Injectable polyethylene glycol-laponite composite hydrogels as articular cartilage scaffolds with superior mechanical and rheological properties

In this study, injectable PEG-based hydrogels containing Laponite particles with mechanical and structural properties close to the natural articular cartilage are introduced. The nanocomposites are fabricated by imide ring opening reactions utilizing synthesized copolymers containing PEG blocks and nanoclay through a two-step thermal poly-(amic acid) process. Butane diamine is used as nucleophilic reagent and hydrogels with interconnected pores with sizes in the range of 100–250?µm are prepared. Improved viscoelastic properties compared with the conventional PEG hydrogels are shown. Evaluation of cell viability utilizing human mesenchymal stem cells determines cytocompatibility of the nanocomposite hydrogels.     

A method for determining rewetting velocity under generalized boiling conditions

A method is presented for the solution of the quasi-steady state two-dimensional rewetting conduction problem. Using the method of separation of variables, a solution is presented for the case of an arbitrary heat transfer coefficient profile. Numerical results are also presented for the particular case in which a sputting region exists immediately behind the wet front. These results show that value of the heat transfer coefficient in the sputtering region determines the rewetting temperature if the sputtering region length exceeds one quarter of the class thickness. The numerical results in general show that the rewetting phenomenon is very localized with respect to the wet front. Results are compared favorably with experimental data in the low to moderate flow rate range.     

Integrated all-optical infrared switchable plasmonic quantum cascade laser

We report a type of infrared switchable plasmonic quantum cascade laser, in which far field light in the midwave infrared (MWIR, 6.1 μm) is modulated by a near field interaction of light in the telecommunications wavelength (1.55 μm). To achieve this all-optical switch, we used cross-polarized bowtie antennas and a centrally located germanium nanoslab. The bowtie antenna squeezes the short wavelength light into the gap region, where the germanium is placed. The perturbation of refractive index of the germanium due to the free carrier absorption produced by short wavelength light changes the optical response of the antenna and the entire laser intensity at 6.1 μm significantly. This device shows a viable method to modulate the far field of a laser through a near field interaction.     

P75 and S100 gene expression induced by cell-imprinted substrate and beta-carotene to nerve tissue engineering

Here we aimed to differentiate adipose derived stem cells (ADSCs) to Schwann cells (SCs), as one of the major and instrumental cell sources in nerve regeneration, by synergistic application of imprinting method and β-carotene. Accordingly, the topography of Schwann cells was imprinted on poly dimethyl siloxane (PDMS) substrates via mold casting and human ADSCs seeded on substrates; moreover, β-carotene was added to induce hADSCs differentiation. Physiochemical evaluations of PDMS by FTIR spectra presented its silicon-methyl bond (Si CH₃) at 1260 cm⁻¹. Morphology analysis by crystal violet, picrosirus red staining, and SEM images illustrated that MSCs seeded on imprinted substrates have formed SC-like morphology. Furthermore, according to q-PCR and ICC evaluations, SCs specific markers; S100 and P75 in addition of 5 μl β-carotene (BC) were upregulated (p-value<0.001). Also, the expression was detected on the imprinted surfaces without β-carotene to a lesser degree. Our study revealed that Schwann cell imprinted substrates can mimic the morphology and topography of SCs and induce differentiation signals in mesenchymal stem cells (MSCs). In addition, the potency of β-carotene as an organic substance in boosting and stimulating the neural differentiation was demonstrated. Relevantly, the reports have confirmed the synergistic pivotal roles of β-carotene and patterned surfaces in directing MSCs into SC-like cells differentiation without applying expensive and less safe chemical growth factors.     

