Cross-linking mechanisms of calcium and zinc in production of alginate microspheres

Advances and challenges in serratiopeptidase topical formulation

Enzymes are a key part of most metabolic processes and are required for the correct functioning of the human body, either directly or indirectly. Proteolytic enzymes aid in the digestion of proteins in the body. Proteolytic enzymes are created in the pancreas naturally, but they can also be found in certain diets. Serratiopeptidase is an enzyme found in the stomach wall of silkworms and produced from S. marcescens strain. Less solubility, toxicity, instability, incompatibility, and less penetration are all common issues with Serratiopeptidase drug delivery. Because of its proteinaceous nature, serratiopeptidase is susceptible to enzymatic breakdown in the gastrointestinal system. It also has a low permeability through the intestinal barrier due to its hydrophilic nature. Depending on the features of the medicine, a suitable delivery mechanism is required. Topical formulation may eliminate the risk of gastric degradation of drug and increase direct permeation through skin and show effects. Topical SRP may effectively lower inflammatory markers, as it has been found to have superior anti-inflammatory effects than topical NSAIDs. Serratiopeptidase topical formulations could be more effective than nonsteroidal anti-inflammatory medications in treating local inflammation. This article reviews studies on various topical formulations.

Chitosan and sodium alginate nanocarrier system: Controlling the release of rapeseed-derived peptides and improving their therapeutic efficiency of anti-diabetes

Rapeseed-derived peptides (RPPs) can maintain the homeostasis of human blood glucose by inhibiting Dipeptidyl Peptidase-IV (DPP-IV) and activating the calcium-sensing receptor (CaSR). However, these peptides are susceptible to hydrolysis in the gastrointestinal tract. To enhance the therapeutic potential of these peptides, we developed a chitosan/sodium alginate-based nanocarrier to encapsulate two RPP variants, rapeseed-derived cruciferin peptide (RCPP) and rapeseed-derived napin peptide (RNPP). A convenient three-channel device was employed to prepare chitosan (CS)/sodium alginate (ALG)-RPPs nanoparticles (CS/ALG-RPPs) at a ratio of 1:3:1 for CS, ALG, and RPPs. CS/ALG-RPPs possessed optimal encapsulation efficiencies of 90.7 % (CS/ALG-RNPP) and 91.4 % (CS/ALG-RCPP), with loading capacities of 15.38 % (CS/ALG-RNPP) and 16.63 % (CS/ALG-RCPP) at the specified ratios. The electrostatic association between CS and ALG was corroborated by zeta potential and near infrared analysis. 13C NMR analysis verified successful RPPs loading, with CS/ALG-RNPP displaying superior stability. Pharmacokinetics showed that both nanoparticles were sustained release and transported irregularly (0.43 < n < 0.85). Compared with the control group, CS/ALG-RPPs exhibited significantly increased glucose tolerance, serum GLP-1 (Glucagon-like peptide 1) content, and CaSR expression which play pivotal roles in glucose homeostasis (*p < 0.05). These findings proposed that CS/ALG-RPPs hold promise in achieving sustained release within the intestinal epithelium, thereby augmenting the therapeutic efficacy of targeted peptides.

Ionically bridged dexamethasone sodium phosphate-zinc-PLGA nanocomplex in alginate microgel for the local treatment of ulcerative colitis

Colon-targeted oral drug delivery systems comprising nanoparticles and microparticles have emerged as promising tools for the treatment of ulcerative colitis (UC) because they minimize side effects and maximize the local drug concentration. Dexamethasone sodium phosphate (DSP) is a potent anti-inflammatory glucocorticoid used for the treatment of UC. However, it remains a rather short-term treatment option owing to its side effects. In the present study, we developed the alginate gel encapsulating ionically bridged DSP-zinc-poly(lactic-co-glycolic acid) (PLGA) nanocomplex (DZP-NCs-in-microgel) for the oral local treatment of UC. The successful encapsulation of DSP-zinc-PLGA nanocomplex (DZP-NCs) in alginate microgel was confirmed by SEM imaging. The prepared gel released DZP-NCs in the stimulated intestinal fluid and dampened the release of DSP in the upper gastrointestinal tract. Furthermore, DZP-NCs-in-microgel alleviated colonic inflammation in a mouse model of dextran sodium sulfate-induced colitis by relieving clinical symptoms and histological marks. Our results suggest a novel approach for the oral colon-targeted delivery of dexamethasone sodium phosphate for the treatment of UC.

Anisotropic, Hydrogel Microparticles as pH-Responsive Drug Carriers for Oral Administration of 5-FU

In the last 20 years, the development of stimuli-responsive drug delivery systems (DDS) has received great attention. Hydrogel microparticles represent one of the candidates with the most potential. However, if the role of the cross-linking method, polymer composition, and concentration on their performance as DDS has been well-studied, still, a lot needs to be explained regarding the effect caused by the morphology. To investigate this, herein, we report the fabrication of PEGDA-ALMA-based microgels with spherical and asymmetric shapes for 5-fluorouracil (5-FU) on-demand loading and in vitro pH-triggered release. Due to anisotropic properties, the asymmetric particles showed an increased drug adsorption and higher pH responsiveness, which in turn led to a higher desorption efficacy at the target pH environment, making them an ideal candidate for oral administration of 5-FU in colorectal cancer. The cytotoxicity of empty spherical microgels was higher than the cytotoxicity of empty asymmetric microgels, suggesting that the gel network's mechanical proprieties of anisotropic particles were a better three-dimensional environment for the vital functions of cells. Upon treatment with drug-loaded microgels, the HeLa cells' viability was lower after incubation with asymmetric particles, confirming a minor release of 5-FU from spherical particles.

