Jian-Tao Zhang

Micro-structured smart hydrogels with enhanced protein loading and release efficiency.

A series of temperature-responsive poly(N-isopropylacrylamide) (PNIPAAm) hydrogels with highly porous microstructures were successfully prepared by using hydrophobic polydimethylsiloxane (PDMS) and sodium dodecyl sulfate as liquid template and stabilizer, respectively. These newly prepared hydrogels possess highly porous structures. In contrast to the conventional PNIPAAm hydrogel, the swelling ratios of the porous gels at room temperature were higher, and their response rates were significantly faster as the temperature was raised above the lower critical solution temperature. For example, the novel hydrogel prepared with 40% PDMS template lost over 95% water within 5 min, while the conventional PNIPAAm gel only lost approximately 14% water in the same time. The improved properties are achieved due to the presence of liquid PDMS templates in the reaction solutions, which lead to the formation of porous structures during the polymerization/crosslinking. Lysozyme and bovine serum albumin (BSA) as protein models were for the first time loaded into these micro-structured smart hydrogels through a physical absorption method. The experimental results show that the loading efficiency of BSA with a higher molecular weight is lower than that of lysozyme due to the size exclusion effect, and the loading efficiencies of both proteins in the porous hydrogel are much higher than those in the conventional PNIPAAm hydrogel. For example, the loading efficiency of BSA in porous hydrogel is 0.114, approximately 200% higher than that in conventional hydrogel (0.035). Both lysozyme and BSA were completely released from the porous hydrogel at 22 degrees C. Furthermore, the release kinetics of the proteins from the porous hydrogel could be modulated by tuning the environmental temperature. These newly prepared porous materials provide an avenue to increase the loading efficiency and to control the release patterns of macromolecular drugs from hydrogels, and show great promise for application in protein or gene delivery.

Templating α-helical poly(L-lysine)/polyanion complexes by nanostructured uniaxially oriented ultrathin polyethylene films.

We report a templating effect of uniaxially oriented melt-drawn polyethylene (MD-PE) films on α-helical poly(L-lysine)/poly(styrenesulfonate) (α-PLL/PSS) complexes deposited by the layer-by-layer (LBL) method. The melt-drawing process induced an MD-PE fiber texture consisting of nanoscale lamellar crystals embedded in amorphous regions on the MD-PE film surface whereby the common crystallographic c axis is the PE molecular chain direction parallel to the uniaxial melt-drawing direction. The MD-PE film and the α-PLL/PSS deposit were analyzed by atomic force microscopy (AFM) and in situ attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR) using polarized light as a complementary method. Both methods revealed that α-PLL/PSS complexes adsorbed at the MD-PE surface were anisotropic and preferentially oriented perpendicular to the crystallographic c direction of the MD-PE film. Quantitatively, from AFM image analysis and ATR-FTIR dichroism of the amide II band of the α-PLL, mean cone opening angles of 12-18° for both rodlike α-PLL and the anisotropic α-PLL/PSS complexes with respect to the PE lamellae width direction were obtained. A model for the preferred alignment of α-PLL along the protruding PE lamellae is discussed, which is based on possible hydrophobic driving forces for the minimization of surface free energy at molecular and supermolecular topographic steps of the PE surface followed by electrostatic interactions between the interconnecting PSS and the α-PLL during layer-by-layer adsorption. This study elucidates the requirements and mechanisms involved in orienting biomolecules and may open up a path for designing templates to induce directed protein adsorption and cell growth by oriented polypeptide- or protein-modified PE surfaces.

Novel 1-D biophotonic nanohybrids: protein nanofibers meet quantum dots

Protein nanofibers (PNFs) created by controlling the self-assembly of protein molecules are contemporary biomacromolecular precursors to construct novel functional nanomaterials. We report here on a facile approach to prepare PNF-based biophotonic nanohybrids. For the first time we demonstrate the creation of fibronectin (FN) nanofibers in highly concentrated ethanol solution and subsequently present the organization of N-hydroxysulfosuccinimide (NHS) modified CdSe–ZnS core–shell quantum dots (QDs) on the self-assembled FN nanofibers by covalent interaction. AFM and TEM results indicate that the formation of FN nanofibers is controllable and the created FN nanofibers are uniform in diameter and length. UV-vis and XPS data identified the successful modification of QDs. The one-dimensional (1-D) PNF–QD biophotonic nanohybrids created by organizing QDs onto FN nanofibers were imaged with AFM, TEM, and confocal laser scanning microscopy, and the results show that the created FN nanofibers can serve as feasible templates to organize QDs for construction of biophotonic nanohybrids. The PNF–QD nanohybrids have potential applications in optical, biomedical and nanotechnological fields.