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Electrospraying (ES) is becoming popular in tissue engineering owing to its ability to produce customized micro- or nanoscale particles for delivering bioactive molecules (e.g., growth factors, genes, enzymes, and therapeutic molecules possessing antimicrobial, anti-inflammatory) and living cells aimed at skin, bone, cartilage, and neural tissue repair and regeneration. Compared to conventional delivery methods, ES significantly reduces the denaturation of growth factors (such as BMP-2, BMP-7, VEGF, PDGF, and SDF-1) because of the limited exposure to organic solvents. Bioelectrospraying (BES) allows the encapsulation of living cells, including stem cells, fibroblasts, ligament cells, epithelial and endothelial cells, etc. Electrospray nanocarriers containing cells and other bioactive compounds can be further integrated into intricate three-dimensional (3D) constructs intended for implantation into defects to achieve targeted delivery and tissue regeneration. The chapter highlights ES’s principles, advantages, and significant applications in tissue repair and regeneration and outlines the key challenges and limitations.
Department of Medical Devices, National Institute of Pharmaceutical Education and Research Kolkata
Pritiprasanna Maity*
Department of Regenerative Medicine and Cell Biology, Medical University of South Carolina, Charleston, SC, USA
Kausik Kapat*
Department of Medical Devices, National Institute of Pharmaceutical Education and Research Kolkata
*Address all correspondence to: maity@musc.edu and kausik.kapat@niperkolkata.ac.in
1. Introduction
The process of repairing a wound involves the replacement of injured tissue with new tissue through collagen synthesis, epithelialization, and angiogenesis. During natural wound healing, fibroblasts and other reparative cells cause random deposition of the collagen matrix, often associated with scar tissue formation. Tissue regeneration involving three key elements—reparative cells, growth factors (GFs), or other signaling molecules like chemokines, cytokines, etc., and biomaterials or scaffolds, also known as tissue engineering TRIAD, could be a better strategy for complete wound recovery [1]. Scaffolds provide several epitopes that facilitate the formation of an extracellular milieu, support cell homing, and steer intracellular signaling pathways linked to cell motility, proliferation, and differentiation [2, 3]. The conventional scaffold manufacturing techniques, namely solvent casting, particulate leaching, freeze drying, electrospinning, gas foaming, etc., often involve cytotoxic solvents and sometimes encounter challenges like long processing time, inadequate strength, pore interconnectivity, and irregular pore size [4]. Advanced 3D printing techniques based on photopolymerization involve large monomers, often subjected to high-temperature treatment for efficient conversion into polymeric structures.
The electrohydrodynamic (EHD) techniques, namely electrospinning and electrospraying (ES), are the other advanced methods of producing nano-/micro fibrous scaffolds and particles of different shapes and sizes, respectively, utilizing electrostatic forces (Figure 1) [5]. They principally differ in terms of (a) collectors, a liquid bath in wet ES and a solid plate in dry electrospinning; (b) nozzles: triaxial, coaxial, and uniaxial; and (c) final product: particles vs. nano/microfibers. In electrospinning, a syringe pump propels a polymer solution through a needle, forming a Taylor cone at the needle tip. As the repulsion force exceeds surface tension and viscoelastic forces, the polymer jet subsequently erupts into fragmented droplets, which are then drawn toward the collector-generating nanofibers. On the other hand, ES produces micro/nanodroplets at ambient temperature and pressure, which are then converted into hollow spheres, nano cups, Janus particles, porous, cell-shaped/core-shell, and multilayered micro- or nanospheres with a narrow size distribution. In ES, a polymer solution containing drugs or bioactive molecules is loaded into the syringe and sprayed through a capillary or small-bore stainless steel needle at a constant rate using a syringe pump and applied voltage of 1–30 kV (mostly in DC mode) [6]. The solvent evaporates from the droplets as they separate from the Taylor cone. It creates dense, solid particles collected on a rotating drum collector or grounded flat plate positioned 7–30 cm apart from the capillary. Polycaprolactone (PCL), chitosan, polylactide (PLA), poly(lactic-co-glycolic acid) (PLGA), etc., are frequently used to encapsulate a variety of hydrophilic and hydrophobic model drugs/proteins [7]. Optimization of electrosprayed particle characteristics (particle size distribution, encapsulation efficacy, % loading, and release profile) is a complex process since it involves the manipulation of process variables, such as voltage, tip-to-collector distance, needle diameter, viscosity, flow rate, nature of drug/polymer/solvent, drug or protein-to-polymer ratio, organic-to-aqueous solvent ratio, surfactant, and conductivity [8].
