Alginate: properties and biomedical applications

Multipotent stromal cells derived from common marmoset Callithrix jacchus within alginate 3D environment: Effect of cryopreservation procedures

Multipotent stromal cells derived from the common marmoset monkey Callithrix jacchus (cjMSCs) possess high phylogenetic similarity to humans, with a great potential for preclinical studies in the field of regenerative medicine. Safe and effective long-term storage of cells is of great significance to clinical and research applications. Encapsulation of such cell types within alginate beads that can mimic an extra-cellular matrix and provide a supportive environment for cells during cryopreservation, has several advantages over freezing of cells in suspension. In this study we have analysed the effect of dimethyl sulfoxide (Me2SO, 2.5-10%, v/v) and pre-freeze loading time of alginate encapsulated cjMSCs in Me2SO (0-45 min) on the viability and metabolic activity of the cells after freezing using a slow cooling rate (-1°C/min). It was found that these parameters affect the stability and homogeneity of alginate beads after thawing. Moreover, the cjMSCs can be frozen in alginate beads with lower Me2SO concentration of 7.5% after 30 min of loading, while retaining high cryopreservation outcome. We demonstrated the maximum viability, membrane integrity and metabolic activity of the cells under optimized, less cytotoxic conditions. The results of this study are another step forward towards the application of cryopreservation for the long-term storage and subsequent applications of transplants in cell-based therapies.

Coaxial electrospray of liquid core-hydrogel shell microcapsules for encapsulation and miniaturized 3D culture of pluripotent stem cells

A novel coaxial electrospray technology is developed to generate microcapsules with a hydrogel shell of alginate and an aqueous liquid core of living cells using two aqueous fluids in one step. Approximately 50 murine embryonic stem (ES) cells encapsulated in the core with high viability (92.3 ± 2.9%) can proliferate to form a single ES cell aggregate of 128.9 ± 17.4 μm in each microcapsule within 7 days. Quantitative analyses of gene and protein expression indicate that ES cells cultured in the miniaturized 3D liquid core of the core-shell microcapsules have significantly higher pluripotency on average than the cells cultured on the 2D substrate or in the conventional 3D alginate hydrogel microbeads without a core-shell architecture. The higher pluripotency is further suggested by their significantly higher capability of differentiation into beating cardiomyocytes and higher expression of cardiomyocyte specific gene markers on average after directed differentiation under the same conditions. Considering its wide availability, easiness to set up and operate, reusability, and high production rate, the novel coaxial electrospray technology together with the microcapsule system is of importance for mass production of ES cells with high pluripotency to facilitate translation of the emerging pluripotent stem cell-based regenerative medicine into the clinic.

Delivering MC3T3-E1 cells into injectable calcium phosphate cement through alginate-chitosan microcapsules for bone tissue engineering

OBJECTIVE

To deliver cells deep into injectable calcium phosphate cement (CPC) through alginate-chitosan (AC) microcapsules and investigate the biological behavior of the cells released from microcapsules into the CPC.

METHODS

Mouse osteoblastic MC3T3-E1 cells were embedded in alginate and AC microcapsules using an electrostatic droplet generator. The two types of cell-encapsulating microcapsules were then mixed with a CPC paste. MC3T3-E1 cell viability was investigated using a Wst-8 kit, and osteogenic differentiation was demonstrated by an alkaline phosphatase (ALP) activity assay. Cell attachment in CPC was observed by an environment scanning electron microscopy.

RESULTS

Both alginate and AC microcapsules were able to release the encapsulated MC3T3-E1 cells when mixed with CPC paste. The released cells attached to the setting CPC scaffolds, survived, differentiated, and formed mineralized nodules. Cells grew in the pores concomitantly created by the AC microcapsules in situ within the CPC. At Day 21, cellular ALP activity in the AC group was approximately four times that at Day 7 and exceeded that of the alginate microcapsule group (P<0.05). Pores formed by the AC microcapsules had a diameter of several hundred microns and were spherical compared with those formed by alginate microcapsules.

CONCLUSIONS

AC microcapsule is a promising carrier to release seeding cells deep into an injectable CPC scaffold for bone engineering.

