Key Engineering Materials Vols. 288-289

Abstract: Here, a two-dimensional microarray of ten thousand (100x100) hepatocyte hetero-spheroids, underlaid with endothelial cells, was successfully constructed with a 100 µm spacing in an active area of 20x20 mm on micro-fabricated glass substrates coated with poly(ethylene glycol) (PEG) brushes (Fig. 1). Co-cultivation of hepatocytes with endothelial cells was essential to stabilize hepatocyte viability and liver-specific functions, allowing us to obtain hepatocyte spheroids with a diameter of 100 µm, functioning as a miniaturized liver to secret albumin for at least three weeks. The spheroid array constructed here is highly useful as a platform of TBB and CBB to detect a wide variety of clinically, pharmacologically, and toxicologically active compounds through a cellular physiological response.

Abstract: Tetramethylpyrazine(TMPZ) is an active ingredient of a Chinese herbal medicine Chuanxiong (Liqusticum wallichii Franchat). In order to enhance its stability and delivery in vivo TMPZ-capped poly(ethylene glycol) conjugate was designed and synthesized efficiently by the condensation reaction of 2-cardoxyl-3, 5, 6-trimethylpyrazine (TMPZCOOH) with PEG(M=2000) in the presence of dicyclohexylcarbodiimide (DCCI). The TMPZ-PEG conjugate obtained was then purified by gel filtration chromatography (SephadexG-15 column,1.6×100cm; eluent: distilled water) and characterized by FTIR, UV spectra. FTIR (KBr): 2868cm-1(CH2), 1718cm-1(C=O), 1455cm-1 (-C=N-), 1113cm-1(O-CH2-CH2). The degree of end-capping of TMPZ per PEG molecules was estimated to be 87% from UV absorbance at 294nm. The anticoagulant activity of the conjugate was evaluated by in vitro coagulation time test. The result showed that the activated partial thromboplastin time (APTT) of the TMPZ-PEG conjugate is nearly equal to that of blank plasma in our experiment conditions, this behavior is similar to that of TMPZ. But TMPZCOOH, one of the main metabolic products of TMPZ in vivo, exhibited more potent anticoagulant activity than TMPZ and TMPZ-PEG, its APTT is even larger than the maximum clotting time set by the instrument. It is also found that APTT of the conjugate increased as the time of the sample stayed in water bath at 37°C. This is probably because the ester bond between TMPZCOOH and PEG hydrolyzed during the stay time and released the free TMPZCOOH.

Abstract: A novel prosthesis using silk fibroin with blending heparin and sulfonated silk fibroin was studied. Anticoagulation activities of heparin/silk fibroin and sulfonated silk fibroin/silk fibroin vascular and mechanical property results showed that heparin/silk fibroin and sulfonated silk fibroin/silk fibroin vascular could meet the requirement of small caliber grafts. This study indicated that silk fibroin could be used for developing tissue engineering biological vascular grafts that could use for human coronary or low extremity artery bypasses.

Abstract: A commercial available amphiphilic polymer, Cholesterol terminated PEO (Chol-PEO), was used as novel biomimetic drug delivery system. The association behavior of Chol-PEOs in aqueous solution was studied by fluorescence probe technique and transmission electron microscope (TEM). Fluorescence excitation spectra for pyrene probe solubilized in the aggregates of Chol-PEOs suggested the presence of a critical micelle concentration (cmc) in water. TEM images of the aggregates suggested that the PEO block formed the biocompatible micelle coronas and the cholesterol block formed the hydrophobic micelle cores. These new biomimetic diblock copolymers were evaluated as nanocapsules for the delivery of hydrophobic drugs and drug release behavior of a hydrophobic anti-cancer drug, adriamycin (ADR), was examined.

Abstract: Polyamides containing amino acid residues were synthesized through a chemoenzymatic route. At first, monomers containing amino acid esters at both ends were prepared from amino acid esters and bifunctional acid chlorides through a Scotten-Baumann reaction under organic condition. Diamine was used as bifunctional nucleophilic reagent to aminolysis the amino acid ester bonds of these monomers under protease catalysts, leading to the polycondensation to form the desired polyamides containing amino acid residues. Spectra characterizations confirmed the structure of obtained polyamides. The factors that influence the polymerization, including the type of enzymes, the amount of enzymes, and the water contents in the solvent, were also discussed. It is expected that the obtained polyamides have the potential for biomaterial applications.

Abstract: Inspired by the annual ring structure of wood, a cylindrical semi-permeable chitosan gel membrane was chosen as a template to separate chitosan solution from NaOH coagulation solution. Three dimensions (3D) chitosan (CS) rods (Φ5×80 mm) with layered structure similar to annual ring of wood were prepared via a novel and simple in-situ intermittently precipitating method. These chitosan rods presented quite good mechanical properties with bending strength and shear strength of 102MPa and 31MPa respectively. The concentric circles layered structure was approved by SEM characterization, the mechanism of preparation and the relationship between structure and properties of chitosan rods were also discussed.

Abstract: This paper focuses on an effective way to improve the thermostability of poly-β-hydroxybutyrate (PHB). Maleic anhydride (MA) is grafted onto PHB by 60Co γ of radiation. The spectra of both 1HNMR and 13CNMR were investigated following the radiation-induced polymerization. The results are consistent with successful grafting of the MA monomer onto the PHB, with a low graft degree. The graft degree and viscosity-average molecular weight Mηof the radiated samples were also investigated. The results observed through TGA demonstrate that thermostability has been measurably improved with the introduction of MA groups. These significant results suggest that wide commercial application of PHB may be possible.

Abstract: The purpose of present study was to evaluate the influence of different base materials on the marginal integrity of posterior direct composite resin restorations. Conventional mesio-occluso-distal(MOD) cavity preparations, with margins in enamel and dentin, were prepared in 24 extracted human mandibular molars and randomly divided into four equal groups. One of three base materials (RMGI, compomer, flowable resin) was placed on the pulpal floors of the teeth of the groups. One group of teeth, which served as the control group, was not given any base material. Then, all teeth were restored with composite resin. The micromorphology of the tooth/restoration interfaces along the entire surfaces of the restorations was quantitatively analyzed using microscope at 150 magnifications immediately after finishing and after completion of thermo-mechanical stress. Marginal adaptation was assessed along the entire margin and % perfect margin (%PM) was calculated. The %PMs before and after thermo-mechanical stress in the groups were compared with Two- way ANOVA with Tukey test at the 95% confidence level. Before thermo-mechanical stress, there was no difference in marginal adaptation between groups. After the thermo-mechanical stress, the RMGI group showed the highest marginal adaptation rate among the tested groups. In compomer and flowable resin groups, the marginal adaptation was lower after thermomechanical stresses than before the stress (p<0.05).

Abstract: Orbital implant, used for filling the space after enucleation, played an important role in the optical orthopedic operations. However, the clinical application of soft orbital implants was in a limited extent. This paper focused on the synthetic method of a new kind of soft poly (2-hydroxyethyl methacrylate) (PHEMA) orbital implant. This method included two steps, making the orbital implant with through-holes by salt leaking method and improving the compress property of PHEMA by copolymerizing it with methyl methacrylate (MMA). Scanning electronic microscope (SEM), thermo gravimetric analysis (TGA), and compress experiment were carried out to evaluate the physical properties of the implant. And to evaluate the biocompatibility of this poly (HEMA-co-MMA) orbital implant, short term and long term observations were studied after subcutaneous implantation of material blocks and implantation of orbital implants (diameter in 14mm) in rabbits’ orbits.