Paul De Bank

Injectable scaffolds for tissue regeneration

Tissue engineering aims to develop functional substitutes for damaged or diseased tissues through complex constructs of living cells, bioactive molecules and three-dimensional porous scaffolds, which support cell attachment, proliferation and differentiation. Such constructs can be formed either by seeding cells within a pre-formed scaffold or through injection of a solidifiable precursor and cell mixture to the defective tissue. As cell and bioactive molecule carriers, injectable scaffolds are appealing, particularly from the clinical point of view, because they offer the possibility of homogeneously distributing cells and molecular signals throughout the scaffold and can be injected directly into cavities, even of irregular shape and size, in a minimally invasive manner. In this paper the challenges in designing an injectable scaffold from the viewpoint of materials chemistry and the solidification mechanisms of injectable precursors are discussed. The applications of injectable scaffolds in angiogenesis, bone repair and cartilage regeneration are described.

Chemical modification of mammalian cell surfaces

The mammalian cell surface is a highly heterogeneous chemical environment with proteins, carbohydrates, lipids and composite molecules controlling vital cell functions. Chemical modification of this environment is a challenge due to the complexity of the surface chemistry and the fragility of the cell. Here, we review recent attempts to perform targeted, non-genetically controlled, changes to cell surface chemistry. Potential applications of cell surface engineering are presented.

Synthesis and antiproliferative activity of some 3-(pyrid-2-yl)-pyrazolines

The synthesis and antiproliferative activity of eleven 3-(pyrid-2-yl)-pyrazolines in two cancer cell lines are reported. X-ray crystallography was obtained of the lead compound 8i which was screened in the NCI 60 human tumour cell line and displayed sub-micromolar activity. Cell cycle analysis, in vitro tubulin assay and confocal microscopy are also reported and suggest that the lead compound disrupts microtubule formation.

Oxidized alginate hydrogels as niche environments for corneal epithelial cells

Chemical and biochemical modification of hydrogels is one strategy to create physiological constructs that maintain cell function. The aim of this study was to apply oxidised alginate hydrogels as a basis for development of a biomimetic niche for limbal epithelial stem cells that may be applied to treating corneal dysfunction. The stem phenotype of bovine limbal epithelial cells (LEC) and the viability of corneal epithelial cells (CEC) were examined in oxidised alginate gels containing collagen IV over a 3-day culture period. Oxidation increased cell viability (P ≤ 0.05) and this improved further with addition of collagen IV (P ≤ 0.01). Oxidised gels presented larger internal pores (diameter: 0.2–0.8 µm) than unmodified gels (pore diameter: 0.05–0.1 µm) and were significantly less stiff (P ≤ 0.001), indicating that an increase in pore size and a decrease in stiffness contributed to improved cell viability. The diffusion of collagen IV from oxidised alginate gels was similar to that of unmodified gels suggesting that oxidation may not affect the retention of extracellular matrix proteins in alginate gels. These data demonstrate that oxidised alginate gels containing corneal extracellular matrix proteins can influence corneal epithelial cell function in a manner that may impact beneficially on corneal wound healing therapy.

Platelet lysate gel and endothelial progenitors stimulate microvascular network formation in vitro : tissue engineering implications

Revascularisation is a key step for tissue regeneration and complete organ engineering. We describe the generation of human platelet lysate gel (hPLG), an extracellular matrix preparation from human platelets able to support the proliferation of endothelial colony forming cells (ECFCs) in 2D cultures and the formation of a complete microvascular network in vitro in 3D cultures. Existing extracellular matrix preparations require addition of high concentrations of recombinant growth factors and allow only limited formation of capillary-like structures. Additional advantages of our approach over existing extracellular matrices are the absence of any animal product in the composition hPLG and the possibility of obtaining hPLG from patients to generate homologous scaffolds for re-implantation. This discovery has the potential to accelerate the development of regenerative medicine applications based on implantation of microvascular networks expanded ex vivo or the generation of fully vascularised organs.

