Straightforward route to superhydrophilic poly(2-oxazoline)s via acylation of well-defined polyethylenimine

Herein, we describe a new method for the synthesis of superhydrophilic poly(2-alkyl-2-oxazoline)s (PAOx) from poly(2-ethyl-2-oxazoline) (PEtOx). A well-defined linear polyethylenimine was prepared from PEtOx by controlled acidic hydrolysis of its side-chains followed by reacylation with different carboxylic acids. Using this protocol, we obtained a series of new hydrophilic PAOx containing side-chain ether groups with potential in biomaterials science. The relative hydrophilicity of the polymers was assessed, revealing that poly(2-methoxymethyl-2-oxazoline) (PMeO-MeOx) is the most hydrophilic PAOx reported to date. Additionally, the amorphous poly(2-methoxy-ethoxy-ethoxymethyl-2-oxazoline) (PDEGOx) shows the lowest reported glass transition temperature (-25 degrees C) within the PAOx family to date. The biomedical potential of the prepared polymers was further fortified by an in vitro cytotoxicity study, where all polymers appeared to be noncytotoxic. The described synthetic protocol is universal and can be extremely versatile, especially for PAOx that are difficult to prepare by conventional cationic ring-opening polymerization due to the monomer interference and/or degradation

Visualization and design of the functional group distribution during statistical copolymerization

Even though functional copolymers with a low percentage of functional comonomer units (up to 20 mol%) are widely used, for instance for the development of polymer therapeutics and hydrogels, insights in the functional group distribution over the actual chains are lacking and the average composition is conventionally used to describe the functionalization degree. Here we report the visualization of the monomer distribution over the different polymer chains by a synergetic combination of experimental and theoretical analysis aiming at the construction of functionality-chain length distributions (FUNC-CLDs). A successful design of the chemical structure of the comonomer pair, the initial functional comonomer amount (13 mol%), and the temperature (100 °C) is performed to tune the FUNC-CLD of copoly(2-oxazoline)s toward high functionalization degree for both low (100) and high (400) target degrees of polymerization. The proposed research strategy is generic and extendable to a broad range of copolymerization chemistries, including reversible deactivation radical polymerization

Conformational properties of biocompatible poly(2-ethyl-2-oxazoline)s in phosphate buffered saline

Inspired by the increasing popularity of poly(2-ethyl-2-oxazoline) (PEtOx) for biomedical applications, this study reports the complete and thorough solution analysis of the homologous series of biocompatible PEtOx samples in a very broad range of molecular weights ranging from 11.2 x 10(3) g mol(-1) up to 260 x 10(3) g mol(-1). The main focus of the research was on the determination of the conformational properties of PEtOx macromolecules at a temperature of 37 degrees C in phosphate buffered saline (PBS) simulating the parameters of physiological media. The polymers were studied in PBS solutions by analytical ultracentrifugation, dynamic light scattering (DLS), translational diffusion, and intrinsic viscosity measurements in a temperature range from 15 degrees C up to 72 degrees C. The complete set of Kuhn-Mark-Houwink-Sakurada scaling relationships revealed linear trends over the whole range of the studied molar masses, while the determined scaling indices at 37 degrees C correspond to the coil conformation in a thermodynamically good solvent ([eta] = 0.045 x M-0.62, s(0) = 0.010 x M-0.46 and D-0 = 1750 x M-0.54). Based on the intrinsic viscosity values (most sensitive characteristic to the size variations of polymer coils, [eta] similar to r(3)), it was demonstrated that PEtOx macromolecules in PBS solutions undergo a transition from swollen polymer coils with gradual deterioration of thermodynamic quality of solutions within the temperature range of 15-45 degrees C, reaching theta-conditions at 55 degrees C with further precipitation at 62-72 degrees C. Also, to the best of our knowledge, the conformational parameters (equilibrium rigidity/the Kuhn segment length and the diameter of the polymer chain) of PEtOx macromolecules were evaluated under physiological conditions for the first time and constitute A = 1.8 +/- 0.3 nm and d = 0.7 +/- 0.4 nm. These equilibrium rigidity values classify PEtOx as a flexible macromolecule with rigidity similar to that of poly(ethylene glycol). For the first time, we were able to demonstrate a direct influence of thermosensitivity on the rigidity of the biocompatible polymer: PEtOx. The Kuhn segment length is undoubtedly decreasing when approaching the LCST

Conformational Parameters and Hydrodynamic Behavior of Poly(2-Methyl-2-Oxazoline) in a Broad Molar Mass Range