Figure 1.
Principle and applications of electrospraying and electrospinning.
Electrospray nano/micro-particles are useful in encapsulating sensitive biomolecules (growth factor, peptide) and living cells with high encapsulation efficiency, occupying significant space in wound healing and tissue regeneration [5, 9, 10, 11]. The factors involved in ES are not fully known and require a systematic study [12].
The principles of electrospraying, established by Rayleigh, Zeleny, and Taylor, are based on the capacity of an electric field to deform the liquid drop interface by generating an electric charge (electrostatic of Coulomb force) inside the droplet, which contests with the intrinsic cohesive force to the liquid droplet [8, 13]. High-voltage external electrical fields and columbic repulsion are necessary for electrospraying [14]. The phenomenon commences at the Taylor Cone, where the unstable, charged macro-droplet is gradually contracted into a cone, causing the expulsion of the smaller charged droplets as the Coulomb force dominates over the surface tension. Depending on the process parameters, micro- or nanometre-sized droplets are produced when the electrostatic force supersedes the cohesive force. “Rayleigh limit” refers to this breakdown point (LR). After disintegration, the liquid droplets quickly desolvate and are deposited on the collector as solid micro- and nanosized particles [5].
By adjusting the operational parameters (flow rate, external voltage, and polymer concentration), ES has proven to be one of the most efficient, quick, and adaptable methods for creating nanofibrous membranes and micro-/nano-particles with variable shape and sizes that influence their cellular or tissue uptake. During ES, the biomolecules in the spray liquid get entrapped and randomly dispersed inside the polymer matrix as the solvent evaporates from the liquid droplet [15, 16]. Drugs and other biomolecules have been successfully encapsulated and delivered via ES [17].
3.1.1 Drugs
3.1.1.1 Antimicrobial drugs
Curcumin is well known for its anti-inflammatory, anti-cancer, antibacterial, and antilipidemic properties. However, conventional delivery systems failed to achieve adequate bioavailability because of their limited water solubility and heat, pH, and light sensitivity. Several drug delivery systems, such as ES, have been investigated to enhance bio-, cyto-, and hemo-compatibility, besides cell activity.
As shown in Figure 2(i), curcumin as the model drug was successfully entrapped into the polylactic acid (PLA)-based microcapsules prepared by ES the mixture of drugs with the polymer solution, displaying entrapment efficiency over 95%, in vitro drug release over 200 h, significant biocompatibility, besides excellent antibacterial activities against Staphylococcus aureus and Escherichia coli (Table 1) [18]. In a similar study, curcumin-loaded PLGA microparticles were prepared by coaxial ES, and the same exhibited optimal in vitro drug release profiles compared to burst release from conventional microparticles [22]. Coaxial jet electrospray was used to encapsulate Mentha piperita oil with broad-spectrum antimicrobial activity. The micro-nanocapsules core containing peppermint oil was entrapped in the alginate shell using Tween 20 as an emulsifier. The same exhibited 100% inhibition of S. aureus and E. coli, similar to pure peppermint oils [23].
AgNP-laden alginate beads were produced by ES silver nanoparticles (AgNPs) and sodium alginate solution into a calcium chloride bath. These beads were then embedded into gelatin scaffolds and showed more potent antibacterial activity against S. aureus than E. coli. Additionally, they demonstrated noncytotoxic effects on normal human dermal fibroblasts (NHDF) cells, suggesting their potential as wound dressing materials [24]. Cefoxitin, a cephalosporin antibiotic used to treat postoperative infections, was electrosprayed as nanoparticles (551 ± 293 nm) interconnected with nanofibers (61 ± 13 nm in diameter) of hyaluronic acid (HA) thin films. Their effectiveness against Klebsiella pneumoniae, S. aureus, and Listeria monocytogenes, with zones of inhibition of 24.3 ± 0.5, 13 ± 1, and 1.1 ± 0.2 mm, respectively, indicates that they could be used as nanofibrous scaffolds in surgical dressings to control postoperative infections [25]. Ciprofloxacin, a poorly soluble drug, was added to electrosprayed biodegradable poly-butyl-succinate (PBS) microparticles that demonstrated excellent antibacterial activity against S. aureus and Pseudomonas aeruginosa, which are frequently implicated in diabetic foot, venous leg ulcers, and nonhealing surgical wounds. Additionally, the microparticles demonstrated the ability to counteract P. aeruginosa biofilm formation implicated in chronic wounds [26].
