Stabilizing gelatin-based bioinks under physiological conditions by incorporation of ethylene-glycol-conjugated Fmoc-FF peptides.

Over the last decade, three-dimensional (3D) printing technologies have attracted the interest of researchers due to the possibility of fabricating tissue- and organ-like structures with similarities to the organ of interest. One of the most widely used materials for the fabrication of bioinks is gelatin (Gel) due to its excellent biocompatibility properties. However, in order to fabricate stable scaffolds under physiological conditions, the most common approach is to use gelatin methacrylate (GelMA) that allows the crosslinking and therefore the stabilization of the hydrogel through UV crosslinking. The crosslinking process can be harmful to cells thus decreasing total cell viability. To overcome the need for post-printing crosslinking, a new approach of bioink formulation was studied, incorporating the Fluorenylmethoxycarbonyl diphenylalanine (Fmoc-FF) peptide into the Gel bioink. However, although Fmoc-FF possesses excellent mechanical properties, the lack of elasticity and viscosity makes it unsuitable for 3D-printing. Here, we demonstrate that covalent conjugation of two different ethylene glycol (EG) motifs to the Fmoc-FF peptide increases the hydrophilicity and elasticity properties, which are essential for 3D-printing. This new approach for bioink formulation avoids the need for any post-printing manufacturing processes, such as chemical or UV crosslinking.

From Folding to Assembly: Functional Supramolecular Architectures of Peptides Comprised of Non-Canonical Amino Acids.

The engineering of biological molecules is the fundamental concept behind the design of complex materials with desirable functions. Over the last few decades, peptides and proteins have emerged as useful building blocks for well-defined nanostructures with controlled size and dimensions. Short peptides in particular have received much attention due to their inherent biocompatibility, lower synthetic cost, and ease of tunability. In addition to the diverse self-assembling properties of short peptides comprising coded amino acids and their emerging applications in nanotechnology, there is now growing interest in the properties of peptides composed of non-canonical amino acids. Such non-natural oligomers have been shown in recent years to form well-defined secondary structures similar to natural proteins, with the ability to self-assemble to generate a wide variety of nanostructures with excellent biostability. This review describes recent events in the development of supramolecular assemblies of peptides composed completely of non-coded amino acids and their hybrid analogues. Special attention is paid to understanding the supramolecular assemblies at the atomic level and to considering their potential applications in nanotechnology.

Hyaluronic Acid and a Short Peptide Improve the Performance of a PCL Electrospun Fibrous Scaffold Designed for Bone Tissue Engineering Applications.

Bone tissue engineering is a rapidly developing, minimally invasive technique for regenerating lost bone with the aid of biomaterial scaffolds that mimic the structure and function of the extracellular matrix (ECM). Recently, scaffolds made of electrospun fibers have aroused interest due to their similarity to the ECM, and high porosity. Hyaluronic acid (HA) is an abundant component of the ECM and an attractive material for use in regenerative medicine; however, its processability by electrospinning is poor, and it must be used in combination with another polymer. Here, we used electrospinning to fabricate a composite scaffold with a core/shell morphology composed of polycaprolactone (PCL) polymer and HA and incorporating a short self-assembling peptide. The peptide includes the arginine-glycine-aspartic acid (RGD) motif and supports cellular attachment based on molecular recognition. Electron microscopy imaging demonstrated that the fibrous network of the scaffold resembles the ECM structure. In vitro biocompatibility assays revealed that MC3T3-E1 preosteoblasts adhered well to the scaffold and proliferated, with significant osteogenic differentiation and calcium mineralization. Our work emphasizes the potential of this multi-component approach by which electrospinning, molecular self-assembly, and molecular recognition motifs are combined, to generate a leading candidate to serve as a scaffold for bone tissue engineering.

Engineering of Doxorubicin-Encapsulating and TRAIL-Conjugated Poly(RGD) Proteinoid Nanocapsules for Drug Delivery Applications.

