Antimicrobial electrospun fibers of polyester loaded with engineered cyclic gramicidin analogues

Biodegradable polyester fibers have been loaded with two engineered analogues of gramicidin soviet. In these cyclic peptide derivatives, which were designed in a previous work to stabilize the bioactive conformation while enhancing the antimicrobial activity, the D-Phe was replaced by D-Pro, and the L-Pro was changed by 1-aminocyclopropanecarboxylic acid (Ac3c) or by an Ac3c derivative with two vicinal phenyl substituents in a trans relative disposition (S,S-c3diPhe). The diameter, topography, thermal stability and wettability of the polyester fibers, which have been obtained by electrospinning, strongly depend on the molecular constraints and stability of the loaded peptides. More specifically, unloaded and linear gramicidin-loaded fibers (used as control) are hydrophobic, rough and micrometric, while fibers loaded with the cyclic peptides are hydrophilic, ultra-smooth, nanometric and less thermally stable. The activity of the two cyclic peptides increases when loaded into polyester fibers, suggesting that the polymeric matrix stabilizes the bioactive β-sheet structure. The peptide with S,S-c3diPhe displays higher antibiotic potency and biocompatibility than that with Ac3c, which indicates not only that the bioactive conformation is better preserved by the former but also the significant role played by the phenyl rings in the recognition by living cells.Peer ReviewedPostprint (published version

Preparation, surface characterization ans anticorrosive behavior of polynailine and poly(3,4-ethylenedioxythiophene) deposited on aluminum alloy AA2024-T3

Peer ReviewedPostprint (author's final draft

Paradigm shift for preparing versatile M2+-free gels from unmodified sodium alginate

This manuscript describes a new route to prepare rapidly Ca2+-free hydrogels from unmodified sodium alginate by simply mixing with small organic molecules such as poly(carboxylic acid) compounds as cross-linker agents instead of classical divalent metal salts such as CaCl2. Dimethyl sulfoxide (DMSO) was also found to induce the rapid gelation of aqueous alginate solutions. The gelation process takes place at room temperature, and depending on the composition, gels with good thermal (90-100 °C) and mechanical properties compared to classical metal-containing analogs are obtained. DMSO-based gels showed remarkable self-supporting and thixotropic properties, which can be tuned by the biopolymer concentration. Furthermore, oxalic acid-based gels show superior elasticity than HCl, CaCl2 and DMSO-based gels. The possibility to prepare monoliths, beads, and films of these gels provide them with significant versatility. In particular, films made of alginate and oxalic acid show good potential as synergistic anticancer drug delivery carrier. Computational studies using both quantum mechanical and classical force-field methodologies reveal that hydrogen bonding networks between water and DMSO molecules located close to the alginate chains are responsible for the stability of DMSO-based gels. In contrast, the cohesion of oxalic acid-based gels is a consequence of the coexistence of multiple ionic associations involving oxalate, alginate, and Na+ counterions, which stabilize the system and keep all the interacting species grouped.Peer ReviewedPostprint (author's final draft

Hierarchical self-assembly of di-, tri- and tetraphenylalanine peptides capped with two fluorenyl functionalities: from polymorphs to dendrites

Homopeptides with 2, 3 and 4 phenylalanine (Phe) residues and capped with fluorenylmethoxycarbonyl and fluorenylmethyl esters at the N-terminus and C-terminus, respectively, have been synthesized to examine their self-assembly capabilities. Depending on the conditions, the di-and triphenylalanine derivatives self-organize into a wide variety of stable polymorphic structures, which have been characterized: stacked braids, doughnut-like shapes, bundled arrays of nanotubes, corkscrew-like shapes and spherulitic microstructures. These highly aromatic Phe-based peptides also form incipient branched dendritic microstructures, even though they are highly unstable, making their manipulation very difficult. Conversely, the tetraphenylalanine derivative spontaneously self-assembles into stable dendritic microarchitectures made of branches growing from nucleated primary frameworks. The fractal dimension of these microstructures is similar to 1.70, which provides evidence for self-similarity and two-dimensional diffusion controlled growth. DFT calculations at the M06L/6-31G(d) level have been carried out on model beta-sheets since this is the most elementary building block of Phe-based peptide polymorphs. The results indicate that the antiparallel beta-sheet is more stable than the parallel one, with the difference between them growing with the number of Phe residues. Thus, the cooperative effects associated with the antiparallel disposition become more favorable when the number of Phe residues increases from 2 to 4, while those of the parallel disposition remained practically constant.Peer ReviewedPostprint (author's final draft

Weighing biointeractions between fibrin (ogen) and clot-binding peptides using microcantilever sensors

