Cellulose nanocrystals (CNC) reinforced shape memory polyurethane ribbons for future biomedical applications and design

Abstract

Shape memory materials are an innovative type of materials that reversibly store a temporary shape and recover back to the original dimensions with the application of an external mechanism such as heat. Shape memory polymers (SMP), specifically thermoplastic SMP (e.g. shape memory polyurethane (SMPU)) have received much attention during the past decade because of the promising future applications and advantages such as ease of processability for thermoplastic SMP (e.g. by 3-D printing), cost, and biocompatibility. In the biomedical field, applications such as stents, surgical sutures, and orthodontic devices, amongst others have been proposed. The addition of fillers to the material can modify the material to improve their load bearing capabilities. Bio-based fillers such as cellulose nanocrystals (CNC) have been proposed in a variety of reinforcing applications. The present work focuses on the experimental description of the addition of nonmodified CNC to SMPU. The work studied the effect on melt-extruded ribbons, for 0, 0.5, 1, 2, and 4 wt%. An increase of yield point, toughness, flexural modulus, recovery rate, and decrease of total time showed that SMPU/CNC nanocomposites are a potential candidate to use in future biomedical applications.

Cellulose nanocrystals reinforced shape memory polymer cardiovascular stent

“…The addition of up to 7 Wt.% CNC did not change T m significantly. Similar results were also obtained in previous work (Garces et al, 2018). Although the start of melting was seen at around 156°C in the DSC results, this temperature could not be used as the printing temperature in the EBAM process.…”

“…As the amount of CNC further increases, T g remained stable. Similar results were also reported earlier (Garces et al, 2018). The reduction of T g implies that the CNC addition may enhance the recovery performance of the material, as the recovery of an SMP was typically triggered at around T g (Huang et al, 2011).…”

“…PRISM USA LAB 16 twin-screw extruder (Thermo Fisher Scientific, USA) was used to perform the melt-compounding extrusion. Based on our group's previous works (Garces et al, 2018;Villacres et al, 2018), the nozzle temperature was set at 230°C and there was a 5°C decrement in each of the three subsequent heating zones toward the hopper. After the extrusion, the materials were cooled in a water bath and pelletized with a length of 1 mm.…”

“…Therefore, under our experimental condition (temperature range 23-40°C), CNCs were expected to behave like a linear elastic material. In addition, CNCs were found to have a high Young's modulus of 100-140GPa (Garces et al, 2018;Klemm et al, 2005;Nicharat et al, 2017). By adding CNCs, the elastic component effectively increased [Figure 5(b)], leading to the appearance of a residual force after cooling.…”

“…Based on these facts, PU and CNCs can be identified as compatible candidates for the fabrication of polymer composites (Özgür Seydibeyoǧlu and Oksman, 2008). In our group's previous work, CNCs have been successfully embedded into PU-based SMP matrix with a simple melt-mixing technique and they were shown to improve the toughness, flexural modulus and recovery properties of the nanocomposites (Garces et al, 2018).…”