In this work, we report our results on the hydrodynamic behavior of poly(2-methyl-2-oxazoline) (PMeOx). PMeOx is gaining significant attention for use as hydrophilic polymer in pharmaceutical carriers as an alternative for the commonly used poly(ethylene glycol) (PEG), for which antibodies are found in a significant fraction of the human population. The main focus of the current study is to determine the hydrodynamic characteristics of PMeOx under physiological conditions, which serves as basis for better understanding of the use of PMeOx in pharmaceutical applications. This goal was achieved by studying PMeOx solutions in phosphate-buffered saline (PBS) as a solvent at 37 °C. This study was performed based on two series of PMeOx samples; one series is synthesized by conventional living cationic ring-opening polymerization, which is limited by the maximum chain length that can be achieved, and a second series is obtained by an alternative synthesis strategy based on acetylation of well-defined linear poly(ethylene imine) (PEI) prepared by controlled side-chain hydrolysis of a defined high molar mass of poly(2-ethyl-2-oxazoline). The combination of these two series of PMeOx allowed the determination of the Kuhn–Mark–Houwink–Sakurada equations in a broad molar mass range. For intrinsic viscosity, sedimentation and diffusion coefficients, the following expressions were obtained: η=0.015M0.77, s0=0.019M0.42 and D0=2600M−0.58, respectively. As a result, it can be concluded that the phosphate-buffered saline buffer at 37 °C represents a thermodynamically good solvent for PMeOx, based on the scaling indices of the equations. The conformational parameters for PMeOx chains were also determined, revealing an equilibrium rigidity or Kuhn segment length, (A) of 1.7 nm and a polymer chain diameter (d) of 0.4 nm. The obtained value for the equilibrium rigidity is very similar to the reported values for other hydrophilic polymers, such as PEG, poly(vinylpyrrolidone) and poly(2-ethyl-2-oxazoline), making PMeOx a relevant alternative to PEG

Toll-like receptor signaling in thymic epithelium controls monocyte-derived dendritic cell recruitment and Treg generation

The development of thymic regulatory T cells (Treg) is mediated by Aire-regulated self-antigen presentation on medullary thymic epithelial cells (mTECs) and dendritic cells (DCs), but the cooperation between these cells is still poorly understood. Here we show that signaling through Toll-like receptors (TLR) expressed on mTECs regulates the production of specific chemokines and other genes associated with post-Aire mTEC development. Using single-cell RNA-sequencing, we identify a new thymic CD14(+)Sirp alpha (+) population of monocyte-derived dendritic cells (CD14(+)moDC) that are enriched in the thymic medulla and effectively acquire mTEC-derived antigens in response to the above chemokines. Consistently, the cellularity of CD14(+)moDC is diminished in mice with MyD88-deficient TECs, in which the frequency and functionality of thymic CD25(+)Foxp3(+) Tregs are decreased, leading to aggravated mouse experimental colitis. Thus, our findings describe a TLR-dependent function of mTECs for the recruitment of CD14(+)moDC, the generation of Tregs, and thereby the establishment of central tolerance. Immune tolerance is mediated by the deletion of autoreactive T cells via medullary thymic epithelial cells (mTEC) and dendritic cells (DC), and by the induction of regulatory T cells (Treg). Here the authors show that mTEC receiving toll-like receptor signaling control the recruitment of CD14(+)Sirp alpha (+) DC population that is capable of inducing Treg for establishing tolerance

High aboveground carbon stock of African tropical montane forests

Tropical forests store 40-50 per cent of terrestrial vegetation carbon(1). However, spatial variations in aboveground live tree biomass carbon (AGC) stocks remain poorly understood, in particular in tropical montane forests(2). Owing to climatic and soil changes with increasing elevation(3), AGC stocks are lower in tropical montane forests compared with lowland forests(2). Here we assemble and analyse a dataset of structurally intact old-growth forests (AfriMont) spanning 44 montane sites in 12 African countries. We find that montane sites in the AfriMont plot network have a mean AGC stock of 149.4 megagrams of carbon per hectare (95% confidence interval 137.1-164.2), which is comparable to lowland forests in the African Tropical Rainforest Observation Network(4) and about 70 per cent and 32 per cent higher than averages from plot networks in montane(2,5,6) and lowland(7) forests in the Neotropics, respectively. Notably, our results are two-thirds higher than the Intergovernmental Panel on Climate Change default values for these forests in Africa(8). We find that the low stem density and high abundance of large trees of African lowland forests(4) is mirrored in the montane forests sampled. This carbon store is endangered: we estimate that 0.8 million hectares of old-growth African montane forest have been lost since 2000. We provide country-specific montane forest AGC stock estimates modelled from our plot network to help to guide forest conservation and reforestation interventions. Our findings highlight the need for conserving these biodiverse(9,10) and carbon-rich ecosystems. The aboveground carbon stock of a montane African forest network is comparable to that of a lowland African forest network and two-thirds higher than default values for these montane forests.Peer reviewe

