Self-Assembling Peptides and Carbon Nanomaterials Join Forces for Innovative Biomedical Applications

Self-assembling peptides and carbon nanomaterials have attracted great interest for their respective potential to bring innovation in the biomedical field. Combination of these two types of building blocks is not trivial in light of their very different physico-chemical properties, yet great progress has been made over the years at the interface between these two research areas. This concise review will analyze the latest developments at the forefront of research that combines self-assembling peptides with carbon nanostructures for biological use. Applications span from tissue regeneration, to biosensing and imaging, and bioelectronics

Smart Hydrogels Meet Carbon Nanomaterials for New Frontiers in Medicine

Carbon nanomaterials include diverse structures and morphologies, such as fullerenes, nano-onions, nanodots, nanodiamonds, nanohorns, nanotubes, and graphene-based materials. They have attracted great interest in medicine for their high innovative potential, owing to their unique electronic and mechanical properties. In this review, we describe the most recent advancements in their inclusion in hydrogels to yield smart systems that can respond to a variety of stimuli. In particular, we focus on graphene and carbon nanotubes, for applications that span from sensing and wearable electronics to drug delivery and tissue engineering

Nanostructured Ceria: Biomolecular Templates and (Bio)applications

4Ceria (CeO2) nanostructures are well-known in catalysis for energy and environmental preservation and remediation. Recently, they have also been gaining momentum for biological applications in virtue of their unique redox properties that make them antioxidant or pro-oxidant, depending on the experimental conditions and ceria nanomorphology. In particular, interest has grown in the use of biotemplates to exert control over ceria morphology and reactivity. However, only a handful of reports exist on the use of specific biomolecules to template ceria nucleation and growth into defined nanostructures. This review focusses on the latest advancements in the area of biomolecular templates for ceria nanostructures and existing opportunities for their (bio)applications.Part of the described research was funded by the University of Trieste (FRA2021 to M.M.).openopenRozhin, Petr; Melchionna, Michele; Fornasiero, Paolo; Marchesan, SilviaRozhin, Petr; Melchionna, Michele; Fornasiero, Paolo; Marchesan, Silvi

Hydrogels from a Self-Assembling Tripeptide and Carbon Nanotubes (CNTs): Comparison between Single-Walled and Double-Walled CNTs

Supramolecular hydrogels obtained from the self-organization of simple peptides, such as tripeptides, are attractive soft materials. Their viscoelastic properties can be enhanced through the inclusion of carbon nanomaterials (CNMs), although their presence can also hinder self-assembly, thus requiring investigation of the compatibility of CNMs with peptide supramolecular organization. In this work, we compared single-walled carbon nanotubes (SWCNTs) and double-walled carbon nanotubes (DWCNTs) as nanostructured additives for a tripeptide hydrogel, revealing superior performance by the latter. Several spectroscopic techniques, as well as thermogravimetric analyses, microscopy, and rheology data, provide details to elucidate the structure and behavior of nanocomposite hydrogels of this kind

Self-Assembly and Gelation Study of Dipeptide Isomers with Norvaline and Phenylalanine

Dipeptides have emerged as attractive building blocks for supramolecular materials thanks to their low-cost, inherent biocompatibility, ease of preparation, and environmental friendliness as they do not persist in the environment. In particular, hydrophobic amino acids are ideal candidates for self-assembly in polar and green solvents, as a certain level of hydrophobicity is required to favor their aggregation and reduce the peptide solubility. In this work, we analyzed the ability to self-assemble and the gel of dipeptides based on the amino acids norvaline (Nva) and phenylalanine (Phe), studying all their combinations and not yielding to enantiomers, which display the same physicochemical properties, and hence the same self-assembly behavior in achiral environments as those studied herein. A single-crystal X-ray diffraction of all the compounds revealed fine details over their molecular packing and non-covalent interactions

A Double-Walled Tetrahedron with AgI 4 Vertices Binds Different Guests in Distinct Sites

A double-walled tetrahedral metal-organic cage assembled in solution from silver(I), 2-formyl-1,8-naphthyridine, halide, and a threefold-symmetric triamine. The AgI 4 X clusters at its vertices each bring together six naphthyridine-imine moieties, leading to a structure in which eight tritopic ligands bridge four clusters in an (AgI 4 X)4 L8 arrangement. Four ligands form an inner set of tetrahedron walls that are surrounded by the outer four. The cage has significant interior volume, and was observed to bind anionic guests. The structure also possesses external binding clefts, located at the edges of the cage, which bound small aromatic guests. Halide ions bound to the silver clusters were observed to exchange in a well-defined hierarchy, allowing modulation of the cavity volume. The principles uncovered here may allow for increasingly more sophisticated cages with silver-cluster vertex architectures, with post-assembly tuning of the interior cavity volume enabling targeted binding behavior

