Alginate-Based Biomaterials for Regenerative Medicine Applications

Protamine-based nanoparticles as new antigen delivery systems

The use of biodegradable nanoparticles as antigen delivery vehicles is an attractive approach to overcome the problems associated with the use of Alum-based classical adjuvants. Herein we report, the design and development of protamine-based nanoparticles as novel antigen delivery systems, using recombinant hepatitis B surface antigen as a model viral antigen. The nanoparticles, composed of protamine and a polysaccharide (hyaluronic acid or alginate), were obtained using a mild ionic cross-linking technique. The size and surface charge of the nanoparticles could be modulated by adjusting the ratio of the components. Prototypes with optimal physicochemical characteristics and satisfactory colloidal stability were selected for the assessment of their antigen loading capacity, antigen stability during storage and in vitro and in vivo proof-of-concept studies. In vitro studies showed that antigen-loaded nanoparticles induced the secretion of cytokines by macrophages more efficiently than the antigen in solution, thus indicating a potential adjuvant effect of the nanoparticles. Finally, in vivo studies showed the capacity of these systems to trigger efficient immune responses against the hepatitis B antigen following intramuscular administration, suggesting the potential interest of protamine-polysaccharide nanoparticles as antigen delivery systems.

3D brown adipogenesis to create "Brown-Fat-in-Microstrands"

The ability of brown adipocytes (fat cells) to dissipate energy as heat shows great promise for the treatment of obesity and other metabolic disorders. Employing pluripotent stem cells, with an emphasis on directed differentiation, may overcome many issues currently associated with primary fat cell cultures. In addition, three-dimensional (3D) cell culture systems are needed to better understand the role of brown adipocytes in energy balance and treating obesity. To address this need, we created 3D "Brown-Fat-in-Microstrands" by microfluidic synthesis of alginate hydrogel microstrands that encapsulated cells and directly induced cell differentiation into brown adipocytes, using mouse embryonic stem cells (ESCs) as a model of pluripotent stem cells, and brown preadipocytes as a positive control. Brown adipocyte differentiation within microstrands was confirmed by immunocytochemistry and qPCR analysis of the expression of the brown adipocyte-defining marker uncoupling protein 1 (UCP1), as well as other general adipocyte markers. Cells within microstrands were responsive to a β-adrenergic agonist with an increase in gene expression of thermogenic UCP1, indicating that these "Brown-Fat-in-Microstrands" are functional. The ability to create "Brown-Fat-in-Microstrands" from pluripotent stem cells opens up a new arena to understanding brown adipogenesis and its implications in obesity and metabolic disorders.

In-situ assembly of Ca-alginate gels with controlled pore loading/release capability

Development of tailor-made porous polymer scaffolds acting as a temporary tissue-construct for cellular organization is of primary importance for tissue engineering applications. Control over the gel porosity is a critical issue due to the need for cells to proliferate and migrate and to ensure the transport of nutrition and metabolites. Gel loading with bioactive molecules is desired for target release of soluble signals to guide cell function. Calcium-alginate hydrogels are one of the most popular gels successfully utilized as polymer scaffolds. Here we propose a benchtop approach to design porous alginate gels by dispersion of CaCO3 vaterite crystals in sodium alginate followed by the crystal elimination. CaCO3 crystals play a triple role being (i) cross-linkers (a source of calcium ions to cross-link gel network), (ii) pore-makers (leaching of crystals retains the empty pores), and (iii) reservoirs with (bio)molecules (by molecule preloading into the crystals). Pore dimensions, interconnectivity, and density can be adjusted by choosing the size, concentration, and packing of the sacrificial CaCO3 crystals. An opportunity to load the pores with biomolecules was demonstrated using FITC-labeled dextrans of different molecular masses from 10 to 500 kDa. The dextrans were preloaded into CaCO3 vaterite crystals, and the subsequent crystal removal resulted in encapsulation of dextrans inside the pores of the gel. The dextran release rate from the gel pores depends on the equilibration of the gel structure as concluded by comparing dextran release kinetics during gelation (fast) and dextran diffusion into the performed gel (slower). Macromolecule binding to the gel is electrostatically driven as found for lysozyme and insulin. The application of porous gels as scaffolds potentially offering biomacromolecule encapsulation/release performance might be useful for alginate gel-based applications such as tissue engineering.

