Evaluation of sodium alginate for bone marrow cell tissue engineering

A hydrophobically-modified alginate gel system: utility in the repair of articular cartilage defects

Alginate is a family of natural polysaccharides, widely used in industry and medicine for many applications, with its non toxic nature, gentle sol/gel transition procedure and low cost, alginate inferior biomechanical properties have limited its utility especially in tissue engineering. Additionally, ionically cross-linked alginate hydrogels generally lose most of their initial mechanical and swelling properties within a few hours in physiological solution. In order to overcome these limitations, the referenced alginate was treated by covalent fixation of octadecyl chains onto the polysaccharide backbone by esterification. In semi dilute solution, intermolecular hydrophobic interactions of long alkyl chains result in the formation of physical hydrogels, which can then be reinforced by the addition of calcium chloride. FTIR studies clearly showed the presence of ester bonds at 1612 and 1730 cm(-1) indicating that the alkyl groups are incorporated in the backbone of resulting polymer. The endothermic peak and exothermic peak present in the DSC thermogram of Alg-C18 had shifted to lower temperatures comparing to native alginate (from 106 to 83°C and from 250 to 245°C, respectively) due to the esterification reaction that leads to high hydrophobic nature of the modified sample. From rheological experiments, it can be inferred that the combination of both calcium bridges and intermolecular hydrophobic interaction in the treated alginate leads to enhanced gel strength accompanied by more stable structure in physiological solution comparing to native sodium alginate hydrogel. Finally, the modified alginate tended to have no toxic effects on mesenchymal stem cell culture, rather it supported MSC chondrogenic differentiation.

Formation of an aggregated alginate construct in a tubular perfusion system

Tissue engineering strategies are often limited by in vitro culture techniques of three dimensional scaffolds. Here we develop a method to form an aggregated cell-containing construct in vitro in a bioreactor system. Human mesenchymal stem cells (hMSCs) are cultured in individual alginate beads in a tubular perfusion system (TPS) bioreactor and then aggregated to form a single large construct. Mechanical evaluation of this construct demonstrated that aggregated alginate constructs (AACs) made from beads with 2.15 mm diameters had a Young's modulus of 85.6±15.8 kPa, a tensile strength of 3.24±0.55 kPa and a yield strength of 1.44±0.27 kPa. These mechanical properties were shown to be dependent on the bead size used to fabricate the AACs with smaller bead sizes resulting in stronger constructs. Analysis of metabolic activity revealed that hMSCs encapsulated in alginate exposed to AAC treatment sustained metabolic activity while live dead staining indicated cells remain viable. These results demonstrate the formation of AACs in the TPS bioreactor as an elegant method to create tissue engineering constructs in vitro.

Fabrication of chitin-chitosan/nano ZrO(2) composite scaffolds for tissue engineering applications

The urge to repair and regenerate natural tissues can now be satisfactorily fulfilled by various tissue engineering approaches. Chitin and chitosan are the most widely accepted biodegradable and biocompatible materials subsequent to cellulose. The incorporation of nano ZrO(2) onto the chitin-chitosan scaffold is thought to enhance osteogenesis. Hence a nanocomposite scaffold was fabricated by lyophilization technique using chitin-chitosan with nano ZrO(2). The prepared nanocomposite scaffolds were characterized using SEM, FTIR, XRD and TGA. In addition, the swelling, degradation, biomineralization, cell viability and cell attachment of the composite scaffolds were also evaluated. The results demonstrated better swelling and controlled degradation in comparison to the control scaffold. Cell viability studies proved the non toxic nature of the nanocomposite scaffolds. Cells were found to be attached to the pore walls and spread uniformly throughout the scaffolds. All these results suggested that the developed nanocomposite scaffolds possess the prerequisites for tissue engineering scaffolds and could be used for various tissue engineering applications.

Continuum-level modelling of cellular adhesion and matrix production in aggregates

Key regulators in tissue-engineering processes such as cell culture and cellular organisation are the cell-cell and cell-matrix interactions. As mathematical models are increasingly applied to investigate biological phenomena in the biomedical field, it is important, for some applications, that these models incorporate an adequate description of cell adhesion. This study describes the development of a continuum model that represents a cell-in-gel culture system used in bone-tissue engineering, namely that of a cell aggregate embedded in a hydrogel. Cell adhesion is modelled through the use of non-local (integral) terms in the partial differential equations. The simulation results demonstrate that the effects of cell-cell and cell-matrix adhesion are particularly important for the survival and growth of the cell population and the production of extracellular matrix by the cells, concurring with experimental observations in the literature.

