An injectable, biodegradable hydrogel composite of oligo(poly(ethylene glycol) fumarate) (OPF) and gelatin microparticles (MPs) has been investigated as a cell and growth factor carrier for cartilage tissue engineering applications. In this study, hydrogel composites with different swelling ratios were prepared by crosslinking OPF macromers with poly(ethylene glycol) (PEG) repeating units of varying molecular weights from 1,000 ~ 35,000. Rabbit marrow mesenchymal stem cells (MSCs) and MPs loaded with transforming growth factor-β1 (TGF-β1) were encapsulated in the hydrogel composites in order to examine the effect of the swelling ratio of the hydrogel composites on the chondrogenic differentiation of encapsulated rabbit marrow MSCs both in the presence and absence of TGF-β1. The swelling ratio of the hydrogel composites increased as the PEG molecular weight in the OPF macromers increased. Chondrocyte-specific genes were expressed at higher levels in groups containing TGF-β1-loaded MPs and varied with the swelling ratio of the hydrogel composites. OPF hydrogel composites with PEG repeating units of molecular weight 35,000 and 10,000 with TGF-β1-loaded MPs exhibited a 159 ± 95 and a 89 ± 31 fold increase in type II collagen gene expression at day 28, respectively, while OPF hydrogel composites with PEG repeating units of molecular weight 3,000 and 1,000 with TGF-β1-loaded MPs showed a 27 ± 10 and a 17 ± 7 fold increase in type II collagen gene expression, respectively, as compared to the composites with blank MPs at day 0. The results indicate that chondrogenic differentiation of encapsulated rabbit marrow MSCs within OPF hydrogel composites could be affected by their swelling ratio, thus suggesting the potential of OPF composite hydrogels as part of a novel strategy for controlling the differentiation of stem cells.

The effective desorption kinetic parameters of CO on the Pd(111) surface have been studied by thermal desorption spectroscopy. The zero coverage effective desorption activation energy and the preexponential factor were found to be 35.5 kcal/mol and 1013.5 s−1, respectively. As a function of CO coverage, a four-stage correlation between Ed(θ) and the development of stable low-energy electron desorption (LEED) structures was observed for the first time at Tads= 200 K. Ed and ν1 showed a strong compensation effect with Tc=519 K. The adsorption temperature dependence of Ed from Tads=87 to 200 K was observed and interpreted qualitatively by a model involving the production of different domain structures at various adsorption temperatures and the preservation of domain structures at higher coverages during temperature programmed desorption.

This work investigated the delivery of marrow mesenchymal stem cells (MSCs), with or without the growth factor transforming growth factor-β1 (TGF-β1), from biodegradable hydrogel composites on the repair of osteochondral defects in a rabbit model. Three formulations of oligo(poly(ethylene glycol) fumarate) (OPF) hydrogel composites containing gelatin microparticles (GMPs) and MSCs were implanted in osteochondral defects, including (1) OPF/GMP hydrogel composites; (2) OPF/ GMP hydrogel composites encapsulating MSCs; and (3) OPF hydrogel composites containing TGF-β1 loaded GMPs and MSCs. At 12 weeks, the quality of new tissue formed in chondral and subchondral regions of defects was evaluated based on subjective and quantitative histological analysis. OPF hydrogel composites were partially degraded and the defects were filled with newly formed tissue at 12 weeks with no sign of persistent inflammation. With the implantation of scaffolds alone, newly formed chondral tissue had an appearance of hyaline cartilage with zonal organization and intense staining for glycosaminoglycans, while in the subchondral region hypertrophic cartilage with some extent of bone formation was often observed. The addition of MSCs, especially with TGF-β1 loaded GMPs, facilitated subchondral bone formation, as evidenced by more trabecular bone appearance. However, the delivery of MSCs with or without TGF-β1 at the dosage investigated did not improve cartilage morphology. While OPF-based hydrogel composites supported osteochondral tissue generation, further investigations are necessary to elucidate the effects of MSC seeding density and differentiation stage on new tissue formation and regeneration.

In this study, electrospun poly(ε-caprolactone) (PCL) microfiber scaffolds, coated with cartilaginous extracellular matrix (ECM), were fabricated by first culturing chondrocytes under dynamic conditions in a flow perfusion bioreactor and then decellularizing the cellular constructs. The decellularization procedure yielded acellular PCL/ECM composite scaffolds containing glycosaminoglycan and collagen. PCL/ECM composite scaffolds were evaluated for their ability to support the chondrogenic differentiation of mesenchymal stem cells (MSCs) in vitro using serumfree medium with or without the addition of transforming growth factor-β1 (TGF-β1). PCL/ECM composite scaffolds supported chondrogenic differentiation induced by TGF-β1 exposure, as evidenced in the up-regulation of aggrecan (11.6 ± 3.8 fold) and collagen type II (668.4 ± 317.7 fold) gene expression. The presence of cartilaginous matrix alone reduced collagen type I gene expression to levels observed with TGF-β1 treatment. Cartilaginous matrix further enhanced the effects of growth factor treatment on MSC chondrogenesis as evidenced in the higher glycosaminoglycan synthetic activity for cells cultured on PCL/ECM composite scaffolds. Therefore, flow perfusion culture of chondrocytes on electrospun microfiber scaffolds is a promising method to fabricate polymer/extracellular matrix composite scaffolds that incorporate both natural and synthetic components to provide biological signals for cartilage tissue engineering applications.

