Synthesis and characterization of disulfide-crosslinked alginate hydrogel scaffolds

Oxidized alginate-gelatin (ADA-GEL)/silk fibroin/Cu-Ag doped mesoporous bioactive glass nanoparticle-based hydrogels for potential wound care treatments

The present work focuses on developing 5% w/v oxidized alginate (alginate di aldehyde, ADA)-7.5% w/v gelatin (GEL) hydrogels incorporating 0.25% w/v silk fibroin (SF) and loaded with 0.3% w/v Cu-Ag doped mesoporous bioactive glass nanoparticles (Cu-Ag MBGNs). The microstructural, mechanical, and biological properties of the composite hydrogels were characterized in detail. The porous microstructure of the developed ADA-GEL based hydrogels was confirmed by scanning electron microscopy, while the presence of Cu-Ag MBGNs in the synthesized hydrogels was determined using energy dispersive x-ray spectroscopy. The incorporation of 0.3% w/v Cu-Ag MBGNs reduced the mechanical properties of the synthesized hydrogels, as investigated using micro-tensile testing. The synthesized ADA-GEL loaded with 0.25% w/v SF and 0.3% w/v Cu-Ag MBGNs showed a potent antibacterial effect againstEscherichia coliandStaphylococcus aureus. Cellular studies using the NIH3T3-E1 fibroblast cell line confirmed that ADA-GEL films incorporated with 0.3% w/v Cu-Ag MBGNs exhibited promising cellular viability as compared to pure ADA-GEL (determined by WST-8 assay). The addition of SF improved the biocompatibility, degradation rate, moisturizing effects, and stretchability of the developed hydrogels, as determinedin vitro. Such multimaterial hydrogels can stimulate angiogenesis and exhibit desirable antibacterial properties. Therefore further (in vivo) tests are justified to assess the hydrogels' potential for wound dressing and skin tissue healing applications.

Diverse Applications of Three-Dimensional Printing in Biomedical Engineering: A Review

A three-dimensional (3D) printing is a robotically controlled state-of-the-art technology that is promising for all branches of engineering with a meritorious emphasis to biomedical engineering. The purpose of 3D printing (3DP) is to create exact superstructures without any framework in a brief period with high reproducibility to create intricate and complex patient-tailored structures for organ regeneration, drug delivery, imaging processes, designing personalized dose-specific tablets, developing 3D models of organs to plan surgery and to understand the pathology of disease, manufacturing cost-effective surgical tools, and fabricating implants and organ substitute devices for prolonging the lives of patients, etc. The formulation of bioinks and programmed G codes help to obtain precise 3D structures, which determines the stability and functioning of the 3D-printed structures. Three-dimensional printing for medical applications is ambitious and challenging but made possible with the culmination of research expertise from various fields. Exploring and expanding 3DP for biomedical and clinical applications can be life-saving solutions. The 3D printers are cost-effective and eco-friendly, as they do not release any toxic pollutants or waste materials that pollute the environment. The sampling requirements and processing parameters are amenable, which further eases the production. This review highlights the role of 3D printers in the health care sector, focusing on their roles in tablet development, imaging techniques, disease model development, and tissue regeneration.

Controlled Release of Growth Factor from Heparin Embedded Poly(aldehyde guluronate) Hydrogels and Its Effect on Vascularization

To deliver growth factors controllably for tissue regeneration, poly(aldehyde guluronate) (PAG) was obtained from alginate and covalently cross-linked with aminated gelatin (AG) to form PAG/AG hydrogel as a growth factors carrier. The prepared hydrogel exhibits a slow degradation rate and excellent cytocompatibility. Heparin was conjugated with gelatin and embedded into the hydrogel to reserve and stabilize growth factors. Basic fibroblast growth factor (bFGF) was immobilized into the hydrogel and performed sustained release as the hydrogel degraded. The bFGF loaded hydrogel can improve vascularization effectively in a rat dorsal sac model. To summarize, heparin embedded PAG/AG hydrogels would serve as a promising biodegradable vehicle for the controlled delivery of growth factors and promoting vascularization in regenerative medicine.