Tubular perfusion system for the long-term dynamic culture of human mesenchymal stem cells

In vitro culture techniques must be improved to increase the feasibility of cell-based tissue engineering strategies. To enhance nutrient transport we have developed a novel bioreactor, the tubular perfusion system (TPS), to culture human mesenchymal stem cells (hMSCs) in three-dimensional scaffolds. This system utilizes an elegant design to create a more effective environment for cell culture. In our design, hMSCs in the TPS bioreactor are encapsulated in alginate beads that are tightly packed in a tubular growth chamber. The medium is perfused by a peristaltic pump through the growth chamber and around the tightly packed scaffolds enhancing nutrient transfer while exposing the cells to shear stress. Results demonstrate that bioreactor culture supports early osteoblastic differentiation of hMSCs as shown by alkaline phosphatase gene expression. After 14 and 28 days of culture significant increases in the gene expression levels of osteocalcin, osteopontin, and bone morphogenetic protein-2 were observed with bioreactor culture, and expression of these markers was shown to increase with media flow rate. These results demonstrate the TPS bioreactor as an effective means to culture hMSCs and provide insight to the effect of long-term shear stresses on differentiating hMSCs.

Differentiation of bone marrow-derived mesenchymal stem cells into hepatocyte-like cells in an alginate scaffold

OBJECTIVES

Alginate scaffolds are the most frequently investigated biomaterials in tissue engineering. Tissue engineering techniques that generate liver tissue have become important for treatment of a number of liver diseases and recent studies indicate that bone marrow-derived stem cells (BMSCs) can differentiate into hepatocyte-like cells. The goal of the study described here, was to examine in vitro hepatic differentiation potential of BMSCs cultured in an alginate scaffold.

MATERIALS AND METHODS

To investigate the potential of BMSCs to differentiate into hepatocyte-like cells, we cultured BMSCs in alginate scaffolds in the presence of specific growth factors including hepatocyte growth factor, epidermal growth factor and fibroblast growth factor-4.

RESULTS

We can demonstrate that alginate scaffolds are compatible for growth of BMSCs and when cultured in alginate scaffolds for several days they display several liver-specific markers and functions. Specifically, they expressed genes encoding alpha-foetoprotein, albumin (ALB), connexin 32 and CYP7A1. In addition, these BMSCs produced both ALB and urea, expressed cytokeratin-18 (CK-18) and were capable of glycogen storage. Percentage of CK-18 positive cells, a marker of hepatocytes, was 56.7%.

CONCLUSIONS

Our three-dimensional alginate scaffolds were highly biocompatible with BMSCs. Furthermore, culturing induced their differentiation into hepatocyte-like cells. Therefore, BMSCs cultured in alginate scaffolds may be applicable for hepatic tissue engineering.

Cold gelation of alginates induced by monovalent cations

A new reversible gelation pathway is described for alginates in aqueous media. From various samples differing by their mannuronic/guluronic content (M/G), both enthalpic and viscoelastic experiments demonstrate that alginates having a high M content are able to form thermoreversible assemblies in the presence of potassium salts. The aggregation behavior is driven by the low solubility of M-blocks at low temperature and high ionic strength. In semidilute solutions, responsive assemblies induce a strong increase of the viscosity below a critical temperature. A true physical gel is obtained in the entangled regime, although the length scale of specific interactions between M-blocks decreases with increasing density of entanglements. Cold setting takes place at low temperatures, below 0 °C for potassium concentrations lower than 0.2 mol/kg, but the aggregation process can be easily shifted to higher temperatures by increasing the salt concentration. The self-assembling process of alginates in solution of potassium salts is characterized by a sharp gelation exotherm and a broad melting endotherm with a large hysteresis of 20-30 °C between the transition temperatures. The viscoelastic properties of alginate gels in potassium salts closely depend on thermal treatment (rate of cooling, time, and temperature of storage), polymer and salt concentrations, and monomer composition as well. In the case of alginates with a high G content, a similar aggregation behavior is also evidenced at higher salt concentrations, but the extent of the self-assembling process remains too weak to develop a true gelation behavior in solution.