Cathode-Electrolyte Interface Modification by Binder Engineering for High-Performance Aqueous Zinc-Ion Batteries

A stable cathode-electrolyte interface (CEI) is crucial for aqueous zinc-ion batteries (AZIBs), but it is less investigated. Commercial binder poly(vinylidene fluoride) (PVDF) is widely used without scrutinizing its suitability and cathode-electrolyte interface (CEI) in AZIBs. A water-soluble binder is developed that facilitated the in situ formation of a CEI protecting layer tuning the interfacial morphology. By combining a polysaccharide sodium alginate (SA) with a hydrophobic polytetrafluoroethylene (PTFE), the surface morphology, and charge storage kinetics can be confined from diffusion-dominated to capacitance-controlled processes. The underpinning mechanism investigates experimentally in both kinetic and thermodynamic perspectives demonstrate that the COO- from SA acts as an anionic polyelectrolyte facilitating the adsorption of Zn2+ ; meanwhile fluoride atoms on PTFE backbone provide hydrophobicity to break desolvation penalty. The hybrid binder is beneficial in providing a higher areal flux of Zn2+ at the CEI, where the Zn-Birnessite MnO2 battery with the hybrid binder exhibits an average specific capacity 45.6% higher than that with conventional PVDF binders; moreover, a reduced interface activation energy attained fosters a superior rate capability and a capacity retention of 99.1% in 1000 cycles. The hybrid binder also reduces the cost compared to the PVDF/NMP, which is a universal strategy to modify interface morphology.

Innovative bio-waste-based multilayer hydrogel fertilizers as a new solution for precision agriculture

The aim of the research work was to present a multilayer hydrogel capsule with controlled nutrient release properties as an innovative fertilizer designed for sustainable agriculture. Preparation of the capsules included the following steps: sorption of micronutrients (Cu, Mn, Zn) on eggshells (1) and their immobilization in sodium alginate, with the crosslinking agent being the NPK solution (2). The capsules were coated with an additional layer of a mixture of biopolymers (0.79% alginate, 0.24% carboxymethylcellulose and 8.07% starch)by means of dipping and spraying techniques. The biocomposites were characterized by limited (<10% within 100 h for the structures encapsulated by the dipping method) release of fertilizer ions (except for small K⁺ ions). The hydrogel fertilizer formulations were analyzed for physicochemical properties such as macro- and micronutrient content, surface morphology analysis, coating structure evaluation, mechanical properties, swelling and drying kinetics. High nutrient bioavailability was confirmed in vitro (extraction in water and neutral ammonium citrate). Germination and pot tests have revealed that the application of multicomponent hydrogel fertilizers increases the length of cucumber roots by 20%, compared to the commercial product.

Novel alginate immobilized TiO2 reusable functional hydrogel beads with high photocatalytic removal of dye pollutions

TiO2 semiconductor photocatalysis is an effective technology for the treatment of wastewater containing organic dye pollutants, which has been received extensive focus. However, the problems in the recovery and reutilization process impede the large-scale applications of particulate photocatalytic materials. Herein, a macro sized hydrogel bead loaded with nano TiO2 powder was successfully prepared by taking advantage of the cross-linking and gel property of alginate salt, which could form egg-box structure naturally when Na+ ions in sodium alginate (SA) were replaced by divalent ions such as Cu2+, Co2+, and Sr2+ ions. The photocatalytic degradation rate of methyl orange (MO) solution in the presence of the hydrogel beads reaches 99% within 60 min under the ultraviolet light irradiation, which is competitive with that of TiO2 nano powder. Furthermore, the hydrogel beads prepared by this strategy maintain over 95% photocatalytic degradation rate after 10 cycles of degradation process. The results indicate that the network structure of alginate could immobilize and disperse TiO2 particle effectively, and it is readily for the spherical beads to contact and harvest the light, making the alginate beads have excellent photocatalytic functions. Also, the alginate based beads integrate good performance with high stability and excellent recyclability perfectly.

Investigation of Collagen-Incorporated Sodium Alginate Bioprinting Hydrogel for Tissue Engineering

Tissue engineering is a promising area that is aimed at tissue regeneration and wound repair. Sodium alginate (SA) has been widely used as one of the most biocompatible materials for tissue engineering. The cost-efficiency and rapid gel ability made SA attractive in would healing and regeneration area. To improve printability and elasticity, many hydrogel-based bioinks were developed by mixing SA with other natural or synthetic polymers. In this paper, composite SA/COL bioink was used for the bioprinting of artificial cartilage tissue mimicries. The results showed that the concentration of both SA and COL has significant effects on filament diameter and merging. A higher concentration of the bioink solution led to better printing fidelity and less deformation. Overall, a higher SA concentration and a lower COL concentration contributed to a lower shrinkage ratio after crosslinking. In summary, the SA/COL composite bioink has favorable rheological properties and this study provided material composition optimization for future bioprinting of engineered tissues.

Single-cell droplet microfluidics for biomedical applications

This review focuses on the recent advances in the fundamentals of single-cell droplet microfluidics and its applications in biomedicine, providing insights into design and establishment of single-cell microsystems and their further performance.

