Utilization of Nitrogen-Doped Graphene Quantum Dots to Neutralize ROS and Modulate Intracellular Antioxidant Pathways to Improve Dry Eye Disease Therapy

Purpose

Patients afflicted with dry eye disease (DED) experience significant discomfort. The underlying cause of DED is the excessive accumulation of ROS on the ocular surface. Here, we investigated the nitrogen doped-graphene quantum dots (NGQDs), known for their ROS-scavenging capabilities, as a treatment for DED.

Methods

NGQDs were prepared by using citric acid and urea as precursors through hydrothermal method. The antioxidant abilities of NGQDs were evaluated through: scavenging the ROS both extracellular and intracellular, regulating the nuclear factor-erythroid 2-related factor (Nrf2) antioxidant pathway of human corneal epithelial cells (HCECs) and their transcription of inflammation related genes. Furthermore, NGQDs were modified by Arg-Gly-Asp-Ser (RGDS) peptides to obtain RGDS@NGQDs. In vivo, both the NGQDs and RGDS@NGQDs were suspended in 0.1% Pluronic F127 (w/v) and delivered as eye drops in the scopolamine hydrobromide-induced DED mouse model. Preclinical efficacy was compared to the healthy and DPBS treated DED mice.

Results

These NGQDs demonstrated pronounced antioxidant properties, efficiently neutralizing free radicals and activating the intracellular Nrf2 pathway. In vitro studies revealed that treatment of H2O2-exposed HCECs with NGQDs induced a preservation in cell viability. Additionally, there was a reduction in the transcription of inflammation-associated genes. To prolong the corneal residence time of NGQDs, they were further modified with RGDS peptides and suspended in 0.1% Pluronic F127 (w/v) to create RGDS@NGQDs F127 eye drops. RGDS@NGQDs exhibited superior intracellular antioxidant activity even at low concentrations (10 μg/mL). Subsequent in vivo studies revealed that RGDS@NGQDs F127 eye drops notably mitigated the symptoms of DED mouse model, primarily by reducing ocular ROS levels.

Conclusion

Our findings underscore the enhanced antioxidant benefits achieved by modifying GQDs through nitrogen doping and RGDS peptide tethering. Importantly, in a mouse model, our novel eye drops formulation effectively ameliorated DED symptoms, thereby representing a novel therapeutic pathway for DED management.

A tissue-adhesive F127 hydrogel delivers antioxidative copper-selenide nanoparticles for the treatment of dry eye disease

Dry eye disease (DED) is currently the most prevalent condition seen in ophthalmology outpatient clinics, representing a significant public health issue. The onset and progression of DED are closely associated with oxidative stress-induced inflammation and damage. To address this, an aldehyde-functionalized F127 (AF127) hydrogel eye drop delivering multifunctional antioxidant Cu2-xSe nanoparticles (Cu2-xSe NPs) was designed. The research findings revealed that the Cu2-xSe nanoparticles exhibit unexpected capabilities in acting as superoxide dismutase and glutathione peroxidase. Additionally, Cu2-xSe NPs possess remarkable efficacy in scavenging reactive oxygen species (ROS) and mitigating oxidative damage. Cu2-xSe NPs displayed promising therapeutic effects in a mouse model of dry eye. Detailed investigation revealed that the nanoparticles exert antioxidant, anti-apoptotic, and inflammation-mitigating effects by modulating the NRF2 and p38 MAPK signalling pathways. The AF127 hydrogel eye drops exhibit good adherence to the ocular surface through the formation of Schiff-base bonds. These findings suggest that incorporating antioxidant Cu2-xSe nanoparticles into a tissue-adhesive hydrogel could present a highly effective therapeutic strategy for treating dry eye disease and other disorders associated with reactive oxygen species. STATEMENT OF SIGNIFICANCE: A new formulation for therapeutic eye drops to be used in the treatment of dry eye disease (DED) was developed. The formulation combines copper-selenium nanoparticles (Cu2-xSe NPs) with aldehyde-functionalized Pluronic F127 (AF127). This is the first study to directly examine the effects of Cu2-xSe NPs in ophthalmology. The NPs exhibited antioxidant capabilities and enzyme-like properties. They effectively eliminated reactive oxygen species (ROS) and inhibited apoptosis through the NRF2 and p38 MAPK signalling pathways. Additionally, the AF127 hydrogel enhanced tissue adhesion by forming Schiff-base links. In mouse model of DED, the Cu2-xSe NPs@AF127 eye drops demonstrated remarkable efficacy in alleviating symptoms of DED. These findings indicate the potential of Cu2-xSe NPs as a readily available and user-friendly medication for the management of DED.