Repair of large cranial defects by hBMP-2 expressing bone marrow stromal cells: comparison between alginate and collagen type I systems

Despite a wide range of available sources for bone repair, significant limitations persist. To bioengineer bone, we have previously transferred adenovirus-mediated human BMP-2 gene into autologous bone marrow stromal cells (MSC). We have successfully repaired large, full thickness, cranial defects using this approach. We report now the effectiveness of various hydrogels as the scaffold for this type of bone regeneration, comparing specifically alginate with Type I collagen. Cultured MSC of miniature swine were infected with BMP-2 or beta-gal adenovirus 7 days before implantation. These cells were mixed with alginate, ultrapure alginate, alginate-RGD, or type I collagen to fabricate the MSC/biomaterial constructs. The results of cranial bone regeneration were assessed by gross examination, histology, 3D CT, and biomechanical tests at 6 weeks and 3 months after implantation. We found that the BMP-2 MSC/collagen type I construct, but not the beta-gal control, effectively achieved nearly complete repair of the cranial defects. No bone regeneration was observed with the other hydrogels. Biomechanical testing showed that the new bone strength was very close and only slightly inferior to that of normal cranial bone. Controlling for the integration of stem cells and ex vivo gene transfer, the alginate scaffolds has a significant negative impact on the success of the construct. Our study demonstrates better bone regeneration by collagen type I over alginate. This may have therapeutic implications for tissue engineered bone repair.

Encapsulation of fibroblasts causes accelerated alginate hydrogel degradation

Calcium-alginate hydrogel has been widely studied as a material for cell encapsulation for tissue engineering. At present, the effect that cells have on the degradation of alginate hydrogel is largely unknown. We have shown that fibroblasts encapsulated at a density of 7.5 x 10(5) cells ml(-1) in both 2% and 5% w/v alginate remain viable for at least 60 days. Rheological analysis was used to study how the mechanical properties exhibited by alginate hydrogel changed during 28 days in vitro culture. Alginate degradation was shown to occur throughout the study but was greatest within the first 7 days of culture for all samples, which correlated with a sharp release of calcium ions from the construct. Fibroblasts were shown to increase the rate of degradation during the first 7 days when compared with acellular samples in both 2% and 5% w/v gels, but after 28 days both acellular and cell-encapsulating samples retained disc-shaped morphologies and gel-like spectra. The results demonstrate that although at an early stage cells influence the mechanical properties of encapsulating alginate, over a longer period of culture, the hydrogels retain sufficient mechanical integrity to exhibit gel-like properties. This allows sustained immobilization of the cells at the desired location in vivo where they can produce extracellular matrix and growth factors to expedite the healing process.

Effect of Nell-1 delivery on chondrocyte proliferation and cartilaginous extracellular matrix deposition

Cartilage tissue engineering using chondrogenic growth factors is an attractive strategy to promote cartilage repair. Bone morphogenetic proteins have been widely studied for their application in cartilage repair. However, functional heterogeneity of bone morphogenetic proteins and unpredictable effects such as cyst formation may limit their therapeutic use. Thus, the use of alternative growth factors with greater osteochondral specificity may be advantageous for cartilage regeneration. Nel-like molecule-1 (Nell-1; Nel is a protein strongly expressed in neural tissue encoding epidermal growth factor-like domain) is a novel growth factor believed to specifically target cells committed to the osteochondral lineage. Mutation of the Nell-1 gene has been shown to disrupt normal cartilage growth and development in rodents. This study investigates the chondrogenic potential of recombinant human Nell-1 protein in a three-dimensional alginate hydrogel microenvironment containing rabbit chondrocytes. To provide controlled delivery and maximize biological efficiency, Nell-1 was incorporated in chitosan microparticles. Over 42 days of culture, chondrocyte proliferation and cluster formation was significantly enhanced by Nell-1 in a dose-dependent manner. Further, the clusters formed in the presence of Nell-1 contained more type II collagen and glycosaminoglycans than clusters formed within Nell-free control gels. These findings demonstrate the ability of Nell-1 to promote chondrocyte proliferation and deposition of cartilage-specific extracellular matrix materials.

Cell microencapsulation

In the past several decades, many attempts have been made to prevent the rejection of transplanted cells by the immune system. Cell encapsulation is primary machinery for cell transplantation and new materials and approaches were developed to encapsulate various types of cells to treat a wide range of diseases. This technology involves placing the transplanted cells within a biocompatible membrane in attempt to isolate the cells from the host immune attack and enhance or prolong their function in vivo. In this chapter, we will review the situation of cell microencapsulation field and discuss its potentials and challenges for cell therapy and regeneration of tissue function.

