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Hydrogels are 3D polymeric networks, which exhibit properties such as softness, viscoelasticity and their ability to absorb large amounts of water. These characteristics make them exceptionally suitable in biomedicine as e.g. tissue scaffolds, drug delivery systems, wound dressings or contact lenses. One of these hydrogels is the biocompatible, hydrophilic and photopolymerizable poly(ethylene glycol) diacrylate (PEGDA). It is used in different biomedical applications due to its tunable mechanical characteristics. In our study, the mechanical properties of different PEGDA hydrogel compositions with variyng molecular masses and contents of water/methanol, were investigated. Different compositions containing 20 m%, 30 m% or 40 m% of PEGDA4K(4,000 g/mol), PEGDA10K(10,000 g/mol) or PEGDA20K(20,000 g/mol) in ultrapure water/methanol (1:2) were produced. Dumbbell-shaped samples were prepared in molds via photopolymerization in a UV chamber. Lithium phenyl-2,4,6-trimethylbenzoylphosphinate (LAP) was used as photoinitiator (0.5% w/w). The mechanical testing was performed using a uniaxial testing system. The obtained results showed averagely 78% higher tensile strength (σmax) values for 30 m% and 40 m% samples in comparison with 20 m% samples for all of the tested polymers. PEGDA20K30 m% samples showed the highest σmax among all of the samples with 12.8 MPa. All of the PEGDA20K samples exhibited the highest elongation at break (εB) values (up to 958%), whereas the lowest values were found for PEGDA4K(up to 105%). The obtained stress-strain curves for most of the samples were typical for deformable, amorphous polymers with a deformation upon reaching a critical stress point. The PEGDA materials showed variable mechanical characteristics according to changing molecular mass or polymer concentration. These promising results showed that it should be possible to compose scaffolds with desired mechanical stability according to the needed application.

The effect of molecular weight Mwon the polymorphous crystallization and melting behavior of poly(Llactide) PLLA (L206, L210 and L214) were systemically studied by differential scanning calorimetry (DSC). Melting and reorganization of conformationally disordered crystals (α′-phase) of PLLA are analyzed with respect to the cooling rate qcin a range between about 4 and 50 K/min and the heating rate qhin a range between about 5 and 200 K/min. It was shown that the α′- to α-crystalline phase transition prior to the dominant melting depends on cooling rate qcand Mw. Unlike very high-MwPLLA L214, for low-MwPLLA L206 crystallized at high qc, the α′-form crystals only partially transformed into the α-modification, and certain amounts of α′-form crystals melted directly without α′- to α-transition during the heating process. With increasing qc, the melting of PLLA L210 changed from phase-transition- and -melting mechanism to the common melt-recrystallization mechanism. It was also found that the polymorphism of PLLA significantly affected the crystallization kinetics. Consequently, the reorganization of α′-crystals into stable α- crystals could be inhibited by fast heating (qh> 150 K/min).

To simulate the specific material properties of thermoplastic polymers a suitable constitutive model is essential. The parallel rheological framework (PRF) model was calibrated and evaluated in this study as potential constitutive model for polymer stent application. Tensile as well as recovery tests with different loading rates were performed using PLLA specimens. In order to calibrate the constitutive model, the conducted material tests were simulated accordingly. The parameters of the model were iteratively varied to obtain good accordance of the simulation with the material tests. In contrast to elastic plastic material models, viscoelastic material behavior can be represented with the nonlinear viscoelastic-plastic PRF model. The generated and possibly further refined model can be used for the simulation of polymer stents.

In this study, DSC experiments were used to elaborate an annealing protocol for injection molded very high molecular weight (VHMW) PLLA with two molecular masses, 320,000 g/mol and 700,000 g/mol. The initial material obtained from the injection molding process was found to be highly amorphous and not in thermodynamic equilibrium state, as distinct cold crystallization and enthalpy relaxation were observed in DSC data. Thermal annealing to 85 °C for 60 - 90 min under controlled conditions using a DSC device showed to be sufficient to stabilize the polymer and increase the crystallinity to up to 50 %. Annealing did not result in any signs of thermal decomposition. The elaborated thermal treatment has been transferred to manual annealing of large specimen geometries for subsequent DMA analysis.

