Linear Polyethyleneimine: Optimized Synthesis and Characterization - On the Way to “Pharmagrade” Batches

Reduction of Pro-Inflammatory Markers in RAW264.7 Macrophages by Polyethylenimines

The physiological problem of chronic inflammation and its associated pathologies attract ongoing attention with regard to methods for their control. Current systemic pharmacological treatments present problematic side effects. Thus, the possibility of new anti-inflammatory compounds with differing mechanisms of action or biophysical properties is enticing. Cationic polymers, with their ability to act as carriers for other molecules or to form bio-compatible materials, present one such possibility. Although not well described, several polycations such as chitosan and polyarginine, have displayed anti-inflammatory properties. The present work shows the ubiquitous laboratory transfection reagent, polyethylenimine (PEI) and more specifically low molecular weight branched PEI (B-PEI) as also possessing such properties. Using a RAW264.7 murine cell line macrophage as an inflammation model, it is found the B-PEI 700 Da as being capable of reducing the production of several pro-inflammatory molecules induced by the endotoxin lipopolysaccharide. Although further studies are required for elucidation of its mechanisms, the revelation that such a common lab reagent may present these effects has wide-ranging implications, as well as an abundance of possibilities.

Efficient in vitro and in vivo transfection of self-amplifying mRNA with linear poly(propylenimine) and poly(ethylenimine-propylenimine) random copolymers as non-viral carriers

Messenger RNA (mRNA) based vaccines have been introduced worldwide to combat the Covid-19 pandemic. These vaccines consist of non-amplifying mRNA formulated in lipid nanoparticles (LNPs). Consequently, LNPs are considered benchmark non-viral carriers for nucleic acid delivery. However, the formulation and manufacturing of these mRNA-LNP nanoparticles are expensive and time-consuming. Therefore, we used self-amplifying mRNA (saRNA) and synthesized novel polymers as alternative non-viral carrier platform to LNPs, which enable a simple, rapid, one-pot formulation of saRNA-polyplexes. Our novel polymer-based carrier platform consists of randomly concatenated ethylenimine and propylenimine comonomers, resulting in linear, poly(ethylenimine-ran-propylenimine) (L-PEIx-ran-PPIy) copolymers with controllable degrees of polymerization. Here we demonstrate in multiple cell lines, that our saRNA-polyplexes show comparable to higher in vitro saRNA transfection efficiencies and higher cell viabilities compared to formulations with Lipofectamine MessengerMAX™ (LFMM), a commercial, lipid-based carrier considered to be the in vitro gold standard carrier. This is especially true for our in vitro best performing saRNA-polyplexes with N/P 5, which are characterised with a size below 100 nm, a positive zeta potential, a near 100% encapsulation efficiency, a high retention capacity and the ability to protect the saRNA from degradation mediated by RNase A. Furthermore, an ex vivo hemolysis assay with pig red blood cells demonstrated that the saRNA-polyplexes exhibit negligible hemolytic activity. Finally, a bioluminescence-based in vivo study was performed over a 35-day period, and showed that the polymers result in a higher and prolonged bioluminescent signal compared to naked saRNA and L-PEI based polyplexes. Moreover, the polymers show different expression profiles compared to those of LNPs, with one of our new polymers (L-PPI250) demonstrating a higher sustained expression for at least 35 days after injection.

Clickable polyethyleneimine incorporated into triblock copolymeric micelles as an efficient platform in the delivery of siRNA to NSCLC cells

The efficacy of transfection vectors to cross the endosomal membrane into the cytosol is a central aspect in the development of nucleic acid-based therapeutics. The challenge remains the same: Delivery, Delivery, Delivery. Despite a rational and appropriate construct of triblock polymeric micelles, which could serve as an ideal platform for the co-delivery of siRNAs and hydrophobic anticancer drugs, we show here its inability to properly convey oligonucleotides to their final destination. In order to overcome biological barriers, a linear PEI comprising two orthogonal groups was synthesized, holding an appropriate balance between safety and efficacy. Micellar carriers were then formulated with this polymer to enhance endosomal siRNA release. This chemical technology also addresses the two major challenges to consider when developing novel micellar products for siRNA delivery, namely cytotoxicity of polycations and endosomal escape. Herein, we demonstrate successful release of siRNA using a polymer tailoring strategy combined with a relevant in vitro approach, considering STAT3 as a promising target in the treatment of non-small cell lung cancer (NSCLC).

