Universal Concept for the Implementation of a Single Cleavable Unit at Tunable Position in Functional Poly(ethylene glycol)s

Antiadhesion Biomaterials in Tendon Repair: Application Status and Future Prospect

The healing process after tendon injury is often accompanied by the formation of peritendinous adhesion, contributing to limb dysfunction and exerting detrimental effects on the individuals, as well as the development of society and economy. With the continuous development of material science, as well as the augmented understanding of tendon healing and the mechanism of peritendinous adhesion formation, materials used for the fabrication of barrier membranes against peritendinous adhesion emerge endlessly. In this article, based on the analysis of the mechanism of adhesion formation, we first review the commonly used natural and synthetic materials, along with their corresponding fabrication strategies, in order to furnish valuable insights for the future optimization and development of antiperitendinous adhesion barrier membranes. This article also discusses the interaction between antiadhesion materials and cells for ameliorating peritendinous adhesion.

Power of the Disulfide Bond: An Ideal Random Copolymerization of Biodegradable Redox-Responsive Hyperbranched Polyglycerols

The development of copolymerization techniques that can randomly incorporate biodegradable moieties into the hyperbranched polyglycerol backbone is an option to prevent its bioaccumulation in vivo. In this study, redox-responsive and biocompatible hyperbranched polyglycerol copolymers of glycidol and 1,4,5-oxadithiepan-2-one were synthesized with an adjustable molecular weight and a defined disulfide bond content through anionic and coordination-insertion ring-opening polymerization. A truly random incorporation of the monomers was achieved under both copolymerization mechanisms. The copolymers were further characterized in terms of their aggregation behavior in solution, degradability, in vitro cell viability, and blood compatibility for potential future biomedical applications. Transmission electron microscopy revealed that the copolymer assembled into nanoparticles with a size range of 20 nm. The copolymers underwent degradation when incubated with two different reducing agents, resulting in smaller fragments of the polymer with thiol end groups. The copolymers demonstrated good biocompatibility, making them suitable for further investigation in biomedical applications.

Design of Cationic Lipids with Acetal Linkers: Conformational Preferences, Hydrolytic Stability, and High Drug-Loading Abilities

Lipids are key constituents of numerous biomedical drug delivery technologies. Here, we present the design, synthesis and biophysical characterizations of a library of cationic lipids containing an acetal residue in their linker region. These cationic acetal lipids (CALs) were conveniently prepared through a trans-acetalization protocol from commercially available precursors. NMR studies highlighted the conformational rigidity at the acetal residue and the high hydrolytic stability of these CALs. Fluorescence anisotropy studies revealed that the CAL with a pyridinium headgroup (CAL1) formed highly cohesive vesicular aggregates in water. These structural and self-assembly features of the CAL1 allowed up to 196 % w/w loading of curcumin (Cur) as a representative hydrophobic drug. A reconstitutable formulation of Cur was obtained as a result, which could deliver the drug inside mammalian cells with very high efficiency. The hemocompatibility and cytocompatibility of CAL1 was significantly enhanced by creating a coating of polydopamine (PDA) onto its vesicular assemblies to produce hybrid lipid-polymer nanocapsules. This work demonstrates rapid access to the useful synthetic lipid formulations with high potential in drug and gene delivery applications.

Rational Control of Protein-Protein Interactions with Protein-ATRP-Generated Protease-Sensitive Polymer Cages