Sustained Release of Voriconazole Using 3D-Crosslinked Hydrogel Rings and Rods for Use in Corneal Drug Delivery

Corneal disorders and diseases are prevalent in the field of clinical ophthalmology. Fungal keratitis, one of the major factors leading to visual impairment and blindness worldwide, presents significant challenges for traditional topical eye drop treatments. The objective of this study was to create biocompatible 3D-crosslinked hydrogels for drug delivery to the cornea, intending to enhance the bioavailability of ophthalmic drugs. Firstly, a series of flexible and porous hydrogels were synthesized (free-radical polymerization), characterized, and evaluated. The materials were prepared by the free-radical polymerization reaction of 1-vinyl-2-pyrrolidinone (also known as N-vinylpyrrolidone or NVP) and 1,6-hexanediol dimethacrylate (crosslinker) in the presence of polyethylene glycol 1000 (PEG-1000) as the porogen. After the physicochemical characterization of these materials, the chosen hydrogel demonstrated outstanding cytocompatibility in vitro. Subsequently, the selected porous hydrogels could be loaded with voriconazole, an antifungal medication. The procedure was adapted to realize a loading of 175 mg voriconazole per ring, which slightly exceeds the amount of voriconazole that is instilled into the eye via drop therapy (a single eye drop corresponds with approximately 100 mg voriconazole). The voriconazole-loaded rings exhibited a stable zero-order release pattern over the first two hours, which points to a significantly improved bioavailability of the drug. Ex vivo experiments using the established porcine eye model provided confirmation of a 10-fold increase in drug penetration into the cornea (after 2 h of application of the hydrogel ring, 35.8 ± 3.2% of the original dose is retrieved from the cornea, which compares with 3.9 ± 1% of the original dose in the case of eye drop therapy). These innovative hydrogel rods and rings show great potential for improving the bioavailability of ophthalmic drugs, which could potentially lead to reduced hospitalization durations and treatment expenses.

Polymeric Microspheres Designed to Carry Crystalline Drugs at Their Surface or Inside Cavities and Dimples

Injectable polymer microparticles with the ability to carry and release pharmacologically active agents are attracting more and more interest. This study is focused on the chemical synthesis, characterization, and preliminary exploration of the utility of a new type of injectable drug-releasing polymer microparticle. The particles feature a new combination of structural and physico-chemical properties: (i) their geometry deviates from the spherical in the sense that the particles have a cavity; (ii) the particles are porous and can therefore be loaded with crystalline drug formulations; drug crystals can reside at both the particle's surfaces and inside cavities; (iii) the particles are relatively dense since the polymer network contains covalently bound iodine (approximately 10% by mass); this renders the drug-loaded particles traceable (localizable) by X-ray fluoroscopy. This study presents several examples. First, the particles were loaded with crystalline voriconazole, which is a potent antifungal drug used in ophthalmology to treat fungal keratitis (infection/inflammation of the cornea caused by penetrating fungus). Drug loading as high as 10% by mass (=mass of immobilized drug/(mass of the microparticle + mass of immobilized drug) × 100%) could be achieved. Slow local release of voriconazole from these particles was observed in vitro. These findings hold promise regarding new approaches to treat fungal keratitis. Moreover, this study can help to expand the scope of the transarterial chemoembolization (TACE) technique since it enables the use of higher drug loadings (thus enabling higher local drug concentration or extended therapy duration), as well as application of hydrophobic drugs that cannot be used in combination with existing TACE embolic particles.

A novel approach to achieve semi-sustained drug delivery to the eye through asymmetric loading of soft contact lenses

Soft contact lenses are increasingly being explored as a vehicle for controlled delivery of ophthalmic drugs. However, traditional methods of drug-loading by soaking have limitations such as burst delivery and the release of drugs at the front side of the lens, leading to poor drug efficacy and systemic side effects. This study introduces a new methodology, termed asymmetric drug loading, whereby the ophthalmic drug 'Rebamipide' is attached to and released from the post-lens (=cornea-contacting) surface exclusively. The methodology involves using polymeric microparticles that carry a lipophilic crystalline ophthalmic drug at their surface. These drug-loaded microparticles first transfer the drug to the concave surface of the contact lens, and when worn, the drug is transferred again, now from the lens to the cornea. This is achieved through the diffusion of the drug from one hydrophobic microenvironment (the silicone moieties of the contact lens polymer network) to another hydrophobic microenvironment (the corneal epithelium) over a short pathway. The second drug transfer was observed and studied in experiments using an ex vivo porcine eye model. The results show that the drug amount that was absorbed by the cornea after applying the rebamipide-loaded contact lenses is approximately 3× (10.7 ± 3.1 μg) as much as the amount of rebamipide that gets transferred after the instillation of one eye drop (1% solution (p < 0.001). The new drug-loading method offers a practical and reproducible means of delivering ophthalmic drugs to the cornea through soft contact lenses. The drug payloads achieved are comparable to dosages used during eye drop therapy.

Flexible Coils with a Drug-Releasing Hydrophilic Coating: A New Platform for Controlled Delivery of Drugs to the Eye?

Delivery of drugs to the front-side of the eye is routinely done through eye drops. It is known that approximately 80% of each eye-drop is lost, as a result of rapid clearance of the tear fluid via the naso-lacrymal canal. Consequently, repeated administration through several droplets is usually necessary to achieve a desired effect, such as widening of the pupil prior to corneal surgery. A new ocular drug delivery device was studied. The new device is believed to provide a basis for a more convenient and efficient method for ocular drug delivery. The device is a metallic coil with a hydrophilic, drug-containing polymeric coating. The coil is placed in the conjuctival fornix (under the lower eye-lid) and the drug is slowly released by diffusion into the tear fluid. The capacity of the device could be increased by using the lumen of the coils as a depot for the drug to be released. Preliminary experiments with the new device were performed largely in vitro and in vivo. The latter experiments involved the release of a fluorescent dye and atropine (a potent mydriatic agent) in the eye of several healthy volunteers. The first results obtained with the new device indicate its potential utility. More research and development work is required to define the optimal design of the coil in order to minimize the risk of irritation. Furthermore, the parameters that define the kinetics of the intraocular drug release must be defined and optimized with respect to the exact application.