Reversible Amidation Chemistry Enables Closed-Loop Chemical Recycling of Carbon Fiber Reinforced Polymer Composites to Monomers and Fibers

Highly efficient recycling of carbon fiber reinforced polymer composites into monomers and fibers is a formidable challenge. Herein, we present a closed-loop recycling approach for carbon fiber reinforced polymer composites using reversible amidation chemistry, which enables the complete recovery of intact carbon fibers and pure monomers. The polymer network, synthesized by amidation between a macromonomer linear polyethyleneimine and a bifunctional maleic anhydride cross-linker, serves as a matrix for the construction of composites with exceptional mechanical properties, thermal stability and solvent resistance. The matrices can be fully depolymerized under the acidic condition at ambient temperature, allowing the effective separation and recovery of both carbon fibers and the two monomers. The reclaimed carbon fibers retain nearly identical mechanical properties to pristine ones, while pure monomers are recycled with high separation yields (>93 %). They can be reused in for multiple cycles for the manufacture of new composites, whose mechanical properties recover over 95 % of their original properties. This line of research presents a promising approach for the design of high-performance and sustainable thermoset composites, offering significant environmental and economic benefits.

Stochasticity of poly(2-oxazoline) oligomer hydrolysis determined by tandem mass spectrometry

Understanding modification of synthetic polymer structures is necessary for their accurate synthesis and potential applications. In this contribution, a series of partially hydrolyzed poly(2-oxazoline) species were produced forming poly[(2-polyoxazoline)-co-(ethylenimine)] (P(EtOx-co-EI)) copolymers; EI being the hydrolyzed product of Ox. Bulk mass spectrometry (MS) measurements accurately measured the EI content. Tandem mass spectrometry analysis of the EI content in the copolymer samples determined the distribution of each monomer within the copolymer and corresponded to a theoretically modelled random distribution. The EI distribution across the polymers was shown to be effected by the choice of terminus, with a permanent hydrolysis event observed at an OH terminus. A neighbouring group effect wasn't observed at the polymer length analysed (approximately 25-mer species), suggesting that previously observed neighbouring group effects require a larger polymer chain. Although clearly useful for random polymer distribution this approach may be applied to many systems containing non-specific modifications to determine if they are directed or random locations across peptides, proteins, polymers, and nucleic acids.

Tandem mass spectrometry can be used to better understand modification sites of synthetic polymer structures providing more complete chemical knowledge which is necessary for their accurate synthesis and potential applications.

Physicochemical and Mechanical Properties of Bis-GMA/TEGDMA Dental Composite Resins Enriched with Quaternary Ammonium Polyethylenimine Nanoparticles

Modification of dental monomer compositions with antimicrobial agents must not cause deterioration of the structure, physicochemical, or mechanical properties of the resulting polymers. In this study, 0.5, 1, and 2 wt.% quaternary ammonium polyethylenimine nanoparticles (QA-PEI-NPs) were obtained and admixed with a Bis-GMA/TEGDMA (60:40) composition. Formulations were then photocured and tested for their degree of conversion (DC), polymerization shrinkage (S), glass transition temperature (T_g), water sorption (WS), solubility (SL), water contact angle (WCA), flexural modulus (E), flexural strength (σ), hardness (HB), and impact resistance (a_n). We found that the DC, S, Tg, WS, E, and HB were not negatively affected by the addition of QA-PEI-NPs. Changes in these values rarely reached statistical significance. On the other hand, the SL increased upon increasing the QA-PEI-NPs concentration, whereas σ and a_n decreased. These results were usually statistically significant. The WCA values increased slightly, but they remained within the range corresponding to hydrophilic surfaces. To conclude, the addition of 1 wt.% QA-PEI-NPs is suitable for applications in dental materials, as it ensures sufficient physicochemical and mechanical properties.