Poly(lactic acid)/Zinc/Alginate Complex Material: Preparation and Antimicrobial Properties

The aim of this study was to investigate an antimicrobial and degradable composite material consisting of melt-blown poly(lactic acid) nonwoven fabrics, alginate, and zinc. This paper describes the method of preparation and the characterization of the physicochemical and antimicrobial properties of the new fibrous composite material. The procedure consists of fabrication of nonwoven fabric and two steps of dip-coating modification: (1) impregnation of nonwoven samples in the solution of alginic sodium salt and (2) immersion in a solution of zinc (II) chloride. The characterization and analysis of new material included scanning electron microscopy (SEM), specific surface area (SSA), and total/average pore volume (BET). The polylactide/alginate/Zn fibrous composite were subjected to microbial activity tests against colonies of Gram-positive (Staphylococcus aureus), Gram-negative (Escherichia coli) bacterial strains, and the following fungal strains: Aspergillus niger van Tieghem and Chaetomium globosum. These results lay a technical foundation for the development and potential application of new composite as an antibacterial/antifungal material in biomedical areas.

Improved functionality of Ligilactobacillus salivarius Li01 in alleviating colonic inflammation by layer-by-layer microencapsulation

The low viability during gastrointestinal transit and poor mucoadhesion considerably limits the effectiveness of Ligilactobacillus salivarius Li01 (Li01) in regulating gut microbiota and alleviating inflammatory bowel disease (IBD). In this study, a delivery system was designed through layer-by-layer (LbL) encapsulating a single Li01cell with chitosan and alginate. The layers were strengthened by cross-linking to form a firm and mucoadhesive shell (~10 nm thickness) covering the bacterial cell. The LbL Li01 displayed improved viability under simulated gastrointestinal conditions and mucoadhesive function. Almost no cells could be detected among the free Li01 after 2 h incubation in digestive fluids, while for LbL Li01, the total reduction was around 3 log CFU/mL and the viable number of cells remained above 6 log CFU/mL. Besides, a 5-fold increase in the value of rupture length and a two-fold increase in the number of peaks were found in the (bacteria-mucin) adhesion curves of LbL Li01, compared to those of free Li01. Oral administration with LbL Li01 on colitis mice facilitated intestinal barrier recovery and restoration of the gut microbiota. The improved functionality of Li01 by LbL encapsulation could increase the potential for the probiotic to be used in clinical applications to treat IBD; this should be explored in future studies.

Novel synthesis of natural cation exchange resin by crosslinking the sodium alginate as a natural polymer with 1,6-hexamethylene diisocyanate in inert solvents: Characteristics and applications

Novel synthesis of natural polymeric cation exchanger from sodium alginate reagent as natural polymer (CAlg-Na)_n has been developed. This procedure takes place by crosslinking the solid sodium alginate with 1,6-hexamethylene diisocyanate (HDI) in dryness benzene as inert solvent (DB). The experimental results for crosslinking the alginate using different degrees of crosslinking of HDI/DB (w/w) showed that the capacity of the synthesized resin for binding the polyvalent metal ions reached its maximum at 30% of (HDI/D) ratio. This work aims to present a novel synthesis of cation exchange resin from natural polymers as an alternative promising competitor of low-cost, high performance and non-toxicity for removal of the toxic heavy metal ions in wastewater remediation and radionuclide pollutants from environmental contaminated media. The results obtained from various applied techniques for determining the bounded metal ion concentrations with (CAlg-Na)_n indicated that the resin capacity was followed the order U(VI) > Cu(II) > Sr(II) > Ca(II) at 25 °C, respectively. The factors influenced the alginate affinity for chelating the metal ions were explained in some correlation terms between the alginate capacity and some physicochemical properties of chelated metal ions and its respective formed complexes. Speculated geometrical configurations for chelation were suggested and discussed.

Engineering in vitro human neural tissue analogs by 3D bioprinting and electrostimulation

There is a fundamental need for clinically relevant, reproducible, and standardized in vitro human neural tissue models, not least of all to study heterogenic and complex human-specific neurological (such as neuropsychiatric) disorders. Construction of three-dimensional (3D) bioprinted neural tissues from native human-derived stem cells (e.g., neural stem cells) and human pluripotent stem cells (e.g., induced pluripotent) in particular is appreciably impacting research and conceivably clinical translation. Given the ability to artificially and favorably regulate a cell's survival and behavior by manipulating its biophysical environment, careful consideration of the printing technique, supporting biomaterial and specific exogenously delivered stimuli, is both required and advantageous. By doing so, there exists an opportunity, more than ever before, to engineer advanced and precise tissue analogs that closely recapitulate the morphological and functional elements of natural tissues (healthy or diseased). Importantly, the application of electrical stimulation as a method of enhancing printed tissue development in vitro, including neuritogenesis, synaptogenesis, and cellular maturation, has the added advantage of modeling both traditional and new stimulation platforms, toward improved understanding of efficacy and innovative electroceutical development and application.

Application and outlook of topical hemostatic materials: a narrative review

Bleeding complications can cause significant morbidities and mortalities in both civilian and military conditions. The formation of stable blood clots or hemostasis is essential to prevent major blood loss and death from excessive bleeding. However, the body's self-coagulation process cannot accomplish timely hemostasis without the assistance of hemostatic agents under some conditions. In the past two decades, topical hemostatic materials and devices containing platelets, fibrin, and polysaccharides have been gradually developed and introduced to induce faster or more stable blood clot formation, updating or iterating traditional hemostatic materials. Despite the various forms and functions of topical hemostatic materials that have been developed for different clinical conditions, uncontrolled hemorrhage still causes over 30% of trauma deaths across the world. Therefore, it is important to fabricate fast, efficient, safe, and ready-to-use novel hemostatic materials. It is necessary to understand the coagulation process and the hemostatic mechanism of different materials to develop novel topical hemostatic agents, such as tissue adhesives and sealants from various natural and synthetic materials. This review discusses the structural features of topical hemostatic materials related to the stimulation of hemostasis, summarizes the commercially available products and their applications, and reviews the ongoing clinical trials and recent studies concerning the development of different hemostatic materials.