3.1.1.2 Anti-inflammatory drugs and antioxidants
Alpha-lipoic acid, known for its anti-inflammatory and antioxidant properties, was encapsulated in single-capillary electrosprayed poly(ethylene oxide)-chitosan nanoparticles (707 ± 66.7 nm) with a zeta potential of 57.7 ± 0.5 mV. Due to an effective electrostatic interaction with cell-surface molecules, the attached particles were quickly endocytosed by the lipopolysaccharide (LPS)-treated Raw 264.7 macrophages, demonstrating the anti-inflammatory effects of nanoparticles [27].
PLGA microparticles encapsulating ranibizumab, a nonsteroidal anti-inflammatory drug (NSAID), were prepared by coaxial ES. The same resulted in 70% encapsulation efficacy, higher stability, and sustained release of the drug from microparticles for over a month without significant loss of bioactivity. The absence of any long-term microglial activity or apoptotic effects was observed after an intravitreal injection of 200 μg microparticles [28].
Transplantation of encapsulated islets can be a better choice for functional recovery of the damaged pancreas in diabetic patients. However, to maximize graft life and prevent fibrotic growth from the host response, the encapsulated islets need to be immuno-isolated. In a study by Dang et al., in a chemically-induced type I diabetic mouse model, electrosprayed alginate microcapsules co-encapsulating antioxidant and anti-inflammatory curcumin with pancreatic rat islets significantly decreased fibrotic overgrowth and enhanced glycemic control [29].
Doxorubicin (DOX)-loaded chitosan nanoparticles (300–570 nm) were created by electrospray ionization utilizing a 26-gauge needle, 13 kV voltage, 0.5 mL/h flow rate, with 8 cm working distance, and tripolyphosphate as the stabilizer. Their drug encapsulation efficiency ranged from 63.4 to 67.9% at 1–0.25% DOX loading with a prolonged drug release for 7 hours [55].
3.1.2 Biomacromolecules
A variety of bioactive proteins (such as hormones and growth factors), peptides, and nucleic acids intended for tissue regeneration and wound healing have been effectively delivered by ES.
3.1.2.1 Growth factor
Because of the limited stability, short half-life, high inactivation rate, and risk of overdose that can lead to cancer, in vivo growth factor delivery in tissue engineering encounters severe challenges in promoting cell migration, proliferation, and differentiation. In this context, electrosprayed microcarriers were better for delivering growth factors [11].
Numerous studies have demonstrated the potential benefits of administering stromal-derived factor-1α (SDF-1α) in treating myocardial infarction (MI) by drawing native stem cells to the injured myocardium. PLGA core-shell particles prepared by coaxial ES with SDF-1α incorporated resulted in a controlled release of the growth factor for more than 40 days, along with 38% higher migration (chemotactic activity) and proliferation of mesenchymal stem cells (MSCs), and the ability to inject the particles for in situ cardiac regeneration (Figure 2(ii)) [19]. The recombinant human bone morphogenetic protein-2 (rhBMP-2) and bovine serum albumin (BSA) as stabilizer were loaded into core-shell PLGA microspheres with a size of 2.5–8 μm, prepared by coaxial ES. In vitro release studies showed a stable, prolonged rhBMP-2 release for up to 21 days after a burst release within the first 6 hours with little chance of protein denaturation. Particle size substantially impacted the release rates in relation to rhBMP-2 loading. Cell proliferation was steadily increased for 7 days with minimal cytotoxicity within the studied dosage range when bone marrow-derived MSCs (BMSCs) were cultured with rhBMP-2-loaded PLGA microspheres, which showed great promises for bone tissue regeneration [30]. Electrosprayed PLGA core/PDLA shell spheres that were loaded with angiogenic VEGF to stimulate endothelial cell proliferation and osteogenic BMP-2 to stimulate osteogenic differentiation showed an initial burst release with ~80% release of the VEGF in the first 10 days and up to 30 days of stable, sustained release of BMP-2. BMSCs cultured with VEGF/BMP-2 spheres for 14 days significantly increased osteogenic-related gene (ALP, OPN, and BMP-2) expression. Micro-computed tomography and histological analysis of critical-sized rat cranial defects treated with VEGF/BMP-2 spheres showed faster bone regeneration with vascular tissue ingrowth [31].