Multicellular aggregation of maltol-modified cells triggered by Fe3+ ions

The synthesis of a maltol-derived hydrazide is described which, once attached to a cell surface, induces rapid multicellular aggregation selectively in the presence of Fe(3+) ions. Heterocellular aggregates are also reported.

Dual crosslinked pectin–alginate network as sustained release hydrophilic matrix for repaglinide

Repaglinide, an oral antidiabetic agent, has a rapid onset of action and short half-life of approximately 1h. Developing a controlled and prolonged release delivery system is required to maintain its therapeutic plasma concentration and to eliminate its adverse effects particularly hypoglycemia. The present study aimed to develop controlled release repaglinide loaded beads using sodium alginate and pectin with dual cross-linking for effective control of drug release. The prepared beads were characterized for size, percentage drug entrapment efficiency, in vitro drug release and the morphological examination using scanning electron microscope. For the comparative study, the release profile of a marketed conventional tablet of repaglinide (Prandin® tablets 2mg, Novo Nordisk) was determined by the same procedure as followed for beads. The particle size of beads was in the range of 698±2.34-769±1.43μm. The drug entrapment efficiency varied between 55.24±4.61 to 82.29±3.42%. The FTIR results suggest that there was no interaction between repaglinide and excipients. The XRD and DSC results suggest partial molecular dispersion and amorphization of the drug throughout the system. These results suggest that repaglinide did not dissolve completely in the polymer composition and seems not to be involved in the cross-linking reaction. The percent drug release was decreased with higher polymer concentrations. In conclusion, the developed beads could enhance drug entrapment efficiency, prolong the drug release and enhance bioavailability for better control of diabetes.

The effect of ozone gas sterilization on the properties and cell compatibility of electrospun polycaprolactone scaffolds

Abstract The growing area of tissue engineering has the potential to alleviate the shortage of tissues and organs for transplantation, and electrospun biomaterial scaffolds are extremely promising devices for translating engineered tissues into a clinical setting. However, to be utilized in this capacity, these medical devices need to be sterile. Traditional methods of sterilization are not always suitable for biomaterials, especially as many commonly used biomedical polymers are sensitive to chemical-, thermal- or radiation-induced damage. Therefore, the objective of this study was to evaluate the suitability of ozone gas for sterilizing electrospun scaffolds of polycaprolactone (PCL), a polymer widely utilized in tissue engineering and regenerative medicine applications, by evaluating if scaffolds composed of either nanofibres or microfibres were differently affected by the sterilization method. The sterility, morphology, mechanical properties, physicochemical properties, and response of cells to nanofibrous and microfibrous PCL scaffolds were assessed after ozone gas sterilization. The sterilization process successfully sterilized the scaffolds and preserved most of their initial attributes, except for mechanical properties. However, although the scaffolds became weaker after sterilization, they were still robust enough to use as tissue engineering scaffolds and this treatment increased the proliferation of L929 fibroblasts while maintaining cell viability, suggesting that ozone gas treatment may be a suitable technique for the sterilization of polymer scaffolds which are significantly damaged by other methods.

Altered cellular response to adsorbed matrix protein by chemoselective ligation of small molecules

In the field of tissue engineering, there is a constant drive to develop materials that enable control over cell adhesion, growth and differentiation for optimal tissue development. In many cases, these materials incorporate or are coated with extracellular matrix proteins to increase cell adhesion and spreading. Here we show that chemoselective modification of an adsorbed matrix protein can be used to selectively alter the response of cultured cells. Using the glycoprotein laminin-1, it was shown that oxidation of terminal sialic acid moieties resulted in the generation of aldehyde groups which could be employed to chemoselectively ligate hydrazide-bearing biomolecules. The hydrazide derivative of the tripeptide Leu–Arg–Glu, a “stop” signal for motoneuron outgrowth, was ligated to periodate-treated laminin and shown to inhibit the mean neurite length of primary spinal cord motoneurons by 39% in comparison to controls. These results demonstrate that adsorbed glycoproteins can be readily modified in order to alter the cell response and could enable matrices to be tailored to different cell types.