Controlled release of heparin-binding growth factors using heparin-containing particulate systems for tissue regeneration

Controlled release of chitosan/heparin nanoparticle-delivered VEGF enhances regeneration of decellularized tissue-engineered scaffolds

Regeneration deficiency is one of the main obstacles limiting the effectiveness of tissue-engineered scaffolds. To develop scaffolds that are capable of accelerating regeneration, we created a heparin/chitosan nanoparticle-immobilized decellularized bovine jugular vein scaffold to increase the loading capacity and allow for controlled release of vascular endothelial growth factor (VEGF). The vascularization of the scaffold was evaluated in vitro and in vivo. The functional nanoparticles were prepared by physical self-assembly with a diameter of 67–132 nm, positive charge, and a zeta potential of ∼30 mV and then the nanoparticles were successfully immobilized to the nanofibers of scaffolds by ethylcarbodiimide hydrochloride/hydroxysulfosuccinimide modification. The scaffolds immobilized with heparin/chitosan nanoparticles exhibited highly effective localization and sustained release of VEGF for several weeks in vitro. This modified scaffold significantly stimulated endothelial cells’ proliferation in vitro. Importantly, utilization of heparin/chitosan nanoparticles to localize VEGF significantly increased fibroblast infiltration, extracellular matrix production, and accelerated vascularization in mouse subcutaneous implantation model in vivo. This study provided a novel and promising system for accelerated regeneration of tissue-engineering scaffolds.

Strategies for organ level tissue engineering

The field of tissue engineering has made considerable strides since it was first described in the late 1980s. The advent and subsequent boom in stem cell biology, emergence of novel technologies for biomaterial development and further understanding of developmental biology have contributed to this accelerated progress. However, continued efforts to translate tissue-engineering strategies into clinical therapies have been hampered by the problems associated with scaling up laboratory methods to produce large, complex tissues. The significant challenges faced by tissue engineers include the production of an intact vasculature within a tissue-engineered construct and recapitulation of the size and complexity of a whole organ. Here we review the basic components necessary for bioengineering organs-biomaterials, cells and bioactive molecules-and discuss various approaches for augmenting these principles to achieve organ level tissue engineering. Ultimately, the successful translation of tissue-engineered constructs into everyday clinical practice will depend upon the ability of the tissue engineer to "scale up" every aspect of the research and development process.

Release kinetics and in vitro bioactivity of basic fibroblast growth factor: effect of the thickness of fibrous matrices

In this study, we fabricated non-woven matrices using blends of polycaprolactone and gelatin with various spinning volumes to control the immobilized heparin content, which was ultimately intended to increase the immobilization efficiency of bFGF. The amount of bFGF on the heparin conjugated fibrous matrices depended on the thicknesses of the swollen matrices ranging from 35.4 ± 6.5 to 162.3 ± 14.0 ng and ≈90% of the bFGF was gradually released over a period of up to 56 d. The released bFGF enhanced the proliferation of human umbilical vein endothelial cells and human mesenchymal stem cells. In conclusion, our heparin-conjugated fibrous matrices have the potential to be used as a growth factor delivery system in tissue engineering applications.

Intracellular delivery and anti-cancer effect of self-assembled heparin-Pluronic nanogels with RNase A

A novel self-assembled nanogel was prepared for the intracellular delivery of ribonuclease A (RNase A) and the anti-cancer efficacy of RNase A delivery was investigated. The physical properties of self-assembled heparin-Pluronic (HP) nanogels incorporating RNase A (HPR nanogels) were characterized by dynamic light scattering (DLS), ξ-potential, and transmission electron microscopy (TEM). RNase A showed a strong affinity for the HP nanogel, resulting in a high loading efficiency (>78%) and significantly decreased hydrodynamic size (from 89 to ~29). HPR nanogels were efficiently internalized into HeLa cells and localized in the cytosol as well as the nucleus. In the mechanism study of cellular uptake, treating with methoxy β-cyclodextrin (Mβ-CD) decreased the uptake efficiency of HP nanogel, indicating that internalization occurs via caveolae/lipid-raft mediated endocytosis. Localization in the nucleus most likely occurred because the conjugated heparin facilitated nucleus penetration. The cytotoxicity of HPR nanogels was significantly increased when the RNase A concentration was increased, which resulted from the degradation of single stranded RNAs in the cytosol and the nucleus due to the intracellular localization of the HPR nanogels. These results demonstrate that self-assembled HP nanogels are a remarkable vehicle for intracellular protein delivery and hold promise for use as cancer chemotherapeutics.

Analytical approaches to uptake and release of hydrogel-associated FGF-2

Strategies to control the delivery of growth factors are critically important in the design of advanced biomaterials. In this study we investigated the binding and release of fibroblast growth factor 2 (FGF-2) to/from a biohybrid hydrogel matrix by four independent analytical methods: radioisotope and fluorescence labeling, amino acid analysis and Enzyme-Linked Immunosorbent Assays (ELISA). The compared analyses provided qualitatively similar uptake characteristics while the results of the FGF-2 quantification strongly depended on the particular experimental conditions. The release kinetics of FGF-2 from the gels could be monitored sensitively by (125)I labeling and by ELISA-techniques. The latter method was concluded to be advantageous since it permits the application of unmodified ("native") growth factors.

Surface-functionalized electrospun nanofibers for tissue engineering and drug delivery

Electrospun nanofibers with a high surface area to volume ratio have received much attention because of their potential applications for biomedical devices, tissue engineering scaffolds, and drug delivery carriers. In order to develop electrospun nanofibers as useful nanobiomaterials, surfaces of electrospun nanofibers have been chemically functionalized for achieving sustained delivery through physical adsorption of diverse bioactive molecules. Surface modification of nanofibers includes plasma treatment, wet chemical method, surface graft polymerization, and co-electrospinning of surface active agents and polymers. A variety of bioactive molecules including anti-cancer drugs, enzymes, cytokines, and polysaccharides were entrapped within the interior or physically immobilized on the surface for controlled drug delivery. Surfaces of electrospun nanofibers were also chemically modified with immobilizing cell specific bioactive ligands to enhance cell adhesion, proliferation, and differentiation by mimicking morphology and biological functions of extracellular matrix. This review summarizes surface modification strategies of electrospun polymeric nanofibers for controlled drug delivery and tissue engineering.

Nucleus pulposus tissue engineering: a brief review

Symptomatic intervertebral disc degeneration is associated with several spinal diseases, which cause losses of life quality and money. Tissue engineering provides a promising approach to recover the functionality of the degenerative intervertebral disc. Most studies are directed toward nucleus pulposus (NP) tissue engineering because disc degeneration is believed to originate in NP region, and considerable progress has been made in the past decade. Before this important technique is utilized for clinical treatment of disc degeneration, many challenges need to address including in all three principal components of tissue engineering, i.e., seed cells, signals and biomaterial scaffolds. This article briefly gives certain aspects of state of the art in this field, as well as pays a little more attention to our work published in the past 5 years, on growth and differentiation factor-5 (GDF-5), adipose-derived stem cells (ADSCs) and heparin functionalization of scaffold. We suggest that combinatorial application of ADSCs, GDF-5, heparin functionalization and injectable hydrogels will be advantageous in NP tissue engineering.