Biofunctionalization of TiO2 surfaces with self-assembling oligopeptides in different pH and Ionic Strength conditions: Charge effects and molecular organization

Techniques for characterizing biofunctionalized surfaces for bioanalysis purposes

Surface biofunctionalization is an essential stage in the preparation of any bioassay affecting its analytical performance. However, a complete characterization of the biofunctionalized surface, considering studies of coverage density, distribution and orientation of biomolecules, layer thickness, and target biorecognition efficiency, is not met most of the time. This review is a critical overview of the main techniques and strategies used for characterizing biofunctionalized surfaces and the process in between. Emphasis is given to scanning force microscopies as the most versatile and suitable tools to evaluate the quality of the biofunctionalized surfaces in real-time dynamic experiments, highlighting the helpful of atomic force microscopy, Kelvin probe force microscopy, electrochemical atomic force microscopy and photo-induced force microscopy. Other techniques such as optical and electronic microscopies, quartz crystal microbalance, X-ray photoelectron spectroscopy, contact angle, and electrochemical techniques, are also discussed regarding their advantages and disadvantages in addressing the whole characterization of the biomodified surface. Scarce reviews point out the importance of practicing an entire characterization of the biofunctionalized surfaces. This is the first review that embraces this topic discussing a wide variety of characterization tools applied in any bioanalysis platform developed to detect both clinical and environmental analytes. This survey provides information to the analysts on the applications, strengths, and weaknesses of the techniques discussed here to extract fruitful insights from them. The aim is to prompt and help the analysts to accomplish an entire assessment of the biofunctionalized surface, and profit from the information obtained to enhance the bioanalysis output.

Strategies for the Covalent Anchoring of a BMP-2-Mimetic Peptide to PEEK Surface for Bone Tissue Engineering

Researchers in the field of tissue engineering are always searching for new scaffolds for bone repair. Polyetheretherketone (PEEK) is a chemically inert polymer that is insoluble in conventional solvents. PEEK's great potential in tissue engineering applications arises from its ability to not induce adverse reactions when in contact with biological tissues and its mechanical properties, which are similar to those of human bone. These exceptional features are limited by the bio-inertness of PEEK, which causes poor osteogenesis on the implant surface. Here, we demonstrated that the covalent grafting of the sequence (48-69) mapped on the BMP-2 growth factor (GBMP1α) significantly enhances the mineralization and gene expression of human osteoblasts. Different chemical methods were employed for covalently grafting the peptide onto 3D-printed PEEK disks: (a) the reaction between PEEK carbonyls and amino-oxy groups inserted in the peptides' N-terminal sites (oxime chemistry) and (b) the photoactivation of azido groups present in the peptides' N-terminal sites, which produces nitrene radicals able to react with PEEK surface. The peptide-induced PEEK surface modification was assessed using X-ray photoelectron measurements, while the superficial properties of the functionalized material were analyzed by means of atomic force microscopy and force spectroscopy. Live and dead assays and SEM measurements showed greater cell cover on functionalized samples than the control, without any cytotoxicity induction. Moreover, functionalization improved the rate of cell proliferation and the amount of calcium deposits, as demonstrated by the AlamarBlue™ and alizarin red results, respectively. The effects of GBMP1α on h-osteoblast gene expression were assayed using quantitative real-time polymerase chain reaction.

Cu(I) and Cu(II) Complexes Based on Lonidamine-Conjugated Ligands Designed to Promote Synergistic Antitumor Effects

Bis(pyrazol-1-yl)- and bis(3,5-dimethylpyrazol-1-yl)-acetates were conjugated with the 2-hydroxyethylester and 2-aminoethylamide derivatives of the antineoplastic drug lonidamine to prepare Cu(I) and Cu(II) complexes that might act through synergistic mechanisms of action due to the presence of lonidamine and copper in the same chemical entity. Synchrotron radiation-based complementary techniques [X-ray photorlectron spectroscopy and near-edge X-ray absorption fine structure (NEXAFS)] were used to characterize the electronic and molecular structures of the complexes and the local structure around the copper ion (XAFS) in selected complexes. All complexes showed significant antitumor activity, proving to be more effective than the reference drug cisplatin in a panel of human tumor cell lines, and were able to overcome oxaliplatin and multidrug resistance. Noticeably, these Cu complexes appeared much more effective than cisplatin against 3D spheroids of pancreatic PSN-1 cancer cells; among these, PPh₃-containing Cu(I) complex 15 appeared to be the most promising derivative. Mechanistic studies revealed that 15 induced cancer cell death by means of an apoptosis-alternative cell death.

