Klaus-Peter Schmitz

University of Rostock, Rostock, Mecklenburg-Vorpommern, Germany

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Publications (87)220.75 Total impact

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    ABSTRACT: Minimally invasive treatment of vertebral fractures is basically characterized by cement augmentation. Using the combination of a permanent implant plus cement, it is now conceivable that the amount of cement can be reduced and so this augmentation could be an attractive opportunity for use in traumatic fractures in young and middle-aged patients. The objective of this study was to determine the smallest volume of cement necessary to stabilize fractured vertebrae comparing the SpineJack system to the gold standard, balloon kyphoplasty. 36 fresh frozen human cadaveric vertebral bodies (T11-L3) were utilized. After creating typical compression wedge fractures (AO A1.2.1), the vertebral bodies were reduced by SpineJack (n=18) or kyphoplasty (n=18) under preload (100N). Subsequently, different amounts of bone cement (10%, 16% or 30% of the vertebral body volume) were inserted. Finally, static and dynamic biomechanical tests were performed. Following augmentation and fatigue tests, vertebrae treated with SpineJack did not show any significant loss of intraoperative height gain, in contrast to kyphoplasty. In the 10% and 16%-group the height restoration expressed as a percentage of the initial height was significantly increased with the SpineJack (>300%). Intraoperative SpineJack could preserve the maximum height gain (mean 1% height loss) better than kyphoplasty (mean 16% height loss). In traumatic wedge fractures it is possible to reduce the amount of cement to 10% of the vertebral body volume when SpineJack is used without compromising the reposition height after reduction, in contrast to kyphoplasty that needs a 30% cement volume. Copyright © 2015 Elsevier Ltd. All rights reserved.
    Clinical biomechanics (Bristol, Avon) 05/2015; DOI:10.1016/j.clinbiomech.2015.04.015 · 1.88 Impact Factor
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    ABSTRACT: Drug eluting stents (DES) consist of platform, coating and drug. The platform often is a balloon-expandable bare metal stent made of the CoCr alloy L-605 or stainless steel 316L. The function of the coating, typically a permanent polymer, is to hold and release the drug, which should improve therapeutic outcome. Before implantation, DES are compressed (crimped) to allow implantation in the human body. During implantation, DES are expanded by balloon inflation. Crimping, as well as expansion, causes high stresses and high strains locally in the DES struts, as well as in the polymer coating. These stresses and strains are important design criteria of DES. Usually, they are calculated numerically by finite element analysis (FEA), but experimental results for validation are hardly available. In this work, the X-ray diffraction (XRD) sin(2)ψ-technique is applied to in-situ determination of stress conditions of bare metal L-605 stents, and Poly-(L-lactide) (PLLA) coated stents. This provides a realistic characterization of the near-surface stress state and a validation option of the numerical FEA. XRD-results from terminal stent struts of the bare metal stent show an increasing compressive load stress in tangential direction with increasing stent expansion. These findings correlate with numerical FEA results. The PLLA-coating also bears increasing compressive load stress during expansion. Copyright © 2015 Elsevier Ltd. All rights reserved.
    Journal of the Mechanical Behavior of Biomedical Materials 04/2015; 49. DOI:10.1016/j.jmbbm.2015.04.020 · 3.05 Impact Factor
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    ABSTRACT: Drug-coated balloons (DCB), which have emerged as a therapeutic alternative to drug-eluting stents in percutaneous cardiovascular intervention, are well described with regard to clinical efficacy and safety within a number of clinical studies. In vitro studies elucidating the correlation between coating additive and DCB performance are however rare but considered important for the understanding of DCB requirements and the improvement of established DCB. In this regard, we examined three different DCB-systems, which were developed in former studies based on the ionic liquid cetylpyridinium salicylate, the body-own hydrogel hyaluronic acid and the pharmaceutically well-established hydrogel polyvinylpyrrolidone, considering coating morphology, coating thickness, drug-loss, drug-transfer to the vessel wall, residual drug-concentration on the balloon surface and entire drug-load during simulated use in an in vitro vessel model. Moreover, we investigated particle release of the different DCB during simulated use and determined the influence of the three coatings on the mechanical behavior of the balloon catheter. We could show that coating characteristics can be indeed correlated with the performance of DCB. For instance, paclitaxel incorporation in the matrix can reduce the drug wash-off and benefit a high drug transfer. Additionally, a thin coating with a smooth surface and high but delayed solubility can reduce drug wash-off and decrease particle burden. As a result, we suggest that it is very important to characterize DCB in terms of mentioned properties in vitro in addition to their clinical efficacy in order to better understand their function and provide more data for the clinicians to improve the tool of DCB in coronary angioplasty.
