Ellipsoidal polymer particles can be prepared from spheres by unidirectional stretching at elevated temperatures, while the particles' aspect ratios (AR) that result from this phantom stretching methodology are often not precisely predictable. Here, an elastic deformation model was exemplarily evaluated for ~50 µm spherical microparticles from PPDL-PTHF block copolymers. The prolate ellipsoidal particles, obtained by stretching in polyvinyl alcohol phantoms, differed in dimensions at identical relative phantoms elongations up to 150%, depending on the relative polymer composition and their systematically altered mechanical properties. Importantly, the resulting particle shapes within the studied range of AR up to ~4 matched the predictions of the elastic deformation model, which includes information of the elastic moduli of phantom and particle materials. These data suggest that the model may be applicable to predict the conditions needed to precisely prepare ellipsoids of desired AR and may be applicable to various deformable particle materials.

Diamond-like carbon (DLC) films combine several excellent properties like high hardness, low friction coefficients and chemical inertness. The DLC coating material can be further classified in two main groups, the hydrogenated amorphous carbon (a-C:H, ta-C:H) and the hydrogen free amorphous carbon (a-C, ta-C). By adding other elements like metals (a-C:H:Me) or non-metal elements like silicon, oxygen, fluorine or others (a-C:H:X), several modifications of the properties can be adjusted according to application requirements. First reports on hard amorphous carbon films were published in the 1950s and about 20years later there began worldwide intensive research activities on DLC. In the following years the number of publications increased continuously and the importance for industrial applications became more and more evident. Several deposition techniques were applied to prepare a-C:H, ta-C, metal containing a-C:H:Me and non-metal containing a-C:H:X coatings. In parallel the structure and deposition mechanisms of DLC coatings were extensively studied. An essential obstacle for a broad industrial application was the high compressive stress level in a-C:H films causing delamination and limiting the film thicknesses. With metal based intermediate layer systems most adhesion problems could be solved satisfactorily and thus from the mid-1990s the pre-conditions for a broad application especially in the automotive industry were given. With modified a-C:H:X and a-C:X coatings a considerable friction reduction or surface energy adjustments could be achieved.

Detailed atomistic simulations were carried out for swelling polymer/gas systems related to experimental sorption and dilation data for CO2 and CH4 in three glassy polymers (polysulfone PSU, the polyimide 6FDA-TrMPD, and a polymer of intrinsic microporosity PIM-1) at 308K (35°C) and pressures up to 50bar. Corresponding experiments were performed with a gravimetric sorption balance and a dilatometer based on a capacitance distance sensor. For each polymer/gas system molecular packing models were prepared and equilibrated for two reference states: the pure polymer is taken as reference for the respective “unswollen” state and similarly the state of the highest penetrant pressure reached in the corresponding experiment is taken to represent the “swollen” state. Models for the latter were constructed in agreement with experimental data (pressure, temperature, gas concentration and volume dilation). Concentration–pressure isotherms of each polymer/gas system were obtained using Grand Canonical Monte Carlo (GCMC) simulations for both reference states (depleted of gas molecules), which are in good agreement with the experimental data in the respective pressure range. As expected these isotherms – due to the simulation technique used, merely based on hole-filling in a static host matrix – do not represent the sorption behavior over a broader range of gas pressures which may involve significant structural rearrangements as well as swelling and relaxational phenomena. Nevertheless, a linear combination of the two GCMC-isotherms allows the interpolation in order to describe the nonlinear gas sorption in the glassy polymers under investigation covering the penetrant pressure range between the reference states in good agreement with the experimental results.

