Self-assembly of ciprofloxacin and a tripeptide into an antimicrobial nanostructured hydrogel Silvia Marchesan a, * , Yue Qu b , Lynne J. Waddington a , Christopher D. Easton a , Veronica Glattauer a , Trevor J. Lithgow b , Keith M. McLean a , John S. Forsythe c , Patrick G. Hartley a a CSIRO Materials Science and Engineering, Bayview Avenue, Clayton, Victoria 3053, Australia b Department of Biochemistry and Molecular Biology, Monash University, Victoria 3800, Australia c Department of Materials Engineering, Monash University, Victoria 3800, Australia article info Article history: Received 21 November 2012 Accepted 26 January 2013 Available online 17 February 2013 Keywords: Self-assembly Hydrogel Peptide Drug release abstract This work reports the self-assembly of a sparingly soluble antibiotic (ciprofloxacin) and a hydrophobic tripeptide ( D LeuePheePhe) into supramolecular nanostructures that yield a macroscopic hydrogel at physiological pH. Drug incorporation results in modified morphology and rheological properties of the self-assembled hydrogel. These changes can be correlated with intermolecular interactions between the drug and the peptide, as confirmed by spectroscopic analysis (fluorescence, circular dichroism, IR). The drug appears bound within the hydrogel by non-covalent interactions, and retains its activity over a prolonged release timescale. Antimicrobial activity of the ciprofloxacin-peptide self-assembled hydrogel was evaluated against Staphylococcus aureus, Escherichia coli, and a clinical strain of Klebsiella pneumoniae. Interestingly, the peptide hydrogel alone exhibited a mild anti-bacterial activity against Gram-negative bacteria. While toxic to bacteria, no major cytotoxicity was seen in haemolysis assays of human red blood cells or in mouse fibroblast cell cultures. This new approach of drug incorporation into the nanostructure of a simple tripeptide hydrogel by self-assembly may have important applications for cost-effective wound dressings and novel antimicrobial formulations. Crown Copyright Ó 2013 Published by Elsevier Ltd. All rights reserved. 1. Introduction Today there is an intense research effort directed towards the development of cost-effective, antimicrobial materials for topical applications such as wound dressings [1,2]. Nanomaterials offer the advantage of high surface area to volume ratio and the possibility to design their physical properties (such as porosity, mechanical strength etc.) to match natural tissue, and to selectively load drug molecules for their controlled release at the wound site [3]. In particular, the use of nanotechnology to develop innovative hydrogels is attractive for wound healing applications [4] since it combines the advantages described above with hydrogel properties known to accelerate the healing process, e.g. the moist and occlusive environment they provide, as well as their ability to allow for cell attachment and infiltration [1,2,5]. Tissue regeneration at the site of injury is often hampered by infection, which can be prevented or eradicated by the sustained release of relevant antimicrobials. Different approaches exist to prevent bacteria colonisation, such as the use of metal nano- particles [6], or the sustained release of antibiotics at a specific site of application [7]. In particular, the fluoroquinolone ciprofloxacin is one of the most effective antibiotics used clinically and has become the gold standard for a variety of topical applications, such as skin and eye infections. Drug formulations capable of sustained release are highly sought after, providing a means for drug concentration to be maintained for long periods of time above the minimum inhibitory concentration (MIC) for relevant pathogens. In order to address these requirements, formulations such as liposomes and gels are typically studied, as they offer good vehicles for the incorporation of this hydrophobic and sparingly soluble drug [7e10]. For delivery applications, hydrogels offer convenient drug de- livery matrices. They are typically composed of natural polymers (e.g. alginate), or crosslinked synthetic macromolecules (e.g. * Corresponding author. Present address: Center of Excellence for Nano- structured Materials, INSTM, Unit of Trieste, Dipartimento di Scienze Chimiche e Farmaceutiche, Università degli Studi di Trieste, Piazzale Europa 1, 34127 Trieste, Italy. E-mail addresses: marchesan.silvia@gmail.com, smarchesan@units.it (S. Marchesan). Contents lists available at SciVerse ScienceDirect Biomaterials journal homepage: www.elsevier.com/locate/biomaterials 0142-9612/$ e see front matter Crown Copyright Ó 2013 Published by Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.biomaterials.2013.01.096 Biomaterials 34 (2013) 3678e3687