Surface modification of polyethylene balloon catheters for local drug delivery

Recent advance in treatment of atherosclerosis: Key targets and plaque-positioned delivery strategies

Atherosclerosis, a chronic inflammatory disease of vascular wall, is a progressive pathophysiological process with lipids oxidation/depositing initiation and innate/adaptive immune responses. The coordination of multi systems covering oxidative stress, dysfunctional endothelium, diseased lipid uptake, cell apoptosis, thrombotic and pro-inflammatory responding as well as switched SMCs contributes to plaque growth. In this circumstance, inevitably, targeting these processes is considered to be effective for treating atherosclerosis. Arriving, retention and working of payload candidates mediated by targets in lesion direct ultimate therapeutic outcomes. Accumulating a series of scientific studies and clinical practice in the past decades, lesion homing delivery strategies including stent/balloon/nanoparticle-based transportation worked as the potent promotor to ensure a therapeutic effect. The objective of this review is to achieve a very brief summary about the effective therapeutic methods cooperating specifical targets and positioning-delivery strategies in atherosclerosis for better outcomes.

Hydrophilic modification of SLA 3D printed droplet generators by photochemical grafting

Few droplet generators manufactured using desktop stereolithography 3D printers have been reported in the literature. Moreover, 3D printed microfluidic chips are typically hydrophobic, limiting their application to water in oil droplets. Herein, we present designs for concentric and planar 3D printed microfluidic devices suitable for making polymeric microparticles using an off-the-shelf commercial stereolithography printer and resin. The devices consist of a microscope slide, binder clips, and printed components. Channels were modified by an ultraviolet grafting of methacrylic acid to the surface of chips, yielding a hydrophilic coating without modification to the bulk polymer. The water contact angle decreased from 97.0° to 25.4° after grafting. The presence of the coating was confirmed by microscopy and spectroscopy techniques. Polystyrene microparticles in the <100 μm size range were generated with varying molecular weights using the described microfluidic chips. Our work provides a facile method to construct droplet generators from commercial stereolithography printers and resins, and a rapid surface modification technique that has been under-utilized in 3D printed microfluidics. A wide range of microfluidic devices for other applications can be engineered using the methods described.

A versatile method of manufacturing and directly modifying the surfaces of 3D printed microfluidic devices was developed. The device functionality was demonstrated by producing o/w emulsions that yielded polystyrene microspheres.

Surface Modification Using Ultraviolet-Ozone Treatment Enhances Acute Drug Transfer in Drug-Coated Balloon Therapy

Endovascular deployment of drug-coated balloons (DCB) is an emerging strategy for the revascularization of arterial disease. Randomized clinical trials have demonstrated DCB effectiveness, but a recent meta-analysis reported increased mortality risk in humans with use of DCBs containing the common antiproliferative drug paclitaxel. While many factors could have contributed to adverse outcomes, current DCB designs have poor drug delivery efficiency, risk of systemic toxicity, and limited potential to retain therapeutic drug concentrations within the arterial wall following the procedure. Our study focuses on developing a strategy to enhance acute drug transfer from the balloon to the arterial wall over the short procedural window (∼30-120 s). We employed ultraviolet-ozone plasma (UVO) treatment to increase the hydrophilicity of a prototypical balloon material (Nylon-12) and subsequently applied a urea-paclitaxel coating previously shown to undergo favorable adhesive interactions with the arterial wall under simulated ex-vivo deployment. A series of assays were performed to characterize our experimental DCBs in terms of UVO-induced alterations in balloon surface hydrophobicity, formed coating microstructure, coating stability, and acute drug transfer to the arterial wall. Obtained results suggest that the UVO-based surface modification of angioplasty balloons is a promising design strategy and highlights the critical role of coating microstructure in determining the drug transfer efficiency in DCB therapy.

A review of electronic skin: soft electronics and sensors for human health

This article reviews several categories of electronic skins (e-skins) for monitoring signals involved in human health. It covers advanced candidate materials, compositions, structures, and integrate strategies of e-skin, focusing on stretchable and wearable electronics. In addition, this article further discusses the potential applications and expected development of e-skins. It is possible to provide a new generation of sensors which are able to introduce artificial intelligence to the clinic and daily healthcare.

