Silk Nanoparticles: A Natural Polymeric Platform for Nitric Oxide Delivery in Biomedical Applications

Nitric oxide-releasing thiolated starch nanoparticles embedded in gelatin sponges for wound dressing applications

This study introduces a novel wound dressing by combining nitric oxide-releasing thiolated starch nanoparticles (NO-TS NPs) with gelatin. First, starch was thiolated (TS), and then its nanoparticles were prepared (TS NPs). Subsequently, NPs were covalently bonded to sodium nitrite to obtain NO-releasing TS NPs (NO-TS-NPs) that were incorporated into gelatin sponges at various concentrations. The resulting spherical TS NPs had a mean size of 85.42 ± 5.23 nm, which rose to 100.73 ± 7.41 nm after bonding with sodium nitrite. FTIR spectroscopy confirmed S-nitrosation on the NO-TS NPs' surface, and morphology analysis showed well-interconnected pores in all sponges. With higher NO-TS NPs content, pore size, porosity, and water uptake increased, while compressive modulus and strength decreased. Composites exhibited antibacterial activity, particularly against E. coli, with enhanced efficacy at higher NPs' concentrations. In vitro release studies demonstrated Fickian diffusion, with faster NO release in sponges containing more NPs. The released NO amounts were non-toxic to fibroblasts, but samples with fewer NO-TS NPs exhibited superior cellular density, cell attachment, and collagen secretion. Considering the results, including favorable mechanical strength, release behavior, antibacterial and cellular properties, gelatin sponges loaded with 2 mg/mL of NO-TS NPs can be suitable for wound dressing applications.

Mechanistic analysis of the photolytic decomposition of solid-state S-nitroso-N-acetylpenicillamine

S-Nitroso-N-acetylpenicillamine (SNAP) is among the most common nitric oxide (NO)-donor molecules and its solid-state photolytic decomposition has potential for inhaled nitric oxide (iNO) therapy. The photochemical NO release kinetics and mechanism were investigated by exposing solid-state SNAP to a narrow-band LED as a function of nominal wavelength and intensity of incident light. The photolytic efficiency, decomposition products, and the photolytic pathways of the SNAP were examined. The maximum light penetration depth through the solid layer of SNAP was determined by an optical microscope and found to be within 100-200 μm, depending on the wavelength of light. The photolysis of solid-state SNAP to generate NO along with the stable thiyl (RS·) radical was confirmed using Electron Spin Resonance (ESR) spectroscopy. The fate of the RS· radical in the solid phase was studied both in the presence and absence of O2 using NMR, IR, ESR, and UPLC-MS. The changes in the morphology of SNAP due to its photolysis were examined using PXRD and SEM. The stable thiyl radical formed from the photolysis of solid SNAP was found to be reactive with another adjacent thiyl radical to form a disulfide (RSSR) or with oxygen to form various sulfonyl and sulfonyl peroxyl radicals {RS(O)xO·, x = 0 to 7}. However, the thiyl radical did not recombine with NO to reform the SNAP. From the PXRD data, it was found that the SNAP loses its crystallinity by generating the NO after photolysis. The initial release of NO during photolysis was increased with increased intensity of light, whereas the maximum light penetration depth was unaffected by light intensity. The knowledge gained about the photochemical reactions of SNAP may provide important insight in designing portable photoinduced NO-releasing devices for iNO therapy.

Carbon nanotubes as a nitric oxide nano-reservoir improved the controlled release profile in 3D printed biodegradable vascular grafts

Small diameter vascular grafts (SDVGs) are associated with a high failure rate due to poor endothelialization. The incorporation of a nitric oxide (NO) releasing system improves biocompatibility by using the NO effect to promote endothelial cell (EC) migration and proliferation while preventing bacterial infection. To circumvent the instability of NO donors and to prolong NO releasing, S-nitroso-N-acetyl-D-penicillamine (SNAP) as a NO donor was loaded in multi-walled carbon nanotubes (MWCNTs). Successful loading was confirmed with a maximum SNAP amount of ~ 5% (w/w) by TEM, CHNS analysis and FTIR spectra. SDVGs were 3D printed from polycaprolactone (PCL) and coated with a 1:1 ratio of polyethylene glycol and PCL dopped with different concentrations of SNAP-loaded matrix and combinations of MWCNTs-OH. Coating with 10% (w/w) SNAP-matrix-10% (w/w) SNAP-MWCNT-OH showed a diminished burst release and 18 days of NO release in the range of 0.5-4 × 10^-10 mol cm^-2 min^-1 similar to the NO release from healthy endothelium. NO-releasing SDVGs were cytocompatible, significantly enhanced EC proliferation and migration and diminished bacterial viability. The newly developed SNAP-loaded MWCNT-OH has a great potential to develop NO releasing biomaterials with a prolonged, controlled NO release promoting in-situ endothelialization and tissue integration in vivo, even as an approach towards personalized medicine.