Similarly, pre-osteoblasts (MC3T3-E1) cultured with electrosprayed PLGA microparticles encapsulating VEGF, bone morphogenetic protein 7 (BMP-7), and stabilizers for 3 weeks significantly induced osteogenic differentiation [32]. Electrosprayed nanoparticles (size <10 nm) loaded with collagen type II specific to cartilage and either hyaluronic acid or chondroitin sulfate enhanced the synthesis of cartilage-specific proteins after culturing with chondrocytes. After internalizing the particles by nonspecific pinocytosis, the expression of chondrogenic genes (transforming growth factor-beta 1, collagen type II, and aggrecan) was significantly increased. The patella grooves of the male New Zealand rabbits implanted with pellets containing chondrocytes and polymeric nanoparticles exhibited signs of early closure of the injured cartilages and neo-tissue formation after 8 weeks of implantation [33].
Electrospray technology was used to manufacture core/shell double-layered microspheres in two steps: first, an alginate core loaded with BMP-2 was prepared, followed by a chitosan shell loaded with SDF-1. The in vitro release study revealed differential release of SDF-1 and BMP-2, with an initial burst release of SDF-1 (~80%) in the first 6 hours and 50% of the latter released in 4 hours without sacrificing bioactivity. The microspheres also demonstrated chemotactic migration of MC3T3-E1 pre-osteoblast cells and in vitro osteogenic differentiation of mice-derived BMSCs as evidenced by enhanced ALP activity after 3 days, development of mineralized modules after 14 days, and increased expression of osteogenic-related genes (Runx2, OCN, Osterix) and Smad signaling genes (Smad 1, 5, 8) after 7 days of osteogenic induction [34]. Platelet-derived growth factor (PDGF), an early mitogenic factor and simvastatin, a late osteogenic inducer were administered to promote dentoalveolar regeneration. PDGF and simvastatin were encapsulated in a double-walled PDLLA–PLGA microspheres using the coaxial electrohydrodynamic atomization technique. Simvastatin (core)/PDGF (shell) microspheres exhibited a faster release of simvastatin than PDGF; however, PDGF (core)/simvastatin (shell) microspheres revealed 60% release of both PDGF and simvastatin concurrently at day 10. When PDGF/simvastatin-loaded microspheres were injected into the maxillary first molar (M1) defect formed in the post-extraction ridge of the Sprague Dawley rats, osteogenesis level at day 14 and BV/TV, TMD, Tb.Th, and Tb.N values at day 28 was higher than control [35].
3.1.2.2 Peptides and hormones
Angiotensin II, a model peptide, was encapsulated using single or coaxial electrospray methods into tristearin and N-octyl-O-sulphate chitosan nanocarriers, respectively. The same resulted in peptide entrapment in the particle matrix or a core-shell structure, depending on the single or coaxial format. The 100–300 nm-sized electrosprayed nanoparticles showed encapsulation efficiencies of about 92 ± 1.8%; nevertheless, cytotoxicity tests indicated that an ideal peptide loading concentration of about 1 mg/ml would result in a triphasic activity slow in the beginning, fast afterward, and diffusive at the end [36].
Genetically modified elastin-like polypeptides (ELP) were used to develop a biodegradable, biocompatible, and bioresponsive polymeric drug nanocarrier by ES technique. DOX-loaded ELP nanoparticles (300–400 nm in diameter) prepared in this way exhibited 20 w/w% drug loading without affecting the particle morphology and a pH-dependent drug release that was correlated with the pH-dependent solubility of the ELPs, indicating their potential as a stimuli-responsive drug nanocarrier [37].