Modulation of Foreign Body Reaction against PDMS Implant by Grafting Topographically Different Poly(acrylic acid) Micropatterns

The surface of poly(dimethylsiloxane) (PDMS) is grafted with poly(acrylic acid) (PAA) layers via surface-initiated photopolymerization to suppress the capsular contracture resulting from a foreign body reaction. Owing to the nature of photo-induced polymerization, various PAA micropatterns can be fabricated using photolithography. Hole and stripe micropatterns ≈100-µm wide and 3-µm thick are grafted onto the PDMS surface without delamination. The incorporation of PAA micropatterns provides not only chemical cues by hydrophilic PAA microdomains but also topographical cues by hole or stripe micropatterns. In vitro studies reveal that a PAA-grafted PDMS surface has a lower proliferation of both macrophages (Raw 264.7) and fibroblasts (NIH 3T3) regardless of the pattern presence. However, PDMS with PAA micropatterns, especially stripe micropatterns, minimizes the aggregation of fibroblasts and their subsequent differentiation into myofibroblasts. An in vivo study also shows that PDMS samples with stripe micropatterns polarized macrophages into anti-inflammatory M2 macrophages and most effectively inhibits capsular contracture, which is demonstrated by investigation of inflammation score, transforming-growth-factor-β expression, number of macrophages, and myofibroblasts as well as the collagen density and capsule thickness.

Development of a stent capable of the controlled release of basic fibroblast growth factor and argatroban to treat cerebral aneurysms: In vitro experiment and evaluation in a rabbit aneurysm model

An ideal stent to treat cerebral aneurysms should have an antithrombotic effect on the inner stent blood-facing side and a tissue organization effect on the outer aneurysmal side of the stent. The objective of this study is to evaluate the feasibility of a drug containing stent in the in vivo treatment of cerebral aneurysms. Argatroban, an antithrombotic drug, is encapsulated in biodegradable poly (d,l-lactide-co-glycolide) (PLGA) microspheres for the controlled release with an in vitro study conducted to evaluate the drug release and anticoagulation behavior of released drug. Basic fibroblast growth factor (bFGF), an organization drug, is released from gelatin hydrogels. The stents are coated with gelatin hydrogels incorporating bFGF and PLGA microspheres containing argatroban, and applied to the carotid artery aneurysm of an elastase-induced rabbit model. Most of the aneurysm cavity is occupied by loose connective tissues in the group treated with drug-coated stents, whereas extensive massive hematomas are observed in the group treated with drug-free stents. The occurrence rate of in-stent thrombus is small in the drug-coated stents. The stent incorporating bFGF and PLGA microspheres containing argatroban is an effective device for cerebral aneurysm treatment. © 2019 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater 107B: 2185-2194, 2019.

Tissue Engineering at the Blood-Contacting Surface: A Review of Challenges and Strategies in Vascular Graft Development

Tissue engineered vascular grafts (TEVGs) are beginning to achieve clinical success and hold promise as a source of grafting material when donor grafts are unsuitable or unavailable. Significant technological advances have generated small-diameter TEVGs that are mechanically stable and promote functional remodeling by regenerating host cells. However, developing a biocompatible blood-contacting surface remains a major challenge. The TEVG luminal surface must avoid negative inflammatory responses and thrombogenesis immediately upon implantation and promote endothelialization. The surface has therefore become a primary focus for research and development efforts. The current state of TEVGs is herein reviewed with an emphasis on the blood-contacting surface. General vascular physiology and developmental challenges and strategies are briefly described, followed by an overview of the materials currently employed in TEVGs. The use of biodegradable materials and stem cells requires careful control of graft composition, degradation behavior, and cell recruitment ability to ensure that a physiologically relevant vessel structure is ultimately achieved. The establishment of a stable monolayer of endothelial cells and the quiescence of smooth muscle cells are critical to the maintenance of patency. Several strategies to modify blood-contacting surfaces to resist thrombosis and control cellular recruitment are reviewed, including coatings of biomimetic peptides and heparin.

