Applications of alginate microspheres in therapeutics delivery and cell culture: Past, present and future

Latest advances to enhance the therapeutic potential of mesenchymal stromal cells for the treatment of immune-mediated diseases

Mesenchymal stromal cells (MSCs) present the capacity to secrete multiple immunomodulatory factors in response to their microenvironment. This property grants them a golden status among the novel alternatives to treat multiple diseases in which there is an unneeded or exaggerated immune response. However, important challenges still make difficult the clinical implementation of MSC-based therapies, being one of the most remarkable the lack of efficacy due to their transient immunomodulatory effects. To overcome this issue and boost the regulatory potential of MSCs, multiple strategies are currently being explored. Some of them consist of ex vivo pre-conditioning MSCs prior to their administration, including exposure to pro-inflammatory cytokines or to low oxygen concentrations. However, currently, alternative strategies that do not require such ex vivo manipulation are gaining special attention. Among them, the recreation of a three dimensional (3D) environment is remarkable. This approach has been reported to not only boost the immunomodulatory potential of MSCs but also increase their in vivo persistence and viability. The present work revises the therapeutic potential of MSCs, highlighting their immunomodulatory activity as a potential treatment for diseases caused by an exacerbated or unnecessary immune response. Moreover, it offers an updated vision of the most widely employed pre-conditioning strategies and 3D systems intended to enhance MSC-mediated immunomodulation, to conclude discussing the major challenges still to overcome in the field.

PDX-Derived Ewing's Sarcoma Cells Retain High Viability and Disease Phenotype in Alginate Encapsulated Spheroid Cultures

Simple Summary

Ewing’s Sarcoma (ES) is the second most frequent bone tumour in children and young adults, with very aggressive behaviour and significant disease recurrence. To better study the disease and find new therapies, experimental models are needed. Recently, patient-derived xenografts (PDX), obtained by implanting patient tumour samples in immunodeficient mice, have been developed. However, when ES cells are extracted from the patient’s tumour or from PDX and placed on plasticware surfaces, they lose their original 3D configuration, cell identity and function. To overcome these issues, we implemented cultures of PDX-derived ES cells, by making them aggregate to form ES cell spheroids and then encapsulating these 3D spheroids into a hydrogel, alginate, to stabilize the culture. We show that this methodology maintained ES cell viability and intrinsic characteristics of the original ES tumour cells for at least one month and that it is suitable for study the effect of anticancer drugs.

Abstract

Ewing’s Sarcoma (ES) is the second most frequent malignant bone tumour in children and young adults and currently only untargeted chemotherapeutic approaches and surgery are available as treatment, although clinical trials are on-going for recently developed ES-targeted therapies. To study ES pathobiology and develop novel drugs, established cell lines and patient-derived xenografts (PDX) are the most employed experimental models. Nevertheless, the establishment of ES cell lines is difficult and the extensive use of PDX raises economic/ethical concerns. There is a growing consensus regarding the use of 3D cell culture to recapitulate physiological and pathophysiological features of human tissues, including drug sensitivity. Herein, we implemented a 3D cell culture methodology based on encapsulation of PDX-derived ES cell spheroids in alginate and maintenance in agitation-based culture systems. Under these conditions, ES cells displayed high proliferative and metabolic activity, while retaining the typical EWSR1-FLI1 chromosomal translocation. Importantly, 3D cultures presented reduced mouse PDX cell contamination compared to 2D cultures. Finally, we show that these 3D cultures can be employed in drug sensitivity assays, with results similar to those reported for the PDX of origin. In conclusion, this novel 3D cell culture method involving ES-PDX-derived cells is a suitable model to study ES pathobiology and can assist in the development of novel drugs against this disease, complementing PDX studies.