    PLoS ONE 03/2015; 10(3):e0116080. DOI:10.1371/journal.pone.0116080 · 3.53 Impact Factor
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    ABSTRACT: Drug-coated balloon catheters are a novel clinical treatment alternative for coronary and peripheral artery diseases. Calcium alginate, poly(vinylethylimidazolium bromide) and polyacrylamide hydrogels were used as vessel models in this in vitro study. In comparison to a simple silicone tube their properties can be easily modified simulating different types of tissue. Local drug delivery after balloon dilation in the first crucial minute was determined in a vessel-simulating flow-through cell by a simulated blood stream. Balloon catheters were coated with paclitaxel using the ionic liquid cetylpyridinium salicylate as a novel carrier. Drug transfer from coated balloon catheters to different simulated vessel walls was evaluated and compared to a silicone tube. The highest paclitaxel delivery upon dilation was achieved with calcium alginate as the vessel model (60%) compared to polyacrylamide with 20% drug transfer. The silicone tube showed the least amount of wash-off (<1%) by a simulated blood stream after one minute from the vessel wall. The vessel-simulating flow-through cell was combined with a model coronary artery pathway to estimate drug loss during simulated use in an in vitro model. Calcium alginate and polyacrylamide hydrogels were used as tissue models for the simulated anatomic implantation process. In both cases, similar transfer rates for paclitaxel upon dilation were detected.
    RSC Advances 01/2015; 5(15). DOI:10.1039/C4RA12524J · 3.71 Impact Factor
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    ABSTRACT: As it has been demonstrated that bioactive substances can be delivered locally using coated surgical suture materials we developed a vascular endothelial growth factor (VEGF)-releasing suture material that should promote vascularization and potentially wound healing. In this context, we focused on the characterization of the developed suture material and the verification of its biological activity, as well as established a coating process which allows reproducible and stable coating of a commercially available polydioxanone (PDS) suture material with poly(L-lactide) (PLLA) and 0.1μg and 1.0μg VEGF. The in vitro VEGF release kinetics was studied using a Sandwich ELISA. The biological activity of the released VEGF was investigated in vitro using human umbilical vein endothelial cells (HUVECs). The potential of the VEGF-releasing suture material was also studied in vivo as five days after implantation in the hind limb of Wistar rats histological findings were analyzed. As essential result, enhanced cell viability in vitro as well as significantly increased vascularization in vivo were achieved using the PLLA/1.0μg VEGF-coated suture material. Furthermore, ELISA measurements revealed a high reproducibility of the VEGF release behavior. Based on the achieved results regarding the dose-effect relationship of VEGF, the stability during its processing and the release behavior it can be predicted that a bioactive suture material would be successful in later in vivo studies. Therefore, this knowledge could be the basis for future studies where bioactive substances with different modes of action will be combined for a targeted, overall enhancement of wound healing.
    Acta Biomaterialia 09/2014; 10(12). DOI:10.1016/j.actbio.2014.09.002 · 5.68 Impact Factor
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    ABSTRACT: The high degree of clinical routine in percutaneous transluminal coronary angioplasty (PTCA) with and without stenting has not changed the fact that a large number of coronary heart disease patients are still affected by post-operative complications such as restenosis and thrombosis. Because re-endothelialization is the crucial aspect of wound healing after cardiovascular implant surgery, there is a need for modern biomaterials to aid endothelial cells in their adhesion and functional recovery post-stenting. This study systematically examines the potential of numerous chemical polymer modifications with regard to endothelialization. Poly(ε-caprolactone) (PCL) and its chemically activated forms are investigated in detail, as well as the impact of polymer surface morphology and precoating with matrix protein. Human umbilical vein endothelial cells (HUVECs) are used to characterize endothelial cell responses in terms of in vitro viability and adhesion. As a potential component in drug eluting implants, VEGF is applied as stimulus to boost endothelial cell proliferation on the polymer. In conclusion, plasma chemical activation of PCL combined with VEGF stimulation best enhances in vitro endothelialization. Examining the impact of morphological, chemical and biological modifications of PCL, this study makes an important new contribution towards the existing body of work on polymer endothelialization.