Since estrogen and progesterone have several adverse effects, phytoestrogens like daidzein may be a viable substitute for hormone therapy in the treatment of osteoporosis. ES was used to create daidzein-loaded microspheres based on poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV), which showed a 7.6% drug release at 1 hour followed by prolonged release over nearly 3 days. As a result, these microspheres may find potential applications in bone tissue engineering and osteoporosis treatment [38].
3.1.2.3 Nucleic acids
The success of gene/plasmid DNA delivery relies on a safe and effective delivery system that can cross the biological barriers of the target cells. Viral or non-viral carrier systems typically deliver plasmid DNA because naked DNA is too big, negatively charged, hydrophilic, and prone to enzymatic destruction to penetrate cell membranes. Non-viral delivery methods (lipid/polymer/inorganic nanocarriers, electroporation, nucleofection, hydrodynamic injection, and microinjection) have a lower risk of immunogenicity and carcinogenicity than viral vectors (adeno-associated virus, lentivirus, and adenovirus), despite having a lower delivery efficiency. Electrospray can be used to develop excellent gene or plasmid delivery carriers [20].
CRISPR plasmids loaded in alginate nanoparticles were developed by ES. Their mean size, encapsulation efficiency, and zeta potential were measured at 228 nm, >99.0%, and −4.42 mV, respectively, without loss of payload integrity (Figure 2(iii)-a). The encapsulated CRISPR plasmids retained adequate cytocompatibility and integrated with HepG2 cells [20]. pET30a-green fluorescent protein (GFP) plasmid and gold nanoparticles were electrosprayed as a thin layer over E. coli, allowing rapid cellular uptake and effective bacterial transformation evidenced by the formation of GFP-expressing bacterial colonies on an agar plate (Figure 2(iii)-b) [39].
BES helps deliver a genetic construct into living cells to increase plasmid DNA stability and transfection efficiency. Human Embryonic Kidney 293T (HEK293T) cells transduced with recombinant self-inactivating lentiviral vectors expressing green fluorescent protein (GFP) were subsequently manipulated by bio-electrospraying (BES). The combined technique offers the creation of live therapeutic constructs that allow for the precise and regulated release of cells or genes, apart from cell or gene therapies [56]. GFP plasmid was electrosprayed onto chick embryos to achieve localized GFP expression. Co-jetting/ES dye-loaded PLGA-polyethyleneimine and imaging/pH-responsive siRNA solutions could result in bicompartmental particles, a viable alternative to bacterial/cell transformation [40]. Nucleic acid-based therapies were also evaluated for treating lung disease. Nucleic acids (siRNA-FITC, luciferase DNA, and mRNA) were locally delivered to pig tracheal tissue and the whole lung ex vivo using a bronchoscopic electrospray administration method [57].
3.2 Cell delivery
BES became an attractive tool for delivering living cells or complete organisms in scaffolds for tissue engineering applications [58]. Many cells, such as fibroblasts, adipose-derived stem cells (ADSCs), bone marrow-derived mesenchymal stem cells, umbilical vascular endothelial cells, gastric epithelial cells, periodontal ligament cells, and retinal pigment epithelial cells have been electrosprayed with low current in the nanoampere range and voltage up to several kilovolts, without significantly affecting the cell morphology, viability, and proliferation [59, 60].
ES of BMSC suspension was accomplished at 6 mL/h flow rate and 7.5–15 kV voltages, with 88% cell survival and a proliferation rate comparable to native BMSCs. An unstable ES with decreased cell viability was noted at higher voltages because of the thermal or electrical shock to the cells. The effective differentiation of BMSCs, electrosprayed at 7.5 kV, into adipogenic, chondrogenic, and osteogenic lineages while maintaining their multipotency, suggests that BES is a safe method for delivering progenitor/stem cells for regenerative purposes [41]. Using 15 kV, 0.46 ml/h flow rate, 4 cm distance, and 15 and 60 minutes spray time, a steady and continuous stream of BES could be formed without affecting the MSC’s survival, proliferation, plasticity, or immunophenotypic profile. DNA damage occurred when the BES time exceeded 30 minutes, but it underwent self-recovery within 5 hours [42]. Similarly, the BES of mouse embryonic stem cells (ESCs) demonstrated that pluripotency retention was established by an alkaline phosphatase assay and gene expression profile [43].