Tailorable Zinc-Substituted Mesoporous Bioactive Glass/Alginate-Methylcellulose Composite Bioinks

Bioactive glasses have been used for bone regeneration applications thanks to their excellent osteoconductivity, an osteostimulatory effect, and high degradation rate, releasing biologically active ions. Besides these properties, mesoporous bioactive glasses (MBG) are specific for their highly ordered mesoporous channel structure and high specific surface area, making them suitable for drug and growth factor delivery. In the present study, calcium (Ca) (15 mol%) in MBG was partially and fully substituted with zinc (Zn), known for its osteogenic and antimicrobial properties. Different MBG were synthesized, containing 0, 5, 10, or 15 mol% of Zn. Up to 7 wt.% of Zn-containing MBG could be mixed into an alginate-methylcellulose blend (algMC) while maintaining rheological properties suitable for 3D printing of scaffolds with sufficient shape fidelity. The suitability of these composites for bioprinting applications has been demonstrated with immortalized human mesenchymal stem cells. Uptake of Ca and phosphorus (P) (phosphate) ions by composite scaffolds was observed, while the released concentration of Zn2+ corresponded to the initial amount of this ion in prepared glasses, suggesting that it can be controlled at the MBG synthesis step. The study introduces a tailorable bioprintable material system suitable for bone tissue engineering applications.

Titanium coating: introducing an antibacterial and bioactive chitosan-alginate film on titanium by spin coating

Coating of titanium (Ti) implants with biocompatible polymers were performed to improve bone healing. In this study, pure Ti implants were coated via chitosan and alginate by spin coating method at 1000, 4000, and 8000 rpm. The coating layer was cross-linked by calcium chloride. Their chemical structures were analyzed by Fourier transform infrared spectroscopy (FTIR) and X-ray diffraction (XRD) evaluations. The morphology of the created coating was observed by scanning electron microscopy (SEM), and the best uniformity was observed in the prepared coating at 8000 rpm (6093× g) spinal speed. The adhesion strength of the coating layer on the substrate was evaluated by the adhesion pull-off test. Also, the best adhesion strength was achieved at an 8000 rpm (6093× g) coating rate. Bioactivity of the chitosan-alginate coating on Ti sheets was evaluated by soaking the samples in a simulated body fluid (SBF) solution. The apatite formation on prepared Ti sheets was investigated by SEM, XRD, and energy dispersive X-ray spectroscopy (EDS). A higher mineralization appeared on coated samples compared with pure Ti. The antibacterial behavior of the implants was analyzed by bacterial counting against Escherichia coli. The presence of chitosan and alginate on the Ti sheets resulted in a better antibacterial effect. In-vitro experiments, with L929 fibroblast cells, confirmed the biocompatibility of the implants. Coating the Ti implants with chitosan and alginate improved biomineralization and biological behavior of the implant especially at the spinal speed of 8000 rpm (6093× g). These implants can support osteoblast cell adhesion and facilitate bone regeneration.

Alginate Hydrogels with Embedded ZnO Nanoparticles for Wound Healing Therapy

INTRODUCTION

In this in-vitro study, we designed a 3D printed composite of zinc oxide (ZnO) nanoparticles (NPs) with photocatalytic activities encapsulated within hydrogel (alginate) constructs, for antibacterial purposes applicable towards wound healing. We primarily sought to confirm the mechanical properties and cell compatibility of these ZnO NP infused scaffolds.

METHODS

The antibacterial property of the ZnO NPs was confirmed by hydroxyl radical generation using ultraviolet (U.V.) photocatalysis. Titanium dioxide (TiO2), a well-known antibacterial compound, was used as a positive control (1% w/v) for the ZnO NP-based alginate constructs and their antibacterial efficacies compared. Among the ZnO group, 3D printed gels containing 0.5% and 1% w/v of ZnO were analyzed and compared with manually casted samples via SEM, swelling evaluation, and rheological analysis. Envisioning an in-vivo application for the 3D printed ZnO NP-based alginates, we studied their antibacterial properties by bacterial broth testing, cytocompatibility via live/dead assay, and moisture retention capabilities utilizing a humidity sensor.

RESULTS

3D printed constructs revealed significantly greater pore sizes and enhanced structural stability compared to manually casted samples. For all samples, the addition of ZnO or TiO2 resulted in significantly stiffer gels in comparison with the alginate control. Bacterial resistance testing on Staphylococcus epidermidis indicated the addition of ZnO NPs to the gels decreased bacterial growth when compared to the alginate only gels. Cell viability of STO-fibroblasts was not adversely affected by the addition of ZnO NPs to the alginate gels. Furthermore, the addition of increasing doses of ZnO NPs to the alginate demonstrated increased humidity retention in gels.

DISCUSSION

The customization of 3D printed alginates containing antibacterial ZnO NPs leads to an alternative that allows accessible mobility of molecular exchange required for improving chronic wound healing. This scaffold can provide a cost-effective and durable antibacterial treatment option.

