Poly(ethylene glycol)s (PEG) are widely and intensely used in the pharmaceutical industry and biomedical applications, and due to this fact, antibodies have recently been reported. Poly(2oxazoline)s (POx) are promising candidates for potential replacement of PEG in related applications, and as such, their hydrodynamic properties and characteristics derived from light scattering experiments are important to reconcile their behavior in solution. In this study, we have investigated the molecular hydrodynamic characteristics of poly(2-methyl-2-oxazoline)s and poly(2-ethyl-2-oxazoline)s in the pharmaceutical molar mass range as base candidates for such applications, prepared by cationic ring-opening polymerization in a microwave reactor. A combined viscometry and sedimentation−diffusion analysis by using sedimentation velocity experiments in an analytical ultracentrifuge includes (i) the study of intrinsic viscosities, (ii) sedimentation coefficients, and (iii) derived translational diffusion coefficients. These characteristics are then interrelated through hydrodynamic invariants that showed consistency between all these hydrodynamic parameters and, consequently, adequate values of derived absolute molar masses. The established scaling relationships of POx could as well be related quantitatively to that of pharmaceutical PEG from a recent study. Complementary, the molar masses were estimated by asymmetrical flow field-flow fractionation (AF4) and size exclusion chromatography (SEC) in conjunction with multiangle laser light scattering (MALLS). Thus, the obtained results of molar masses show an overarching good correlation to that of the hydrodynamic analysis utilizing the ultracentrifuge and viscometry. However, we demonstrate as well that AF4-/SEC-MALLS experiments of macromolecules below 10 000 g mol −1 may provide erroneous information on their molar mass, identified and discussed by the hydrodynamic invariant concept interrelating three independent experimental approaches on the same sample, i.e., (i) intrinsic viscosities, (ii) intrinsic sedimentation coefficients, and (iii) molar masses from light scattering. Our results open the gate for the replacement of pharmaceutical PEG by POx on a physicochemical basis with key first-principles hydrodynamic parameters of interest, all associated with values of the molar mass.

Polymer conjugated biologics form a multibillion dollar market, dominated by poly(ethylene glycol) (PEG). Recent reports linked PEGs to immunological concerns, fueling the need for alternative polymers. Therefore, we are presenting a strategy replacing PEG by poly(2-oxazoline) (POx) polymers using genetically engineered interleukin-4 (IL-4) featuring an unnatural amino acid for site-specific conjugation through bioorthogonal copper-catalyzed azide alkyne cycloaddition (CuAAC). Conjugation yields of IL-4-PEG were poor and did not respond to an increase in the copper catalyst. In contrast, POxylated IL-4 conjugates resulted in homogeneous conjugate outcome, as demonstrated electrophoretically by size exclusion chromatography and analytical ultracentrifugation. Furthermore, POxylation did not impair thermal and chemical stability, and preserved wild-type IL-4 activity for the conjugates as demonstrated by TF-1 cell proliferation and STAT-6 phosphorylation in HEK293T cells, respectively. In conclusion, POxylation provides an interesting alternative to PEGylation with superior outcome for the synthesis yield by CuAAC and resulting in conjugates with excellent thermal and chemical stress profiles as well as biological performances.

The encapsulation of therapeutic compounds into nanosized delivery vectors has become an important strategy to improve efficiency and reduce side effects in drug delivery applications. Here, we report the synthesis of pH-sensitive nanogels, which are based on the monomer N-[(2,2-dimethyl-1,3-dioxolane)­methyl]­acrylamide (DMDOMA) bearing an acid cleavable acetal group. Degradation studies revealed that these nanogels hydrolyze under acidic conditions and degrade completely, depending on the cross-linker, but are stable in physiological environment. The best performing system was further studied regarding its release kinetics using the anticancer drug doxorubicin. In vitro studies revealed a good compatibility of the unloaded nanogel and the capability of the doxorubicin loaded nanogel to mediate cytotoxic effects in a concentration and time-dependent manner with an even higher efficiency than the free drug. Based on the investigated features, the presented nanogels represent a promising and conveniently prepared alternative to existing carrier systems for drug delivery.