The characterization of mechanical properties of materials used in biomedical applications is essential for performance evaluation. In addition to quasi-static tests, dynamic tests extend the range of methods and allow predictions of failure, as well as information on durability. Appropriate specimen grips according to the test sample geometry are crucial for a reliable examination of mechanical testing and therefore valid experimental data. In particular, the investigation of polymers is challenging, as properties show major differences depending on temperature and applied loading rate. This could result in slipping or tearing of samples in the specimen grip area. Numerical simulations of reference grips, as well as alternative custom designs, were performed evaluating damage due to the clamping process and to provide appropriate specimen grips for future dynamic-mechanical investigations of materials with variable properties. Both the results of the numerical simulation and preliminary tests with 3D-printed prototypes show a distinct improvement in specimen clamping. Plastic deformation and local stress peaks were reduced while maintaining the same tightening torque.

Patients with cardiac arrhythmias are currently treated with conventional transvenous rhythm implants. Complications are frequently associated with intracardiac implanted leads primary insulated by silicone and polyurethane. However, experiences show that polyurethanes in particular are susceptible to various degradation mechanisms including hydrolysis, environmental stress cracking (ESC) and metal ion induced oxidation (MIO). In vivo, pacemaker leads are exposed to a complex thermal, chemical, mechanical and biological loading. The current study focusses on in vitro analyses to assess the biostability of Pellethane 2363 55D and the silicone MED 4765 as cardiac pacemaker lead insulations. Degradation processes were simulated in vitro in a load-free state and under static mechanical loading by subjecting a coaxial lead design to bending radii from 3 mm to 19 mm. Physiological environmental conditions were mimicked using a physiological saline solution and a tempered oxidative solution. Surface morphological and thermal analyses were performed before and after in vitro testing by means of scanning electron microscopy (SEM) and differential scanning calorimetry. Melting temperatures of silicones around 40°C were measured, before and after in vitro testing, respectively. Pellethane insulation layers had two endothermal melting regions at 100°C and 170°C before and a third melting region at 45°C after in vitro testing. The additional melting peak may indicate a change of thermal material properties due to degradation. SEM images showed degradation phenomena similar to in vivo studies, varying in severity and depending on the bending radius. Thus, the relevance of mechanical loading for in vitro replication of clinically relevant lead insulation degradation was demonstrated.

Extrusion is a common manufacturing process for semi-finished polymer products in various biomedical applications. Extrusion enables processing of a wide range of biomaterials, as well as different cross-sectional geometries. Furthermore, feasibility of drug elution, as it is used for a variety of medical devices, for example microstents for minimally invasive glaucoma therapy, was assessed. The current study deals with manufacturing of polymeric microtubes by extrusion processing. Semi-finished products were made of biodegradable poly-L-lactide (PLLA) and a non-biodegradable polycarbonate-based silicone elastomer (SIL) and covered with a polymer/drug combination, with resveratrol as active ingredient. Three different concentrations of polymer/resveratrol were applied by means of spray-coating. The release behavior of active ingredient was analyzed in vitro at 37°C and showed a correlation between the amount of drug and release time. With higher drug content, a faster release was observed. In addition, the release from SIL was faster compared with PLLA.

We present a thermal processing device, equipped for local heating and welding of biomaterials, e.g. electrospun nonwovens or polymer films. Depending on the application and choice of materials, we aim to determine appropriate processing parameters for permanent and non-permanent welds. Due to the modular device structure, applicationspecific heating tools can be used. Process temperature up to 250 °C is feasible.

Electrospinning is used for producing nonwovens for medical polymer-based implants, such as prosthetic valves or covered scaffolds. In this study, nonwovens for prosthetic venous valves are investigated regarding their morphology and mechanics in physiological medium. Spinning molds were developed based on previous venous valve leaflet designs, 3D printed in different sizes and covered with electrospun nonwovens. Samples were stored in a physiological 0.9% saline at 37°C to investigate the influence of fiber rearrangement and swelling in medium for several weeks. Two different nonwovens of thermoplastic silicone-based polycarbonaturethane (TSPCU) were compared. Tensile test results show that storage in medium has a relevant influence on the mechanical properties. SEM images of TSPCU show substantially increased fiber diameters after 8 days stored in medium. After detaching the valve leaflet nonwovens from the molds, shrinkage of the material of approximately 12% was detected. A suitable valve size could be identified for joining with the stent structure into an interventional prosthetic venous valve. The results demonstrate the influence of storage conditions on the morphological and mechanical properties of electrospun TSPCU nonwovens. For development and dimensioning of venous valve leaflets, this change in mechanical behavior and possible shrinkage of the material has to be considered.

