Z.G. Zheng

In vitro generation of osteochondral differentiation of human marrow mesenchymal stem cells in novel collagen–hydroxyapatite layered scaffolds

Integrated, layered osteochondral (OC) composite materials and/or engineered OC grafts are considered as promising strategies for the treatment of OC damage. A novel biomimetic collagen-hydroxyapatite (COL-HA) OC scaffold with different integrated layers has been generated by freeze-drying. The capacity of the upper COL layer and the lower COL/HA layer to promote the growth and differentiation of human mesenchymal stem cells (hMSCs) into chondrocytes and osteoblasts respectively was evaluated. Cell viability and proliferation on COL and COL/HA scaffolds were assessed by the MTT test. The chondrogenic differentiation of hMSCs on both scaffolds was evaluated by glucosaminoglycan (GAG) quantification, alcian blue staining, type II collagen immunocytochemistry assay and real-time polymerase chain reaction in chondrogenic medium for 21 days. Osteogenic differentiation was evaluated by alkaline phosphatase activity assay, type I collagen immunocytochemistry staining, alizarin S staining and mRNA expression of osteogenic gene for 14 days in osteogenic medium. The results indicated that hMSCs on both COL and COL/HA scaffolds were viable and able to proliferate over time. The COL layer was more efficient in inducing hMSC chondrogenic differentiation than the COL/HA layer, while the COL/HA layer possessed the superiority on promoting hMSC osteogenic induction over either COL layer or pure HA. In conclusion, the layered OC composite materials can effectively promote cartilage and bone tissue generation in vitro and are potentially usable for OC tissue engineering.

The magnetocaloric effect and critical behavior in amorphous Gd60Co40−xMnx alloys

The amorphous alloys Gd60Co40−xMnx (x = 0, 5, 10, 15) were prepared by melt spinning. The Curie temperature, Tc, increases monotonously with Mn addition, ranging from 198 K for x = 0 to 205 K for x = 15, while the maximum values of −ΔSM under the applied field change from 0 to 5 T are 7.7, 7.1, 6.2 and 5.4 J·kg−1·K−1 for x = 0, 5, 10, and 15, respectively. All samples undergo a second order ferri-paramagnetic phase transition. The critical behavior around the transition temperature is investigated in detail, using both the standard Kouvel-Fisher procedure as well as the study of the field dependence of the magnetocaloric effect. Results indicate that the obtained critical exponents are reliable, and that the present alloys exhibit local magnetic interaction.

Large magnetocaloric effect and refrigerant capacity in Gd–Co–Ni metallic glasses

The thermal stability, magnetocaloric effect, and refrigerant capacity (RC) of Gd–Co–Ni metallic glasses were investigated. These alloys possess high glass transition temperature and crystallization temperature as well as a relatively wide supercooled liquid region ΔTx(ΔTx = Tx − Tg) (40–55 K). With increasing the Co/Ni ratio, the Curie temperature TC of the amorphous Gd–Co–Ni increases from 140 K to 192 K. For a magnetic field change of 0–5 T, the maximum magnetic entropy change (−ΔSMmax) and RC values are in the range of 6.04–6.47 J kg−1 K−1 and 450–502 J kg−1, respectively. These values are comparable with that of La(Fe0.88Si0.12)13 and higher than those for the well known magnetic refrigerant Gd5Si2Ge1.9Fe0.1 alloy. The large magnetic entropy change and refrigerant capacity as well as high thermal stability make the alloys attractive candidates as magnetic refrigeration materials for service temperatures of 100–230 K.

Critical behavior and magnetocaloric effect of Gd65Mn35−xGex (x = 0, 5, and 10) melt-spun ribbons

Gd65Mn35−xGex (x = 0, 5, 10) alloy ribbons were prepared by melt-spinning. A fully amorphous structure was obtained for the alloys with x = 5 and 10, whereas, in melt-spun Gd65Mn35 ribbons, crystalline phases (α-Gd and GdMn2) precipitate in the amorphous matrix. The magnetic phase transition from ferromagnetic to paramagnetic is second order. The critical exponents are deduced from the Kouvel-Fisher method and scaling behavior. The obtained critical exponents are in agreement with the theoretical values of 3D Ising model. The Ising-like behavior suggests the presence of large anisotropy and short-range magnetic-coupling behavior. The maximum magnetic-entropy changes of the melt-spun alloys with x = 0, 5, and 10 for a magnetic field change from 0 to 5 T are 4.2, 4.1, and 4.5 Jkg−1 K−1, respectively. All three alloys have a broad temperature range of the magnetic-entropy peak, resulting in large refrigerant capacities.

Surface modification on polyethylene terephthalate films with 2-methacryloyloxyethyl phosphorylcholine.