Application and Research Prospect of Functional Polymer Gels in Oil and Gas Drilling and Development Engineering

Polymer gel materials are formed by physically crosslinking and chemically crosslinking to form a gel network system with high mechanical properties and reversible performance. Due to their excellent mechanical properties and intelligence, polymer gel materials are widely used in biomedical, tissue engineering, artificial intelligence, firefighting and other fields. Given the current research status of polymer gels at home and abroad and the current application status of oilfield drilling, this paper reviews the mechanism of polymer gels formed by physically crosslinking and chemically crosslinking, summarizes the performance characteristics and the mechanism of action of polymer gels formed by non-covalent bonding, such as hydrophobic bonding, hydrogen bonding, electrostatic and Van der Waals interactions interactions, and covalent bonding such as imine bonding, acylhydrazone bonding and Diels-Alder reaction. The current status and outlook of the application of polymer gels in drilling fluids, fracturing fluids and enhanced oil recovery are also introduced. We expand the application fields of polymer gel materials and promote the development of polymer gel materials in a more intelligent direction.

A label-free electrochemical immunosensor based on 11-mercaptoundecanoic acid grafted chitosan and poly(N-methylaniline) for the detection of carcinoembryonic antigen

Carcinoembryonic antigen (CEA) is a cancer marker used for monitoring cancer treatment. Herein, a label-free electrochemical immunosensor for determining CEA concentration composed of the thiolated chitosan (tCHI) and the doped poly(N-methylaniline) (dPNMA) is proposed. The tCHI served as a support matrix for the immobilization of CEA antibodies (anti-CEA) and was prepared by using 11-mercaptoundecanoic acid (MUA) as a grafting agent on chitosan (CHI). The excellent electrical conductivity of the dPNMA was utilized as an electron transfer layer for the proposed immunosensor. The successful preparation of the tCHI was confirmed by the attenuated-total reflection Fourier transform spectroscopy (ATR-FTIR), X-ray photoelectron spectroscopy (XPS), and scanning electron microscopy (SEM). Cyclic voltammetry (CV), differential pulse voltammetry (DPV) and electrochemical impedance spectroscopy (EIS) were used to illustrate the performance of the proposed immunosensor. The determination of CEA concentration was relied on the decrease in the DPV current response with increasing CEA concentration from the creation of the antigen-antibody immunocomplex. The proposed immunosensor demonstrated a broad concentration range of 0.01 to 30 ng mL^-1 with a low limit of detection (LOD) of 0.01 ng mL^-1. In addition, the present sensor exhibited excellent selectivity, reproducibility, and long-term stability, suggesting its potential use to determine CEA in clinical immunoassay.

Thiolated Polymeric Hydrogels for Biomedical Applications: A Review

Hydrogels are a three-dimensional (3D) network of hydrophilic polymers. The physical and chemical crosslinking of polymeric chains maintains the structure of the hydrogels even when they are swollen in water. They can be modified with thiol by thiol epoxy, thiol-ene, thiol-disulfide, or thiol-one reactions. Their application as a matrix for protein and drug delivery, cellular immobilization, regenerative medicine, and scaffolds for tissue engineering was initiated in the early 21st century. This review focuses on the ingredients, classification techniques, and applications of hydrogels, types of thiolation by different thiol-reducing agents, along with their mechanisms. In this study, different applications for polymers used in thiolated hydrogels, including dextran, gelatin, polyethylene glycol (PEG), cyclodextrins, chitosan, hyaluronic acid, alginate, poloxamer, polygalacturonic acid, pectin, carrageenan gum, arabinoxylan, carboxymethyl cellulose (CMC), gellan gum, and polyvinyl alcohol (PVA) are reviewed.

