Cytosolic Delivery of Single-Chain Polymer Nanoparticles

FRET-Based Investigation of the Dynamics of Peptide-Folded Single Chain Nanoparticles Inside Cancer Cells

Single chain nanoparticles (SCNPs) prepared using diphenylalanine (LFF) as crosslinker have recently been proposed as protein-inspired drug delivery carriers. The aim of this work is to learn more about the stability of these peptide-based supramolecular systems in biological environments using Förster resonance energy transfer and fluorescence lifetime imaging microscopy (FRET-FLIM). Two self-folding poly(N,N-dimethyl acrylamide) PDMA with 10 mol.% pendant LFF, labeled at the omega chain end with the cyanine dyes Cy5 and Cy3, respectively, are formed into SCNPs with sizes below 10 nm. The particles are found to be stable in water and do not aggregate in a cellular environment (MCF-7 breast cancer cells). The SCNPs are uptaken by these cells slightly faster than a control nanoparticle of the same polymers (≈100 nm in cell culture media) and with similar total uptake after 1 h. Temperature-dependent studies demonstrate that while the larger nanoparticles are dependent on endocytosis for uptake, the SCNPs can cross the membrane via diffusion. This study demonstrates the value of FRET-FLIM in understanding the behavior of self-assembled nanoparticles in vitro and provides additional evidence for the alternate cell uptake pathways that SCNPs can access over traditional nanoparticle based drug carriers.

Concurrent Folding and Fluorescent Functionalization of Single-Chain Nanoparticles via Heterogeneous Photochemistry

The controlled folding of synthetic polymers, mimicking the complex behaviors of biomacromolecules, offers the potential to create sophisticated nanostructures with diverse functionalities. Of great significance is the integration of functionalization directly with chain folding, especially through the incorporation of artificial elements not found in nature, which allows unprecedented flexibility in materials design. However, this approach faces significant synthetic challenges, owing to the intricate integration of multiple chemical processes within a single chain. Here, a heterogeneous photochemistry strategy is presented to achieve single-chain polymer folding alongside concurrent fluorescent functionalization, inspired by the stepwise folding mechanism of green fluorescent protein. This method involves pre-folding amphiphilic heterograft random copolymers in water, which facilitates heterogeneous aggregation into distinct domains within single-particle nanostructures, including closely aggregated and molecularly dispersed regions. By employing spatial organization-dependent photochemical reactivity of cyanostilbene moieties, two concurrent processes are enabled: intrachain crosslinking via photodimerization in aggregated domains and fluorescent functionalization via photocyclization to form a green fluorophore in dispersed regions. Additionally, the incorporation of fluorescent dyes via intrachain excitation energy transfer allows for the modulation of emission properties, extending from green to red, and even including white light, making them promising candidates for bioimaging and related applications.

Efficient Cytosolic Delivery of Single-Chain Polymeric Artificial Enzymes for Intracellular Catalysis and Chemo-Dynamic Therapy

Designing artificial enzymes for in vivo catalysis presents a great challenge due to biomacromolecule contamination, poor biodistribution, and insufficient substrate interaction. Herein, we developed single-chain polymeric nanoparticles with Cu/N-heterocyclic carbene active sites (SCNP-Cu) to function as peroxidase mimics for in vivo catalysis and chemo-dynamic therapy (CDT). Compared with the enzyme mimics based on unfolded linear polymer scaffold and multichain cross-linked scaffold, SCNP-Cu exhibits improved tumor accumulation and CDT efficiency both in vitro and in vivo. Protein-like size of the SCNP scaffold promotes passive diffusion, whereas positive surface charge allows its active transcytosis for deep tumor penetration and hence accumulation in the tumor site. The submolecular compartments of the SCNP scaffold effectively protect the active sites from protein bindings, thereby providing a "cleaner" microenvironment for catalysis within a living system. The folded structure of SCNP-Cu facilitates their cytosolic delivery of and free diffusion within cytosol, ensuring efficient contact with endogenous H2O2, in situ generation of toxic hydroxyl radicals (·OH), and effective damage of intracellular targets (i.e., lipids, nucleic acids). This work establishes versatile SCNP-based nanoplatforms for developing artificial enzymes for in vivo catalysis.