Diamond-like carbon (DLC) coatings are used in many industrial applications like valvetrain-, fuel injection- and piston-systems. For DLC (a-C:H) coatings, prepared by a magnetron based technique using graphite targets, high indentation hardness values of more than 40GPa were achieved. The wear resistance, the microhardness and the coefficient of friction are shown as a function of the hydrogen concentration in the coatings. In order to reduce the coefficient of friction even more and to increase the operational temperature of the coatings from about 350°C for DLC to near 500°C, a new Si-DLC (a-C:H:Si) based layer system was developed using a special magnetron sputter target configuration. This Si-DLC based layer system combines the benefits of a reduced coefficient of friction with a high wear resistance. The DC magnetron cathode based production method allows the deposition of Si-DLC coatings in a wide range of compositions with 4 to 40at.% Si at low hydrogen contents down to 5at.%. These new Si-DLC based coatings with a silicon concentration around 25at.% Si exhibited under dry conditions friction coefficients with only the half of the value of pure a-C:H. This is rather promising for present and future industrial applications.

Many biomaterial-based regenerative therapies require foam structures, which temporarily mimic the extracellular matrix. The pore structure of these scaffolds needs to be tailored to the specific requirements of the clinical application. Poly(ɛ-caprolactone) (PCL) is a semi-crystalline, aliphatic polyester, which is applied as degradable implant material. In this paper we explored how thermodynamic and kinetic conditions in a supercritical CO2 (scCO2) supported foaming process influence the final morphology of the foam. With help of a view cell, we have systematically investigated the foaming with scCO2 in the pressure range from 78 to 200bar at temperatures between 25 and 50°C. Foams were obtained both above the pressure dependent melting temperature (Tm) but also below this temperature, i.e. from supercooled melt states. Foams were characterized by μCT X-ray computed tomography and scanning electron microscopy. The pore size distributions of the obtained foams show characteristic properties (widths, maxima) depending on the initial thermodynamic state of the CO2/PCL system before pressure quenching, the rate of the pressure decay, and the thermal history of the system. We try to rationalize the dependency of foam morphology and quench conditions with thermodynamic model calculations. The initial amount of CO2 in the PCL melt was calculated with the Sanchez-Lacombe equation of state. Pressure quenching with a slow pressure decay rate is considered an isothermal process where for a fast rate an adiabatic process is assumed. Both processes differ in their phase separation mechanism. It turned out that the CO2-induced melting point depression of the semi-crystalline polymer is an important factor. The variation of foaming conditions allows the preparation of scaffolds with specific morphological parameters (mean pore size, pore distribution, and pore connectivity).

A multiscale method for the evaluation of the fluid solubility in glassy polymers with high glass transition temperature T-g is presented and applied to the case of two polyimides. Ultem and Kapton. The method adopts Molecular Dynamics (MD) to simulate the polymer pressure-volume-temperature (pVT) behavior at temperatures above T-g not experimentally accessible. Such values are used to obtain the polymer parameters for the Perturbed Chain Statistical Associating Fluid Theory (PC-SAFT) Equation of State (EoS) required to calculate the gas solubility in the polymers below T-g with the Non Equilibrium PC-SAFT model. The MD-simulated polymer density values agree with the experimental and simulated data available, and the solubility calculated with the Non Equilibrium model represents correctly the experimental values for CH4. N-2, O-2 and CO2 sorption in Ultem, and the CO2 and SO2 solubility in Kapton at different temperatures. The approach can be applied to other high-T-g glassy polymers. (C) 2012 Elsevier B.V. All rights reserved.

The regeneration of tissues and organs has been a matter of dream and Greek mythology since ancient times as the liver regeneration in Prometheus punished by Zeus. It is now emerging a new way of treating injuries and diseases, which is based on regenerative medicine.Clinical and social needs related to the aging and diseases led to innovative medical therapies that will enable the repairing and regeneration of damaged tissues and organs.This position paper gives a future vision for 2030 of the biohybrid organs and tissues that will be used for patient therapy and in the overcoming the age-related pathologies. The research strategies for the next 20 years will focus on the implantation of bioartificial tissues and the induction of the regeneration. Biomaterials and bioreactor technologies will play pivotal roles in the regeneration and in the production of individualized biological implants. Future challenges will include the development of multifunctional biohybrid organs and tissues. These concepts are based on a multidisciplinary approach bringing together various scientific fields, which will contribute to the new and fascinating medical therapies.