Alginate-Derived Oligosaccharide Inhibits Neuroinflammation and Promotes Microglial Phagocytosis of β-Amyloid

Alginate from marine brown algae has been widely applied in biotechnology. In this work, the effects of alginate-derived oligosaccharide (AdO) on lipopolysaccharide (LPS)/β-amyloid (Aβ)-induced neuroinflammation and microglial phagocytosis of Aβ were studied. We found that pretreatment of BV2 microglia with AdO prior to LPS/Aβ stimulation led to a significant inhibition of production of nitric oxide (NO) and prostaglandin E₂ (PGE₂), expression of inducible nitric oxide synthase (iNOS) and cyclooxygenase-2 (COX-2) and secretion of proinflammatory cytokines. We further demonstrated that AdO remarkably attenuated the LPS-activated overexpression of toll-like receptor 4 (TLR4) and nuclear factor (NF)-κB in BV2 cells. In addition to the impressive inhibitory effect on neuroinflammation, we also found that AdO promoted the phagocytosis of Aβ through its interaction with TLR4 in microglia. Our results suggested that AdO exerted the inhibitory effect on neuroinflammation and the promotion effect on microglial phagocytosis, indicating its potential as a nutraceutical or therapeutic agent for neurodegenerative diseases, particularly Alzheimer’s disease (AD).

Modular Small Diameter Vascular Grafts with Bioactive Functionalities

We report the fabrication of a novel type of artificial small diameter blood vessels, termed biomimetic tissue-engineered blood vessels (bTEBV), with a modular composition. They are composed of a hydrogel scaffold consisting of two negatively charged natural polymers, alginate and a modified chitosan, N,O-carboxymethyl chitosan (N,O-CMC). Into this biologically inert scaffold two biofunctionally active biopolymers are embedded, inorganic polyphosphate (polyP) and silica, as well as gelatin which exposes the cell recognition signal, Arg-Gly-Asp (RGD). These materials can be hardened by exposure to Ca(2+) through formation of Ca(2+) bridges between the polyanions, alginate, N,O-CMC, and polyP (alginate-Ca(2+)-N,O-CMC-polyP). The bTEBV are formed by pressing the hydrogel through an extruder into a hardening solution, containing Ca(2+). In this universal scaffold of the bTEBV biomaterial, polycations such as poly(L-Lys), poly(D-Lys) or a His/Gly-tagged RGD peptide (three RGD units) were incorporated, which promote the adhesion of endothelial cells to the vessel surface. The mechanical properties of the biopolymer material (alginate-Ca(2+)-N,O-CMC-polyP-silica) revealed a hardness (elastic modulus) of 475 kPa even after a short incubation period in CaCl2 solution. The material of the artificial vascular grafts (bTEBVs with an outer size 6 mm and 1.8 mm, and an inner diameter 4 mm and 0.8 mm, respectively) turned out to be durable in 4-week pulsatile flow experiments at an alternating pressure between 25 and 100 mbar (18.7 and 75.0 mm Hg). The burst pressure of the larger (smaller) vessels was 850 mbar (145 mbar). Incorporation of polycationic poly(L-Lys), poly(D-Lys), and especially the His/Gly-tagged RGD peptide, markedly increased the adhesion of human, umbilical vein/vascular endothelial cells, EA.HY926 cells, to the surface of the hydrogel. No significant effect of the polyP samples on the clotting of human plasma is measured. We propose that the metabolically degradable polymeric scaffold bTEBV is a promising biomaterial for future prosthetic vascular grafts.