Controllable Fabrication of Composite Core-Shell Capsules at a Macroscale as Organoid Biocarriers

The cell encapsulation technology is promising for generation of functional carriers with well-tailored structures for efficient transplantation and immunoprotection of cells/tissues. Stem cell organoids are highly potential for recapitulating the intricate architectures and functionalities of native organs and also providing an unlimited cell source for cellular replacement therapy. However, it remains challenging for loading the organoids with hundreds of micrometers size by current existing cell carriers. Herein, a simple and facile coextrusion strategy is developed for controllable fabrication of Ca-alginate/poly(ethylene imine) (Alg/PEI) macrocapsules for efficient encapsulation and cultivation of organoids. Human-induced pluripotent stem cell (hiPSC)-derived islet organoids are encapsulated in the aqueous compartments of the capsules and immunoisolated by a semipermeable Alg/PEI shell. Via electrostatic interactions, a PEI polyelectrolyte can be incorporated in the shell for restricting its swelling, thus effectively improving the stability of the capsules. The Alg/PEI macrocapsules are featured with desirable selective permeability for immunoisolation of antibodies from reaching the loaded organoids. Meanwhile, they also exhibit excellent permeability for mass transfer due to their well-defined core-shell structure. As such, the encapsulated islet organoids contain islet-specific multicellular components, with high viability and sensitive glucose-stimulated insulin secretion function. The proposed approach provides a versatile encapsulation system for tissue engineering and regenerative medicine applications.

A Full Set of In Vitro Assays in Chitosan/Tween 80 Microspheres Loaded with Magnetite Nanoparticles

Microspheres have been proposed for different medical applications, such as the delivery of therapeutic proteins. The first step, before evaluating the functionality of a protein delivery system, is to evaluate their biological safety. In this work, we developed chitosan/Tween 80 microspheres loaded with magnetite nanoparticles and evaluated cell damage. The formation and physical-chemical properties of the microspheres were determined by FT-IR, Raman, thermogravimetric analysis (TGA), energy-dispersive X-ray spectroscopy (EDS), dynamic light scattering (DLS), and SEM. Cell damage was evaluated by a full set of in vitro assays using a non-cancerous cell line, human erythrocytes, and human lymphocytes. At the same time, to know if these microspheres can load proteins over their surface, bovine serum albumin (BSA) immobilization was measured. Results showed 7 nm magnetite nanoparticles loaded into chitosan/Tween 80 microspheres with average sizes of 1.431 µm. At concentrations from 1 to 100 µg/mL, there was no evidence of changes in mitochondrial metabolism, cell morphology, membrane rupture, cell cycle, nor sister chromatid exchange formation. For each microgram of microspheres 1.8 µg of BSA was immobilized. The result provides the fundamental understanding of the in vitro biological behavior, and safety, of developed microspheres. Additionally, this set of assays can be helpful for researchers to evaluate different nano and microparticles.

Alginate-based hydrogels for cancer therapy and research

Cancer is a major health issue concerning to all of us. Current treatment options are still limited due to not-selective action. Encapsulation is contemplated as an innovative approach to address systemic toxicity and tumor resistance caused by traditional therapies, while increasing encapsulated compounds bioavailability. The coating material of capsules strongly determines the success of the system. Since alginate has been proved non-toxic, biocompatible and biodegradable, it is considered a potential vehicle for therapeutic factors encapsulation. Besides, it has the particular ability to form hydrogels, which hold a high-water content and greatly resemble to natural soft tissues. The present review exposes the state-of-the-art and the most sophisticated alginate-based systems for cancer therapy and research. It begins with an overview of alginate hydrogels and the qualities that make them especially suitable for biomedical applications. In the following section, the application of alginate hydrogels as pioneering strategies for cancer treatment is described. Several examples of alginate-based delivery systems of therapeutic drugs, proteins and nucleic acids are provided. Significant emphasis is placed in both oral delivery systems and colorectal cancer therapy. Moreover, the role of alginate 3-D scaffolds for both cell culture and delivery is explained. Lastly, other applications of alginate-based hydrogels such as tumor biomarkers immunosensing and fluorescent surgical marker are included.