Technologies and Formulation Design of Polysaccharide-Based Hydrogels for Drug Delivery

Polysaccharide-based hydrogel particles (PbHPs) are very promising carriers aiming to control and target the release of drugs with different physico-chemical properties. Such delivery systems can offer benefits through the proper encapsulation of many drugs (non-steroidal and steroidal anti-inflammatory drugs, antibiotics, etc) ensuring their proper release and targeting. This review discusses the different phases involved in the production of PbHPs in pharmaceutical technology, such as droplet formation (SOL phase), sol-gel transition of the droplets (GEL phase) and drying, as well as the different methods available for droplet production with a special focus on prilling technique. In addition, an overview of the various droplet gelation methods with particular emphasis on ionic cross-linking of several polysaccharides enabling the formation of particles with inner highly porous network or nanofibrillar structure is given. Moreover, a detailed survey of the different inner texture, in xerogels, cryogels or aerogels, each with specific arrangement and properties, which can be obtained with different drying methods, is presented. Various case studies are reported to highlight the most appropriate application of such systems in pharmaceutical field. We also describe the challenges to be faced for the breakthrough towards clinic studies and, finally, the market, focusing on the useful approach of safety-by-design (SbD).

Structures, properties and application of alginic acid: A review

Alginic acid is a natural polysaccharide, which has been widely concerned and applied due to its excellent water solubility, film formation, biodegradability and biocompatibility. This paper briefly describes the source, properties, structure and application of sodium alginate by summarizing and analyzing the current literature. This paper reviews the application of sodium alginate in the fields of food industry, catalyst, health, water treatment, packaging, immobilized cells, and looks forward to its application prospects.

Comparative Study on Enzyme Immobilization Using Natural Hydrogel Matrices—Experimental Studies Supported by Molecular Models Analysis

Currently, great attention is focused on conducting manufacture processes using clean and eco-friendly technologies. This research trend also relates to the production of immobilized biocatalysts of industrial importance using matrices and methods that fulfill specified operational and environmental requirements. For that reason, hydrogels of natural origin and the entrapment method become increasingly popular in terms of enzyme immobilization. The presented work is the comparative research on invertase immobilization using two natural hydrogel matrices—alginate and gelatin. During the study, we provided the molecular insight into the structural characteristics of both materials regarding their applicability as effective enzyme carriers. In order to confirm our predictions of using these hydrogels for invertase immobilization, we performed the typical experimental studies. In this case, the appropriate conditions of enzyme entrapment were selected for both types of carrier. Next, the characterization of received invertase preparations was made. As a final experimental result, the gelatin-based hydrogel was selected as an effective carrier for invertase immobilization. Hereby, using mild conditions and a pro-ecological, biodegradable matrix, it was possible to obtain very stable and reactive biocatalyst. The choice of gelatin-immobilized invertase preparation was compatible with our predictions based on the molecular models of hydrogel matrices and enzyme used.

Zinc and Calcium Cations Combination in the Production of Floating Alginate Beads as Prednisolone Delivery Systems

The aim of this research was to verify the application of alginate in combination with Ca²⁺ and Zn²⁺ ions to produce a floating and prolonged release system for the oral administration of prednisolone. Hollow and floating gel-beads were designed using prilling/ionotropic gelation as the microencapsulation technique, zinc acetate in the gelling solution as the alginate external crosslinker, and calcium carbonate in the feed as the internal crosslinking agent able to generate gas when in contact with the acidic zinc acetate solution. To achieve this goal, drug/alginate solutions were opportunely combined with different amounts of calcium carbonate. The effect of the addition of calcium carbonate into the feed solution on buoyancy, encapsulation efficiency, morphology, size distribution, as well as in vitro drug release profile of the alginate particles was studied. Moreover, the ability of the floating beads to modulate in vivo the anti-inflammatory response was assayed using the carrageenan-induced acute oedema in rat paw. The proposed strategy allowed obtaining alginate beads with extremely high encapsulation efficiency values (up to 94%) and a very porous inner matrix conferring buoyancy in vitro in simulated gastric fluid up to 5 h. Moreover, in vivo, the best formulation, F4, resulted in the ability to prolong the anti-inflammatory effect up to 15 h compared with raw prednisolone.

Enhancing the Removal of Sb (III) from Water: A Fe3O4@HCO Composite Adsorbent Caged in Sodium Alginate Microbeads

To remove antimony (Sb) ions from water, a novel composite adsorbent was fabricated from ferriferous oxide and waste sludge from a chemical polishing process (Fe3O4@HCO) and encapsulated in sodium alginate (SAB). The SAB adsorbent performed well with 80%–96% removal of Sb (III) ions within a concentration range of 5–60 mg/L. The adsorption mechanism of Sb (III) was revealed to be the synergy of chemisorption (ion exchange) and physisorption (diffusion reaction). The adsorption isotherms and kinetics conformed to the Langmuir isotherm and the pesudo-second-order kinetic model. Both initial pH and temperature influenced the adsorption performance with no collapse of microbeads within solution pH range 3–7. Most importantly for practical applications, these microspheres can be separated and recovered from aqueous solution by a magnetic separation technology to facilitate large-scale treatment of antimony-containing wastewater.

A Novel Inherently Flame-Retardant Composite Based on Zinc Alginate/Nano-Cu2O

A novel flame-retardant composite material based on zinc alginate (ZnAlg) and nano-cuprous oxide (Cu₂O) was prepared through a simple, eco-friendly freeze-drying process and a sol-gel method. The composites were characterized and their combustion and flammability behavior were tested. The composites had high thermal stability and achieved nearly non-flammability with a limiting oxygen index (LOI) of 58. The results show remarkable improvement of flame-retardant properties in the ZnAlg/Cu₂O composites, compared to ZnAlg. Furthermore, the pyrolysis behavior was determined by pyrolysis-gas chromatography-mass spectrometry (Py-GC-MS) and the flame-retardant mechanism was proposed based on the combined experimental results. The prepared composites show promising application prospects in building materials and the textile industry.