Tadpole-like cationic single-chain nanoparticles display high cellular uptake

The successful delivery of nanoparticles (NPs) to cancer cells is dependent on various factors, including particle size, shape, surface properties such as hydrophobicity/hydrophilicity, charges, and functional moieties. Tailoring these properties has been explored extensively to enhance the efficacy of NPs for drug delivery. Single-chain polymer nanoparticles (SCNPs), notable for their small size (sub-20 nm) and tunable properties, are emerging as a promising platform for drug delivery. However, the impact of surface charge on the biological performance of SCNPs in cancer cells remains underexplored. In this study, we prepared a library of SCNPs with varying charge types (neutral, anionic, cationic, and zwitterionic), charge densities, charge positions, and crosslinking densities to evaluate their effects on cellular uptake in MCF-7 breast cancer cells. Key findings include that cationic SCNPs are more likely to translocate into cells than neutral, anionic, or zwitterionic counterparts. Furthermore, cellular uptake was enhanced with increased charge density (from 10 to 15 mol%) before reaching a critical point (20 mol%) where excessive positive charge led to NP adhesion to the cell membrane, resulting in cell death. We also found that the position of the charge on the polymer chain also impacted the delivery of NPs to cancer cells, with tadpole-shaped SCNPs achieving the highest uptake. Furthermore, crosslinking density significantly influenced cellular uptake, with SCNPs at 50% crosslinking conversion showing the highest cytosolic localization, while other densities resulted in retention primarily at the cell membrane. This study offers valuable insights into how charge type, density, position, and crosslinking density affect the biological performance of SCNPs, guiding the rational design of more effective and safer drug delivery systems.

Compartmentalised single-chain nanoparticles and their function

Single-chain nanoparticles (SCNPs) are generated by intramolecular collapse and crosslinking of single polymer chains, thus conceptually resembling the structures of folded proteins. Their chemical flexibility and ability to form compartmentalised nanostructures sized ∼1 nm make them perfect candidates for numerous applications, such as in catalysis and drug delivery. In this review we discuss principles for the design, synthesis and analysis of SCNPs, with a focus on their compartmentalised structures, highlighting our own previous work. As such compartments offer the potential to generate a specific nanoenvironment e.g. for the covalent and non-covalent encapsulation of catalysts or drugs, they represent a novel, exciting, and expanding research area. Starting from the architectural and chemical design of the starting copolymers by controlling their amphiphilic profile, the embedding of blocks-, or secondary-structure-mimetic arrangements, we discuss design principles to form internal compartments inside the SCNPs. While the generation of compartments inside SCNPs is straightforward, their analysis is still challenging and often demands special techniques. We finally discuss applications of SCNPs, also linked to the compartment formation, predicting a bright future for these special nanoobjects.

Solvent Choice during Flow Assembly of Photocross-Linked Single-Chain Nanoparticles and Micelles Affects Cellular Uptake