    Journal of Materials Science Materials in Medicine 05/2014; 25(8). DOI:10.1007/s10856-014-5226-0 · 2.38 Impact Factor
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    ABSTRACT: Enhanced proliferation of human coronary artery smooth muscle cells (HCASMCs) and thereby formation of neointima is one of the factors contributing to failure of coronary stents. Even if the use of drug eluting stents and thereby the local delivery of cytotoxic compounds has significantly improved clinical outcome, unselective cytotoxicity is assumed to hamper clinical success. Novel pharmacological approaches are required to enhance cellular selectivity of locally delivered drugs. Cell specific overexpression of a drug transporter could be used to enhance cellular accumulation and therefore cell specificity. In the herein reported study we tested the possibility of cell specific transporter expression to enhance drug effects in HCASMCs. We generated adenoviral constructs to overexpress the organic cation transporter 1 (OCT1) under control of the promoter of SM22α, which had been previously reported as muscle cell-specific gene. First the activity of the SM22α-promoter was assessed in various cell types supporting the notion of muscle cell-specificity. Subsequently, the activity of the transporter was compared in infected human coronary artery endothelial cells (HCAECs) and HCASMCs revealing enhanced accumulation of substrate drugs in HCASMCs in presence of the SM22α-promoter. Testing the hypothesis that this kind of targeting might serve as a mechanism for cell-specific drug effects we investigated the impact on paclitaxel treatment in HCASMC and HCAECs, showing significantly increased anti-proliferative activity of this substrate drug on muscle cells. Taken together, our findings suggest that cell-specific expression of transport proteins serves as mechanism governing the uptake of cytotoxic compounds for a selective impact on targeted cells.
    Molecular Pharmaceutics 02/2014; 11(3). DOI:10.1021/mp400245g · 4.79 Impact Factor
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    ABSTRACT: Aiming at a speed up of the re-endothelialization process of biodegradable endovascular implants, novel approaches for the functionalization of poly(l-lactide) (PLLA) with anti-CD34 antibodies were established. We propose a three-step process involving PLLA surface activation with functional amino groups, attachment of a protein repelling peptide spacer, and covalent random or site-selective immobilization of the antibodies. Obtainable antibody surface densities and antigen binding capacities were thoroughly evaluated by means of enzyme-linked immunosorbent assay. Results indicate that a lower amount of anchoring sites on the antibody favors high coupling efficiency, while localization of the anchoring sites, facing the antigen binding moiety, strongly enhances the antigen capture capacity of the support. Besides minimization of physisorption and cell adhesion exemplarily shown with bovine serum albumin, avidin, and human umbilical vein endothelial cells, respectively, the inclusion of the protein-repelling spacer strengthened this effect, yielding antigen capture capacities exceeding values so far reported in literature. In contrast, the number of amino groups on the PLLA surfaces, which is indeed highly dependent on the applied activation procedure, does not seem to influence antibody coupling efficiency and antigen capture capacity considerably. This allows the choice of surface activation treatment, plasma or wet-chemical, regarding other processing parameters as for instance sterilizability or favored modification depth. © 2013 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 2013.