Preparation and properties of dopamine-modified alginate/chitosan-hydroxyapatite scaffolds with gradient structure for bone tissue engineering

Three-dimensional (3D) homogenous scaffolds composed of natural biopolymers have been reported as superior candidates for bone tissue engineering. There are still remaining challenges in fabricating the functional scaffolds with gradient structures to similar with natural bone tissues, as well as high mechanical properties and excellent affinity to surround tissues. Herein, inspired by the natural bone structure, a gradient-structural scaffold composed of functional biopolymers was designed to provide an optimized 3D environment for promoting cell growth. To increase the interactions among the scaffolds, dopamine (DA) was employed to modify alginate (Alg) and needle-like nano-hydroxyapatite (HA) was prepared with quaternized chitosan as template. The obtained dopamine-modified alginate (Alg-DA) and quaternized chitosan-templated hydroxyapatite (QCHA) were then used to fabricate the porous gradient scaffold by "iterative layering" freeze-drying technique with further crosslinking by calcium ions (Ca²⁺ ). The as-prepared Alg-DA/QCHA gradient scaffolds were possessed seamlessly integrated layer structures and high levels of porosity at around 77.5%. Moreover, the scaffolds showed higher compression modules (1.7 MPa) than many other biopolyermic scaffolds. The gradient scaffolds showed appropriate degradation rate to satisfy with the time of the bone regeneration. Both human chondrocytes and fibroblasts could adhesive and growth well on the scaffolds in vitro. Furthermore, an excellent osteogenetic activity of the gradient scaffold can effectively promote the regeneration of the bone tissue and accelerate the repair of the bone defects in vivo, compared with that of the scaffold with the homogenous structure. The novel multilayered scaffold with gradient structure provided an interesting option for bone tissue engineering. © 2019 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 107A: 1615-1627, 2019.

Alginate-based composites for environmental applications: A critical review

Alginate-based composites have been extensively studied for applications in energy and environmental sectors due to their biocompatible, nontoxic, and cost-effective properties. This review is designed to provide an overview of the synthesis and application of alginate-based composites. In addition to an overview of current understanding of alginate biopolymer, gelation process, and cross-linking mechanisms, this work focuses on adsorption mechanisms and performance of different alginate-based composites for the removal of various pollutants including dyes, heavy metals, and antibiotics in water and wastewater. While encapsulation in alginate gel beads confers protective benefits to engineered nanoparticles, carbonaceous materials, cells and microbes, alginate-based composites typically exhibit enhanced adsorption performance. The physical and chemical properties of alginate-based composites determine the effectiveness under different application conditions. A series of alginate-based composites and their physicochemical and sorptive properties have been summarized. This critical review not only summarizes recent advances in alginate-based composites but also presents a perspective of future work for their environmental applications.

Bacterial components as naturally inspired nano-carriers for drug/gene delivery and immunization: Set the bugs to work?

Drug delivery is a rapidly growing area of research motivated by the nanotechnology revolution, the ideal of personalized medicine, and the desire to reduce the side effects of toxic anti-cancer drugs. Amongst a bewildering array of different nanostructures and nanocarriers, those examples that are fundamentally bio-inspired and derived from natural sources are particularly preferred. Delivery of vaccines is also an active area of research in this field. Bacterial cells and their components that have been used for drug delivery, include the crystalline cell-surface layer known as "S-layer", bacterial ghosts, bacterial outer membrane vesicles, and bacterial products or derivatives (e.g. spores, polymers, and magnetic nanoparticles). Considering the origin of these components from potentially pathogenic microorganisms, it is not surprising that they have been applied for vaccines and immunization. The present review critically summarizes their applications focusing on their advantages for delivery of drugs, genes, and vaccines.

Microencapsulation of Phosphorylated Human-Like Collagen-Calcium Chelates for Controlled Delivery and Improved Bioavailability

The bioavailability of Phosphorylated Human-like Collagen-calcium chelates (PHLC-Ca) as calcium supplement is influenced by the extremely low pH and proteolytic enzymes in the gastrointestinal tract. This study addresses these issues by microencapsulation technology using alginate (ALG) and chitosan (CS) as wall materials. The different ratio of ALG to PHLC-Ca on microcapsules encapsulation efficiency (EE) and loading capacity (LC) was evaluated and 1:1/2 was selected as the optimal proportion. The microcapsules were micron-sized and spherical in shape. PHLC-Ca was successfully entrapped into the matrix of ALG through forming intermolecular hydrogen bonding or other interactions. The confocal laser scanning microscopy (CLSM) indicated that CS was coated on ALG microspheres. The MTT assay exhibited that CS/ALG-(PHLC-Ca) microcapsules extracts were safe to L929. The animal experiment showed that CS/ALG-(PHLC-Ca) microcapsules was superior to treating osteoporosis than PHLC-Ca. These results illustrated that the bioavailability of PHLC-Ca was improved by microencapsulated.

Modulating the release of proteins from a loaded carrier of alginate/gelatin porous spheres immersed in different solutions

BACKGROUND

A biodegradable porous particle for the controlled biofactor delivery which assembly of pores in scaffolds can improve the permeation and diffusion of drugs or growth factors.

OBJECTIVE

Porous-spheres in millimeter scale were prepared by mixing sodium alginate and gelatin interpenetrating networks with cross-linkers; interconnected open pores were fabricated through solvent casting and particulate leaching.