Fabrication of C-Doped Titanium Dioxide Coatings with Improved Anti-icing and Tribological Behavior

The accumulation of ice on solid surfaces can cause serious losses and accidents. Current anti-icing/deicing coatings find it difficult to maintain their properties under frequent mechanical wear. In this work, the aerosol-assisted chemical vapor deposition method was employed to prepare C-doped titanium dioxide coatings that have both photothermal properties and excellent wear resistance. The temperature of the sample surface reached 37.6 °C after 2 sun (2 kW/m²) irradiation for 30 min at -30 °C. Compared to a pristine titanium dioxide coating, the C-doped titanium dioxide coatings demonstrated superior antifriction behavior, with the friction coefficient reduced by 47% under dry conditions. These wear resistance properties make C-doped titanium dioxide coatings highly suitable for a range of outdoor applications, especially for anti-icing purposes.

Chitosan Covalently Functionalized with Peptides Mapped on Vitronectin and BMP-2 for Bone Tissue Engineering

Worldwide, over 20 million patients suffer from bone disorders annually. Bone scaffolds are designed to integrate into host tissue without causing adverse reactions. Recently, chitosan, an easily available natural polymer, has been considered a suitable scaffold for bone tissue growth as it is a biocompatible, biodegradable, and non-toxic material with antimicrobial activity and osteoinductive capacity. In this work, chitosan was covalently and selectively biofunctionalized with two suitably designed bioactive synthetic peptides: a Vitronectin sequence (HVP) and a BMP-2 peptide (GBMP1a). Nuclear magnetic resonance (NMR), X-ray photoelectron spectroscopy (XPS), and Fourier transform infrared spectroscopy (FT-IR) investigations highlighted the presence of the peptides grafted to chitosan (named Chit-HVP and Chit-GBMP1a). Chit-HVP and Chit-GBMP1a porous scaffolds promoted human osteoblasts adhesion, proliferation, calcium deposition, and gene expression of three crucial osteoblast proteins. In particular, Chit-HVP highly promoted adhesion and proliferation of osteoblasts, while Chit-GBMP1a guided cell differentiation towards osteoblastic phenotype.

Bioactivated Oxidized Polyvinyl Alcohol towards Next-Generation Nerve Conduits Development

The limitations and difficulties that nerve autografts create in normal nerve function recovery after injury is driving research towards using smart materials for next generation nerve conduits (NCs) setup. Here, the new polymer partially oxidized polyvinyl alcohol (OxPVA) was assayed to verify its future potential as a bioactivated platform for advanced/effective NCs. OxPVA-patterned scaffolds (obtained by a 3D-printed mold) with/without biochemical cues (peptide IKVAV covalently bound (OxPVA-IKVAV) or self-assembling peptide EAK (sequence: AEAEAKAKAEAEAKAK), mechanically incorporated (OxPVA+EAK) versus non-bioactivated scaffold (peptide-free OxPVA (PF-OxPVA) supports, OxPVA without IKVAV and OxPVA without EAK control scaffolds) were compared for their biological effect on neuronal SH-SY5Y cells. After cell seeding, adhesion/proliferation, mediated by (a) precise control over scaffolds surface ultrastructure; (b) functionalization efficacy guaranteed by bioactive cues (IKVAV/EAK), was investigated by MTT assay at 3, 7, 14 and 21 days. As shown by the results, the patterned groove alone stimulates colonization by cells; however, differences were observed when comparing the scaffold types over time. In the long period (21 days), patterned OxPVA+EAK scaffolds distinguished in bioactivity, assuring a significantly higher total cell amount than the other groups. Experimental evidence suggests patterned OxPVA-EAK potential for NCs device fabrication.