Entirely S-protected thiolated hydroxyethylcellulose: Design of a dual cross-linking approach for hydrogels

AIM

The aim of this study was the synthesis and evaluation of entirely S-protected thiolated hydroxyethylcellulose (HEC) with low and high viscosity, as well as thiolated poly-L-lysine (poly-L-Lys) used as dual-acting ionic as well as thiol-disulfide exchange mediated cross-linking hydrogel.

METHODS

Bis(mercaptosuccinic acid) was covalently attached to low and high viscous HECs via Fisher esterification, obtaining S-protected polymers. Poly-L-Lys-cysteine was synthesized via amidation of poly-L-Lys-HBr with cysteine (Cys). Thiolated polymers were examined in terms of cytotoxicity and rheological behavior of hydrogels containing these thiomers was evaluated with a cone-plate rheometer.

RESULTS

Thiomers showed less cytotoxicity compared to the corresponding unmodified polymers. Rheological studies showed that cross-linking occurred between the two polymers via thiol-disulfide exchange reactions facilitated by the complementary charges. Employing poly-L-Lys-Cys in a concentration of either 0.5 or 5% (m/v) resulted in a 34.5-fold or 17.3-fold as well as a 53.6-fold or 29.6-fold improvement in dynamic viscosity within 5 min at 37 °C on S-protected thiolated low and high viscous HEC, compared to the corresponding unmodified HECs, respectively.

CONCLUSION

By the combination of anionic S-protected thiolated polymers with a cationic thiolated polymer, dual-acting hydrogels exhibiting a time dependent increase in viscosity can be designed.

Structure and in vitro bioactive properties of O/W emulsions generated with fava bean protein hydrolysates

The use of plant-derived proteins in the generation of food products is gaining popularity as an alternative to proteins of animal origin. This study described the emulsifying and bioactive properties of fava bean protein hydrolysates (FBH) generated at low and high degree of hydrolysis (DH), i.e., FBH₈ (low DH: 8.4 ± 0.3) and FBH₂₁₀ (high DH: 15.6 ± 0.7) when adjusted to three different pHs (3.0, 5.0 and 8.0). Overall, FBH₈, had more favourable emulsifying properties compared to the FBH_210. The emulsion generated with FBH₈ at pH 8.0 also had the highest antioxidant activity when measured by the oxygen radical absorbance capacity (ORAC) and ferric reducing antioxidant power (FRAP) assays with values of 1108.6 ± 3.8 and 1159.9 ± 20.5 μmol Trolox Eq·g^-1 emulsion, respectively. The antioxidant activity of the emulsions, in most cases, remained unchanged following in vitro simulated gastrointestinal digestion. Both the FBH₈ and FBH₂₁₀ emulsions following in vitro simulated gastrointestinal digestion were able to inhibit the activities of dipeptidyl peptidase-IV (DPP-IV) and angiotensin converting enzyme (ACE) with ∼45% and 65% inhibition, respectively. These results indicated that hydrolysates from fava bean may find use for the generation of bioactive emulsions.

Highly Effective Covalently Crosslinked Composite Alginate Cryogels for Cationic Dye Removal

Currently, macroporous hydrogels have been receiving attention in wastewater treatment due to their unique structures. As a natural polymer, alginate is used to remove cationic dyes due to its sustainable features such as abundance, low cost, processability, and being environmentally friendly. Herein, alginate/montmorillonite composite macroporous hydrogels (cryogels) with high porosity, mechanical elasticity, and high adsorption yield for methylene blue (MB) were generated by the one-step cryogelation technique. These cryogels were synthesized by adding montmorillonite into gel precursor, followed by chemical cross-linking employing carbodiimide chemistry in a frozen state. The as-prepared adsorbents were analyzed by FT-IR, SEM, gel fraction, swelling, uniaxial compression, and MB adsorption tests. The results indicated that alginate/montmorillonite cryogels exhibited high gelation yield (up to 80%), colossal water uptake capacity, elasticity, and effective dye adsorption capacity (93.7%). Maximum adsorption capacity against MB was 559.94 mg g^-1 by linear regression of Langmuir model onto experimental data. The Pseudo-Second-Order model was fitted better onto kinetic data compared to the Pseudo-First-Order model. Improved porosity and mechanical elasticity yielding enhanced dye removal capacity make them highly potential alternative adsorbents compared to available alginate/montmorillonite materials for MB removal.