METHODS

Morphological characteristics, degradation, and bovine serum albumin (BSA) release rates of the porous-spheres immersed in three different solutions, namely, deionized distilled water, simulated body fluid (SBF), and phosphate-buffered saline (PBS), were detected.

RESULTS

Porous-spheres with a large amount of gelatin exhibited an increase in water absorption rates without affecting scaffold strength and no cytotoxicity was elicited. Highly interconnected pores with a diameter of 100-200 µm were uniformly distributed in scaffolds. The weight loss in PBS was faster than that in other solutions; the highest release rate of BSA in SBF was observed for 2 h. The release rates also exhibited linear patterns from 2 h to 24 h in all of the groups.

CONCLUSIONS

After 1 d of immersion in solutions, BSA release rates in scaffolds logarithmically decreased for 14 d. The degradation of porous-spheres also showed an inverse pattern.

Anisotropic dehydration of hydrogel surfaces

Efforts to develop tissue-engineered skin for regenerative medicine have explored natural, synthetic, and hybrid hydrogels. The creation of a bilayer material, with the stratification exhibited by native skin, is a complex problem. The mechanically robust, waterproof epidermis presents the stratum corneum at the tissue/air interface, which confers many of these protective properties. In this work, we explore the effect of high temperatures on alginate hydrogels, which are widely employed for tissue engineering due to their excellent mechanical properties and cellular compatibility. In particular, we investigate the rapid dehydration of the hydrogel surface which occurs following local exposure to heated surfaces with temperatures in the range 100–200 °C. We report the creation of a mechanically strengthened hydrogel surface, with improved puncture resistance and increased coefficient of friction, compared to an unheated surface. The use of a mechanical restraint during heating promoted differences in the rate of mass loss; the rate of temperature increase within the hydrogel, in the presence and absence of restraint, is simulated and discussed. It is hoped that the results will be of use in the development of processes suitable for preparing skin-like analogues; application areas could include wound healing and skin restoration.

A Multiplexed, Gradient-Based, Full-Hydrogel Microfluidic Platform for Rapid, High-Throughput Antimicrobial Susceptibility Testing

Antimicrobial resistance has become an immediate threat to modern healthcare systems as it continues to spread across the globe. As development of novel antibiotics stalls, preserving the effectiveness of existing agents has become a priority. One of the major driving forces behind antimicrobial resistance is the misuse and overuse of antibiotics, often a result of data on the susceptibility of pathogens not being obtained in a convenient and timely manner, a need that conventional antimicrobial susceptibility testing struggles to meet. Here, a hydrogel microfluidic platform is reported for antimicrobial susceptibility testing purposes, capable of handling real samples and yielding results within 2.5 h of culture. By using a multiplayer design with channels crossing overhead of each other, multiple experiments, either one- or two-dimensional, can be staged on the same device. Bacteria grown on the surface of the hydrogel can be easily visualized with standard Gram staining after being transferred onto a glass slide. Coupled with software-based image analysis, the system can yield a variety of useful information on bacterial susceptibility and the effects of drugs, such as minimum inhibitory concentration and morphological changes in bacteria, either individually or in combination. Compared to conventional testing methods, this system requires less labor, reagents, and equipment to operate, and has significantly higher speed and efficiency.

Synergistic effect of divalent cations in improving technological properties of cross-linked alginate beads

Gelling solution parameters are some of the most important variables in ionotropic gelation and consequently influence the technological characteristics of the product. To date, only a few studies have focused on the simultaneous use of multiple cations as gelling agents. With the aim to deeply explore this possibility, in this research we investigated the effect of two divalent cations (Ca²⁺ and Zn²⁺) on alginate beads formation and properties. Alginate beads containing prednisolone (P) as model drug were prepared by prilling technique. The main critical variables of the ionotropic gelation process i.e. composition of the aqueous feed solutions (sodium alginate and prednisolone concentration) and cross-linking conditions (Ca²⁺, Zn²⁺ or Ca²⁺+Zn²⁺), were studied. The obtained beads were characterized and their in vitro release performances were assessed in conditions simulating the gastrointestinal environment. Results evidenced a synergistic effect of the two cations, affecting positively both the encapsulation efficiency and the ability of the alginate polymeric matrix to control the drug release. A Ca²⁺/Zn²⁺ ratio of 4:1, in fact, exploited the Ca²⁺ ability of establish quicker electrostatic interactions with guluronic groups of alginate and the Zn²⁺ ability to establish covalent-like bonds with carboxylate groups of both guluronic and mannuronic moieties of alginate.

S. S, Agarwal T, Pradhan S, Pal K, Giri S, Maiti TK, Banerjee I. Gum tragacanth–alginate beads as proangiogenic–osteogenic cell encapsulation systems for bone tissue engineering

The presence of gum tragacanth in calcium alginate beads makes them more osteo-conductive and proangiogenic.

Engineered Gellan Polysaccharides in the Design of Controlled Drug Delivery Systems

Natural polysaccharides are getting increasing attention in the development of pharmaceutical dosage forms due to their encouraging reports on nontoxicity and biodegradability. Natural gums can also be engineered to have better materials for drug delivery system design. Gellan gum originates from microbial fermentation and has been declared as safe by US FDA for human consumption. It possesses gelling ability in presence of multivalent earth metal cations and thus enabled the design of mutiparticulate drug delivery systems in completely aqueous environment avoiding the use of organic solvents. Due to faster drug release profiles of divalent cation-induced gellan gum particles, nowadays chemically modified forms of gellan polysaccharide are currently being investigated for the controlled release of drugs. This chapter discusses the factors contributing to the varying gelling characteristics of gellan gum and the recent developments in its chemical modification towards the fabrication of novel controlled drug delivery devices.