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Oxygen adsorption on the Pd(111) surface has been studied at 100 and 300 K by temperature programmed desorption (TPD) and isotopic mixing experiments. At 100 K, the sticking coefficient is determined to be 1 up to the coverage of 0.3 O/Pd. The saturation coverage is 0.62 O/Pd, 27% of which dissociates during thermal desorption. Three molecular desorption processes are observed with the activation energy of 7.6, 9.1, and 12.3 kcal/mol, respectively. At 300 K, the sticking coefficient increases with coverage from ∼0.14 at zero coverage to 0.87 at θ≊0.05 O/Pd, then decreases to zero at a saturation coverage of 0.25 O/Pd. The desorption activation energy of 53 kcal/mol is calculated for the associative desorption process with a lateral repulsive interaction of 0.7 kcal/mol. Based on the isotopic mixing results and previous high resolution electron energy loss spectroscopy (HREELS) data, a more complete picture concerning adsorption, conversion, equilibration, desorption, and dissociation processes is suggested.

Injectable, biodegradable hydrogel composites of crosslinked oligo(poly(ethylene glycol) fumarate) (OPF) and gelatin microparticles (MPs) were utilized to fabricate a bilayered osteochondral construct consisting of a chondrogenic layer and an osteogenic layer, and to investigate the differentiation of rabbit marrow mesenchymal stem cells (MSCs) encapsulated in both layers in vitro. The results showed that MSCs in the chondrogenic layer were able to undergo chondrogenic differentiation, especially in the presence of TGF-β1-loaded MPs. In the osteogenic layer, cells maintained their osteoblastic phenotype. Although calcium deposition in the osteogenic layer was limited, cells in the osteogenic layer significantly enhanced chondrogenic differentiation of MSCs in the chondrogenic layer. The greatest effect was observed when MSCs were encapsulated with TGF-β1-loaded MPs and cultured with osteogenic cells in the bilayered constructs. Overall, this study demonstrates the fabrication of bilayered hydrogel composites that mimic the structure and function of osteochondral tissue, along with the application of these composites as cell and growth factor carriers.

We have made the first dynamic measurement of the (1 xl)-CO island growth rate and the simultaneous CO coverage on the quasihexagonal reconstructed (hex-/?) phase during the CO-induced hex-/? -(1 xl) phase transformation on Pt{l00}. The island growth rate is described by a strongly nonlinear power law with respect to the local CO coverage on the hex-/? phase at surface temperatures between 380 and 410 K, with an apparent reaction order of 4.5 ±0.4. These kinetics manifest themselves as a strongly flux dependent net sticking probability.PACS numbers: 68.35.Bs, 68.45.Da Numerous observations have now been made of surface structural phase changes induced by the presence of adsorbates. Despite this, there are no studies available which establish the growth mechanism of the islands of the new phase from the stable clean surface phase. In this Letter we present a study of the conversion of the stable surface of clean Pt{l00}, described as hex-/?, to a (lxl) configuration during CO adsorption. It represents the first dynamic measurement of the (1 x l)-CO island growth rate and the simultaneous CO coverage on the hex-/? phase during the surface structural transformation. The results show that 4 to 5 CO molecules are involved in the restructuring process, leading to a strongly nonlinear growth dependence. This is crucial to the understanding of the nucleation and growth mechanism and also oscillatory reactions involving CO on Pt{l00} [1,2].The most stable phase of the clean Pt{l00} surface is a reconstructed phase in which the surface layer of Pt atoms has a quasihexagonal structure. Following Heilmann, Heinz, and Muller [3], we will refer to this surface as Pt{l00}-hex-/?0.7° or simply hex-/?. A metastable (lxl) clean surface (the bulk truncation structure) can be prepared which reconstructs irreversibly above =^ 400 K [4,5] to form the "hex" surface, which in turn reconstructs to form the hex-/? surface at ^ 1100 K. The hex and hex-/? surfaces differ by a rotation of the hexagonal layer by -0.7° with respect to the bulk. The hex and hex-/? reconstructions are lifted by the adsorption of CO, NO, O2, and other adsorbates to yield the (lxl) phase. The driving force of the CO-induced hex-* (lxl) surface phase transition was identified by Thiel et al. [6] from a low energy electron diffraction (LEED) study to be the higher heat of adsorption of CO on the (lxl) phase than on the reconstructed phase. Thiel et al. also proposed that the transformation occurs by sequential steps of adsorption on the reconstructed surface followed by migration and "trapping" of CO onto growing "islands" of the (lxl) surface, initially formed by nucleation. It is known that a critical CO coverage of ca. 0.05 monolayer (ML) on the hex phase is required to induce the hex-* (lxl) phase transformation [7,8] [where