In silico Mechano-Chemical Model of Bone Healing for the Regeneration of Critical Defects: The Effect of BMP-2

The healing of bone defects is a challenge for both tissue engineering and modern orthopaedics. This problem has been addressed through the study of scaffold constructs combined with mechanoregulatory theories, disregarding the influence of chemical factors and their respective delivery devices. Of the chemical factors involved in the bone healing process, bone morphogenetic protein-2 (BMP-2) has been identified as one of the most powerful osteoinductive proteins. The aim of this work is to develop and validate a mechano-chemical regulatory model to study the effect of BMP-2 on the healing of large bone defects in silico. We first collected a range of quantitative experimental data from the literature concerning the effects of BMP-2 on cellular activity, specifically proliferation, migration, differentiation, maturation and extracellular matrix production. These data were then used to define a model governed by mechano-chemical stimuli to simulate the healing of large bone defects under the following conditions: natural healing, an empty hydrogel implanted in the defect and a hydrogel soaked with BMP-2 implanted in the defect. For the latter condition, successful defect healing was predicted, in agreement with previous in vivo experiments. Further in vivo comparisons showed the potential of the model, which accurately predicted bone tissue formation during healing, bone tissue distribution across the defect and the quantity of bone inside the defect. The proposed mechano-chemical model also estimated the effect of BMP-2 on cells and the evolution of healing in large bone defects. This novel in silico tool provides valuable insight for bone tissue regeneration strategies.

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.

Polysaccharide-Coated Magnetic Nanoparticles for Imaging and Gene Therapy

Today, nanotechnology plays a vital role in biomedical applications, especially for the diagnosis and treatment of various diseases. Among the many different types of fabricated nanoparticles, magnetic metal oxide nanoparticles stand out as unique and useful tools for biomedical applications, because of their imaging characteristics and therapeutic properties such as drug and gene carriers. Polymer-coated magnetic particles are currently of particular interest to investigators in the fields of nanobiomedicine and fundamental biomaterials. Theranostic magnetic nanoparticles that are encapsulated or coated with polymers not only exhibit imaging properties in response to stimuli, but also can efficiently deliver various drugs and therapeutic genes. Even though a large number of polymer-coated magnetic nanoparticles have been fabricated over the last decade, most of these have only been used for imaging purposes. The focus of this review is on polysaccharide-coated magnetic nanoparticles used for imaging and gene delivery.

Physiologically inspired cardiac scaffolds for tailored in vivo function and heart regeneration

Tissue engineering is well suited for the treatment of cardiac disease due to the limited regenerative capacity of native cardiac tissue and the loss of function associated with endemic cardiac pathologies, such as myocardial infarction and congenital heart defects. However, the physiological complexity of the myocardium imposes extensive requirements on tissue therapies intended for these applications. In recent years, the field of cardiac tissue engineering has been characterized by great innovation and diversity in the fabrication of engineered tissue scaffolds for cardiac repair and regeneration to address these problems. From early approaches that attempted only to deliver cardiac cells in a hydrogel vessel, significant progress has been made in understanding the role of each major component of cardiac living tissue constructs (namely cells, scaffolds, and signaling mechanisms) as they relate to mechanical, biological, and electrical in vivo performance. This improved insight, accompanied by modern material science techniques, allows for the informed development of complex scaffold materials that are optimally designed for cardiac applications. This review provides a background on cardiac physiology as it relates to critical cardiac scaffold characteristics, the degree to which common cardiac scaffold materials fulfill these criteria, and finally an overview of recent in vivo studies that have employed this type of approach.

Adhesive and sealant interfaces for general surgery applications

The main functions of biological adhesives and sealants are to repair injured tissues, reinforce surgical wounds, or even replace common suturing techniques. In general surgery, adhesives must match several requirements taking into account clinical needs, biological effects, and material features; these requirements can be fulfilled by specific polymers. Natural or synthetic polymeric materials can be employed to generate three-dimensional networks that physically or chemically bind to the target tissues and act as hemostats, sealants, or adhesives. Among them, fibrin, gelatin, dextran, chitosan, cyanoacrylates, polyethylene glycol, and polyurethanes are the most important components of these interfaces; various aspects regarding their adhesion mechanisms, mechanical performance, and resistance to body fluids should be taken into account to choose the most suitable formulation for the target application. This review aims to describe the main adhesives and sealant materials for general surgery applications developed in the past decades and to highlight the most important aspects for the development of future formulations.

