Ives Swennen

Evaluation of Photocrosslinked Lutrol Hydrogel for Tissue Printing Applications

Application of hydrogels in tissue engineering and innovative strategies such as organ printing, which is based on layered 3D deposition of cell-laden hydrogels, requires design of novel hydrogel matrices. Hydrogel demands for 3D printing include: 1) preservation of the printed shape after the deposition; 2) maintaining cell viability and cell function and 3) easy handling of the printed construct. In this study we analyze the applicability of a novel, photosensitive hydrogel (Lutrol) for printing of 3D structured bone grafts. We benefit from the fast temperature-responsive gelation ability of thermosensitive Lutrol-F127, ensuring organized 3D extrusion, and the additional stability provided by covalent photocrosslinking allows handling of the printed scaffolds. We studied the cytotoxicity of the hydrogel and osteogenic differentiation of embedded osteogenic progenitor cells. After photopolymerization of the modified Lutrol hydrogel, cells remain viable for up to three weeks and retain the ability to differentiate. Encapsulation of cells does not compromise the mechanical properties of the formed gels and multilayered porous Lutrol structures were successfully printed.

Cell survival and proliferation after encapsulation in a chemically modified Pluronic® F127 hydrogel

Pluronic® F127 is a biocompatible, injectable, and thermoresponsive polymer with promising biomedical applications. In this study, a chemically modified form, i.e., Pluronic ALA-L with tailored degradation rate, was tested as an encapsulation vehicle for osteoblastic cells. UV cross-linking of the modified polymer results in a stable hydrogel with a slower degradation rate. Toxicological screening showed no adverse effects of the modified Pluronic ALA-L on the cell viability. Moreover, high viability of embedded cells in the cross-linked Pluronic ALA-L was observed with life/death fluorescent staining during a 7-day-culture period. Cells were also cultured on macroporous, cross-linked gelatin microbeads, called CultiSpher-S® carriers, and encapsulated into the modified cross-linked hydrogel. Also, in this situation, good cell proliferation and migration could be observed in vitro. Preliminary in vivo tests have shown the formation of new bone starting from the injected pre-loaded CultiSpher-S® carriers.

Epoxy Polymer Surface Roughness Modeling Based on Kinetic Studies of Wet Chemical Treatments

Epoxy polymers are frequently used for constructing buildup layers. Atop the dielectric polymer metal layers are plated by means of a wet-chemical electroless and/or electroplating process. The adhesion of the plated metal layers to this polymer surface is of prime importance for reliability of the interconnection. An increase in the roughness of the polymer surface plays an important part in the adhesion strength of plated metal layers by increasing the total area of interface between both layers. Hence, the evolution of polymer surface roughness with time due to the chemical treatment is of prime importance for determining the reliability of interconnections. A kinetic study of wet solution swellers and oxidizers is made, based on atomic force microscopy roughness measurements. Each chemical or combination of chemical treatments in a certain sequence has its influence on the evolution of roughness. The evolution of surface roughness also indicates the mechanisms that lead to the formation of roughness on the surface. Different models are proposed to explain the influence of sweller agents on polymer surface roughness. The kinetics of roughness formation under influence of swellers is modeled and the bases of the influence of swellers on oxidizing treatments are examined.