Abstract Polymerbasierte, abbaubare Biomaterialien sind eine Schlüsseltechnik für die moderne Medizin. Sie kommen in verschiedenen Medizinprodukten und Wirkstofffreisetzungssystemen zum Einsatz. Es ist zu erwarten, dass multifunktionale Polymere wesentliche Beiträge zu kausalen (regenerative Medizin), schonenden (minimalinvasive Medizin) und gezielten (Nanomedizin) Therapien leisten werden.

We present a method which allows to calculate gas sorption in complex polymers where, as slow processes, gas induced plasticization and volume dilation are important factors. Since the relaxational swelling of the polymer matrix that is observed at elevated gas concentrations takes hours or days, the swelling process is orders of magnitudes too slow to simulate the respective molecular dynamics in reasonable time and effort. To address this apparent incompatibility of experiment and simulation, we use single representative reference states from experiment and construct atomistic packing models according to these specifications. Gas sorption of CO2 and CH4 was successfully calculated on polysulfone, a 6FDA-polyimide, and a polymer of intrinsic microporosity, PIM-1, at 308 K and pressures up to 50 bar.

The dual- and triple-shape effects of multiphase polymer networks that contain two crystallizable chain segments have been assessed in situ by combining X-ray measurements with thermomechanical investigations. The studied polymer, named CLEG, is a multiphase polymer network of crystallizable poly(ε-caprolactone) (PCL) with grafted poly(ethylene glycol) (PEG) side chains. Wide-angle (WAXS) and small-angle X-ray scattering (SAXS) measurements were combined with temperature-controlled in situ tensile testing experiments. This integrated approach enables systematic investigation and interpretation of relevant structural features during the programming procedures and the thermally-induced recovery process. Main results concern the combined effect of PCL and PEG crystals on shape fixation, the specific role of low-melting PCL crystallites in the fixation of the low temperature temporary shape, and the different orientation behavior of PCL and PEG crystals during certain stages of the programming procedure. These results demonstrate that crystal orientation effects are dominant for the PCL crystals. The effects of the low temperature PCL crystals could only be investigated when synchrotron radiation was applied. These findings indicate the great potential of in situ X-ray investigations for the creation of design-relevant knowledge about the microscopic foundations of dual- and triple-shape effects in appropriate polymer systems.

Molecular models of gelatin-based materials formed the basis for the knowledge-based design of a physically cross-linked polymer system. The computational models with 25 wt.-% water content were validated by comparison of the calculated structural properties with experimental data and were then used as predictive tools to study chain organization, cross-link formation, and estimation of mechanical properties. The introduced tyrosine-derived side groups, desaminotyrosine (DAT) and desaminotyrosyl tyrosine (DATT), led to the reduction of the residual helical conformation and to the formation of physical net-points by π-π interactions and hydrogen bonds. At 25 wt.-% water content, the simulated and experimentally determined mechanical properties were in the same order of magnitude. The degree of swelling in water decreased with increasing the number of inserted aromatic functions, while Young's modulus, elongation at break, and maximum tensile strength increased.

Biodegradable polymers are applied in temporary implants, such as surgical sutures and controlled drug delivery systems. They are also of relevance in biomaterial-based Regenerative Therapies, where they provide a temporary substitute of the extra-cellular matrix. A major limitation of established degradable implant materials is the fact, that their degradation behavior can not be reliably predicted applying existing experimental methodologies. Therefore a knowledge-based approach is clearly needed to overcome this problem and to enable the tailored design of biodegradable polymers. Here we describe two methods, which can be applied in this approach: molecular modeling combining atomistic bulk and interface models with quantum chemical studies and experimental investigations of macromolecule degradation in Langmuir monolayers. The polymers utilized to exemplarily illustrate the concepts are aliphatic (co)polyesters [e.g. poly(-caprolactone) (PCL), polyglycolide (PGA), poly(rac-lactide) (PDLLA), poly[(rac-lactide)-co-glycolide] (PLGA)] and copoly(ether)esteruretanes as multiblock copolymers. The molecular modeling approach permits to efficiently investigate the influence of micro-structural properties like free volume distribution, cohesive energy density and concentration of polar functional groups on the bulk water uptake as one constituent part of hydrolytic degradation. The Langmuir monolayer investigations on polymer degradation on the other hand yield the dynamics of bond splitting during degradation within hours separately from time consuming diffusion processes, which may take months in bulk samples.