Microsphere integrated microfluidic disk: synergy of two techniques for rapid and ultrasensitive dengue detection

The application of microfluidic devices in diagnostic systems is well-established in contemporary research. Large specific surface area of microspheres, on the other hand, has secured an important position for their use in bioanalytical assays. Herein, we report a combination of microspheres and microfluidic disk in a unique hybrid platform for highly sensitive and selective detection of dengue virus. Surface engineered polymethacrylate microspheres with carefully designed functional groups facilitate biorecognition in a multitude manner. In order to maximize the utility of the microspheres' specific surface area in biomolecular interaction, the microfluidic disk was equipped with a micromixing system. The mixing mechanism (microballoon mixing) enhances the number of molecular encounters between spheres and target analyte by accessing the entire sample volume more effectively, which subsequently results in signal amplification. Significant reduction of incubation time along with considerable lower detection limits were the prime motivations for the integration of microspheres inside the microfluidic disk. Lengthy incubations of routine analytical assays were reduced from 2 hours to 5 minutes while developed system successfully detected a few units of dengue virus. Obtained results make this hybrid microsphere-microfluidic approach to dengue detection a promising avenue for early detection of this fatal illness.

Effect of anti-ApoA-I antibody-coating of stents on neointima formation in a rabbit balloon-injury model

Background and Aims

Since high-density lipoprotein (HDL) has pro-endothelial and anti-thrombotic effects, a HDL recruiting stent may prevent restenosis. In the present study we address the functional characteristics of an apolipoprotein A-I (ApoA-I) antibody coating in vitro. Subsequently, we tested its biological performance applied on stents in vivo in rabbits.

Materials and Methods

The impact of anti ApoA-I- versus apoB-antibody coated stainless steel discs were evaluated in vitro for endothelial cell adhesion, thrombin generation and platelet adhesion. In vivo, response to injury in the iliac artery of New Zealand white rabbits was used as read out comparing apoA-I-coated versus bare metal stents.

Results

ApoA-I antibody coated metal discs showed increased endothelial cell adhesion and proliferation and decreased thrombin generation and platelet adhesion, compared to control discs. In vivo, no difference was observed between ApoA-I and BMS stents in lumen stenosis (23.3±13.8% versus 23.3±11.3%, p=0.77) or intima surface area (0.81±0.62 mm² vs 0.84±0.55 mm², p=0.85). Immunohistochemistry also revealed no differences in cell proliferation, fibrin deposition, inflammation and endothelialization.

Conclusion

ApoA-I antibody coating has potent pro-endothelial and anti-thrombotic effects in vitro, but failed to enhance stent performance in a balloon injury rabbit model in vivo.

Polymethacrylate coated electrospun PHB fibers: An exquisite outlook for fabrication of paper-based biosensors

Electrospun polyhydroxybutyrate (PHB) fibers were dip-coated by polymethyl methacrylate-co-methacrylic acid, poly(MMA-co-MAA), which was synthesized in different molar ratios of the monomers via free-radical polymerization. Fabricated platfrom was employed for immobilization of the dengue antibody and subsequent detection of dengue enveloped virus in enzyme-linked immunosorbent assay (ELISA). There is a major advantage for combination of electrospun fibers and copolymers. Fiber structre of electrospun PHB provides large specific surface area available for biomolecular interaction. In addition, polymer coated parts of the platform inherited the premanent presence of surface carboxyl (-COOH) groups from MAA segments of the copolymer which can be effectively used for covalent and physical protein immobilization. By tuning the concentration of MAA monomers in polymerization reaction the concentration of surface -COOH groups can be carefully controlled. Therefore two different techniques have been used for immobilization of the dengue antibody aimed for dengue detection: physical attachment of dengue antibodies to the surface and covalent immobilization of antibodies through carbodiimide chemistry. In that perspective, several different characterization techniques were employed to investigate the new polymeric fiber platform such as scanning electron microscopy (SEM), atomic force microscopy (AFM), water contact angle (WCA) measurement and UV-vis titration. Regardless of the immobilization techniques, substantially higher signal intensity was recorded from developed platform in comparison to the conventional ELISA assay.

