Tuning the phase transition temperature of thermal-responsive OEGylated poly-L-glutamate via random copolymerization with L-alanine

Thermo-induced physically crosslinked polypeptide-based block copolymer hydrogels for biomedical applications

Stimuli-responsive synthetic polypeptide-containing block copolymers have received considerable attention in recent years. Especially, unique thermo-induced sol-gel phase transitions were observed for elaborately-designed amphiphilic diblock copolypeptides and a range of poly(ethylene glycol) (PEG)-polypeptide block copolymers. The thermo-induced gelation mechanisms involve the evolution of secondary conformation, enhanced intramolecular interactions, as well as reduced hydration and increased chain entanglement of PEG blocks. The physical parameters, including polymer concentrations, sol-gel transition temperatures and storage moduli, were investigated. The polypeptide hydrogels exhibited good biocompatibility in vitro and in vivo, and displayed biodegradation periods ranging from 1 to 5 weeks. The unique thermo-induced sol-gel phase transitions offer the feasibility of minimal-invasive injection of the precursor aqueous solutions into body, followed by in situ hydrogel formation driven by physiological temperature. These advantages make polypeptide hydrogels interesting candidates for diverse biomedical applications, especially as injectable scaffolds for 3D cell culture and tissue regeneration as well as depots for local drug delivery. This review focuses on recent advances in the design and preparation of injectable, thermo-induced physically crosslinked polypeptide hydrogels. The influence of composition, secondary structure and chirality of polypeptide segments on the physical properties and biodegradation of the hydrogels are emphasized. Moreover, the studies on biomedical applications of the hydrogels are intensively discussed. Finally, the major challenges in the further development of polypeptide hydrogels for practical applications are proposed.

Local delivery of biocompatible lentinan/chitosan composite for prolonged inhibition of postoperative breast cancer recurrence

Postsurgical localized chemotherapy for breast cancer recurrence (BCR) still faces many problems which dampen researchers' enthusiasm and discounted prognosis. Simple strategies with controllable toxicities are expected to address these hurdles. Lentinan (LNT) has excellent biocompatibility and notable antitumor activity but rather low bioavailability after intravenous or oral administration. Here, a sponge-like LNT/chitosan composite (LNT/CS sponge) was prepared for efficient local delivery to prevent postoperative BCR. The obtained sponges exhibit uniform porosity and sustained release of LNT in vitro and in vivo. Furthermore, the sponges were implanted and showed significant reduction of postsurgical recurrence and suppression of long-term tumor regrowth with favorable biocompatibility in a subcutaneous postsurgical recurrence mouse model. Subsequent studies revealed that LNT can restrain the stemness of breast cancer cells, which may account for the long-term inhibition of tumor relapse. Therefore, LNT/CS sponge has a great potential as a promising alternative for postsurgical BCR.

Rapidly Thermoreversible and Biodegradable Polypeptide Hydrogels with Sol-Gel-Sol Transition Dependent on Subtle Manipulation of Side Groups

Thermoreversible hydrogels are attractive materials for biomedical applications, but their applications are still limited by nonbiodegradability and/or slow temperature-dependent gel-to-sol transition rates. In this research, we prepared a range of amphiphilic diblock, triblock, and four-armed star block copolymers composed of poly(ethylene glycol) (PEG) and poly(γ-(2-(2-ethoxyethoxy)ethyl)-l-glutamate) (P(EEO₂LG)) segments, which can form rapidly thermoreversible hydrogels at physiological temperature. Intriguingly, the obtained hydrogels can transform from gel to sol within 10-70 s in response to the temperature decrease from 37 to 0 °C. The thermosensitive sol-gel-sol transitions are markedly faster than previously reported thermoreversible PEG-poly(l-glutamate) derivative hydrogels with subtle differences in the side groups and a widely studied poly(d,l-lactide-co-glycolide)-b-PEG-b-poly(d,l-lactide-co-glycolide) (PLGA-PEG-PLGA) hydrogel that required a much longer time of 40∼150 min. Further investigation of the relationship between the hydrogel property and polymer structure is performed, and the self-assembly mechanisms of different copolymers are proposed. Cytotoxicity assays and subcutaneous degradation experiments reveal that the PEG/P(EEO₂LG) block copolymers are biocompatible and biodegradable. The polypeptide hydrogel can therefore be used as a three-dimensional platform for facile cell culture and collection by regulating the temperature.

Advances and Biomedical Applications of Polypeptide Hydrogels Derived from α-Amino Acid N-Carboxyanhydride (NCA) Polymerizations

Polypeptide hydrogels, having the ability to mimic certain properties of natural, native extracellular matrix components, are being actively designed and described for various applications in the construction of tissue engineering scaffolds, living cell encapsulation, and drug delivery systems. Compared to conventional hydrogels, polypeptide hydrogels possess biocompatibility, biodegradability, bioactivity, functional diversity, and structural advantage based on the unique secondary structures (α-helix and β-sheet). Furthermore, the progresses in functional N-carboxyanhydride polymerization combined with advanced orthogonal conjugation techniques significantly promote the development of the polypeptide materials. This progress report focuses on the recent advances in designing and engineering polypeptide hydrogels obtained from ring opening polymerization, highlighting the precise manipulation of their properties for biomedical applications.

CO2-responsive self-healable hydrogels based on hydrophobically-modified polymers bridged by wormlike micelles

A versatile and simple strategy is proposed to design CO₂-responsive self-healable hydrogels based on hydrophobically-modified polymers bridged by worm like micelles.

Recent trends in pH/thermo-responsive self-assembling hydrogels: from polyions to peptide-based polymeric gelators

In this article, we highlight some recent developments in "smart" physical hydrogels achieved by self-assembling of block type macromolecules. More precisely we focus on two interesting types of gelators namely conventional ionic (or ionogenic) block copolymers and peptide-based polymers having as a common feature their responsiveness to pH and/or temperature which are the main triggers used for potential biomedical applications. Taking advantage of the immense skills of conventional block copolymer hydrogelators, namely macromolecular design, self-assembling mechanism, gel rheological properties, responsiveness to various triggers and innovative applications, the development of novel self-assembling gelators, integrating the new knowledge emerging from the peptide-based systems, opens new horizons towards bio-inspired technologies.

Temperature-responsive in situ nanoparticle hydrogels based on hydrophilic pendant cyclic ether modified PEG-PCL-PEG

Thermo-sensitive injectable hydrogels based on poly(ε-caprolactone)/poly(ethylene glycol) (PCL/PEG) block copolymers have attracted considerable attention for sustained drug release and tissue engineering applications.

Reversible thermo-sensitivity induced from varying the hydrogen bonding between the side residues of rationally designed polypeptides

Rationally designed polypeptides with similar molecular structures but varying patterns of hydrogen bonding between the side groups have been synthesized and demonstrated to possess distinct solubility and thermal behaviors. Further balancing the ratio of both isopropylamine and ethylenediamine side groups endows the random copolymer with reversible thermo-sensitivity.

Disclosing the nature of thermo-responsiveness of poly(N-isopropyl acrylamide)-based polymeric micelles: aggregation or fusion?

We disclose a fusion-dominated thermo-responsive behaviour of a poly(N-isopropyl acrylamide)-based copolymer micelle by TEM after in situ photo-cross-linking morphologies.

Covalent modification of graphene as a 2D nanofiller for enhanced mechanical performance of poly(glutamate) hybrid gels

Covalently functionalized graphene via grafting of poly(glutamate) as interfacial adhesive junctions may show sustainable potential in more robust polypeptide hybrid organogels.