Light-responsive iron(III)-polysaccharide coordination hydrogels for controlled delivery

Visible-light responsive gels were prepared from two plant-origin polyuronic acids (PUAs), alginate and pectate, coordinated to Fe(III) ions. Comparative quantitative studies of the photochemistry of these systems revealed unexpected differences in the photoreactivity of the materials, depending on the polysaccharide and its composition. The roles that different functional groups play on the photochemistry of these biomolecules were also examined. Mannuronic-rich alginates were more photoreactive than guluronic acid-rich alginate and than pectate. The microstructure of alginates with different mannuronate-to-guluronate ratios changed with polysaccharide composition. This influenced the gel morphology and the photoreactivity. Coordination hydrogel beads were prepared from both Fe-alginate and Fe-pectate. The beads were stable carriers of molecules as diverse as the dye Congo Red, the vitamin folic acid, and the antibiotic chloramphenicol. The photoreactivity of the hydrogel beads mirrored the photoreactivity of the polysaccharides in solution, where beads prepared with alginate released their cargo faster than beads prepared with pectate. These results indicate important structure-function relationships in these systems and create guidelines for the design of biocompatible polysaccharide-based materials where photoreactivity and controlled release can be tuned on the basis of the type of polysaccharide used and the metal coordination environment.

Evaluation of the ability of natural and synthetic scaffolds in providing an appropriate environment for growth and chondrogenic differentiation of adipose-derived mesenchymal stem cells

BACKGROUND

Although progenitor cells have been observed in articular cartilage, this part has a limited ability to repair due to a lack of blood supply. Formerly, tissue engineering was mainly based on collecting chondrocytes from the joint surface, culturing them on resorbable scaffolds such as poly D, L-lactic glycolic acid (PLGA) and then autologous transplantation. In recent times, due to difficulties in collecting chondrocytes, most of the researchers are focused on stem cells for producing these cells. Among the important factors in this approach, is using appropriate scaffolds with good mechanical and biological properties to provide optimal environment for growth and development of stem cells. In this study, we evaluated the potential of fibrin glue, PLGA and alginate scaffolds in providing a suitable environment for growth and chondrogenic differentiation of mesenchymal stem cells (MSCs) in the presence of transforming growth factor-β3.

MATERIALS AND METHODS

Fibrin glue, PLGA and alginate scaffolds were prepared and MSCs were isolated from human adipose tissue. Cells were cultured separately on the scaffolds and 2 weeks after differentiation, chondrogenic genes, cell proliferation ability and morphology in each scaffold were evaluated using real time-polymerase chain reaction, MTT chondrogenic assay and histological examination, respectively.

RESULTS

Proliferation of differentiated adipose tissue derived mesenchymal stem cells (AD-MSCs) to chondrogenic cells in Fibrin glue were significantly higher than in other scaffolds. Also, Fibrin glue caused the highest expression of chondrogenic genes compared to the other scaffolds. Histological examination revealed that the pores of the Fibrin glue scaffolds were filled with cells uniformly distributed.

CONCLUSION

According to the results of the study, it can be concluded that natural scaffolds such as fibrin can be used as an appropriate environment for cartilage differentiation.

Synthesis and characterization of a novel injectable alginate–collagen–hydroxyapatite hydrogel for bone tissue regeneration

This novel fabrication process allowed for the development of an injectable hydrogel system with a gelation time suitable for a surgical setting and components necessary for promoting enhanced bone regeneration.

Transformation of vaterite nanoparticles to hydroxycarbonate apatite in a hydrogel scaffold: relevance to bone formation

Vaterite nanoparticles incorporated in a biodegradable PEG hydrogel transform to hydroxycarbonate apatite upon incubation in simulated body fluid. The vaterite-loaded hydrogels did not have inflammatory effects on endothelial cells.