Preparation and characterization of an injectable composite

Hydrogels are increasingly used in medicine due to their potential to be delivered into the body in a minimally invasive manner and to be gelated at the site of introduction subsequently. The aim of this study was to develop a novel injectable and in situ-forming gel composite (GC) comprised of calcium alginate hydrogel and nano-hydroxyapatite/collagen (nHAC), assess its rheological, mechanical and in vitro degradable properties, and discuss the gelation mechanism. Injectable property test showed that the injectability of GC was tunable. Rheological results indicated that three phases of pre-gel, sol-gel phase transformation and post-gel could be found in the process of gelation. The compressive elastic modulus (E) and shear modulus (G) are in the range of 17.0-56.0 kPa and 24.7-55.0 kPa, respectively. During the in vitro degradation, the wet weight increased in the first week, then declined in the following 3 weeks, but the dry weight lost continuously during whole study. Meanwhile, the surface changed greatly after 2 weeks, but samples did not break down up to 28 days. These data indicate that GC exhibits controllable initial setting time and final setting time, tunable injectability, which provides a possible injectable material for bone repair and bone tissue engineering.

Preparation of injectable 3D-formed beta-tricalcium phosphate bead/alginate composite for bone tissue engineering

A novel, injectable bone tissue engineering material was developed that consisted of beta-tricalcium phosphate (beta-TCP) beads as the solid phase and alginate as the gel phase. To prepare the instantaneously formed composite scaffold, an aqueous calcium chloride solution was dried on the surface of beta-TCP beads and crosslinked with an alginic acid sodium solution, thereby forming stable beta-TCP beads and alginate gel which were injectable via a syringe. This biodegradable composite was a three-dimensional (3D) material that could be used as an injectable scaffold for bone tissue engineering. In particular, the composite with 2.0 wt% alginate concentration exhibited a compressive strength of 69 kPa in dry conditions, which was significantly higher than that exhibited by 1.0 wt%. Furthermore, mesenchymal stem cells (MSC) were 3D-cultured within the composite and then investigated for osteogenic markers. MSC-loaded composite was subjected to scanning electron microscope (SEM) examination and implanted subcutaneously for in vivo experiment. Results showed that the scaffold provided support for osteogenic differentiation. In light of the encouraging results obtained, this novel injectable composite material may be useful for bone tissue engineering.

Wound healing dressings and drug delivery systems: a review

The variety of wound types has resulted in a wide range of wound dressings with new products frequently introduced to target different aspects of the wound healing process. The ideal dressing should achieve rapid healing at reasonable cost with minimal inconvenience to the patient. This article offers a review of the common wound management dressings and emerging technologies for achieving improved wound healing. It also reviews many of the dressings and novel polymers used for the delivery of drugs to acute, chronic and other types of wound. These include hydrocolloids, alginates, hydrogels, polyurethane, collagen, chitosan, pectin and hyaluronic acid. There is also a brief section on the use of biological polymers as tissue engineered scaffolds and skin grafts. Pharmacological agents such as antibiotics, vitamins, minerals, growth factors and other wound healing accelerators that take active part in the healing process are discussed. Direct delivery of these agents to the wound site is desirable, particularly when systemic delivery could cause organ damage due to toxicological concerns associated with the preferred agents. This review concerns the requirement for formulations with improved properties for effective and accurate delivery of the required therapeutic agents. General formulation approaches towards achieving optimum physical properties and controlled delivery characteristics for an active wound healing dosage form are also considered briefly.

Osteogenic behavior of alginate encapsulated bone marrow stromal cells: an in vitro study