Adsorption of albumin on flax fibers increases endothelial cell adhesion and blood compatibility in vitro

The physical and chemical properties of flax (linen) are attractive from the perspective of biomaterials science and engineering. Flax textiles uniquely combine hydrophilicity and strength, with the technical know-how to produce precisely engineered two- and three-dimensional knitted or woven structures. It is, however, extremely difficult to completely remove endotoxins from the flax, and this essentially precludes the use of linen for implant purposes. Herein, the potential utility of flax textiles for blood-contacting applications is investigated, using purified two-dimensional mesh specimens, with and without an albumin surface coating. It was hypothesized that the albumin coating will abolish the effect of adherent endotoxins at the flax's surface. In vitro cell viability assays showed that the flax mesh ± albumin is not cytotoxic. The albumin coating reduced (but not abolished) the effect of surface-exposed endotoxins (Limulus amebocyte lysate test). Under dynamic conditions, the albumin coating favors coverage with endothelial cells. Experiments with fresh human blood plasma (platelet-rich and platelet-free) showed that the albumin coating reduces the thrombogenicity in vitro. Platelets adhered to the albumin-coated flax mesh showed a less flattened structure. Although the results of this work cannot be extrapolated easily to in vivo situations, the data reveal that woven or knitted tubular structures produced from flax fibers may hold promise as implantable blood contacting devices like for instance vascular grafts.

A nontoxic additive to introduce x-ray contrast into poly(lactic acid). Implications for transient medical implants such as bioresorbable coronary vascular scaffolds

Bioresorbable coronary vascular scaffolds are about to revolutionize the landscape of interventional cardiology. These scaffolds, consisting of a poly(L-lactic acid) interior and a poly(D,L-lactic acid) surface coating, offer a genuine alternative for metallic coronary stents. Perhaps the only remaining drawback is that monitoring during implantation is limited to two X-ray contrast points. Here, a new approach to make the biodegradable scaffolds entirely radiopaque is explored. A new contrast agent is designed and synthesized. This compound is miscible with poly(D,L-lactic acid) matrix, and nontoxic to multiple cell types. Blends of poly(D,L-lactic acid) and the contrast agent are found to be hemocompatible, noncytotoxic, and radiopaque. The data show that it is possible to manufacture fully radiopaque bioresorbable coronary vascular scaffolds. Whole-stent X-ray visibility helps interventionalists ensure that the scaffold deploys completely. This important advantage may translate into improved safety, accuracy, and clinical performance of cardiac stents.

Antimicrobial and anti-thrombogenic features combined in hydrophilic surface coatings for skin-penetrating catheters. Synergy of co-embedded silver particles and heparin

Percutaneous (skin-penetrating) catheters such as central venous catheters (CVCs), are used ubiquitously in the treatment of critically ill patients, although it is known that the risks for serious complications, particularly bloodstream infection and thromboembolism, are high. Materials science and engineering offer important new perspectives regarding further improvement of CVCs. A promising approach is the use of synthetic biocompatible hydrogel coatings with both silver particles and heparin embedded therein. Such formulations combine the well-known broad-spectrum antimicrobial features of silver with the anticoagulant activity of immobilized heparin. Previous work revealed that heparin augments antimicrobial activity of silver, while maintaining its anticoagulant function. This study set out to investigate the synergy of heparin and silver in more detail. Exit-challenge tests, experiments on bacterial killing and adherence, as well as in vitro challenge tests with three Staphylococcus aureus strains (one reference strain, and two clinical isolates) consistently showed the synergistic effect. In addition, the impact of changing the coating's hydrophilicity, and changing the silver concentration in the coatings, were examined. The experimental results, taken together and combined with data from the literature, point out that synergy of heparin and silver is best explained by binding of Ag(+) ions to heparin within the swollen coating, followed by release of heparin-Ag(+) complexes upon immersion of the coatings in an aqueous environment such as blood. Possible implications of this work regarding the development of improved/safer CVCs are briefly discussed.

Influence of powder-to-liquid monomer ratio on properties of an injectable iodine-containing acrylic bone cement for vertebroplasty and balloon kyphoplasty

The interventional radiological techniques of vertebroplasty (VP) and balloon kyphoplasty (BKP) are widely used in cases where the pain secondary to compression fractures of vertebral bodies is severe, persistent, and refractory to conservative treatments. In the majority of VP and BKP cases, an injectable poly(methyl methacrylate) (PMMA) bone cement and different values of powder-to-liquid monomer ratio (PLMR) are used. A systematic study of the influence of PLMR on relevant cement properties is lacking. This was the subject of the present study, with the injectable PMMA bone cement used being an experimental one whose radiopacity is provided by an iodine-containing compound in the powder. The PLMRs used-1.54, 2.22, and 3.08 g mL(-1)-are within the range used in clinical reports on VP and BKP. One property of the curing cement, namely, the polymerization rate at 37 degrees C (k'), was estimated using nonisothermal differential scanning calorimetry results. The fatigue lives (N(f)) of cured cement specimens were obtained under axial loading corresponding to axial stresses (S) of +/-20.0, 15.0, 12.5, and 10.0 MPa, at a frequency of 2 Hz. The fatigue limit of the cement was estimated from the fit of the S - N(f) results to the Olgive equation. With increase in PLMR, k' increased significantly, but the influence of PLMR on the fatigue limit and on another property also estimated from the S - ln N(f) results is not significant.