Chemically Modified Biopolymers for the Formation of Biomedical Hydrogels

Biopolymers are natural polymers sourced from plants and animals, which include a variety of polysaccharides and polypeptides. The inclusion of biopolymers into biomedical hydrogels is of great interest because of their inherent biochemical and biophysical properties, such as cellular adhesion, degradation, and viscoelasticity. The objective of this Review is to provide a detailed overview of the design and development of biopolymer hydrogels for biomedical applications, with an emphasis on biopolymer chemical modifications and cross-linking methods. First, the fundamentals of biopolymers and chemical conjugation methods to introduce cross-linking groups are described. Cross-linking methods to form biopolymer networks are then discussed in detail, including (i) covalent cross-linking (e.g., free radical chain polymerization, click cross-linking, cross-linking due to oxidation of phenolic groups), (ii) dynamic covalent cross-linking (e.g., Schiff base formation, disulfide formation, reversible Diels-Alder reactions), and (iii) physical cross-linking (e.g., guest-host interactions, hydrogen bonding, metal-ligand coordination, grafted biopolymers). Finally, recent advances in the use of chemically modified biopolymer hydrogels for the biofabrication of tissue scaffolds, therapeutic delivery, tissue adhesives and sealants, as well as the formation of interpenetrating network biopolymer hydrogels, are highlighted.

Multifunctional injectable pluronic-cystamine-alginate-based hydrogel as a novel cellular delivery system towards tissue regeneration

This paper presents a new thermal sensitive hydrogel system based on cystamine-functionalised sodium alginate-g-pluronic F127 (ACP). The introduction of cystamine to the alginate backbone not only creates a covalent bond with pluronic F127 but also provides intrinsic anti-bacterial activity for the resultant hydrogel. The amount of water uptake inside the hydrogel remained ~200% for 6 days and the degradation was completed in 12 days in physiological media. The ACP copolymer solution could form a hydrogel at body temperature (~37 °C) and could return to the solution phase if the temperature decreased below 25o °C. Fibroblast encapsulated in situ in the ACP hydrogel maintained their viability (≥90% based on the live/dead assay) for 7 days, demonstrating the good biocompatibility of the ACP hydrogel for long-term cell cultivation. In addition, three-dimensional (3D) culture showed that fibroblast attached to the hydrogels and successfully mimicked the porous structure of the ACP hydrogel after 5 days of culture. Fibroblast cells could migrate from the cell-ACP clusters and form a confluent cell layer on the surface of the culture dish. Altogether, the obtained results indicate that the thermal-responsive ACP hydrogel synthesised in this study may serve as a cellular delivery platform for diverse tissue engineering applications.

Biomaterial-based cell delivery strategies to promote liver regeneration

Chronic liver disease and cirrhosis is a widespread and untreatable condition that leads to lifelong impairment and eventual death. The scarcity of liver transplantation options requires the development of new strategies to attenuate disease progression and reestablish liver function by promoting regeneration. Biomaterials are becoming an increasingly promising option to both culture and deliver cells to support in vivo viability and long-term function. There is a wide variety of both natural and synthetic biomaterials that are becoming established as delivery vehicles with their own unique advantages and disadvantages for liver regeneration. We review the latest developments in cell transplantation strategies to promote liver regeneration, with a focus on the use of both natural and synthetic biomaterials for cell culture and delivery. We conclude that future work will need to refine the use of these biomaterials and combine them with novel strategies that recapitulate liver organization and function in order to translate this strategy to clinical use.

pH-Responsive Au(i)-disulfide nanoparticles with tunable aggregation-induced emission for monitoring intragastric acidity

