Effects of Drug Conjugation on the Biological Activity of Single-Chain Nanoparticles

The field of single-chain nanoparticles (SCNPs) continues to mature, and an increasing range of reports have emerged that explore the application of these small nanoparticles. A key application for SCNPs is in the field of drug delivery, and recent work suggests that SCNPs can be readily internalized by cells. However, limited attention has been directed to the delivery of small-molecule drugs using SCNPs. Moreover, studies on the physicochemical effects of drug loading on SCNP performance is so far missing, despite the accepted view that such small nanoparticles should be significantly affected by the drug loading content. To address this gap, we prepared a library of SCNPs bearing different amounts of a covalently conjugated therapeutic drug-sulfasalazine (SSZ). We evaluated the impact of the conjugated drug loading on both the synthesis and biological activity of SCNPs on pancreatic cancer cells (AsPC-1). Our results reveal that covalent drug conjugation to the side chains of the SCNP polymer precursor interferes with chain collapse and cross-linking, which demands optimization of reaction conditions to reach high degrees of cross-linking efficiencies. Small-angle neutron scattering and diffusion-ordered spectroscopy nuclear magnetic resonance (DOSY NMR) analyses reveal that SCNPs with a higher drug loading display larger sizes and looser structures, as well as increased hydrophobicity associated with a higher SSZ content. Increased SSZ loading led to reduced cellular uptake when assessed in vitro, whereby SCNP aggregation on the surface of AsPC-1 cells led to reduced toxicity. This work highlights the effects of drug loading on the drug delivery efficiency and biological behavior of SCNPs.

Tuning the Internal Compartmentation of Single-Chain Nanoparticles as Fluorescent Contrast Agents

Controlling the internal structures of single-chain nanoparticles (SCNPs) is an important factor for their targeted chemical design and synthesis, especially in view of nanosized compartments presenting different local environments as a main feature to control functionality. We here design SCNPs bearing near-infrared fluorescent dyes embedded in hydrophobic compartments for use as contrast agents in pump-probe photoacoustic (PA) imaging, displaying improved properties by the location of the dye in the hydrophobic particle core. Compartment formation is controlled via single-chain collapse and subsequent crosslinking of an amphiphilic polymer using external crosslinkers in reaction media of adjustable polarity. Different SCNPs with hydrodynamic diameters of 6-12 nm bearing adjustable label densities are synthesized. It is found that the specific conditions for single-chain collapse have a major impact on the formation of the desired core-shell structure, in turn adjusting the internal nanocompartments together with the formation of excitonic dye couples, which in turn increase their fluorescence lifetime and PA signal generation. SCNPs with the dye molecules accumulate at the core also show a nonlinear PA response as a function of pulse energy-a property that can be exploited as a contrast mechanism in molecular PA tomography.

Recent advances in the self-assembly of sparsely grafted amphiphilic copolymers in aqueous solution

This review describes the self-assembly of sparsely grafted amphiphilic copolymers and highlights the effects of structural factors and solvents on their self-assembly behaviour.

Fluorescent and Water Dispersible Single-Chain Nanoparticles: Core-Shell Structured Compartmentation

Single-chain nanoparticles (SCNPs) are highly versatile structures resembling proteins, able to function as catalysts or biomedical delivery systems. Based on their synthesis by single-chain collapse into nanoparticular systems, their internal structure is complex, resulting in nanosized domains preformed during the crosslinking process. In this study we present proof of such nanocompartments within SCNPs via a combination of electron paramagnetic resonance (EPR) and fluorescence spectroscopy. A novel strategy to encapsulate labels within these water dispersible SCNPs with hydrodynamic radii of ≈5 nm is presented, based on amphiphilic polymers with additional covalently bound labels, attached via the copper catalyzed azide/alkyne "click" reaction (CuAAC). A detailed profile of the interior of the SCNPs and the labels' microenvironment was obtained via electron paramagnetic resonance (EPR) experiments, followed by an assessment of their photophysical properties.

Advances in the Multi-Orthogonal Folding of Single Polymer Chains into Single-Chain Nanoparticles

The folding of certain proteins (e.g., enzymes) into perfectly defined 3D conformations via multi-orthogonal interactions is critical to their function. Concerning synthetic polymers chains, the "folding" of individual polymer chains at high dilution via intra-chain interactions leads to so-called single-chain nanoparticles (SCNPs). This review article describes the advances carried out in recent years in the folding of single polymer chains into discrete SCNPs via multi-orthogonal interactions using different reactive chemical species where intra-chain bonding only occurs between groups of the same species. First, we summarize results from computer simulations of multi-orthogonally folded SCNPs. Next, we comprehensively review multi-orthogonally folded SCNPs synthesized via either non-covalent bonds or covalent interactions. Finally, we conclude by summarizing recent research about multi-orthogonally folded SCNPs prepared through both reversible (dynamic) and permanent bonds.

Mediating covalent crosslinking of single-chain nanoparticles through solvophobicity in organic solvents

The photoinduced intrachain crosslinking of coumarin-containing copolymers in various organic solvents was mediated through the solvophobic effect, providing control over the reaction rate and the compaction of the final single-chain nanoparticles.

100th Anniversary of Macromolecular Science Viewpoint: Re-examining Single-Chain Nanoparticles

Single-chain nanoparticles (SCNP) are a class of polymeric nanoparticles obtained from the intramolecular cross-linking of polymers bearing reactive pendant groups. The development of SCNP has drawn tremendous attention since the fabrication of SCNP mimics the self-folding behavior in natural biomacromolecules and is highly desirable for a variety of applications ranging from catalysis, nanomedicine, nanoreactors, and sensors. The versatility of novel chemistries available for SCNP synthesis has greatly expanded over the past decade. Significant progress was also made in the understanding of a structure-property relationship in the single-chain folding process. In this Viewpoint, we discuss the effect of precursor polymer topology on single polymer folding. We summarize the progress in SCNP of complex architectures and highlight unresolved issues in the field, such as scalability and topological purity of SCNP.