Characterization and cytocompatibility of a new injectable multiphasic bone substitute based on a combination of polysaccharide gel-coated OSPROLIFE(®) HA/TTCP granules and bone marrow concentrate

The purpose of this study was to examine the in vitro cytocompatibility of a novel injectable multiphasic bone substitute (MBS) based on polysaccharide gel-coated OSPROLIFE(®) hydroxyapatite (HA)/tetracalcium phosphate (TTCP) granules combined with bone marrow concentrate (BMC). Polysaccharide gel-coated granules loaded in syringe were combined with BMC diluted in ionic crosslinking solution. The product was then maintained in culture to investigate the cytocompatibility, distribution, and osteogenic differentiation function of cells contained in the BMC. The in vitro cytocompatibility was assessed after 0, 24, and 96 h from the injectable MBS preparation using the LIVE/DEAD(®) staining kit. The results highlighted that cells remained viable after combination with the polysaccharide gel-coated granules; also, viability was maintained over time. The distribution of the cells in the product, observed using confocal microscopy, showed viable cells immersed in the polysaccharide gel formed between the granules after ionic crosslinking. The mesenchymal stromal cells (MSC) contained in the injectable MBS, the basic elements for bone tissue regeneration, were able to differentiate toward osteoblasts, producing an osteogenic matrix as evidenced by alizarin red-s (AR-S) staining. In conclusion, we found that the injectable MBS may have the potential to be used as a bone substitute by applying a "one-step" procedure in bone tissue engineering applications. © 2015 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 104B: 894-902, 2016.

Surface Modification and Characterisation of Silk Fibroin Fabric Produced by the Layer-by-Layer Self-Assembly of Multilayer Alginate/Regenerated Silk Fibroin

Silk-based medical products have a long history of use as a material for surgical sutures because of their desirable mechanical properties. However, silk fibroin fabric has been reported to be haemolytic when in direct contact with blood. The layer-by-layer self-assembly technique provides a method for surface modification to improve the biocompatibility of silk fibroin fabrics. Regenerated silk fibroin and alginate, which have excellent biocompatibility and low immunogenicity, are outstanding candidates for polyelectrolyte deposition. In this study, silk fabric was degummed and positively charged to create a silk fibroin fabric that could undergo self-assembly. The multilayer self-assembly of the silk fibroin fabric was achieved by alternating the polyelectrolyte deposition of a negatively charged alginate solution (pH = 8) and a positively charged regenerated silk fibroin solution (pH = 2). Finally, the negatively charged regenerated silk fibroin solution (pH = 8) was used to assemble the outermost layer of the fabric so that the surface would be negatively charged. A stable structural transition was induced using 75% ethanol. The thickness and morphology were characterised using atomic force microscopy. The properties of the self-assembled silk fibroin fabric, such as the bursting strength, thermal stability and flushing stability, indicated that the fabric was stable. In addition, the cytocompatibility and haemocompatibility of the self-assembled silk fibroin fabrics were evaluated. The results indicated that the biocompatibility of the self-assembled multilayers was acceptable and that it improved markedly. In particular, after the self-assembly, the fabric was able to prevent platelet adhesion. Furthermore, other non-haemolytic biomaterials can be created through self-assembly of more than 1.5 bilayers, and we propose that self-assembled silk fibroin fabric may be an attractive candidate for anticoagulation applications and for promoting endothelial cell adhesion for vascular prostheses.

Hollow chitosan/alginate nanocapsules for bioactive compound delivery

This work aimed at the development of biodegradable nanocapsules as carriers of two bioactive compounds, 5-aminosalycilic acid and glycomacropeptide. Nanocapsules were produced through layer-by-layer (LbL) deposition of chitosan (CH) and alginate (ALG) layers on polystyrene nanoparticles. The bioactive compounds were incorporated on the third layer of the nanocapsules being its encapsulation efficiency and release behaviour evaluated. The LbL deposition process, stability, morphology and size of the multilayer nanocapsules were monitored by means of zeta potential and transmission electron microscopy (TEM). The bioactive compounds release from the CH/ALG nanocapsules was successfully described by a mathematical model (linear superimposition model - LSM), which allowed concluding that bioactive compounds release is due to both Brownian motion and the polymer relaxation of the CH/ALG layers. Final results demonstrated that the synthesized LbL hollow nanocapsules presented spherical morphology and a good capacity to encapsulate different bioactive compounds, being the best results obtained for the system containing 5-aminosalycilic acid (with an encapsulation efficiency of approximately 70%). CH/ALG multilayer nanocapsules could be a promising carrier of bioactive compounds for applications in food and pharmaceutical industries.