Protease-protease interactions lie at the heart of the biological cascades that provide rapid molecular responses to living systems. Blood clotting cascades, apoptosis signaling networks, bacterial infection, and virus trafficking have all evolved to be activated and sustained by protease-protease interactions. Biomimetic strategies designed to target drugs to specific locations have generated proprotein drugs that can be activated by proteolytic cleavage to release native protein. We have previously demonstrated that the modification of enzymes with a custom-designed comb-shaped polymer nanoarmor can shield the enzyme surface and eliminate almost all protein-protein interactions. We now describe the synthesis and characterization of protease-sensitive comb-shaped nanoarmor cages using poly(ethylene glycol) [Sundy, J. S. Arthritis Rheum. 2008, 58(9), 2882-2891]methacrylate macromonomers where the PEG tines of the comb are connected to the backbone of the growing polymer chain by peptide linkers. Protease-induced cleavage of the tines of the comb releases a polymer-modified protein that can once again participate in protein-protein interactions. Atom transfer radical polymerization (ATRP) was used to copolymerize the macromonomer and carboxybetaine methacrylate from initiator-labeled chymotrypsin and trypsin enzymes, yielding proprotease conjugates that retained activity toward small peptide substrates but prevented activity against proteins. Native proteases triggered the release of the PEG side chains from the polymer backbone within 20 min, thereby increasing the activity of the conjugate toward larger protein substrates by 100%. Biomimetic cascade initiation of nanoarmored protease-sensitive protein-polymer conjugates may open the door to a new class of responsive targeted therapies.

Mimic Lipoproteins Responsive to Intratumoral pH and Allosteric Enzyme for Efficient Tumor Therapy

Discoid-reconstituted high-density lipoprotein (d-rHDL) is advantageous for tumor-targeted drug delivery due to its small size, long circulation, and efficient internalization into cancer cells. Nevertheless, an allosteric reaction catalyzed by serum lecithin-cholesterol acyltransferase (LCAT) may cause drug leakage from d-rHDL and reduce its targeting efficiency. Conversely, similar "structural weakening" catalyzed by acyl-coenzyme A-cholesterol acyltransferase (ACAT) inside tumor cells can stimulate precise intracellular drug release. Therefore, we synthesized and characterized a pH-sensitive n-butyraldehyde bi-cholesterol (BCC) to substitute for cholesterol in the d-rHDL particle, and bovine serum albumin (BSA) was used as the targeting agent. This dual pH- and ACAT-sensitive d-rHDL (d-d-rHDL) was small with a disk-like appearance. Morphological transformation observation, in vitro release assays, and differences in internalization upon LCAT treatment confirmed that BCC effectively inhibited the remodeling behavior and enhanced the tumor-targeting efficiency. The accumulation of d-d-rHDL in HepG2 cells was significantly higher than that in LO2 cells, and accumulation was inhibited by free BSA. The pH sensitivity was verified, and d-d-rHDL achieved efficient drug release in vitro and inside tumor cells after exposure to acidic conditions and ACAT. Confocal laser scanning microscopy demonstrated that d-d-rHDL escaped from lysosomes and became distributed evenly throughout cells. Moreover, in vivo imaging assays in a tumor-bearing mouse model demonstrated tumor-targeting properties of d-d-rHDL, and paclitaxel-loaded d-d-rHDL showed strong anticancer activity in these mice. This dual-sensitive d-d-rHDL thus combines structural stability in plasma and an intracellular pH/ACAT-triggered drug release to facilitate inhibition of tumor growth.

Poly(ethylene glycol)s With a Single Cinnamaldehyde Acetal Unit for Fabricating Acid-Degradable Hydrogel

A synthetic route to prepare a poly(ethylene glycol) with a single cinnamaldehyde acetal unit in the polymer chain, was successfully established using a newly synthesized cinnamaldehyde acetal diethylene glycol (CADEG) as initiator. This HO-PEG(ca)-OH is non-toxic and would be degraded into a cinnamaldehyde and two PEG diols in acid environment. A whole polyethylene glycol based hydrogel was easily fabricated by thiol-ene “click” reaction in alkalescence aqueous solution using acrylate-PEG(ca)-acrylate and 4-arm PEG-SH as raw materials at room temperature. The gel time was dependent on the pH of the solution and its alkalinity can promote gel. The hydrogel can be degradable in acidic conditions and the stronger the acidity, the faster the degradation. This HO-PEG(ca)-OH also can be used in synthesis of cinnamaldehyde containing PEG derivatives, block copolymers or other acid degradable materials.

