Biological Stimuli-Induced Phase Transition of a Synthesized Block Copolymer: Preferential Interactions between PNIPAM-b-PNVCL and Heme Proteins

The Method of Direct and Reverse Phase Portraits as a Tool for Systematizing the Results of Studies of Phase Transitions in Solutions of Thermosensitive Polymers

It is shown that a more than significant amount of experimental data obtained in the field of studying systems based on thermosensitive hydrophilic polymers and reflected in the literature over the past decades makes the issue of their systematization and classification relevant. This, in turn, makes relevant the question of choosing the appropriate classification criteria. It is shown that the basic classification feature can be the number of phase transition stages, which can vary from one to four or more depending on the nature of the temperature-sensitive system. In this work, the method of inverse phase portraits is proposed for the first time. It was intended, among other things, to identify the number of phase transition stages. Moreover, the accuracy of this method significantly exceeds the accuracy of the previously used method of direct phase portraits since, for the first time, the operation of numerical differentiation is replaced by the operation of numerical integration. A specific example of the application of the proposed method for the analysis of a previously studied temperature-sensitive system is presented. It is shown that this method also allows for a quantitative comparison between the results obtained by the differential calorimetry method and the turbidimetry method. Issues related to increasing the resolution of the method of direct phase portraits are discussed.

Smart Anisotropic Colloidal Composites: A Suitable Platform for Modifying the Phase Transition of Diblock Copolymers by Gold Nanoparticles

Surface modification of metallic nanoparticles (NPs) by stimuli-responsive polymers is a benign method to prepare smart colloidal composites which tune the characteristic properties of individual systems. The temperature-dependent transition of diblock copolymer poly(N-isopropylacrylamide)-block-poly(N-vinylcaprolactam) (PNIPMA-b-PVCL) synthesized using reversible addition-fragmentation chain transfer polymerization was studied by incorporating anisotropic gold NPs (AGPs) such as spheres (AuNSs), rods (AuNRs), cubes (AuNCs), and rhombic dodecahedrals (AuRDs). Shape-dependent physiochemical properties of nanostructures alter the lower critical solution temperature (LCST) of the chemical inhomogeneous diblock copolymer. Heterogeneous nucleation of AuNPs was facilitated by seed-mediated synthesis for incorporating uniformity. In the mixed system, the presence of PNIPAM-b-PVCL modifies the surface of AGPs through physisorption which is supported by transmission electron microscopy and field emission scanning electron microscopy showing the NPs embedding in the polymeric matrix. Furthermore, steady state fluorescence spectroscopy and Fourier transform infrared spectroscopy were performed to examine the phase transition behavior of PNIPAM-b-PVCL in AGPs. The formation of a smart polymer nanocomposite alters the physiochemical properties of the diblock copolymer as demonstrated from the variation of LCST in the dynamic light scattering measurement. Henceforth, functionalizing the surfaces of AGPs with a thermoresponsive diblock copolymer provides combinatorial benefits in the properties of smart polymeric colloidal systems with potential applications in bioimaging and drug delivery.

Ionic Liquids Mediated Micellization of Pluronic Copolymers: Aggregation Behavior of Amphiphilic Triblock Copolymers

Understanding the micellization of amphiphilic triblock copolymers, especially Pluronics can play a persuasive role in engineering "smart" formulations for drug delivery applications. Their underlying self-assembly in the presence of designer solvents such as ionic liquids (ILs) provides combinatorial benefits of unique munificent properties of ILs and copolymers. The complex molecular interactions in the Pluronic copolymers/ILs mixed system influence the aggregation mechanism of copolymers depending on various aspects with no standardized factors to govern the structure-property relationship, which led to the practical applications. Here, we summarized recent progress in understanding the micellization process of IL-Pluronic mixed systems. Special emphasis was given to pure Pluronic systems (i.e., PEO-PPO-PEO) without any structural modifications, such as copolymerization with other functional groups, and ILs having cholinium and imidazolium groups. We expect that the correlation between existing/developing experimental and theoretical studies will provide the necessary basis and impetus for successful utilization in drug delivery applications.

