ATRP of Methacrylic Derivative of Camptothecin Initiated with PLA toward Three-Arm Star Block Copolymer Conjugates with Favorable Drug Release

Location of a Hydrophobic Load in Poly(oligo(ethylene glycol) methyl ether methacrylate)s (PEGMAs) Dissolved in Water and Probed by Fluorescence

Two series of pyrene-labeled poly(oligo(ethylene glycol) methyl ether methacrylate)s referred to as PyEG5-PEGnMA and PyC4-PEGnMA were prepared to probe the region surrounding the polymethacrylate backbone by using the fluorescence of the dye pyrene. PyEG5-PEGnMA and PyC4-PEGnMA were prepared by copolymerizing the EGnMA methacrylate monomers with penta(ethylene glycol) 1-pyrenemethyl ether methacrylate or 1-pyrenebutyl methacrylate, respectively. In organic solvents, the much longer 18 non-hydrogen atom linker connecting the pyrene moieties to the polymethacrylate backbone in the PyEG5-PEGnMA samples enabled the deployment of the pyrenyl labels into the solution. In water, however, an excited pyrene for PyEG5-PEGnMA was found to probe a same volume as for the PyC4-PEGnMA samples where a much shorter 6 non-hydrogen atom spacer connected pyrene to the backbone. Another surprising observation, considering that the hydrophobicity of pyrene induces strong pyrene aggregation for many pyrene-labeled water-soluble polymers (Py-WSPs) in water, was the little pyrene aggregation found for the PyEG5-PEGnMA and PyC4-PEGnMA samples in water. These effects could be related to the organic-like domain (OLD) generated by the oligo(ethylene glycol) side chains densely arranged around the polymethacrylate backbone of the polymeric bottlebrush (PBB). Additional fluorescence experiments conducted with the penta(ethylene glycol) 1-pyrenemethyl ether derivative indicated that the cylindrical OLD surrounding the polymethacrylate backbone had a chemical composition similar to that of ethylene glycol. Binding of hydrophobic pyrene molecules to unlabeled PEGnMA bottlebrushes in water further supported the existence of the OLD. The demonstration, that PEGnMA samples form an OLD in water, which can host and protect hydrophobic cargoes like pyrene, should lead to the development of improved PEGnMA-based drug delivery systems.

Recent Advances in the Application of ATRP in the Synthesis of Drug Delivery Systems

Advances in atom transfer radical polymerization (ATRP) have enabled the precise design and preparation of nanostructured polymeric materials for a variety of biomedical applications. This paper briefly summarizes recent developments in the synthesis of bio-therapeutics for drug delivery based on linear and branched block copolymers and bioconjugates using ATRP, which have been tested in drug delivery systems (DDSs) over the past decade. An important trend is the rapid development of a number of smart DDSs that can release bioactive materials in response to certain external stimuli, either physical (e.g., light, ultrasound, or temperature) or chemical factors (e.g., changes in pH values and/or environmental redox potential). The use of ATRPs in the synthesis of polymeric bioconjugates containing drugs, proteins, and nucleic acids, as well as systems applied in combination therapies, has also received considerable attention.

Structural Engineering of Star Block Biodegradable Polymer Unimolecular Micelles for Drug Delivery in Cancer Cells

The present investigation reports the structural engineering of biodegradable star block polycaprolactone (PCL) to tailor-make aggregated micelles and unimolecular micelles to study their effect on drug delivery aspects in cancer cell lines. Fully PCL-based star block copolymers were designed by varying the arm numbers from two to eight while keeping the arm length constant throughout. Multifunctional initiators were exploited for stepwise solvent-free melt ring-opening polymerization of ε-caprolactone and γ-substituted caprolactone to construct star block copolymers having a PCL hydrophobic core and a carboxylic PCL hydrophilic shell, respectively. A higher arm number and a higher degree of branching in star polymers facilitated the formation of unimolecular micelles as opposed to the formation of conventional multimicellar aggregates in lower arm analogues. The dense core of the unimolecular micelles enabled them to load high amounts of the anticancer drug doxorubicin (DOX, ∼12-15%) compared to the aggregated micelles (∼3-4%). The star unimolecular micelle completely degraded leading to 90% release of the loaded drug upon treatment with the lysosomal esterase enzyme in vitro. The anticancer efficacies of these DOX-loaded unimolecular micelles were tested in a breast cancer cell line (MCF-7), and their IC₅₀ values were found to be much lower compared to those of aggregated micelles. Time-dependent cellular uptake studies by confocal microscopy revealed that unimolecular micelles were readily taken up by the cells, and enhancement of the drug concentration was observed at the intracellular level up to 36 h. The present work opens new synthetic strategies for building a next-generation biodegradable unimolecular micellar nanoplatform for drug delivery in cancer research.

Polylactide Perspectives in Biomedicine: From Novel Synthesis to the Application Performance

The incessant developments in the pharmaceutical and biomedical fields, particularly, customised solutions for specific diseases with targeted therapeutic treatments, require the design of multicomponent materials with multifunctional capabilities. Biodegradable polymers offer a variety of tailored physicochemical properties minimising health adverse side effects at a low price and weight, which are ideal to design matrices for hybrid materials. PLAs emerge as an ideal candidate to develop novel materials as are endowed withcombined ambivalent performance parameters. The state-of-the-art of use of PLA-based materials aimed at pharmaceutical and biomedical applications is reviewed, with an emphasis on the correlation between the synthesis and the processing conditions that define the nanostructure generated, with the final performance studies typically conducted with either therapeutic agents by in vitro and/or in vivo experiments or biomedical devices.