    Journal of Biomedical Materials Research Part B Applied Biomaterials 02/2014; 102(2). DOI:10.1002/jbm.b.33012 · 2.33 Impact Factor
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    ABSTRACT: Impaired re-endothelialization and stent thrombosis are a safety concern associated with drug-eluting stents (DES). PI3K/p110α controls cellular wound healing pathways, thereby representing an emerging drug target to modulate vascular homoeostasis after injury. PI3K/p110α was inhibited by treatment with the small molecule inhibitor PIK75 or a specific siRNA. Arterial thrombosis, neointima formation, and re-endothelialization were studied in a murine carotid artery injury model. Proliferation and migration of human vascular smooth muscle cell (VSMC) and endothelial cell (EC) were assessed by cell number and Boyden chamber, respectively. Endothelial senescence was evaluated by the β-galactosidase assay, endothelial dysfunction by organ chambers for isometric tension. Arterial thrombus formation was delayed in mice treated with PIK75 when compared with controls. PIK75 impaired arterial expression and activity of tissue factor (TF) and plasminogen activator inhibitor-1 (PAI-1); in contrast, plasma clotting and platelet aggregation did not differ. In VSMC and EC, PIK75 inhibited expression and activity of TF and PAI-1. These effects occurred at the transcriptional level via the RhoA signalling cascade and the transcription factor NFkB. Furthermore, inhibition of PI3K/p110α with PIK75 or a specific siRNA selectively impaired proliferation and migration of VSMC while sparing EC completely. Treatment with PIK75 did not induce endothelial senescence nor inhibit endothelium-dependent relaxations. In line with this observation, treatment with PIK75 selectively inhibited neointima formation without affecting re-endothelialization following vascular injury. Following vascular injury, PI3K/p110α inhibition selectively interferes with arterial thrombosis and neointima formation, but not re-endothelialization. Hence, PI3K/p110α represents an attractive new target in DES design.
    European Heart Journal 12/2013; 35(12). DOI:10.1093/eurheartj/eht496 · 14.72 Impact Factor
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    ABSTRACT: Polyvinylpyrrolidone (PVP) is a conventionally applied hydrophilic lubricious coating on catheter-based cardiovascular devices, used in order to ease movement through the vasculature. Its use as drug reservoir and transfer agent on drug-coated balloons (DCB) is therefore extremely promising with regard to the simplification of its approval as a medical device. Here, we developed a PVP-based coating for DCB, containing paclitaxel (PTX) as a model drug, and studied the impact of crosslinking via UV radiation on drug stability, wash off, and transfer during simulated use in an in vitro vessel model. We showed that crosslinking was essential for coating stability and needed to be performed prior to PTX incorporation due to decreased drug bioavailability as a result of photodecomposition and/or involvement in vinylic polymerization with PVP under UV radiation. Moreover, the crosslinking time needed to be carefully controlled. While short radiation times did not provide enough coating stability, associated with high wash off rates during DCB insertion, long radiation times lowered drug transfer efficiency upon balloon expansion. A ten minutes radiation of PVP, however, combined a minimized drug wash off rate of 34% with an efficient drug transfer of 49%, underlining the high potential of photochemically crosslinked PVP as a coating matrix for DCB.
    Coatings Magazine 12/2013; DOI:10.3390/coatings3040253
  • Axel Haverich, Klaus-Peter Schmitz
    Biomedizinische Technik/Biomedical Engineering 10/2013; 58(5):387-388. DOI:10.1515/bmt-2013-0098 · 2.43 Impact Factor
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    ABSTRACT: Drug-coated balloons (DCB), which have emerged as therapeutic alternative to drug-eluting stents in percutaneous cardiovascular intervention, are well described with regard to clinical efficiency and safety within a number of clinical studies. In vitro studies elucidating the correlation of coating method and composition with DCB performance are however rare but considered important for the understanding of DCB requirements and the improvement of established DCB. In this context, we evaluated the applicability of a pipetting, dip-coating, and spray-coating process for the establishment of DCB based on paclitaxel (PTX) and the ionic liquid cetylpyridinium salicylate (Cetpyrsal) as novel innovative additive in three different compositions. Among tested methods and compositions, the pipetting process with 50wt.% PTX resulted in most promising coatings as drug load was less controllable by the other processes and higher PTX contents led to considerable drug crystallization, as visualized by electron microscopy, accelerating PTX loss during short-term elution. Applying these conditions, homogeneous coatings could be applied on balloon catheter, whose simulated use in an in vitro vessel model revealed percental drug losses of 36 and 28% during transit and percental drug transfers of 12 and 40% under expansion for coatings applied in expanded and folded balloon condition, respectively. In comparison to literature values, these results support the high potential of Cetpyrsal as novel DCB matrix regarding low drug loss and efficient drug transfer.