Polymeric micelles have widely been used as drug delivery carriers, and recently, single-chain nanoparticles (SCNPs) emerged as potential, smaller-sized, alternatives. In this work, we are comparing both NPs side by side and evaluate their ability to be internalized by breast cancer cells (MCF-7) and macrophages (RAW 264.7). To be able to generate these NPs on demand, the polymers were assembled by flow, followed by the stabilization of the structures by photocross-linking using blue light. The central aim of this work is to evaluate how the type of solvent affects self-assembly and ultimately the structure of the final NP. Therefore, a library of copolymers with different sequences, including block copolymers (AB, ABA, BAB), and statistical copolymers (rAB and rAC) was synthesized using PET-RAFT with A denoting poly(ethylene glycol) methyl ether acrylate (PEGMEA), B as 2-hydroxyethyl acrylate (HEA), and C as 4-hydroxybutyl acrylate (HBA). The polymers were conjugated with a quinoline derivative to enable the formation of cross-linked structures by photocross-linking during flow assembly. Using water as the dispersant for photocross-linking led to the preassembly of these amphiphilic polymers into compact SCNPs and cross-linked micelles, resulting in a quick photoreaction. In contrast, acetonitrile led to fully dissolved polymers but a low rate of the photoreaction. These intramolecularly cross-linked polymers were then placed in water to result in more dynamic micelles and looser SCNPs. Small-angle X-ray scattering (SAXS), dynamic light scattering (DLS), and size exclusion chromatography (SEC) coupled with a viscosity detector show that cross-linking in acetonitrile results in better-defined NPs with a shell rich in PEGMEA. Cross-linking in acetonitrile led to NPs with significantly higher cellular uptake. Interestingly, passive transport was identified as the main pathway for the delivery of our NPs on MCF-7 cells, confirmed by the uptake of NPs on cells treated with inhibitors and by red blood cells. This work underscored the importance of the polymer precursor's structure and the choice of solvent during intramolecular cross-linking in determining the drug delivery efficiency and biological behavior of SCNPs.

Imaging Diffusion and Stability of Single-Chain Polymeric Nanoparticles in a Multi-Gel Tumor-on-a-Chip Microfluidic Device

The performance of single-chain polymeric nanoparticles (SCPNs) in biomedical applications highly depends on their conformational stability in cellular environments. Until now, such stability studies are limited to 2D cell culture models, which do not recapitulate the 3D tumor microenvironment well. Here, a microfluidic tumor-on-a-chip model is introduced that recreates the tumor milieu and allows in-depth insights into the diffusion, cellular uptake, and stability of SCPNs. The chip contains Matrigel/collagen-hyaluronic acid as extracellular matrix (ECM) models and is seeded with cancer cell MCF7 spheroids. With this 3D platform, it is assessed how the polymer's microstructure affects the SCPN's behavior when crossing the ECM, and evaluates SCPN internalization in 3D cancer cells. A library of SCPNs varying in microstructure is prepared. All SCPNs show efficient ECM penetration but their cellular uptake/stability behavior depends on the microstructure. Glucose-based nanoparticles display the highest spheroid uptake, followed by charged nanoparticles. Charged nanoparticles possess an open conformation while nanoparticles stabilized by internal hydrogen bonding retain a folded structure inside the tumor spheroids. The 3D microfluidic tumor-on-a-chip platform is an efficient tool to elucidate the interplay between polymer microstructure and SCPN's stability, a key factor for the rational design of nanoparticles for targeted biological applications.

Dual-reactive single-chain polymer nanoparticles for orthogonal functionalization through active ester and click chemistry

Glucose has been extensively studied as a targeting ligand on nanoparticles for biomedical nanoparticles. A promising nanocarrier platform are single-chain polymer nanoparticles (SCNPs). SCNPs are well-defined 5-20 nm semi-flexible nano-objects, formed by intramolecularly crosslinked linear polymers. Functionality can be incorporated by introducing labile pentafluorophenyl (PFP) esters in the polymer backbone, which can be readily substituted by functional amine-ligands. However, not all ligands are compatible with PFP-chemistry, requiring different ligation strategies for increasing versatility of surface functionalization. Here, we combine active PFP-ester chemistry with copper(I)-catalyzed azide alkyne cycloaddition (CuAAC) click chemistry to yield dual-reactive SCNPs. First, the SCNPs are functionalized with increasing amounts of 1-amino-3-butyne groups through PFP-chemistry, leading to a range of butyne-SCNPs with increasing terminal alkyne-density. Subsequently, 3-azido-propylglucose is conjugated through the glucose C1- or C6-position by CuAAC click chemistry, yielding two sets of glyco-SCNPs. Cellular uptake is evaluated in HeLa cancer cells, revealing increased uptake upon higher glucose-surface density, with no apparent positional dependance. The general conjugation strategy proposed here can be readily extended to incorporate a wide variety of functional molecules to create vast libraries of multifunctional SCNPs.