Incorporation of antimicrobial peptides on functionalized cotton gauzes for medical applications

A large group of low molecular weight natural compounds that exhibit antimicrobial activity has been isolated from animals and plants during the past two decades. Among them, peptides are the most widespread resulting in a new generation of antimicrobial agents with higher specific activity. In the present study we have developed a new strategy to obtain antimicrobial wound-dressings based on the incorporation of antimicrobial peptides into polyelectrolyte multilayer films built by the alternate deposition of polycation (chitosan) and polyanion (alginic acid sodium salt) over cotton gauzes. Energy dispersive X ray microanalysis technique was used to determine if antimicrobial peptides penetrated within the films. FTIR analysis was performed to assess the chemical linkages, and antimicrobial assays were performed with two strains: Staphylococcus aureus (Gram-positive bacterium) and Klebsiella pneumonia (Gram-negative bacterium). Results showed that all antimicrobial peptides used in this work have provided a higher antimicrobial effect (in the range of 4 log-6 log reduction) for both microorganisms, in comparison with the controls, and are non-cytotoxic to normal human dermal fibroblasts at the concentrations tested.

Microbial trench-based optofluidic system for reagentless determination of phenolic compounds

Phenolic compounds are one of the main contaminants of soil and water due to their toxicity and persistence in the natural environment. Their presence is commonly determined with bulky and expensive instrumentation (e.g. chromatography systems), requiring sample collection and transport to the laboratory. Sample transport delays data acquisition, postponing potential actions to prevent environmental catastrophes. This article presents a portable, miniaturized, robust and low-cost microbial trench-based optofluidic system for reagentless determination of phenols in water. The optofluidic system is composed of a poly(methyl methacrylate) structure, incorporating polymeric optical elements and miniaturized discrete auxiliary components for optical transduction. An electronic circuit, adapted from a lock-in amplifier, is used for system control and interfering ambient light subtraction. In the trench, genetically modified bacteria are stably entrapped in an alginate hydrogel for quantitative determination of model phenol catechol. Alginate is also acting as a diffusion barrier for compounds present in the sample. Additionally, the superior refractive index of the gel (compared to water) confines the light in the lower level of the chip. Hence, the optical readout of the device is only altered by changes in the trench. Catechol molecules (colorless) in the sample diffuse through the alginate matrix and reach bacteria, which degrade them to a colored compound. The absorbance increase at 450 nm reports the presence of catechol simply, quickly (~10 min) and quantitatively without addition of chemical reagents. This miniaturized, portable and robust optofluidic system opens the possibility for quick and reliable determination of environmental contamination in situ, thus mitigating the effects of accidental spills.

Alginate/nanohydroxyapatite scaffolds with designed core/shell structures fabricated by 3D plotting and in situ mineralization for bone tissue engineering

Composite scaffolds, especially polymer/hydroxyapatite (HAP) composite scaffolds with predesigned structures, are promising materials for bone tissue engineering. Various methods including direct mixing of HAP powder with polymers or incubating polymer scaffolds in simulated body fluid for preparing polymer/HAP composite scaffolds are either uncontrolled or require long times of incubation. In this work, alginate/nano-HAP composite scaffolds with designed pore parameters and core/shell structures were fabricated using 3D plotting technique and in situ mineralization under mild conditions (at room temperature and without the use of any organic solvents). Light microscopy, scanning electron microscopy, microcomputer tomography, X-ray diffraction, and Fourier transform infrared spectroscopy were applied to characterize the fabricated scaffolds. Mechanical properties and protein delivery of the scaffolds were evaluated, as well as the cell response to the scaffolds by culturing human bone-marrow-derived mesenchymal stem cells (hBMSC). The obtained data indicate that this method is suitable to fabricate alginate/nano-HAP composite scaffolds with a layer of nano-HAP, coating the surface of the alginate strands homogeneously and completely. The surface mineralization enhanced the mechanical properties and improved the cell attachment and spreading, as well as supported sustaining protein release, compared to pure alginate scaffolds without nano-HAP shell layer. The results demonstrated that the method provides an interesting option for bone tissue engineering application.