A strategy combining therapeutic stem/progenitor cells and angiogenic proteins is attractive for treating vascular disease. Injectable multifunctional microgels comprising arginine-glycine-aspartic acid (RGD)-conjugated alginate encapsulated with outgrowth endothelial cells (OECs), VEGF, and hepatocyte growth factor (HGF) were developed by ES, which showed a time-dependent growth factor release, improved cell proliferation, viability, and human umbilical vein endothelial cells (HUVECs)-mediated tube formation and ex vivo sprouting of rat aorta. Mice treated with RGD-microgel containing OECs and other growth factors for 1 week showed an increased level of angiogenesis and capillary density in the subcutaneous pocket of the abdomen, while an enhanced blood flow perfusion into a hindlimb ischemia model (Figure 2(iv)) [21].
Extended gastrointestinal retention of probiotics is crucial for enhancing their functional efficacy. Mucoadhesive probiotic formulations (spherical with a 60–1300 μm diameter) containing Lactobacillus plantarum based on resistant starch-reinforced and mucoadhesive chitosan-coated alginate microparticles were developed using an electrospray approach. When the in vitro wash-off mucoadhesion of the formulations was evaluated using fluorescence microscopy, the alginate-starch electrosprayed formulations showed better protection against simulated gastric fluid than the alginate ones, though not as good as the chitosan-coated ones [44].
3.3 Implant coating
Drug-eluting stents (DESs) are more effective in preventing in-stent restenosis in injured arteries following percutaneous coronary intervention (PCI), which is frequently associated with increased leukotrienes [61]. Montelukast, an anti-inflammatory and anti-proliferative drug, has often been used to treat various inflammatory diseases. ES montelukast/PLGA particles onto DES could effectively prevent the development of neointimal hyperplasia, which is the cause of in-stent restenosis, without affecting the healing of the stented vessel [45]. The bioactive coating of antioxidant vitamin E and antimicrobial chitosan onto the polyethylene (PE) surface, accomplished by electrosprayed, significantly inhibited bacterial growth and exerted potent antioxidant and pH-responsive properties [46]. An antibacterial coating was created on titanium surfaces by loading the cationic and amphipathic peptide chicken cathelicidin-2 between layers of poly(D,L-lactide-co-glycolide) (PDLG) and gelatin methacryloyl (GelMA), which were electrosprayed in a layer-by-layer (LbL) assembly fashion. The coating was biocompatible with hMSCs and macrophages while exhibiting potent antibacterial activity against E. coli and S. aureus for 4 days. Such coating provides a suitable platform for preventing peri-implantitis (Figure 3(i)) [47].
Using the ES technique, the PLA loaded with dexamethasone (DEX), an anti-inflammatory drug, was coated onto medical implants. Compared to spin-coated stents, electrosprayed stents demonstrated a suitable drug release profile and more remarkable HUVEC survival after 1 and 4 days [48]. Similarly, titanium implants coated with fibroblast growth factor (β-FGF)-loaded PLGA by ES showed enhanced osseointegration (bone-to-implant contact) following implantation in rabbit tibial defects [49].
3.4 Scaffold fabrication
Coaxial ES was used to create bioactive insulin-encapsulated silk fibroin (SF) microparticles to treat chronic wounds. The SF sponge loaded with microparticles was a bioactive wound dressing assessed for in vivo therapeutic effects on dorsal full-thickness wounds in diabetic Sprague–Dawley rats. The result demonstrated evidence of vascularization, collagen deposition, and faster wound closure, which considerably facilitated the healing process [50].