Sodium alginate is a useful polymer for the encapsulation and immobilization of a variety of cells in tissue engineering because it is biocompatible, biodegradable and easy to process into injectable microbeads. Despite these properties, little is known of the efficacy of calcium cross-linked alginate gel beads as a biodegradable scaffold for osteogenic cell proliferation and differentiation. In this study, we investigated the ability of rabbit derived bone marrow cells (BMCs) to proliferate and differentiate in alginate microbeads and compared them with BMCs cultured in poly-L-lysine (PLL) coated microbeads and on conventional 2D plastic surfaces. Results show that levels of proliferation and differentiation in microbeads and on tissue culture plastics were comparable. Cell proliferation in microbeads however diminished after fortification with a coating layer of PLL. Maximum cell numbers observed were, 3.32 x 10(5) +/- 1.72 x 103; 3.11 x 10(5) +/- 1.52 x 10(3) and 3.28 x 10(5) +/- 1.21 x 10(3 ) for the uncoated, PLL coated and plastic surface groups respectively. Alkaline phosphatase and protein expressions reflected the stage of cell differentiation. We conclude that calcium cross-linked alginate microbeads can act as a scaffold for BMC proliferation and osteogenic differentiation and has potential for use as 3D degradable scaffold.

Tendon tissue engineering using scaffold enhancing strategies

Tendon traumas or diseases are prevalent and debilitating lesions that affect the quality of life among populations worldwide. As a novel solution, tendon tissue engineering aims to address these lesions by integrating engineered, living substitutes with their native counterparts in vivo, thereby restoring the defective functions in situ. For such a purpose, competent scaffolding materials are essential. To date, three major categories of scaffolding materials have been employed: polyesters, polysaccharides, and collagen derivatives. Furthermore, with these materials as a base, a variety of specialized methodologies have been developed or adopted to enhance neo-tendogenesis. These strategies include cellular hybridization, interfacing improvement, and physical stimulation.

Hydrogels as Extracellular Matrices for Skeletal Tissue Engineering: State-of-the-Art and Novel Application in Organ Printing

Organ printing, a novel approach in tissue engineering, applies layered computer-driven deposition of cells and gels to create complex 3-dimensional cell-laden structures. It shows great promise in regenerative medicine, because it may help to solve the problem of limited donor grafts for tissue and organ repair. The technique enables anatomical cell arrangement using incorporation of cells and growth factors at predefined locations in the printed hydrogel scaffolds. This way, 3-dimensional biological structures, such as blood vessels, are already constructed. Organ printing is developing fast, and there are exciting new possibilities in this area. Hydrogels are highly hydrated polymer networks used as scaffolding materials in organ printing. These hydrogel matrices are natural or synthetic polymers that provide a supportive environment for cells to attach to and proliferate and differentiate in. Successful cell embedding requires hydrogels that are complemented with biomimetic and extracellular matrix components, to provide biological cues to elicit specific cellular responses and direct new tissue formation. This review surveys the use of hydrogels in organ printing and provides an evaluation of the recent advances in the development of hydrogels that are promising for use in skeletal regenerative medicine. Special emphasis is put on survival, proliferation and differentiation of skeletal connective tissue cells inside various hydrogel matrices.

Regulating Myoblast Phenotype Through Controlled Gel Stiffness and Degradation

Mechanical stiffness and degradability are important material parameters in tissue engineering. The aim of this study was to address the hypothesis that these variables regulate the function of myoblasts cultured in 2-D and 3-D microenvironments. Development of cell-interactive alginate gels with tunable degradation rates and mechanical stiffness was established by a combination of partial oxidation and bimodal molecular weight distribution. Higher gel mechanical properties (13 to 45 kPa) increased myoblast adhesion, proliferation, and differentiation in a 2-D cell culture model. Primary mouse myoblasts were more highly responsive to this cue than the C2C12 myoblast cell line. Myoblasts were then encapsulated in gels varying in degradation rate to simultaneously investigate the effect of degradation and subsequent reduction of mechanical properties on cells in a 3-D environment. C2C12 cells in more rapidly degrading gels exhibited lower proliferation, as they exited the cell cycle to differentiate, compared to those in nondegradable gels. In contrast, mouse primary myoblasts illustrated significantly higher proliferation in degradable gels than in nondegradable gels, and exhibited minimal differentiation in either type of gel. Altogether, these studies suggest that a critical balance between material degradation rate and mechanical properties may be required to regulate formation of engineered skeletal muscle tissue, and that results obtained with the C2C12 cell line may not be predictive of the response of primary myoblasts to environmental cues. The principles delineated in these studies may be useful to tailor smart biomaterials that can be applied to many other polymeric systems and tissue types.

