[Cold atmospheric pressure plasma for the treatment of acute and chronic wounds]. / Kaltes Atmosphärendruckplasma zur Behandlung akuter und chronischer Wunden.

BACKGROUND: Besides acute wounds (through trauma or surgical interventions), chronic wounds comprise a relatively large and heterogeneous group of diseases. These include leg ulcers with venous disease greatly prevailing arterial disease, diabetic foot syndrome, and pressure ulcers. Due to a considerable treatment resistance against such therapies, new and effective, additive treatment options especially for chronic wounds are needed. Wound treatment with cold atmospheric plasma (CAP) constitutes such an innovative option. OBJECTIVES: Current research regarding the efficacy of cold plasma for healing of acute and chronic wounds is summarized. MATERIALS AND METHODS: The literature on CAP applications in wound healing has been screened and reviewed. RESULTS: With CAP, several effects that promote wound healing can be simultaneously applied in one application. On the one hand, CAP exerts a strong and broad antimicrobial activity against biofilm. On the other hand, the plasma cocktail, which consists of reactive nitrogen and oxygen species, UV, and charged particles (electrical current), mediates tissue-stimulating, blood flow-promoting, and anti-inflammatory effects. Marked germ reduction on wounds and accelerated wound healing have already been convincingly demonstrated in controlled clinical studies. CONCLUSIONS: The comprehensive CAP study landscape with structured case report summaries and randomized case-control studies allows the conclusion that CAP is safe, effective, and easy to handle for wound treatment. The utilization of CAP in addition to standard wound treatments is starting to enter routine clinical practice.

Biocompatibility and thermodynamic properties of PEGDA and two of its copolymer.

During the last years substantial effort was taken in order to provide an effective and safe pharmacotherapy that can be adjusted to the individual needs of patients. Stereolithography is a simple and accurate additive manufacturing technology. According to these characteristics, it may offer unique opportunities for the industrial fabrication of structured drug delivery systems (DDS), which can be tailored to individual needs. During the stereolithographic process photopolymerizable biomaterial is transformed, layer by layer, into the designed polymer DDS. Combined with inkjet printing in an innovative 3D building system it enables selective and precise incorporation of the drug depot into the basic body of the DDS. Poly(ethylene glycol) diacrylate (PEGDA), a hydrophilic and low-immunogenic compound, is a suitable material as drug depot in a photopolymerizable basic biomaterial for this purpose. By combination of PEGDA with other acrylates, the physical properties of the DDS can be adjusted towards the desired characteristics. Therefore, it should be possible to modify the drug release profile through the positioning of drug depots and the diffusion of the drug and adjust it for a wide range of applications. In this study we investigated basic biological and thermodynamic properties of conventionally photocured systems consisting of PEGDA and its coacrylates: 1,3-butanediol diacrylate and pentaerythritol triacrylate. Our preliminary outcomes demonstrate the hydrophilic character of the samples and the importance of a rinsing process. They also show that the addition of different amounts of co-monomers influence the glass transition temperature, which increases with increasing content of coacrylate. Therefore, PEGDA/comonomer composition can be used as a tool for the modification of drug release properties. Consequently, these materials may be regarded as interesting and promising components for DDS via novel additive manufacturing with the ability of highly controlled drug release.

[Biomechanical investigations on accommodation of the eye]. / Biomechanische Untersuchungen zur Akkommodation des Auges.

BACKGROUND: The biomechanics of accommodation are of particular interest in terms of the causes of presbyopia and the function of intraocular lenses. OBJECTIVE: The aim of the present article is to model the mechanism of accommodation in detail. MATERIALS AND METHODS: The state of the art of applying biomechanical models to accommodation is presented, which enables the accommodation process to be understood. RESULTS AND CONCLUSION: The established models, which are based on the Helmholtz theory, can explain the accommodation process in a plausible manner. These models thereby also enable further investigations on the genesis of presbyopia as well as on the development of accommodative intraocular lenses and implants. However, measurements are always necessary to compare the simulation results with reality, and to provide input and material data as well as geometric dimensions of components of the eye.