Antimicrobial Effect and Cytotoxic Evaluation of Mg-Doped Hydroxyapatite Functionalized with Au-Nano Rods

Hydroxyapatite (HA) is the main inorganic mineral that constitutes bone matrix and represents the most used biomaterial for bone regeneration. Over the years, it has been demonstrated that HA exhibits good biocompatibility, osteoconductivity, and osteoinductivity both in vitro and in vivo, and can be prepared by synthetic and natural sources via easy fabrication strategies. However, its low antibacterial property and its fragile nature restricts its usage for bone graft applications. In this study we functionalized a MgHA scaffold with gold nanorods (AuNRs) and evaluated its antibacterial effect against S. aureus and E. coli in both suspension and adhesion and its cytotoxicity over time (1 to 24 days). Results show that the AuNRs nano-functionalization improves the antibacterial activity with 100% bacterial reduction after 24 h. The toxicity study, however, indicates a 4.38-fold cell number decrease at 24 days. Although further optimization on nano-functionalization process are needed for cytotoxicity, these data indicated that Au-NRs nano-functionalization is a very promising method for improving the antibacterial properties of HA.

Hydroxyapatite Surfaces Functionalized with a Self-Assembling Peptide: XPS, RAIRS and NEXAFS Study

Hydroxyapatite (HAP) coatings can improve the biocompatibility and bioactivity of titanium alloys, such as Ti6Al4V, commonly used as material for orthopedic prostheses. In this framework, we have studied the surface of HAP coatings enriched with Mg and either Si or Ti deposited by RF magnetron sputtering on Ti6Al4V. HAP coatings have been furtherly functionalized by adsorption of a self-assembling peptide (SAP) on the HAP surface, with the aim of increasing the material bioactivity. The selected SAP (peptide sequence AbuEAbuEAbuKAbuKAbuEAbuEAbuKAbuK) is a self-complementary oligopeptide able to generate extended ordered structures by self-assembling in watery solutions. Samples were prepared by incubation of the HAP coatings in SAP solutions and subsequently analyzed by X-Ray Photoelectron Spectroscopy (XPS), Fourier Transform Infrared (FTIR) and Near Edge X-Ray Absorption Fine Structure (NEXAFS) spectroscopies, in order to determine the amount of adsorbed peptide, the peptide stability and the structure of the peptide overlayer on the HAP coatings as a function of the HAP substrate and of the pH of the mother SAP solution. Experimental data yielded evidence of SAP adsorption on the HAP surface, and peptide overlayers showed ordered structure and molecular orientation. The thickness of the SAP overlayer depends on the composition of the HAP coating.

Cysteine-Modified Self-Assembling Peptides on Gold: The Role of the Head and Tail

Molecular self-assembly consists of the spontaneous aggregation of molecules into a well-defined structure guided by noncovalent bonds. The self-assembly strategy is ubiquitous in nature and recently has been proposed as a nature-mimetic strategy in polymer science and biomaterial engineering. In this context, we aim at designing and testing innovative but simple chemical strategies to efficiently modify surfaces by exploiting minor modifications in the bioactive molecule functionalities, for example, introducing cysteine (Cys) as a terminal residue in self-assembling peptides (SAPs). In this work, we report the attenuated total reflection-Fourier transform infrared spectroscopy, synchrotron radiation-induced X-ray photoelectron spectroscopy, near-edge X-ray absorption fine structure spectroscopy, and time-of-flight secondary ion mass spectrometry investigation of self-assembled layers of oligopeptides anchored onto gold surfaces through cysteine residues, opportunely inserted in an SAP (EAK16-II) main chain in three different positions: at the amine end group, at the carboxyl end group, and at both terminal groups (i.e., a bidentate SAP). This study, which allowed us to individuate in the bidentate SAP the best candidate for the controlled production of ordered SAP layers on the gold substrate surface, is envisaged to open wide perspectives for efficient chemical modification of surfaces with biomolecules, leading to obtaining innovative bioactive materials for applications in the field of tissue engineering.