Aggregation-induced emission (AIE)-featuring Au(i) complexes are superior probes for physiological environment monitoring in living organisms owing to their excellent biocompatibility and efficient luminescent properties. However, the intrinsic obstacle of poor water stability and lack of response to biological stimuli greatly restrict their practical application in biological systems. Herein, water-stable and pH-responsive Au(i)-disulfide nanoparticles (NPs) with AIE characteristics were designed. The NPs were prepared by integrating a pH-responsive moiety, cysteine (Cys), into Au(i)-thiolate (SR) complexes, and the Au(i)-SR-Cys structure was formed through disulfide bonds. Hydrophilic Cys was located on the outer layer of the NPs, endowing the spherical NPs with high stability and remarkable monodispersity in water. In addition, Cys endowed the NPs with pH-responsive characteristics. These unique advantages enable them to hold great promise as luminescent probes to monitor intragastric acidity in an acid suppression therapy. To the best of our knowledge, this work is the first example of luminescent Au(i) materials to monitor physiological changes.

Advanced Biomaterials and Processing Methods for Liver Regeneration: State-of-the-Art and Future Trends

Liver diseases contribute markedly to the global burden of mortality and disease. The limited organ disposal for orthotopic liver transplantation results in a continuing need for alternative strategies. Over the past years, important progress has been made in the field of tissue engineering (TE). Many of the early trials to improve the development of an engineered tissue construct are based on seeding cells onto biomaterial scaffolds. Nowadays, several TE approaches have been developed and are applied to one vital organ: the liver. Essential elements must be considered in liver TE-cells and culturing systems, bioactive agents or growth factors (GF), and biomaterials and processing methods. The potential of hepatocytes, mesenchymal stem cells, and others as cell sources is demonstrated. They need engineered biomaterial-based scaffolds with perfect biocompatibility and bioactivity to support cell proliferation and hepatic differentiation as well as allowing extracellular matrix deposition and vascularization. Moreover, they require a microenvironment provided using conventional or advanced processing technologies in order to supply oxygen, nutrients, and GF. Herein the biomaterials and the conventional and advanced processing technologies, including cell-sheets process, 3D bioprinting, and microfluidic systems, as well as the future trends in these major fields are discussed.

Crosslinking of hybrid scaffolds produced from collagen and chitosan

The development of biodegradable scaffolds able to support cell growth has recently become of great importance. Therefore, the main objective of this work was the development of hybrid scaffolds made from the mixture of two biopolymers (collagen and chitosan) and the comparison of the effect of glutaraldehyde as crosslinking agent with three different crosslinking methods (chemical: genipin; physical: temperature and enzymatic: transglutaminase) in order to look for a promising candidate to substitute it. To achieve this purpose, the mechanical properties, structure, porosity, degree of crosslinking and swelling of the different scaffolds were assessed. The best ratio of biopolymers (collagen:chitosan) to form hybrid scaffolds was 1:1, which improve their mechanical and morphological properties compared to unitary scaffolds (only collagen or chitosan). In addition, the incorporation of 10% w/w transglutaminase (crosslinking agent) with respect to the mass of biopolymers made these scaffolds a good structure for the growth and proliferation of cells.

Biocompatible disulphide cross-linked sodium alginate derivative nanoparticles for oral colon-targeted drug delivery

The application of layer-by-layer (LbL) approach on nanoparticle surface coating improves the colon-specific drug delivery of insoluble drugs. Here, we aimed to formulate a self-assembled cysteamine-based disulphide cross-linked sodium alginate with LbL self-assembly to improve the delivery of paclitaxel (PCX) to colonic cancer cells. Cysteamine was conjugated to the backbone of oxidized SA to form a core of self-assembled disulphide cross-linked nanospheres. P3DL was selected for PCX loading and fabricated LbL with poly(allylamine hydrochloride) (PAH) and poly(4-styrenesulfonic acid-co-maleic acid) sodium salt (PSSCMA) resulting from characterization and drug release studies. P3DL-fabricated PCX-loaded nanospheres (P3DL/PAH/PSSCMA) exhibited an encapsulation efficiency of 77.1% with cumulative drug release of 45.1%. Dynamic light scattering analysis was reported at 173.6 ± 2.5 nm with polydispersity index of 0.394 ± 0.105 (zeta potential= -58.5 mV). P3DL/PAH/PSSCMA demonstrated a pH-dependent swelling transition; from pH 1 to 7 (102.2% increase). The size increased by 33.0% in reduction response study after incubating with 10 mM glutathione (day 7). HT-29 cells showed high viabilities (86.7%) after treatment with the fabricated nanospheres at 0.8 µg/mL. Cellular internalization was successful with more than 70.0% nanospheres detected in HT-29 cells. Therefore, this fabricated nanospheres may be considered as potential nanocarriers for colon cancer-targeted chemotherapeutic drug delivery.