This is the peer reviewed version of the following article: “Puiggalí, A., Del Valle, L.J., Aleman, C. and Pérez, M. (2017) Weighing biointeractions between fibrin (ogen) and clot-binding peptides using microcantilever sensors. Journal of peptide science, (23) 2: 162–171.” which has been published in final form at [doi: 10.1002/psc.2938]. This article may be used for non-commercial purposes in accordance with Wiley Terms and Conditions for Self-Archiving."Peptides homing tumor vasculature are considered promising molecular imaging agents for cancer detection at an early stage. In addition to their high binding affinity, improved tissue penetrating ability, and low immunogenicity, they can deliver targeted anticancer drugs, thus expanding therapeutic treatments. Among those, CREKA, a linear peptide that specifically binds to clotted-plasma proteins in tumor vessels, has been recently employed to design bioactive systems able to target different cancer types. Within this context, this paper explores the biorecognition event between CR(NMe)EKA, an engineered CREKA-analog bearing a noncoded amino acid (N-methyl-Glu) that is responsible for its enhanced activity, and clotted-plasma proteins (fibrin and fibrinogen) by nanomechanical detection. Specifically, the tumor-homing peptide was covalently attached via epoxysilane chemistry onto silicon microcantilever chips that acted as sensors during dynamic mode experiments. Before that, each step of the functionalization process was followed by contact angle measurements, interferometry, X-ray photoelectron spectroscopy, and atomic force microscopy, thus revealing the applied protocol as a suitable strategy. The fibrin(ogen)-binding induced by CR(NMe)EKA was detected by the resonance frequency shift of the cantilevers, and a detection limit of 100¿ng/mL was achieved for both proteins. Even though further development is required, this work reflects the promising application of emerging technologies capable of assisting in the comprehension of biological interactions and their implications in the biotechnological field.Peer ReviewedPostprint (author's final draft

Composites based on epoxy resins and poly(3-thiophene methyl acetate) nanoparticles: mechanical and electrical properties

Conducting polymer nanocomposites (CPnC) have been prepared by loading different concentrations of poly(3-thiophene methyl acetate) (P3TMA) nanoparticles to an epoxy network. Therefore, the typical limitations of CPs applicability, i.e., reduced solubility and difficult processability, have been overcome. The influence of different factors (i.e., curing temperature, solvent used to disperse nanoparticles, and concentration of P3TMA) on the CPnC properties has been evaluated. The major requirement to obtain homogeneously distributed materials has been found to be the P3TMA-solvent compatibility. Xylene, which is typically used in epoxy resins, has been practically eliminated to avoid the formation of aggregates and has been replaced by tetrahydrofuran. Although properties like chemical structure and doping level as well as morphology and P3TMA nanoparticle distribution into the epoxy matrix have been examined for CPnC samples, particular attention has been paid to evaluate their mechanical and electrical properties. The Young's modulus and tensile strength values increase upon the addition of a small concentration of P3TMA, independently of the curing temperature, with the exception of 25 wt% P3TMA composition that exceeds the percolation limit for this material. The electrical DC conductivity determined for samples with 12 and 25 wt% P3TMA ranged from 6.0 x10(-7) to 8.2x 10(-7) S/cm. Therefore, CPnC films exhibited a semiconductor behavior with conductivity values at least three to four orders of magnitude higher compared to that of the pure insulating epoxy (10(-11) to 10(-13) S/cm). POLYM. COMPOS., 37:734-745, 2016. (c) 2014 Society of Plastics EngineersPeer ReviewedPostprint (author's final draft

Weighing biointeractions between fibrin (ogen) and clot-binding peptides using microcantilever sensors

This is the peer reviewed version of the following article: “Puiggalí, A., Del Valle, L.J., Aleman, C. and Pérez, M. (2017) Weighing biointeractions between fibrin (ogen) and clot-binding peptides using microcantilever sensors. Journal of peptide science, (23) 2: 162–171.” which has been published in final form at [doi: 10.1002/psc.2938]. This article may be used for non-commercial purposes in accordance with Wiley Terms and Conditions for Self-Archiving."Peptides homing tumor vasculature are considered promising molecular imaging agents for cancer detection at an early stage. In addition to their high binding affinity, improved tissue penetrating ability, and low immunogenicity, they can deliver targeted anticancer drugs, thus expanding therapeutic treatments. Among those, CREKA, a linear peptide that specifically binds to clotted-plasma proteins in tumor vessels, has been recently employed to design bioactive systems able to target different cancer types. Within this context, this paper explores the biorecognition event between CR(NMe)EKA, an engineered CREKA-analog bearing a noncoded amino acid (N-methyl-Glu) that is responsible for its enhanced activity, and clotted-plasma proteins (fibrin and fibrinogen) by nanomechanical detection. Specifically, the tumor-homing peptide was covalently attached via epoxysilane chemistry onto silicon microcantilever chips that acted as sensors during dynamic mode experiments. Before that, each step of the functionalization process was followed by contact angle measurements, interferometry, X-ray photoelectron spectroscopy, and atomic force microscopy, thus revealing the applied protocol as a suitable strategy. The fibrin(ogen)-binding induced by CR(NMe)EKA was detected by the resonance frequency shift of the cantilevers, and a detection limit of 100¿ng/mL was achieved for both proteins. Even though further development is required, this work reflects the promising application of emerging technologies capable of assisting in the comprehension of biological interactions and their implications in the biotechnological field.Peer Reviewe