Progress in Modern Marine Biomaterials Research

The growing demand for new, sophisticated, multifunctional materials has brought natural structural composites into focus, since they underwent a substantial optimization during long evolutionary selection pressure and adaptation processes. Marine biological materials are the most important sources of both inspiration for biomimetics and of raw materials for practical applications in technology and biomedicine. The use of marine natural products as multifunctional biomaterials is currently undergoing a renaissance in the modern materials science. The diversity of marine biomaterials, their forms and fields of application are highlighted in this review. We will discuss the challenges, solutions, and future directions of modern marine biomaterialogy using a thorough analysis of scientific sources over the past ten years.

Increased c-di-GMP Levels Lead to the Production of Alginates of High Molecular Mass in Azotobacter vinelandii

Azotobacter vinelandii produces the linear exopolysaccharide alginate, a compound of significant biotechnological importance. The biosynthesis of alginate in A. vinelandii and Pseudomonas aeruginosa has several similarities but is regulated somewhat differently in the two microbes. Here, we show that the second messenger cyclic dimeric GMP (c-di-GMP) regulates the production and the molecular mass of alginate in A. vinelandii The hybrid protein MucG, containing conserved GGDEF and EAL domains and N-terminal HAMP and PAS domains, behaved as a c-di-GMP phosphodiesterase (PDE). This activity was found to negatively affect the amount and molecular mass of the polysaccharide formed. On the other hand, among the diguanylate cyclases (DGCs) present in A. vinelandii, AvGReg, a globin-coupled sensor (GCS) DGC that directly binds to oxygen, was identified as the main c-di-GMP-synthesizing contributor to alginate production. Overproduction of AvGReg in the parental strain phenocopied a ΔmucG strain with regard to alginate production and the molecular mass of the polymer. MucG was previously shown to prevent the synthesis of high-molecular-mass alginates in response to reduced oxygen transfer rates (OTRs). In this work, we show that cultures exposed to reduced OTRs accumulated higher levels of c-di-GMP; this finding strongly suggests that at least one of the molecular mechanisms involved in modulation of alginate production and molecular mass by oxygen depends on a c-di-GMP signaling module that includes the PAS domain-containing PDE MucG and the GCS DGC AvGReg.IMPORTANCE c-di-GMP has been widely recognized for its essential role in the production of exopolysaccharides in bacteria, such as alginate produced by Pseudomonas and Azotobacter spp. This study reveals that the levels of c-di-GMP also affect the physical properties of alginate, favoring the production of high-molecular-mass alginates in response to lower OTRs. This finding opens up new alternatives for the design of tailor-made alginates for biotechnological applications.

Inventing a facile method to construct Bombyx mori (B. mori) silk fibroin nanocapsules for drug delivery

Bombyx mori (B. mori) silk fibroin (SF) microcapsules have acted as a great candidate in delivering drugs. However, it is difficult to fabricate SF nanocapsules using the present layer-by-layer (LBL) technique. In addition, the current SF microcapsules have limits in loading negatively charged drugs. Here, we invent a novel LBL method by introducing silane (APTES) as a structure indicator to produce SF nanocapsules that can load drugs with negative or positive charge. LBL assembly was completed by alternately coating SF and APTES on the template of polystyrene (PS) nanospheres by electrostatic attraction. SF nanocapsules were obtained after removal of the PS templates. Zeta potential analysis proved LBL assembly was indeed driven by the interaction between negative charge of SF and positive charge of APTES. Fluorescence images and electric microscope images indicated that SF nanocapsules had a hollow and stable structure with diameter at nearly 250 nm. The highest encapsulation rate of DOX or Ce6 were up to 80% and 90%, respectively, indicating SF nanocapsules have a high loading capability for both cationic and anionic drugs. In vitro cell experiments proved the biocompatibility of SF nanocapsules and their burst drug release in response to acidic environment. Furthermore, chemotherapy and photodynamic therapy proved SF nanocapsules loaded with DOX or Ce6 had significant inhibition on tumor cells. Our results suggested that this LBL technique is a facile method for polymers with negative charge to fabricate nanocapsules for antitumor drug carrier.