Design of a Versatile pH-Responsive Hydrogel for Potential Oral Delivery of Gastric-Sensitive Bioactives

A pH-responsive hydrogel system was prepared by free radical polymerization of acrylamide and methyl acrylic acid in the presence of N-N′-methylene bisacrylamide. Sodium bicarbonate was further applied as a blowing agent, which afforded a porous hydrogel structure. The hydrogel system achieved a constant super swelling rate within simulated intestinal buffer (~4%/min) and remained relatively static within simulated gastric buffer (~0.8%/min). The hydrogel system was able to achieve matrix resilience greater than 30% under a relatively high strain of 40%. In addition, the hydrogel system demonstrated significant swelling properties in response to simulated intestinal environmental over 24 h, with contrasting characteristics in simulated gastric buffer. The hydrogel demonstrated type IV isotherm porosity characteristics, with remarkable MRI and SEM variations in gastric and intestinal simulated fluids. Drug loading was observed to be greater than 98% using theophylline as a prototype drug, evaluating its controlled release kinetics over 24 h. The hydrogel exhibited substantial pH-responsive activity, which could be used as a versatile platform for targeted release of gastric-sensitive therapeutics to the small intestine.

Tissue engineering: Dentin - pulp complex regeneration approaches (A review)

Dental pulp is a highly specialized tissue that preserves teeth. It is important to maintain the capabilities of dental pulp before a pulpectomy by creating a local restoration of the dentin-pulp complex from residual dental pulp. The articles identified were selected by two reviewers based on entry and exit criteria. All relevant articles indexed in PubMed, Springer, Science Direct, and Scopus with no limitations from 1961 to 2016 were searched. Factors investigated in the selected articles included the following key words: Dentin-Pulp Complex, Regeneration, Tissue Engineering, Scaffold, Stem Cell, and Growth Factors. Of the 233 abstracts retrieved, the papers which were selected had evaluated the clinical aspects of the application of dentin-pulp regeneration. Generally, this study has introduced a new approach to provoke the regeneration of the dentin-pulp complex after a pulpectomy, so that exogenous growth factors and the scaffold are able to induce cells and blood vessels from the residual dental pulp in the tooth root canal. This study further presents a new strategy for local regeneration therapy of the dentin-pulp complex. This review summarizes the current knowledge of the potential beneficial effects derived from the interaction of dental materials with the dentin-pulp complex as well as potential future developments in this exciting field.

Carbon nanodots crosslinked photoluminescent alginate hydrogels

Multicolor, fluorescent, stable, alginate hydrogels are synthesized by crosslinking alginate chains with phenylenediamine based carbon nanodots.

Microstructural, mechanical, and histological evaluation of modified alginate-based scaffolds

Scaffolds are three-dimensional structures used for tissue regeneration being the base in tissue engineering. These scaffolds are obtained from natural and/or synthetic polymers and they should satisfy some specific requirements such as biocompatibility, suitable mechanical, and microstructural properties to favor cellular adhesion and neovascularization. This work shows a preclinic study about the production of low and medium molecular weight alginate through the use of calcium salts (calcium glutamate). The results showed prove that better structures, distribution, and pore sizes as well as better mechanical properties correspond to medium molecular weight alginate and higher calcium salts concentration. This type of scaffold, after muscular cells cultivation, has been proved as an excellent material for muscle growth. The histopathological analysis shows a low inflammatory response, without a foreign body reaction, suitable neovascularization and good fibroblasts incorporation. © 2016 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 104A: 3107-3114, 2016.