Increased Surface Roughness in Polydimethylsiloxane Films by Physical and Chemical Methods

Two methods, the first physical and the other chemical, were investigated to modify the surface roughness of polydimethylsiloxane (PDMS) films. The physical method consisted of dispersing multi-walled carbon nanotubes (MWCNTs) and magnetic cobalt ferrites (CoFe₂O₄) prior to thermal cross-linking, and curing the composite system in the presence of a uniform magnetic field H. The chemical method was based on exposing the films to bromine vapours and then UV-irradiating. The characterizing techniques included scanning electron microscopy (SEM), energy-dispersive spectroscopy (EDS), Fourier transform infrared (FTIR) spectroscopy, optical microscopy, atomic force microscopy (AFM) and magnetic force microscopy (MFM). The surface roughness was quantitatively analyzed by AFM. In the physical method, the random dispersion of MWCNTs (1% w/w) and magnetic nanoparticles (2% w/w) generated a roughness increase of about 200% (with respect to PDMS films without any treatment), but that change was 400% for films cured in the presence of H perpendicular to the surface. SEM, AFM and MFM showed that the magnetic particles always remained attached to the carbon nanotubes, and the effect on the roughness was interpreted as being due to a rupture of dispersion randomness and a possible induction of structuring in the direction of H. In the chemical method, the increase in roughness was even greater (1000%). Wells were generated with surface areas that were close to 100 μm² and depths of up to 500 nm. The observations of AFM images and FTIR spectra were in agreement with the hypothesis of etching by Br radicals generated by UV on the polymer chains. Both methods induced important changes in the surface roughness (the chemical method generated the greatest changes due to the formation of surface wells), which are of great importance in superficial technological processes.

Development of antimicrobial coating by layer-by-layer [corrected] dip coating of chlorhexidine-loaded micelles

Layer-by-layer (LbL) dip coating, accompanying with the use of micelle structure, allows hydrophobic molecules to be coated on medical devices' surface via hydrogen bonding interaction. In addition, micelle structure also allows control release of encapsulated compound. In this research, we investigated methods to coat and maximize the amount of chlorhexidine (CHX) on silicone surface through LbL dip coating method utilizing hydrogen bonding interaction between PEG on micelle corona and PAA. The number of coated cycles was varied in the process and 90 coating cycles provided the maximum amount of CHX loaded onto the surface. In addition, pre-coating the surface with PAA enhanced the amount of coated CHX by 20%. Scanning electron microscope (SEM) and Fourier Transform Infrared Spectroscopy (FTIR) were used to validate and characterize the coating. For control release aspect, the coated film tended to disrupt at physiological condition; hence chemical crosslinking was performed to minimize the disruption and maximize the release time. Chemical crosslinking at pH 2.5 and 4.5 were performed in the process. It was found that chemical crosslinking could help extend the release period up to 18 days. This was significantly longer when compared to the non-crosslinking silicone tube that could only prolong the release for 5 days. In addition, chemical crosslinking at pH 2.5 gave higher and better initial burst release, release period and antimicrobial properties than that of pH 4.5 or the normal used pH for chemical crosslinking process.

A Robust Method to Generate Mechanically Anisotropic Vascular Smooth Muscle Cell Sheets for Vascular Tissue Engineering

In arterial tissue engineering, mimicking native structure and mechanical properties is essential because compliance mismatch can lead to graft failure and further disease. With bottom-up tissue engineering approaches, designing tissue components with proper microscale mechanical properties is crucial to achieve the necessary macroscale properties in the final implant. This study develops a thermoresponsive cell culture platform for growing aligned vascular smooth muscle cell (VSMC) sheets by photografting N-isopropylacrylamide (NIPAAm) onto micropatterned poly(dimethysiloxane) (PDMS). The grafting process is experimentally and computationally optimized to produce PNIPAAm-PDMS substrates optimal for VSMC attachment. To allow long-term VSMC sheet culture and increase the rate of VSMC sheet formation, PNIPAAm-PDMS surfaces were further modified with 3-aminopropyltriethoxysilane yielding a robust, thermoresponsive cell culture platform for culturing VSMC sheets. VSMC cell sheets cultured on patterned thermoresponsive substrates exhibit cellular and collagen alignment in the direction of the micropattern. Mechanical characterization of patterned, single-layer VSMC sheets reveals increased stiffness in the aligned direction compared to the perpendicular direction whereas nonpatterned cell sheets exhibit no directional dependence. Structural and mechanical anisotropy of aligned, single-layer VSMC sheets makes this platform an attractive microstructural building block for engineering a vascular graft to match the in vivo mechanical properties of native arterial tissue.

