Block-Sequence-Specific Polypeptides from α‑Amino Acid <i>N</i>‑Carboxyanhydrides: Synthesis and Influence on Polypeptide Properties

Sequential addition of benzyl-l-glutamate and <i>tert</i>-butyl-l-glutamate <i>N</i>-carboxyanhydrides (NCAs) under optimized reaction conditions was used to synthesize block-sequence-defined polypeptides. Alternating octablock, tetrablock, and diblock as well as statistical polypeptides were obtained with comparable total compositions and total number of units. All of them were able to adopt helical secondary structures. Selective deprotection of the <i>tert</i>-butyl side chain yielded polypeptides with alternating benzyl-l-glutamate and l-glutamic acid block sequences available for further selective modification of individual block sequences. This was exploited for the conjugation with PEG side chains selectively on the glutamic acid block sequences. A detailed investigation revealed significant differences in properties as a function of the block-sequenced composition. Polypeptides with shorter alternating block sequences showed better water solubility. Dynamic light scattering revealed the presence of individual polypeptide chains in water in the case of the octablock polypeptide, while increasing aggregation was observed with increasing block length as well as for the statistical polypeptide. Moreover, the octablock polypeptide displayed a defined cloud point at 60 °C, while no defined transition could be observed with any of the other polypeptide block sequences. The results demonstrate the dependence of polypeptide properties on their block-sequenced composition and open opportunities for a polymerization approach complementary to the stepwise synthesis of peptidomimetics

Chemo-Enzymatic Synthesis of Poly(4-piperidine lactone‑<i>b</i>‑ω-pentadecalactone) Block Copolymers as Biomaterials with Antibacterial Properties

With increasing troubles in bacterial contamination and antibiotic-resistance, new materials possessing both biocompatibility and antimicrobial efficacy are supposed to be developed for future biomedical application. Herein, we demonstrated a chemo-enzymatic ring opening polymerization (ROP) approach for block copolyester, that is, poly­(4-benzyl formate piperidine lactone-<i>b</i>-ω-pentadecalactone) (PNPIL-<i>b</i>-PPDL), in a one-pot two-step process. Afterward, cationic poly­(4-piperidine lactone-<i>b</i>-ω-pentadecalactone) (PPIL-<i>b</i>-PPDL) with pendent secondary amino groups was obtained via acidic hydrolysis of PNPIL-<i>b</i>-PPDL. The resulting cationic block copolyester exhibited high antibacterial activity against Gram negative E. coli and Gram positive S. aureus, while showed low toxicity toward NIH-3T3 cells. Moreover, the antibacterial property, cytotoxicity and degradation behavior could be tuned simply by variation of PPIL content. Therefore, we anticipate that such cationic block copolymers could potentially be applied as biomaterials for medicine or implants

Biologically Active Polymersomes from Amphiphilic Glycopeptides

Polypeptide block copolymers with different block length ratios were obtained by sequential ring-opening polymerization of benzyl-l-glutamate and propargylglycine (PG) <i>N</i>-carboxyanhydrides. Glycosylation of the poly­(PG) block was obtained by Huisgens cycloaddition “click” reaction using azide-functionalized galactose. All copolymers were self-assembled using the nanoprecipitation method to obtain spherical and wormlike micelles as well as polymersomes depending on the block length ratio and the nanoprecipitation conditions. These structures display bioactive galactose units in the polymersome shell, as proven by selective lectin binding experiments

Cleavable epoxy networks using azomethine-bearing amine hardeners

This work is a proof-of-concept of the use of azomethine-bearing diamines as novel hardeners of standard epoxy  compounds to yield cleavable and thermoformable covalent adaptable networks (CANs), with functional properties otherwise comparable to conventional epoxy networks. A suitable aromatic diamine (TPA-o-PD) was  synthesised at acceptable purity for the intended use and successfully reacted with DGEBA. The resulting  azomethine-bearing cured epoxy networks exhibited glass transition temperature values and a thermal stability  profile similar to conventional epoxy network counterparts. In contrast to their conventional counterparts  however, the azomethine-bearing networks were shown to dissolve in mixtures of chloroform and methanesulfonic acid, due to acid hydrolysis of at least some of the azomethine bonds of the network. The resulting  recyclate material after evaporating the solvent was consistent with the profile of a thermoplastic polymer of  high molecular weight, suggesting limited depolymerisation/network cleavage during dissolution in the chloroform/methanesulfonic acid mixture. The recyclates were soluble in polar aprotic solvents and showed good  thermal stability, high Tg and molecular weight values, consistent with the attributes of engineering thermoplastics. Lastly, the cured networks were shown to be thermoformable at 200 ◦C, yielding self-standing films with  only minor reduction of properties.  </p