Monodisperse and Polydisperse PEGylation of Peptides and Proteins: A Comparative Study

Although PEGylation is widely used in biomedicine with great success, it suffers from many drawbacks, such as polydispersity, nonbiodegradability, and loss of precursor potency. Recently, the search for polyethylene glycol (PEG) substitutes has attracted considerable attention. Some of the substitutes partially address the drawbacks of PEGs, but sacrifice the "stealth" effect of PEGs and bring in new issues. Herein, we developed monodisperse oligoethylene glycol (M-OEG) polyamides over 5000 Da as biodegradable and monodisperse PEGylation (M-PEGylation) agents, which provided M-PEGylated peptides and proteins with high monodispersity and a biodegradable PEG moiety. Compared to regular PEGylated proteins with a complex "stealth" cloud of PEG, the hydrogen bond interactions between the M-OEG polyamides and proteins provided the M-PEGylated protein with a biodegradable "stealth" cloak. The monodisperse and biodegradable M-PEGylation strategy as well as the peculiar protein-M-OEG polyamide interactions may shed light on many long-lasting issues during the development of PEGylated biologic drugs, such as monodispersity, biodegradability, and tunable conformation.

Chemoselective Polymerization of Epoxides from Carboxylic Acids: Direct Access to Esterified Polyethers and Biodegradable Polyurethanes

Carboxylic-acid-initiated ring-opening polymerization (ROP) of epoxides is a fast approach to esterified polyethers which are cleavable at the termini or centers. A major challenge lies in conventional ROP methods because of the lability of ester groups formed in the initiation step. Here, we describe chemoselective ROP of epoxides from aliphatic, aromatic, and methacrylic carboxylic acids using two-component metal-free catalysts. Transesterification is clearly absent so that well-defined α-(carboxylic ester)-ω-hydroxy polyethers are generated in one step from monocarboxylic acids. The livingness of the ROP is verified despite the slow initiation mode. The ester end group can be readily cleaved from the polyether hydrolytically. An α,ω-dihydroxy poly(propylene oxide) with two central ester groups is generated from a diacid initiator and transformed in situ by the same catalyst to polyurethane which shows distinct enzymatic degradability. This study provides convenient access to α,ω-heterobifunctional polyethers with cleavable, releasable, or modifiable end groups and to biodegradable polyether-based materials.

Liposomal delivery of CRISPR/Cas9

Liposomes are one of the most widely investigated carriers for CRISPR/Cas9 delivery. The surface properties of liposomal carriers, including the surface charge, PEGylation, and ligand modification can significantly affect the gene silencing efficiency. Three barriers of systemic CRISPR/Cas9 delivery (long blood circulation, efficient tumor penetration, and efficient cellular uptake/endosomal escape) are analyzed on liposomal carriers with different surface charges, PEGylations, and ligand modifications. Cationic formulations dominate CRISPR/Cas9 delivery and neutral formulations also have good performance while anionic formulations are generally not proper for CRISPR/Cas9 delivery. The PEG dilemma (prolonged blood circulation vs. reduced cellular uptake/endosomal escape) and the side effect of repeated PEGylated formulation (accelerated blood clearance) were discussed. Effects of ligand modification on cationic and neutral formulations were analyzed. Finally, we summarized the achievements in liposomal CRISPR/Cas9 delivery, outlined existing problems, and provided some future perspectives. Liposomes are one of the most widely investigated carriers for CRISPR/Cas9 delivery. The surface properties of liposomal carriers, including the surface charge, PEGylation, and ligand modification can significantly affect the gene silencing efficiency. Three barriers of systemic siRNA delivery (long blood circulation, efficient tumor penetration, and efficient cellular uptake/endosomal escape) are analyzed on liposomal carriers with different surface charges, PEGylations, and ligand modifications. Cationic formulations dominate CRISPR/Cas9 delivery and neutral formulations also have good performance while anionic formulations are generally not proper for CRISPR/Cas9 delivery. The PEG dilemma (prolonged blood circulation vs. reduced cellular uptake/endosomal escape) and the side effect of repeated PEGylated formulation (accelerated blood clearance) were discussed. Effects of ligand modification on cationic and neutral formulations were analyzed. Finally, we summarized the achievements in liposomal CRISPR/Cas9 delivery, outlined existing problems, and provided some future perspectives.

