The biocompatibility and performance of reagents for in vivo contrast-enhanced magnetic resonance imaging (MRI) are essential for their translation to the clinic. The quality of the surface coating of nanoparticle-based MRI contrast agents, such as ultrasmall superparamagnetic iron oxide nanoparticles (USPIONs), is critical to ensure high colloidal stability in biological environments, improved magnetic performance, and dispersion in circulatory fluids and tissues. Herein, we report the design of a library of 21 peptides and ligands and identify highly stable self-assembled monolayers on the USPIONs' surface. A total of 86 different peptide-coated USPIONs are prepared and selected using several stringent criteria, such as stability against electrolyte-induced aggregation in physiological conditions, prevention of nonspecific binding to cells, and absence of cellular toxicity and contrast-enhanced in vivo MRI. The bisphosphorylated peptide 2PG-S*VVVT-PEG4-ol provides the highest biocompatibility and performance for USPIONs, with no detectable toxicity or adhesion to live cells. The 2PG-S*VVVT-PEG4-ol-coated USPIONs show enhanced magnetic resonance properties, r (2.4 mM·s) and r (217.8 mM·s) relaxivities, and greater r/ r relaxivity ratios (>90) when compared to those of commercially available MRI contrast agents. Furthermore, we demonstrate the utility of 2PG-S*VVVT-PEG4-ol-coated USPIONs as a T contrast agent for in vivo MRI applications. High contrast enhancement of the liver is achieved as well as detection of liver tumors, with significant improvement of the contrast-to-noise ratio of tumor-to-liver contrast. It is envisaged that the reported peptide-coated USPIONs have the potential to allow for the specific targeting of tumors and hence early detection of cancer by MRI.
Hydrogels have become popular in biomedical applications, but their applications in muscle and tendon-like bioactuators have been hindered by low toughness and elastic modulus. Recently, a significant toughness enhancement of a single hydrogel network has been successfully achieved by the Hofmeister effect. However, little has been conducted for the Hofmeister effect on the hybrid hydrogels, although they have a special network structure consisting of two types of polymer components. Herein we fabricated hybrid poly(2-hydroxyethyl methacrylate) (PHEMA)–gelatin hydrogels with high mechanical performance and stimuli response. An ideal bicontinuous phase separation structure of the PHEMA (rigid) and gelatin (ductile) was observed with embedded microdisc-like gelatin in the three-dimensional polymeric network of PHEMA. A significant enhancement of mechanical performance by the Hofmeister effect was attributed to the salting-out-induced stronger and closer interphase interaction between PHEMA and gelatin. A superior comprehensive mechanical performance with fracture elongation over 650%, tensile strength of 5.2 MPa, toughness of 13.5 MJ/m3, and modulus of 45.6 MPa was achieved with the salting-out effect. More specifically, the synergy of phase separation and Hofmeister effect enable the hydrogel to contract with an enhanced modulus in high-concentration salt solutions, while the same hydrogel swells and relaxes in dilute solutions, exhibiting an ionic stimulus response and excellent shape-memory properties like those of most artificial muscle. This is manifested in highly stretched, twisted, and knotted hydrogel strips that can rapidly recover their original shape in a dilute salt solution. The high strength and modulus, ionic stimuli response, and shape memory property make the hybrid hydrogel a promising material for bioactuators in various biomedical applications.
Two-way shape memory polymers (SMPs) have received much attention due to their ability to enable stimuli-responsive reversible structures without requiring repeated human intervention, which may be useful for application in many fields where multiple actuation cycles are desired. However, many layered or composite SMP systems are not integrated structures and suffer from several disadvantages, such as poor interlayer adhesion with limited actuation repeatability. In addition, twoway SMPs are limited by their manufacturing method to producing userdefined, complex, high-precision devices and parts. In this work, we developed a 3D-printable resin comprising two polyurethane-based oligomers with distinctly different transition temperatures�polypentadecalactone diacrylate (PPDLDA) and polycaprolactone diacrylate (PCLDA)�together with other monomers to fabricate single-network two-way shape memory smart materials by digital light projection 3D printing. The chemical, mechanical, and thermal properties of printed products can be easily tuned by facile manipulation of monomer and oligomer compositions. The PCLDA and PPDLDA switching segments were found to exhibit high mean shape fixity ratios (R f ) of >97% and high shape recovery ratios (R r ) of >89%. The strategy for achieving 3D-printable single-network two-way SMPs presented herein holds promise for applications in soft robotics, medicine, and so forth.
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