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Stimuli-responsive peptide-based biomaterials are increasingly gaining interest for various specific and targeted treatments, including drug delivery and tissue engineering. Among all stimuli, pH can be especially useful because endogenous pH changes are often associated with abnormal microenvironments. pH-Responsive amino acids and organic linkers can be easily incorporated into peptides that self-assemble into various nanostructures. Thus, these largely biocompatible and easily tunable platforms are ideal candidates for drug release and as fibrous materials capable of mimicking the native extracellular matrix. In this review, we highlight common design motifs and mechanisms of pH-responsiveness in self-assembling peptide-based biomaterials, focusing on recent advances of these biomaterials applied in drug delivery and tissue engineering. Finally, we suggest future challenges and areas for potential development in pH-responsive self-assembling peptide-based biomaterials.

Inducing high levels of reactive oxygen species (ROS) inside tumor cells is a cancer therapy method termed chemodynamic therapy (CDT). Relying on delivery of Fenton reaction promoters such as Fe(2+), CDT takes advantage of overproduced ROS in the tumor microenvironment. We developed a peptide–H(2)S donor conjugate, complexed with Fe(2+), termed AAN-PTC–Fe(2+). The AAN tripeptide was specifically cleaved by legumain, an enzyme overexpressed in glioma cells, to release carbonyl sulfide (COS). Hydrolysis of COS by carbonic anhydrase formed H(2)S, an inhibitor of catalase, an enzyme that detoxifies H(2)O(2). Fe(2+) and H(2)S together increased intracellular ROS levels and decreased viability in C6 glioma cells compared with controls lacking either Fe(2+), the AAN sequence, or the ability to generate H(2)S. AAN-PTC–Fe(2+) performed better than temezolimide while exhibiting no cytotoxicity toward H9C2 cardiomyocytes. This study provides an H(2)S-amplified, enzyme-responsive platform for synergistic cancer treatment.

A library of N-thiocarboxyanhydrides (NTAs) derived from natural amino acids with benign byproducts and controlled H2S-release kinetics is reported. Minimal acute in vitro toxicity was observed in multiple cell lines, while longer-term toxicity in cancer cells was observed, with slow-releasing donors exhibiting the greatest cytotoxic effects.

We report an elastase-responsive, H2S-releasing hydrogel prepared by covalently crosslinking a mixture of carboxymethylcellulose and poly(ethylene glycol) with an elastase-degradable peptide functionalized with an H2S-releasing S-aroylthiooxime (SATO) unit. Addition of elastase triggered a gel-to-sol transition, which exposed SATOs, leading to more and longer H2S release compared to untriggered gels.

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Graphene (GE) and graphene/zinc ferrite (GE/ZnFe 2 O 4 ) composites were prepared by means of oxidation-reduction and chemical coprecipitation methods. The phase structures, compositions and morphologies of the samples were characterized by the modern testing technologies. The antibacterial properties of the samples on Escherichia coli, Staphylococcus aureus and Candida albicans were studied. The results show that the antibacterial activities of the samples are influenced by the mass ratio of GE to ZnFe 2 O 4 ( m G/Z ) of the GE/ZnFe 2 O 4 composite and strain. In which, the composite with m G/Z = 0.4 has the best antibacterial activity; its minimal inhibitory concentrations are 25, 25 and 12.5 μg/mL on the three stains, respectively. Each composite has best antibacterial effect on Candida albicans , related to the structure of the strain. Moreover, the antibacterial mechanisms of the samples were discussed further.

A series of multi-walled carbon nanotube/titanium dioxide (MWCNT/TiO2) composites were prepared by the sol–gel method. The structure, composition and morphology of the as-prepared samples were characterized. Taking methyl orange (MO) as the simulate organic pollutant, the influences of various factors on the decontamination of the samples and its reusing performance were researched. The results showed that the decontamination activity of the MWCNT/TiO2 composite with mass ratio of MWCNT to TiO2 equal to 1/2 and 450 °C of sintering was optimum in the MO solution of pH = 2, and the composite has good performance for repeated use. What is more, the possible mechanism of decontamination was studied further.