Disruption and activation of blood platelets in contact with an antimicrobial composite coating consisting of a pyridinium polymer and AgBr nanoparticles

Composite materials made up from a pyridinium polymer matrix and silver bromide nanoparticles embedded therein feature excellent antimicrobial properties. Most probably, the antimicrobial activity is related to the membrane-disrupting effect of both the polymer matrix and Ag(+) ions; both may work synergistically. One of the most important applications of antimicrobial materials would be their use as surface coatings for percutaneous (skin-penetrating) catheters, such as central venous catheters (CVCs). These are commonly used in critical care, and serious complications due to bacterial infection occur frequently. This study aimed at examining the possible effects of a highly antimicrobial pyridinium polymer/AgBr composite on the blood coagulation system, i.e., (i) on the coagulation cascade, leading to the formation of thrombin and a fibrin cross-linked network, and (ii) on blood platelets. Evidently, pyridinium/AgBr composites could not qualify as coatings for CVCs if they trigger blood coagulation. Using a highly antimicrobial composite of poly(4-vinylpyridine)-co-poly(4-vinyl-N-hexylpyridinium bromide) (NPVP) and AgBr nanoparticles as a thin adherent surface coating on Tygon elastomer tubes, it was found that contacting blood platelets rapidly acquire a highly activated state, after which they become substantially disrupted. This implies that NPVP/AgBr is by no means blood-compatible. This disqualifies the material for use as a CVC coating. This information, combined with earlier findings on the hemolytic effects (i.e., disruption of contacting red blood cells) of similar materials, implies that this class of antimicrobial materials affects not only bacteria but also mammalian cells. This would render them more useful outside the biomedical field.

VEGF-E enhances endothelialization and inhibits thrombus formation on polymeric surfaces

Thrombotic complications of long-term blood-contacting devices can be avoided by formation of an endothelial cell layer on the blood-contacting surface. The endothelial cells form a bioactive boundary between the synthetic surface and blood, regulating haemostasis and inflammation. Biofunctionalization of synthetic blood-contacting surfaces is necessary to accommodate growth of endothelial cells. Vascular endothelial growth factor E (VEGF-E) or collagen I may stimulate endothelialization of a polymeric surface coating of a prototype small diameter vascular prosthesis. VEGF-E was produced in Escherichia coli and could be easily purified in large quantities. Recombinant VEGF-E or purified collagen I was allowed to adsorb onto the polymeric surfaces and enhanced formation of an endothelial cell layer. Adsorption of VEGF-E was increased by the inclusion of the anti-coagulant drug heparin in the polymeric coating. Collagen I adsorption induced rapid thrombin generation and increased platelet adhesion on surfaces with or without heparin. VEGF-E inhibited thrombus formation, and did not interfere with the anti-thrombogenic effect of heparin. Additionally, VEGF-E did not affect platelet adhesion. Adsorption of VEGF-E, especially on heparin containing surfaces, provides an economical strategy to improve endothelialization of cardiovascular implants without disturbing blood-compatibility.

Synthesis and characterization of radiopaque iodine-containing degradable PVA hydrogels

Poly (vinyl alcohol) (PVA) hydrogels are highly attractive for biomedical applications, especially for controlled release of drugs and proteins. Recently, degradable PVA hydrogels have been described, having the advantage that the material disappears over time from the implantation site. Herein, we report the synthesis of radiopaque degradable PVA, which gives a further advantage that the position of the hydrogel can precisely be determined by X-ray fluoroscopy. Radiopacity has been introduced by replacing 0.5% of the pendent alcohol groups on the PVA with 4-iodobenzoylchloride. This level of substitution rendered the polymer adequately radiopaque. The subsequent modification of 0.8% of the pendent hydroxyl groups with an ester acrylate functional group allowed for cross-linking of the macromers. The radiopaque hydrogels degraded over a time span of 140 days. Rheology data suggested that the macromer solutions were appropriate for injection.

Polymers with tunable toxicity: a reference scale for cytotoxicity testing of biomaterial surfaces

A series of copolymers, with varying ratio di-methylamino-ethylmethacrylate (DMAEMA) and methyl-methacrylate (MMA), was designed as a potential scale for cytotoxicity. These copolymers were characterized for toxicity of their surface. The surfaces of washed copolymers display increasing toxicity with increasing DMAEMA content. The toxicity was observed for three different cell-types, namely mouse fibroblasts, human endothelial cells and human osteoblast-like cells. With an increasing toxic surface, cell growth was inhibited as was indicated by the proliferation marker Ki-67. Staining for F-actin revealed that with increasing DMAEMA, cells adopted a more and more round morphology, resulting in decreased surface-contact area. Immuno-staining for phospho-tyrosine or vinculin demonstrated gradual loss of focal adhesions on increasingly toxic surfaces. Surprisingly loss of focal adhesions coincided with an increase in paxillin and vinculin protein, indicating cells try compensating for loss of adhesion. This series of copolymers may have potential as a cytotoxicity scale. They provoke cellular responses ranging from highly toxic to completely non-toxic, with some showing intermediate toxicity.

Capacity and tolerance of a new device for ocular drug delivery

A new method to increase the drug-capacity of the OphthaCoil, a flexible and tubular device for delivery of drugs to the tear film of the eye, was explored. Poly(2-hydroxyethyl methacrylate)- and poly(2-hydroxyethyl methacrylate-co-1-vinyl-2-pyrrolidone)-microspheres were prepared by suspension polymerization. The resultant particles were swollen in a highly concentrated solution of either the dye fluorescein sodium or the antibiotic chloramphenicol. The loaded particles were placed in the central cavity of the ocular device. In vitro release profiles showed a six-fold increase of the capacity for the dye fluorescein sodium, but not for the antibiotic chloramphenicol. Flexibility measurements revealed that by introducing microspheres in the central cavity of the device, flexibility did not decrease. Finally, a preliminary in vivo evaluation of the device (n=5) was done for a 2h-period to assess the tolerance of the device in the human eye. Ophthalmologic examinations and photographs of the eye indicated no signs of irritation. Volunteers reported that the presence of the device in the eye could be noticed, but no irritation was reported.