A thermoresponsive, micro-roughened cell culture surface

Surface topography has been shown to play a major role in cell behavior, but has yet to be seriously exploited in the field of cell surface engineering. In the present work, surface roughness has been used in combination with the thermoresponsive polymer polyisopropylacrylamide (PIPAAm) to generate cell sheets with tailored biochemical properties. Micro-roughened polystyrene (PS) with 1.5-5.5 μm features was derivatized with PIPAAm to form a cell culture surface for the growth of human fibroblast cell sheets that exhibit a modified cytoskeleton and extracellular matrix. Fibroblasts cell sheets cultured on the rough surfaces had fewer actin stress fibers and twice the average fibronectin (FN) fibril formation when compared to cell sheets on flat substrates. The cell sheets harvested from the roughened PS were collected after only 2 days of culture and detached from the PIPAAm grafted surface in <1h after cooling the culture system. The simple and rapid method for generating cell sheets with increased FN fibril formation has applications in tissue grafts or wound repair and has demonstrated that the thermoresponsive surface can be used for reliable cell sheet formation.

Ultrathin, biomimetic, superhydrophilic layers of cross-linked poly(phosphobetaine) on polyethylene by photografting

Ultrathin, biomimetic, superhydrophilic hydrogel layers, composed of cross-linked poly(2-methacryloyloxyethyl phosphorylcholine), are formed on low-density polyethylene films via ultraviolet-initiated surface graft polymerization. The layers are 19-58 nm thick as revealed by electron microscopy and have three-dimensional networks; the unique network structure, along with its zwitterionic nature, rather than surface roughness results in superhydrophilicity, that is, the water contact angle around 5°. This superhydrophilicity depends on a variety of factors, including the concentration of the monomer and cross-linker, the type of reaction solvents, the reaction and drying time, the intensity of UV light, and the way of measurement of water contact angles. Superhydrophilicity is obtained under a fixed ratio (e.g., 1/1) of the monomer to cross-linker, a reaction time over 120 s, a short drying time, (75%) ethanol as the reaction solvent, and low-intensity UV light, largely because these factors together generate optimal three-dimensional networks of cross-links.

Preparation and characterization of a thrombin inhibitor grafted polyethersulfone blending membrane with improved antithrombotic property

A thrombin inhibitor grafted polyethersulfone membrane with improved antithrombotic property.

Silicone surface with drug nanodepots for medical devices

An ideal surface of poly(dimethylsiloxane) (PDMS) medical devices requires sustained drug release to combat various tissue responses and infection. At present, a noncovalent surface coating with drug molecules using binders possesses a detachment problem, while covalently linking drug molecules to the surface provides no releasable drug. Here, a platform that allows the deposition of diverse drugs onto the PDMS surface in an adequate quantity with reliable attachment and a sustained-release character is demonstrated. First, a PDMS surface with carboxyl functionality (PDMS-COOH) is generated by subjecting a PDMS piece to an oxygen plasma treatment to obtain silanol moieties on its surface, then condensing the silanols with (3-aminopropyl)triethoxysilane molecules to generate amino groups, and finally reacting the amino groups with succinic anhydride. The drug-loaded carriers with hydroxyl groups on their surface can then be esterified to PDMS-COOH, resulting in a PDMS surface covalently grafted with drug-filled nanocarriers so that the drugs inside the securely grafted carriers can be released. Demonstrated here is the covalent linking of the surface of a PDMS endotracheal tube with budesonide-loaded ethylcellulose nanoparticles. A secure and high drug accumulation at the surface of the tubes (0.025 mg/cm2) can be achieved without changes in its bulk property such as hardness (Shore-A), and sustained release of budesonide with a high release flux during the first week followed by a reduced release flux over the subsequent 3 weeks can be obtained. In addition, the grafted tube possesses more hydrophilic surface and thus is more tissue-compatible. The grafted PDMS pieces show a reduced in vitro inflammation in cell culture and a lower level of in vivo tissue responses, including a reduced level of inflammation, compared to the unmodified PDMS pieces, when implanted in rats. Although demonstrated with budesonide and a PDMS endotracheal tube, this platform of grafting a PDMS surface with drug-loaded particles can be applied to other drugs and other devices.