Naturally derived and synthetic scaffolds for skeletal muscle reconstruction

Skeletal muscle tissue has an inherent capacity for regeneration following injury. However, severe trauma, such as volumetric muscle loss, overwhelms these natural muscle repair mechanisms prompting the search for a tissue engineering/regenerative medicine approach to promote functional skeletal muscle restoration. A desirable approach involves a bioscaffold that simultaneously acts as an inductive microenvironment and as a cell/drug delivery vehicle to encourage muscle ingrowth. Both biologically active, naturally derived materials (such as extracellular matrix) and carefully engineered synthetic polymers have been developed to provide such a muscle regenerative environment. Next generation naturally derived/synthetic "hybrid materials" would combine the advantageous properties of these materials to create an optimal platform for cell/drug delivery and possess inherent bioactive properties. Advances in scaffolds using muscle tissue engineering are reviewed herein.

Functionalizing Soft Matter for Molecular Communication

The information age was enabled by advances in microfabrication and communication theory that allowed information to be processed by electrons and transmitted by electromagnetic radiation. Despite immense capabilities, microelectronics has limited abilities to access and participate in the molecular-based communication that characterizes our biological world. Here, we use biological materials and methods to create components and fabricate devices to perform simple molecular communication functions based on bacterial quorum sensing (QS). Components were created by protein engineering to generate a multidomain fusion protein capable of sending a molecular QS signal, and by synthetic biology to engineer E. coli to receive and report this QS signal. The device matrix was formed using stimuli-responsive hydrogel-forming biopolymers (alginate and gelatin). Assembly of the components within the device matrix was achieved by physically entrapping the cell-based components, and covalently conjugating the protein-based components using the enzyme microbial transglutaminase. We demonstrate simple devices that can send or receive a molecular QS signal to/from the surrounding medium, and a two-component device in which one component generates the signal (i.e., issues a command) that is acted upon by the second component. These studies illustrate the broad potential of biofabrication to generate molecular communication devices.

3D Cell Culture in Alginate Hydrogels

This review compiles information regarding the use of alginate, and in particular alginate hydrogels, in culturing cells in 3D. Knowledge of alginate chemical structure and functionality are shown to be important parameters in design of alginate-based matrices for cell culture. Gel elasticity as well as hydrogel stability can be impacted by the type of alginate used, its concentration, the choice of gelation technique (ionic or covalent), and divalent cation chosen as the gel inducing ion. The use of peptide-coupled alginate can control cell-matrix interactions. Gelation of alginate with concomitant immobilization of cells can take various forms. Droplets or beads have been utilized since the 1980s for immobilizing cells. Newer matrices such as macroporous scaffolds are now entering the 3D cell culture product market. Finally, delayed gelling, injectable, alginate systems show utility in the translation of in vitro cell culture to in vivo tissue engineering applications. Alginate has a history and a future in 3D cell culture. Historically, cells were encapsulated in alginate droplets cross-linked with calcium for the development of artificial organs. Now, several commercial products based on alginate are being used as 3D cell culture systems that also demonstrate the possibility of replacing or regenerating tissue.

Calcium alginate gels as stem cell matrix-making paracrine stem cell activity available for enhanced healing after surgery

Regeneration after surgery can be improved by the administration of anabolic growth factors. However, to locally maintain these factors at the site of regeneration is problematic. The aim of this study was to develop a matrix system containing human mesenchymal stem cells (MSCs) which can be applied to the surgical site and allows the secretion of endogenous healing factors from the cells. Calcium alginate gels were prepared by a combination of internal and external gelation. The gelling behaviour, mechanical stability, surface adhesive properties and injectability of the gels were investigated. The permeability of the gels for growth factors was analysed using bovine serum albumin and lysozyme as model proteins. Human MSCs were isolated, cultivated and seeded into the alginate gels. Cell viability was determined by AlamarBlue assay and fluorescence microscopy. The release of human VEGF and bFGF from the cells was determined using an enzyme-linked immunoassay. Gels with sufficient mechanical properties were prepared which remained injectable through a syringe and solidified in a sufficient time frame after application. Surface adhesion was improved by the addition of polyethylene glycol 300,000 and hyaluronic acid. Humans MSCs remained viable for the duration of 6 weeks within the gels. Human VEGF and bFGF was found in quantifiable concentrations in cell culture supernatants of gels loaded with MSCs and incubated for a period of 6 weeks. This work shows that calcium alginate gels can function as immobilization matrices for human MSCs.