A reversible triple-shape effect is achieved for multi-phase polymer networks based on two different crystallizable segments The reversibility of the two shape-changes is based on crystallization induced elongation (CIE) occurring during cooling and melting-induced contraction (MIC) during heating under constant stress

This chapter contains sections titled: Introduction Basics of Molecular Modeling of Polymer-Based Membrane Materials Selected Applications Summary References

A comparative study of five different experimental and computational methods is presented for the characterization of the overall free volume (FV) and the free volume element (FVE) size and shape distribution in amorphous glassy perfluoropolymers (PFPs). Experimental results from the photochromic probe (PCP) method, positron annihilation lifetime spectroscopy (PALS), and inverse gas chromatography (IGC) were confronted with literature data from Xe-129 NMR spectroscopy, and the experimental data were further compared with molecular dynamics (MD) simulations and a combination of MD studies and the well-known Bondi method as well as a modified Bondi method. An evaluation of the advantages and the limits of each method is presented. This is the first reported study on a so vast number of complementary techniques applied on a single glassy polymer, in this case Hyflon AD perfluoropolymer, and is also the first successful application of the photochromic probe technique in such materials. In two different grades of Hyflon AD, the polymer with the highest content of the stiff cyclic comonomer was found to have a slightly larger average FVE size but a lower void concentration, explaining the nearly identical density and fractional free volume (FFV) of the two samples. PALS furthermore demonstrated a similar trend for solution-cast samples in comparison with melt-pressed samples, the latter having FVEs with a smaller size but a higher concentration. The data from IGC seem to correspond most closely to those of the PCP method. Differences between the results from the individual techniques derive mainly from the fundamentally diverse nature of the various probing methods but also from the different capacity to take into account the FVE shape. Only MD Simulation studies, using detailed atomistic packing models, can give such deep insight into the spatial arrangement of the FVEs directly. Besides giving the highest level of detail, MD simulations can thus help to understand the possible limits of the experimental methods. Knowledge of their free volume distribution is of fundamental importance to gain more insight into the mass transport phenomena in these materials, relevant for their successful application in the emerging Field of synthetic membranes for gas and vapor separations.

The concept of hydrolytically degradable biomaterials was developed to enable the design of temporary implants that substitute or fulfill a certain function as long as required to support (wound) healing processes or to control the release of drugs. Examples are surgical implants, e.g., sutures, or implantable drug depots for treatment of cancer. In both cases degradability can help to avoid a second surgical procedure for explanation. Although degradable surgical sutures are established in the clinical practice for more than 30 years, still more than 40% of surgical sutures applied in clinics today are nondegradable.1 A major limitation of the established degradable suture materials is the fact that their degradation behavior cannot reliably be predicted by applying existing experimental methodologies. Similar concerns also apply to other degradable implants. Therefore, a knowledge-based approach is clearly needed to overcome the described problems and to enable the tailored design of biodegradable polymer materials. In this Progress Report we describe two methods (as examples for tools for this fundamental approach): molecular modeling combining atomistic bulk interface models with quantum chemical studies and experimental investigations of macromolecule degradation in monolayers on Langmuir-Blodgett (LB) troughs. Finally, an outlook on related future research strategies is provided.