Electrospinning (ES) is a suitable and cost effective method to mimic the chemical composition, morphology, and functional surface of natural tissues, for example of the nervous, dermal, vascular, and musculoskeletal systems. This technique is a versatile tool to obtain tailored fibrous scaffolds from various polymer materials. By varying the diameter, porosity, orientation, layering, surface structuring, mechanical properties and biodegradability of the fibers the properties can be adapted for specific applications ranging from implantable medical devices to wound repair and protective clothing. Especially the combination of different polymer types offers a high potential. In this study electrospun two-component nonwoven structures of thermoplastic copolyester elastomer (TPC-ET) and bioresorbable polylactide (PLLA) were fabricated, using different ES setups. A comparative evaluation in terms of porosity, thermal and mechanical properties as well as required fabrication effort, was performed. Nonwovens made from polymer blends and coaxial spun core-sheath fibers showed similar tensile strength, which was higher than dual electrospun fabrics. Porosity was found to be in the range of 80 - 90%. By modifying the polymer solution and process parameters multicomponent nonwoven structures with tailored properties and drug release profiles can be manufactured.

The selection of appropriate test conditions is of critical importance in mechanical testing of biomaterials. In particular the definition of dynamic test conditions is requiring high efforts. In this work, a thermoplastic semicrystalline polymer was characterized regarding mechanical properties by dynamic mechanical analysis (DMA). Timetemperature- superposition (TTS) of dynamic mechanical data provides an efficient method for the experimental design of follow-up studies. Our focus was to provide test conditions for cyclic tests, which correspond to viscoelastic materials. The results show, that the test temperature for dynamic mechanical fatigue tests, as an indicator of mechanical modification for viscoelastic materials, should necessarily remain below the onset temperatures of storage modulus and loss modulus. Moreover, changes in material characteristics due to varying frequencies should be considered when constructing a master curve for the evaluation of test frequencies. Therefore, TTS is particularly beneficial for the rapid determination of test parameters for accelerated material examination.

The novel concept of stenting the Eustachian tube was established to provide an effective and safe therapy of Eustachian tube dysfunction. Biodegradable polymer stents are being developed to restore impaired tube function. As the supporting effect may be required for different time periods, PLA-co-PEG copolymers, PLLGA, PDLLA and PDS, having shorter degradation times compared to PLLA, were evaluated as potential stent materials. Since tensile tests and thermal analyses of solvent cast films from PLA-co-PEG copolymers showed comparable properties to PLLA, stent samples were manufactured from these materials. Mechanical stent testing revealed an increase of elastic recoil and slight decrease of collapse pressure compared to PLLA. In a short term accelerated degradation study a considerable percentage molar mass reduction and an increasing degree of crystallinity depending on PEG content was found. Based on the results obtained, the tested polymers offer a promising, faster degradable alternative to the established stent material PLLA.

Polymer materials can be manufactured with high reproducibility and do offer the potential for chemical modification. This enables matrix property modification and fine-tuning of several material characteristics, such as tissue-implant interaction, inflammatory potential or susceptibility to biofilm formation. Whereas manufacturing protocols are crucial for the resulting material properties, also the evaluation in terms of performance and safety has to be considered. Regarding this, both, temperature and composition of test medium may affect the physicochemical properties of implant materials. The present study addresses the influence of test medium compared to dry test conditions, each at two different temperatures, on the mechanical properties of elastomeric film and nonwoven materials.

The development and advancement of polymeric implant materials is a frequent focus in current research. The combination of polymeric materials with diverging properties provides a wide range of new materials with innovative characteristics. One technology for combining materials is to apply a coated layer onto a base material. In this work, a hyperelastic, synthetic base material was combined with a rigid biopolymer coating layer. A multilayered material with combined characteristics of both was built. In the field of processed polymers, the analysis of coating adhesion is not feasible using established methods. Therefore, a dynamic-mechanical method was investigated, which supplements the uniaxial tensile test and provides knowledge regarding mechanical resistance of the multilayered polymer structure. Furthermore, the method gets validated by SEM-imaging and evaluation of coating composition before and after testing under dynamic conditions.

Fast scanning calorimetry (FSC) is an effective analytical tool to characterize the thermal properties of polymers. Heating rates up to 100 000 K/s allow studies at time scales inaccessible with conventional calorimeters, whose rates are typically less than about 0.5 K/s. Recent studies have successfully demonstrated methods for obtaining quantitative analysis of thermal properties of polymer samples using chip-based FSC. Therefore very small sample sizes, such as particles or nonwovens, can be characterized. In this study, we investigated the thermal properties of poly(L-lactide) PLLA with FSC compared to the results from standard DSC methods. PLLA specimens were fabricated via solution casting and needle electrospinning. The results suggest a significant influence of heating rates on the melting temperature of PLLA. The results show that different fabrication methods lead to changes in crystallinity and that FSC results are not completely comparable with standard DSC measurements.