Hybrid amphiphilic bimodal hydrogels having mechanical and biological recognition characteristics for cardiac tissue engineering

Tissue engineering strategies rely on the favourable microniche scaffolds for 3D cell growth.

Improved cell infiltration of highly porous nanofibrous scaffolds formed by combined fiber-fiber charge repulsions and ultra-sonication

A significant problem affecting electrospun nanofibrous tissue scaffolds is poor infiltration of cells into their three-dimensional (3D) structure. Environmental and physical manipulation, however, can enhance cellular infiltration into electrospun scaffolds. In this work, RGD-modified alginate mats with increased thickness and porosity were achieved by pairing high humidity electrospinning with post-processing ultra-sonication. RGD-modified alginate, polyethylene oxide (PEO), and an FDA-approved, nonionic surfactant blends were electrospun in 20 and 50% relative humidity conditions. Mats electrospun in high humidity conditions resulted in significantly increased mat thickness and decreased fiber diameters. The mats' alginate content was then isolated via ionic crosslinking and PEO/surfactant extraction. Finally, the alginate-only mat was post-processed by ultra-sonication to further enhance its cross-sectional thickness. Cell morphology, proliferation, and infiltration into the scaffolds were evaluated by seeding fibroblasts onto the alginate mat. Cell spreading, growth and infiltration improved with increased humidity and ultra-sonication. This approach shows great promise for the design of cell-permeable nanofibrous scaffolds for tissue-engineering applications.

Effects of purified alginate sponge on the regeneration of chondrocytes: in vitro and in vivo

Regeneration science has been studied using tissue engineering techniques due to the self-renewal difficulties of damaged or degenerated cartilage. A scaffold with biodegradability and biocompatibility features plays a key role in developing cartilage tissue similar to human biological materials. Herein, we have fabricated three-dimensional sponge using purified alginate for the regeneration of chondrocytes cells and formation of cartilage. We demonstrated that the alginate purification can effectively minimize inflammatory reaction through reducing the content of mannuronic acid causing immune rejection. Cartilage regeneration research was performed using three-dimensional non-purified and purified alginate sponges synthesized by modified Korbutt method. In vitro cell viability and specific gene expression in the cartilage cells were investigated using 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay and reverse transcriptase-polymerase chain reaction (RT-PCR) after seeding chondrocytes on the as-fabricated sponges. Specific extracellular matrix (ECM) of chondrocytes, sGAG, and the content of collagen were also measured. Histological staining was carried out after purified alginate sponge seeded with chondrocytes and was implanted in subcutaneous nude mouse followed by extraction. Compared to the non-purified ones, the purified alginate sponges showed positive effects on maintaining affinities and phenotype of chondrocytes. From these results, it can be suggested that the purified alginate sponges provide a promising platform for cartilage regeneration.

Cell growth and protein expression of Shewanella oneidensis in biofilms and hydrogel-entrapped cultures

The performance of biofilm-based bioprocesses is difficult to predict and control because of the intrinsic heterogeneous and dynamic properties of microbial biofilms. Biofilm mimics, such as microbial cells entrapped in polymeric scaffolds that are permeable for nutrients, have been proposed to replace real biofilms to achieve long-term robust performance in engineering applications. However, the physiological differences between cells that are physically entrapped in a synthetic polymeric matrix and biofilm cells that are encased in a self-produced polymeric matrix remain unknown. In this study, using Shewanella oneidensis as a model organism and alginate hydrogel as a model synthetic matrix, we compared the cell growth and protein expression in entrapped cultures and biofilms. The hydrogel-entrapped cultures were found to exhibit a growth rate comparable with biofilms. There was no substantial difference in cell viability, surface charge, as well as hydrophobicity between the cells grown in alginate hydrogel and those grown in biofilms. However, the gel-entrapped cultures were found to be physiologically different from biofilms. The gel-entrapped cultures had a higher demand for metabolic energy. The siderophore-mediated iron uptake was repressed in the gel-entrapped cells. The presence of the hydrogel matrix decreased the expression of proteins involved in biofilm formation, while inducing the production of extracellular DNA (eDNA) in the gel-entrapped cultures. These results advance the fundamental understanding of the physiology of hydrogel-entrapped cells, which can lead to more efficient biofilm mimic-based applications.

