Synthesis and properties of biodegradable supramolecular polymers based on polylactide-block -poly(δ -valerolactone)-block -polylactide triblock copolymers

Synthesis of Functionalized Triblock Copolyesters Derived from Lactic Acid and Macrolactones for Bone Tissue Regeneration

Synthetic and functional grafts are a great alternative to conventional grafts. They can provide a physical support and the precise signaling for cells to heal damaged tissues. In this study, a novel RGD peptide end-functionalized poly(ethylene glycol)-b-poly(lactic acid)-b-poly(globalide)-b-poly(lactic acid)-b-poly(ethylene glycol) (RGD-PEG-PLA-PGl-PLA-PEG-RGD) is synthetized and used to prepare functional scaffolds. The PGl inner block is obtained by enzymatic ring-opening polymerization of globalide. The outer PLA blocks are obtained by ring-opening polymerization of both, l-lactide or a racemic mixture, initiated by the α-ω-telechelic polymacrolactone. The presence of PGl inner block enhances the toughness of PLA-based scaffolds, with an increase of the elongation at break up to 300% when the longer block of PGl is used. PLA-PGl-PLA copolymer is coupled with α-ω-telechelic PEG diacids by esterification reaction. PEGylation provides hydrophilic scaffolds as the contact angle is reduced from 114° to 74.8°. That difference improves the contact between the scaffolds and the culture media. Moreover, the scaffolds are functionalized with RGD peptides at the surface significantly enhancing the adhesion and proliferation of bone marrow-derived primary mesenchymal stem cells and MC3T3-E1 cell lines in vitro. These results place this multifunctional polymer as a great candidate for the preparation of temporary grafts.

Toughening Poly(l-lactide) Blends: Effectiveness of Sequence-Controlled Six-Arm Star-Branched Block Copolymers of Poly(l-lactide) and Poly(ε-caprolactone)

Well-defined six-arm star-branched bio-degradable block copolymers of l-lactide and ε-caprolactone were prepared using controlled ring-opening polymerization and a sequential monomer addition method using dipentaerythritol as the initiator core and organocatalysts at low temperatures in solution. Sequence of enchainment was changed by reversing the order of monomer addition giving, either, a crystalline PLA block or an amorphous PCL block as the outer segment. Well-defined six-arm poly(ε-caprolactone-b-l-lactide, 6s-PCL-b-PLA) block copolymers were obtained with a range of segment molecular weights. However, in the case of six-arm poly(l-lactide-b-ε-caprolactone, 6s-PLA-b-PCL), disruption of the block structure was observed on account of competing transesterification reactions accompanying a chain-growth reaction. Such sequence-controlled block copolymers showed interesting phase morphologies, as evidenced by differential scanning calorimetry (DSC) studies. 6s-PCL-b-PLA showed two glass-transition temperatures and two melting temperatures characteristic of the amorphous and crystalline blocks. 6s-PCL-b-PLA and 6s-PLA-b-PCL with different segment chain lengths were solution blended (10 wt %) with a commercially sourced PLA. All the blends were highly transparent. The structure and properties of the blend were examined by DSC, measurement of mechanical properties, and scanning electron microscopy. The results show that a phase-separated 6s-PCL-b-PLA copolymer results in two- to three-fold improvement in tensile toughness without the loss of modulus. A possible hypothesis for the mechanism of tensile toughness in the blend has been proposed.

Recent advances in supramolecular block copolymers for biomedical applications

Supramolecular block copolymers (SBCs) have received considerable interest in polymer chemistry, materials science, biomedical engineering and nanotechnology owing to their unique structural and functional advantages, such as low cytotoxicity, outstanding biodegradability, smart environmental responsiveness, and so forth. SBCs comprise two or more different homopolymer subunits linked by noncovalent bonds, and these polymers, in particular, combine the dynamically reversible nature of supramolecular polymers with the hierarchical microphase-separated structures of block polymers. A rapidly increasing number of publications on the synthesis and applications of SBCs have been reported in recent years; however, a systematic summary of the design, synthesis, properties and applications of SBCs has not been published. To this end, this review provides a brief overview of the recent advances in SBCs and describes the synthesis strategies, properties and functions, and their widespread applications in drug delivery, gene delivery, protein delivery, bioimaging and so on. In this review, we aim to elucidate the general concepts and structure-property relationships of SBCs, as well as their practical bioapplications, shedding further valuable insights into this emerging research field.

Poly(trimethylene carbonate-co-valerolactone) copolymers are materials with tailorable properties: from soft to thermoplastic elastomers

Aliphatic poly(ester-carbonates) are receiving extensive research attention as tailorable materials suitable for multiple applications from tissue engineering and 3D scaffold printing to drug delivery. Thus, simple reliable procedures for producing easily tailorable poly(ester-carbonates) without metal residues are continuously sought after. In this work, we report on one-pot synthesis of random copolymers of TMC and δ-VL using metal-free biocompatible 1,5,7-triazabicyclo[4.4.0]dec-5-ene as a catalyst and benzyl alcohol and poly(ethylene oxide) as initiators. Random poly(ester-carbonates) with TMC : VL unit ratios ranging from 80 : 20 to 20 : 80 were synthesized via ring-opening polymerization while displaying excellent agreement of comonomers' ratios in the feed and copolymer chains. The copolymers' supramolecular structure, thermal and mechanical properties were thoroughly analyzed by various methods. The obtained results clearly indicated that the physicochemical properties can be controlled simply by varying the ratio of comonomers and the length of segments in the copolymer chain. Several copolymers exhibited behavior of thermoplastic elastomers with the most promising one exhibiting a 2200% increase in elongation at break compared to the poly(valerolactone) homopolymer while retaining tensile strength and Young's modulus suitable for biomedical applications. Overall, our work contributed to widening the portfolio of tailorable copolymers for specialized bioapplications and possibly paving a way for the use of more sustainable polymers in the biomedical field.

Aliphatic Polyester Thermoplastic Elastomers Containing Hydrogen-Bonding Ureidopyrimidinone Endgroups

Polylactide- block-poly(γ-methyl-ε-caprolactone)- block-polylactide (LML) is a sustainable thermoplastic elastomer (TPE) candidate that exhibits competitive mechanical properties as compared to traditional styrenic TPEs. The relatively low glass transition temperature of the polylactide endblocks, however, results in stress relaxation and low levels of elastic recovery. We report the synthesis and characterization of poly(γ-methyl-ε-caprolactone) (PMCL) and LML end-functionalized with ureidopyrimidinone (UPy) hydrogen-bonding moieties to improve the elastic performance of these polymers. Although UPy-functionalized PMCL shows dynamical mechanical behavior that is distinct from the unfunctionalized homopolymer, it does not exhibit elastomeric behavior at room temperature. The addition of UPy endgroups to LML increases the ultimate tensile strength, elongation at break, and tensile toughness compared to unfunctionalized LML. Stress relaxation studies at a fixed strain show reduced levels of stress relaxation in LML with UPy endgroups. The stress relaxation was further reduced by including semicrystalline poly(( S, S)-lactide) as endblocks with UPy endgroups.