In vivo stability and biocompatibility of implanted calcium alginate disks

Alginate is a commonly used biomedical hydrogel whose in vivo degradation behavior is only beginning to be understood. The use of alginate in the central nervous system is gaining popularity as an electrode coating, cell encapsulation matrix, and for duraplasty. However, it is necessary to understand how the hydrogel will behave in vivo to aid in the development of alginate for use as a neural interface material. The goal of the current study was to compare the rheological behavior of explanted alginate disks and the inflammatory response to subcutaneously implanted alginate hydrogels over a 3-month period. Specifically, the effects due to (1) in situ gelling, (2) diffusion gelling, and (3) use of a poly-l-lysine (PLL) coating were investigated. While all samples' complex moduli decreased 80% in the first day, in situ gelled alginate was more stable for the first week of implantation. The PLL coating offered some stability increases for diffusion gelled alginate, but the stability in both conditions remained significantly lower than that in in situ gelled alginate. There were no differences in biocompatibility that clearly suggested one gelation method over another. These results indicate that in situ gelation is the preferred method in neural interface applications where stability is the primary concern.

3D culture of bone-derived cells immobilised in alginate following light-triggered gelation

Photoreactive liposomes have been exploited as a means of developing 3D tissue constructs. Liposomes formulated using the photosensitive lipid 1,2-bis(4-(n-butyl)phenylazo-4'-phenylbutyroyl)phosphatidylcholine (Bis Azo PC), which undergoes conformational change on stimulation with long wavelength ultraviolet light, were prepared with entrapped CaCl(2) before being incorporated into a 4% alginate solution. It was shown that stimulation of the photosensitive lipid using a light emitting diode (LED) (peak emission at 385 nm, dose equivalent to 9 mJ/cm(2)) caused the release of liposome-entrapped CaCl(2), resulting in cross-linking of the alginate solution and immobilisation of bone-derived cells over a range of seeding densities, approximately 97% of which remained viable for periods of up to 14 days in culture. Entrapment volumes of a variety of liposome types were evaluated and interdigitating fusion vesicles were identified as having the highest payload (24%), however the inclusion of cholesterol as a means of shifting Bis Azo PC sensitivity into the visible light wavelengths resulted in an approximately 10-fold reduction in calcium entrapment. This application of light-sensitised liposomes offers the potential to create complex tissue engineering substrates containing cells immobilised in precise locations, in contrast with substrates onto which cells are seeded post-production.

Comparison of Hydrogels in theIn VivoFormation of Tissue-Engineered Bone Using Mesenchymal Stem Cells and Beta-Tricalcium Phosphate

Availability of grafts and morbidity at the donor site limit autologous transplantation in patients requiring bone reconstruction. A tissue-engineering approach can overcome these limitations by producing bone-like tissue of custom shape and size from isolated cells. Several hydrogels facilitate osteogenesis on porous scaffolds; however, the relative suitability of various hydrogels has not been rigorously assessed. Fibrin glue, alginate, and collagen I hydrogels were mixed with swine bone marrow-derived differentiated mesenchymal stem cells (MSCs), applied to 3-dimensionally printed porous beta-tricalcium phosphate (beta-TCP) scaffolds and implanted subcutaneously in nude mice. Although noninvasive assessment of osteogenesis in 3 dimensions is desirable for monitoring new bone formation in vivo, correlations with traditional histological and mechanical testing need to be established. High-resolution volumetric computed tomography (VCT) scanning, histological examination, biomechanical compression testing, and osteonectin (ON) expression were performed on excised scaffolds after 1, 2, 4, and 6 weeks of subcutaneous implantation in mice. Statistical correlation analyses were performed between radiological density, stiffness, and ON expression. Use of collagen I as a hydrogel carrier produced superior bone formation at 6 weeks, as demonstrated using VCT scanning with densities similar to native bone and the highest compression values. Continued contribution of the seeded MSCs was demonstrated using swine-specific messenger ribonucleic acid probes. Radiological density values correlated closely with the results of histological and biomechanical testing and ON expression. High-resolution VCT is a promising method for monitoring osteogenesis.