Simulation of electron beam transport within hollow electron lens using warp and development of calibration method for beam loss monitors

The High Luminosity LHC aims to double the stored beam energy up to 700 MJ which challenges its collimation system and consequent beam losses measurements to new, greater performances. This thesis describes a proposed new stage of LHC collimation system, the Hollow Electron Lens (HEL) and a radiation-hard Diamond Beam Loss Monitors (dBLMs). The practical part of the work discusses relative calibration of the dBLMs response to LHC25ns like bunch train. A measurement was carried out to relatively calibrate the analog and digital chain of every dBLM at LHC in order to provide users with a rough measure of the relative beam losses. Calibration coefficients for the dBLM intallations were calculated and readied for use in the control system. Further, a hollow electron beam was simulated in the first part of HEL using Warp code. The trajectory of the beam was found to be stable, with a beam offset of ≈ 1.5 mm after a bend, agreeing with the CST simulations. Mesh bending was studied and found to introduce no artifacts in the trajectory or the beam profile

Drug delivery systems based on poly(2-oxazoline)s and p(2-oxazine)s

Poly(2-oxazoline)s (PAOx) represent an established class of polymer materials with a wide range of applications. In contrast, the homologous poly(2-oxazine)s (PAOzi) are only gaining increasing attention in the past years. Despite their high synthetic modularity and excellent biological properties, reports describing their use as a platform for construction of drug delivery systems are still relatively sparse. In this report, an overview of the recent progress in the field of drug delivery systems based on PAOx and PAOzi polymers is provided and a comparison is made with systems based on other polymer carriers, particularly poly(ethylene glycol) (PEG) and poly(N-hydroxypropylmethacrylamide) (PHPMA). The emerging potential of PAOx and PAOzi is highlighted in the context of current polymer therapeutics research

Synthesis of defined high molar mass poly(2-methyl-2-oxazoline)

In this communication, we report for the first time the synthesis of defined high molar mass poly(2-methyl-2-oxazoline) (PMeOx), a water-soluble polymer with excellent anti-fouling properties. So far, there has been no report on low dispersity (D < 1.2) PMeOx longer than 10 kg mol(-1). Higher molar mass would be beneficial for synthesis of polymer-drug conjugates, excipients as well as for other biomedical applications. We report our attempts to prepare defined high molar mass PMeOx via living cationic ring-opening polymerization (CROP) of its monomer using our optimized method that failed due to extensive chain transfer and chain coupling side reactions. Therefore, we proposed an alternative strategy to high molar mass PMeOx based on acetylation of well-defined linear polyethyleneimine (PEI) prepared by controlled side-chain hydrolysis of defined high molar mass PEtOx. This method allowed us to synthesize a series of low-dispersity PMeOx up to 58 kg mol(-1) (D = 1.07). Considering the biomedical potential of PMeOx, the synthesis of such polymers might open a way to a new class of effective polymer-based therapeutics

Poly(2-amino-2-oxazoline)s : a new class of thermoresponsive polymers

In this report, we describe the synthesis and properties of poly(2-dialkylamino-2-oxazoline)s (PAmOx), a new class of thermoresponsive polymers. These polymers were synthesized by acylation of linear polyethyleneimine, as the conventional cationic ring-opening polymerization of the respective monomers led to extensive chain transfer reactions. The hydrophilicity of obtained poly(2-dialkylamino-2-oxazoline)s was highly dependent on the side-chain substituents, ranging from very hydrophilic poly(2-dimethylamino-2-oxazoline) to the hydrophobic poly(2-diisopropylamino-2-oxazoline). Notably, the poly(2-diethylamino-2-oxazoline) (PDEAOx) shows fast-response LCST behavior around room temperature (24 degrees C), as well as low T-g (-10 degrees C), which can be beneficial in the construction of new stimuli-responsive biomaterials. Overall, PAmOx represent a novel polymer platform for a wide range of possible applications