Shape memory polymers with visible and near-infrared imaging modalities: synthesis, characterization and in vitro analysis

Abstract

Shape memory polymers (SMPs) are promising for non-invasive medical devices and tissue scaffolds, but are limited by a lack of visibility under clinical imaging. Fluorescent dyes are an alternative to radiocontrast agents in medical applications, they can be utilized in chemical sensors and monitors and may be anti-microbial agents. Thus, a fluorescent SMP could be a highly valuable biomaterial system. Here, we show that four fluorescent dyes (phloxine B (PhB), eosin Y (Eos), indocyanine green(IcG), and calcein (Cal)) can be crosslinked into the polymer backbone to enhance material optical properties without alteration of shape memory and thermomechanical properties. Examinations of the emission wavelengths of the materials compared with the dye solutions showed a slight red shift in the peak emissions, indicative of crosslinking of the material. Quantitative analysis revealed that PhB enabled visibility through 1 cm of blood and through soft tissue. We also demonstrate the utility of these methods in combination with radio-opaque microparticle additives and the use of laser-induced shape recovery to allow for rapid shape recovery below the glass transition temperature. The crosslinking of fluorescent dyes into the SMP enables tuning of physical properties and shape memory and independently of the fluorescence functionality. This fluorescent SMP biomaterial system allows for use of multiple imaging modalities with potential application in minimally invasive medical devices.

Mesoporous Silica Nanoparticles to Tune Oxidative Degradation Rates in Composite Shape Memory Polymers

“…In order to determine antioxidant retention and interactions with particles and films, the fluorescent dye PhB was incorporated in the same manner as the antioxidants into MSNs. However, the majority of the dye seemingly is not reacted and remains as small molecules in the pores of the particles, as demonstrated by the lack of change in the emission or excitation wavelengths of the PhB in the MSNs ( Figure S3), similar to behavior found when using polyurethane microparticles compared to small molecule PhB in the SMP foams [11,24]. This emission spectra change indicates that the small molecules are accumulating in the MSN pores, rather than on the particle surface, and will therefore retain their functionality after polyurethane network formation, rather than being incorporated into the SMP backbone [17].…”

“…This distinct shoulder at 1458 cm -1 may correspond to the peak at 1445 cm -1 displayed in the MSN FTIR spectra, indicating the particle presence in the films. Greater analysis of the these SMPs and the characteristic FTIR peaks are discussed elsewhere [5,10,11,15,16,24]. Importantly, use of antioxidants in the particles did not significantly alter the spectroscopic signal from the SMPs, indicating that the antioxidants may be accumulated within the pores rather than on the particle surface and is therefore not interacting significantly with the material matrix during polyurethane synthesis.…”

“…Fluorescence wavelengths were examined using a Fluoromax Fluorometer (Horiba UK Limited, Middlesex, UK). Selected excitation wavelengths were determined from the literature and confirmed by excitation scans; PhB was excited with approximately 515 nm [11,24].…”

“…Particles were collected and washed in the same manner as described above. Release studies were performed as described for poly(urethane urea) microparticles; emission wavelength shifts were used to characterized structural changes in the dyes at neutral pH (PBS, pH = 7.4) [11,24]. The fluorescence emissions of virgin dye and dye released from MSNs at neutral pH (PBS, pH = 7.4), and high pH (1 M KOH) was used to further confirm no structural changes had occurred.…”

“…In short, fluorescent-dye containing MSNs were incorporated into films in the same manner as for other payload-containing MSNs. After curing, films were immersed in 37 °C PBS, and released dye was characterized in the same manner as previously described [24]. For analysis of degradation rates, cleaned samples were completely immersed in respective solutions of 3% H 2 O 2 (real time oxidation) and 20% H 2 O 2 with 0.1 M CoCl 2 (accelerated oxidation), both stored at 37 ˚C, based upon previously published procedures [5].…”