Chondrocyte-alginate bioconstructs: An nuclear magnetic resonance relaxation study

Proton nuclear magnetic resonance (NMR) relaxometry can give informations about hydrogel scaffold properties. As these properties can be modified with culture time and conditions according to scaffold biodegradability and new tissue biosynthesis, the aim of this research was to test the efficiency of this noninvasive NMR technique in the follow-up of 3D cultures for tissue engineering. The distributions of proton relaxation times T1 and T2 have been measured on cylindrical gel samples of different types of alginate, in the presence or absence of hyaluronate, in gels or bioconstructs with encapsulated chondrocytes cultured for 30 days in normal or reduced weight conditions. It was found that T2 increases with the mannuronate/guluronate ratio in alginate samples and with the presence of hyaluronate. The distributions of both T1 and T2 result wider for bioconstructs cultured in normal gravity than for those cultured in reduced weight conditions. Neither cell growing nor collagen production but only GAG neosynthesis have been demonstrated in our experimental conditions. In conclusion, T2 is sensitive to the gel properties (possibly to the rigidity of macromolecular components). The homogeneity of bioconstructs can be monitored by the distribution of T1 and T2. We propose that nonspatially resolved NMR relaxometry can efficiently be used in monitoring tissue development in a biodegradable scaffold for tissue engineering.

A novel method of encapsulating and cultivating adherent mammalian cells within collagen microcarriers

A novel method of preparing collagen microcarriers was developed and used to entrap adherent cells for cell culturing. This new technique involved seeding of cells in micro gel beads comprised of collagen fibrils dispersed in alginate. The gel beads were washed with phosphate buffered saline (PBS) to remove alginate and the resulting microspheres, about 300-500 microm in diameter, contained evenly distributed collagen fibrils which provided a 3D biomimetic environment for cell growth. The applicability of this microencapsulating system was demonstrated by its ability to support the growth of C2C12 myoblast cells. When seeded and cultured within the 3D collagen microcarriers, the population of C2C12 cells entrapped within the microcarriers increased by 1.5 folds in 7 days after inoculation. This encapsulation technique is potentially useful for culturing cells and especially useful for adherent cells that require a 3D fibrillar collagen environment.

Structurally Colored Thin Films of Ca2+-Cross-Linked Alginate

Alginate, or alginic acid, is an unbranched binary copolymer of (1-->4)-linked beta-D-mannuronic acid and alpha-L-guluronic acid. Alginate readily forms binding interactions with a variety of divalent metal ions, such as calcium. This binding has been used to cross-link bulk alginates for a wide variety of applications, particularly in areas of tissue engineering, medical devices, and wound-healing dressings. A new method is identified here for producing Ca2+-cross-linked thin films of sodium alginate, using an aerosolized spray of CaCl2 solution. These thin films exhibit structural color that varies with film thickness. It is demonstrated that this structural color is highly reproducible and can also be tuned to produce a wide range of colored films. The noted ability of alginates to bind metal ions is used in combination with the structural coloration afforded by the thin film structure as a basis for color-based optical sensing of metal ions in aqueous solutions. Changes in film thickness, refractive index, and reflectivity in response to metal ions have been measured and reported. For certain ions such as Cr(III) and Cr(VI), changes in film thickness are the predominate factors in shifting the reflected film color. In the case of other ions such as Pb(II), a change in film refractive index plays a significant role in the reflectance properties of films.

Environmental cues to guide stem cell fate decision for tissue engineering applications

The human body contains a variety of stem cells capable of both repeated self-renewal and production of specialised, differentiated progeny. Critical to the implementation of these cells in tissue engineering strategies is a thorough understanding of which external signals in the stem cell microenvironment provide cues to control their fate decision in terms of proliferation or differentiation into a desired, specific phenotype. These signals must then be incorporated into tissue regeneration approaches for regulated exposure to stem cells. The precise spatial and temporal presentation of factors directing stem cell behaviour is extremely important during embryogenesis, development and natural healing events, and it is possible that this level of control will be vital to the success of many regenerative therapies. This review covers existing tissue engineering approaches to guide the differentiation of three disparate stem cell populations: mesenchymal, neural and endothelial. These progenitor cells will be of central importance in many future connective, neural and vascular tissue regeneration technologies.

