pH-Responsive Poly(ethylene glycol)-b-poly(2-vinylpyridine) Micelles for the Triggered Release of Therapeutics

Position Matters: Pyridine Regioisomers Influence Secondary Structure and Micelle Morphology in Polymer-Homopolypeptide Micelles

Polymer-homopolypeptide block copolymers are a class of bioinspired materials that combine the processability and stability of synthetic polymers with the biocompatibility and unique secondary structures of peptides, such as α-helices and β-sheets. These properties make them ideal candidates for a wide variety of applications, for example, in the pharmaceutical field, where they are frequently explored as building blocks for polymeric micelle drug delivery systems. While homopolypeptide side chains can be furnished with an array of different moieties to impart the copolymers with desirable properties, such as stimulus responsivity, pyridine derivatives represent an underutilized functional group for this purpose. Additionally, the interplay between polypeptide side chain structure, secondary conformation, and micelle morphology is not yet well understood, particularly in the case of structural regioisomers. Therefore, in this work, a series of polymer-homopolypeptide copolymers were prepared from a poly(ethylene glycol)-b-poly(glutamic acid) (PEG-b-PGA) backbone, where the pendant carboxylic acid groups were covalently conjugated to a series of pyridine regioisomers by carbodiimide coupling. These pyridine regioisomers differed only in the position of the nitrogen heteroatom, ortho, meta or para, relative to the linking group, generating a series of PEG-b-poly(pyridinylmethyl glutamate) (PEG-b-PMG) copolymers. Following self-assembly of the copolymers in aqueous solutions, dynamic light scattering (DLS) revealed differences in micelle hydrodynamic diameter (Dh) (ranging from ∼60 to 120 nm), while transmission electron microscopy (TEM) and small-angle X-ray scattering (SAXS) revealed distinctive morphologies ranging from ellipsoidal, to cylindrical, and disc-like, suggesting that subtle changes in positional isomers in the polypeptide block may influence the micelle structure. Analysis of the PEG-b-PMG copolymer micelles by circular dichroism (CD) and attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopy revealed that differences in the morphology were associated with changes in polypeptide secondary structure, which in turn was influenced by the position of the pyridine heteroatom. Overall, these findings contribute to the broader understanding of the relationship between polypeptide structure and micelle morphology and serve as useful insight for the rational design of polymer-polypeptide nanoparticles.

A Remarkable Impact of pH on the Thermo-Responsive Properties of Alginate-Based Composite Hydrogels Incorporating P2VP-PEO Micellar Nanoparticles

A heterograft copolymer with an alginate backbone, hetero-grafted by polymer pendant chains displaying different lower critical solution temperatures (LCSTs), combined with a pH-responsive poly(2-vinyl pyridine)-b-poly(ethylene oxide) (P2VP-b-PEO) diblock copolymer forming micellar nanoparticles, was investigated in aqueous media at various pHs. Due to its thermo-responsive side chains, the copolymer forms hydrogels with a thermo-induced sol-gel transition, above a critical temperature, Tgel (thermo-thickening). However, by lowering the pH of the medium in an acidic regime, a remarkable increase in the elasticity of the formulation was observed. This effect was more pronounced in low temperatures (below Tgel), suggesting secondary physical crosslinking, which induces significant changes in the hydrogel thermo-responsiveness, transforming the sol-gel transition to soft gel-strong gel. Moreover, the onset of thermo-thickening shifted to lower temperatures followed by the broadening of the transition zone, implying intermolecular interactions between the uncharged alginate backbone with the PNIPAM side chains, likely through H-bonding. The shear-thinning behavior of the soft gel in low temperatures provides injectability, which allows potential applications for 3D printing. Furthermore, the heterograft copolymer/nanoparticles composite hydrogel, encapsulating a model hydrophobic drug in the hydrophobic cores of the nanoparticles, was evaluated as a pH-responsive drug delivery system. The presented tunable drug delivery system might be useful for biomedical potential applications.