Polypeptide-Grafted Macroporous PolyHIPE by Surface-Initiated <i>N</i>-Carboxyanhydride (NCA) Polymerization as a Platform for Bioconjugation

A new class of functional macroporous monoliths from polymerized high internal phase emulsion (polyHIPE) with tunable surface functional groups was developed by direct polypeptide surface grafting. In the first step, amino-functional polyHIPEs were obtained by the addition of 4-vinylbenzyl or 4-vinylbenzylphthalimide to the styrenic emulsion and thermal radical polymerization. The obtained monoliths present the expected open-cell morphology and a high surface area. The incorporated amino group was successfully utilized to initiate the ring-opening polymerization of benzyl-l-glutamate <i>N</i>-carboxyanhydride (BLG NCA) and benzyloxycarbonyl-l-lysine (Lys­(Z)) NCA, which resulted in a dense homogeneous coating of polypeptides throughout the internal polyHIPE surfaces as confirmed by SEM and FTIR analysis. The amount of polypeptide grafted to the polyHIPE surfaces could be modulated by varying the initial ratio of amino acid NCA to amino-functional polyHIPE. Subsequent removal of the polypeptide protecting groups yielded highly functional polyHIPE-<i>g</i>-poly­(glutamic acid) and polyHIPE-<i>g</i>-poly­(lysine). Both types of polypeptide-grafted monoliths responded to pH by changes in their hydrohilicity. The possibility to use the high density of function (−COOH or −NH₂) for secondary reaction was demonstrated by the successful bioconjugation of enhanced green fluorescent protein (eGFP) and fluorescein isocyanate (FITC) on the polymer 3D-scaffold surface. The amount of eGFP and FITC conjugated to the polypeptide-grafted polyHIPE was significantly higher than to the amino-functional polyHIPE, signifying the advantage of polypeptide grafting to achieve highly functional polyHIPEs

Degradable 3D-Printed Hydrogels Based on Star-Shaped Copolypeptides

We present a star copolypeptide-based hydrogel ink capable of structural microfabrication using 3D extrusion printing. The material comprises an amphiphilic block copolymer structure of poly­(benzyl-l-glutamate)-<i>b</i>-oligo­(l-valine), which spontaneously forms hydrogels through hydrophobic interactions. The chemical design allows the bulk phase of the hydrogel to remain intact after application of shear due to its self-recovery behavior. It is demonstrated that the composition of the materials is ideally suited for 3D printing with scaffolds capable of maintaining structural cohesion after extrusion. Post extrusion UV-triggered fixation of the printed structures is carried out, resulting in stable hydrogel constructs. The constructs were found to be degradable, exhibited favorable release of encapsulated molecular cargo, and do not appear to affect the metabolic health of the commonly used fibroblastic cell line Balb/3T3 in the absence of the reactive diluent <i>N</i>,<i>N</i>′-methylenebis­(acrylamide). The star copolypeptide inks allow for rapid prototyping enabling the fabrication of defined intricate microstructures, providing a platform for complex scaffold development that would otherwise be unattainable with other processing techniques such as molding or casting

