Kai Kan

Stereocomplex Film Using Triblock Copolymers of Polylactide and Poly(ethylene glycol) Retain Paxlitaxel on Substrates by an Aqueous Inkjet System

The stereocomplex formation of poly(L,L-lactide) (PLLA) and poly(D,D-lactide) (PDLA) using an inkjet system was expanded to the amphiphilic copolymers, using poly(ethylene glycol) (PEG) as a hydrophilic polymer. The diblock copolymers, which are composed of PEG and PLLA (MPEG-co-PLLA) and PEG and PDLA (MPEG-co-PDLA), were employed for thin-film preparation using an aqueous inkjet system. The solvent and temperature conditions were optimized for the stereocomplex formation between MPEG-co-PLLA and MPEG-co- PDLA. As a result, the stereocomplex was adequately formed in acetonitrile/water (1:1, v/v) at 40 °C. The aqueous conditions improved the stereocomplex film preparation, which have suffered from clogging when using the organic solvents in previous work. The triblock copolymers, PLLA-co-PEG-co-PLLA and PDLA-co-PEG-co-PDLA, were employed for square patterning with the inkjet system, which produced thin films. The amphiphilic polymer film was able to retain hydrophobic compounds inside. The present result contributed to the rapid film preparation by inkjet, retaining drugs with difficult solubility in water, such as paclitaxel within the films.

Catechin-Modified Polylactide Stereocomplex at Chain End Improved Antibiobacterial Property.

Using different type of initiators, the antibacterial moieties are introduced at the chain end of poly(L,L-lactide) (PLLA) and poly(D,D-lactide) (PDLA), and the thermal properties are simultaneously improved using the stereocomplex approach. The physical interaction of polymers and antibacterial compounds is investigated. The double bonds at the chain end are utilized for the interaction of silver ion; however, the silver ions are not detected after stereocomplexation of PLLA and PDLA. On the other hand, catechin (CT) is selected as an initiator precursor of lactide polymerization, protecting the phenolic hydroxyl groups. The linear PLLA and PDLA are obtained by the initiator, resulting in CT conjugated PLAs at the chain end groups after deprotection of phenolic hydroxyl groups. The antibacterial properties are determined by proliferation tests of staphylococcus aureus. The results suggest that the antibacterial properties of CT modified PLAs are derived from the original CT parts.

Development of a rapid in vitro tissue deadhesion system using the thermoresponsive sol-gel transition of hydroxybutyl chitosan

Abstract In regenerative medicine, it has become increasingly important to collect cultured tissues using non-invasive methods. Enzymatic deadhesion is normally used to collect cells, but this method cannot be used when trying to collect whole tissues in order to avoid damaging cell–cell interactions. In order to resolve this issue, a thermoresponsive culture dish with poly(N-isopropyl acrylamide) (PNIPAAm) has been employed. This system can change its hydrophobicity depending on temperature. Thus, tissues can attach above 37 °C and be detached below 20 °C. However, the PNIPAAm system has some issues related to cost and detachment time. In this study, we developed a novel thermoresponsive detachment system using a polysaccharide derivative. We chose hydroxy butyl chitosan (HBC) as the thermoresponsive polymer because of its high biocompatibility and rapid phase transition. We developed a novel method of HBC synthesis in conditions that were milder than previously reported. We used spin-coating to make a thin coating on two kinds of culture dishes with various concentrations of HBC solution. Seeded cells attached to the surface at less than 0.5 mg/ml HBC coating concentration, and they could be successfully detached by simply lowering the temperature of the suspension dishes without enzymatic treatment; the cells took only 5–20 min to detach. To evaluate this system, we measured three metrics related to cell culturing on culture dishes: initial attachment rate, detachment rate and tissue detachment time. The study revealed that tissues could be detached faster on the suspension dishes used in this study than on PNIPAAm grafted dishes when HBC was coated at 0.5 mg/ml. We successfully developed a novel tissue detachment system using HBC. These results suggest that smart polymers may be useful in regenerative medicine.

Force Estimation on the Contact of Poly(l,l-lactide) and Poly(d,d-lactide) Surfaces Regarding Stereocomplex Formation.

The stereocomplex formation of poly(l,l-lactide) (PLLA) and poly(d,d-lactide) (PDLA) was selected in order to investigate the interaction of the two surfaces including hydrogen bonding and van der Waals interaction. Adhesion force measurement using surface force apparatus (SFA) equipped with an optical microscope was conducted on the PLLA and PDLA spin-coated films. The adhesion forces, Fad, phenomenologically followed the linear relation with the applied normal load, L. For the force Fad between PLLA and PDLA films with low molecular weights (PLLA, Mn = 2800; PDLA, : Mn = 2100), the slope of linear fitting of Fad vs L was significantly larger for the heterointerface (PLLA/PLDA) compared with that for the homointerface (PLLA/PLLA and PDLA/PDLA). However, when polymers with higher molecular weights (PLLA, Mn = 8500; PDLA, Mn = 8300) were measured, the slopes of linear fitting lines were almost the same for hetero- and homointerfaces. This indicated that the mobility of the lower molecular weight PLLA/PDLA films promoted the selective interaction of PLLA and PDLA under the applied normal loads. The adhesion between the outermost PLLA layer and PDLA layer prepared by layer-by-layer (LbL) assembly was also measured. It is interesting that the adhesion force was very weak in this case. This weak adhesion could be explained by the much less mobility of the polymer chain due to the stereocomplex formation within the LbL layers. This study demonstrated that the adhesion force due to the selective interaction of PLLA and PDLA between PLLA/PDLA films could be directly measured, and depended on the mobility of the outermost polymer chains, which reflected the different structures of polymer chains in the organized complex films.