Green materials science and engineering reduces biofouling: approaches for medical and membrane-based technologies

Numerous engineered and natural environments suffer deleterious effects from biofouling and/or biofilm formation. For instance, bacterial contamination on biomedical devices pose serious health concerns. In membrane-based technologies, such as desalination and wastewater reuse, biofouling decreases membrane lifetime, and increases the energy required to produce clean water. Traditionally, approaches have combatted bacteria using bactericidal agents. However, due to globalization, a decline in antibiotic discovery, and the widespread resistance of microbes to many commercial antibiotics and metallic nanoparticles, new materials, and approaches to reduce biofilm formation are needed. In this mini-review, we cover the recent strategies that have been explored to combat microbial contamination without exerting evolutionary pressure on microorganisms. Renewable feedstocks, relying on structure-property relationships, bioinspired/nature-derived compounds, and green processing methods are discussed. Greener strategies that mitigate biofouling hold great potential to positively impact human health and safety.

Comparison of the topical haemostatic efficacy of nano-micro particles of clinoptilolite and kaolin in a rat model of haemorrhagic injury

PURPOSE

This study was designed to investigate if the potential haemostatic efficacy of gauze-impregnated clinoptilolite created with nano-technology is as strong as the widely used kaolin to control pulsatile arterial bleeding due to major vascular injury.

METHODS

42 rats were separated into three groups of kaolin, clinoptilolite and control groups. The femoral artery was isolated and active arterial haemorrhage was performed. After 30 s of free arterial haemorrhage, compression was applied with a standard 100 g scale and haemostasis was assessed at the 1st, 3rd and 5th minutes. All groups were observed throughout 60 min for survival without any fluid resuscitation and the mean arterial pressure, pulse, body/surface temperature and arterial blood gas values were measured.

RESULTS

In the control group, haemostasis did not develop in any of the 12 rats and the survival rate was 5/12 (41.66 %). In the kaolin group, haemostasis developed in seven rats and of these, bleeding reoccurred in four. The survival rate was 10/13 (76.92 %). In the clinoptilolite group, haemostasis developed in eight rats and bleeding recurred in only one. The survival rate was 100 %. In terms of survival, the clinoptilolite and kaolin groups showed superiority to the control group (p = 0.002, p = 0.082). In the evaluation of recurrent haemorrhaging in the rats with haemostasis, clinoptilolite was observed to provide better coagulation than kaolin.

CONCLUSION

A statistically significant difference was determined in clinoptilolite and kaolin group, when they are separately compared with the control group in respect of the effect on MAP, HCO3 (-), lactate, base excess, haemostasis duration and survival rates. The effect of clinoptilolite on haemostasis and survival time was observed to be at least as good as that of kaolin; therefore, clinoptilolite can be used as an active ingredient in a topical haemostat.

Digital microfluidic three-dimensional cell culture and chemical screening platform using alginate hydrogels

Electro wetting-on-dielectric (EWOD) digital microfluidics (DMF) can be used to develop improved chemical screening platforms using 3-dimensional (3D) cell culture. Alginate hydrogels are one common method by which a 3D cell culture environment is created. This paper presents a study of alginate gelation on EWOD DMF and investigates designs to obtain uniform alginate hydrogels that can be repeatedly addressed by any desired liquids. A design which allows for gels to be retained in place during liquid delivery and removal without using any physical barriers or hydrophilic patterning of substrates is presented. A proof of concept screening platform is demonstrated by examining the effects of different concentrations of a test chemical on 3D cells in alginate hydrogels. In addition, the temporal effects of the various chemical concentrations on different hydrogel posts are demonstrated, thereby establishing the benefits of an EWOD DMF 3D cell culture and chemical screening platform using alginate hydrogels.