Thermoresponsive Block Copolymer Core-Shell Nanoparticles with Tunable Flow Behavior in Porous Media

With the purpose of investigating new polymeric materials as potential flow modifiers for their future application in enhanced oil recovery (EOR), a series of amphiphilic poly(di(ethylene glycol) methyl ether methacrylate-co-oligo(ethylene glycol) methyl ether methacrylate) [P(DEGMA-co-OEGMA)]-based core-shell nanoparticles were prepared by aqueous reversible addition-fragmentation chain transfer-mediated polymerization-induced self-assembly. The developed nano-objects were shown to be thermoresponsive, demonstrating a reversible lower-critical solution temperature (LCST)-type phase transition with increasing solution temperature. Characterization of their thermoresponsive nature by variable-temperature UV-vis and dynamic light scattering analyses revealed that these particles reversibly aggregate when heated above their LCST and that the critical transition temperature could be accurately tuned by simply altering the molar ratio of core-forming monomers. Sandpack experiments were conducted to evaluate their pore-blocking performance at low flow rates in a porous medium heated at temperatures above their LCST. This analysis revealed that particles aggregated in the sandpack column and caused pore blockage with a significant reduction in the porous medium permeability. The developed aggregates and the increased pressure generated by the blockage were found to remain stable under the injection of brine and were observed to rapidly dissipate upon reducing the temperature below the LCST of each formulation. Further investigation by double-column sandpack analysis showed that the blockage was able to reform when re-heated and tracked the thermal front. Moreover, the rate of blockage formation was observed to be slower when the LCST of the injected particles was higher. Our investigation is expected to pave the way for the design of "smart" and versatile polymer technologies for EOR applications in future studies.

Ultraslow Biological Water-Like Dynamics in Waterless Liquid Protein

Fluorescence correlation spectroscopy and time-dependent fluorescence Stokes shift have been employed to elucidate dynamics in different time scales, ranging from picoseconds to nanoseconds, for human serum albumin, in its native and cationized forms as well as in the self-assembled complex of the cationized protein with the polymer surfactant (PS) glycolic acid ethoxylate lauryl ether. The effect of crowding in this complex, especially in the waterless condition, is of prime importance in this context. Excellent correlation of the dynamics with the structures, obtained by circular dichroism and Fourier transform infrared spectroscopy, has been observed. Slow solvation, associated classically with biological water, has been observed in these systems, even in the waterless condition. This apparently intriguing observation has been rationalized by the relaxation of segments of the protein and the PS in the microenvironment of the fluorescent probe.

Role of protein-copolymer assembly in controlling micellization process of amphiphilic triblock copolymer

HYPOTHESIS

Triblock copolymer poly(ethylene glycol)-block-poly(propylene glycol)-block-poly(ethylene glycol) (PEG-PPG-PEG) forms a well-known micellar assembly at a particular temperature. Apart from regular assembly within the copolymer, it is crucial to explore additional assembly behaviour via simple exposure of proteins which unveils biased interactions with blocks of copolymer. The current work focuses on the examination of Pluronic F108 i.e. PEG-PPG-PEG with two different proteins i.e. α-chymotrypsin (CT) and lysozyme (LSZ), aiming at probing the critical micellization temperature (CMT) and molecular level interactions.

EXPERIMENTS

Potential role of protein-copolymer assembly formation at a particular concentration of protein in modulating CMT was shown by a systematic experimental approach combined with a series of physicochemical methods. The sophisticated multiple techniques include fluorescence spectroscopy, Fourier transform infrared (FTIR) spectroscopy, Raman spectroscopy, dynamic light scattering (DLS), zeta potential measurements, scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Furthermore, molecular docking studies were also employed to correlate theoretical insights with experimental findings.

FINDINGS

CT and LSZ decrease CMT in regular concentration-dependent manner except for particular concentration (1.5 mg/mL) of LSZ which shows anomalous behaviour in steady-state fluorescence spectroscopy, temperature dependent fluorescence spectroscopy, Raman spectroscopy and DLS measurements. SEM and TEM results clearly reveal protein-copolymer assembly formation. The assembled structure has different biophysical properties. Docking studies elucidate several bio macromolecular interactions which can be involved in assembly formation. Based on obtained results from biophysical techniques mechanism of CMT variation was deduced. Obtained results can be useful in biosensors and targeted drug delivery systems.