Highly Biocompatible Apigenin-Loaded Silk Fibroin Nanospheres: Preparation, Characterization, and Anti-Breast-Cancer Activity

Breast cancer is among the most common fatal diseases among women. Low-toxicity apigenin (AGN) is of interest due to its good antitumor activity, but its clinical application is severely limited due to its poor water solubility and low bioavailability. An effective strategy to enhance the anti-breast-cancer activity of AGN is to develop it as a nanodelivery system. Silk fibroin (SF) is an ideal drug carrier with good biocompatibility, biodegradability, and a simple extraction process. This paper develops a novel and efficient apigenin-loaded silk fibroin nanodelivery system (SF-AGN) by nanoprecipitation with SF as a carrier. The system was characterized in terms of morphology, zeta potential, particle size, ultraviolet (UV), infrared (IR), and synchronous thermal analyses (TG-DSC), and the in vitro cytotoxicity and in vivo pharmacokinetics were examined. Finally, the chronic toxicity of SF-AGN in mice was studied. The SF-AGN nanodelivery system has good dispersibility, a hydrated particle size of 163.35 nm, a zeta potential of -18.5 mV, an average drug loading of 6.20%, and good thermal stability. MTT studies showed that SF-AGN significantly enhanced the inhibitory effect of AGN on 4T1 and MDA-MB-231 cells. Pharmacokinetic studies have demonstrated that SF-AGN can dramatically improve the bioavailability of AGN. The results of toxicity experiments showed that SF-AGN is biocompatible and does not alter normal tissues or organs. In sum, the SF-AGN nanodelivery system is a promising drug-delivery system for the clinical treatment of breast cancer.

Progress in silk and silk fiber-inspired polymeric nanomaterials for drug delivery

The fields of drug and gene delivery have been revolutionized by the discovery and characterization of polymer-based materials. Polymeric nanomaterials have emerged as a strategy for targeted delivery because of features such as their impressive biocompatibility and improved availability. Use of naturally derived polymers in these nanomaterials is advantageous due to their biodegradability and bioresorption. Natural biopolymer-based particles composed of silk fibroins and other silk fiber-inspired proteins have been the focus of research in drug delivery systems due to their simple synthesis, tunable characteristics, and ability to respond to stimuli. Several silk and silk-inspired polymers contain a high proportion of reactive side groups, allowing for functionalization and addition of targeting moieties. In this review, we discuss the main classes of silk and silk-inspired polymers that are being used in the creation of nanomaterials. We also focus on the fabrication techniques used in generating a tunable design space of silk-based polymeric nanomaterials and detail how that translates into use for drug delivery to several distinct microenvironments.

Pharmacological applications of nitric oxide-releasing biomaterials in human skin

Nitric oxide (NO) is an important endogenous molecule that plays several roles in biological systems. NO is synthesized in human skin by three isoforms of nitric oxide synthase (NOS) and, depending on the produced NO concentration, it can actuate in wound healing, dermal vasodilation, or skin defense against different pathogens, for example. Besides being endogenously produced, NO-based pharmacological formulations have been developed for dermatological applications targeting diverse pathologies such as bacterial infection, wound healing, leishmaniasis, and even esthetic issues such as acne and skin aging. Recent strategies focus mainly on developing smart NO-releasing nanomaterials/biomaterials, as they enable a sustained and targeted NO release, promoting an improved therapeutic effect. This review aims to overview and discuss the main mechanisms of NO in human skin, the recent progress in the field of dermatological formulations containing NO, and their application in several skin diseases, highlighting promising advances and future perspectives in the field.

Nanoparticle-based delivery of nitric oxide for therapeutic applications

Nitric oxide (NO), a low molecular weight signaling molecule, plays critical roles in both cellular health and disease. There is continued interest in new modalities for the controlled therapeutic delivery of NO to cells and tissues. The physicochemical properties of NO (including its short half-life and on-demand synthesis at the point of function), however, pose considerable challenges for its specific and efficient delivery. Recently, a number of nanoparticle (NP)-based systems are described that address some of these issues by taking advantage of the unique attributes of the NP carrier to effect efficient NO delivery. This review highlights the progress that has been made over the past 5 years in the use of various constructs for the therapeutic delivery of NO.