Tyrosine-Modification of Polypropylenimine (PPI) and Polyethylenimine (PEI) Strongly Improves Efficacy of siRNA-Mediated Gene Knockdown

The delivery of small interfering RNAs (siRNA) is an efficient method for gene silencing through the induction of RNA interference (RNAi). It critically relies, however, on efficient vehicles for siRNA formulation, for transfection in vitro as well as for their potential use in vivo. While polyethylenimines (PEIs) are among the most studied cationic polymers for nucleic acid delivery including small RNA molecules, polypropylenimines (PPIs) have been explored to a lesser extent. Previous studies have shown the benefit of the modification of small PEIs by tyrosine grafting which are featured in this paper. Additionally, we have now extended this approach towards PPIs, presenting tyrosine-modified PPIs (named PPI-Y) for the first time. In this study, we describe the marked improvement of PPI upon its tyrosine modification, leading to enhanced siRNA complexation, complex stability, siRNA delivery, knockdown efficacy and biocompatibility. Results of PPI-Y/siRNA complexes are also compared with data based on tyrosine-modified linear or branched PEIs (LPxY or PxY). Taken together, this establishes tyrosine-modified PPIs or PEIs as particularly promising polymeric systems for siRNA formulation and delivery.

Organocatalytic Ring-Opening Polymerization of N-Acylated-1,4-oxazepan-7-ones Toward Well-Defined Poly(ester amide)s: Biodegradable Alternatives to Poly(2-oxazoline)s

We report a series of poly(ester amide)s (PEAs) synthesized by organocatalytic ring-opening polymerization (ROP) of N-acylated-1,4-oxazepan-7-one (OxP) monomers, produced from N-acylated-4-piperidones using the Baeyer-Villiger oxidation reaction. The ROP of OxPs, conducted in CH₂Cl₂ at room temperature with benzyl alcohol as initiator and TBD/TU (1,5,7-triazabicyclo[4.4.0]dec-5-ene/thiourea) as a binary organocatalytic system, revealed a controlled/living character. The thermodynamics of the ROP highly depends on the N-acylated substituent of monomers, with the following reactivity order: OxP_Ph > OxP_Me > OxP_Pr > OxP_Bn. Based on NMR results, it seems that our system follows the hydrogen bonding bifunctional activation mechanism. All intermediates and final products were characterized by NMR, MALDI-TOF MS, SEC, and DSC techniques. All poly(N-acylated-1,4-oxazepan-7-one) (POxP) polymers are amorphous with different glass transition temperatures (T_g), depending on the N-acylated substituent (T_g: -2.90 to 43.75 °C). Among the synthesized polymers, only POxP_Me was water-soluble and it degraded much faster than polycaprolactone in an aqueous phosphate buffer saline solution (pH = 7.4). Therefore, poly(N-acylated-1,4-oxazepan-7-one)s are potential biodegradable alternatives to poly(2-oxazoline)s.

Linear Well-Defined Polyamines via Anionic Ring-Opening Polymerization of Activated Aziridines: From Mild Desulfonylation to Cell Transfection