Biomimetic scaffolds comprising aligned PCL microfibrous scaffolds co-sprayed with collagen or conductive polypyrrole nanoparticles were developed for simultaneously delivering topographic cues and electrotransduction by integrating ES with electrospinning. While PC12 cells were oriented and elongated along the fibers’ direction on collagen-coated PCL microfibrous scaffold, more functional expressions, including elongation, gene expression, and protein expression, were observed on PPy-coated aligned fibers, which led to increased neurogenesis [51]. Electrosprayed bovine serum albumin (BSA)-loaded core-shell PLGA nanospheres produced by coaxial ES were collected on an electrically grounded highly aligned electrospun PCL microfibrous mat. The study suggested that when cultured with rat pheochromocytoma (PC-12) and astrocyte cell lines, the nanocomposite scaffold was promising for directing neural tissue growth along the fibers and regeneration (Figure 3(ii)) [52]. A composite scaffold prepared by ES of nano-hydroxyapatite on electrospun collagen significantly increased the proliferation of human dermal fibroblasts, keratinocytes, and hMSCs differentiation in addition to inhibiting bacterial adhesion. The scaffold exhibited no adverse reactions following implantation in a rat subcutaneous pocket, indicating its potential for application as a dressing material or skin wound regeneration [53].
Theranostic agents were created using the electrospray technology, which allowed for the simultaneous administration of therapeutic and diagnostic compounds [62]. In situ synthesized magnetic iron oxide (Fe3O4) nanoparticles were encapsulated in PVA microspheres by one-step ES to be used as an MRI contrast agent. The PVA matrix was further cross-linked to facilitate embolization. In vivo evaluation of Fe3O4@PVA microspheres in the rabbit renal artery revealed increased MRI contrast, an embolic effect with excellent biocompatibility. On the other hand, the ability of doxorubicin (DOX)-loaded Fe3O4@PVA microspheres to release DOX over an extended period indicates its potential as a theranostic agent [10]. Superparamagnetic iron oxide nanoparticles (SPIONs), which may be steered by external magnetic fields to create localized hypothermia to damage targeted cells, have been widely investigated as MRI contrast agents due to their capacity to reduce drastically spin–spin relaxation (T2) time. In a fluorophore (BODIPY) integrated tristearin core-shell system, a model drug, genistein, an isoflavonoid, and SPIONs (10–15 nm) were encapsulated with a 92% drug encapsulation efficiency utilizing coaxial ES. These particles showed low toxicity and were internalized by the cells in 4 hours, indicating the possibility of developing multimodal particles for integrated imaging and therapy [36]. One-step ES was used to create calcium alginate microspheres (Ta@CaAlg) loaded with tantalum nanoparticles and DOX, which not only allowed for a maximum 97.3 mg DOX loading per mL of beads and a pH-dependent release profile but also demonstrated embolic effects as revealed by digital subtraction angiography. The microspheres also produced good X-ray/CT contrast, allowing their real-time monitoring at embolized sites for up to 4 weeks (Figure 4(i)) [54].
ES can quickly and easily prepare nano/micro-carriers with varying sizes, shapes, and encapsulation efficiency; however, low throughput is one of the major disadvantages of ES, mainly when using the cone-jet mode [63]. The technique is well ahead of industrial-scale production since only about 300 mg of particles could be created after 24 hours of spraying. Alternative approaches by applying a flute-like multipore emitter device [64], customized multi-hole spinneret [65], and needleless apparatus with microchannels made of two parallel glass plates sharpened and grooved at their edges forming multiple spraying jets under high electric potential [66] were suggested to increase production rate through ES. There has been limited success in enhancing yield through multiplex electrospraying devices, which have several emitters fitted with a cone-jet at each emitter. Maintaining a constant electrical field across the emitters to produce equal jets is challenging [67]. BES has the potential to cause electrical stress on biomacromolecules and cells, perhaps leading to detrimental effects on their bioactivity. Although preliminary research suggests that ES does not influence the stability of proteins, enzymes, nucleic acids, and cells, further research is needed to determine the long-term implications of organic solvents and high voltages involved in ES [16]. More attention is required to create environmentally friendly ES methods that use aqueous-based solvents, as organic solvents are mostly hazardous and can harm intracellular components, payloads, and the viability of cells [68]. Integrating BES with the techniques to fabricate an organ-on-a-chip can eventually replace animal testing for determining the toxicity of therapeutic substances toward cells and tissues.
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Written By
Rahul Sable, Pritiprasanna Maity and Kausik Kapat
Submitted: 01 April 2024Reviewed: 02 April 2024Published: 05 June 2024
Open access peer-reviewed chapter - ONLINE FIRST