Proteinoids are non-toxic biodegradable polymers prepared by thermal step-growth polymerization of amino acids. Here, P(RGD) proteinoids and proteinoid nanocapsules (NCs) based on D-arginine, glycine, and L-aspartic acid were synthesized and characterized for targeted tumor therapy. Doxorubicin (Dox), a chemotherapeutic drug used for treatment of a wide range of cancers, known for its adverse side effects, was encapsulated during self-assembly to form Dox/P(RGD) NCs. In addition, tumor necrosis factor-related apoptosis-inducing ligand (TRAIL), which can initiate apoptosis in most tumor cells but undergoes fast enzyme degradation, was stabilized by covalent conjugation to hollow P(RGD) NCs. The effect of polyethylene glycol (PEG) conjugation was also studied. Cytotoxicity tests on CAOV-3 ovarian cancer cells demonstrated that Dox/P(RGD) and TRAIL-P(RGD) NCs were as effective as free Dox and TRAIL with cell viability of 2% and 10%, respectively, while PEGylated NCs were less effective. Drug-bearing P(RGD) NCs offer controlled release with reduced side effects for improved therapy.

Synthesis and Characterization of Poly(RGD) Proteinoid Polymers and NIR Fluorescent Nanoparticles of Optimal d,l-Configuration for Drug-Delivery Applications-In Vitro Study.

RGD sequence is a tripeptide composed of three amino acids: arginine (R), glycine (G), and aspartic acid (D). The RGD peptide has a high affinity to the integrin alpha v beta 3, which is overexpressed on the membrane of many cancer cells and is attracted to areas of angiogenesis. Proteinoids are biodegradable polymers based on amino acids which are formed by bulk thermal step-growth polymerization mechanism. Hollow proteinoid nanoparticles (NPs) may be formed via self-assembly process of the proteinoid polymers. We propose using novel RGD-based proteinoid polymers to manufacture NPs in which the RGD motif is self-incorporated in the proteinoid backbone. Such P(RGD) NPs can act both as a drug carrier (by encapsulation of a desired drug) and as a targeting delivery system. This article presents the synthesis of four RGD proteinoids with different RGD optical configurations, (d) or (l) arginine, glycine, and (d) or (l) aspartic acid, in order to determine which configuration is optimal as a drug-targeting carrier. These new RGD proteinoid polymers possess high molecular weights and molecular weight monodispersity. Homonuclear nuclear magnetic resonance methods were employed to predict the expected concentration of RGD tripeptide sequence in the polymer. Near infrared fluorescent NPs have been prepared by the encapsulation of indocyanine green (ICG) dye within the different P(RGD) NPs. The dry diameters of the hollow P(RdGDd), P(RdGD), P(RGD), and P(RGDd) NPs are 55 ± 13, 48 ± 9, 45 ± 11, and 42 ± 9 nm, respectively, whereas those of the ICG-encapsulated NPs were significantly higher, 141 ± 24, 95 ± 13, 86 ± 11, and 87 ± 12 nm, respectively. The ICG-encapsulated P(RdGD) NPs exhibited higher selectivity toward epithelial injury, as demonstrated using an in vitro scratch assay, because the P(RdGD) NPs accumulated in the injured area at higher concentrations when compared to other P(RGD) NPs with different chiralities. Therefore, the P(RdGD) polymer configuration is the polymer of choice for use as a targeted drug carrier to areas of angiogenesis, such as in tumors, wounds, or cuts.

Engineering of NIR fluorescent PEGylated poly(RGD) proteinoid polymers and nanoparticles for drug delivery applications in chicken embryo and mouse models.