[Finite Element Modelling of the Eye for the Investigation of Accommodation]. / Finite-Elemente-Modellierung des Auges zur Untersuchung der Akkommodation.

Background: Accommodation research increasingly uses engineering methods. This article presents the use of the finite element method in accommodation research. Material and Methods: Geometry, material data and boundary conditions are prerequisites for the application of the finite element method. Published data on geometry and materials are reviewed. It is shown how boundary conditions are important and how they influence the results. Results: Two dimensional and three dimensional models of the anterior chamber of the eye are presented. With simple two dimensional models, it is shown that realistic results for the accommodation amplitude can always be achieved. More complex three dimensional models of the accommodation mechanism - including the ciliary muscle - require further investigations of the material data and of the morphology of the ciliary muscle, if they are to achieve realistic results for accommodation. Discussion and Conclusion: The efficiency and the limitations of the finite element method are especially clear for accommodation. Application of the method requires extensive preparation, including acquisition of geometric and material data and experimental validation. However, a validated model can be used as a basis for parametric studies, by systematically varying material data and geometric dimensions. This allows systematic investigation of how essential input parameters influence the results.

Biodegradable polymeric stents for vascular application in a porcine carotid artery model: English version.

Over the past years the development of biodegradable polymeric stents has made great progress; nevertheless, essential problems must still be solved. Modifications in design and chemical composition should optimize the quality of biodegradable stents and remove the weaknesses. New biodegradable poly-L-lactide/poly-4-hydroxybutyrate (PLLA/P4HB) stents and permanent 316L stents were implantedendovascularly into both common carotid arteries of 10 domestic pigs. At 4 weeks following implantation, computed tomography (CT) angiography was carried out to identify the distal degree of stenosis. The PLLA/P4HB group showed a considerably lower distal degree of stenosis by additional oral application of atorvastatin (mean 39.81 ± 8.57 %) compared to the untreated PLLA/P4HB group without atorvastatin (mean 52.05 ± 5.80 %). The 316L stents showed no differences in the degree of distal stenosis between the group treated with atorvastatin (mean 44.21 ± 2.34 %) and the untreated group (mean 35.65 ± 3.72 %). Biodegradable PLLA/P4HB stents generally represent a promising approach to resolving the existing problems in the use of permanent stents. Restitutio ad integrum is only achievable if a stent is completely degraded.

[Coupled Analysis of Fluid-Structure Interaction of a Micro-Mechanical Valve for Glaucoma Drainage Devices]. / Gekoppelte Analyse der Fluid-Struktur-Interaktion eines mikromechanischen Ventils für Glaukomdrainageimplantate.

BACKGROUND: Glaucoma is the leading cause of irreversible blindness worldwide. In therapeutically refractory cases, alloplastic glaucoma drainage devices (GDD) are being increasingly used to decrease intraocular pressure. Current devices are mainly limited by fibrotic encapsulation and postoperative hypotension. Preliminary studies have described the development of a glaucoma microstent to control aqueous humour drainage from the anterior chamber into the suprachoroidal space. One focus of these studies was on the design of a micro-mechanical valve placed in the anterior chamber to inhibit postoperative hypotension. The present report describes the coupled analysis of fluid-structure interaction (FSI) as basis for future improvements in the design micro-mechanical valves. MATERIALS AND METHODS: FSI analysis was carried out with ANSYS 14.5 software. Solid and fluid geometry were combined in a model, and the corresponding material properties of silicone (Silastic Rx-50) and water at room temperature were assigned. The meshing of the solid and fluid domains was carried out in accordance with the results of a convergence study with tetrahedron elements. Structural and fluid mechanical boundary conditions completed the model. The FSI analysis takes into account geometric non-linearity and adaptive remeshing to consider changing geometry. RESULTS: A valve opening pressure of 3.26 mmHg was derived from the FSI analysis and correlates well with the results of preliminary experimental fluid mechanical studies. Flow resistance was calculated from non-linear pressure-flow characteristics as 8.5 × 10(-3) mmHg/µl  · min(-1) and 2.7 × 10(-3) mmHg/µl  · min(-1), respectively before and after valve opening pressure is exceeded. FSI analysis indicated leakage flow before valve opening, which is due to the simplified model geometry. CONCLUSIONS: The presented bidirectional coupled FSI analysis is a powerful tool for the development of new designs of micro-mechanical valves for GDD and may help to minimise the time and cost expended on manufacturing and testing prototypes. Further optimisation of the FSI model is expected to ensure further convergence between the simulation and the results of experimental investigations.