Preparation of a mimetic and degradable poly(ethylene glycol) by a non-eutectic mixture of organocatalysts (NEMO) via a one-pot two-step process

A one-pot, two-step method for the preparation of degradable PEG is here presented. The full process addresses the requirements imposed by green chemistry and involves the use of a single and nontoxic non-eutectic mixture of organocatalysts. The strategy relies on the polycondensation of PEG800 after its functionalization by bio-derived 5-membered γ-butyrolactone.

A one-pot, two-step method for the preparation of degradable PEG is here presented.

Degradable poly(ethylene oxide) through metal-free copolymerization of ethylene oxide with l-lactide

A simple and convenient method for the preparation of degradable poly(ethylene oxide) (PEO) is presented in this work.

Dual pH-Responsive Shell-Cleavable Polycarbonate Micellar Nanoparticles for in Vivo Anticancer Drug Delivery

To exploit tumor and intracellular microenvironments, pH-responsive diblock copolymers of poly(ethylene glycol) and catechol-functionalized polycarbonate with acid-labile acetal bond as the linker are synthesized to prepare micellar nanoparticles that shed the shell at acidic tumor tissues and inside cancer cells, hence accelerating drug release at the target. The pH-dependent cleavage of the shell is demonstrated at pH 5.0 and 6.5 using ¹H NMR. Bortezomib (BTZ, an anticancer drug containing a phenylboronic acid group) is conjugated to the polymers through formation of pH-responsive boronate ester bond between boronic acid and catechol in the polymers. Dual pH-responsive bortezomib-polymer conjugates (BTZ-PC) self-assemble into micellar nanoparticles of small size (<110 nm) with narrow size distribution and high drug loading capacity. Acidic pH accelerates BTZ release from BTZ-PC micelles and enhances intracelluar uptake of the micelles, hence increasing in vitro cytotoxicity against human breast cancer cells. More importantly, the BTZ-PC micelles achieve a stronger antitumor effect in a human breast cancer BT-474 xenograft mouse model than free BTZ and mitigate in vivo hepatotoxicity of BTZ. These dual pH-responsive shell-cleavable nanoparticles are a potentially promising carrier for BTZ delivery.

Bioorthogonal strategies for site-directed decoration of biomaterials with therapeutic proteins

Emerging strategies targeting site-specific protein modifications allow for unprecedented selectivity, fast kinetics and mild reaction conditions with high yield. These advances open exciting novel possibilities for the effective bioorthogonal decoration of biomaterials with therapeutic proteins. Site-specificity is particularly important to the therapeutics' end and translated by targeting specific functional groups or introducing new functional groups into the therapeutic at predefined positions. Biomimetic strategies are designed for modification of therapeutics emulating enzymatic strategies found in Nature. These strategies are suitable for a diverse range of applications - not only for protein-polymer conjugation, particle decoration and surface immobilization, but also for the decoration of complex biomaterials and the synthesis of bioresponsive drug delivery systems. This article reviews latest chemical and enzymatic strategies for the biorthogonal decoration of biomaterials with therapeutic proteins and inter-positioned linker structures. Finally, the numerous reports at the interface of biomaterials, linkers, and therapeutic protein decoration are integrated into practical advice for design considerations intended to support the selection of productive ligation strategies.

One-pot and gram-scale synthesis of biodegradable polyglycerols under ambient conditions: nanocarriers for intradermal drug delivery

Biodegradable and biocompatible hyperbranched polymers are synthesized and their potential for dermal drug delivery is investigated.