Proteinoids are non-toxic biodegradable polymers based on thermal step-growth polymerization of natural or synthetic amino acids. Hollow proteinoid nanoparticles (NPs) may then be formed via a self-assembly process of the proteinoid polymers in an aqueous solution. In the present article polymers and NPs based on d-arginine, glycine and l-aspartic acid, poly(RDGD), were synthesized for tumor targeting, particularly due to the high affinity of the RGD motif to areas of angiogenesis. Near IR fluorescent P(RDGD) NPs were prepared by encapsulating the fluorescent NIR dye indocyanine green (ICG) within the formed P(RDGD) NPs. Here, we investigate the effect of the covalent conjugation of polyethylene glycol (PEG), with different molecular weights, to the surface of the near IR encapsulated P(RDGD) NPs on the release of the dye to human serum due to bio-degradation of the proteinoid NPs and on the uptake by tumors. This work illustrates that the release of the encapsulated ICG from the non-PEGylated NPs is significantly faster than for that observed for the PEGylated NPs, and that the higher molecular weight is the bound PEG spacer the slower is the dye release profile. In addition, in a chicken embryo model, the non-PEGylated ICG-encapsulated P(RDGD) NPs exhibited a higher uptake in the tumor region in comparison to the PEGylated ICG-encapsulated P(RDGD) NPs. However, in a tumor xenograft mouse model, which enables a prolonged experiment, the importance of the PEG is clearly noticeable, when a high concentration of PEGylated P(RDGD) NPs was accumulated in the area of the tumor compared to the non-PEGylated P(RDGD). Moreover, the length of the PEG chain plays a major role in the ability to target the tumor. Hence, we can conclude that selectivity towards the tumor area of non-PEGylated and the PEGylated ICG-encapsulated P(RDGD) NPs can be utilized for targeting to areas of angiogenesis, such as in the cases of tumors, wounds or cuts, etc.

Engineering of a New Bisphosphonate Monomer and Nanoparticles of Narrow Size Distribution for Antibacterial Applications.

In recent years, many bacteria have developed resistance to commonly used antibiotics. It is well-known that calcium is essential for bacterial function and cell wall stability. Bisphosphonates (BPs) have high affinity to calcium ions and are effective calcium chelators. Therefore, BPs could potentially be used as antibacterial agents. This article provides a detailed description regarding the synthesis of a unique BP vinylic monomer MA-Glu-BP (methacrylate glutamate bisphosphonate) and polyMA-Glu-BP nanoparticles (NPs) for antibacterial applications. polyMA-Glu-BP NPs were synthesized by dispersion copolymerization of the MA-Glu-BP monomer with the primary amino monomer N-(3-aminopropyl)methacrylamide hydrochloride (APMA) and the cross-linker monomer tetra ethylene glycol diacrylate, to form cross-linked NPs with a narrow size distribution. The size and size distribution of polyMA-Glu-BP NPs were controlled by changing various polymerization parameters. Near-infrared fluorescent polyMA-Glu-BP NPs were prepared by covalent binding of the dye cyanine7 N-hydroxysuccinimide to the primary amino groups belonging to the APMA monomeric units on the polyMA-Glu-BP NPs. The affinity of the near-infrared fluorescent polyMA-Glu-BP NPs toward calcium was demonstrated in vitro by a coral model. Cytotoxicity, cell uptake, and antibacterial properties of the polyMA-Glu-BP NPs against two common bacterial pathogens representing Gram-negative bacteria, Escherichia coli and Pseudomonas aeruginosa, and two representing Gram-positive bacteria, Listeria innocua and Staphylococcus aureus, were then demonstrated.

Graft polymerization of styryl bisphosphonate monomer onto polypropylene films for inhibition of biofilm formation.

There has been increased concern during the past few decades over the role bacterial biofilms play in causing a variety of health problems, especially since they exhibit a high degree of resistance to antibiotics and are able to survive in hostile environments. Biofilms consist of bacterial aggregates enveloped by a self-produced matrix attached to the surface. Ca(2+) ions promote the formation of biofilms, and enhance their stability, viscosity, and strength. Bisphosphonates exhibit a high affinity for Ca(2+) ions, and may inhibit the formation of biofilms by acting as sequestering agents for Ca(2+) ions. Although the antibacterial activity of bisphosphonates is well known, research into their anti-biofilm behavior is still in its early stages. In this study, we describe the synthesis of a new thin coating composed of poly(styryl bisphosphonate) grafted onto oxidized polypropylene films for anti-biofilm applications. This grafting process was performed by graft polymerization of styryl bisphosphonate vinylic monomer onto O2 plasma-treated polypropylene films. The surface modification of the polypropylene films was confirmed using surface measurements, including X-ray photoelectron spectroscopy, atomic force microscopy, and water contact angle goniometry. Significant inhibition of biofilm formation was achieved for both Gram-negative and Gram-positive bacteria.