Gelatin-based hydrogel for vascular endothelial growth factor release in peripheral nerve tissue engineering: VEGF-releasing hydrogel

Optimizing combination of vascular endothelial growth factor and mesenchymal stem cells on ectopic bone formation in SCID mice

INTRODUCTION

Insufficient blood supply may limit bone regeneration in bone defects. Vascular endothelial growth factor (VEGF) promotes angiogenesis by increasing endothelial migration. This outcome, however, could depend on time of application. Sheep mesenchymal stem cells (MSCs) in severe combined immunodeficient (SCID) mice were used in this study to evaluate optimal time points for VEGF stimulation to increase bone formation.

METHODS

Twenty-eight SCID (NOD.CB17-Prkdc^scid /J) mice had hydroxyapatite granules seeded with 5 × 10⁵ MSCs inserted subcutaneous. Pellets released VEGF on days 1-7, days 1-14, days 1-21, days 1-42, days 7-14, and days 21-42. After 8 weeks, the implant-bone-blocks were harvested, paraffin embedded, sectioned, and stained with both hematoxylin and eosin (HE) and immunohistochemistry for human vimentin (hVim) staining. Blood samples were collected for determination of bone-related biomarkers in serum.

RESULTS

The groups with 5 × 10⁵ MSCs and VEGF stimulation on days 1-14 and days 1-21 showed more bone formation when compared to the control group of 5 × 10⁵ MSCs alone (p < 0.01). Serum biomarkers had no significant values. The hVim staining confirmed the ovine origin of the observed ectopic bone formation.

CONCLUSION

Optimal bone formation of MSCs was reached when stimulating with VEGF during the first 14 or 21 days after surgery. © 2017 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 105A: 3326-3332, 2017.

Development of hydrogels for regenerative engineering

The aim of regenerative engineering is to restore complex tissues and biological systems through convergence in the fields of advanced biomaterials, stem cell science, and developmental biology. Hydrogels are one of the most attractive biomaterials for regenerative engineering, since they can be engineered into tissue mimetic 3D scaffolds to support cell growth due to their similarity to native extracellular matrix. Advanced nano- and micro-technologies have dramatically increased the ability to control properties and functionalities of hydrogel materials by facilitating biomimetic fabrication of more sophisticated compositions and architectures, thus extending our understanding of cell-matrix interactions at the nanoscale. With this perspective, this review discusses the most commonly used hydrogel materials and their fabrication strategies for regenerative engineering. We highlight the physical, chemical, and functional modulation of hydrogels to design and engineer biomimetic tissues based on recent achievements in nano- and micro-technologies. In addition, current hydrogel-based regenerative engineering strategies for treating multiple tissues, such as musculoskeletal, nervous and cardiac tissue, are also covered in this review. The interaction of multiple disciplines including materials science, cell biology, and chemistry, will further play an important role in the design of functional hydrogels for the regeneration of complex tissues.

In Situ Release of VEGF Enhances Osteogenesis in 3D Porous Scaffolds Engineered with Osterix-Modified Adipose-Derived Stem Cells

Adipose-derived stem cells (ADSCs) can differentiate into various cell types and thus have great potential for regenerative medicine. Herein, rat ADSCs were isolated; transduced with lentiviruses expressing Osterix (Osx), a transcriptional factor essential for osteogenesis. Osx overexpression upregulated key osteogenesis-related genes, such as special AT-rich binding protein 2, alkaline phosphatase, osteocalcin, and osteopontin, at both mRNA and protein levels. In addition, mineral nodule formation and alkaline phosphatase activity were enhanced in Osx-overexpressing ADSCs. The expression of dickkopf-related protein 1, a potent Wnt signaling pathway inhibitor, was also increased, whereas that of β-catenin, an intracellular signal transducer in the Wnt pathway, was decreased. β-catenin expression was partially recovered by treatment with lithium chloride, a canonical Wnt pathway activator. The Osx-expressing ADSCs were then combined with 3D gelatin-coated porous poly(ɛ-caprolactone) scaffolds with a unique release prolife of entrapped recombinant human vascular endothelial growth factor (VEGF). The controlled release of VEGF promoted osteogenic differentiation capacity in vitro. When the scaffold-ADSC complexes were transplanted into rat calvarial critical-sized defects, more bone formed on the gelatin/VEGF-coated scaffolds than on other scaffold types. Taken together, the results indicate that, Osx-overexpression promotes ADSCs' osteogenesis both in vitro and in vivo, which could be enhanced by release of VEGF.

The Effect of Insulin Like Growth Factor-1 on Recovery of Facial Nerve Crush Injury

OBJECTIVES

The aim of this study is to investigate the efficacy of locally applied insulin-like growth factor 1 (IGF-1) on the recovery of facial nerve functions after crush injury in a rabbit model.

METHODS

The rabbits were randomly assigned into three groups. Group 1 consisted of the rabbits with crush injury alone; group 2, the animals applied saline solution onto the crushed facial nerve and group 3, IGF-1 implemented to the nerve in the same manner. Facial nerve injury was first electrophysiologically studied on 10th and 42nd days of the procedure. The damage to the facial nerves was then investigated histopathologically, after sacrification of the animals.