Injectable bottlebrush hydrogels with tissue-mimetic mechanical properties

Injectable hydrogels are desired in many biomedical applications due to their minimally invasive deployment to the body and their ability to introduce drugs. However, current injectables suffer from mechanical mismatch with tissue, fragility, water expulsion, and high viscosity. To address these issues, we design brush-like macromolecules that concurrently provide softness, firmness, strength, fluidity, and swellability. The synthesized linear-bottlebrush-linear (LBL) copolymers facilitate improved injectability as the compact conformation of bottlebrush blocks results in low solution viscosity, while the thermoresponsive linear blocks permit prompt gelation at 37°C. The resulting hydrogels mimic the deformation response of supersoft tissues such as adipose and brain while withstanding deformations of 700% and precluding water expulsion upon gelation. Given their low cytotoxicity and mild inflammation in vivo, the developed materials will have vital implications for reconstructive surgery, tissue engineering, and drug delivery applications.

Thermoresponsivity of poly(N-isopropylacrylamide) microgels in water-trehalose solution and its relation to protein behavior

HYPOTHESES

Additives are commonly used to tune macromolecular conformational transitions. Among additives, trehalose is an excellent bioprotectant and among responsive polymers, PNIPAM is the most studied material. Nevertheless, their interaction mechanism so far has only been hinted without direct investigation, and, crucially, never elucidated in comparison to proteins. Detailed insights would help understand to what extent PNIPAM microgels can effectively be used as synthetic biomimetic materials, to reproduce and study, at the colloidal scale, isolated protein behavior and its sensitivity to interactions with specific cosolvents or cosolutes.

EXPERIMENTS

The effect of trehalose on the swelling behavior of PNIPAM microgels was monitored by dynamic light scattering; Raman spectroscopy and molecular dynamics simulations were used to explore changes of solvation and dynamics across the swelling-deswelling transition at the molecular scale.

FINDINGS

Strongly hydrated trehalose molecules develop water-mediated interactions with PNIPAM microgels, thereby preserving polymer hydration below and above the transition while drastically inhibiting local motions of the polymer and of its hydration shell. Our study, for the first time, demonstrates that slowdown of dynamics and preferential exclusion are the principal mechanisms governing trehalose effect on PNIPAM microgels, at odds with preferential adsorption of alcohols, but in full analogy with the behavior observed in trehalose-protein systems.

Understanding the close encounter of heme proteins with carboxylated multiwalled carbon nanotubes: a case study of contradictory stability trend for hemoglobin and myoglobin

Carbon nanotubes (CNTs) are one of the unique and promising nanomaterials that possess plenty of applications, such as biosensors, advanced drug delivery systems and biotechnology. CNTs bind rapidly with proteins, which result in the formation of a protein coating layer known as a "protein corona" around the surface of the nanomaterial. This hinders their applications as a drug carrier and influences the properties of biological macromolecules. The present work focuses on studying the thermal stability and molecular level interactions of two heme proteins, hemoglobin (Hb) and myoglobin (Mb), in the presence of carboxylated functionalized multi-walled CNTs (CA-MWCNTs). Through the current study, the following steps have been taken to distinguish the biocompatibility of the hydrophilic surface CA-MWCNTs for heme proteins via a series of spectroscopic techniques and differential scanning calorimetry (DSC). UV-Visible and steady-state fluorescence spectroscopy were used to reveal changes in the aromatic amino acid residues of heme proteins upon the addition of CA-MWCNTs. Circular dichroism spectroscopy (CD) shows the alteration in the native structure of proteins in the presence of the nanomaterial. A tremendous increase in the size of the protein CA-MWCNTs system is observed in dynamic light scattering (DLS), which clearly manifests the protein corona formation. Unexpectedly, both proteins interact differently with CA-MWCNTs, which is observed in CD spectroscopy and DSC. In the presence of CA-MWCNTs, an increase in the transition temperature (T_m) was observed for Hb, while the T_m value decreases for Mb. Different interactions with proteins at the molecular scale may be the reason for this unexpected behavior. Henceforth, the present results can help in the design of the next-generation drug carrier nanomaterials with the idea of the heme protein corona formation prior to development.