Preparation and in vitro release of mPEG-PLA microspheres of Panax notoginseng saponins

This study was performed to promote the clinical application of Panax notoginseng saponins (PNS), which present anti-inflammatory and antitumor activities, and provided insights for the preparation of controlled-release dosage forms of traditional Chinese medicine. A series of drug-loaded microspheres with degradable amphiphilic polymer material polyethylene glycol monomethyl ether-polylactic acid (mPEG-PLA) as the carrier was synthesized. The degradation, sustained-release behavior, and biocompatibility of the drug-loaded microspheres were studied through in vitro release, degradation, hemolysis, anticoagulation, and cytotoxicity experiments. The pharmacological activities of the microspheres were studied through anti-inflammatory and antitumor experiments. The results showed that the best carrier material was mPEG_2k-PLA (1:9), with an average particle size of 3.47 ± 0.35 μm, a drug load of 5.50 ± 0.28 %, and an encapsulation efficiency of 38.52 ± 1.93 %. This material could be released stably for approximately 24 days and degrade in approximately 60 days. Moreover, the microspheres had good biocompatibility and anti-inflammatory and antitumor activities.

Grafted Lactic Acid Oligomers on Lignocellulosic Filler towards Biocomposites

Lactic acid oligomers (OLAs) were in situ synthesized from lactic acid (LAc) and grafted onto chokeberry pomace (CP) particleboards by direct condensation. Biocomposites of poly (lactic acid) (PLA) and modified/unmodified CP particles containing different size fractions were obtained using a mini-extruder. To confirm the results of the grafting process, the FTIR spectra of filler particles were obtained. Performing ¹HNMR spectroscopy allowed us to determine the chemical structure of synthesized OLAs. The thermal degradation of modified CP and biocomposites were studied using TGA, and the thermal characteristics of biocomposites were investigated using DSC. In order to analyse the adhesion between filler particles and PLA in biocomposites, SEM images of brittle fracture surfaces were registered. The mechanical properties of biocomposites were studied using a tensile testing machine. FTIR and ¹HNMR analysis confirmed the successful grafting process of OLAs. The modified filler particles exhibited a better connection with hydrophobic PLA matrix alongside improved mechanical properties than the biocomposites with unmodified filler particles. Moreover, a DSC analysis of the biocomposites with modified CP showed a reduction in glass temperature on average by 9 °C compared to neat PLA. It confirms the plasticizing effect of grafted and ungrafted OLAs. The results are promising, and can contribute to increasing the use of agri-food lignocellulosic residue in manufacturing biodegradable packaging.

Advances in amphiphilic polylactide/vinyl polymer based nano-assemblies for drug delivery

Micelles from self-assembled amphiphilic copolymers are highly attractive in drug delivery, due to their small size and hydrophilic stealth corona allowing prolonged lifetimes in the bloodstream and thus improved drug bioavailability. Polylactide (PLA)-based amphiphilic copolymer micelles are key candidates in this field, owing to the well-established biodegradability and biocompatibility of PLA. While PLA-b-poly(ethylene glycol) (PEG) block copolymer micelles can be seen as the "gold standard" in drug delivery research so far, the progresses in controlled radical polymerizations (Atom Transfer Radical Polymerization, Reversible Addition-Fragmentation Transfer and Nitroxide Mediated Polymerization) have offered new opportunities in the design of advanced amphiphilic copolymers for drug delivery due to their flexibility in many regards: (i) they can be easily combined with ring-opening polymerization (ROP) of lactide, with a diversity in types of architectures (e.g., block, graft, star), (ii) they allow (co)polymerization of a wide range of vinyl monomers, possibly circumventing PEG limitations, (iii) functionalization (with biomolecules or stimuli-cleavable moieties) is versatile due to end-group fidelity and copolymerization ability with reactive/functional comonomers. In this review, we report on the advances in the past decade of such amphiphilic PLA/vinyl polymer based nano-carriers, regarding key properties such as stealth character, cell targeting and stimuli-responsiveness.

Effect of structural factors on release profiles of camptothecin from block copolymer conjugates with high load of drug

The aim of the present work was the synthesis and study the kinetics and profiles of camptothecin (CPT) release form block co- and ter-polymer conjugates comprising polylactide (PLA) segments and CPT moieties, structurally diverse by degrees of branching, content of d-PLA units and poly(ethylene glycol) methyl ether methacrylate (PEGMA). Six PLA, non-toxic macroinitiators (MIs), terminated with α-bromoester were synthesized. MIs were subjected to polymerization of CPT methacrylic derivative (CPTMA) with PEGMA at various ratios. The average contents of CPT from elemental analysis, NMR and UV-GPC were approximate to each other. The number of CPT molecules and PEGMA units was in the range of 9-195 and 0-280 per conjugate, respectively. PEGMA units plasticized PLA causing increase of its crystallinity, whereas 7% and more of d-PLA caused material amorphous. PEGMA units decreased thermal stability of conjugates, however it compatibillized the separated phases of PLA and PCPTMA, based on AFM. In vitro release rate of CPT from linear PLA conjugates deposited on injection-molded PLA bars increased by introduction of PEGMA units with zero-order kinetics and Korsmeyer-Peppas model indicating the super case II transport. Branched conjugates revealed some burst release and then the release was rather of first-order-kinetics with respect to CPT with non-Fickian transport.