3D porous calcium-alginate scaffolds cell culture system improved human osteoblast cell clusters for cell therapy

Age-related orthopedic disorders and bone defects have become a critical public health issue, and cell-based therapy is potentially a novel solution for issues surrounding bone tissue engineering and regenerative medicine. Long-term cultures of primary bone cells exhibit phenotypic and functional degeneration; therefore, culturing cells or tissues suitable for clinical use remain a challenge. A platform consisting of human osteoblasts (hOBs), calcium-alginate (Ca-Alginate) scaffolds, and a self-made bioreactor system was established for autologous transplantation of human osteoblast cell clusters. The Ca-Alginate scaffold facilitated the growth and differentiation of human bone cell clusters, and the functionally-closed process bioreactor system supplied the soluble nutrients and osteogenic signals required to maintain the cell viability. This system preserved the proliferative ability of cells and cell viability and up-regulated bone-related gene expression and biological apatite crystals formation. The bone-like tissue generated could be extracted by removal of calcium ions via ethylenediaminetetraacetic acid (EDTA) chelation, and exhibited a size suitable for injection. The described strategy could be used in therapeutic application and opens new avenues for surgical interventions to correct skeletal defects.

Clinical applications of naturally derived biopolymer-based scaffolds for regenerative medicine

Naturally derived polymeric biomaterials, such as collagens, silks, elastins, alginates, and fibrins are utilized in tissue engineering due to their biocompatibility, bioactivity, and tunable mechanical and degradation kinetics. The use of these natural biopolymers in biomedical applications is advantageous because they do not release cytotoxic degradation products, are often processed using environmentally-friendly aqueous-based methods, and their degradation rates within biological systems can be manipulated by modifying the starting formulation or processing conditions. For these reasons, many recent in vivo investigations and FDA-approval of new biomaterials for clinical use have utilized natural biopolymers as matrices for cell delivery and as scaffolds for cell-free support of native tissues. This review highlights biopolymer-based scaffolds used in clinical applications for the regeneration and repair of native tissues, with a focus on bone, skeletal muscle, peripheral nerve, cardiac muscle, and cornea substitutes.

Natural-based nanocomposites for bone tissue engineering and regenerative medicine: a review

Tissue engineering and regenerative medicine has been providing exciting technologies for the development of functional substitutes aimed to repair and regenerate damaged tissues and organs. Inspired by the hierarchical nature of bone, nanostructured biomaterials are gaining a singular attention for tissue engineering, owing their ability to promote cell adhesion and proliferation, and hence new bone growth, compared with conventional microsized materials. Of particular interest are nanocomposites involving biopolymeric matrices and bioactive nanosized fillers. Biodegradability, high mechanical strength, and osteointegration and formation of ligamentous tissue are properties required for such materials. Biopolymers are advantageous due to their similarities with extracellular matrices, specific degradation rates, and good biological performance. By its turn, calcium phosphates possess favorable osteoconductivity, resorbability, and biocompatibility. Herein, an overview on the available natural polymer/calcium phosphate nanocomposite materials, their design, and properties is presented. Scaffolds, hydrogels, and fibers as biomimetic strategies for tissue engineering, and processing methodologies are described. The specific biological properties of the nanocomposites, as well as their interaction with cells, including the use of bioactive molecules, are highlighted. Nanocomposites in vivo studies using animal models are also reviewed and discussed.

Recent Advances in Nanocomposite Materials of Graphene Derivatives with Polysaccharides

This review article presents the recent advances in syntheses and applications of nanocomposites consisting of graphene derivatives with various polysaccharides. Graphene has recently attracted much interest in the materials field due to its unique 2D structure and outstanding properties. To follow, the physical and mechanical properties of graphene are then introduced. However it was observed that the synthesis of graphene-based nanocomposites had become one of the most important research frontiers in the application of graphene. Therefore, this review also summarizes the recent advances in the synthesis of graphene nanocomposites with polysaccharides, which are abundant in nature and are easily synthesized bio-based polymers. Polysaccharides can be classified in various ways such as cellulose, chitosan, starch, and alginates, each group with unique and different properties. Alginates are considered to be ideal for the preparation of nanocomposites with graphene derivatives due to their environmental-friendly potential. The characteristics of such nanocomposites are discussed here and are compared with regard to their mechanical properties and their various applications.