Alginate hydrogel protects encapsulated hepatic HuH-7 cells against hepatitis C virus and other viral infections

Cell microencapsulation in alginate hydrogel has shown interesting applications in regenerative medicine and the biomedical field through implantation of encapsulated tissue or for bioartificial organ development. Although alginate solution is known to have low antiviral activity, the same property regarding alginate gel has not yet been studied. The aim of this work is to investigate the potential protective effect of alginate encapsulation against hepatitis C virus (HCV) infection for a hepatic cell line (HuH-7) normally permissive to the virus. Our results showed that alginate hydrogel protects HuH-7 cells against HCV when the supernatant was loaded with HCV. In addition, alginate hydrogel blocked HCV particle release out of the beads when the HuH-7 cells were previously infected and encapsulated. There was evidence of interaction between the molecules of alginate hydrogel and HCV, which was dose- and incubation time-dependent. The protective efficiency of alginate hydrogel towards HCV infection was confirmed against a variety of viruses, whether or not they were enveloped. This promising interaction between an alginate matrix and viruses, whose chemical mechanisms are discussed, is of great interest for further medical therapeutic applications based on tissue engineering.

Preparation methods of alginate nanoparticles

This article reviews available methods for the formation of alginate nano-aggregates, nanocapsules and nanospheres. Primarily, alginate nanoparticles are being prepared by two methods. In the "complexation method", complex formation on the interface of an oil droplet is used to form alginate nanocapsules, and complex formation in an aqueous solution is used to form alginate nano-aggregates. In a second method w/o emulsification coupled with gelation of the alginate emulsion droplet can be used to form alginate nanospheres. We review advantages and disadvantages of these methods, and give an overview of the properties of the alginate particles produced with these methods.

The bactericidal effect of dendritic copper microparticles, contained in an alginate matrix, on Escherichia coli

Although the bactericidal effect of copper has been known for centuries, there is a current resurgence of interest in the use of this element as an antimicrobial agent. During this study the use of dendritic copper microparticles embedded in an alginate matrix as a rapid method for the deactivation of Escherichia coli ATCC 11775 was investigated. The copper/alginate produced a decrease in the minimum inhibitory concentration from free copper powder dispersed in the media from 0.25 to 0.065 mg/ml. Beads loaded with 4% Cu deactivated 99.97% of bacteria after 90 minutes, compared to a 44.2% reduction in viability in the equivalent free copper powder treatment. There was no observed loss in the efficacy of this method with increasing bacterial loading up to 10(6) cells/ml, however only 88.2% of E. coli were deactivated after 90 minutes at a loading of 10(8) cells/ml. The efficacy of this method was highly dependent on the oxygen content of the media, with a 4.01% increase in viable bacteria observed under anoxic conditions compared to a >99% reduction in bacterial viability in oxygen tensions above 50% of saturation. Scanning electron micrographs (SEM) of the beads indicated that the dendritic copper particles sit as discrete clusters within a layered alginate matrix, and that the external surface of the beads has a scale-like appearance with dendritic copper particles extruding. E. coli cells visualised using SEM indicated a loss of cellular integrity upon Cu bead treatment with obvious visible blebbing. This study indicates the use of microscale dendritic particles of Cu embedded in an alginate matrix to effectively deactivate E. coli cells and opens the possibility of their application within effective water treatment processes, especially in high particulate waste streams where conventional methods, such as UV treatment or chlorination, are ineffective or inappropriate.

