Electrohydrodynamic Bubbling: An Alternative Route to Fabricate Porous Structures of Silk Fibroin Based Materials

Maillard Reaction Crosslinked Alginate-Albumin Scaffolds for Enhanced Fenofibrate Delivery to the Retina: A Promising Strategy to Treat RPE-Related Dysfunction

There are limited treatments currently available for retinal diseases such as age-related macular degeneration (AMD). Cell-based therapy holds great promise in treating these degenerative diseases. Three-dimensional (3D) polymeric scaffolds have gained attention for tissue restoration by mimicking the native extracellular matrix (ECM). The scaffolds can deliver therapeutic agents to the retina, potentially overcoming current treatment limitations and minimizing secondary complications. In the present study, 3D scaffolds made up of alginate and bovine serum albumin (BSA) containing fenofibrate (FNB) were prepared by freeze-drying technique. The incorporation of BSA enhanced the scaffold porosity due to its foamability, and the Maillard reaction increased crosslinking degree between ALG with BSA resulting in a robust scaffold with thicker pore walls with a compression modulus of 13.08 KPa suitable for retinal regeneration. Compared with ALG and ALG-BSA physical mixture scaffolds, ALG-BSA conjugated scaffolds had higher FNB loading capacity, slower release of FNB in the simulated vitreous humour and less swelling in water and buffers, and better cell viability and distribution when tested with ARPE-19 cells. These results suggest that ALG-BSA MR conjugate scaffolds may be a promising option for implantable scaffolds for drug delivery and retinal disease treatment.

Electrospray mode discrimination with current signal using deep convolutional neural network and class activation map

The electrospray process has been extensively applied in various fields, including energy, display, sensor, and biomedical engineering owing to its ability to generate of functional micro/nanoparticles. Although the mode of the electrospray process has a significant impact on the quality of micro/nano particles, observing and discriminating the mode of electrospray during the process has not received adequate attention. This study develops a simple automated method to discriminate the mode of the electrospray process based on the current signal using a deep convolutional neural network (CNN) and class activation map (CAM). The solution flow rate and applied voltage are selected as experimental variables, and the electrospray process is classified into three modes: dripping, pulsating, and cone-jet. The current signal through the collector is measured to detect the deposition of electrospray droplets on the collector. The 1D CNN model is trained using frequency data converted from the current data. The model exhibits excellent performance with an accuracy of 96.30%. Adoption of the CAM configuration enables the model to provide a discriminative cue for each mode and elucidate the decision-making process of the CNN model.

Development of silk fibroin‑sodium alginate scaffold loaded silk fibroin nanoparticles for hemostasis and cell adhesion

During wound healing process, it is essential to promote hemostasis and cell adhesion. Herein, we incorporated a scaffold with nanoparticles to improve the hemostatic properties and stimulate cell adhesion. The nanoparticles were prepared by self-assembling of silk fibroin, and the scaffold loaded nanoparticles were synthesized by crosslinking and freeze-drying. Macroscopical images showed that the nanoparticles distributed uniformly and increased the surface roughness of scaffold pore wall. The addition of nanoparticles decreased the pore size, enhanced the compression strength, lowered the degradation rate, and maintained the resilience and water uptake capacity. Compared with pure scaffold, the scaffold loaded nanoparticles revealed higher blood clotting index and promoted platelets adhesion. Furthermore, in vitro tests showed that scaffold loaded nanoparticles exhibited excellent biocompatibility, and stimulation effects on cell proliferation, migration, and adhesion for both L929 cells and HUVECs. Therefore, the scaffold loaded nanoparticles possessed great potential as a wound dressing for efficient hemostasis and subsequent wound healing.

