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1.  Bacteria Inside Semiconductors as Potential Sensor Elements: Biochip Progress 
Sensors (Basel, Switzerland)  2014;14(6):11225-11244.
It was discovered at the beginning of this Century that living bacteria—and specifically the extremophile Pseudomonas syzgii—could be captured inside growing crystals of pure water-corroding semiconductors—specifically germanium—and thereby initiated pursuit of truly functional “biochip-based” biosensors. This observation was first made at the inside ultraviolet-illuminated walls of ultrapure water-flowing semiconductor fabrication facilities (fabs) and has since been, not as perfectly, replicated in simpler flow cell systems for chip manufacture, described here. Recognizing the potential importance of these adducts as optical switches, for example, or probes of metabolic events, the influences of the fabs and their components on the crystal nucleation and growth phenomena now identified are reviewed and discussed with regard to further research needs. For example, optical beams of current photonic circuits can be more easily modulated by integral embedded cells into electrical signals on semiconductors. Such research responds to a recently published Grand Challenge in ceramic science, designing and synthesizing oxide electronics, surfaces, interfaces and nanoscale structures that can be tuned by biological stimuli, to reveal phenomena not otherwise possible with conventional semiconductor electronics. This short review addresses only the fabrication facilities' features at the time of first production of these potential biochips.
PMCID: PMC4118370  PMID: 24961215
biochips; germanium; crystals; nucleation; Pseudomonas syzgii; fabs; optics
2.  Effect of cleaning and sterilization on titanium implant surface properties and cellular response 
Acta biomaterialia  2011;8(5):1966-1975.
Titanium (Ti) has been widely used as an implant material due to the excellent biocompatibility and corrosion resistance of its oxide surface. Biomaterials must be sterile before implantation, but the effects of sterilization on their surface properties have been less well studied. The effects of cleaning and sterilization on surface characteristics were bio-determined using contaminated and pure Ti substrata first manufactured to present two different surface structures: pretreated titanium (PT, Ra = 0.4 μm) (i.e. surfaces that were not modified by sandblasting and/or acid etching); (SLA, Ra = 3.4 μm). Previously cultured cells and associated extracellular matrix were removed from all bio-contaminated specimens by cleaning in a sonicator bath with a sequential acetone–isopropanol–ethanol–distilled water protocol. Cleaned specimens were sterilized with autoclave, gamma irradiation, oxygen plasma, or ultraviolet light. X-ray photoelectron spectroscopy (XPS), contact angle measurements, profilometry, and scanning electron microscopy were used to examine surface chemical components, hydrophilicity, roughness, and morphology, respectively. Small organic molecules present on contaminated Ti surfaces were removed with cleaning. XPS analysis confirmed that surface chemistry was altered by both cleaning and sterilization. Cleaning and sterilization affected hydrophobicity and roughness. These modified surface properties affected osteogenic differentiation of human MG63 osteoblast-like cells. Specifically, autoclaved SLA surfaces lost the characteristic increase in osteoblast differentiation seen on starting SLA surfaces, which was correlated with altered surface wettability and roughness. These data indicated that recleaned and resterilized Ti implant surfaces cannot be considered the same as the first surfaces in terms of surface properties and cell responses. Therefore, the reuse of Ti implants after resterilization may not result in the same tissue responses as found with never-before-implanted specimens.
PMCID: PMC3618465  PMID: 22154860
Titanium; Sterilization; Roughness; Hydrophilicity; MG63 cells
3.  New Variable Porosity Flow Diverter (VPOD) Stent Design for Treatment of Cerebrovascular Aneurysms 
Conference Proceedings  2011;2011:1105-1108.
Using flow diverting Stents for intracranial aneurysm repair has been an area of recent active research. While current commercial flow diverting stents rely on a dense mesh of braided coils for flow diversion, our group has been developing a method to selectively occlude the aneurysm neck, without endangering nearby perforator vessels. In this paper, we present a new method of fabricating the low porosity patch, a key element of such asymmetric vascular stents (AVS).