We introduce xanthate-functionalized poly(cyclic imino ethers)s (PCIEs), specifically poly(2-ethyl-2-oxazoline) and poly(2-ethyl-2oxazine) given their stealth characteristics, as an attractive alternative to conventional thiol-based ligands for the synthesis of highly monodisperse and fluorescent gold nanoclusters (AuNCs). The xanthate in the PCIEs interacts with Au ions, acting as a well-controlled template for the direct formation of PCIE-AuNCs. This method yields red-emitting AuNCs with a narrow emission peak (λ em = 645 nm), good quantum yield (4.3−4.8%), long fluorescence decay time (∼722−844 ns), and unprecedented product yield (>98%). The PCIE-AuNCs exhibit long-term colloidal stability, biocompatibility, and antifouling properties, enabling a prolonged blood circulation, lower nonspecific accumulation in major organs, and better renal clearance when compared with AuNCs without polymer coating. The advances made here in the synthesis of metal nanoclusters using xanthate-functionalized PCIEs could propel the production of highly monodisperse, biocompatible, and renally clearable nanoprobes in large-scale for different theranostic applications.

In recent years, polymers bearing reactive groups have received significant interest for biomedical applications. Numerous functional polymer platforms have been introduced, which allow for the preparation of materials with tailored properties via post-polymerization modifications. However, because of their reactivity, many functional groups are not compatible with the initial polymerization. The nitrile group is a highly interesting and relatively inert functionality that has mainly received attention in radical polymerizations. In this Article, a nitrile-functionalized 2-oxazoline monomer (2-(4-nitrile-butyl)-2-oxazoline, BuNiOx) is introduced, and its compatibility with the cationic ring-opening polymerization is demonstrated. Subsequently, the versatility of nitrile-functionalized poly­(2-oxazoline)­s (POx) is presented. To this end, diverse (co)­polymers are synthesized and characterized by nuclear resonance spectroscopy, size-exclusion chromatography, and mass spectrometry. Amphiphilic block copolymers are shown to efficiently encapsulate the hydrophobic drug curcumin (CUR) in aqueous solution, and the anti-inflammatory effect of the CUR-containing nanostructures is presented in BV-2 microglia. Furthermore, the availability of the BuNiOx repeating units for post-polymerization modifications with hydroxylamine to yield amidoxime (AO)-functionalized POx is demonstrated. These AO-containing POx were successfully applied for the complexation of Fe­(III) in a quantitative manner. In addition, AO-functionalized POx were shown to release nitric oxide intracellularly in BV-2 microglia. Thus nitrile-functionalized POx represent a promising and robust platform for the design of polymer therapeutics for a wide range of applications.

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The synthesis of new amino acid-containing, cell-specific, therapeutically active polymers is presented. Amino acids served as starting material for the preparation of tailored polymers with different amino acids in the side chain. The reversible addition–fragmentation chain-transfer (RAFT) polymerization of acrylate monomers yielded polymers of narrow size distribution (Đ ≤ 1.3). In particular, glutamate (Glu)-functionalized, zwitterionic polymers revealed a high degree of cytocompatibility and cellular specificity, i.e., showing association to different cancer cell lines, but not with nontumor fibroblasts. Energy-dependent uptake mechanisms were confirmed by means of temperature-dependent cellular uptake experiments as well as localization of the polymers in cellular lysosomes determined by confocal laser scanning microscopy (CLSM). The amino acid receptor antagonist O-benzyl-l-serine (BzlSer) was chosen as an active ingredient for the design of therapeutic copolymers. RAFT copolymerization of Glu acrylate and BzlSer acrylate resulted in tailored macromolecules with distinct monomer ratios. The targeted, cytotoxic activity of copolymers was demonstrated by means of multiday in vitro cell viability assays. To this end, polymers with 25 mol % BzlSer content showed cytotoxicity against cancer cells, while leaving fibroblasts unaffected over a period of 3 days. Our results emphasize the importance of biologically derived materials to be included in synthetic polymers and the potential of zwitterionic, amino acid-derived materials for cellular targeting. Furthermore, it highlights that the fine balance between cellular specificity and unspecific cytotoxicity can be tailored by monomer ratios within a copolymer.

Amino acids have emerged as a sustainable source for the design of functional polymers. Besides their wide availability, especially their high degree of biocompatibility makes them appealing for a broad range of applications in the biomedical research field. In addition to these favorable characteristics, the versatility of reactive functional groups in amino acids (i.e., carboxylic acids, amines, thiols, and hydroxyl groups) makes them suitable starting materials for various polymerization approaches, which include step-and chain-growth reactions. This review aims to provide an overview of strategies to incorporate amino acids into polymers. To this end, it focuses on the preparation of polymerizable monomers from amino acids, which yield main chain or side chain-functionalized polymers. Furthermore, postpolymerization modification approaches for polymer side chain functionalization are discussed. Amino acids are presented as a versatile platform for the development of polymers with tailored properties.