Porous Polymeric Microspheres With Controllable Pore Diameters for Tissue Engineered Lung Tumor Model Development

Complex cell cultures are more representative of in vivo conditions than conventionally used monolayer cultures, and are hence being investigated for predictive screening of therapeutic agents. Poly lactide co-glycolide (PLGA) polymer is frequently used in the development of porous substrates for complex cell culture. Substrates or scaffolds with highly interconnected, micrometric pores have been shown to positively impact tissue model formation by enhancing cell attachment and infiltration. We report a novel alginate microsphere (AMS)-based controlled pore formation method for the development of porous, biodegradable PLGA microspheres (PPMS), for tissue engineered lung tumor model development. The AMS porogen, non-porous PLGA microspheres (PLGAMS) and PPMS had spherical morphology (mean diameters: 10.3 ± 4, 79 ± 21.8, and 103 ± 30 μm, respectively). The PPMS had relatively uniform pores and a porosity of 45.5%. Degradation studies show that PPMS effectively maintained their structural integrity with time whereas PLGAMS showed shrunken morphology. The optimized cell seeding density on PPMS was 25 × 103 cells/mg of particles/well. Collagen coating on PPMS significantly enhanced the attachment and proliferation of co-cultures of A549 lung adenocarcinoma and MRC-5 lung fibroblast cells. Preliminary proof-of-concept drug screening studies using mono- and combination anti-cancer therapies demonstrated that the tissue-engineered lung tumor model had a significantly higher resistance to the tested drugs than the monolayer co-cultures. These studies indicate that the PPMS with controllable pore diameters may be a suitable platform for the development of complex tumor cultures for early in vitro drug screening applications.

Polymeric nanostructure vaccines: applications and challenges

INTRODUCTION

The use of biocompatible polymers, from natural or synthetic sources, opened the door for a new era in vaccine research. These polymers offer the possibility to develop nanostructured antigen carriers that can be easily internalized by antigen-presenting cells, due to their nanometric size. Besides, the incorporation of an adjuvant allows increasing and modulating the immune response for both, polymers with or without self-adjuvant properties.

AREAS COVERED

The historical background and the state-of-the-art in the use of polymers as antigen carriers are addressed in the first part of this review. Then, an overview of the immunology of vaccination is provided. Finally, the main advances in the field, based on the prototypes that are licensed or undergoing clinical trials, but also the challenges that limit the translation of many polymer-based nanostructure vaccines with promising preclinical results, are discussed.

EXPERT OPINION

Polymeric nanostructured vaccines have a great potential in modern vaccinology. However, the translation into the market is hampered due to several limitations. Studies on correlates of protection to provide suitable biomarkers, new and better methods of synthesis to produce more reproducible nanovaccines, a deeper knowledge in the immune system and in the physiopathology of the infectious diseases will surely improve and boost the field in the next years.

Natural Polymeric Scaffolds in Bone Regeneration

Despite considerable advances in microsurgical techniques over the past decades, bone tissue remains a challenging arena to obtain a satisfying functional and structural restoration after damage. Through the production of substituting materials mimicking the physical and biological properties of the healthy tissue, tissue engineering strategies address an urgent clinical need for therapeutic alternatives to bone autografts. By virtue of their structural versatility, polymers have a predominant role in generating the biodegradable matrices that hold the cells in situ to sustain the growth of new tissue until integration into the transplantation area (i.e., scaffolds). As compared to synthetic ones, polymers of natural origin generally present superior biocompatibility and bioactivity. Their assembly and further engineering give rise to a wide plethora of advanced supporting materials, accounting for systems based on hydrogels or scaffolds with either fibrous or porous architecture. The present review offers an overview of the various types of natural polymers currently adopted in bone tissue engineering, describing their manufacturing techniques and procedures of functionalization with active biomolecules, and listing the advantages and disadvantages in their respective use in order to critically compare their actual applicability potential. Their combination to other classes of materials (such as micro and nanomaterials) and other innovative strategies to reproduce physiological bone microenvironments in a more faithful way are also illustrated. The regeneration outcomes achieved in vitro and in vivo when the scaffolds are enriched with different cell types, as well as the preliminary clinical applications are presented, before the prospects in this research field are finally discussed. The collection of studies herein considered confirms that advances in natural polymer research will be determinant in designing translatable materials for efficient tissue regeneration with forthcoming impact expected in the treatment of bone defects.

