Ming-Hua Ho

Preparation of porous scaffolds by using freeze-extraction and freeze-gelation methods.

Freeze-fixation and freeze-gelation methods are presented in this paper which can be used to prepare highly porous scaffolds without using the time and energy consuming freeze-drying process. The porous structure was generated during the freeze of a polymer solution, following which either the solvent was extracted by a non-solvent or the polymer was gelled under the freezing condition; thus, the porous structure would not be destructed during the subsequent drying stage. Compared with the freeze-drying method, the presented methods are time and energy-saving, with less residual solvent, and easier to be scaled up. Besides, the problem of formation of surface skin can be resolved and the limitation of using solvent with low boiling point can be lifted by the presented methods. With the freeze-extraction and freeze-gelation methods, porous PLLA, PLGA, chitosan and alginate scaffolds were successfully fabricated. In addition to the presentation of the morphologies of the fabricated scaffolds, preliminary data of cell culture on them are as well included in the present work.

Use of Dicarboxylic Acids To Improve and Diversify the Material Properties of Porous Chitosan Membranes

Several nontoxic dicarboxylic acid solutions (oxalic acid, succinic acid, malic acid, and adipic acid solutions) instead of an acetic acid solution were used as solvents for chitosan dissolution. The amount of free amino groups of the chitosan in the solution decreased due to the ionic cross-linking of the dicarboxylic acids with chitosan. These solutions were used to fabricate porous chitosan membranes. Replacing acetic acid with these dicarboxylic acids for membrane preparation improved the water uptake (by 35% at most), tensile strength (by 110% at most), and elongation capability (by 50% at most) of the membranes. These dicarboxylic acid solutions not only act as solvents but also improve the material properties of the chitosan membranes due to the ionic cross-linking and hydrogen bond formation. In brief, a nontoxic and straightforward cross-linking method has been developed for chitosan material; this method does not result in a brittle product, thus making it better than the use of toxic cross-linking reagents.

Interactions between chitosan and cells measured by AFM.

Chitosan, a biocompatible material that has been widely used in bone tissue engineering, is believed to have a high affinity to osteoblastic cells. This research is the first to prove this hypothesis. By using atomic force microscopy (AFM) with a chitosan-modified cantilever, quantitative evaluation of the interforce between chitosan and cells was carried out. A chitosan tip functionalized with Arg-Gly-Asp (RGD) was also used to measure the interforce between RGD-chitosan and osteoblastic cells. This research concluded by examining cell adhesion and spreading of chitosan substrates as further characterization of the interactions between cells and chitosan. The force measured by AFM showed that the interforce between chitosan and osteoblasts was the highest (209 nN). The smallest adhesion force (61.8 nN) appeared between chitosan and muscle fibroblasts, which did not demonstrate any osteoblastic properties. This result proved that there was a significant interaction between chitosan and bone cells, and correlated with the observations of cell attachment and spreading. The technique developed in this research directly quantified the adhesion between chitosan and cells. This is the first study to demonstrate that specific interaction exists between chitosan and osteoblasts.