Applications SMPs in minimally invasive surgery

The implantation of medical devices frequently involves complicated surgical procedures. MIS causes minimal damage to body tissues, greatly reduces the risks associated with surgical procedures, reduces trauma to the patient and accelerates their recovery. Medical devices for MIS need 

SMPs represent a major opportunity for the design of MIS devices for the removal of clots from blood vessels to treat ischaemic strokes. A promising approach presented by Maitland et al. (2002) consists of a polyurethane-based device which can be introduced into the thrombus in a rod-like form via a catheter. When activated photothermaUy the device attains a coil- or umbrella-like form capable of trapping the clot, which can then be mechanically removed from the artery, together with the device (Maitland et al., 2002 Metzger et ai, 2002). 

Block copolymers based on hard segments of crystallizable poly((R)-3-hydroxybutyrate-co-(R)-3-hydroxyvalerate) (PHBV) and switching segments of hyperbranched three-arm poly(3-caprolactone) were proposed by Xue et al. (2010) as biodegradable SMPs for fast, self-deploying stents. Those containing copolymer with 25 wt% PHBV demonstrated almost complete self-expansion at 37°C within just 25 s, which is much faster than current self-deployable stents. 

Gall et al. (2005) also demonstrated the shape recovery of stent prototypes made of thermo-responsive acrylate-based SMPs at physiological temperature. And Wache et aL (2003) proposed a drug-eluting stent based on thermoplastic shape memory polyurethane showing steady drug release characteristics. 

For the optimization of SMP-based stents, their deployment process after insertion can be simulated. Previous simulations of braided stents based on shape memory polyurethanes showed gradual expansion with increasing temperature up to physiological temperature, so that abrupt overpressures to the arteries are avoided during the process (Hyun Kim et a/., 2010). 

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