PMCID: PMC3401081  PMID: 22254507
4.  Junction formation of Cu3BiS3 investigated by Kelvin probe force microscopy and surface photovoltage measurements 
Recently, the compound semiconductor Cu3BiS3 has been demonstrated to have a band gap of ~1.4 eV, well suited for photovoltaic energy harvesting. The preparation of polycrystalline thin films was successfully realized and now the junction formation to the n-type window needs to be developed. We present an investigation of the Cu3BiS3 absorber layer and the junction formation with CdS, ZnS and In2S3 buffer layers. Kelvin probe force microscopy shows the granular structure of the buffer layers with small grains of 20–100 nm, and a considerably smaller work-function distribution for In2S3 compared to that of CdS and ZnS. For In2S3 and CdS buffer layers the KPFM experiments indicate negatively charged Cu3BiS3 grain boundaries resulting from the deposition of the buffer layer. Macroscopic measurements of the surface photovoltage at variable excitation wavelength indicate the influence of defect states below the band gap on charge separation and a surface-defect passivation by the In2S3 buffer layer. Our findings indicate that Cu3BiS3 may become an interesting absorber material for thin-film solar cells; however, for photovoltaic application the band bending at the charge-selective contact has to be increased.
PMCID: PMC3323917  PMID: 22497001
buffer layer; Cu3BiS3; Kelvin probe force microscopy; solar cells
5.  Partially Polyurethane-Covered Stent for Cerebral Aneurysm Treatment 
Partially polyurethane-covered stent (PPCS) is proposed for the treatment of cerebral aneurysms. The PPCSs were observed to substantially modify the flow entering the aneurysm in a patient-specific aneurysm phantom (PSAP). These stents can act as flow modulators and the polyurethane (PU) membrane can provide a smooth scaffold for restoring the structural integrity of the diseased vessel. Partial coating of the stent aids in sealing only the entrance to the aneurysm while keeping the perforators around the aneurysm open and patent. Biocompatibility of the PU membrane was monitored using contact angle measurements to show that critical surface tension (CST) values remained in the thromboresistant range of 20–30 mN/m. Stent flexibility, stiffness, and pressure–diameter relationship showed no significant change after asymmetric PU film application. No delamination of the PU membrane from the stent was observed within the working strains of the stent. The flow modulating capability of the PPCS was monitored by intentionally orienting the stent to cover either the proximal or the distal regions along the neck of the PSAP. Time density curves (TDCs) compared the relative metrics of input rate, washout rate, residence time, and influx in the aneurysm before and after the stent placement.
PMCID: PMC2720836  PMID: 18837459
stents; polyurethane coatings; flow studies; mechanical properties; biocompatibility
6.  Cross-competition of CD8+ T cells shapes the immunodominance hierarchy during boost vaccination 
The Journal of Experimental Medicine  2007;204(9):2187-2198.
CD8+ T cell responses directed against multiple pathogen-derived epitopes are characterized by defined immunodominance hierarchy patterns. A possible explanation for this phenomenon is that CD8+ T cells of different specificities compete for access to epitopes on antigen-presenting cells, and that the outcome of this so-called cross-competition reflects the number of induced T cells. In our study using a vaccinia virus infection model, we found that T cell cross-competition is highly relevant during boost vaccination, thereby shaping the immunodominance hierarchy in the recall. We demonstrate that competition was of no importance during priming and was unaffected by the applied route of immunization. It strongly depended on the timing of viral antigen expression in infected APCs, and it was characterized by poor proliferation of T cells recognizing epitopes derived from late viral proteins. To our knowledge, this is the first demonstration of the functional importance of T cell cross-competition during a viral infection. Our findings provide a basis for novel strategies for how boost vaccination to defined antigens can be selectively improved. They give important new insights into the design of more efficient poxviral vectors for immunotherapy.
PMCID: PMC2118691  PMID: 17709425

Results 1-6 (6)