Shape-memory porous alginate scaffolds for regeneration of the annulus fibrosus: effect of TGF-β3 supplementation and oxygen culture conditions

Disc herniation as a result of degenerative or traumatic injury is believed to be the primary instigator of low back pain. At present there is a lack of viable treatment options to repair damaged annulus fibrosus (AF) tissue. Developing alternative strategies to fill and repair ruptured AF tissue is a key challenge. In this work we developed a porous alginate scaffold with shape-memory properties which can be delivered using minimally invasive approaches and recover its original geometry once hydrated. Covalently cross-linked alginate hydrogels were created using carbodiimide chemistry, followed by a freeze-drying step to impart porosity and create porous scaffolds. Results showed that porous alginate scaffolds exhibited shape-memory recovery and mechanical behaviour that could be modulated depending on the cross-linker concentrations. The scaffold can be repeatedly compressed and expanded, which provides the potential to deliver the biomaterial directly to the damaged area of the AF tissue. In vitro experiments demonstrated that scaffolds were cytocompatible and supported cell seeding, penetration and proliferation under intervertebral-disc-like microenvironmental conditions (low glucose media and low oxygen concentration). Extracellular matrix (ECM) was secreted by AF cells with TGF-β3 stimulation and after 21days had filled the porous scaffold network. This biological matrix was rich in sulfated glycosaminoglycan and collagen type I, which are the main compounds of native AF tissue. Successful ECM deposition was also confirmed by the increase in the peak stress of the scaffold. However, the immaturity of the matrix network after only 21days of in vitro culture was not sufficient to attain native AF tissue mechanical properties. The ability to deliver porous scaffolds using minimal invasive approaches that can potentially promote the regeneration of AF defects provides an exciting new avenue for disc repair.

Alginate Particles as Platform for Drug Delivery by the Oral Route: State-of-the-Art

Pharmaceutical research and development aims to design products with ensured safety, quality, and efficacy to treat disease. To make the process more rational, coherent, efficient, and cost-effective, the field of Pharmaceutical Materials Science has emerged as the systematic study of the physicochemical properties and behavior of materials of pharmaceutical interest in relation to product performance. The oral route is the most patient preferred for drug administration. The presence of a mucus layer that covers the entire gastrointestinal tract has been exploited to expand the use of the oral route by developing a mucoadhesive drug delivery system that showed a prolonged residence time. Alginic acid and sodium and potassium alginates have emerged as one of the most extensively explored mucoadhesive biomaterials owing to very good cytocompatibility and biocompatibility, biodegradation, sol-gel transition properties, and chemical versatility that make possible further modifications to tailor their properties. The present review overviews the most relevant applications of alginate microparticles and nanoparticles for drug administration by the oral route and discusses the perspectives of this biomaterial in the future.

[The synthesis of RGD peptide derivatives containing glutaric and adipic residues]

A method of the synthesis of RGD peptide derivatives containing glutaric or adipic residues linked with α-amino group of L-arginine and allowing carrying out their coupling with other biomolecules and nanoparticles.

Towards ready-to-use 3-D scaffolds for regenerative medicine: adhesion-based cryopreservation of human mesenchymal stem cells attached and spread within alginate-gelatin cryogel scaffolds

Cultivation and proliferation of stem cells in three-dimensional (3-D) scaffolds is a promising strategy for regenerative medicine. Mesenchymal stem cells with their potential to differentiate in various cell types, cryopreserved adhesion-based in fabricated scaffolds of biocompatible materials can serve as ready-to-use transplantation units for tissue repair, where pores allow a direct contact of graft cells and recipient tissue without further preparation. A successful cryopreservation of adherent cells depends on attachment and spreading processes that start directly after cell seeding. Here, we analyzed different cultivation times (0.5, 2, 24 h) prior to adhesion-based cryopreservation of human mesenchymal stem cells within alginate-gelatin cryogel scaffolds and its influence on cell viability, recovery and functionality at recovery times (0, 24, 48 h) in comparison to non-frozen control. Analysis with confocal laser scanning microscopy and scanning electron microscopy indicated that 2 h cultivation time enhanced cryopreservation success: cell number, visual cell contacts, membrane integrity, motility, as well as spreading were comparable to control. In contrast, cell number by short cultivation time (0.5 h) reduced dramatically after thawing and expanded cultivation time (24 h) decreased cell viability. Our results provide necessary information to enhance the production and to store ready-to-use transplantation units for application in bone, cartilage or skin regenerative therapy.