3-Dimensional porous nanocomposite scaffolds based on cellulose nanofibers for cartilage tissue engineering: tailoring of porosity and mechanical performance

Fully bio-based 3D porous scaffold based on cellulose nanofibers with potential use in cartilage tissue engineering was developed.

Functionalized scaffolds to control dental pulp stem cell fate

Emerging understanding about interactions between stem cells, scaffolds, and morphogenic factors has accelerated translational research in the field of dental pulp tissue engineering. Dental pulp stem cells constitute a subpopulation of cells endowed with self-renewal and multipotency. Dental pulp stem cells seeded in biodegradable scaffolds and exposed to dentin-derived morphogenic factors give rise to a pulplike tissue capable of generating new dentin. Notably, dentin-derived proteins are sufficient to induce dental pulp stem cell differentiation into odontoblasts. Ongoing work is focused on developing ways of mobilizing dentin-derived proteins and disinfecting the root canal of necrotic teeth without compromising the morphogenic potential of these signaling molecules. On the other hand, dentin by itself does not appear to be capable of inducing endothelial differentiation of dental pulp stem cells despite the well-known presence of angiogenic factors in dentin. This is particularly relevant in the context of dental pulp tissue engineering in full root canals in which access to blood supply is limited to the apical foramina. To address this challenge, scientists are looking at ways to use the scaffold as a controlled-release device for angiogenic factors. The aim of this article was to present and discuss current strategies to functionalize injectable scaffolds and customize them for dental pulp tissue engineering. The long-term goal of this work is to develop stem cell-based therapies that enable the engineering of functional dental pulps capable of generating new tubular dentin in humans.

Chemically crosslinked alginate porous microcarriers modified with bioactive molecule for expansion of human hepatocellular carcinoma cells

Microcarrier is an essential matrix for the large-scale culture of anchorage-dependent cells. In this study, chemical cross-linked alginate porous microcarriers (AMC) were prepared using microemulsion and freeze-drying technology. Moreover, chitosan was coated on the surface of microcarriers (AMC-CS) via electrostatic interactions to improve the mechanical strength. The size of AMC can be modulated through adjusting the concentration of alginate, amount of dispersant and stirring rate. The surface chemical characteristics and morphology of AMC-CS were evaluated by Fourier transformed infrared, X-ray photoelectron spectroscopy, and scanning electron microscope. Fibronectin (Fn) or heparin/basic fibroblast growth factor (bFGF) was then immobilized on the surface of microcarriers via layer-by-layer technology to improve the cytocompatibility. Our data suggested that the size of AMC can be accurately modulated from 90 μm to 900 μm with a narrow size distribution. Micropore structures of AMC-CS were relatively disordered and the pore size ranged between 20 μm and 100 μm. Using AMC after modified with Fn or bFGF as the cell expansion microcarriers, we showed that the proliferation rates of HepG2 cells increased significantly, reaching to more than 30-fold of cell expansion after 10 days of culture, with minor cellular damage caused by the microcarriers. Moreover, the AMC microcarriers modified with Fn or bFGF can increase albumin secretion of HepG2. We suggest that our new modified AMC-based microcarriers will be an attractive candidate for the large-scale cell culture of therapeutic cells.