Features and applications of Ent35-MccV hybrid bacteriocin: current state and perspectives

Bacteriocins are peptides of ribosomal synthesis that are active against bacteria related to the producing strain. They have been widely used in the food industry as biopreservatives. The generation of hybrid peptides by combining the genes that encode two different bacteriocins has made it possible to study the mechanisms of action of the bacteriocins that compose them and also develop new peptides with improved biotechnological applications. Hybrid bacteriocins may be obtained in several ways. In our laboratory, by combining enterocin CRL35 and microcin V (Ent35-MccV), we obtained a broad-spectrum peptide that is active against both Gram-positive and Gram-negative bacteria. Ent35-MccV is sensitive to the action of intestinal proteases and is heat resistant, which makes it a good candidate for use as a biopreservative. For this reason, the peptide was tested in skim milk and beef burgers as food models. We also obtained more potent variants of the hybrid by modifying the central amino acid of the hinge region that connects the two bacteriocins. This review also discusses future applications and perspectives regarding the Ent35-MccV and other hybrid peptides.Key Points• Ent35-MccV is a new broad-spectrum bacteriocin.• The mechanism of action of bacteriocins can be studied using hybrid peptides.• Genetic engineering allows obtaining improved bacteriocin derivatives.• Hybrid peptides can be used in the food, pharmaceutical, and veterinary applications.

Alginate Formulations: Current Developments in the Race for Hydrogel-Based Cardiac Regeneration

Cardiovascular diseases, including myocardial infarction (MI), represent the main worldwide cause of mortality and morbidity. In this scenario, to contrast the irreversible damages following MI, cardiac regeneration has emerged as a novel and promising solution for in situ cellular regeneration, preserving cell behavior and tissue cytoarchitecture. Among the huge variety of natural, synthetic, and hybrid compounds used for tissue regeneration, alginate emerged as a good candidate for cellular preservation and delivery, becoming one of the first biomaterial tested in pre-clinical research and clinical trials concerning cardiovascular diseases. Although promising results have been obtained, recellularization and revascularization of the infarcted area present still major limitations. Therefore, the demand is rising for alginate functionalization and its combination with molecules, factors, and drugs capable to boost the regenerative potential of the cardiac tissue. The focus of this review is to elucidate the promising properties of alginate and to highlight its benefits in clinical trials in relation to cardiac regeneration. The definition of hydrogels, the alginate characteristics, and recent biomedical applications are herewith described. Afterward, the review examines in depth the ongoing developments to refine the material relevance in cardiac recovery and regeneration after MI and presents current clinical trials based on alginate.

Multifunctional carriers for controlled drug delivery

In the review we describe a method for concentration of anionic liposomes with encapsulated water-soluble substances within a small volume via electrostatic liposome adsorption on the surface of polymer particles with grafted cationic chains (spherical polycationic brushes), or cationic microgel particles. Dozens of intact liposomes can be bound to each polymer particle, the resulting polymer/liposome complex does not dissociate into the original components in a physiological solution. This allows fabrication of multi-liposomal complexes (MLCs) with a required ratio of encapsulated substances. Two approaches are discussed for the synthesis of stimuli-sensitive MLCs. The first is to incorporate the conformation switch, morpholinocyclohexanol-based lipid, into the liposomal membrane thus forming pH-sensitive liposomes capable of releasing their cargo when acidifying the surrounding solution. These liposomes complexed with the brushes release encapsulated substances much faster than the uncomplexed liposomes. The second is to adsorb liposomes on cationic thermo-responsive microgels. The resulting MLCs contracts upon heating over a volume phase transition temperature from the swollen to the collapsed state of microgel, thus causing the adsorbed liposomes to change drastically their morphology and release an encapsulated substance. Complexation of anionic liposomes with chitosan microgels and polylactide micelles gives MLCs which degrade in the presence of enzymes down to small particles, 10–15 nm in diameter. A novel promising approach suggests that immobilized liposomes can act as a capacious depot for biologically active compounds and ensure their controllable leakage to surrounding solution.