New acrylic microspheres for arterial embolization: Combining radiopacity for precise localization with immobilized thrombin to trigger local blood coagulation

Particles currently used in arterial embolization therapy have several disadvantages, most importantly their radiolucency. This means the radiologist cannot precisely asses the fate of embolization particles. Microspheres that combine two additional features have been designed. By incorporating an iodine containing monomer, radiopaque microspheres were obtained that display good visibility under standard X-ray conditions. Incorporation of methacrylic acid makes the surface of the spheres suitable for surface functionalization. Here, thrombin was covalently attached to the surface of the radiopaque microspheres. By induction of a thrombus, improved anchoring of the embolization spheres in the blood vessel can be obtained. The immobilized thrombin induced a biphasic response of the blood namely: (1) fast deposition of fibrin on the surface resulting in sphere aggregation and (2) additional thrombin generation in the surrounding blood and a subsequent local thrombus formation. These microspheres with both intrinsic X-ray visibility and a biofunctionalized surface can potentially improve embolization therapies.

Biocompatibility of a new radiopaque iodine-containing acrylic bone cement

Radiopacity in the vast majority of the commercially available acrylic bone cements that are used clinically is provided by particles of either BaSO(4) or ZrO(2). Literature reports have shown these agents to have a detrimental effect on some mechanical properties of the cements as well as on its biological response. We, therefore, have developed a new type of bone cement, for which radiopacity results from the presence of an iodine-containing methacrylic copolymer. The focus of the present work was the comparison of the biocompatibility of this new cement and a commercially available cement that contains barium sulfate. In vitro experiments show that both cements are cytocompatible materials, for which no toxic leachables are found. Implantation of the cements in a rabbit for three months resulted in the occasional presence of a thin fibrous tissue at the cement-bone interface, which is common for acrylic bone cements. Consideration of all the results led to the conclusion that the new cement is as biocompatible as the BaSO(4)-containing one.

Thrombus Formation at the Surface of Guide-Wire Models: Effects of Heparin-releasing or Heparin-exposing Surface Coatings

PURPOSE

This study was conducted to investigate whether thrombus formation at the surface of guide wires occurs, and--if so--whether this can be suppressed or prevented through incorporation of heparin in the surface coating.

MATERIALS AND METHODS

Five guide wire models were examined; three had a polymeric hydrophilic surface coating (90/10 guide wire), which was either heparin-free, impregnated with sodium-heparin (Na-hep), or impregnated with benzalkonium heparin (BAK-hep). The other two guide wires had a coating of polytetrafluoroethylene (PTFE), either without heparin, or impregnated with BAK-hep. Release of heparin, exposure of heparin at the surface of the guide wires, thrombogenicity (under static and flow conditions) and their propensity to attract blood platelets were investigated.

RESULTS

The guide wire 90/10 Na-hep releases approximately 150-200 mU active heparin per cm coil within the first few minutes after incubation in buffer. The PTFE BAK-hep shows a relatively slow release of 60-70 mU active heparin per cm coil. The 90/10 BAK-hep showed no released heparin but the most exposed heparin. In a static experiment with human full blood excessive thrombus formation occurred at the heparin-free models, whereas the others remained essentially clean. In a thrombin-generation assay under flow the authors observed strong retardation of thrombin formation in the case of the 90/10 Na-hep guide wire.

CONCLUSIONS

The static and dynamic in vitro assays, taken together, show that the 90/10 Na-hep provides a coating with an extremely low level of surface thrombogenicity. Use of a guide wire with a hydrophilic distal coating that releases and exposes sodium heparin may contribute to the safety of diagnostic and therapeutic interventional procedures.

Towards a functional radiopaque hydrogel for nucleus pulposus replacement

Patients with severe back pain, attributed to a herniation of the nucleus pulposus of the intervertebral disc, can benefit from a replacement of only the nucleus pulposus, provided the annulus fibrosus is still functional. This study investigated four intrinsically radiopaque hydrogel biomaterials, which were designed specifically to replace the herniated nucleus pulposus. The important characteristic of these hydrogels is that they can be visualized entirely with both MRI and X-rays. The materials are based on copolymers of N-vinyl-2-pyrrolidinone (NVP) or 2-hydroxyethyl methacrylate (HEMA) and a radiopacity introducing monomer, 2-(4'-iodobenzoyl)-oxo-ethyl methacrylate (4IEMA). Two of the formulations also contain the chemical crosslinker allyl methacrylate (AMA). Physical-mechanical properties like the water-uptake, biocompatibility, stiffness, and fatigue and creep behavior were studied, while keeping an eye on the intended application. All four materials were designed with 5-6 mass % of iodine to ensure sufficient X-ray visibility between two vertebrae. It was found that the materials display appropriate stiffness and biocompatibility. The crosslinked materials hold most promise as a functional nucleus prosthesis, as they combine these properties also with high water content, fatigue resistance, and recovery after loading.