Cleavable Polyethylene Glycol: 3,4-Epoxy-1-butene as a Comonomer to Establish Degradability at Physiologically Relevant pH

Polyethylene glycol (PEG) has been used for decades to improve the pharmacokinetic properties of protein drugs, and several PEG-protein conjugates are approved by the FDA. However, the nondegradability of PEG restricts its use to a limiting molecular weight to permit renal excretion. In this work, we introduce a simple strategy to overcome the nondegradability of PEG by incorporating multiple pH-sensitive vinyl ether moieties into the polyether backbone. Copolymerization of 3,4-epoxy-1-butene (EPB) with ethylene oxide via anionic ring-opening polymerization (AROP) provides access to allyl moieties that can be isomerized to pH-cleavable propenyl units (isoEPB). Well-defined P(EPB-co-EG) copolymers (Đ = 1.05-1.11) with EPB contents of ∼4 mol% were synthesized in a molecular weight range of 3000 to 10000 g mol^-1. ¹H NMR kinetic studies served to investigate acidic hydrolysis in a pH range of 4.4 to 5.4 and even allowed to distinguish between the hydrolysis rates of (E)- and (Z)-isoEPB units, demonstrating faster hydrolysis of the (Z)-isomer. SEC analysis of degradation products revealed moderate dispersities Đ of 1.6 to 1.8 and consistent average molecular weights M_n of ∼1000 g mol^-1. The presence of a defined hydroxyl end group permits attachment to other functional molecules. The novel pH-degradable PEGs combine various desirable properties such as excellent long-term storage stability and cleavage in a physiologically relevant pH-range that render them promising candidates for biomedical application.

Degradable Polyphosphoester-Protein Conjugates: "PPEylation" of Proteins

Pharmacokinetic properties determine the efficacy of protein therapeutics. The covalent attachment of poly(ethylene glycol) (PEG) extends the half-life of such biologicals to maintain a therapeutically effective concentration over a prolonged period of time and improves administration and compliance. A major obstacle of these polymer-protein conjugates is the chemical stability of the PEG preventing its metabolism and leading to side effects. Instead, we propose the PPEylation, that is, the conjugation of degradable poly(phosphoester)s (PPE) to proteins, in order to generate fully biodegradable polymer-protein conjugates. The structure of the PPEylated protein conjugates was verified with mass spectrometry and size exclusion chromatography. They were compared to structural analogues, except classical, PEGylated proteins, and exhibit comparable bioactivity, but avoiding any nondegradable polymer in the conjugate. We proved the degradation of the protective polymer shell surrounding the conjugate in aqueous environments at physiological conditions by online triple detection size exclusion chromatography and gel electrophoresis. We believe that this research will provide an attractive alternative for future drug design with implications for the clinical use of biologicals.

Synthesis of Degradable Poly[(Ethylene Glycol)-co-(Glycolic Acid)] via the Post-Polymerization Oxyfunctionalization of Poly(Ethylene Glycol)

To enhance the limited degradability of poly(ethylene glycol) (PEG), a straightforward method of synthesizing poly[(ethylene glycol)-co-(glycolic acid)] (P(EG-co-GA)) via a ruthenium-catalyzed, post-polymerization oxyfunctionalization of various PEGs is developed. Using this method, a set of copolymers with GA compositions of up to 8 mol% are prepared with minimal reduction in molecular weight (<10%) when compared to their commercially available starting materials. The P(EG-co-GA) copolymers are shown to undergo hydrolysis under mild conditions.