Anastomotic stenting in a porcine aortoiliac graft model.

The purpose of the study was to evaluate the feasibility of anastomotic stent application in a porcine aortoiliac graft model. In a total of 10 pigs, a polytetrafluoroethylene aortobi-iliac graft was implanted through a midline abdominal incision. The lower edge of the iliac vessel was graft-inverted about 1 mm to produce irregularities at the downstream anastomosis. After transverse graft incision, six stainless-steel stents, six poly-L-lactic acid (PLLA) stents and four PLLA stents with 10% polycaprolactone (PCL) were implanted at the iliac anastomotic site using a 6 mm balloon dilatation catheter. Four anastomotic sites were left untreated. After two weeks, the patency of graft limbs was evaluated by contrast-enhanced computed tomography (CT). Both metal and polymeric stent designs provided adequate flexibility to manoeuvre across the anastomotic site for expansion in the chosen position. After deployment, the stent-arterial wall contact was complete on a macroscopic view. On CT scan, all metal and PLLA-stented graft limbs were free of stenosis, whereas all PLLA/PCL stents were occluded. The non-stented graft limbs showed a stenosis of 50-70%. In summary, this model is feasible to assess preclinically the deployment and patency rate of an anastomotic stent and to test future stent developments.

[Design strategy for balloon-expandable stents made of biodegradable polymers using finite element analysis]. / Design strategy for balloon-expandable stents made of biodegradable polymers using finite element analysis.

Stents made of biodegradable polymers have first been suggested to treat cardiovascular diseases more than ten years ago. Despite the enormous potential of local drug delivery there is no biodegradable coronary stent available today. Some of the problems concern the insufficient mechanical properties of the stent designs. Therefore a design strategy was developed to improve the mechanical properties of balloon-expandable polymer stents. Starting with compiling the possible geometric strut forms we proceeded to design strut features exhibiting an improved deformation behaviour. The addition of functional structures to improve certain stent characteristics led to stent designs, whose mechanical properties, recoil and collaps behaviour, were determined by 3D Finite Element Analysis. Finally, a mechanical in vitro testing of these stent prototypes was conducted.

Trackability, crossability, and pushability of coronary stent systems--an experimental approach.

Trackability, crossability and pushability are essential properties determining the handling characteristics and deliverability of stent systems. We present objective test methods to assess these parameters quantitatively in an in vitro model. The model consisted of a 6F guiding catheter, a guide wire (0.014") and a coronary vessel model (HD-PE tubing, I.D. 2.5 mm), all immersed in 37 degrees C water. Two attached sensors measured the reactive forces occurring at the proximal catheter shaft and the distal catheter and stent segments during model passage. For crossability assessment, the setup was completed by a stenosis model, mimicking two types of eccentric circular stenoses. A comparative study provided distinctive differences in trackability, stenosis crossability, and pushability. Analyzing the proximal and distal force measurements, these differences were quantified and the qualification of a particular stent system to be successfully delivered to a model target stenosis could be rated.

The impact of material characteristics on the mechanical properties of a poly(L-lactide) coronary stent.

Biodegradable polymer stents as an alternative to metallic vascular stents have long been under discussion. However, for various reasons no such stent concept has been made available for commercial use until today. One reason may be, that still little is known about the mechanical properties of polymer stents and their dependency on the material characteristics. In this study, finite element analysis is used to investigate the mechanical properties of a balloon expandable PLLA stent under various load conditions. It is shown, how material parameters, such as elastic modulus, yield level and material hardening, influence stent recoil and collapse behavior.