    10/2013; 33(7):4244-50. DOI:10.1016/j.msec.2013.06.021
  • Biomedizinische Technik/Biomedical Engineering 09/2013; DOI:10.1515/bmt-2013-4090 · 2.43 Impact Factor
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    ABSTRACT: Abstract Fully absorbable drug-eluting stent platforms are currently entering the clinical arena for the interventional treatment of coronary artery disease. This new technology also holds potential for application in peripheral vascular settings. Our study reports on the development of a sirolimus- (SIR) eluting absorbable polymer stent made from a blend of poly(l-lactide) and poly(4-hydroxybutyrate) (PLLA/P4HB) for peripheral vascular intervention. Stent prototypes were laser-cut from PLLA/P4HB tubes (I.D.=2.2 mm, t=250 µm), spray-coated with different PLLA/P4HB/SIR solutions, and bench-tested to determine expansion properties, fatigue, trackability and in vitro drug release kinetics. The stent prototypes were expanded with a 5.0×20 mm balloon catheter, and exhibited a recoil of 3.6% upon balloon deflation. Stent collapse pressure of 0.4 bar (300 mm Hg) was measured under external pressure load. Sustained scaffolding properties were observed in vitro over 14 weeks of radial fatigue loading (50±25 mm Hg at 1.2 Hz). Trackability was demonstrated in bench tests with an 8 French contralateral introducer sheath. SIR release kinetics were adjusted over a broad range by varying the PLLA/P4HB ratio of the coating matrix. The newly developed absorbable SIR-eluting PLLA/P4HB stent successfully fulfilled the requirements for peripheral vascular intervention under in vitro conditions.
    Biomedizinische Technik/Biomedical Engineering 07/2013; 58(5):1-9. DOI:10.1515/bmt-2012-0050 · 2.43 Impact Factor
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    ABSTRACT: Abstract Purpose: For developing injectable lenses the retention properties of the capsular bag are important. Therefore the apparent permeability coefficients of sodium fluorescein and fluorescent dextrans of different sizes were determined for the human anterior lens capsule to calculate a molecular weight cutoff from these data. In addition, permeability coefficients of drugs helpful for the suppression of secondary cataract were determined. Materials and Methods: Capsulorhexis specimens were fixed in a specially designed two compartment diffusion chamber to investigate the permeation of sodium fluorescein and fluorescent dextrans of different sizes (10, 40, 70 and 150 kDa) for 24 h (n ≥ 3) and of the antiproliferative drugs actinomycin D and methotrexate for 0.5, 24, 48 and 72 h (n ≥ 3). Results: The molecular weight cutoff of the anterior lens capsule was found to be 166 ± 82 kDa. After 0.5 h, no passage of actinomycin D and methotrexate was detectable through the lens capsule. The apparent permeability coefficients for actinomycin D and methotrexate were calculated to 0.71 ± 0.02 µm/s and to 0.80 ± 0.13 µm/s, respectively. Conclusions: The capsular bag retains fluorescent dextrans with a molecular weight of >166 kDa. Hence, prepolymers are required to polymerize rapidly to be retained inside of the capsular bag. In addition, low-molecular substances intended as antiproliferative drugs for secondary cataract prevention should be applied within a time frame of five minutes in such a way that cells adjacent to the capsular bag will not be damaged.
    Current eye research 07/2013; DOI:10.3109/02713683.2013.803288 · 1.66 Impact Factor
  • Journal of Neurointerventional Surgery 07/2013; 5(Suppl 2):A55-A56. DOI:10.1136/neurintsurg-2013-010870.107 · 1.38 Impact Factor
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    ABSTRACT: Within the context of novel stent designs we developed a dual drug-eluting stent (DDES) with an abluminally focussed release of the potent anti-proliferative drug sirolimus and a luminally focussed release of atorvastatin with stabilizing effect on atherosclerotic deposits and stimulating impact on endothelial function, both from biodegradable poly(L-lactide)-based stent coatings. With this concept we aim at simultaneous inhibition of in-stent restenosis as a result of disproportionally increased smooth muscle cell proliferation and migration as well as thrombosis due to failed or incomplete endothelialisation. The especially adapted spray-coating processes allowed the formation of smooth form-fit polymer coatings at the abluminal and luminal side with 70 % respectively 90 % of the drug/polymer solution being deposited at the intended stent surface. The impacts of tempering, sterilization, and layer composition on drug release are thoroughly discussed making use of a semi-empirical model. While tempering at 80 °C seems to be necessary for the achievement of adequate and sustained drug release, the coating sequence for DDES should be rather abluminal-luminal than luminal-abluminal, as reduction of the amount of sirolimus eluted luminally could then potentially minimize the provocation of endothelial dysfunction. In vitro proliferation and viability assays with smooth muscle and endothelial cells underline the high potential of the developed DDES.