Evaluation of the chondrogenic differentiation of mesenchymal stem cells on hybrid biomimetic scaffolds

Hybrid materials are widely and promisingly used as scaffolds in cartilage tissue remodeling. In this study, hybrid scaffolds consist of polycaprolactone (PCL), poly(vinyl alcohol) (PVA) with/without gelatin (GEL) to mimic natural cartilage extracellular matrix (ECM) were investigated. Scaffolds were prepared by freeze drying and characterized by scanning electron microscopy and compressive mechanical testing. Biological assays of mesenchymal stem cell (MSC) cultures, 3‐(4,5‐dimethylthiazol‐2‐yl)‐2,5‐diphenyltetrazolium bromide, and dimethyl methylene blue were performed, and real‐time polymerization chain reaction analysis of the cartilage‐specific ECM gene marker expression was done. The results show an open interconnected porous structure with a compression modulus of 1.27 ± 0.04 MPa. The surface of the scaffolds showed an excellent efficiency in the adhesion and proliferation of MSCs. A significant increase in the proteoglycan content from 3.70 ± 0.96 to 5.4 ± 1.13 μg/mL was observed after 14 days in the PCL–PVA–GEL scaffolds. The expression amount of the sex‐determining region Y–Box 9 (SOX9) and collagen II (COL2) mRNA levels of the MSCs showed significant increases in SOX9 and COL2, respectively in comparison with PCL–PVA scaffold. The study revealed that the aforementioned scaffold as a blend of natural and synthetic polymers may be a promising substrate in tissue engineering for cartilage repair with MSC transplantation. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40635.     

Fabrication of biocompatible titanium scaffolds using space holder technique

Open-pore titanium scaffolds were fabricated by sintering of compressed mixtures of TiH_1.924 and urea. Spherical and irregular shaped space holders were used to investigate the effect of pore shape on cellular behavior. After removal of the space holder, the shape of the spacers was replicated to the pores. Average diameter of the pores was in the range of 300–600?μm. SEM images showed that titanium hydride resulted in higher surface roughness and larger micro porosities than pure titanium. In vitro evaluations were carried out by using MTT assay, measuring alkaline phosphatase activity and alizarin red staining in flow perfusion bioreactor for cell culture. Observations revealed excellent attachment and proliferation of G-292 cells to the highly porous scaffolds fabricated with titanium hydride and urea of this research.     

A low-power high-performance SiGe BiCMOS 802.11a/b/g transceiver IC for cellular and bluetooth Co-existence applications

This paper describes a high-performance WLAN 802.11a/b/g radio transceiver, optimized for low-power in mobile applications, and for co-existence with cellular and Bluetooth systems in the same terminal. The direct-conversion transceiver architecture is optimized in each mode for low-power operation without compromising the challenging RF performance targets. A key transceiver requirement is a sensitivity of -77 dBm (at the LNA input) in 54 Mb/s OFDM mode while in the presence of a GSM1900 transmitter interferer. The receiver chain achieves an overall noise figure of 2.8/3.2 dB, consuming 168/185 mW at 2.8 V for the 2.4/5GHz bands, respectively. Signal loopback and transmit power detection techniques are used in conjunction with the baseband modem processor to calibrate the transmitter LO leakage and the transceiver I/Q imbalances. Fabricated in a 70 GHz f/sub T/ 0.25-/spl mu/m SiGe BiCMOS technology for system-in-package (SiP) use, the dual-band, tri-mode transceiver occupies only 4.6 mm/sup 2/.     

Biological evaluation of polyvinyl alcohol hydrogel crosslinked by polyurethane chain for cartilage tissue engineering in rabbit model

Polyvinyl alcohol (PVA) hydrogel chains were crosslinked by urethane pre-polymer (PPU) in order to fabricate a new substitute for cartilage lesions. The microscopy images showed that the cultured chondrocytes had spherical morphology on PVA–PPU sample after 4 weeks of isolation in vitro. The alcian blue and safranin O staining proved the presence of proteoglycan on the surface of PVA–PPU sample secreted by cultured chondrocytes. This was confirmed by the detection of sulfate ions in the wavelength dispersive X-ray (WDX) analysis. In addition, the expression of collagen type II and aggrecan were observed in chondrocytes cultured on PVA–PPU by RT-PCR. Moreover, the implantation of the PVA–PPU sample with autologous cultured chondrocytes revealed the formation of neocartilage tissue in a rabbit model during 12 weeks follow up. In conclusion, the results verified that isolated chondrocytes cultured on PVA–PPU retain their original phenotype and this composition can be considered as promising substrate for cartilage tissue engineering.