In an effort to better understand the initial mechanism of selectivity and membrane association of the synthetic antimicrobial peptide NK‐2, we have applied molecular dynamics simulation techniques to elucidate the interaction of the peptide with the membrane interfaces. A homogeneous dipalmitoylphosphatidylglycerol (DPPG) and a homogeneous dipalmitoylphosphatidylethanolamine (DPPE) bilayers were taken as model systems for the cytoplasmic bacterial and human erythrocyte membranes, respectively. The results of our simulations on DPPG and DPPE model membranes in the gel phase show that the binding of the peptide, which is considerably stronger for the negatively charged DPPG lipid bilayer than for the zwitterionic DPPE, is mostly governed by electrostatic interactions between negatively charged residues in the membrane and positively charged residues in the peptide. In addition, a characteristic distribution of positively charged residues along the helix facilitates a peptide orientation parallel to the membrane interface. Once the peptides reside close to the membrane surface of DPPG with the more hydrophobic side chains embedded into the membrane interface, the peptide initially disturbs the respective bilayer integrity by a decrease of the order parameter of lipid acyl chain close to the head group region, and by a slightly decrease in bilayer thickness. We found that the peptide retains a high content of helical structure on the zwitterionic membrane‐water interface, while the loss of α‐helicity is observed within a peptide adsorbed onto negatively charged lipid membranes. Copyright © 2009 European Peptide Society and John Wiley & Sons, Ltd.

Phosphatidylgylcerols (PGs) and Phosphatidylethanolamines (PEs) are of considerable interest because they are major lipid components of bacterial membranes and the non-charged PE can also serve as a model for cell membranes of multi-cellular organisms. Here, we report molecular dynamics (MD) simulations studies of the structural and dynamics properties of negatively charged POPG and zwitterionic POPE bilayers. The hydrocarbon chain fluidity and the electron density distribution of various groups along the bilayer were extensively analyzed and compared with the available experimental data. A specific focus was given on hydrogen bond formations and position of sodium ions in the lipid bilayers. These validated and equilibrated models were subsequently employed to investigate selectivity and mechanism of action of the antimicrobial peptide of interest. We found that hydrogen bonding and electrostatic interactions potentially play a role in the adsorption of a peptide to the membrane interface. We observed the peptide's insertion into the membrane can decrease the order parameter and induce local membrane deformation.

The super-molecular structure and morphology of shape-memory polymers (SMP) have an evident influence on the shape-memory effect (SME). More detailed information on these structure-function relations during the dynamic processes of programming and shape recovery are required to better understand the SME. Here we explore whether wide and small angle x-ray scattering (WAXS, SAXS) in combination with deformation experiments can help to characterize and better understand the respective materials super-molecular structure (spatial organization of chain segments in crystalline and non-crystalline regions, characterized by parameters such as crystallinity, crystallite-sizes, domain-sizes and -arrangements) and its changes upon varying mechanical loads and temperature increase as stimulus. Multiphase polymer networks based on poly(s-caprolactone) and poly(cyclohexyl methacrylate), whose molecular structures allow formation of at least two separated domains, were investigated using WAXS and SAXS, to describe the respective super-molecular structures and morphologies and their development during cyclic, thermomechanical tensile tests reproducing key features of shape-memory programming and recovery. The creation of the triple-shape capability for this AB polymer network system is performed by a one-step process, which is similar to a conventional dual-shape programming process. It could be shown via SAXS that a long period between crystalline domains exists for these polymer networks. The value of this long period changes by some nanometers as a consequence of programming and the resulting elongation of the respective sample. Further insights could be obtained by investigating WAXS diffraction peaks, detected at different steps during the ther-momechanical treatment. It could be shown that crystal sizes in this polymer system remain unaffected by the programming process, while the crystallization of the stretched samples during the cooling process leads to a spatial rearrangement (preferential orientation) of crystalline do-mains.

This paper reports computational simulations at two different scales employed to investigate the hydrolytic degradation of two homopolyesters: polyglycolide, PGA and poly(L-lactide), PLLA. Atomistic bulk models were used to investigate the dry and various hydrated states of the two systems. In addition, the first moments of contact between the polymers and water were studied employing atomistic interface models. A higher affinity of water to polyglycolide in comparison with poly(L-lactide) was observed, while diffusion of water was found to be lower in the first polymer. Quantum chemical calculations for the first step of the water-assisted hydrolysis revealed a higher resistance to hydrolytical scission of the L-lactyl units in comparison to glycolyl units.