Silk Fibroin-Based Biomaterials for Hemostatic Applications

Hemostasis plays an essential role in all surgical procedures. Uncontrolled hemorrhage is the primary cause of death during surgeries, and effective blood loss control can significantly reduce mortality. For modern surgeons to select the right agent at the right time, they must understand the mechanisms of action, the effectiveness, and the possible adverse effects of each agent. Over the past decade, various hemostatic agents have grown intensely. These agents vary from absorbable topical hemostats, including collagen, gelatins, microfibrillar, and regenerated oxidized cellulose, to biologically active topical hemostats such as thrombin, biological adhesives, and other combined agents. Commercially available products have since expanded to include topical hemostats, surgical sealants, and adhesives. Silk is a natural protein consisting of fibroin and sericin. Silk fibroin (SF), derived from silkworm Bombyx mori, is a fibrous protein that has been used mostly in fashion textiles and surgical sutures. Additionally, SF has been widely applied as a potential biomaterial in several biomedical and biotechnological fields. Furthermore, SF has been employed as a hemostatic agent in several studies. In this review, we summarize the several morphologic forms of SF and the latest technological advances on the use of SF-based hemostatic agents.

Evaluation of sustained-release in-situ injectable gels, containing naproxen sodium, using in vitro, in silico and in vivo analysis

The study aimed to fabricate naproxen sodium loaded in-situ gels of sodium alginate. Different in-situ gel forming solutions of naproxen sodium and sodium alginate were prepared and gel formation was studied in different physiological ions i.e., CaCl₂ and Ca-gluconate. The prepared gel formulations were evaluated for different physical attributes such as gelation time, sol-gel fraction, ATR-FTIR spectroscopy and in silico molecular dynamics (MD) simulations. Drug release studies were carried out in a dialysis membrane using USP dissolution basket apparatus-I. In vivo anti-inflammatory studies were performed in Sprague-Dawley rats having carrageenan-induced hind paw inflammation. Higher polymer concentration in formulations resulted in decreased gelation time and an increased gel fraction. The ATR-FTIR and MD simulation revealed H-bonding between the alginate and naproxen sodium at 3500-3200 cm^-1 with a RMSD of ∼2.8 Å and binding free energy ΔG_{pred (GB)} = -10.93 kcal/mol. In vitro drug release studies from F8CAG suggested a sustained release of naproxen sodium. In vivo studies revealed a continuous decrease in swelling degree (≈-5.28± 0.210 mm) in inflamed hind paw of Sprague-Dawley rats over 96 h. The in-situ gel forming injectable preparation (F8CAG) offers a sustained release of naproxen sodium in the articular cavity which promises the treatment of chronic inflammatory conditions such as arthritis.

Electrohydrodynamic atomisation driven design and engineering of opportunistic particulate systems for applications in drug delivery, therapeutics and pharmaceutics

Electrohydrodynamic atomisation (EHDA) technologies have evolved significantly over the past decade; branching into several established and emerging healthcare remits through timely advances in the engineering sciences and tailored conceptual process designs. More specifically for pharmaceutical and drug delivery spheres, electrospraying (ES) has presented itself as a high value technique enabling a plethora of different particulate structures. However, when coupled with novel formulations (e.g. co-flows) and innovative device aspects (e.g., materials and dimensions), core characteristics of particulates are manipulated and engineered specifically to deliver an application driven need, which is currently lacking, ranging from imaging and targeted delivery to controlled release and sensing. This demonstrates the holistic nature of these emerging technologies; which is often overlooked. Parametric driven control during particle engineering via the ES method yields opportunistic properties when compared to conventional methods, albeit at ambient conditions (e.g., temperature and pressure), making this extremely valuable for sensitive biologics and molecules of interest. Furthermore, several processing (e.g., flow rate, applied voltage and working distance) and solution (e.g., polymer concentration, electrical conductivity and surface tension) parameters impact ES modes and greatly influence the production of resulting particles. The formation of a steady cone-jet and subsequent atomisation during ES fabricates particles demonstrating monodispersity (or near monodispersed), narrow particle size distributions and smooth or textured morphologies; all of which are successfully incorporated in a one-step process. By following a controlled ES regime, tailored particles with various intricate structures (hollow microspheres, nanocups, Janus and cell-mimicking nanoparticles) can also be engineered through process head modifications central to the ES technique (single-needle spraying, coaxial, multi-needle and needleless approaches). Thus, intricate formulation design, set-up and combinatorial engineering of the EHDA process delivers particulate structures with a multitude of applications in tissue engineering, theranostics, bioresponsive systems as well as drug dosage forms for specific delivery to diseased or target tissues. This advanced technology has great potential to be implemented commercially, particularly on the industrial scale for several unmet pharmaceutical and medical challenges and needs. This review focuses on key seminal developments, ending with future perspectives addressing obstacles that need to be addressed for future advancement.