Electrospun fiber nonwoven materials of different polymer classes provide promising perspectives in almost all fields of application, including medical science. In this paper we present the fiber generation of selected biostable polymers (PBT, TPC-ET, PA 6.12 and PVDF) by direct electrospinning, as an extremely powerful tool for manufacturing of new superfiber implant materials. This initial study includes the variation of some relevant process parameters, such as polymer concentrations or electrode spacing. The influence on fiber morphology, tensile strength and biocompatibility is shown. The results presented indicate that the choice and combination of materials is crucial for the application on load-bearing implants, independent of the processing technology and thus of the fiber bonding, delamination or fiber strength.

While the current generation of devices for minimally invasive treatment of severe symptomatic aortic valve stenosis is based on xenogenic leaflet-material, artificial polymeric leaflet-structures represent a promising approach for future improvement of heart valve performance. For enhanced long-term success of polymeric leafletstructures, limitations regarding calcification and durability have to be addressed. The objective of the presented study was the development of a constitutive law representing the material properties of artificial polymeric leaflet-structures of transcatheter heart valve prostheses in numerical simulation to assess the in silico leaflet-performance. Mechanical characterization of cast films and nonwoven specimens of a polycarbonate based silicone elastomer were conducted by means of uniaxial tension and planar shear testing, respectively. For validation purposes, experimental data were compared with the results of finite-element analysis (FEA) using different hyperelastic models. Strain energy function for third-order ogden hyperelastic model achieved the best fit of the non-linear stress-strain behavior of the isotropic polymeric material with the experimental data. It was chosen for further FEA of valve leaflet-performance under physiological pressurization to analyze the suitability of various manufacturing processes for polymeric leafletstructures. Therefore a specific leaflet-design with a wall thickness of 400 μm was used. As a result of FEA, time dependent leaflet-deformation, leaflet coaptation surface area (CSA) and leaflet opening area (LOA) of cast and nonwoven leaflet-structures were calculated. While LOA was comparable for cast and nonwoven leaflet-structures, obtained leaflet-dynamics in a cardiac cycle under physiological pressurization demonstrated crucial influence of the manufacturing process. For nonwoven leafletstructures, an enhanced CSA could be demonstrated in comparison to cast structures. FEA using a validated hyperelastic constitutive law represents a useful tool for in silico performance evaluation of polymeric leaflet-structures under physiological loading and proves the suitability of the polymeric artificial leaflet-material for percutaneous heart valve prostheses.

Mimicking the structural properties of natural tissue was aimed to be achieved by combining complementary mechanical properties of materials showing high tensile strength with those of high elasticity. By using two polymers with different properties, the advantages of both can be combined to access innovative materials for biomedical applications. Dual co-electrospinning was established to generate biocompatible nonwoven fibre composites with fused properties from polyamide (PA6) and polyurethane based silicone elastomers (PU-co-Si), respectively. By electrospinning both compounds simultaneously, significant advantages, such as combining different fibre thicknesses and mechanical properties, are accessible. Furthermore, the effect on the fibres via an optional post-processing step in the shape of different thermal treatments was investigated. Initial results concerning surface morphology, biocompatibility and tensile properties of the obtained electrospun nonwovens are very auspicious. Thus, the suitability of two complementary polymer classes for tissue biomimicry through a synthetic approach was shown, offering the opportunity of novel implant materials for permanent replacement of biological tissue.

Electrospinning is a method for producing fibrous polymer scaffolds that can be applied in drug delivery systems as well as for polymer-based implants. Biodegradable polymers for the purpose of cardiac tissue engineering are often applied as fibrous scaffolds for morphological mimikry of natural matrices but also drugeluting approaches are very promising. Hydrolytic degradation is one of the key parameters for successful application. The focus of our investigations is on monitoring accelerated in vitro degradation of electrospun nonwoven scaffolds. In the presented study degradation of poly(Llactide) is accelerated by alkaline hydrolysis. The process is characterized by weight loss, loss of molecular mass, surface morphology and thermal behavior of nonwoven samples, showing a fast degradation of the fibrous material within two weeks.