Self-assembled gold coating enhances X-ray imaging of alginate microcapsules

Therapeutic biomolecules produced from cells encapsulated within alginate microcapsules (MCs) offer a potential treatment for a number of diseases. However the fate of such MCs once implanted into the body is difficult to establish. Labelling the MCs with medical imaging contrast agents may aid their detection and give researchers the ability to track them over time thus aiding the development of such cellular therapies. Here we report the preparation of MCs with a self-assembled gold nanoparticle (AuNPs) coating which results in distinctive contrast and enables them to be readily identified using a conventional small animal X-ray micro-CT scanner. Cationic Reversible Addition-Fragmentation chain Transfer (RAFT) homopolymer modified AuNPs (PAuNPs) were coated onto the surface of negatively charged alginate MCs resulting in hybrids which possessed low cytotoxicity and high mechanical stability in vitro. As a result of their high localized Au concentration, the hybrid MCs exhibited a distinctive bright circular ring even with a low X-ray dose and rapid scanning in post-mortem imaging experiments facilitating their positive identification and potentially enabling them to be used for in vivo tracking experiments over multiple time-points.

Novel alginate-based nanocarriers as a strategy to include high concentrations of hydrophobic compounds in hydrogels for topical application

The cutaneous penetration of hydrophobic active molecules is of foremost concern in the dermatology and cosmetic formulation fields. The poor solubility in water of those molecules limits their use in hydrophilic forms such as gels, which are favored by patients with chronic skin disease. The aim of this work is to design a novel nanocarrier of hydrophobic active molecules and to determine its potential as an ingredient of a topical form. The nanocarrier consists of an oily core surrounded by a protective shell of alginate, a natural polysaccharide isolated from brown algae. These calcium alginate-based nanocarriers (CaANCs) were prepared at room temperature and without the use of organic solvent by an accelerated nanoemulsification-polymer crosslinking method. The size (hydrodynamic diameter ~200 nm) and surface charge (zeta potential ~ - 30 mV) of the CaANCs are both compatible with their application on skin. CaANCs loaded with a fluorescent label were stable in model hydrophilic galenic forms under different storage conditions. Curcumin was encapsulated in CaANCs with an efficiency of ~95%, fully retaining its antioxidant activity. The application of the curcumin-loaded CaANCs on excised human skin led to a significant accumulation of the active molecules in the upper layers of the skin, asserting the potential of these nanocarriers in active pharmaceutical and cosmetic ingredients topical delivery.

Polymeric micelles in mucosal drug delivery: Challenges towards clinical translation

Polymeric micelles are nanostructures formed by the self-aggregation of copolymeric amphiphiles above the critical micellar concentration. Due to the flexibility to tailor different molecular features, they have been exploited to encapsulate motley poorly-water soluble therapeutic agents. Moreover, the possibility to combine different amphiphiles in one single aggregate and produce mixed micelles that capitalize on the features of the different components substantially expands the therapeutic potential of these nanocarriers. Despite their proven versatility, polymeric micelles remain elusive to the market and only a few products are currently undergoing advanced clinical trials or reached clinical application, all of them for the therapy of different types of cancer and administration by the intravenous route. At the same time, they emerge as a nanotechnology platform with great potential for non-parenteral mucosal administration. However, for this, the interaction of polymeric micelles with mucus needs to be strengthened. The present review describes the different attempts to develop mucoadhesive polymeric micelles and discusses the challenges faced in the near future for a successful bench-to-bedside translation.

Anti-inflammatory activity of guluronate oligosaccharides obtained by oxidative degradation from alginate in lipopolysaccharide-activated murine macrophage RAW 264.7 cells