Effect of cross-linkers in fabrication of carrageenan-alginate matrices for tissue engineering application

The three-dimensional (3D) scaffold serves as a structural substrate and as a niche for cell proliferation to ensure tissue regeneration. Ideal scaffolds should have porous structures with high pore interconnectivity to allow cell adherence, differentiation, and proliferation while ensuring suitable mechanical strength and biodegradability without inflicting any immune response. Cross-linker is one of the major factors that affect the mechanical and biological properties of scaffolds. In this study, different chemical cross-linker effects on scaffold architecture were examined. Porous 3D scaffolds based on carrageenan and alginate (CA) were successfully fabricated by a freeze-drying technique and using various cross-linkers like glutaraldehyde (GA), genipin, and ethyl (dimethylamino propyl) carbodiimide/N-hydroxysuccinimide (EDC/NHS). The chemical cross-linker effects on the CA scaffold were characterized by scanning electron microscopy, differential scanning calorimetry, and thermogravimetry. A human fibroblast cell line (L929) was seeded into the fabricated scaffold, and cell proliferation was assessed by MTT and live/dead assay. Overall results suggested the potential cross-linkers for ideal CA biomaterial could be EDC/NHS among other agents tested as the scaffold CAEN was found to be porous, interconnected, and physically and mechanically stable. When compared to matrices with other cross-linkers, higher cell attachment, better cellular response, and higher metabolic activity could be observed in the scaffold synthesized using EDC/NHS as cross-linker.

Redox-responsive alginate nanogels with enhanced anticancer cytotoxicity

Although doxorubicin (Dox) has been widely used in the treatment of different types of cancer, its insufficient cellular uptake and intracellular release is still a limitation. Herein, we report an easy process for the preparation of redox-sensitive nanogels that were shown to be highly efficient in the intracellular delivery of Dox. The nanogels (AG/Cys) were obtained through in situ cross-linking of alginate (AG) using cystamine (Cys) as a cross-linker via a miniemulsion method. Dox was loaded into the AG/Cys nanogels by simply mixing it in aqueous solution with the nanogels, that is, by the establishment of electrostatic interactions between the anionic AG and the cationic Dox. The results demonstrated that the AG/Cys nanogels are cytocompatible, have a high drug encapsulation efficiency (95.2 ± 4.7%), show an in vitro accelerated release of Dox in conditions that mimic the intracellular reductive conditions, and can quickly be taken up by CAL-72 cells (an osteosarcoma cell line), resulting in higher Dox intracellular accumulation and a remarkable cell death extension when compared with free Dox. The developed nanogels can be used as a tool to overcome the problem of Dox resistance in anticancer treatments and possibly be used for the delivery of other cationic drugs in applications beyond cancer.

In vitro and in vivo evaluation of chitosan-gelatin scaffolds for cartilage tissue engineering

Chitosan-gelatin polyelectrolyte complexes were fabricated and evaluated as tissue engineering scaffolds for cartilage regeneration in vitro and in vivo. The crosslinker for the gelatin component was selected among glutaraldehyde, bisepoxy, and a water-soluble carbodiimide (WSC) based upon the proliferation of chondrocytes on the crosslinked gelatin. WSC was found to be the most suitable crosslinker. Complex scaffolds made from chitosan and gelatin with a component ratio equal to one possessed the proper degradation rate and mechanical stability in vitro. Chondrocytes were able to proliferate well and secrete abundant extracellular matrix in the chitosan-gelatin (1:1) complex scaffolds crosslinked by WSC (C1G1WSC) compared to the non-crosslinked scaffolds. Implantation of chondrocytes-seeded scaffolds in the defects of rabbit articular cartilage confirmed that C1G1WSC promoted the cartilage regeneration. The neotissue formed the histological feature of tide line and lacunae in 6.5 months. The amount of glycosaminoglycans in C1G1WSC constructs (0.187±0.095 μg/mg tissue) harvested from the animals after 6.5 months was 14 wt.% of that in normal cartilage (1.329±0.660 μg/mg tissue). The average compressive modulus of regenerated tissue at 6.5 months was about 0.539 MPa, which approached to that of normal cartilage (0.735 MPa), while that in the blank control (3.881 MPa) was much higher and typical for fibrous tissue. Type II collagen expression in C1G1WSC constructs was similarly intense as that in the normal hyaline cartilage. According to the above results, the use of C1G1WSC scaffolds may enhance the cartilage regeneration in vitro and in vivo.