Polyhedral oligosilsesquioxane (POSS)-based biodegradable polymers were investigated as stent coating for drug delivery from drug-eluting stents and as polymeric scaffold for fully bioabsorbable stents. A highly efficient and precise electrospraying technique, one of the electrostatic processing techniques, was developed for the stent coating application. The roughness of stent coatings produced was varied conveniently by the electrospraying technique utilizing different electrospraying mode or Coulombic fission, and was further modified using post-treatments of pure solvent electrospraying or vapor welding. Abluminal stent coatings were achieved utilizing the targeting nature of the charged electrospraying droplets to avoid luminal coating on stents by applying nonconductive materials temporarily contacting the inner surface of the stents.
Long-standing questions of paclitaxel (PTx)-polymer blend miscibility and interactions were studied for particular polymer blends using characterization methods. It was found that paclitaxel is amorphous in all proportions in the blends of paclitaxel with POSS-based thermoplastic polyurethanes (POSS TPUs), and serves as an antiplasticizer by increasing the blend Tg gradually from the polymer Tg up to the substantially higher Tg of amorphous paclitaxel. The polyethylene glycol (PEG) segment incorporated in POSS TPUs exhibited specific hydrogen-bonding interactions with the paclitaxel and promoted the miscibility in the blends.
Highly adjustable release of paclitaxel was achieved from both thermoplastic stent coatings utilizing P(DLLA-co-CL)-based POSS TPUs, and thermoset stent coatings employing PLGA-POSS end-linked thiol-ene network. Using a newly-developed drug release approximation model describing the entire drug release profile, paclitaxel release mechanisms from these biodegradable stent coatings were interpreted quantitatively, including the effects of polymer glass transition temperature, polymer initial molecular weight, degradation, coating swelling, POSS content, drug concentration, and coating thickness.
Fully bioabsorbable shape-memory stents were fabricated using four cost-effective methods, including dipping coating method, fiber tube fabrication using electrospinning technique, which is another electrostatic processing method, mesh tube welding, and stent writing extrusion. The stent mechanical testing methods to characterize the radial stiffness and collapse pressure of stents were also improved using dynamic mechanical analysis (DMA) combined with a newly-designed stent compression holder.