Integration of microbubbles with biomaterials in tissue engineering for pharmaceutical purposes

Tissue engineering with the aid of biomaterials is a novel and promising knowledge aiming at improving human life expectancy. Besides, microbubbles are increasingly employed in biomedical applications due to their capability as a reservoir of therapeutic agents and oxygen molecules. In the present study, Microbubbles as the backbone of the research are produced as one of the potent devices in tissue engineering approaches, including drug delivery, wound healing, 3D printing, and scaffolding. It was shown that microbubbles are capable of promoting oxygen penetration and boosting the wound healing process by supplying adequate oxygen. Microbubbles also demonstrated their strength and potency in advancing drug delivery systems by reinforcing mass transfer phenomena. Furthermore, microbubbles developed the mechanical and biological characteristics of engineered scaffolds by manipulating the pores. Increasing cell survival, the biological activity of cells, angiogenesis, cell migration, and also nutrient diffusion into the inner layers of the scaffold were other achievements by microbubbles. In conclusion, the interest of biomedical communities in simultaneous usage of microbubbles and biomaterials under tissue engineering approaches experiences remarkable growth in Pharmaceutical studies.

Fabrication of hierarchically porous silk fibroin-bioactive glass composite scaffold via indirect 3D printing: Effect of particle size on physico-mechanical properties and in vitro cellular behavior

In order to regenerate bone defects, bioactive hierarchically scaffolds play a key role due to their multilevel porous structure, high surface area, enhanced nutrient transport and diffusion. In this study, novel hierarchically porous silk fibroin (SF) and silk fibroin-bioactive glass (SF-BG) composite were fabricated with controlled architecture and interconnected structure, by combining indirect three-dimensional (3D) inkjet printing and freeze-drying methods. Further, the effect of 45S5 Bioactive glass particles of different sizes (<100 nm and 6 μm) on mechanical strength and cell behavior was investigated. The results demonstrated that the hierarchical structure in this scaffold was composed of two levels of pores in the order of 500-600 μm and 10-50 μm. The prepared SF-BG composite scaffolds utilized by nano and micro particles possessed mechanical properties with a compressive strength of 0.94 and 1.2 MPa, respectively, in dry conditions. In a wet condition, the hierarchically porous scaffolds did not exhibit any fluctuation after compression load cell and were incredibly flexible, with excellent mechanical stability. The SF-BG composite scaffold with nanoparticles presented a significant 50% increase in attachment of human bone marrow stem cells in comparison with SF and SF-BG scaffold with microparticles. Moreover, SF-BG scaffolds promoted alkaline phosphatase activity as compared to SF scaffolds without BG particles on day 14. In brief, the 3D porous silk fibroin-based composites containing BG nanoparticles with excellent mechanical properties are promising scaffolds for bone tissue regeneration in high load-bearing applications.

Advanced Silk Fibroin Biomaterials and Application to Small-Diameter Silk Vascular Grafts

As the incidences of cardiovascular diseases have been on the rise in recent years, the need for small-diameter artificial vascular grafts is increasing globally. Although synthetic polymers such as expanded polytetrafluoroethylene or poly(ethylene terephthalate) have been successfully used for artificial vascular grafts ≥6 mm in diameter, they fail at smaller diameters (<6 mm) due to thrombus formation and intimal hyperplasia. Thus, development of vascular grafts for small diameter vessel replacement that are <6 mm in diameter remains a major clinical challenge. Silk fibroin (SF) from Bombyx mori silkworm is well-known as an excellent textile and also has been used as suture material in surgery for more than 2000 years. Many attempts to develop small-diameter SF vascular grafts with <6 mm in diameter have been reported. Here, research and development in small-diameter vascular grafts with SF are reviewed as follows: (1) the heterogeneous structure of SF fiber (Silk II), including the packing arrangements and type II β-turn structure of SF (Silk I*) before spinning; (2) SF modified by transgenic silkworm, which is more suitable for vascular grafts; (3) preparation of small-diameter SF vascular grafts; (4) characterization of SF in the hydrated state, including dynamics of water molecules by nuclear magnetic resonance; and (5) evaluation of the SF grafts by in vivo implantation experiment. According to the findings, SF is a promising material for small-diameter vascular graft development.