In this study, the surface of polyethylene terephthalate (PET) was modified to improve the protein and cell adhesion behavior with low temperature ammonia plasma treatment followed by 2-methacryloyloxyethyl phosphorylcholine (MPC) grafting. The x-ray photoelectron spectroscopy (XPS) results showed that the -COO(-), -N-C=O and -P-O-H groups were successfully incorporated onto the sample surface after MPC grafting. Furthermore, formation of new bonds, -N= and N-H on the sample surface grafted with MPC was recorded by Fourier transform infrared spectroscopy (FTIR). A large number of spherical particles at submicron to nanometer scale were also observed on the surface by atomic force microscopy (AFM). The cell adhesion experiments on PET film surfaces were evaluated and the highly hydrophilic surfaces could not promote cell adhesion and spreading. All results achieved in this study have clearly indicated that the method combining low temperature ammonia plasma treatment and MPC grafting is an effective way of producing a suitably hydrophilic PET surface with the capability of weakening the protein adsorption greatly.

Biological protein-resistance layer construction of recombinant hirudin on polymethyl methacrylate IOL surface

In this article, the surface of intraocular len material PMMA was first aminated for activation on which some polar groups generated such as C-N, COO(-), -OH, NH3(+), etc. Then the anticoagulant drugs recombinant hirudin (rH) was grafted with amido bonds to look forward to resist the adsorption of nonspecific protein or cells in tear, even the cataract. The detailed analysis and discussion about the grafting quantity, molography, wettability, electric charges, chemical structure, and the dynamic adsorption of protein Fn on the material surface were carried on by the technology of ultraviolet photometric, contact angle, solid Zeta potential, X-ray photoelectron spectroscopy, and quartz crystal microbalance. The surface with a certain amount of rH modification existed more hydrophilic due to the amphiphilic structure than before, on which the protein adsorption was the most unstable. The results indicated that the rH modification improved the resistance of PMMA to nonspecific adsorption of protein Fn to achieve the expectative effect.

Magnetic properties and magnetocaloric effects in GdCo9Si2 compound with multiple magnetic phase transitions

The structure and magnetic properties of polycrystalline GdCo9Si2 compound have been investigated. It has a BaCd11 structure and undergoes two magnetic phase transitions: an antiferromagnetic to ferrimagnetic transition occurring at ∼93 K, and a ferrimagnetic to paramagnetic transition at 420 K, which results in a positive and a negative magnetic entropy change, respectively. The two peak values of magnetic entropy change are −0.6 and 1.1 J·kg−1·K−1 for ΔH = 5 T. Furthermore, there exists a metal-semiconductor transition temperature (TP), below which the resistance increases with increasing temperature, while the semiconductor characteristic is observed above TP. The magnetic domain structures are characterized by stripe and grid structures 1 μm wide. Although the MCE is small for applications, its study is useful to clearly understand the nature of multiple magnetic phase transitions in the GdCo9Si2 compound.

Low hysteresis and large room temperature magnetocaloric effect of Gd5Si2.05−xGe1.95−xNi2x (2x = 0.08, 0.1) alloys

Gd5Si2.05−xGe1.95−xNi2x (2x = 0.08, 0.1) alloys were prepared by arc melting followed by annealing at 1273 K for 96 h. Mixed monoclinic Gd5Si2Ge2-type phase, orthorhombic Gd5Si4-type phase, and a small amount of Gd5Si3-type phase were obtained in these alloys. Gd5Si2.01Ge1.91Ni0.08 alloy undergoes a second-order transition (TC) around 300 K, whereas Gd5Si2Ge1.9Ni0.1 alloy exhibits two transitions including a first-order transition (TCІІ) at ∼295 K and second-order transition (TCІ) at ∼301 K. Ni substitution can effectively reduce the thermal hysteresis and magnetic hysteresis while maintaining large magnetic entropy change. The maximum magnetic entropy changes (|ΔSMmax|) of Gd5Si2.05−xGe1.95−xNi2x alloys with 2x = 0.08 and 0.1 are 4.4 and 5.0 J kg−1 K−1, respectively, for 0–2 T, and are 8.0 and 9.1 J kg−1 K−1, respectively, for 0–5 T. Low hysteresis performance and relatively large magnetic entropy change make these alloys favorable for magnetic refrigeration applications.

Biological performance of functionalized biomedical polymers for potential applications as intraocular lens

To study the biological performance of surface-modified biomedical polymer materials, a model of the functional mechanism of nonspecific adsorption resistance was constructed. Cell behavior on the surface and in vivo transplantation features of intraocular lens (IOL) materials, such as hydrophobic acrylic ester and polymethyl methacrylate (PMMA), were investigated. The results of cell adhesion and proliferation studies showed that the addition of hirudin can significantly resist epithelial cell adhesion, better than the pure amination process, and thereby inhibit excessive proliferation on the surface. Experiments on the eyes of rabbits indicated that the IOL surfaces with hirudin modification reduced the incidence of cell aggregation and inflammation. Combined with a study of protein-resistant layer construction with recombinant hirudin on the material surface, the mechanism of surface functionalization was determined. The biological performance indicated that nonspecific adsorption is greatly decreased due to the existence of amphiphilic ions or hydration layers, which lead to stability and long-term resistance to nonspecific adsorption. These results offer a theoretical basis for the use of traditional biomedical polymer materials in long-term clinical applications.