Nitric Oxide-Releasing Nanofibrous Scaffolds Based on Silk Fibroin and Zein with Enhanced Biodegradability and Antibacterial Properties

Clinical applications of scaffolds and implants have been associated with bacterial infection resulting in impaired tissue regeneration. Nanofibers provide a versatile structure for both antimicrobial molecule delivery and tissue engineering. In this study, the nitric oxide (NO) donor molecule S-nitrosoglutathione (GSNO) and the natural biodegradable polymer zein (ZN) were combined with silk fibroin (SF) to develop antibacterial and biodegradable nanofibrous scaffolds for tissue engineering applications. The compatibility and intermolecular interactions of SF and ZN were studied using differential scanning calorimetry and Fourier transform infrared spectroscopy. The incorporation of ZN increased the hydrophobicity of the fibers and resulted in a more controlled and prolonged NO release profile lasting for 48 h. Moreover, the degradation kinetics of the fibers was significantly improved after blending with ZN. The results of tensile testing indicated that the addition of ZN and GSNO had a positive effect on the strength and stretchability of SF fibers and did not adversely affect their mechanical properties. Finally, due to the antibacterial properties of both NO and ZN, the SF-ZN-GSNO fibers showed a synergistically high antibacterial efficacy with 91.6 ± 2.5% and 77.5 ± 3.1% reduction in viability of adhered Staphylococcus aureus and Escherichia coli after 24 h exposure, respectively. The developed NO-releasing fibers were not only antibacterial but also non-cytotoxic and successfully enhanced the proliferation and growth of fibroblast cells, which was quantitatively studied by a CCK-8 assay and visually observed through fluorescent staining. Overall, SF-ZN-GSNO fibers developed in this study were biodegradable and highly antibacterial and showed great cytocompatibility with fibroblasts, indicating their promising potential for a range of tissue engineering and medical device applications.

Protein by-products: Composition, extraction, and biomedical applications

Significant upsurge in animal by-products such as skin, bones, wool, hides, feathers, and fats has become a global challenge and, if not properly disposed of, can spread contamination and viral diseases. Animal by-products are rich in proteins, which can be used as nutritional, pharmacologically functional ingredients, and biomedical materials. Therefore, recycling these abundant and renewable by-products and extracting high value-added components from them is a sustainable approach to reclaim animal by-products while addressing scarce landfill resources. This article appraises the most recent studies conducted in the last five years on animal-derived proteins' separation and biomedical application. The effort encompasses an introduction about the composition, an overview of the extraction and purification methods, and the broad range of biomedical applications of these ensuing proteins.

Cu(II)-functionalized silk fibroin films for the catalytic generation of nitric oxide

In situ release of nitric oxide (NO) has been suggested to be a potential functionalization strategy for blood-contacting implants. In this study, the NO generation capability catalyzed by the copper ion-incorporated silk fibroin (SF) films in the presence of S-nitroso-N-acetyl-dl-penicillamine (SNAP) is demonstrated. Cu(II) is effectively bound to the surface of the SF film based on metal-protein coordination. The x-ray photoelectron spectroscopy results indicate that copper ions may exist on the surface of the SF film in the form of Cu(II)/Cu(I) coexistence. The degradation behavior showed that the bound copper ions on the surface of the SF films can maintain a slow release in phosphate-buffered saline (PBS) or collagenase IA solution for 7 days. There was no significant difference in the release of copper ions between PBS degradation and enzyme degradation. The loading of copper ions significantly improved the release of NO from SNAP through catalysis. Based on the biological effects of copper ions and the ability to catalyze the release of NO from S-nitrosothiols, copper ion loading provides an option for the construction of bioactive SF biomaterials.