Linear polyethylenimine (L-PEI), a standard for nonviral gene delivery, is usually prepared by hydrolysis from poly(2-oxazoline)s. Lately, anionic polymerization of sulfonamide-activated aziridines had been reported as an alternative pathway toward well-defined L-PEI and linear polyamines. However, desulfonylation of the poly(sulfonyl aziridine)s typically relied on harsh conditions (acid, microwave) or used a toxic solvent (e.g., hexamethylphosphoramide). In addition, the drastic change of polarity requires solvents, which keep poly(sulfonyl aziridine)s as well as L-PEI in solution, and only a limited number of strategies were reported. Herein, we prepared 1-(4-cyanobenzenesulfonyl) 2-methyl-aziridine (1) as a monomer for the anionic ring-opening polymerization. It was polymerized to well-defined and linear poly(sulfonyl aziridine)s. The 4-cyanobenzenesulfonyl-activating groups were removed under mild conditions to linear polypropylenimine (L-PPI). Using dodecanethiol and diazabicyclo-undecene (DBU) allowed ≥98% desulfonylation and a reliable purification toward polyamines with high purity and avoiding main-chain scission. This method represents a fast approach in comparison to previous methods used for postpolymerization desulfonylation and produces linear well-defined polyamines. The high control over molecular weight and dispersities achieved by living anionic polymerization are the key advantages of our strategy, especially if used for biomedical applications, in which molecular weight might correlate with toxicity. The synthesized polypropylenimine was further tested as a cell-transfection agent and proved, with 16.1% transfection efficiency of the cationic nanoparticles, to be an alternative to L-PEI obtained from the 2-oxazoline route. This general strategy will allow the preparation of complex macromolecular architectures containing polyamine segments, which were not accessible before.

pH-Responsive Side Chains as a Tool to Control Aqueous Self-Assembly Mechanisms

pH-Tunable nanoscale morphology and self-assembly mechanism of a series of oligo(p-phenyleneethynylene) (OPE)-based bolaamphiphiles featuring poly(ethylene imine) (PEI) side chains of different length and degree of hydrolysis are described. Protonation and deprotonation of the PEI chains by changing the pH alters the hydrophilic/hydrophobic balance of the systems and, in turn, the strength of intermolecular interactions between the hydrophobic OPE moieties. Low pH values (3) lead to weak interaction between the OPEs and result in spherical nanoparticles, in which aggregation follows an isodesmic mechanism. In contrast, higher pH values (11) induce deprotonation of the polymer chains and lead to a stronger, cooperative aggregation into anisotropic nanostructures. Our results demonstrate that pH-responsive chains can be exploited as a tool to tune self-assembly mechanisms, which opens exciting possibilities to develop new stimuli-responsive materials.

Oxidation-Resistant, Cost-Effective Epoxide-Modified Polyamine Adsorbents for CO2 Capture from Various Sources Including Air

CO₂ adsorbents based on the reaction of pentaethylenehexamine (PEHA) or tetraethylenepentamine (TEPA) with propylene oxide (PO) were easily prepared in "one pot" by impregnation on a silica support in water. The starting materials were readily available and inexpensive, facilitating the production of the adsorbents on a large scale. The prepared polyamine/epoxide adsorbents were efficient in capturing CO₂ and could be regenerated under mild conditions (50-85 °C). They displayed a much-improved stability compared with their unmodified amine counterparts, especially under oxidative conditions. Leaching of the active organic amine became minimal or nonexistent after treatment with the epoxide. The adsorption as well as desorption kinetics were also greatly improved. The polyamine/epoxide adsorbents were able to capture CO₂ from various sources including ambient air and indoor air with CO₂ concentrations of only 400-1000 ppm. The presence of water, far from being detrimental, increased the adsorption capacity. Their use for indoor air quality purposes was explored.

Microwave-Assisted Desulfonylation of Polysulfonamides toward Polypropylenimine

Linear polyethylenimine (L-PEI) has been the gold standard for gene delivery and is typically prepared by hydrolysis from poly(2-oxazoline)s. Recently, also the anionic polymerization of activated aziridines was reported as a potential pathway toward linear and well-defined polyamines. However, only sulfonamide-activated aziridines so far undergo the living anionic polymerization and their desulfonylation was only reported scarcely. This is mainly due to the relatively high stability of the sulfonamides and the drastic change in solubility during the desulfonylation. Herein, we investigated the desulfonylation of such poly(aziridine)s prepared from tosylated or mesylated propyleneimine to afford linear polypropylenimine (L-PPI) as an alternative to L-PEI. Different desulfonylation strategies for tosylated (Ts) and mesylated (Ms) PPI were studied. The reductive cleavage of the sulfonamide with sodium bis(2-methoxy ethoxy) aluminum hydride yielded 80% of deprotected amine groups. Quantitative conversion to L-PPI was obtained, when the tosylated PPI was hydrolyzed under acidic conditions with pTsOH under microwave (MW) irradiation. The same treatment removed 90% of the mesyl groups from the mesylated PPI analog. The MW-assisted acidic hydrolysis represents a fast, inexpensive and easy approach in comparison to other methods, where complex reaction conditions and tedious purifications are major drawbacks, however some chain scission may occur. The high purity of the obtained products, in combination with the versatility of the activated aziridine chemistry, demonstrate many advantages of our strategy, especially for future biomedical implementations.