Enhanced dielectric performance of a block copolymer-polythiophene nanocomposite

Dielectric elastomer actuators (DEAs) transform electrical energy into mechanical work. However, despite displaying exceptional features, the low permittivity of elastomers restricts their application. Hence, to overcome this limitation, DEAs are fabricated by dispersing poly(3-methylthiophene acetate) (P3TMA), a polarizable conducting polymer, into poly[styrene-b-(ethylene-co-butylene)-b-styrene] (SEBS), a thermoplastic elastomer with excellent mechanical properties. Although high-quality SEBS:P3TMA films are obtained for all compositions (between 0.5 and 20 wt % P3TMA), their thickness and surface roughness increase with the nano-sized filler content. Moreover, the conducting particles are well integrated into the SEBS network with no evidence of aggregation or significant change in the mechanical properties of the composites. P3TMA, which forms encapsulated conductive domains within the polymeric matrix, improves the dielectric behavior of SEBS:P3TMA by increasing their dielectric constant with low dielectric losses and no current leakage. Thus, indicating the potential future application of these nanocomposites as elastomer actuators or high energy density capacitors.Postprint (published version

Electrospray loading and release of hydrophobic gramicidin in polyester microparticles

Gramicidin (GA), a very hydrophobic pentadecapeptide with important biological activities (i.e. in addition to its well-known antimicrobial and antibiotic activities, GA has been recently identified as a potent therapeutic agent against different carcinomas), has been loaded by electrospraying in poly(tetramethylene succinate) (PE44), a biodegradable and biocompatible aliphatic polyester. Microspheres (average diameter: 5.0 +/- 0.7 mm) were successfully obtained from the mixture of GA and PE44 solutions in ethanol and chloroform, respectively. The loading of the peptide, which has been proved by FTIR and X-ray photoelectron spectroscopies, essentially occurred at the surface of the microspheres, as was reflected by scanning electron microscopy micrographs and atomic force microscopy phase images. In spite of this, the thermal stability of the polyester matrix remained essentially unaltered, even though the wettability decreased. The release of GA in phosphate buffer saline (PBS) was limited by the very low solubility of the peptide in aqueous solution, a fast burst effect followed by the establishment of equilibrium after 5 days of being observed in this hydrophilic environment. The release behaviour was very different when the hydrophilicity of the medium was reduced by adding ethanol. In this case, a very fast but sustained release was identified during the first few hours. On the other hand, biological tests have demonstrated that GA retains its antimicrobial activity after loading and does not alter the biocompatibility of PE44. Our results prove that, despite its hydrophobicity and relatively large number of residues, the loading of GA in a polymeric matrix represents an alternative strategy for the release of this versatile peptide in cancer therapy.Peer ReviewedPostprint (author's final draft

Poly-y-glutamic Acid Hydrogels as Electrolyte for Poly(3,4-ethylenedioxythiophene)-Based Supercapacitors

Biosynthetic poly-¿-glutamic acid (¿-PGA) has been used to produce hydrogels using cystamine as cross-linker and 1-[3-(dimethylamino)propyl]-3-ethylcarbodiimide methiodide (EDC methiodide) as condensing agent. Eight different hydrogels with different properties were formulated by varying both the molecular weight of ¿-PGA and the ¿-PGA/EDC/cystamine ratio and subsequently characterized. The most appropriate ¿-PGA hydrogel was selected to perform as solid electrolytic medium in organic electrochemical supercapacitors (OESCs) using poly(3,4-ethylenedioxythiophene) (PEDOT) electrodes based on their mechanical behavior (consistency and robustness to hold the PEDOT electrodes), morphology, and influence on the electrochemical response of the organic electrode (i.e., specific capacitance and both maximum energy and power density values). Hence, PEDOT/¿-PGA energy storage devices fabricated using the most adequate hydrogel formulation displayed a supercapacitor response of 168 F/g and a capacitance retention of 81%. Moreover, after evaluating the maximum energy and power densities (Ragone plot), cyclability, long-term stability, leakage current, and self-discharging response of PEDOT/¿-PGA OESC devices, results allow us to highlight the merits and great potential of ¿-PGA hydrogels as sustainable ion-conductive electrolytes for environmentally friendly energy storage technologies.Peer ReviewedPostprint (author's final draft