The effect of a polyurethane coating incorporating both a thrombin inhibitor and nitric oxide on hemocompatibility in extracorporeal circulation

Nitric oxide (NO) releasing (NORel) materials have been extensively investigated to create localized increases in NO concentration by the proton driven diazeniumdiolate-containing polymer coatings and demonstrated to improve extracorporeal circulation (ECC) hemocompatibility. In this work, the NORel polymeric coating composed of a diazeniumdiolated dibutylhexanediamine (DBHD-N2O2)-containing hydrophobic Elast-eon™ (E2As) polyurethane was combined with a direct thrombin inhibitor, argatroban (AG), and evaluated in a 4 h rabbit thrombogenicity model without systemic anticoagulation. In addition, the immobilizing of argatroban to E2As polymer was achieved by either a polyethylene glycol-containing (PEGDI) or hexane methylene (HMDI) diisocyanate linker. The combined polymer film was coated on the inner walls of ECC circuits to yield significantly reduced ECC thrombus formation compared to argatroban alone ECC control after 4 h blood exposure (0.6 ± 0.1 AG/HMDI/NORel vs 1.7 ± 0.2 cm(2) AG/HMDI control). Platelet count (2.8 ± 0.3 AG/HMDI/NORel vs 1.9 ± 0.1 × 10(8)/ml AG/HMDI control) and plasma fibrinogen levels were preserved after 4 h blood exposure with both the NORel/argatroban combination and the AG/HMDI control group compared to baseline. Platelet function as measured by aggregometry remained near normal in both the AG/HMDI/NORel (63 ± 5%) and AG/HMDI control (58 ± 7%) groups after 3 h compared to baseline (77 ± 1%). Platelet P-selectin mean fluorescence intensity (MFI) as measured by flow cytometry also remained near baseline levels after 4 h on ECC to ex vivo collagen stimulation (16 ± 3 AG/HMDI/NORel vs 11 ± 2 MFI baseline). These results suggest that the combined AG/HMDI/NORel polymer coating preserves platelets in blood exposure to ECCs to a better degree than AG/PEGDI/NORel, NORel alone or AG alone. These combined antithrombin, NO-mediated antiplatelet effects were shown to improve thromboresistance of the AG/HMDI/NORel polymer-coated ECCs and move potential nonthrombogenic polymers closer to mimicking vascular endothelium.

Occlusion of canine aneurysms using microporous self-expanding stent grafts: long-term follow-up

PURPOSE

The treatment of large or giant cerebral aneurysms by surgical and/or endovascular techniques is difficult and poses relatively high risks. Therefore, a microporous self-expanding (hybrid) stent graft composed of a thin, expandable, segmented polyurethane (SPU) membrane with micropores and a drug-delivery system was developed.

MATERIALS AND METHODS

A commercially available, self-expanding carotid stent was covered with a thin microporous SPU membrane fabricated by the dip-coating method and the excimer laser ablation technique, with an intraluminal coating of argatroban. Experimentally fabricated lateral-wall aneurysms in canine carotid arteries using venous pouches were occluded with the hybrid stent graft (bale-shaped pore density of 23.6%) on one side and a bare-metal stent on the other side without systemic antiplatelet therapy.

