Effect of Core Nanostructure on the Thermomechanical Properties of Soft Nanoparticles

Abstract

The mechanical properties of nanoparticles, especially those designed for biomedical purposes, have a large impact on their performance and have been scarcely studied. Thermoresponsive polymer-based nanoparticles are increasingly being used in biomedical applications; therefore, it is crucial to determine their thermomechanical response in the regime beyond their volume phase transition temperature (VPTT). The morphological characterization and comparison of thermoresponsive nanogels (NGs), silica core nanogels (SiO2@NGs), and nanocapsules (NCs) in liquids, both below and above the VPTT, are explored in this study. We employed atomic force microscopy in Peak Force QNM mode as well as dynamic light scattering, nanoparticle tracking analysis, and cryogenic electron microscopy (cryo-TEM). Surprisingly, nanocapsules presented increased resistance to deformation, when compared to nanogels, above the VPTT. This was attributed to differences in the cross-link density radial distribution between nanogels and nanocapsules derived from the synthetic approach employed. In addition, the Young’s modulus was calculated from nanoindentations and by computer simulations, showing a significant change in NCs upon crossing the VPTT from MPa to GPa. Conversely, NGs displayed a Young’s modulus in the kPa range, both below and above the VPTT. The findings of this study show that structural design and thermoresponsivity strongly influence the thermomechanical properties of nanoparticles. This in turn needs to be taken into consideration in the design of future nanocarriers.

Polyglycerol-Based Thermoresponsive Nanocapsules Induce Skin Hydration and Serve as a Skin Penetration Enhancer

“…19−23 Furthermore, seeded precipitation polymerization was performed, in which the methacrylic groups acted as anchoring points to grow a polymeric network around the silica NPs, resulting in the formation of SiO 2 @NGs. 24 N-Isopropylacryl amide (NIPAM) in combination with Nisopropylmethacryl amide (NIPMAM) in different ratios served as thermoresponsive building blocks and dendritic polyglycerol (dPG) as a macrocross-linker (Scheme 1). dPG is a well-known, highly hydrophilic, and biocompatible macro-molecule, which can be easily functionalized.…”

“…These "defects" within the polymeric network could result in highly flexible NPs even above the volume phase transition temperature (VPTT). 24,27 In this study, 33-weight percent (wt %) of dPG was kept constant in all reactions to ensure a similar structure and physical properties throughout the study, as well as sufficient hydrophilicity within the particles to avoid aggregation and precipitation upon increasing temperature above VPTT. 28 It was aimed to obtain SiO 2 @NGs with soft and dense shells and total diameters of around 150−300 nm (comprising a core diameter of ca.…”

Environmental Liquid Cell Technique for Improved Electron Microscopic Imaging of Soft Matter in Solution

“…Previous reports on the structure of PNIPAM NGs reveal an inhomogeneous structure in which the crosslinking density is parabolically higher at the core than at the shell, giving a core-shell appearance (Kratz et al, 2001;Takata et al, 2002;Stieger et al, 2004;Crassous et al, 2009;Nishizawa et al, 2019;Osorio-Blanco et al, 2020). Considering this structure and the density of PNIPAM (1.149 g/cm 3 ) chains, it is realistic that we could not resolve the outer hairy structure of the NG.…”

“…The resultant NGs were dispersed in water at 1 mg/mL. PNIPAM NGs with a silica nanoparticle in their core were prepared following a previously reported methodology (Osorio-Blanco et al, 2020). Briefly, 90-nm-size silica nanoparticles were synthesized using the Stöber method and then modified with 3-(trimethoxysilyl) propyl methacrylate (5.3982 × 10 −18 g TPM per silica nanoparticle) by stirring the silica nanoparticles together with the silane for 12 h at room temperature and then refluxing the mixture for 1 h. The modified silica nanoparticles were centrifuged (6,000 rpm) three times and re-dispersed in denatured ethanol.…”

Adaptive Flexible Sialylated Nanogels as Highly Potent Influenza A Virus Inhibitors

“…The mechanical properties of NGs were studied by stable sample immobilization on a substrate by atomic force microscopy (AFM) in PeakForce QNM (Quantitative NanoMechanics) mode (Figure c). The technique has been applied to quantify the elasticity and deformation capacity of soft NGs and nanocapsules in solution . In PeakForce mode, the AFM tip repeatedly pushes the sample surface with a constant maximal force at each point being scanned.…”