Radio-Opaque and Surface-Functionalized Polymer Microparticles: Potentially Safer Biomaterials for Different Injection Therapies

Injectable polymer particles with a diameter in the range of 30-300 microm find applications as a biomaterial in different clinical fields, such as cosmetic surgery, reconstructive surgery, and urology. However, clinical effects tend to disappear after several months, either due to migration of the particles away from the injection site (caused by weak adherence with the surrounding soft tissues) or due to fibrosis (caused by excessive encapsulation of the particles by fibrous tissue). Little is known about the fate of injected microparticles, due to the fact that they are extremely difficult to trace in a noninvasive manner. Design, synthesis, and characterization of new polymeric microspheres with two additional features that can enhance safety and can help to overcome drawbacks of existing products are reported. First, the new microparticles feature clear radio-opacity (X-ray visibility) as they are prepared on the basis of a reactive methacrylic monomer that contains covalently bound iodine. Model experiments reveal that the level of X-ray contrast is sufficient for clinical monitoring; they can be visualized both during the injection and afterward. The particles feature excellent cytocompatibility in vitro and in vivo. Second, a method is explored to functionalize the surface of the particles, for example, through immobilization of collagen. Other extracellular matrix proteins can also be immobilized, and this provides a mechanism to control anchoring of the particles in soft tissue. The results are briefly discussed in the context of improved biomaterials, contemporary X-ray imaging, and control over biomaterial-soft tissue interactions in vivo.

The effect of high-density-lipoprotein on thrombus formation on and endothelial cell attachement to biomaterial surfaces

Cardiovascular implants such as vascular grafts fail frequently because they lack genuine blood-compatibility. The blood-contacting surface should simultaneously prevent thrombus formation and promote formation of a confluent endothelial cell layer, to achieve sustained haemostasis. Contact activation and endothelialization are known to be determined by the plasma proteins which adsorb onto virtually all synthetic surfaces almost immediately upon contact with blood. A common approach in blood-compatibility research is, therefore, to use hydrophilic biomaterials, which are sometimes claimed to be "protein-repellent". We report here that, for synthetic polymeric surfaces, hydrophilicity is by no means synonymous to protein-repellency. We discovered that significant amounts of proteins, especially high-density lipoprotein, adsorb to hydrophilic surfaces. Pre-incubation of hydrophilic synthetic surfaces with high-density lipoprotein provides a blood-biomaterial interface, which inhibits thrombin generation and subsequent thrombus formation, and also accommodates overgrowth with a confluent endothelial layer. This approach may open the way to truly functional small-caliber arterial prostheses, and may also be relevant to cardiovascular tissue engineering in which de novo vascular tissues are cultured on or within a biomaterial scaffold.

Intrinsically radiopaque hydrogels for nucleus pulposus replacement

Degeneration of the intervertebral disc is the most common cause of back pain. In case of early stage degenerative disc disease or traumatic herniations, a suitable treatment may be to replace the nucleus pulposus, preserving the annulus fibrosus. Eight new hydrogel biomaterials were prepared and studied for their potential as a nucleus replacement. The hydrogels were designed according to the following criteria: (i), they should exhibit adequate radiopacity; (ii), they should be non-cytotoxic; (iii), implantation in the dry state and subsequent swelling in situ to fill the entire nucleus cavity; (iv), after swelling they should match the physical-mechanical properties of the native nucleus. The approach was to use copolymers consisting of 2-(4'-iodobenzoyl)-oxo-ethyl methacrylate (4IEMA) and a hydrophilic building block (either N-vinyl-2-pyrrolidinone (NVP) or 2-hydroxyethyl methacrylate (HEMA)); 4 copolymers of NVP/4IEMA and 4 copolymers of HEMA/4IEMA in different compositions (5, 10, 15 and 20 mol% 4IEMA). The study comprised 1H-NMR analysis of the copolymerization reaction NVP+4IEMA. Furthermore, the copolymers were studied with respect to their swelling behavior, mechanical properties, cytotoxicity in vitro and X-ray contrast. Hydrogels with 5 mol% 4IEMA appear to meet all criteria: they are non-cytotoxic, have adequate physical-mechanical properties and feature sufficient radiopacity in a realistic model. The potential implications of these new results with respect to treatment of degenerative disc disease are discussed briefly.

Development of new injectable bulking agents: biocompatibility of radiopaque polymeric microspheres studied in a mouse model

Radiopaque polymeric microspheres have a potential as new bulking agents for treatment of stress urinary incontinence (SUI). The advantage over existing bulking agents lies in their X-ray visibility in situ; other polymeric bulking agents (e.g., PTFE or silicone rubbers) are practically radiolucent (i.e., incapable of absorbing X-radiation). Radiopacity is useful in practice because of the high spatial accuracy of X-ray imaging. For instance, X-ray fluoroscopy can be used to assess possible migration of the bulking agent over time or to provide guidance in cases in which a second injection of a bulking agent is necessary (repeated treatment of SUI). Biocompatibility of injected radiopaque microspheres was investigated in vivo by using the mouse as a model. Microspheres were injected subcutaneously (9 animals) or intramuscularly (9 animals), and follow-up was 8 days or 3 months. X-ray fluoroscopy gave clear images of the microspheres as an ensemble, and it was found that no migration occurred during 3 months. Histopathology confirmed that all microspheres stayed close to the site of the injection. The microspheres appeared to be well tolerated; only a few giant cells, manifesting a mild inflammatory reaction, were encountered. At 3 months, capillary blood vessels were observed throughout the microsphere beds, and macrophages and fibroblast cells were seen in between the microspheres. This is encouraging with respect to the intended application, although it must be acknowledged that the data refer merely to a mouse model. Further experiments with larger, more representative models (rabbit and goat) are in progress.

