Unconstrained recovery characterization of shape-memory polymer networks for cardiovascular applications

Abstract

Shape-memory materials have been proposed in biomedical device design due to their ability to facilitate minimally invasive surgery and recover to a predetermined shape in-vivo. Use of the shapememory effect in polymers is proposed for cardiovascular stent interventions to reduce the catheter size for delivery and offer highly controlled and tailored deployment at body temperature. Shapememory polymer networks were synthesized via photopolymerization of tert-butyl acrylate and poly (ethylene glycol) dimethacrylate to provide precise control over the thermomechanical response of the system. The free recovery response of the polymer stents at body temperature was studied as a function of glass transition temperature (T g ), crosslink density, geometrical perforation, and deformation temperature, all of which can be independently controlled. Room temperature storage of the stents was shown to be highly dependent on T g and crosslink density. The pressurized response of the stents is also demonstrated to depend on crosslink density. This polymer system exhibits a wide range of shape-memory and thermomechanical responses to adapt and meet specific needs of minimally invasive cardiovascular devices.

Reduced time as a unified parameter determining fixity and free recovery of shape memory polymers

“…Its liquid monomer tert-butyl acrylate (tBA), liquid crosslinker poly (ethylene glycol) dimethacrylate (PEGDMA) and the photo polymerization initiator (2,2-dimethoxy-2-phenylacetophenone) in powder form were ordered from Aldrich and used in their as received conditions without any further purification. The synthesis procedure of the SMP followed Yakacki et al 31 by mixing the tBA monomer, crosslinker and photo polymerization initiator with a weight ratio of 4,000:1,000:1, and the solution was then exposed to UV irradiation for 10 min before the final heat treatment at 90°C for 1 h to assist the complete conversion of monomers. All the experiments involved in this paper were conducted on a Dynamic Mechanical Analyzer (DMA, TA Instruments, Model Q800) in the tensile mode.…”

“…When an environmental stimulus is applied, the SMP could either provide recovery stresses or return to their permanent shapes, depending on whether or not the external loads still exist, namely the constrained or free recovery condition [14][15][16][17][18][19][20][21][22][23][24][25][26][27][28][29][30] . Since SMPs can sense the environmental changes and then take reactions in a predetermined sequence with deformation, they are considered as a promising alternative for the future's spontaneous shape changing and tunable components in various applications such as microelectromechanical systems, surface patterning, biomedical devices, aerospace deployable structures and morphing structures [31][32][33][34][35][36][37][38][39] .…”

“…Previous experimental work revealed complicated dependency of the SM performance on thermo-temporal conditions in an SM cycle. For example, the recovery of SMPs programmed under the same conditions strongly depends on the recovery temperature and heating rate in the recovery step 43,[46][47][48][49][50][51][52] ; in addition, the programming temperature has been shown to affect significantly the free recovery behaviour for SMPs under the same thermo-temporal recovery conditions 31,[53][54][55][56][57] . To date, because the recovery behaviour of an SMP depends on the aforementioned multiple thermo-temporal input parameters, there is no clear understanding how these input parameters can affect the SM performance individually or collectively.…”

Mechanisms of the Shape Memory Effect in Polymeric Materials

“…On the other hand, a few new shape memory phenomena have been discovered [31][32][33][34][35][36][37][38][39][40][41][42][43][44][45][46][47], which not only enhance the flexibility of the current shape memory technology, but also add in new dimensions for extended versatility and adoptability. Consequently, a number of novel concepts have been proposed for a range of engineering applications [45,[48][49][50][51][52][53][54], in particular in the field of biomedical engineering as of the last couple of years [24,43,[55][56][57][58][59][60][61][62][63][64][65][66][67][68][69][70].…”

Shape‐Controlled, Self‐Wrapped Carbon Nanotube 3D Electronics

“…Recently, significant progress has been made on the fabrication of 3D shapes using shape memory polymers, which undergo shape change in response to external stimulus, such as heat, light, electrical, or magnetic field 5. Examples include the fabrication of microfluidic channels,6 cell encapsulation containers,7, 8 drug delivery microcapsules,8, 9 3D tissue scaffolds,10 and vascular stents 11. In addition, organic transistors have been fabricated onto shape memory polymer substrates for bio‐interface applications 12.…”