins and aggregation are investigated.

     

Clickable Poly(ethylene glycol)‐Microsphere‐Based Cell Scaffolds

Clickable poly(ethylene glycol) (PEG) derivatives are used with two sequential aqueous two‐phase systems to produce microsphere‐based scaffolds for cell encapsulation. In the first step, sodium sulfate causes phase separation of the clickable PEG precursors and is followed by rapid geleation to form microspheres in the absence of organic solvent or surfactant. The microspheres are washed and then deswollen in dextran solutions in the presence of cells, producing tightly packed scaffolds that can be easily handled while also maintaining porosity. Endothelial cells included during microsphere scaffold formation show high viability. The clickable PEG‐microsphere‐based cell scaffolds open up new avenues for manipulating scaffold architecture as compared with simple bulk hydrogels.

     

PEG hydrogel degradation and the role of the surrounding tissue environment

Poly(ethylene glycol) (PEG)‐based hydrogels are extensively used in a variety of biomedical applications, due to ease of synthesis and tissue‐like properties. Recently there have been varied reports regarding PEG hydrogel's degradation kinetics and in vivo host response. In particular, these studies suggest that the surrounding tissue environment could play a critical role in defining the inflammatory response and degradation kinetics of PEG implants. In the present study we demonstrated a potential mechanism of PEG hydrogel degradation, and in addition we show potential evidence of the role of the surrounding tissue environment on producing variable inflammatory responses. Copyright © 2013 John Wiley & Sons, Ltd.     

Axonal fusion via conduit-based delivery of hydrophilic polymers

Background

Hydrophilic polymers have been shown to improve physiologic recovery following repair of transected nerves with microsutures. Our study was designed to combine hydrophilic polymer therapy with nerve tubes (NT) to enhance polymer delivery to the site of nerve injury.

Methods

Using a rat sciatic nerve injury model, a single transection injury was repaired in an end-to-end fashion with NT + polyethylene glycol (PEG) to NT alone. Compound action potentials (CAPs) were recorded before nerve transection and after repair. Behavioral testing was performed for 5 weeks.

Results

PEG therapy restored CAPS in all, but one, animals, while no CAPS were recorded in animals not receiving PEG. Behavioral nerve function was measured using the standardized functional assessment technique and foot fault asymmetry scores (FF). FF scores were improved for the PEG therapy groups on postoperative days 7, 14, and 21. However, after expected eventual axonal outgrowth, the benefit was less noticeable at days 28 and 35. Immunohistochemistry of the distal axon segments showed an increase number of sensory and motor axons in the NT + PEG group as compared to NT alone.

Conclusion

These data suggest that PEG delivery via a conduit may provide a simple, effective way to fuse severed axons and regain early nerve function. For proximal nerve injuries in large animals, recovery of axonal continuity could dramatically improve outcomes, even if fusion only occurs in a small percentage of axons.     

Long term efficacy, safety, and tolerabilitity of low daily doses of isosmotic polyethylene glycol electrolyte balanced solution (PMF-100) in the treatment of functional chronic constipation

AIMS: To assess the long term therapeutic effectiveness, safety, and tolerability of low daily doses of isosmotic PEG electrolyte solutions (PMF-100) administered for a six month period for the treatment of functional constipation, in a double blind, placebo controlled, parallel group study. METHODS: After an initial four week run in period with PMF-100 (250 ml twice daily; PEG 14.6 g twice daily), 70 patients suffering from chronic constipation (58 females, aged 42 (15) years) with normalised bowel frequency (>3 bowel movements (bm)/week) were randomly allocated to receive either PMF-100 or placebo, contained in sachets (one sachet in 250 ml of water twice daily) for 20 weeks. Patients were assessed at four week intervals, and reported frequency and modality of evacuation, laxative use, and relevant symptoms on a diary card. At weeks 1, 12, and 24, a physical examination and laboratory tests were performed. RESULTS: Complete remission of constipation was reported by a significantly (p<0.01) higher number of patients treated with PMF-100 compared with placebo at each four week visit. At the end of the study, 77% of the PMF-100 group and 20% of the placebo group were asymptomatic. Compared with placebo, patients treated with PMF-100 reported hard/pellety stools and straining at defecation less frequently, a significantly higher bowel frequency (week 12: 7. 4 (3.1) v 4.3 (2.5) bm/week, 95% CI 1.64, 4.42; week 24: 7.4 (3.2) v 5.4 (2.1) bm/week, 95% CI 0.13,3.93), reduced consumption of laxative/four weeks (week 12: 0.7 (2.7) v 2.2 (3.3), 95% CI -2.29, 0. 03; week 24: 0.2 (0.8) v 1.4 (2), 95% CI -2.07, -0.023), reduced mean number of sachets used (week 12: 33 (13) v 43 (12), 95% CI -17. 24, 4.56; week 24: 33 (13) v 44 (12), 95% CI -19.68, -2.24), and reduced number of drop outs for therapy failure (16 v 3; p<0.005). Adverse events, physical findings, laboratory values, palatability, and overall tolerance of the solutions did not differ between groups. CONCLUSIONS: Administration of small daily doses of isosmotic PEG electrolyte balanced solutions was effective over a six month period for the treatment of functional constipation. A mean daily dose of approximately 300 ml of PEG solution (PEG 17.52 g) appeared to be safe, well tolerated, and devoid of significant side effects.     

Elevated serum amylase in patients with chronic pancreatitis: Acute attack or macroamylasemia?

Background and aimAsymptomatic patients with chronic pancreatitis not infrequently have elevated concentrations of amylase, even though detailed examination reveals no indication of an acute exacerbation.MethodsOne hundred and eighty-six consecutive patients with chronic pancreatitis were examined clinically and, if indicated, by ultrasonography and computed tomography. In addition, all patients underwent determination of serum amylase and serum lipase as well as amylase/creatinine clearance, followed as required by a polyethylene glycol test and/or chromatography to demonstrate macroamylase.ResultsTwenty (11%) of the 186 patients had macroamylasemia, and 15 of these 20 had hyperamylasemia. In the remaining five cases the serum amylase levels were within the normal range.ConclusionsPatients with asymptomatic chronic pancreatitis and hyperamylasemia should first be investigated for macroamylasemia, before initiating any costly or complex procedures in the attempt to demonstrate a clinically silent or only mildly symptomatic attack of their disease.