Mimicking (Linear) Low-Density Polyethylenes Using Modified Polymacrolactones

This paper presents a new approach toward the introduction of both short- (SCB) and long-chain branching (LCB) in polyethylene-like polyesters via the ring-opening polymerization of macrolactones. Macrolactones containing an alkyl (<b>S1</b>) or alcohol (<b>S2</b>) branch were obtained using radical thiol–ene chemistry of ambrettolide (Amb). Kinetic studies revealed the need for an excess of thiol to achieve a high conversion of the double bond. Even though homopolymerization of the three monomers Amb, <b>S1</b>, and <b>S2</b> revealed comparable reactivities, the molecular weight buildup during polymerization of <b>S2</b> differs drastically from that of Amb and <b>S1</b>. Instead of the linear increase of <i>M</i>_n with conversion observed for Amb and <b>S1</b>, the molecular weight buildup for the ring-opening polymerization of <b>S2</b> resembles that of a step-growth polymerizationslow buildup at low and moderate conversion followed by a rapid increase in molecular weight at high conversions. This disparity was attributed to the possibility of <b>S2</b> to function as both an initiator and a monomer, leading to oligomers during the first part of the reaction that are subsequently connected to each other at the final stage of the reaction. Copolymerization of pentadecalactone (PDL) with various ratios of Amb, <b>S1</b>, and <b>S2</b> in bulk led to the associated random copolymers containing double bonds, short-chain branches, and long-chain branches. The <i>trans</i>-double bonds in poly­(PDL-<i>co</i>-Amb) are included in the crystal lattice, leading to a slight decrease in the melting temperature, melting enthalpy and yield stress, while up to 20 double bonds/1000 backbone atoms the crystallinity and lamellar thickness remain similar to those of polypentadecalactone. In contrast, SCBs are fully excluded from the crystal lattice, leading to a more significant decrease in melting temperature and enthalpy as well as crystallinity and lamellar thickness with increasing branching density. The stiffness of these SCB-copolymers exponentially decreases as a function of branching content, effectively changing the mechanical behavior from semicrystalline to elastomeric. The LCB-containing polymers show an even larger linear decrease in melting temperature with increasing branching density than their SCB equivalents, likely due to the particular topology of the polymers consisting of a brush to a hyperbranched structure. However, a rapid decrease of molecular weight as was observed upon increasing the <b>S2</b> content is also likely to play a role. The observed low molecular weight can be ascribed to both the fact that (macrocycles of) <b>S2</b> can function as initiator, effectively increasing the amount of polymer chains, and the change of molecular weight buildup

Supramolecular Hydrogels with Reverse Thermal Gelation Properties from (Oligo)tyrosine Containing Block Copolymers

Novel block copolymers comprising poly­(ethylene glycol) (PEG) and an oligo­(tyrosine) block were synthesized in different compositions by <i>N</i>-carboxyanhydride (NCA) polymerization. It was shown that PEG2000-Tyr₆ undergoes thermoresponsive hydrogelation at a low concentration range of 0.25–3.0 wt % within a temperature range of 25–50 °C. Cryogenic transmission electron microscopy (Cryo-TEM) revealed a continuous network of fibers throughout the hydrogel sample, even at concentrations as low as 0.25 wt %. Circular dichroism (CD) results suggest that better packing of the β-sheet tyrosine block at increasing temperature induces the reverse thermogelation. A preliminary assessment of the potential of the hydrogel for in vitro application confirmed the hydrogel is not cytotoxic, is biodegradable, and produced a sustained release of a small-molecule drug

Degradable 3D-Printed Hydrogels Based on Star-Shaped Copolypeptides

We present a star copolypeptide-based hydrogel ink capable of structural microfabrication using 3D extrusion printing. The material comprises an amphiphilic block copolymer structure of poly­(benzyl-l-glutamate)-<i>b</i>-oligo­(l-valine), which spontaneously forms hydrogels through hydrophobic interactions. The chemical design allows the bulk phase of the hydrogel to remain intact after application of shear due to its self-recovery behavior. It is demonstrated that the composition of the materials is ideally suited for 3D printing with scaffolds capable of maintaining structural cohesion after extrusion. Post extrusion UV-triggered fixation of the printed structures is carried out, resulting in stable hydrogel constructs. The constructs were found to be degradable, exhibited favorable release of encapsulated molecular cargo, and do not appear to affect the metabolic health of the commonly used fibroblastic cell line Balb/3T3 in the absence of the reactive diluent <i>N</i>,<i>N</i>′-methylenebis­(acrylamide). The star copolypeptide inks allow for rapid prototyping enabling the fabrication of defined intricate microstructures, providing a platform for complex scaffold development that would otherwise be unattainable with other processing techniques such as molding or casting

Facile Approach to Covalent Copolypeptide Hydrogels and Hybrid Organohydrogels

Crosslinking of tryptophan (Trp) containing copolypeptides with varying ratios of benzyl-l-glutamate (BLG) and Nα-(carbobenzyloxy)-l-lysine (Z-Lys) is achieved by the selective reaction with hexamethylene-bis-TAD (bisTAD). Conversion of the resulting organogels into biocompatible hydrogels by full BLG or Z-Lys deprotection is demonstrated. Moreover, diffusion controlled deprotection allows the design of macroscopic hybrid organohydrogels comprising hydrophilic as well as hydrophobic regions at a desired ratio and position. FTIR and SEM analysis confirm the coexistence of both hydrophilic and hydrophobic segments in one copolypeptide piece. Selective loading of hydrogel and organogel segments with hydrophilic and hydrophobic dyes, respectively, is observed on macroscopic amphiphilic gels and films. These materials offer significant potential as dual-loaded drug release gels as well as tissue engineering platforms