In vitro study of drug-eluting stent coatings based on poly(L-lactide) incorporating cyclosporine A - drug release, polymer degradation and mechanical integrity.

In this study, absorbable polymer stent coatings for localized drug delivery based on poly(L-lactide) (PLLA) and cyclosporine A (CsA) were developed and tested in vitro. Metallic stents were coated with different compositions of PLLA/CsA (70/30, 60/40, 50/50% w/w) and beta-sterilized. The specimens were used to assess the drug release kinetics with HPLC. Sterilization influenced polymer degradation was measured with GPC. Mechanical integrity of the stent coatings was studied with SEM. The interconnection of the coated stents with a balloon-catheter was characterized by the measurement of stent dislodgment force. A migration assay was used to determine the inhibitory effect of the model drug CsA on smooth muscle cell (SMC) migration. The release of CsA was established over time periods up to 24 days in sodium chloride solution and in porcine blood plasma. An inhibition of SMC migration (max. 26-33%) was found for CsA concentrations of 4 x 10(-5) to 4 x 10(-7) mol/l. Marked molecular weight reduction (70-80%) of the PLLA matrix occurred after beta-sterilization. We also observed a substantial decrease of in vitro degradation time. The maintenance of the mechanical integrity of the polymer coating during crimping and dilation of the specimens could be verified, and a sufficient stent dislodgment force of 0.8-0.9 N was measured.

In vitro and in vivo studies on blends of isotactic and atactic poly (3-hydroxybutyrate) for development of a dura substitute material.

Blends of semicrystalline isotactic poly(3-hydroxybutyrate) (PHB) with amorphous atactic PHB (at-PHB) were prepared by solution-casting using 30%, 50% and 70% at-PHB, and were studied for medical applications. The mechanical properties of the blends including the elastic modulus and elongation at break are strongly affected by the blend composition. The elastic modulus decreases with increasing fraction of at-PHB in the blend from 3350 MPa in the case of PHB to 170 MPa of PHB/at-PHB (30/70). In contrast, the elongation at break increases from 2% in pure PHB up to 50% in the case of the blend with 70% at-PHB. The in vitro degradation is changed as well. The molecular weight of PHB/at-PHB (30/70) is reduced to 5% after 2 years storage in phosphate buffer compared to 35% for pure PHB stored at identical conditions. The in vitro cell vitality is slightly reduced depending on the composition. PHB/at-PHB blends with 30% and 50% at-PHB were selected as dura substitute in minipigs based on the results of the in vitro investigation and the mechanical testing. Patch films with a structured surface on one side were fabricated by a dipping-leaching method. Dura defects were clinically and histologically examined 3, 6, and 9 months after implantation, confirming defect closure, prevention of adhesions to brain tissue, and no signs of inflammation or malignant degeneration. The PHB-based patch materials fulfill the requirements which are necessary for a dura substitute.

[In vitro culture of cells from respiratory mucosa on foils of collagen, poly-L-lactide (PLLA) and poly-3-hydroxy-butyrate (PHB)]. / In-vitro-Kultivierung von Zellen der respiratorischen Schleimhaut auf Matrizes aus Kollagen, Poly-L-Laktid (PLLA) und Polyhydroxybuttersäure (PHB).

BACKGROUND: The replacement of respiratory mucosa after surgical resections at different locations in the ENT-field (trachea, nasal septum, sinus maxillaris) seems to be essential or at least of great benefit for patients. Presently a satisfying solution for this challenge does not exist. Therefore we have analysed the growth of cells from respiratory mucosa on different matrices. METHODS: Cell cultures are initiated mainly by growing out cells from tissue pieces but also by seeding of cells after enzymatic dissociation (sequential trypsinization) of mucosa. Cells were cultured with serum-containing and serum-free media on 3 different foils: made of collagen, of Poly-L-lactic acid (PLLA) and Poly-hydroxybutyric acid (PHB). Culturing time was on average about 4 - 5 weeks. RESULTS: On all tested materials fibroblasts and epithelial cells have grown in principle. PLLA was the material with best properties concerning the aim of this study whereas culturing of cells on PHB only happens after surface modification by amino-functionalisation with plasma treatment. Visualisation of cells on materials of collagen could not realised by light-microscopy due to the 3-dimensional structure and the optical properties of this material. Here the cultures were analysed by cell membrane staining and by REM. We could not find a differentiation of epithelial cells with beating cilia 6 weeks after starting the culture. However 20 days after starting the culture on PLLA (good conditions for observation with light-microscope) cells with beating cilia could be observed, in our opinion resulting from dissociated cells from tissue pieces and not from proliferated cells. CONCLUSIONS: In principle the analysed materials are useful for the culturing of cells from respiratory mucosa. However, for obtaining differentiated epithelial cells the culture conditions have to be modified.

In vitro and in vivo degradation studies for development of a biodegradable patch based on poly(3-hydroxybutyrate).

For the development of a resorbable gastrointestinal patch, the in vitro degradation of solution-cast films of poly(3-hydroxybutyrate) (PHB), modifications of PHB expected to influence its degradation time, as well a poly(L-lactide) (PLLA) was examined. The molecular weight of pure PHB decreased by one-half after 1 year in buffer solution (pH 7.4, 37 degrees C). Acceleration in molecular weight decrease was observed by blending with atactic PHB, whereas no influence was found with low-molecular weight PHB. Leaching of a water-soluble additive led to a slight acceleration of PHB degradability. In contrast, a deceleration in degradation rate was observed with the addition of a hydrophobic plasticizer. In vitro tests indicated an accelerating effect of pancreatin on PHB degradation, whereas PLLA degradation remained essentially uninfluenced. In comparison to simple hydrolysis, the degradation rate of PHB was accelerated about threefold. From the in vitro results, a PHB/atactic PHB blend was selected for repair of a bowel defect in Wistar rats. A patch film was fabricated by a dipping/leaching method. Twenty-six weeks post-implantation, material remnants were found in only one of four animals. The bowel defects were closed in all cases. It could be assessed that the patch material resists the intestinal secretions for a sufficiently long time but that it finally degrades completely.