The Power of Shielding: Low Toxicity and High Transfection Performance of Cationic Graft Copolymers Containing Poly(2-oxazoline) Side Chains

We show the potential of oligo(2-ethyl-2-oxazoline) (Ox_n)-shielded graft copolymers of (2-aminoethyl)-methacrylate and N-methyl-(2-aminoethyl)-methacrylate for pDNA delivery in HEK cells. For the effect of grafting density and side chain length concerning improved transfection properties through the concept of shielding to be investigated, copolymers were synthesized via the macromonomer method using a combination of cationic ring opening polymerization and reversible addition-fragmentation chain transfer polymerization to vary the degree of grafting (DG = 10 and 30%) as well as the side chain degree of polymerization (DP = 5 and 20). Investigations of the polyplex formation, in vitro flow cytometry, and confocal laser scanning microscopy measurements on the copolymer library revealed classical shielding properties of the Ox side chains, including highly reduced cytotoxicity and a partial decrease in transfection efficiency, as also reported for polyethylene glycol shielding. In terms of the transfection efficiency, the best performing copolymers (A- g-Ox₅(10) and M- g-Ox₅(10)) revealed equal or better performances compared to those of the corresponding homopolymers. In particular, the graft copolymers with low DG and side chain DP transfected well with over 10-fold higher IC₅₀ values. In contrast, a DG of 30% resulted in a loss of transfection efficiency due to missing ability for endosomal release, and a side chain DP of 20 hampered the cellular uptake.

Living Anionic Copolymerization of 1-(Alkylsulfonyl)aziridines to Form Poly(sulfonylaziridine) and Linear Poly(ethylenimine)

The anionic ring-opening copolymerization of 1-(methylsulfonyl)aziridine (MsAz) and 1-(sec-butylsulfonyl)aziridine (^sBsAz) produces a soluble random copolymer P(MsAz-r-^sBsAz), which can subsequently be converted to linear poly(ethylenimine) (lPEI). The copolymerization of MsAz and ^sBsAz is living and allows for the synthesis of copolymers with low molecular weight distributions. Sequential anionic polymerization of MsAz and ^sBsAz with 2-methyl-1-(methylsulfonyl)aziridine (MsMAz) creates P(MsAz-r-^sBsAz)-b-P(MeMsAz). Removal of the sulfonyl groups from P(MsAz-r-^sBsAz)-b-P(MsMAz) gives lPEI-b-poly(propylenimine). For the first time, lPEI can be synthesized by a controlled anionic polymerization.

Multihydroxy Polyamines by Living Anionic Polymerization of Aziridines

Acetal-protected and sulfonamide-activated aziridines (Az) have been prepared and polymerized by living anionic polymerization with molecular weight dispersities in most cases below Đ < 1.2 and controlled molecular weights. Three new monomers have been prepared varying in the length of the pendant chain. The resulting double protected polymers can be selectively deprotected in order to release the polyamine or the polyol structures. Detailed structural characterization was performed for all polymers, and chain extension proves their living polymerization behavior and the formation of block copolymers. Thermal analysis can be used in order to follow the deprotection steps. These new protected monomers broaden the scope of the azaanionic polymerization of aziridines and may find useful applications as well-defined functional poly(ethylene imine) derivatives.