Nanocomposite Hydrogels with Self-Assembling Peptide-Functionalized Carbon Nanostructures

Carbon nanostructures (CNSs) are attractive components to attain nanocomposites, yet their hydrophobic nature and strong tendency to aggregate often limit their use in aqueous conditions and negatively impact their properties. In this work, carbon nanohorns (CNHs), multi-walled carbon nanotubes (CNTs), and graphene (G) are first oxidized, and then reacted to covalently anchor the self-assembling tripeptide L-Leu-D-Phe-D-Phe to improve their dispersibility in phosphate buffer, and favor the formation of hydrogels formed by the self-organizing L-Leu-D-Phe-D-Phe present in solution. The obtained nanocomposites are then characterized by transmission electron microscopy (TEM), oscillatory rheology, and conductivity measurements to gain useful insights as to the key factors that determine self-healing ability for the future design of this type of nanocomposites.Carbon nanostructures (CNS) morphology and functionalization effects are studied to attain nanocomposite and supramolecular hydrogels with a self-assembling tripeptide. The latter is covalently anchored onto carbon nanotubes and carbon nanohorns, and the resulting nanocomposite soft matter is characterized at the nanoscale and macroscale to rationalize the self-healing ability of the hydrogel, and the CNS influence on peptide fibrillation in aqueous buffer.imag

Hydrogels from a Self-Assembling Tripeptide and Carbon Nanotubes (CNTs): Comparison between Single-Walled and Double-Walled CNTs

Supramolecular hydrogels obtained from the self-organization of simple peptides, such as tripeptides, are attractive soft materials. Their viscoelastic properties can be enhanced through the inclusion of carbon nanomaterials (CNMs), although their presence can also hinder self-assembly, thus requiring investigation of the compatibility of CNMs with peptide supramolecular organization. In this work, we compared single-walled carbon nanotubes (SWCNTs) and double-walled carbon nanotubes (DWCNTs) as nanostructured additives for a tripeptide hydrogel, revealing superior performance by the latter. Several spectroscopic techniques, as well as thermogravimetric analyses, microscopy, and rheology data, provide details to elucidate the structure and behavior of nanocomposite hydrogels of this kind