    Journal of Materials Science Materials in Medicine 07/2013; 24(11). DOI:10.1007/s10856-013-5001-7 · 2.38 Impact Factor
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    ABSTRACT: For an aqueous shunt draining from the anterior chamber into the choroidal space, fibroblasts from the choroidea and/or the sclera are most likely responsible for a fibrotic response around the outflow region of such a shunt. The prevention of fibrosis should extend the operating life of the shunt. A detailed characterization of fibroblasts derived from choroidea and sclera should provide information about whether a fibrosis reaction can be inhibited by cell type-specific agents. We generated mRNA profiles of fibroblasts from the choroidea, sclera, and Tenon's space by gene array hybridization to provide a basis on which to search for potential pharmacological targets for fibrosis prevention. Hybridization data were analyzed by the Rosetta Resolver system and Limma to obtain mRNA profiles of the three fibroblast types. The three fibroblast types investigated shared fibroblast-specific gene expression patterns concerning extracellular matrix proteins as collagens and fibronectin, but also showed distinct mRNA patterns. Individual mRNA species overexpressed in one of the fibroblast types might serve as markers for the identification of the fibroblast type in histological analyses. Future in-depth analyses of the gene expression patterns might help identify pharmacological targets for fibrosis prevention.
    Molecular vision 06/2013; 19:1321-1331. · 2.25 Impact Factor
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    ABSTRACT: Abstract Implants providing controlled, local release of active substances are of interest in different medical applications. Therefore, the focus of the present article is the development of implant-associated diffusion- or chemically controlled local drug delivery (LDD) systems based on biodegradable polymeric drug carriers. In this context, we provide new data and review our own recently published data concerning the drug release behavior of diffusion-controlled LDD systems in relation to the kind of polymer, drug content, coating mass/thickness, and layer composition. We demonstrate that polymers allow a wide range of control over the drug release characteristics. In this regard, we show that the glass transition temperature of a polymer has an impact on its drug release. Additionally, the blending of hydrophobic, semicrystalline polymers with amorphous polymers leads to an increase in the rate of drug release compared with the pure semicrystalline polymer. Moreover, the percentage loading of the embedded drug has a considerable effect on the rate and duration of drug release. Furthermore, we discuss chemically controlled LDD systems designed for the release of biomolecules, such as growth factors, as well as nanoparticle-mediated LDD systems. With our own published data on drug-eluting stents, microstents, and cochlear implants, we highlight exemplary implant-associated LDD systems designed to improve implant performance through the reduction of undesirable effects such as in-stent restenosis and fibrosis.
    Biomedizinische Technik/Biomedical Engineering 06/2013; 58(5):1-11. DOI:10.1515/bmt-2012-0049 · 2.43 Impact Factor
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    ABSTRACT: The development of drug-eluting coatings based on hyaluronic acid (HA) is especially promising for implant-associated local drug delivery (LDD) systems, whose implantation provokes high insertion forces, as, for instance, cochlear implants or drug-coated balloons (DCB). The lubricious character of HA can then reduce the coefficient of friction and serve as drug reservoir simultaneously. In this context, we investigated several plasma- and wet-chemical methods for the deposition of HA-based coatings with LDD function on polyamide 12 as a model implant surface, conventionally used for DCB. In contrast to aminosilane, epoxy silane surface layers allowed the covalent attachment of a smooth and uniform HA base layer, which provided good adherence of further HA layers deposited by manual dip coating at a subsequent processing stage. The applied HA-crosslinking procedure during dip coating influences the transfer and release of paclitaxel, which could be reproducibly incorporated via infiltration. While crosslinking with N-(3-dimethylaminopropyl)-N′-ethylcarbodiimide hydrochloride provided HA coatings on DCB, which allowed for an efficient paclitaxel transfer upon expansion in a vessel model, crosslinking with glutardialdehyde resulted in a slower drug release being more appropriate for implants with longer residence time in the body. The developed HA coating is hence well suited for spontaneous and sustained LDD.
    04/2013; 2013. DOI:10.1155/2013/587875