Teaching an Old Dog New Tricks: A Global Approach to Enhancing the Cytotoxicity of Drug-Loaded, Non-responsive Micelles Using Oligoelectrolytes

Polymeric micelles have been extensively studied as vectors for the delivery of hydrophobic drugs for the treatment of cancers and other diseases. Despite intensive research, few formulations provide significant benefits, and even fewer have been clinically approved. While many traditional non-responsive micelles have excellent safety profiles, they lack the ability to respond to the intracellular environment and release their cargo in a spatiotemporally defined manner to effectively deliver large doses of cytotoxic drugs into the cytosol of cells that overwhelm efflux pumps. As a novel and adaptable strategy, we hypothesized that well-established non-responsive polymeric micelles could be augmented with a pH-trigger via the co-encapsulation of cytocompatible oligoelectrolytes, which would allow rapid cargo release in the endosome, leading to increased cytotoxicity. Herein, we demonstrate how this strategy can be applied to render non-responsive micelles pH-responsive, resulting in abrupt cargo release at specific and tunable pH values compatible with endosomal delivery, which significantly increased their cytotoxicity up to 3-fold in an ovarian adenocarcinoma (SKOV-3) cell line compared to non-responsive micelles. In comparison, the oligoelectrolyte-loaded micelles were significantly less toxic to healthy 3T3 fibroblasts, indicating a selective cargo release in cancer cell lines. Oligoelectrolytes can be co-encapsulated in the micelles along with drugs at high encapsulation efficiency percentages, which are both ejected from the micelle core upon oligoelectrolyte ionization. Mechanistically, the increase in cytotoxicity appears to also result from the accelerated endosomal escape of the cargo caused by disruption of the endosomal membrane by the simultaneous release of the oligoelectrolytes from the micelles. Furthermore, we show how this approach is broadly applicable to non-responsive micelles regardless of their composition and various classes of hydrophobic chemotherapeutics. The preliminary studies presented here reveal the versatility and wide scope of oligoelectrolyte-mediated, pH-triggered drug release as a compelling and powerful strategy to enhance the cytotoxicity of non-responsive polymeric micelles.

Recent Advances in Nanotechnology-Based Targeted Delivery Systems of Active Constituents in Natural Medicines for Cancer Treatment

Owing to high efficacy and safety, natural medicines have found their way into the field of cancer therapy over the past few decades. However, the effective ingredients of natural medicines have shortcomings of poor solubility and low bioavailability. Nanoparticles can not only solve the problems above but also have outstanding targeting ability. Targeting preparations can be classified into three levels, which are target tissues, cells, and organelles. On the premise of clarifying the therapeutic purpose of drugs, one or more targeting methods can be selected to achieve more accurate drug delivery and consequently to improve the anti-tumor effects of drugs and reduce toxicity and side effects. The aim of this review is to summarize the research status of natural medicines' nano-preparations in tumor-targeting therapies to provide some references for further accurate and effective cancer treatments.

3D and 4D printing hydroxyapatite-based scaffolds for bone tissue engineering and regeneration

The osseous tissue can be classified as a nanocomposite that encompasses a complex interweaving of organic and inorganic matrices. This intricate amalgamation consists of a collagen component and a mineral phase that are intricately arranged to form elaborate and perforated configurations. Hydroxyapatite, whether synthesized artificially or obtained from natural sources, has garnered considerable attention as a composite material in the field of bone tissue engineering due to its striking resemblance to bone in terms of structure and characteristics. Hydroxyapatite (HA) constitutes the predominant ceramic biomaterial for biomedical applications due to its ability to replicate the mineral composition of vertebrate bone. Nonetheless, it is noteworthy that the present biomimetic substance exhibits unfavorable mechanical characteristics, characterized by insufficient tensile and compressive strength, thus rendering it unsuitable for effective employment in the field of bone tissue engineering. Due to its beneficial attributes, hydroxyapatite (HA) is frequently employed in conjunction with various polymers and crosslinkers as composites to enhance mechanical properties and overall efficacy of implantable biomaterials engineered. The restoration of skeletal defects through the use of customized replacements is an effective way to replace damaged or lost bone structures. This method not only restores the bones' original functions but also reinstates their initial aesthetic appearance. The utilization of hydroxyapatite-polymer composites within 3D-printed grafts necessitates meticulous optimization of both mechanical and biological properties, in order to ensure their suitability for employment in medical devices. The utilization of 3D-printing technology represents an innovative approach in the manufacturing of HA-based scaffolds, which offers advantageous prospects for personalized bone regeneration. The expeditious prototyping method, with emphasis on the application of 3D printing, presents a viable approach in the development of bespoke prosthetic implants, grounded on healthcare data sets. 4D printing approach is an evolved form of 3D printing that utilizes programmable materials capable of altering the intended shape of printed structures, contingent upon single or dual stimulating factors. These factors include aspects such as pH level, temperature, humidity, crosslinking degree, and leaching factors.