Nitric Oxide Release and Antibacterial Efficacy Analyses of S-Nitroso-N-Acetyl-Penicillamine Conjugated to Titanium Dioxide Nanoparticles

Therapeutic agents can be linked to nanoparticles to fortify their selectivity and targeted delivery while impeding systemic toxicity and efficacy loss. Titanium dioxide nanoparticles (TiNPs) owe their rise in biomedical sciences to their versatile applicability, although the lack of inherent antibacterial properties limits its application and necessitates the addition of bactericidal agents along with TiNPs. Structural modifications can improve TiNP's antibacterial impact. The antibacterial efficacy of nitric oxide (NO) against a broad spectrum of bacterial strains is well established. For the first time, S-nitroso-N-acetylpenicillamine (SNAP), an NO donor molecule, was covalently immobilized on TiNPs to form the NO-releasing TiNP-SNAP nanoparticles. The TiNPs were silanized with 3-aminopropyl triethoxysilane, and N-acetyl-d-penicillamine was grafted to them via an amide bond. The nitrosation was carried out by t-butyl nitrite to conjugate the NO-rich SNAP moiety to the surface. The total NO immobilization was measured to be 127.55 ± 4.68 nmol mg^-1 using the gold standard chemiluminescence NO analyzer. The NO payload can be released from the TiNP-SNAP under physiological conditions for up to 20 h. The TiNP-SNAP exhibited a concentration-dependent antimicrobial efficiency. At 5 mg mL^-1, more than 99.99 and 99.70% reduction in viable Gram-positive Staphylococcus aureus and Gram-negative Escherichia coli bacteria, respectively, were observed. No significant cytotoxicity was observed against 3T3 mouse fibroblast cells at all the test concentrations determined by the CCK-8 assay. TiNP-SNAP is a promising and versatile nanoparticle that can significantly impact the usage of TiNPs in a wide variety of applications, such as biomaterial coatings, tissue engineering scaffolds, or wound dressings.

Near-Infrared Light-Triggered Nitric Oxide Nanogenerators for NO-Photothermal Synergistic Cancer Therapy

Cancer is still one of the major health issues faced by human beings today. Various nanomaterials have been designed to treat tumors and have made great progress. Herein, we used amino-functionalized metal organic framework (UiO-66-NH₂) as superior templates and successfully synthesized the UiO-66-NH₂@Au_shell composite nanoparticles (UA) with high loading capacity and excellent photothermal properties through a simple and gentle method. In addition, due to the rich pore structure and excellent biocompatibility of the as-prepared composite nanoparticles, the hydrophobic NO donor BNN6 (N,N′-Di-sec-butyl-N,N′-dinitroso-1, 4-phenylenediamine) molecule was efficiently delivered. Based on the phenomenon where BNN6 molecules can decompose and release NO at high temperature, when UiO-66-NH₂@Au_shell-BNN6 composite nanoparticles (UA-BNN6) entered tumor cells and were irradiated by NIR, the porous gold nanoshells on the surface of composite nanoparticles induced an increase in temperature through the photothermal conversion process and promoted the decomposition of BNN6 molecules, releasing high concentration of NO, thus efficiently killing HeLa cells through the synergistic effect of NO-photothermal therapy. This effective, precise and safe treatment strategy controlled by NIR laser irradiation represents a promising alternative in the field of cancer treatment.

A Review on Antibacterial Silk Fibroin-based Biomaterials: Current State and Prospects

Bacterial contamination of biomaterials is a common problem and a serious threat to human health worldwide. Therefore, the development of multifunctional biomaterials that possess antibacterial properties and can resist infection is a continual goal for biomedical applications. Silk fibroin (SF), approved by U.S. Food and Drug Administration (FDA) as a biomaterial, is one of the most widely studied natural polymers for biomedical applications due to its unique mechanical properties, biocompatibility, tunable biodegradation, and versatile material formats. In the last decade, many methods have been employed for the development of antibacterial SF-based biomaterials (SFBs) such as physical loading or chemical functionalization of SFBs with different antibacterial agents and bio-inspired surface modifications. In this review, we first describe the current understanding of the composition and structure-properties relationship of SF as a leading-edge biomaterial. Then we demonstrate the different antibacterial agents and methods implemented for the development of bactericidal SFBs, their mechanisms of action, and different applications. We briefly address their fabrication methods, advantages, and limitations, and finally discuss the emerging technologies and future trends in this research area.