RESULTS

Angiography at 1, 6, and 12 months of stenting revealed that all arteries were patent without marked stenosis without systemic antiplatelet therapy. All aneurysms treated with hybrid stent grafts remained occluded throughout the 12-month period, while among those treated by bare-metal stents, 2 of 3 aneurysms were occluded at 6 months (67%) and only 1 of 3 aneurysms were occluded at 12 months (33%). Histology revealed that the novel hybrid stent graft had less intimal hyperplasia than the bare-metal stent. The hybrid stent graft was useful for the successful occlusion of these canine carotid aneurysms, even at 12 months.

CONCLUSIONS

The novel hybrid stent grafts are expected to overcome the disadvantages of fully covered stent grafts and simple bare-metal stents, while combining both their merits, and appear to be useful in the treatment of large or giant cerebral aneurysms.

Is there an alternative to systemic anticoagulation, as related to interventional biomedical devices?

To reduce the toxic effects, related clinical problems and complications such as bleeding disorders associated with systemic anticoagulation, it has been hypothesized that by coating the surfaces of medical devices, such as stents, bypass grafts, extracorporeal circuits, guide wires and catheters, there will be a significant reduction in the requirement for systemic anticoagulation or, ideally, it will no longer be necessary. However, current coating processes, even covalent ones, still result in leaching followed by reduced functionality. Alternative anticoagulants and related antiplatelet agents have been used for improvement in terms of reduced restenosis, intimal hyperphasia and device failure. This review focuses on existing heparinization processes, their application in clinical devices and the updated list of alternatives to heparinization in order to obtain a broad overview, it then highlights, in particular, the future possibilities of using heparin and related moieties to tissue engineer scaffolds.

Treatment of rabbit carotid aneurysms by hybrid stents (microporous thin polyurethane-covered stents): preservation of side-branches

Objective

We sought to determine the patency of normal arterial branches from the covered segments of an artery after stenting.

Background

Most intracranial aneurysms occur at arterial branching points (bifurcations, side-branches, or perforators). The post-stenting patency of normal arterial branches from the covered segments of the artery is important. We have previously developed a hybrid stent with micropores to prevent early parent artery occlusion by more early endothelialization, and mid- to long-term parent artery stenosis by control of intimal hyperplasia after aneurysm occlusion.

Methods

We created aneurysms in 10 rabbits by distal ligation and intraluminal incubation of elastase within an endovascularly trapped proximal segment of the common carotid artery. All animals were treated with hybrid stents having micropores. Four animals were observed for one month and three each for three and 12 months. The patency of the side-branches of the subclavian artery was evaluated angiographically and in some cases, histologically.

Results

Aneurysms were completely occluded at all time points other than 12 months. The subclavian artery and brachiocephalic artery were patent, without significant stenosis. All the side-branches of the subclavian artery detected on the preoperative angiogram remained patent at the final assessment.

Conclusion

The use of hybrid stents for aneurysm repair and side-branch patency seems to be effective, as per the long-term results obtained in an animal model.

CHARACTERIZATION OF POLY(ACRYLIC ACID) DIFFUSION DYNAMICS ON THE GRAFTED SURFACE OF POLY(ETHYLENE TEREPHTHALATE) FILMS BY FLUORESCENCE CORRELATION SPECTROSCOPY

Poly(acrylic acid) (PAAc) is a commonly used polymer grafted on poly(ethylene terephthalate) films for the immobilization of bioactive molecules that directly interact with living cells or tissues for the maintenance of their viability and functionality. The diffusion property of the grafted PAAc on the surface is a critical parameter related to the density, length of polymer chains, and ionic strength of the solution. Fluorescence correlation spectroscopy (FCS) is able to measure the diffusion coefficient of fluorescent particles in solution with single molecule sensitivity and specificity. It was used as an effective tool to detect diffusion dynamics of Atto 565 molecules, a good indicator for viscosity of PAAc, in both aqueous polymer solutions and polymer grafted film surfaces immersed in solution. In this work we determine the polymer chain length under different polymerization conditions in solution and deduce the solution viscosity by FCS measurements of Atto 565 as tracer molecule. By using the same tracer on the grafted polymer films we can infer the viscosity of these grafted layers under a variety of conditions, including the PAAc chain length, the UV exposure time during polymerization, the ionic strength, and the pH value of the immersed solution.