Electrospun poly(L-lactide) (PLLA) nonwoven represent potential options for biodegradable medical implants. They can be manufactured with high reproducibility and do offer the potential for chemical modification to alter matrix properties. In our study, we investigate the mechanical, thermal and morphological properties of PLLA fiber matrices. Fibrous nonwovens were fabricated from polymer solution by needle electrospinning. The polymer solutions were loaded with Triton X-100 (TX- 100), formic acid and tetraethyl ammonium chloride (TEAC) with respect to polymer weight. Morphology of the PLLA nonwoven scaffolds was examined with SEM. We performed uniaxial tensile tests and differential scanning calorimetry (DSC). Different concentrations of the additives TEAC, formic acid and Triton X-100 lead to strong changes regarding mechanical and thermal properties of the electrospun PLLA fiber matrices. In comparison with mechanical properties of established biological tissue materials, the results indicate the suitability for medical applications.

Bacterial biofilm formation on surfaces is still a critical challenge regarding the application of implants. Generally, in order to avoid this, an additional systemic administration of antibiotics is given, which can lead to side effects, such as the reduction of the intestinal flora. Continuous treatment may lead to antibiotics resistance. Within this study we investigated the local drug delivery of N-acetyl-L-cysteine (NAC) from a Poly-L-lactide (PLLA) coating, an ished biodegradable polymer and a polyetherurethane (PEU) coating, a promising representative non-degradable polymer for cardiovascular applications as alternative to the administration of antibiotics. The incorporation of NAC influenced the surface properties of PEU in contrast to that of PLLA. The in vitro NAC release is almost completed after 24 h for PEU. For PLLA only small amounts of incorporated NAC, depending on the NAC loading, is released after a short time. Both systems are rather useful as local NAC delivery system directly after implantation.

The usage of synthetic scaffolds is a promising approach in development of implant materials. In this study we fabricated nanofibrous nonwovens of polyamide 6 (PA-6) by means of electrospinning and performed a systematic characterization with regard to the mechanical and biological performance of scaffold materials. Mechanical strength was assessed by uniaxial tensile testing and biological performance was evaluated by measuring cell viability and qualitative analysis of cellular morphology when human umbilical vein endothelial cells (EA.hy926) or human fibroblasts (HT-1080) were grown on polymeric substrates. While all polymeric materials exhibited an excellent biocompatibility with respect to cell viability, their surface topography promoted the adhesion of endothelial but not fibroblast cells. A better understanding of the physicochemical and morphological material properties with a selective impact on cell adhesion will help to further improve biocompatibility of nonwovens for biomedical applications.

Current research activities focus on personalized, comfortable and safe products for systemic or local drug application in patients. Poly(ethylene glycol) diacrylate is in particular interest as a drug delivery material, as it shows appropriate biological properties such as hydrophilicity and low toxicity. Additionally, as an easily photopolymerizable compound it can be also utilized for the production of scaffolds with the use of different techniques such as stereolithography. Even though it is often used as a biomaterial or as a copolymer in many photopolymer systems for drug delivery, thermomechanical analysis and basic understanding are rare.

The technology of pharmaceutical drug delivery systems (DDS) as an individual and adjustable tool for drug administration has been intensively developed in the last years. Additive manufacturing (AM) techniques, such as stereolithography, are a promising approach towards DDS scaffold manufacturing. Stereolithography, by using layerby- photo-polymerisation, creates DDS scaffolds with highly controlled 3D geometry. Combined with inkjet printing it allows a very precise positioning of the drug depot in the basic scaffold and therefore also a better control of the drug release. Furthermore, this hybrid AM technique also allows for the creation of a multi-drug DDS with a several drug depots localized in desired positions within the scaffold. Determination of the scaffold and drug depot material properties is one of the initial steps for such novel DDS development. Basic characteristics, such as stiffness, elasticity or glass transition temperature (Tg), are important for designing and adapting the material for biomedical application. The photosensitive poly(ethylene glycol) diacrylate (PEGDA) can be easily formed into a desired biocompatible scaffold geometry via stereolithography. In this study we have focused on the evaluation of PEGDA (Mn=700 g/mol) as a pure and copolymer system in combination with other acrylates (butanediol diacrylate, pentaerythritol triacrylate) as possible materials for DDS using this novel hybrid AM technique. Irgacure 2959, a biocompatible photoinitiator (PI), was used as a radical starter for photopolymerisation. Samples varying in PI and coacrylate concentration were prepared by conventional photopolymerisation. Physico-chemical analyses of the samples were performed and several parameters, such as stiffness, elongation at break and glass transition temperatures, were determined.