Efficacy of bone marrow-derived stem cells in strengthening osteoporotic bone in a rabbit model

Osteoporosis might be due to defects in mesenchymal stem cells (MSCs) that lead to reduced proliferation and osteoblast differentiation. We hypothesized that transplantation of MSCs into sites at risk for developing osteoporotic bone could improve bone structure and biomechanics. The aim of this study was to establish an osteoporosis rabbit model by ovariectomy (OVX), characterize the autologous MSCs from the OVX rabbits, and transplant the autologous MSCs into the OVX rabbits. MSCs harvested from bone marrow of normal and OVX rabbits were culture expanded and differentiated in osteogenic medium. Phenotypes were evaluated by collagen I immunostaining, von Kossa staining, and quantitative assays of bone-specific alkaline phosphatase (B-ALP) and osteocalcin (OCN). MSCs were transfected with green fluorescence protein (GFP) and implanted in the gluteus muscle to trace their fate in vivo. Cultured autologous MSCs from OVX rabbits were constructed in calcium alginate gels and then transplanted in the distal femurs. At 4 and 8 weeks after implantation, histomorphometrical and biomechanical analyses were performed on the samples. MSCs from OVX rabbits displayed higher B-ALP activity, but had similar OCN levels as compared to those from sham rabbits. After 8 weeks of implantation, more bone apposition was found in the MSC-alginate-treated group. Histomorphometry indicated increased trabecular thickness. Histology also illustrated improved microstructures with newly formed osteoids and enhanced trabecular thickness. In addition, biomechanical testing revealed stronger stiffness in the MSC-alginate treatment group. Therefore, this study implies that transplantation of MSCs can help to strengthen osteoporotic bone in rabbits.

Application of hanging drop technique for stem cell differentiation and cytotoxicity studies

The aim of our study is to explore the possibility of using an ancient method of culture technique- the hanging drop technique for stem cell differentiation and cytotoxicity testing. We demonstrate here a variety of novel applications of this age old technique not only to harness the differentiation potential of stem cells into specific lineages but also for cytotoxicity studies. Here we have prepared hanging drop cultures by placing 20 microl micro-drops of nutrient media and 10% Fetal Calf Serum (FCS) containing cells of interest on the lids of 60 mm dishes. Bottom plates of the dishes were filled with sterile Phosphate Buffer Saline (PBS) to avoid desiccation of samples. Lids were then placed on the bottom plates to achieve hanging drop cultures. We utilized this technique for cultivation of ciliated epithelia to study cytotoxicity and differentiation of bone marrow stromal cells. Most importantly the modified culture technique presented here is simple, economical and cost effective in terms of the time taken and the reagents required and are amenable to goal specific modification such as cytotoxicity testing. It is advantageous over the existing system in terms of retention of viability and functionality for longer duration and for providing three dimensional growth micro-environment making it useful for organotypic cultures and in vivo simulation.

In vitro evaluation of alginate encapsulated adipose-tissue stromal cells for use as injectable bone graft substitute

This study aims to investigate the survival and osteogenic behavior of murine-derived adipose-tissue stromal cells (ATSCs) encapsulated in alginate microcapsules thereby instigating further studies in this cell delivery strategy for in vivo osteogenesis. Cell viability was quantified using a tetrazolium-based assay and osteogenic differentiation was evaluated by both alkaline-phosphatase (ALP) histochemistry and osteocalcin mRNA analysis. Following microencapsulation, cell numbers increased from 3.9 x 10(3) on day 1 to 7.8 x 10(3) on day 7 and maintained excellent viability in the course of 21-day culture. ALP was 6.9, 5.5, and 3.2 times higher than monolayer cultures on days 7, 14, and 21, respectively. In addition, osteocalcin mRNA was detectable in encapsulated cultures earlier (day 14) than monolayer cultures. We conclude that alginate microcapsules can act as three-dimensional matrix for ATSC proliferation and has potential for use as injectable, biodegradable scaffold in bone tissue engineering.

Behavior of adult human mesenchymal stem cells entrapped in alginate-GRGDY beads

This study demonstrates that adult human mesenchymal cells (MSC) can be encapsulated in alginate beads with a substantially retained viability (>80%) and that a Gly-Arg-Gly-Asp-Tyr (GRGDY) derivative encourages attachment and elongation to form a dense network of cells that is required for a tissue substitute. Because the availability of autologous human material is severely limited, we used and examined the beads in this study as a proxy for larger constructs. These bead constructs were assessed using phase contrast microscopy and standard histological preparations. In addition, we used a modified MTT (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide) assay to examine cell proliferation by dissociating the cell/alginate constructs using trisodium citrate and trypsin/EDTA. MSCs did not proliferate within the alginate-GRGDY matrix during the 2 weeks examined. These results were further substantiated by concurrent cell density measurements using a hemocytometer. In addition, the glucose consumption rate was measured and compared to that of MSCs grown in two-dimensional culture vessels, indicating steady consumption albeit at a lower level in the entrapped MSCs.