Surface modification of silicate glass using 3-(mercaptopropyl)trimethoxysilane for thiol-ene polymerization

A thiol-ene polymerization was accomplished on silicate glass slides to graft a series of homopolymers and copolymers using 3-(mercaptopropyl)trimethoxysilane (MTS) as both a silane coupling agent and initiator. MTS was initially covalently bonded to an acid cleaned glass surface via a classical sol-gel reaction. Poly(acrylic acid) (PAA), poly(acrylamide) (PAAm), poly(methyl acrylate) (PMA), poly(acrylamido-2-methyl-propanesulfonic acid) (PAMPS), and the copolymer poly(AA-co-AAm-co-MA-co-AMPS) were grafted from the thiol group of MTS. The surface chemistry of the MTS modified slides and polymer grafts was characterized with attenuated total reflection Fourier transform infrared (ATR-FTIR) spectroscopy and X-ray photoelectron spectroscopy (XPS). Surface texture was evaluated with tapping mode atomic force microscopy (TM-AFM). The Owens-Wendt-Kaelble (OWK) and Lifshitz-van der Waals acid-base (LW-AB) methods were used to evaluate surface energies by sessile drop contact angle method. The synthetic approach demonstrated a facile, rapid method for grafting to glass surfaces.

Development of microporous self-expanding stent grafts for treating cerebral aneurysms: designing micropores to control intimal hyperplasia

Treatment of large (diameter 12-25 mm) or giant (diameter >25 mm) cerebral aneurysms with a broad neck in the cranio-cervical area is difficult and carries relatively high risks, even with surgical and/or endovascular methods. To this end, we have been developing a high-performance, self-expanding stent graft which consists of a commercially available NiTi stent (diameter 5 mm, length 20 mm) initially covered with a thin microporous segmented polyurethane membrane fabricated by the dip-coating method. Micropores are then created by the excimer laser ablation technique, and the outer surface is coated with argatroban. There are 2 types of micropore patterns: circular-shaped pore type (pore: diameter 100 μm, opening ratio 12.6%) and the bale-shaped pore type (pore: size 100 × 268 μm, opening ratio 23.6%). This self-expanding stent graft was tested on side-wall aneurysms of both canine carotid arteries that were experimentally induced using the venous pouches from the external jugular veins, with the self-expanding stent graft on one side and a bare self-expanding stent on the other side. All carotid arteries were patent and free of marked stenosis after 1 month. All aneurysms were occluded by stent grafts, while patent in those treated with bare stents. Histologically, the stent grafts with bale-shaped micropores and a high opening ratio were associated with less intimal hyperplasia (187 ± 98 μm) than the bare stents (341 ± 146 μm) or the stent grafts with circular micropores and a low opening ratio (441 ± 129 μm). A pore ratio of 23.6% was found to control intimal growth.

UV-induced grafting processes with in situ formed photomask for micropatterning of two-component biomolecules

We report a photolithographic process for micropatterning of two-component biomolecules on a transparent organic film via lateral functional polymer brushes of poly(sodium acrylate) (P(AA)) and poly(glycidyl methacrylate) (P(GMA)). The pattern of binary polymer brushes were prepared via consecutive UV-initiated grafting processes, under the assistance of the in situ formed poly (4,4'-bi[N-(4-vinylbenzyl) pyridinium]) (P(BVV)) photomask. The epoxy groups of the P(GMA) microdomains can be aminated for covalently coupling biotin, while the P(AA) microdomains were used for immobilizing immunoglobulin (IgG). The resulting biotin- and IgG-coupled microdomains interact specifically with their corresponding target proteins, avidin and anti-IgG, respectively.