Insertion of a cochlear implant (CI) into the scala tympani evokes electrode insertion trauma that can result in mechanical damage of the lateral and medial wall and causes ingrowth of fibrous tissue on the implant surface. In consequence, it is of great clinical interest to modify the silicone surface of CI electrodes in order to inhibit and minimize the overgrowth by connective tissue. In this case, the covalent coupling of bifunctional polymers on common CI silicone surfaces is a versatile method to influence the implant cell interaction, but is still a challenge due to the chemically unreactive properties of silicone. We present a sophisticated method to apply a biodegradable polymer coating, such as polylactide or polyhydroxybutyrate, on silicone surfaces to generate a drug delivery system using a covalently bound intermediate layer. The adhesive coatings were applied via spincoating processes with different adherence to the intermediate layer. Changes in surface morphology were investigated by comparison of pure silicone and coated silicone. Specific polymer bands of the infrared spectra were detected by IR spectroscopy. Results indicate a complete coating with polylactide or polyhydroxybutyrate. The presented method is a versatile tool for the coating of silicone CI electrodes with degradable polymer layers.

Plasma enhanced chemical vapor deposition is a promising process for the generation of tailor-made polymer coatings on medical devices in order to improve their implant/ host interaction. The ultra-thin coatings can fulfil a variety of purposes, depending on the monomers used, the process conditions and the location of the coated implants in the human body. In addition, even complex geometries can be coated easily and without the application of solvents. Particularly hydrophilic and hydrophobic plasma polymer coatings can improve biocompatibility, especially in blood contact. Furthermore, the selection of the monomers used enables the generation of specific functional groups for further surface immobilization of drugs, such as proteins, by chemical crosslinking. The release of toxic residues from polymeric implants, such as monomers, additives or degraded components, can also be avoided. The aim of our investigation was the generation of plasma polymer films, their characterization and application as coatings for biodegradable metallic biomaterials in order to retard the degradation process. Metallic biomaterials, in various forms are frequently used in orthopaedics, dentistry, cardiovascular and neurosurgical equipment, because of their tensile strength, fracture toughness, fatigue strength and electrical conductivity. Plasma polymerization was performed using the monomers hexamethyldisiloxane and allylamine. The resulting plasma polymers were analysed in an accelerated degradation test. Both plasma polymers appear to be promising, while polyHMDSO appears to degrade over time and polyallylamine indicates to be stable.

The generation of electrospun nonwovens from polyimide (PI) is challenging as the fibers are prone to distinct delamination. In consequence, the resulting nonwoven material has particularly low structural integrity and loose fibre interlocking, demanding for a follow-up treatment, such as high temperature thermal treatment. In this work, a facile method for a post-processed treatment of PI nonwoven is presented in order to obtain a mechanically stable material while maintaining the characteristics of the electrospun nonwoven. The procedure was performed using a solution of EDA in methanol at 37 °C and ambient pressure to achieve a modified fiber interaction. Overall, the developed protocol opens new possibilities in the processing of PI into delamination-free nonwovens. Potential adverse effects of a high temperature thermal treatment are being avoided, and new applications in the field of medical devices may become accessible.

In various biomedical applications extrusion represents a common manufacturing process for polymeric semi-finished products. Extrusion allows the processing of a wide range of biomaterials, as well as different cross-sectional geometries. The present work focuses on the development of an extrusion process for polymer micro-tubes used for medical devices manufacturing, e.g. microstents for minimally invasive glaucoma therapy. Semi-finished products were manufactured by means of extrusion and dip-coating. Morphology was investigated using biaxial laser measurement and scanning electron microscopy (SEM). For the analysis of mechanical and thermal properties of the specimens uniaxial tensile testing and differential scanning calorimetry (DSC) were performed. While dip-coated micro-tubes reveal a smooth and homogeneous surface, SEM micrographs of extruded micro-tubes exhibit some longitudinal grooves. Mechanical properties of extruded and dip-coated micro-tubes are comparable, so that the presented extrusion process can be regarded suitable for the manufacturing of polymer microtubes in a sub-millimeter scale. A future improvement of nozzle design will allow for a smooth surface of extruded semi-finished products.

At present, a main focus in the field of stent technologies is on the development of biodegradable polymeric stents. Due to inferior material characteristics of polymers compared to permanent metals stents require thicker stents struts to accomplish adequate mechanical properties. Therefore, a thermo-mechanical treatment of polymeric stents was tested, which showed a positive effect on mechanical stent characteristics.

