Materials for biomedical applications are often chosen for their bulk properties. Other requirements such as a hemocompatible surface shall be fulfilled by suitable chemical functionalization. Here we show, that linear, side-chain methylated oligoglycerols (OGMe) are more stable to oxidation than oligo(ethylene glycol) (OEG). Poly(ether imide) (PEI) membranes functionalized with OGMes perform at least as good as, and partially better than, OEG functionalized PEI membranes in view of protein resistance as well as thrombocyte adhesion and activation. Therefore, OGMes are highly potent surface functionalizing molecules for improving the hemocompatibility of polymers.
Cell stimulation by bioactive molecules has become an important tool in tissue engineering. The homogeneous incorporation of such molecules within the bulk of a polymer-based scaffold compared to surface coating is considered advantageous for most applications and minimizes a burst effect. An efficient way of bulk loading is the incorporation of these molecules during the scaffold formation process. In this paper, two different integrated processes for the preparation of scaffolds from poly(epsilon-caprolactone) (PCL) loaded with a small molecule are investigated. Both formation and loading of the scaffold is carried out in a single-step process. Sudan Red G was selected as a model compound for lipophilic small molecules. A freeze drying and pressure quench (PQ) formation process was selected, and the influence of the small molecule on the formation processes and on the morphology of the obtained scaffold was evaluated and compared. It could be shown for both processes that the formation of loaded scaffolds is possible, and that the small molecule has a very high impact on the foam morphology. In case of the freeze-drying (FD) method, only a load of 1 wt% Sudan Red G was incorporated within the bulk and showed no influence on the foam morphology. In the case of PQ foaming, an incorporation of 43 wt% Sudan Red G was achieved (although tiny crystal needles of the small molecule were found on the surface) and a strong effect on the foam morphology was found. This paper presents an efficient method of incorporating small molecules by integrated processes.
The chain length and end groups of linear PEG grafted on smooth surfaces is known to influence protein adsorption and thrombocyte adhesion. Here, it is explored whether established structure function relationships can be transferred to application relevant, rough surfaces. Functionalization of poly(ether imide) (PEI) membranes by grafting with monoamino PEG of different chain lengths (Mn =1 kDa or 10 kDa) and end groups (methoxy or hydroxyl) is proven by spectroscopy, changes of surface hydrophilicity, and surface shielding effects. The surface functionalization does lead to reduction of adsorption of BSA, but not of fibrinogen. The thrombocyte adhesion is increased compared to untreated PEI surfaces. Conclusively, rough instead of smooth polymer or gold surfaces should be investigated as relevant models.
Shape-memory polymer foams based on poly(ω-pentadecalactone) (PPDL) and poly(εcaprolactone) (PCL) multiblock copolymer with 60 wt% PCL content were prepared by environmentally-friendly high pressure supercritical carbon dioxide (scCO 2 ) foaming technique. A foam with a density of approximately 0.11 ± 0.02 g/cm 3 and an average pore size of 150-200 μm with excellent compressibility and shape-memory properties was created at 25 bar/s depressurization rate in the temperature range between 78 and 84 o C. The shape-memory behavior of this foam was investigated using different programming modules, such as under stress-free condition and under constant strain condition. The thermally-induced shape-memory effect (SME) was found to be strongly dependent on the programming conditions. Excellent shape fixity has been observed for all foams indicating the high efficiency of the switching domains to fix the temporary shape by crystallization. The stress recovery of this foam could be controlled by changing compression percentage (ε c %) at a constant compression temperature. The production of these foams with unprecedented properties by commercially available processing equipment raises much hope with the potential to provide new materials with a unique combination of shape-memory properties and porous structure as well as desired properties for many industrial and biomedical applications
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