Acid-Labile Amphiphilic PEO-b-PPO-b-PEO Copolymers: Degradable Poloxamer Analogs

Poly ((ethylene oxide)-b-(propylene oxide)-b-(ethylene oxide)) triblock copolymers commonly known as poloxamers or Pluronics constitute an important class of nonionic, biocompatible surfactants. Here, a method is reported to incorporate two acid-labile acetal moieties in the backbone of poloxamers to generate acid-cleavable nonionic surfactants. Poly(propylene oxide) is functionalized by means of an acetate-protected vinyl ether to introduce acetal units. Three cleavable PEO-PPO-PEO triblock copolymers (Mn,total = 6600, 8000, 9150 g·mol(-1) ; Mn,PEO = 2200, 3600, 4750 g·mol(-1) ) have been synthesized using anionic ring-opening polymerization. The amphiphilic copolymers exhibit narrow molecular weight distributions (Ð = 1.06-1.08). Surface tension measurements reveal surface-active behavior in aqueous solution comparable to established noncleavable poloxamers. Complete hydrolysis of the labile junctions after acidic treatment is verified by size exclusion chromatography. The block copolymers have been employed as surfactants in a miniemulsion polymerization to generate polystyrene (PS) nanoparticles with mean diameters of ≈200 nm and narrow size distribution, as determined by dynamic light scattering and scanning electron microscopy. Acid-triggered precipitation facilitates removal of surfactant fragments from the nanoparticles, which simplifies purification and enables nanoparticle precipitation "on demand."

Biodegradable hyperbranched polyether-lipids with in-chain pH-sensitive linkages

Hyperbranched polyether-based lipids with cleavable acetal units were obtained via copolymerization of the epoxide inimer 1-(glycidyloxy)ethyl ethylene glycol ether (GEGE) and glycidol, using anionic ring-opening polymerization.

Polymerization of Ethylene Oxide, Propylene Oxide, and Other Alkylene Oxides: Synthesis, Novel Polymer Architectures, and Bioconjugation

The review summarizes current trends and developments in the polymerization of alkylene oxides in the last two decades since 1995, with a particular focus on the most important epoxide monomers ethylene oxide (EO), propylene oxide (PO), and butylene oxide (BO). Classical synthetic pathways, i.e., anionic polymerization, coordination polymerization, and cationic polymerization of epoxides (oxiranes), are briefly reviewed. The main focus of the review lies on more recent and in some cases metal-free methods for epoxide polymerization, i.e., the activated monomer strategy, the use of organocatalysts, such as N-heterocyclic carbenes (NHCs) and N-heterocyclic olefins (NHOs) as well as phosphazene bases. In addition, the commercially relevant double-metal cyanide (DMC) catalyst systems are discussed. Besides the synthetic progress, new types of multifunctional linear PEG (mf-PEG) and PPO structures accessible by copolymerization of EO or PO with functional epoxide comonomers are presented as well as complex branched, hyperbranched, and dendrimer like polyethers. Amphiphilic block copolymers based on PEO and PPO (Poloxamers and Pluronics) and advances in the area of PEGylation as the most important bioconjugation strategy are also summarized. With the ever growing toolbox for epoxide polymerization, a "polyether universe" may be envisaged that in its structural diversity parallels the immense variety of structural options available for polymers based on vinyl monomers with a purely carbon-based backbone.

Biodegradable pH-Sensitive Poly(ethylene glycol) Nanocarriers for Allergen Encapsulation and Controlled Release

In the last decades, the number of allergic patients has increased dramatically. Allergen-specific immunotherapy (SIT) is the only available cause-oriented therapy so far. SIT reduces the allergic symptoms, but also exhibits some disadvantages; that is, it is a long-lasting procedure and severe side effects like anaphylactic shock can occur. In this work, we introduce a method to encapsulate allergens into nanoparticles to avoid severe side effects during SIT. Degradable nanocarriers combine the advantage of providing a physical barrier between the encapsulated cargo and the biological environment as well as responding to certain local stimuli (like pH) to release their cargo. This work introduces a facile strategy for the synthesis of acid-labile poly(ethylene glycol) (PEG)-macromonomers that degrade at pH 5 (physiological pH inside the endolysosome) and can be used for nanocarrier synthesis. The difunctional, water-soluble PEG dimethacrylate (PEG-acetal-DMA) macromonomers with cleavable acetal units were analyzed with 1H NMR, SEC, and MALDI-ToF-MS. Both the allergen and the macromonomers were entrapped inside liposomes as templates, which were produced by dual centrifugation (DAC). Radical polymerization of the methacrylate units inside the liposomes generated allergen-loaded PEG nanocarriers. In vitro studies demonstrated that dendritic cells (DCs) internalize the protein-loaded, nontoxic PEG-nanocarriers. Furthermore, we demonstrate by cellular antigen stimulation tests that the nanocarriers effectively shield the allergen cargo from detection by immunoglobulins on the surface of basophilic leucocytes. Uptake of nanocarriers into DCs does not lead to cell maturation; however, the internalized allergen was capable to induce T cell immune responses.