Silk nanoparticles: from inert supports to bioactive natural carriers for drug delivery

Silk proteins have been studied and employed for the production of drug delivery (nano)systems. They show excellent biocompatibility, controllable biodegradability and non-immunogenicity and, if needed, their properties can be modulated by blending with other polymers. Silk fibroin (SF), which forms the inner core of silk, is a (bio)material officially recognized by the Food and Drug Administration for human applications. Conversely, the potential of silk sericin (SS), which forms the external shell of silk, could still be considered under evaluation. At the best of our knowledge, nanoparticles based on silk sericin "alone" cannot be produced, due to its physicochemical instability influenced by extreme pH, high water solubility and temperature; for these reasons, it almost always needs to be combined with other polymers for the development of drug delivery systems. In this review, we focused on silk proteins as bioactive natural carriers, since they show not only optimal features as inert excipients, but also remarkable intrinsic biological activities. SF has anti-inflammatory properties, while SS presents antioxidant, anti-tyrosine, anti-aging, anti-elastase and anti-bacterial features. Here, we give an overview on SF or SS silk-based nanosystems, with particular attention on the production techniques.

Porous Polymeric Films from Microbubbles Generated Using a T-Junction Microfluidic Device

In this work, a simple microfluidic junction with a T geometry and coarse (200 μm diameter) capillaries was used to generate monodisperse microbubbles with an alginate polymer shell. Subsequently, these bubbles were used to prepare porous alginate films with good control over the pore structure. The lack of pore size, shape, and surface control in scalable forming of polymeric films is a major application-limiting drawback at present. Controlling the thinning process of the shell of the bubbles to tune the surface of the resulting structures was also explored. Films were prepared with nanopatterned surfaces by controlling the thinning of the bubble shell, with the aid of surfactants, to induce efficient bursting (fragmentation) of bubbles to generate nanodroplets, which become embedded within the film surface. This novel feature greatly expands and enhances the use of hydrophilic polymers in a wide range of biomedical applications, particularly in drug delivery and tissue engineering, such as studying cellular responses to different morphological surfaces.

Microneedle Coating Techniques for Transdermal Drug Delivery

Drug administration via the transdermal route is an evolving field that provides an alternative to oral and parenteral routes of therapy. Several microneedle (MN) based approaches have been developed. Among these, coated MNs (typically where drug is deposited on MN tips) are a minimally invasive method to deliver drugs and vaccines through the skin. In this review, we describe several processes to coat MNs. These include dip coating, gas jet drying, spray coating, electrohydrodynamic atomisation (EHDA) based processes and piezoelectric inkjet printing. Examples of process mechanisms, conditions and tested formulations are provided. As these processes are independent techniques, modifications to facilitate MN coatings are elucidated. In summary, the outcomes and potential value for each technique provides opportunities to overcome formulation or dosage form limitations. While there are significant developments in solid degradable MNs, coated MNs (through the various techniques described) have potential to be utilized in personalized drug delivery via controlled deposition onto MN templates.

Silk fibroin for vascular regeneration

Cardiovascular disease is the primary cause of morbidity and mortality in today's world. Due to the lack of healthy autologous vessels, more tissue-engineered blood vessels are needed to repair or replace the damaged arteries. Biomaterials play an indispensable role in creating a living neovessel with biological responses. Silk fibroin produced by silkworms possesses good cytocompatibility, tailorable biodegradability, suitable mechanical properties, and minimal inflammatory reactions. In addition, regenerated silk fibroin solutions can be processed into various forms of scaffolds such as films, fibers, tubes, and porous sponges. These features make silk fibroin a promising biomaterial for small-diameter vascular grafts. The present article focuses on the applications of silk fibroin for vascular regeneration. A brief overview of the properties of silk fibroin is provided, following which the current research status and future directions of the main types of silk fibroin scaffolds for vascular regeneration are reviewed and discussed. Microsc. Res. Tech. 80:280-290, 2017. © 2015 Wiley Periodicals, Inc.