Hydrophobicity as a design criterion for polymer scaffolds in bone tissue engineering

Porous polymeric scaffolds play a key role in most tissue-engineering strategies. A series of non-degrading porous scaffolds was prepared, based on bulk-copolymerisation of 1-vinyl-2-pyrrolidinone (NVP) and n-butyl methacrylate (BMA), followed by a particulate-leaching step to generate porosity. Biocompatibility of these scaffolds was evaluated in vitro and in vivo. Furthermore, the scaffold materials were studied using the so-called demineralised bone matrix (DBM) as an evaluation system in vivo. The DBM, which is essentially a part of a rat femoral bone after processing with mineral acid, provides a suitable environment for ectopic bone formation, provided that the cavity of the DBM is filled with bone marrow prior to subcutaneous implantation in the thoracic region of rats. Various scaffold materials, differing with respect to composition and, hence, hydrophilicity, were introduced into the centre of DBMs. The ends were closed with rat bone marrow, and ectopic bone formation was monitored after 4, 6, and 8 weeks, both through X-ray microradiography and histology. The 50:50 scaffold particles were found to readily accommodate formation of bone tissue within their pores, whereas this was much less the case for the more hydrophilic 70:30 counterpart scaffolds. New healthy bone tissue was encountered inside the pores of the 50:50 scaffold material, not only at the periphery of the constructs but also in the center. Active osteoblast cells were found at the bone-biomaterial interfaces. These data indicate that the hydrophobicity of the biomaterial is, most likely, an important design criterion for polymeric scaffolds which should promote the healing of bone defects. Furthermore, it is argued that stable, non-degrading porous biomaterials, like those used in this study, provide an important tool to expand our comprehension of the role of biomaterials in scaffold-based tissue engineering approaches.

The use of a newly designed nonabsorbable polymeric stent in reconstructing the vas deferens: a feasibility study in New Zealand white rabbits

OBJECTIVES

To investigate the use of a newly designed stent in the reconstruction of the vas deferens.

MATERIALS AND METHODS

In 26 New Zealand White rabbits, 13 conventional one-layer microscopic reconstructions were compared with 13 stented reconstructions of the vas deferens. The newly designed nonabsorbable polymeric stent was shaped to facilitate the rejoining of the two loose ends of the vas deferens, using a central ridge to prevent migration. Semen was collected before and after surgery, using an artificial vaginal system (26 samples before and 115 after surgery). The individual and average total sperm count, motility and progressive motile sperm density (PMSD), were compared after surgery for both groups. After the final semen analysis, rabbits were killed and patency was assessed histologically at the site of the anastomosis.

RESULTS

After an initial decline the mean total sperm count increased in both groups. The increase was significantly larger (P = 0.05) in the stented rabbits. The mean motility and PMSD showed no significant differences between both groups (P = 0.11 and 0.71, respectively). Histological examination of the anastomosed area showed partial obstruction (>50% narrowing of the original lumen) in five of the 13 conventionally treated rabbits, with no strictures in the stented group. Despite the narrowing in the conventional group the patency rates were not affected. The mean (range) operating time for the conventional and stented groups was 132 (99-168) and 98 (62-113) min, respectively (P < 0.001).

CONCLUSIONS

The total sperm counts, motility and PMSD showed no or little difference after surgery between the conventional and stented rabbits. The stented reconstruction was easy, had no secondary stricturing and reduced the operating time.

Studies on a new device for drug delivery to the eye

Delivery of drugs to the anterior side of the eye is routinely done with eye drops, but this method results in low bioavailability and low patient compliance. Herein, we describe a new device for the delivery of drugs to the eye. The device, called the OphthaCoil, consists of a drug-loaded adherent hydrogel coating on a thin metallic wire, which is coiled. The drug release rates of the dye fluorescein and the antibiotic chloramphenicol have already been evaluated in vitro. In this report the drug release rate of the anti-infective pradofloxacin was evaluated in vitro and in vivo. The data show that the OphthaCoil is capable of sustained drug delivery to the tear film in dogs. Drug levels in the tear fluid of the dogs were well above the MIC-values of relevant bacteria after 16 h, but it should be noted that pradofloxacin has an exceptionally high antimicrobial activity. The study indicates that the OphthaCoil holds promise as a platform for sustained release of drugs to the eye. The device was well tolerated, but the devices were lost when left overnight. Most probably, this is due to the third eyelid pushing the device out of the conjunctival sac during sleep. It should be noted that this complication has no immediate implication for extended wear of the OphthaCoil in humans, as humans do not have third eyelids.