Nitric Oxide-Releasing Gelatin Methacryloyl/Silk Fibroin Interpenetrating Polymer Network Hydrogels for Tissue Engineering Applications

Bacterial infection is one of the principal reasons for the failure of tissue engineering scaffolds. Therefore, the development of multifunctional scaffolds that not only are able to guide tissue regeneration but also can inhibit bacterial colonization is of great importance for tissue engineering applications. In this study, a highly antibacterial, biocompatible, and biodegradable scaffold based on silk fibroin (SF) and gelatin methacryloyl (GelMA) was prepared. Sequential cross-linking of GelMA and SF under UV irradiation and methanol treatment, respectively, resulted in the formation of interpenetrating network (IPN) hydrogels with a porous structure. In addition, impregnation of the hydrogels with a nitric oxide (NO) donor molecule, S-nitroso-N-acetylpenicillamine (SNAP), led to the development of NO-releasing scaffolds with strong antibacterial properties. According to the obtained results, the addition of SF to GelMA hydrogels caused an enhancement in the mechanical properties and NO release kinetics and prevented their rapid enzymatic degradation in aqueous media. Furthermore, swelling the GelMA-SF scaffolds with SNAP resulted in a bacteria reduction efficiency of >99.9% against Gram-positive (Staphylococcus aureus) and Gram-negative (Escherichia coli) bacteria. The scaffolds also showed great cytocompatibility in vitro by increasing the proliferation and supporting the adhesion of 3T3 mouse fibroblast cells. Overall, GelMA-SF-SNAP showed great promise to be used as a scaffold for tissue engineering and wound healing applications.

Recent advances in the development of nitric oxide-releasing biomaterials and their application potentials in chronic wound healing

Chronic wounds, such as pressure ulcers, vascular ulcers and diabetic foot ulcers (DFUs), often stay in a state of pathological inflammation and suffer from persistent infection, excess inflammation, and hypoxia, thus they are difficult to be healed. Nitric oxide (NO) plays a critical role in the regulation of various wound healing processes, including inflammatory response, cell proliferation, collagen formation, antimicrobial action and angiogenesis. The important role of NO in wound healing attracts intensive research focus on NO-based wound healing therapy. However, the application of NO gas therapy needs to resolve the intrinsic shortcomings of gas therapy, such as short storage and release times as well as temporal and spatial uncontrollability of the release mode. So far, various types of NO donors, including organic nitrates (RONO2), nitrites (RONO), S-nitrosothiols (RSNOs), nitrosamines, N-diazeniumdiolates (NONOates), and metal-NO complexes, have been developed to solidify gaseous NO and they were further encapsulated in or conjugated onto a variety of biomaterial vectors to develop NO delivery systems. NO synthetic enzyme mimics to catalyze the production and release of NO from l-arginine have also been developed. This paper reviews recent advances of NO donors, biomaterial vectors, thus-formed NO delivery systems, as well as recently emerged NO synthetic enzyme mimics. Furthermore, this review also summarizes the functions of NO releasing biomaterials that would benefit chronic wound healing, including antibacterial properties and the promotion of angiogenesis, as well as the convenient combination of light/thermal induced NO release with light/thermal therapies, and the prospects for future developing trends in this area.

Nitric oxide releasing halloysite nanotubes for biomedical applications

Halloysite nanotubes (HNTs) are natural aluminosilicate clay that have been extensivelyexplored fordelivery of bioactive agents in biomedical applications because of their desirable features including unique hollow tubular structure, good biocompatibility, high mechanical strength, and extensive functionality. For the first time, in this work, functionalized HNTs are developed as a delivery platform for nitric oxide (NO), a gaseous molecule, known for its important roles in the regulation of various physiological processes. HNTs were first hydroxylated and modified with an aminosilane crosslinker, (3-aminopropyl) trimethoxysilane (APTMS), to enable the covalent attachment of a NO donor precursor, N-acetyl-d-penicillamine (NAP). HNT-NAP particles were then converted to NO-releasing S-nitroso-N-acetyl-penicillamine HNT-SNAP by nitrosation. The total NO loading on the resulting nanotubes was 0.10 ± 0.07 μmol/mg which could be released using different stimuli such as heat and light. Qualitative (Fourier-transform infrared spectroscopy and Nuclear magnetic resonance) and quantitative (Ninhydrin and Ellman) analyses were performed to confirm successful functionalization of HNTs at each step. Field emission scanning electron microscopy (FE-SEM) showed that the hollow tubular morphology of the HNTs was preserved after modification. HNT-SNAP showed concentration-dependent antibacterial effects against Gram-positive Staphylococcus aureus (S. aureus), resulting in up to 99.6% killing efficiency at a concentration of 10 mg/mL as compared to the control. Moreover, no significant cytotoxicity toward 3T3 mouse fibroblast cells was observed at concentrations equal or below 2 mg/mL of HNT-SNAP according to a WST-8-based cytotoxicity assay. The SNAP-functionalized HNTs represent a novel and efficient NO delivery system that holds the potential to be used, either alone or in combination with polymers for different biomedical applications.