Degradable PEGylated Protein Conjugates Utilizing RAFT Polymerization

Poly(ethylene glycol) (PEG)-protein therapeutics exhibit enhanced pharmacokinetics, but have drawbacks including decreased protein activities and polymer accumulation in the body. Therefore a major aim for second-generation polymer therapeutics is to introduce degradability into the backbone. Herein we describe the synthesis of poly(poly(ethylene glycol methyl ether methacrylate)) (pPEGMA) degradable polymers with protein-reactive end-groups via reversible addition-fragmentation chain transfer (RAFT) polymerization, and the subsequent covalent attachment to lysozyme through a reducible disulfide linkage. RAFT copolymerization of cyclic ketene acetal (CKA) monomer 5,6-benzo-2-methylene-1,3-dioxepane (BMDO) with PEGMA yielded two polymers with number-average molecular weight (Mn ) (GPC) of 10.9 and 20.9 kDa and molecular weight dispersities (Ð) of 1.34 and 1.71, respectively. Hydrolytic degradation of the polymers was analyzed by 1H-NMR and GPC under basic and acidic conditions. The reversible covalent attachment of these polymers to lysozyme, as well as the hydrolytic and reductive cleavage of the polymer from the protein, was analyzed by gel electrophoresis and mass spectrometry. Following reductive cleavage of the polymer, an increase in activity was observed for both conjugates, with the released protein having full activity. This represents a method to prepare PEGylated proteins, where the polymer is readily cleaved from the protein and the main chain of the polymer is degradable.

Sequence-controlled degradable polymers by controlled cationic copolymerization of vinyl ethers and aldehydes: precise placement of cleavable units at predetermined positions

Sequence-controlled degradable polymers with precisely placed breakable bonds in the main chain were synthesized by controlled alternating cationic copolymerization of vinyl ethers and aldehydes.

Therapeutic protein-polymer conjugates: advancing beyond PEGylation

Protein-polymer conjugates are widely used as therapeutics. All Food and Drug Administration (FDA)-approved protein conjugates are covalently linked to poly(ethylene glycol) (PEG). These PEGylated drugs have longer half-lives in the bloodstream, leading to less frequent dosing, which is a significant advantage for patients. However, there are some potential drawbacks to PEG that are driving the development of alternatives. Polymers that display enhanced pharmacokinetic properties along with additional advantages such as improved stability or degradability will be important to advance the field of protein therapeutics. This perspective presents a summary of protein-PEG conjugates for therapeutic use and alternative technologies in various stages of development as well as suggestions for future directions. Established methods of producing protein-PEG conjugates and new approaches utilizing controlled radical polymerization are also covered.

Be squared: expanding the horizon of squaric acid-mediated conjugations

Squaric acid diesters can be applied as reagents to couple two amino-functional compounds. Consecutive coupling of two amines allows the synthesis of asymmetric squaric acid bisamides with either low molecular weight compounds but also biomolecules or polymers. The key feature of the squaric acid diester mediated coupling is the reduced reactivity of the resulting ester-amide after the first amidation step of the diester. This allows the sequential amidation and generation of asymmetric squaramides with high selectivity and in high yields. This article gives an overview of the well-established squaric acid diester mediated coupling reactions for glycoconjugates and presents recent advances that aim to expand this very versatile reaction protocol to the modification of peptides and proteins.