Tuning the Cloud-Point and Flocculation Temperature of Poly(2-(diethylamino)ethyl methacrylate)-Based Nanoparticles via a Postpolymerization Betainization Approach

The ability to tune the behavior of temperature-responsive polymers and self-assembled nanostructures has attracted significant interest in recent years, particularly in regard to their use in biotechnological applications. Herein, well-defined poly(2-(diethylamino)ethyl methacrylate) (PDEAEMA)-based core-shell particles were prepared by RAFT-mediated emulsion polymerization, which displayed a lower-critical solution temperature (LCST) phase transition in aqueous media. The tertiary amine groups of PDEAEMA units were then utilized as functional handles to modify the core-forming block chemistry via a postpolymerization betainization approach for tuning both the cloud-point temperature (T _CP) and flocculation temperature (T _CFT) of these particles. In particular, four different sulfonate salts were explored aiming to investigate the effect of the carbon chain length and the presence of hydroxyl functionalities alongside the carbon spacer on the particle's thermoresponsiveness. In all cases, it was possible to regulate both T _CP and T _CFT of these nanoparticles upon varying the degree of betainization. Although T _CP was found to be dependent on the type of betainization reagent utilized, it only significantly increased for particles betainized using sodium 3-chloro-2-hydroxy-1-propanesulfonate, while varying the aliphatic chain length of the sulfobetaine only provided limited temperature variation. In comparison, the onset of flocculation for betainized particles varied over a much broader temperature range when varying the degree of betainization with no real correlation identified between T _CFT and the sulfobetaine structure. Moreover, experimental results were shown to partially correlate to computational oligomer hydrophobicity calculations. Overall, the innovative postpolymerization betainization approach utilizing various sulfonate salts reported herein provides a straightforward methodology for modifying the thermoresponsive behavior of soft polymeric particles with potential applications in drug delivery, sensing, and oil/lubricant viscosity modification.

Analyzing the Effects of Silica Nanospheres on the Sol-Gel Transition Profile of Thermosensitive Hydrogels

The insertion of nanoparticles into smart hydrogels can diversify their functionalities by a synergistic combination of the components properties within the hydrogels. While these hybrid systems are attractive to the biomaterials field, careful design and control of their properties are required since the new interactions between the polymer and the nanoparticles can result in changes or the loss of hydrogels stimuli response. In order to understand the physicochemical aspects of the thermoresponsive systems, nanocomposites of poly(N-vinylcaprolactam) (PNVCL) and silica nanoparticles with different sizes and concentrations were synthesized. The UV-vis and DLS techniques showed that the PNVCL has a sharp phase transition at 34 °C, while the nanocomposites have a diffuse transition. The nanocomposites showed an initial coil-globule transition before the phase transition takes place. This was identified by the evolution of the hydrodynamic diameter of the nanocomposite globules before the cloud point temperature (T_cp), which remained constant for PNVCL. This new transition profile can be described by two stages in which microscopic volume transitions occur first, followed by the macroscopic transition that forms the hydrogel. These results show that the proposed nanocomposites can be designed to have tunable stimuli response to smaller temperature variations with the formation of intermediate globule states.

Large three-dimensional cell constructs for tissue engineering

Much research has been conducted on fabricating biomimetic biomaterials in vitro. Tissue engineering approaches are often conducted by combining cells, scaffolds, and growth factors. However, the degradation rate of scaffolds is difficult to control and the degradation byproducts occasionally limit tissue regeneration. To overcome these issues, we have developed a novel system using a thermo-responsive hydrogel that forms scaffold-free, three-dimensional (3D) cell constructs with arbitrary size and morphology. 3D cell constructs prepared using bone marrow-derived stromal stem cells (BMSCs) exhibited self-organizing ability and formed bone-like tissue with endochondral ossification. Endothelial cells were then introduced into the BMSC construct and a vessel-like structure was formed within the constructs. Additionally, the bone formation ability was promoted by endothelial cells and cell constructs could be freeze-dried to improve their clinical application. A pre-treatment with specific protein protectant allowed for the fabrication of novel bone substitutes composed only of cells. This 3D cell construct technology using thermo-responsive hydrogels was then applied to other cell species. Cell constructs composed of dental pulp stem cells were fabricated, and the resulting construct regenerated pulp-like tissue within a human pulpless tooth. In this review, we demonstrate the approaches for the in vitro fabrication of bone and dental pulp-like tissue using thermo-responsive hydrogels and their potential applications.