Calcium-alginate microparticles for sustained release of catechin prepared via an emulsion gelation technique

Catechin-loaded Ca-alginate beads and microparticles were prepared by an emulsion gelation method using sunflower oil for efficient sustained release of catechin. The emulsion was prepared by sequential mixing of alginate, oil, and oleic acid ester as an emulsifier. Encapsulation efficiency (EE) and inhibition of catechin release of the beads were significantly increased approximately to 453.83 and 148.71% by the emulsion gelation technique, respectively (p<0.05). For the microparticles, the highest inhibition of catechin release after 1 h of incubation (78.82%) was observed at the microparticles prepared by 5% (w/w) oil, 3% (w/w) alginate, 4% (w/v) CaCl₂, and 200 mg catechin with the most hydrophilic emulsifier, decaglycerol mono-ester. Moreover, the catechin release was sustained at acidic conditions and increased with increase in pH of release medium. These results suggest that catechin encapsulation within Ca-alginate particles by emulsion gelation method can be an effective delivery system for catechin.

Mechanically Stiff, Zinc Cross-Linked Nanocomposite Scaffolds with Improved Osteostimulation and Antibacterial Properties

Nanocomposite scaffolds are studied widely due to their resemblance with the natural extracellular matrix of bone; but their use as a bone tissue engineered scaffold is clinically hampered due to low mechanical stiffness, inadequate osteoconduction, and graft associated infections. The purpose of the current study was the development of a mechanically stiff nanocomposite scaffold using biodegradable gellan and xanthan polymers reinforced with bioglass nanoparticles (nB) (Size: 20-120 nm). These nanocomposite scaffolds were cross-linked with zinc sulfate ions to improve their osteoconduction and antibacterial properties for the regeneration of a functional bone. The compressive strength and modulus of the optimized nanocomposite scaffold (1% w/v polymer reinforced with 4%w/v nB nanoparticles, cross-linked with 1.5 mM zinc sulfate) was 1.91 ± 0.31 MPa and 20.36 ± 1.08 MPa, respectively, which was comparable to the trabecular bone and very high compared to nanocomposite scaffolds reported in earlier studies. Further, in vitro simulated body fluid (SBF) study suggested deposition of biomimetic apatite on the surface of zinc cross-linked nanocomposite scaffolds confirming their bioactivity. MG 63 osteoblast-like cells cultured with the nanocomposite scaffolds responded to matrix stiffness with better adhesion, spreading and cellular interconnections compared to the polymeric gellan and xanthan scaffolds. Incorporation of bioglass nanoparticles and zinc cross-linker in nanocomposite scaffolds demonstrated 62% increment in expression of alkaline phosphatase activity (ALP) and 150% increment in calcium deposition of MG 63 osteoblast-like cells compared to just gellan and xanthan polymeric scaffolds. Furthermore, zinc cross-linked nanocomposite scaffolds significantly inhibited the growth of Gram-positive Bacillus subtilis (70% reduction) and Gram-negative Escherichia coli (81% reduction) bacteria. This study demonstrated a facile approach to tune the mechanical stiffness, bioactivity, osteoconduction potential and bacteriostatic properties of scaffolds, which marked it as a potential bone tissue engineered scaffold.

Ion exchange in alginate gels--dynamic behaviour revealed by electron paramagnetic resonance

The formation of alginate gel from low molecular weight alginate and very low molecular weight alginate in the presence of divalent cations was investigated using Electron Paramagnetic Resonance (EPR) spectroscopy. The transition from sol to gel in the presence of divalent cations was monitored by the changes in the dynamics of spin labelled alginate. The immobilisation of the spin labelled alginate in the gel reflects the strength of interaction between the cation and alginate chain. Diffusion experiments showed that both the cation and alginate polyanion in the gel fibres can exchange with molecules in solution. In particular, we showed that dissolved alginate polyanions can replace alginates in the gel fibres, which can hence diffuse through the bulk of the gel. This illustrates the surprisingly highly dynamic nature of these gels and opens up the possibility of preparing multicomponent alginate gels via polyanion exchange process.

Synthesis of conducting asymmetric hydrogel particles showing autonomous motion

In the present work, we introduce a new approach for the synthesis of asymmetric particles made from electrically conducting polyaniline-alginate hydrogels by using bipolar electrochemistry. Such an intrinsic break of symmetry allows the soft beads to exhibit tunable motion at the air/water interface when loaded with ethanol due to controllable directed release of the solvent.

Spatial regulation of controlled bioactive factor delivery for bone tissue engineering

Limitations of current treatment options for critical size bone defects create a significant clinical need for tissue engineered bone strategies. This review describes how control over the spatiotemporal delivery of growth factors, nucleic acids, and drugs and small molecules may aid in recapitulating signals present in bone development and healing, regenerating interfaces of bone with other connective tissues, and enhancing vascularization of tissue engineered bone. State-of-the-art technologies used to create spatially controlled patterns of bioactive factors on the surfaces of materials, to build up 3D materials with patterns of signal presentation within their bulk, and to pattern bioactive factor delivery after scaffold fabrication are presented, highlighting their applications in bone tissue engineering. As these techniques improve in areas such as spatial resolution and speed of patterning, they will continue to grow in value as model systems for understanding cell responses to spatially regulated bioactive factor signal presentation in vitro, and as strategies to investigate the capacity of the defined spatial arrangement of these signals to drive bone regeneration in vivo.