RESULTS

In the electrophysiological study, compound muscle action potential amplitudes of the crushed nerves in the second group were decreased. In pathological specimens of the first and second groups, the orders of axons were distorted; demyelination and proliferation of Schwann cells were observed. However, in IGF-1 treated group axonal order and myelin were preserved, and Schwann cell proliferation was close to normal (P<0.05).

CONCLUSION

Local application of IGF-1 in a slow releasing gel was found efficacious in the recovery of the facial nerve crush injury in rabbits. IGF-1 was considered worthy of being tried in clinical studies in facial nerve injury cases.

Cell-free artificial implants of electrospun fibres in a three-dimensional gelatin matrix support sciatic nerve regeneration in vivo

Surgical repair of larger peripheral nerve lesions requires the use of autologous nerve grafts. At present, clinical alternatives to avoid nerve transplantation consist of empty tubes, which are only suitable for the repair over short distances and have limited success. We developed a cell-free, three-dimensional scaffold for axonal guidance in long-distance nerve repair. Sub-micron scale fibres of biodegradable poly-ε-caprolactone (PCL) and collagen/PCL (c/PCL) blends were incorporated in a gelatin matrix and inserted in collagen tubes. The conduits were tested by replacing 15-mm-long segments of rat sciatic nerves in vivo. Biocompatibility of the implants and nerve regeneration were assessed histologically, with electromyography and with behavioural tests for motor functions. Functional repair was achieved in all animals with autologous transplants, in 12 of 13 rats that received artificial implants with an internal structure and in half of the animals with empty nerve conduits. In rats with implants containing c/PCL fibres, the extent of recovery (compound muscle action potentials, motor functions of the hind limbs) was superior to animals that had received empty implants, but not as good as with autologous nerve transplantation. Schwann cell migration and axonal regeneration were observed in all artificial implants, and muscular atrophy was reduced in comparison with animals that had received no implants. The present design represents a significant step towards cell-free, artificial nerve bridges that can replace autologous nerve transplants in the clinic. Copyright © 2017 John Wiley & Sons, Ltd.

Partially oxidized polyvinyl alcohol as a promising material for tissue engineering

The desired clinical outcome after implantation of engineered tissue substitutes depends strictly on the development of biodegradable scaffolds. In this study we fabricated 1% and 2% oxidized polyvinyl alcohol (PVA) hydrogels, which were considered for the first time for tissue-engineering applications. The final aim was to promote the protein release capacity and biodegradation rate of the resulting scaffolds in comparison with neat PVA. After physical crosslinking, characterization of specific properties of 1% and 2% oxidized PVA was performed. We demonstrated that mechanical properties, hydrodynamic radius of molecules, thermal characteristics and degree of crystallinity were inversely proportional to the PVA oxidation rate. On the other hand, swelling behaviour and protein release were enhanced, confirming the potential of oxidized PVA as a protein delivery system, besides being highly biodegradable. Twelve weeks after in vivo implantation in mice, the modified hydrogels did not elicit severe inflammatory reactions, showing them to be biocompatible and to degrade faster as the degree of oxidation increased. According to our results, oxidized PVA stands out as a novel biomaterial for tissue engineering that can be used to realize scaffolds with customizable mechanical behaviour, protein-loading ability and biodegradability. Copyright © 2015 John Wiley & Sons, Ltd.

The Effect of Electrospun Gelatin Fibers Alignment on Schwann Cell and Axon Behavior and Organization in the Perspective of Artificial Nerve Design

Electrospun fibrous substrates mimicking extracellular matrices can be prepared by electrospinning, yielding aligned fibrous matrices as internal fillers to manufacture artificial nerves. Gelatin aligned nano-fibers were prepared by electrospinning after tuning the collector rotation speed. The effect of alignment on cell adhesion and proliferation was tested in vitro using primary cultures, the Schwann cell line, RT4-D6P2T, and the sensory neuron-like cell line, 50B11. Cell adhesion and proliferation were assessed by quantifying at several time-points. Aligned nano-fibers reduced adhesion and proliferation rate compared with random fibers. Schwann cell morphology and organization were investigated by immunostaining of the cytoskeleton. Cells were elongated with their longitudinal body parallel to the aligned fibers. B5011 neuron-like cells were aligned and had parallel axon growth when cultured on the aligned gelatin fibers. The data show that the alignment of electrospun gelatin fibers can modulate Schwann cells and axon organization in vitro, suggesting that this substrate shows promise as an internal filler for the design of artificial nerves for peripheral nerve reconstruction.

Growth factors in wound healing: the present and the future?

Numerous clinical studies have confirmed the pivotal role growth factors play in wound healing and their diminished levels in the chronic wound. Despite promising early studies treating chronic wounds with growth factors, results with traditional bolus dosing of a single growth factor have yielded insignificant results. Disappointing results have been theorized to be the result of growth factors inherent short half-life, a hostile microenvironment rich in protease activity, and poor delivery mechanisms failing to deliver effective dosages in an appropriate temporal manner. Advances in tissue engineering and regenerative medicine have provided technologies capable of delivering multiple growth factors in a spatially oriented approach. These technologies include polymer systems, scaffolds, and hydrogels that have demonstrated improved response by target tissues when growth factors are delivered in this biomimetic fashion. With improved delivery systems, treatment of chronic wounds with growth factors has the potential to accelerate healing in a manner not previously realized with traditional delivery approaches.