COMPOSITE HYDROGELS WITH CARBON NANOSTRUCTURES AND A SELF-ASSEMBLING TRIPEPTIDE

Hydrogels are promising materials that can be used in different applications such as tissue engineering and drug delivery. The self-assembling peptide L-Leu-D-Phe-D-Phe (Lff) is a popular gelator due to its low cost and easy preparation, and therefore it can give novel composites a great advantage. However, the fragility of the hydrogel based on this short peptide can limit its further application. The introduction of carbon nanomaterials (CNMs) to the hydrogel can overcome its low mechanical properties. In particular, previous studies found that Lff self-assembly is compatible with oxidized multi-walled carbon nanotubes (MWCNTs), graphene oxide (GO), and oxidized carbon nanohorns (CNHs), although the properties of the nanocomposite hydrogels differed, with only gels with oxidized MWCNTs demonstrating self-healing ability, raising questions as to what are the key parameters that enable the acquisition of this interesting property. This thesis describes the research efforts to develop nanocomposite hydrogels with the self-assembling tripeptide Lff and different CNMs to compare the effects of the different CNM morphology on the properties of the final materials to assist in their future design. To this end, the tripeptide was synthesized in solid phase, purified by HPLC, and characterized by standard spectroscopic techniques. CNMs were oxidized by treatment with strong acids (i.e., sufonitric mixture or nitric acid) and characterized by standard techniques, such as Raman and infrared spectroscopy, transmission electron microscopy (TEM), and thermogravimetric analysis. The two components were combined non-covalently by simple mixing (Chapter 4), or also covalently by firstly functionalizing the CNMs with the peptide (Chapter 3) to promote their coating by the free peptide, improve their dispersibility, and reduce their aggregation. The effect of CNT diameter was assessed by comparing the properties of the peptide-gel nanocomposites with MWCNTs, with those obtained with SWCNTs and DWCNTs (Chapter 4). All the materials were characterized by standard techniques, such as oscillatory rheology, infrared and Raman spectroscopy, and TEM. Furthermore, Chapter 5 describes the design of experimental setups to assess the nanocomposite hydrogels’ antibacterial properties on E.coli, and conductive properties, by using the four-probe method and the electrochemical impedance spectroscopy. This study revealed the importance of CNT elongated morphology to impart self-healing ability to the nanocomposite hydrogels, while the CNT diameter was not critical. In particular DWCNTs demonstrated the highest improvement in the viscoelastic properties of the peptide gels. Furthermore, the covalent anchoring of Lff onto the CNMs proved difficult, and did not lead to notable advantages, expect for the case of CNHs that did not self-segregate from the free peptide when they were first also functionalized with it. In the case of CNTs, however, the simple mixing of the free peptide with the oxidized CNTs proved to be the best strategy towards nanocomposite hydrogels with enhanced viscoelastic properties using a very simple protocol. Conductivity measurements did not reveal major differences between the obtained materials, and they revealed that the inorganic buffer contribution played a major role due to ion mobility. Finally, the testing performed on these materials with E.coli did not reveal antibacterial properties of the CNMs, and it is possible that their embedding within the peptide-gel matrix impeded the required contact between bacterial cells and their bare surface. Overall, this work significantly advanced our understanding of these systems to enable their better future design, and highlighted nanocomposites with oxidized DWCNTs as the hydrogels with the best viscoelastic properties that deserve future development for more advanced applications.Hydrogels are promising materials that can be used in different applications such as tissue engineering and drug delivery. The self-assembling peptide L-Leu-D-Phe-D-Phe (Lff) is a popular gelator due to its low cost and easy preparation, and therefore it can give novel composites a great advantage. However, the fragility of the hydrogel based on this short peptide can limit its further application. The introduction of carbon nanomaterials (CNMs) to the hydrogel can overcome its low mechanical properties. In particular, previous studies found that Lff self-assembly is compatible with oxidized multi-walled carbon nanotubes (MWCNTs), graphene oxide (GO), and oxidized carbon nanohorns (CNHs), although the properties of the nanocomposite hydrogels differed, with only gels with oxidized MWCNTs demonstrating self-healing ability, raising questions as to what are the key parameters that enable the acquisition of this interesting property. This thesis describes the research efforts to develop nanocomposite hydrogels with the self-assembling tripeptide Lff and different CNMs to compare the effects of the different CNM morphology on the properties of the final materials to assist in their future design. To this end, the tripeptide was synthesized in solid phase, purified by HPLC, and characterized by standard spectroscopic techniques. CNMs were oxidized by treatment with strong acids (i.e., sufonitric mixture or nitric acid) and characterized by standard techniques, such as Raman and infrared spectroscopy, transmission electron microscopy (TEM), and thermogravimetric analysis. The two components were combined non-covalently by simple mixing (Chapter 4), or also covalently by firstly functionalizing the CNMs with the peptide (Chapter 3) to promote their coating by the free peptide, improve their dispersibility, and reduce their aggregation. The effect of CNT diameter was assessed by comparing the properties of the peptide-gel nanocomposites with MWCNTs, with those obtained with SWCNTs and DWCNTs (Chapter 4). All the materials were characterized by standard techniques, such as oscillatory rheology, infrared and Raman spectroscopy, and TEM. Furthermore, Chapter 5 describes the design of experimental setups to assess the nanocomposite hydrogels’ antibacterial properties on E.coli, and conductive properties, by using the four-probe method and the electrochemical impedance spectroscopy. This study revealed the importance of CNT elongated morphology to impart self-healing ability to the nanocomposite hydrogels, while the CNT diameter was not critical. In particular DWCNTs demonstrated the highest improvement in the viscoelastic properties of the peptide gels. Furthermore, the covalent anchoring of Lff onto the CNMs proved difficult, and did not lead to notable advantages, expect for the case of CNHs that did not self-segregate from the free peptide when they were first also functionalized with it. In the case of CNTs, however, the simple mixing of the free peptide with the oxidized CNTs proved to be the best strategy towards nanocomposite hydrogels with enhanced viscoelastic properties using a very simple protocol. Conductivity measurements did not reveal major differences between the obtained materials, and they revealed that the inorganic buffer contribution played a major role due to ion mobility. Finally, the testing performed on these materials with E.coli did not reveal antibacterial properties of the CNMs, and it is possible that their embedding within the peptide-gel matrix impeded the required contact between bacterial cells and their bare surface. Overall, this work significantly advanced our understanding of these systems to enable their better future design, and highlighted nanocomposites with oxidized DWCNTs as the hydrogels with the best viscoelastic properties that deserve future development for more advanced applications

Carbon Nanomaterials (CNMs) and Enzymes: From Nanozymes to CNM-Enzyme Conjugates and Biodegradation

Carbon nanomaterials (CNMs) and enzymes differ significantly in terms of their physico-chemical properties—their handling and characterization require very different specialized skills. Therefore, their combination is not trivial. Numerous studies exist at the interface between these two components—especially in the area of sensing—but also involving biofuel cells, biocatalysis, and even biomedical applications including innovative therapeutic approaches and theranostics. Finally, enzymes that are capable of biodegrading CNMs have been identified, and they may play an important role in controlling the environmental fate of these structures after their use. CNMs’ widespread use has created more and more opportunities for their entry into the environment, and thus it becomes increasingly important to understand how to biodegrade them. In this concise review, we will cover the progress made in the last five years on this exciting topic, focusing on the applications, and concluding with future perspectives on research combining carbon nanomaterials and enzymes