For a long-term efficient drug-eluting stent for vascular applications, the development of drug-loaded coating, combining the effective inhibition of smooth muscle cell proliferation while promoting the re-endothelialization, is a promising concept. However the mostly required simultaneous incorporation of drugs can influence decisively the stability, efficacy and release of the respective drug. Therefore, the mutual influence of a dual local drug delivery coatings based on poly(L-lactide-co-ε-caprolactone) (PLLA-co-CL) containing vascular endothelial growth factor (VEGF165) coupled to the surface and an embedded drug, such as fluorescein diacetate (FDAc) instead of Paclitaxel (PTX) on the in vitro drug release was investigated. Surprisingly, for the investigated coating the immobilized VEGF loading was enhanced and the release profile was accelerated by FDAc incorporation. Even a manifold increase for the in vitro released amounts of VEGF was detected. In contrast, the immobilization of VEGF seems to have a negligible influence on the in vitro FDAc release profiles.

Xenogenic leaflet material, bovine and porcine pericardium, is widely used for the fabrication of surgically implanted and transcatheter heart valve prostheses. As a biological material, long term durability of pericardium is limited due to calcification, degeneration and homogeneity. Therefore, polymeric materials represent a promising approach for a next generation of artificial heart valve leaflets with improved durability. Within the current study we analyzed the mechanical performance of polymeric structures based on elastomeric materials. Polymeric cast films were prepared and nonwovens were manufactured in an electrospinning process. Analysis of cyclic stress-strain behavior was performed, using a universal testing machine. The uniaxial cyclic tensile experiments of the elastomeric samples yielded a non-linear elastic response due to viscoelastic behavior with hysteresis. Equilibrium of stress-strain curves was found after a specific number of cycles, for cast films and nonwovens, respectively. In conclusion, preconditioning was found obligatory for the evaluation of the mechanical performance of polymeric materials for the use as artificial leaflet material for heart valve prostheses.

In the last decades PLLA-based copolymers have been among the most attractive polymeric candidates used to fabricate devices for drug delivery and stent applications in the cardiovascular system. PLLA is biocompatible and biodegradable, exhibits a wide range of erosion times and has tunable mechanical properties. Therefore, the influence of drug incorporation on the physicochemical properties of biodegradable PLLA copolymers were examined in this study using Fluorescein diacetate (FDAc) and Paclitaxel (PTX). A percental amount of these drugs (17.5 %) were incorporated into poly(L-lactide-co-glycolide) (P(LLA-co-GA)) and poly(L-lactide-co-ε-caprolactone) (P(LLA-co-CL)) made via spray coating. The polymer surface properties, such as surface morphology and hydrophilicity were also examined and remained rather unchanged for both polymers after drug loadings. Furthermore, also the contact angle changed rather marginally. However, both polymers have already different thermal properties without the drug embedded, especially the glass transition temperature (TG) is for P(LLA-co-CL) under 37°C and for P(LLA-co-GA) considerable above with around 66°C. An rather high increase in TG achieved by addition of FDAc or PTX, crucial influences the drug release profiles for P(LLA-co-CL) in contrast to P(LLA-co-GA). Besides these results preliminarily experiments of additional coupling of other drugs on the polymer surface were performed and we obtained an influence of FDAc or PTX. The drug incorporation and physicochemical characterization data obtained in this study is relevant in optimizing the incorporation or coupling of further drugs on the polymer surface and delivery properties of these potential multi drug delivery coatings.

For fabrication of polymeric implants and drug carriers volatile organic solvents, such as chloroform, are widely used. In order to remove solvents for patient safety several processes have to be carried out to avoid changes in the thermal characteristics of the polymers, as well as in the drug release profile and mechanical properties. We analyzed films of the polymer poly(ε−caprolactone) (PCL), a common commercial medical grade polymer which is widely used in implants and drug carriers. Considering the influence on the morphology and thermal properties we screened different post treatment processes. Acceptable chloroform contents according to recommendations of the International Council for Harmonisation of Technical Requirements for Pharmaceuticals for Human Use (ICH) without changes in morphology and crystallinity were achieved via a simple annealing process for 24 h at 40°C and 40 mbar.

Although current drug eluting stents show low risks of in-stent restenosis and stent thrombosis, the presence of a permanent foreign body inside the vessel represents a major limitation. In order to overcome this limitation, stents made of biodegradable polymeric materials are currently being developed. The present work describes an optimized fabrication process for tubular semi-finished products for manufacturing of stents made of poly-L-lactide (PLLA). The impact of the haul-off speed as a major parameter during extrusion processing on the cross-sectional area of tubular specimens was analyzed. It could be shown that the crosssection of the extrudate, in particular the tubing diameter and wall thickness, can be adjusted by varying haul-off speed. In a subsequent blow molding process the influence of the holding time on polymer cold crystallization was analyzed. Thermal properties of the polymeric material after processing were examined by differential scanning calorimetry (DSC). The results showed that there is almost no cold crystallization using a holding time of at least 20 minutes. The investigations showed that semi-finished products with variable geometry and improved mechanical properties can be produced with the described extrusion and blow molding process.