Engineering of bioorthogonal polyzymes through polymer sidechain design

Synthetic polymer scaffolds can encapsulate transition metal catalysts (TMCs) to provide bioorthogonal nanocatalysts. These 'polyzymes' catalyze the in situ generation of therapeutic agents without disrupting native biological processes. The design and modification of polymer scaffolds in these polyzymes can enhance the catalytic performance of TMCs in biological environments. In this study, we explore the hydrophobic design space of an oxanorborneneimide-based polymer by varying the length of its carbon side chain to engineer bioorthogonal polyzymes. Activity studies indicate that modulating the hydrophobicity of the polymer scaffold can be used to enhance the catalyst loading efficacy, catalytic activity, and serum stability of polyzymes. These findings provide insight into the structural elements contributing to improving polymeric nanocatalysts for a variety of applications.

Trastuzumab-functionalized bionic pyrotinib liposomes for targeted therapy of HER2-positive breast cancer

In this study, we prepared a bionic nanosystem of trastuzumab-functionalized SK-BR-3 cell membrane hybrid liposome-coated pyrotinib (Ptb-M-Lip-Her) for the treatment of HER2-positive breast cancer. Transmission electron microscopy, dynamic light scattering, polyacrylamide gel electrophoresis (SDS-PAGE) and western blotting were used to verify the successful preparation of Ptb-M-Lip-Her. In vitro drug release experiments proved that Ptb-M-Lip-Her had a sustained release effect. Cell uptake experiments and in vivo imaging experiments proved that Ptb-M-Lip-Her had good targeting ability to homologous tumor cells (SK-BR-3). The results of cell experiments such as MTT, flow cytometry, immunofluorescence staining and in vivo antitumor experiments showed that Ptb-M-Lip-Her could significantly promote apoptosis and inhibit the proliferation of SK-BR-3 cells. These results clearly indicated that Ptb-M-Lip-Her may be a promising biomimetic nanosystem for targeted therapy of HER2-positive breast cancer.

Förster resonance energy transfer within single chain nanoparticles

Single chain nanoparticles (SCNPs) are a highly versatile polymer architecture consisting of single polymer chains that are intramolecularly crosslinked. Currently, SCNPs are discussed as powerful macromolecular architectures for catalysis, delivery and sensors. Herein, we introduce a methodology based on Förster Resonance Energy Transfer (FRET) to evidence the folding of single polymer chains into SCNPs via fluorescence readout. We initially introduce a molecular FRET pair based on a bimane and nitrobenzoxadiazole (NBD) moiety and study its fluorescence properties in different solvents. We subsequently construct a low dispersity polymer chain carrying NBD units, while exploiting the bimane units for intramolecular chain collapse. Upon chain collapse and SCNP formation - thus bringing bimane and NBD units into close proximity - the SCNPs report their folded state by a strong and unambiguous FRET fluorescence signal. The herein introduced reporting of the folding state of SCNPs solely relies on an optical readout, opening avenues to monitoring SCNP folding without recourse to complex analytical methodologies.

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.

Metamorphosis of a Commodity Plastic like PVC to Efficient Catalytic Single-Chain Nanoparticles

We perform the conversion of a commodity plastic of common use in pipes, window frames, medical devices, flexible hoses, etc. like polyvinyl chloride (PVC) to single-chain nanoparticles (SCNPs). SCNPs are versatile, protein-mimetic soft nano-objects of growing interest for catalysis, sensing, and nanomedicine, among other uses. We demonstrate that the metamorphosis process -as induced through metal-free click chemistry- leads to well-defined, uniform SCNPs that are stable during storage in the solid state for months. All the conversion process (from PVC isolation to PVC-SCNPs synthesis) can be run in a green, dipolar aprotic solvent and involving, when required, a simple mixture of ethanol and water (1/1 vol.) as non-solvent. The resulting PVC-SCNPs are investigated as recyclable, metalloenzyme-mimetic catalysts for several representative Cu(II)-catalyzed organic reactions. The method could be valid for the metamorphosis and valorization of other commodity plastics in which it is feasible to install azide functional groups in their linear polymer chains.