Engineering and Functionalization of Gelatin Biomaterials: From Cell Culture to Medical Applications

Health care and medicine were revolutionized in recent years by the development of biomaterials, such as stents, implants, personalized drug delivery systems, engineered grafts, cell sheets, and other transplantable materials. These materials not only support the growth of cells before transplantation but also serve as replacements for damaged tissues in vivo. Among the various biomaterials available, those made from natural biological sources such as extracellular proteins (collagen, fibronectin, laminin) have shown significant benefits, and thus are widely used. However, routine biomaterial-based research requires copious quantities of proteins and the use of pure and intact extracellular proteins could be highly cost ineffective. Gelatin is a molecular derivative of collagen obtained through the irreversible denaturation of collagen proteins. Gelatin shares a very close molecular structure and function with collagen and thus is often used in cell and tissue culture to replace collagen for biomaterial purposes. Recent technological advancements such as additive manufacturing, rapid prototyping, and three-dimensional printing, in general, have resulted in great strides toward the generation of functional gelatin-based materials for medical purposes. In this review, the structural and molecular similarities of gelatin to other extracellular matrix proteins are compared and analyzed. Current strategies for gelatin crosslinking and production are described and recent applications of gelatin-based biomaterials in cell culture and tissue regeneration are discussed. Finally, recent improvements in gelatin-based biomaterials for medical applications and future directions are elaborated. Impact statement In this study, we described gelatin's biochemical properties and compared its advantages and drawbacks over other extracellular matrix proteins and polymers used for biomaterial application. We also described how gelatin can be used with other polymers in creating gelatin composite materials that have enhanced mechanical properties, increased biocompatibility, and boosted bioactivity, maximizing its benefits for biomedical purposes. The article is relevant, as it discussed not only the chemistry of gelatin, but also listed the current techniques in gelatin/biomaterial manufacturing and described the most recent trends in gelatin-based biomaterials for biomedical applications.

Dual-Functioning Scaffolds for the Treatment of Spinal Cord Injury: Alginate Nanofibers Loaded with the Sigma 1 Receptor (S1R) Agonist RC-33 in Chitosan Films

The present work proposed a novel therapeutic platform with both neuroprotective and neuroregenerative potential to be used in the treatment of spinal cord injury (SCI). A dual-functioning scaffold for the delivery of the neuroprotective S1R agonist, RC-33, to be locally implanted at the site of SCI, was developed. RC-33-loaded fibers, containing alginate (ALG) and a mixture of two different grades of poly(ethylene oxide) (PEO), were prepared by electrospinning. After ionotropic cross-linking, fibers were incorporated in chitosan (CS) films to obtain a drug delivery system more flexible, easier to handle, and characterized by a controlled degradation rate. Dialysis equilibrium studies demonstrated that ALG was able to form an interaction product with the cationic RC-33 and to control RC-33 release in the physiological medium. Fibers loaded with RC-33 at the concentration corresponding to 10% of ALG maximum binding capacity were incorporated in films based on CS at two different molecular weights-low (CSL) and medium (CSM)-solubilized in acetic (AA) or glutamic (GA) acid. CSL- based scaffolds were subjected to a degradation test in order to investigate if the different CSL salification could affect the film behavior when in contact with media that mimic SCI environment. CSL AA exhibited a slower biodegradation and a good compatibility towards human neuroblastoma cell line.