Formation, stability, and mechanical properties of bovine serum albumin stabilized air bubbles produced using coaxial electrohydrodynamic atomization

Bovine serum albumin (BSA) microbubbles were generated using coaxial electrohydrodynamic atomization (CEDHA) using various concentrations of BSA solutions. The bubble characteristics and the long-term stability of the microbubbles were studied through adjustment of processing parameters and the collection media. Bubbles in the range of 40-800 μm were obtained in a controlled fashion, and increasing the flow rate of the BSA solution reduced the polydispersity of the microbubbles. Use of distilled water-glutaraldehyde, glycerol, and glycerol-Tween 80 collection media allowed a remarkable improvement in bubble stability compared to BSA solution collection medium. Possible physical mechanisms were developed to explain the stability of the microbubbles. The collection distance showed a marked influence on stability of the microbubbles. Near-monodisperse particle-reinforced microbubbles were formed with various concentrations of 2,2'-azobis(isobutyramidine) dihydrochloride (AIBA)-polystyrene particle in BSA solution. The bubble size and the size distribution showed negligible change over a period of time irrespective of the concentration of particles at the bubble surface. The compression stiffness of the microbubbles was determined using nanoindentation at ambient temperature and showed that the stiffness of the microbubbles increased from 8 N/m to 20 N/m upon changing the concentration of BSA solution from 5 wt % to 15 wt %.

Smart microneedle coatings for controlled delivery and biomedical analysis

The work presented demonstrates an unconventional approach in the preparation of smart microneedle (MN) coatings utilising electrohydrodynamic atomisation (EHDA) principles. Stainless steel (600-900 µm in height) MNs were coupled to a ground electrode (in the EHDA coating set-up) with the deposition distance and collecting methodology varied for an ethanol:methanol (50:50) vehicle system. The preparation of nano- and micrometre-scaled pharmaceutical coatings was achieved. Fluorescein dye (serving as potential drug, sensory materials or disease state markers) and polyvinylpyrrolidone (PVP, polymer matrix system) formed the remaining components of the coating formulation. Based on these excipients and by varying the coating process, particles (100 nm to 3 µm) and fibres (400 nm to 1 µm) were deposited directly on MNs in controlled and selectable fashion (flow rates variable ∼ 5-50 µL/min, applied voltage variable 6-19 kV). These demonstrated options for multiple targeting and analysis applications. The underlying EHDA process permits room temperature fabrication, controlled output and scale-up potential for emerging MN devices as drug systems or lab-chip testing devices.

Optimization of experimental parameters to determine the jetting regimes in electrohydrodynamic printing

The harmony of ink and printing method is of importance in producing on-demand droplets and jets of ink. Many factors including the material properties, the processing conditions, and the nozzle geometry affect the printing quality. In electrohydrodynamic (EHD) printing where droplets or jets are generated by the electrostatic force, the physical as well as the electrical properties of the fluid should be taken into account to achieve the desired performance. In this study, a systematic approach was suggested for finding the processing windows of the EHD printing. Six dimensionless parameters were organized and applied to the printing system of ethanol/terpineol mixtures. On the basis of the correlation of the dimensionless voltage and the charge relaxation length, the jet diameter of cone-jet mode was characterized, and the semicone angle was compared with the theoretical Taylor angle. In addition, the ratio of electric normal force and electric tangential force on the charged surface of the Taylor cone was recommended as a parameter that determines the degree of cone-jet stability. The cone-jet became more stable as this ratio got smaller. This approach was a systematic and effective way of obtaining the Taylor cone of the cone-jet mode and evaluating the jetting stability. The control of the inks with optimized experimental parameters by this method will improve the jetting performance in EHD inkjet printing.