Amphiphilic Fluorinated Unimer Micelles as Nanocarriers of Fluorescent Probes for Bioimaging

The unique self-assembly properties of unimer micelles are exploited for the preparation of fluorescent nanocarriers embedding hydrophobic fluorophores. Unimer micelles are constituted by a (meth)acrylate copolymer with oligoethyleneglycol and perflurohexylethyl side chains (PEGMA90-co-FA10) in which the hydrophilic and hydrophobic comonomers are statistically distributed along the polymeric backbone. Thanks to hydrophobic interactions in water, the amphiphilic copolymer forms small nanoparticles (<10 nm), with tunable properties and functionality. An easy procedure for the encapsulation of a small hydrophobic molecule (C153 fluorophore) within unimer micelles is presented. UV-vis, fluorescence, and fluorescence anisotropy spectroscopic experimental data demonstrate that the fluorophore is effectively embedded in the nanocarriers. Moreover, the nanocarrier positively contributes to preserve the good emissive properties of the fluorophore in water. The efficacy of the dye-loaded nanocarrier as a fluorescent probe is tested in two-photon imaging of thick ex vivo porcine scleral tissue.

Single-chain polymer nanoparticles in biomedical applications

Single-chain polymer nanoparticles (SCNPs) are a well-defined and uniquely sized class of polymer nanoparticles. The advances in polymer science over the past decades have enabled the development of a variety of intramolecular crosslinking systems, leading to particles in the 5-20 nm size regime. Which is aligned with the size regime of proteins and therefore making SCNPs an interesting class of NPs for biomedical applications. The high modularity of SCNP design and the ease of their functionalization have led to growing research interest. In this review, we describe different crosslinking systems, as well as the preparation of functional SCNPs and the variety of biomedical applications that have been explored.

Recent progress in nanomedicine-mediated cytosolic delivery

Cytosolic delivery of bioactive agents has exhibited great potential to cure undruggable targets and diseases. Because biological cell membranes are a natural barrier for living cells, efficient delivery methods are required to transfer bioactive and therapeutic agents into the cytosol. Various strategies that do not require cell invasive and harmful processes, such as endosomal escape, cell-penetrating peptides, stimuli-sensitive delivery, and fusogenic liposomes, have been developed for cytosolic delivery. Nanoparticles can easily display functionalization ligands on their surfaces, enabling many bio-applications for cytosolic delivery of various cargo, including genes, proteins, and small-molecule drugs. Cytosolic delivery uses nanoparticle-based delivery systems to avoid degradation of proteins and keep the functionality of other bioactive molecules, and functionalization of nanoparticle-based delivery vehicles imparts a specific targeting ability. With these advantages, nanomedicines have been used for organelle-specific tagging, vaccine delivery for enhanced immunotherapy, and intracellular delivery of proteins and genes. Optimization of the size, surface charges, specific targeting ability, and composition of nanoparticles is needed for various cargos and target cells. Toxicity issues with the nanoparticle material must be managed to enable clinical use.

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.

Enhancing Cellular Internalization of Single-Chain Polymer Nanoparticles via Polyplex Formation

Intracellular delivery of nanoparticles is crucial in nanomedicine to reach optimal delivery of therapeutics and imaging agents. Single-chain polymer nanoparticles (SCNPs) are an interesting class of nanoparticles due to their unique site range of 5-20 nm. The intracellular delivery of SCNPs can be enhanced by using delivery agents. Here, a positive polymer is used to form polyplexes with SCNPs, similar to the strategy of protein and gene delivery. The size and surface charge of the polyplexes were evaluated. The cellular uptake showed rapid uptake of SCNPs via polyplex formation, and the cytosolic delivery of the SCNPs was presented by confocal microscopy. The ability of SCNPs to act as nanocarriers was further explored by conjugation of doxorubicin.