Functionalization of nylon membranes via surface-initiated atom-transfer radical polymerization

The ability to manipulate and control the surface properties of nylons is of crucial importance to their widespread applications. In this work, surface-initiated atom-transfer radical polymerization (ATRP) is employed to tailor the functionality of the nylon membrane and pore surfaces in a well-controlled manner. A simple two-step method, involving the activation of surface amide groups with formaldehyde and the reaction of the resulting N-methylol polyamide with 2-bromoisobutyryl bromide, was first developed for the covalent immobilization of ATRP initiators on the nylon membrane and its pore surfaces. Functional polymer brushes of 2-hydroxyethyl methacrylate (HEMA) and poly(ethylene glycol)monomethacrylate (PEGMA) were prepared via surface-initiated ATRP from the nylon membranes. A kinetics study revealed that the chain growth from the membranes was consistent with a "controlled" process. The dormant chain ends of the grafted HEMA polymer (P(HEMA)) and PEGMA polymer (P(PEGMA)) on the nylon membranes could be reactivated for the consecutive surface-initiated ATRP to produce the corresponding nylon membranes functionalized by P(HEMA)-b-P(PEGMA) and P(PEGMA)-b-P(HEMA) diblock copolymer brushes. In addition, membranes with grafted P(HEMA) and P(PEGMA) brushes exhibited good resistance to protein adsorption and fouling under continuous-flow conditions.

Adsorption of plasmid DNA onto N,N'- (dimethylamino)ethyl-methacrylate graft-polymerized poly-L-lactic acid film surface for promotion of in-situ gene delivery

The surface of biodegradable poly-L-lactic acid (PLLA) film was modified with N,N'-(dimethylamino)ethyl-methacrylate (DMAEMA) via UV-induced graft copolymerization, and plasmid DNA molecules were adsorbed onto the surface of modified PLLA film by electrostatic interactions with cationic DMAEMA polymer. We characterized the structure of the modified PLLA film surface by Fourier transform infrared attenuated total reflection (FTIR-ATR) spectroscopy and X-ray photoelectron spectroscopy (XPS). The weight-average molecular weight (Mw) of grafted DMAEMA polymer chains was estimated from the elution time of gel filtration chromatography. C.I. Acid Orange 7 dyeing results indicated that graft density of DMAEMA on PLLA film increased with the UV irradiation time and then reached a saturated value. DNA adsorption density was proportioned to graft density of DMAEMA. Mouse fibroblast L929 cell line was cultured on modified PLLA films, and cell viability and gene transfection efficiency were monitored after 2 days culture. It was found that the DMAEMA grafted PLLA film had obvious cytotoxicity to the cells. On the contrary, cytotoxicity of the surface was highly decreased after adsorption with plasmid DNA. This DNA adsorbed DMAEMA modified PLLA showed the ability to deliver DNA into mammalian cells cultured on the surface with high-transfection efficiency at a low DNA amount. The present results suggest that the DMAEMA grafted PLLA has potentiality to be used as a safe and effective gene delivery system in gene-activated materials.

Osteoblast-like cell attachment to and calcification of novel phosphonate-containing polymeric substrates

In an attempt to interact natural bone and bone cells with biomaterials and to begin to develop modular tissue engineering scaffolds, substrates containing phosphonate groups were identified to mimic mineral-protein and natural polymer-protein interactions. In this study, we investigated poly(vinyl phosphonic acid) copolymer integration with existing materials as a graft-copolymer surface modification. Phosphonate-containing copolymer-modified surfaces were created and shown to have varying phosphate content within different polymeric surfaces. As the phosphonate content in the monomer feed approached 30% vinyl phosphonic acid, increased osteoblast-like cell adhesion (3- to 8-fold increase in adhesion) and proliferation (2- to 10-fold increase in proliferation rate) was observed. Since surfaces modified with 30% vinyl phosphonic acid in the feed exhibited a maximal cell adhesion and proliferation (9.4 x 10(4) cells/cm(2)/day), it was hypothesized that this copolymer composition was optimal for protein-polymer interactions. Osteoblast-like cells formed confluent layers and were able to differentiate on all surfaces that contained vinyl phosphonic acid. Most importantly, cells interacting with these surfaces were able to significantly mineralize the surface. These results suggest that phosphonate-containing polymers can be used to integrate biomaterials with natural bone and could be used for tissue engineering applications.