Alginate has notably diverse pharmacological activities. The present study investigated the anti-inflammatory activity of the guluronate oligosaccharides prepared by oxidative degradation (GOS-OD) from alginate. GOS-OD significantly attenuated the production of nitric oxide (NO), prostaglandin E2 (PGE2), and reactive oxygen species (ROS), the expression of inducible nitric oxide synthase (iNOS) and cyclooxygenase (COX)-2, and the secretion of pro-inflammatory cytokines in lipopolysaccharide (LPS)-activated murine macrophage RAW 264.7 cells. Moreover, GOS-OD potently decreased the binding of LPS to the cell surface and LPS-induced Toll-like receptor 4 (TLR4) and cluster of differentiation (CD) 14 expression. Additionally, GOS-OD could remarkably inhibit the LPS-induced activation of nuclear factor (NF)-κB and mitogen-activated protein (MAP) kinase pathways in RAW 264.7 cells. These results indicate that GOS-OD may reduce the LPS-stimulated inflammatory responses through blocking the activation of NF-κB and MAP kinases, suggesting that GOS-OD may be considered as a potential nutraceutical for inflammation.

Advances in cell encapsulation technology and its application in drug delivery

INTRODUCTION

Cell encapsulation technology has improved enormously since it was proposed 50 years ago. The advantages offered over other alternative systems, such as the prevention of repetitive drug administration, have triggered the use of this technology in multiple therapeutic applications.

AREAS COVERED

In this article, improvements in cell encapsulation technology and strategies to overcome the drawbacks that prevent its use in the clinic have been summarized and discussed. Different studies and clinical trials that have been performed in several therapeutic applications have also been described.

EXPERT OPINION

The authors believe that the future translation of this technology from bench to bedside requires the optimization of diverse aspects: i) biosafety, controlling and monitoring cell viability; ii) biocompatibility, reducing pericapsular fibrotic growth and hypoxia suffered by the graft; iii) control over drug delivery; iv) and the final scale up. On the other hand, an area that deserves more attention is the cryopreservation of encapsulated cells as this will facilitate the arrival of these biosystems to the clinic.

Fabrication of individual alginate-TCP scaffolds for bone tissue engineering by means of powder printing

The development of polymer-calcium phosphate composite scaffolds with tailored architectures and properties has great potential for bone regeneration. Herein, we aimed to improve the functional performance of brittle ceramic scaffolds by developing a promising biopolymer-ceramic network. For this purpose, two strategies, namely, direct printing of a powder composition consisting of a 60:40 mixture of α/β-tricalcium phosphate (TCP) powder and alginate powder or vacuum infiltration of printed TCP scaffolds with an alginate solution, were tracked. Results of structural characterization revealed that the scaffolds printed with 2.5 wt% alginate-modified TCP powders presented a uniformly distributed and interfusing alginate TCP network. Mechanical results indicated a significant increase in strength, energy to failure and reliability of powder-modified scaffolds with an alginate content in the educts of 2.5 wt% when compared to pure TCP, as well as to TCP scaffolds containing 5 wt% or 7.5 wt% in the educts, in both dry and wet states. Culture of human osteoblast cells on these scaffolds also demonstrated a great improvement of cell proliferation and cell viability. While in the case of powder-mixed alginate TCP scaffolds, isolated alginate gels were formed between the calcium phosphate crystals, the vacuum-infiltration strategy resulted in the covering of the surface and internal pores of the TCP scaffold with a thin alginate film. Furthermore, the prediction of the scaffolds' critical fracture conditions under more complex stress states by the applied Mohr fracture criterion confirmed the potential of the powder-modified scaffolds with 2.5 wt% alginate in the educts as structural biomaterial for bone tissue engineering.

The gelation process and protein absorption property of injectable SA-CMBC hydrogel used for procoagulant material

CMBC showed obvious influence on properties of injectable SA-CMBC hydrogel, containing gelation time, mechanical property, protein absorption and procoagulant property.

Biofunctionalized pectin hydrogels as 3D cellular microenvironments

Pectin hydrogels were prepared by internal ionotropic gelation and explored as MSC delivery vehicles.

The role of hydrogen bonding in alginate/poly(acrylamide-co-dimethylacrylamide) and alginate/poly(ethylene glycol) methyl ether methacrylate-based tough hybrid hydrogels

Hybrid hydrogels, with an elastic modulus and compressive toughness of 350 kPa and 70 J m⁻³, was synthesized and reported here.

3D welan gum–graphene oxide composite hydrogels with efficient dye adsorption capacity

In this article, welan gum-graphene oxide (GO) composite hydrogels were prepared by simple self-assembly of both components in aqueous media and the effects of GO on the gelation of welan gum were systematically studied.