Preparation of AIE Functional Single-chain Polymer Nanoparticles and Its Application in H2 O2 Detection through Intermolecular Heavy-atom Effect

Single-chain polymer nanoparticles (SCNPs) are soft matter constructed by intrachain crosslink, with promising prospects in detection and catalysis. Herein, the fluorescent core (SCNPs) with aggregation-induced emission (AIE) was prepared, applying for H₂ O₂ detection through intermolecular heavy-atom effect. In detail, the SCNPs precursors were synthesized by ring-opening copolymerization. Then the SCNPs were prepared by intramolecularly cross-linking via olefin metathesis. Imitating the structure of AIE dots, SCNPs were encapsulated by H₂ O₂ -responsive polymers. Probably due to the stable secondary structure of SCNPs, the obtained micelles show stable fluorescence performance. Furthermore, as the heavy-atom, tellurium was introduced into the carriers to construct the heavy-atom effect. In this micelle-based system, the SCNPs act as the fluorescent core, and the stimuli-responsive polymer acts as the carrier and the fluorescent switch. The hydrophilicity of the tellurium-containing segment is affected by the concentration of H₂ O₂ , resulting in a change in the distance from the SCNPs, which ultimately leads to a change in the fluorescence intensity. And tellurium is particularly sensitive to H₂ O₂ , which can detect low concentrations of H₂ O₂ . The SCNPs were merged with AIE materials, hoping to explore new probe design. This article is protected by copyright. All rights reserved.

Self-Assembled Amphiphilic Fluorinated Random Copolymers for the Encapsulation and Release of the Hydrophobic Combretastatin A-4 Drug

Water-soluble amphiphilic random copolymers composed of tri(ethylene glycol) methacrylate (TEGMA) or poly(ethylene glycol) methyl ether methacrylate (PEGMA) and perfluorohexylethyl acrylate (FA) were synthesized by ARGET-ATRP, and their self-assembling and thermoresponsive behavior in water was studied by dynamic light scattering (DLS) and UV-vis spectroscopy. The copolymer ability to self-fold in single-chain nano-sized structures (unimer micelles) in aqueous solutions was exploited to encapsulate Combretastatin A-4 (CA-4), which is a very hydrophobic anticancer drug. The cloud point temperature (Tcp) was found to linearly decrease with increasing drug concentration in the drug/copolymer system. Moreover, while CA-4 was preferentially incorporated into the unimer micelles of TEGMA-ran-FA, the drug was found to induce multi-chain, submicro-sized aggregation of PEGMA-ran-FA. Anyway, the encapsulation efficiency was very high (≥81%) for both copolymers. The drug release was evaluated in PBS aqueous solutions both below and above Tcp for TEGMA-ran-FA copolymer and below Tcp, but at two different drug loadings, for PEGMA-ran-FA copolymer. In any case, the release kinetics presented similar profiles, characterized by linear trends up to ≈10-13 h and ≈7 h for TEGMA-ran-FA and PEGMA-ran-FA, respectively. Then, the release rate decreased, reaching a plateau. The release from TEGMA-ran-FA was moderately faster above Tcp than below Tcp, suggesting that copolymer thermoresponsiveness increased the release rate, which occurred anyway by diffusion below Tcp. Cytotoxicity tests were carried out on copolymer solutions in a wide concentration range (5-60 mg/mL) at 37 °C by using Balb/3T3 clone A31 cells. Interestingly, it was found that the concentration-dependent micro-sized aggregation of the amphiphilic random copolymers above Tcp caused a sort of "cellular asphyxiation" with a loss of cell viability clearly visible for TEGMA-ran-FA solutions (Tcp below 37 °C) with higher copolymer concentrations. On the other hand, cells in contact with the analogous PEGMA-ran-FA (Tcp above 37 °C) presented a very good viability (≥75%) with respect to the control at any given concentration.