In this study, varying amounts of NIPAAm and an ionic liquid (IL), namely 1-vinyl-3-isopropylimidazolium bromide ([ViPrIm]+[Br]−), have been used to synthesize hybrid hydrogels by radical emulsion polymerization. Amounts of 70/30%, 50/50%, 30/70%, 15/85% and 5/95% (wt/wt) of PIL/pNIPAAm were used to produce hybrid hydrogels as well as the parental hydrogels. The adhesive strength was investigated and evaluated for mechanical characterization. Thermal properties of resulting hydrogels have been investigated using differential scanning calorimetry (DSC) in a default heating temperature range (heating rate 10 K min−1). The presence of poly ionic liquids (PIL) in the polymer matrix leads to a moved LCST (lower critical solution temperature) to a higher temperature range for certain hybrid hydrogels PIL/pNIPAAm. While pNIPAAm exhibits an LCST at 33.9 ± 0.3°C, PIL/pNIPAAm 5/95% and PIL/pNIPAAm 15/85% were found to have LCSTs at 37.6 ± 0.9°C and 52 ± 2°C, respectively. This could be used for controlled drug release that goes along with increasing body temperature in response to an implantation caused infection.

Toxic volatile organic chemicals (VOCs), such as chloroform, are widely used in polymer manufacture in the field of implants and polymeric drug carriers. Several processes have to be carried out in order to remove toxic VOCs for patient safety without changing the thermal characteristics of the polymers. Therefore, we analyze the common commercial implant polymer poly(L-lactide) (PLLA) and screen different annealing- and rinsing processes considering influence on their morphology and thermal properties. For PLLA a rinsing step followed by annealing results in acceptable chloroform contents according to the International Council for Harmonisation of Technical Requirements for Pharmaceuticals for Human Use (ICH) recommendations. Annealing processes reveal the lowest chloroform content after one day, which did not further decrease significantly with extended annealing time.

Conventional permanent stent systems for vascular applications are associated with long-term risks, such as restenosis and thrombosis. To overcome these limitations, novel approaches using various biodegradable materials for stent construction have been investigated. In this context, thermal treatment of polymer materials is investigated to adjust the mechanical properties of biodegradable stents. In this work polymeric tubular specimens of biodegradable poly(L-lactide) (PLLA) were extruded and subjected to a molding process using different temperatures above glass transition temperature TG. Physicochemical properties of the molded samples were analyzed using DSC measurements and uniaxial tensile tests. The molding process resulted in a weakening of the PLLA tubular specimens with a simultaneous increase in the degree of crystallinity (χ).

Novel fabrication techniques based on photopolymerization enable the preparation of complex multi-material constructs for biomedical applications. This requires an understanding of the influence of the used reaction components on the properties of the generated copolymers. The identification of fundamental characteristics of these copolymers is necessary to evaluate their potential for biomaterial applications. Additionally, knowledge of the properties of the starting materials enables subsequent tailoring of the biomaterials to meet individual implantation needs. In our study, we have analyzed the biological, chemical, mechanical and thermal properties of photopolymerized poly(ethyleneglycol) diacrylate (PEGDA) and specific copolymers with different photoinitiator (PI) concentrations before and after applying a post treatment washing process. As comonomers, 1,3-butanediol diacrylate, pentaerythritol triacrylate and pentaerythritol tetraacrylate were used. The in vitro studies confirm the biocompatibility of all investigated copolymers. Uniaxial tensile tests show significantly lower tensile strength (82% decrease) and elongation at break (76% decrease) values for washed samples. Altered tensile strength is also observed for different PI concentrations: on average, 6.2 MPa for 1.25% PI and 3.1 MPa for 0.5% PI. The addition of comonomers lowers elongation at break on average by 45%. Moreover, our observations show glass transition temperatures (Tg) ranging from 27 °C to 56 °C, which significantly increase with higher comonomer content. These results confirm the ability to generate biocompatible PEGDA copolymers with specific thermal and mechanical properties. These can be considered as resins for various additive manufacturing-based applications to obtain personalized medical devices, such as drug delivery systems (DDS). Therefore, our study has advanced the understanding of PEGDA multi-materials and will contribute to the future development of tools ensuring safe and effective individual therapy for patients. [ABSTRACT FROM AUTHOR]