Standard Immersion Research Articles

Surface modification of biodegradable AZ91 magnesium alloy by electrospun polymer nanocomposite: Evaluation of in vitro degradation and cytocompatibility

Magnesium alloys have recently attracted significant attention for the fabrication of biodegradable orthopedic implants and cardiovascular stents. Nevertheless, the high degradation rate of magnesium alloys under physiological conditions is still challenging. We present a surface modification strategy to tailor the degradation rate and in vitro cell behavior of AZ91 alloy through electrospinning of continuous poly (ε-caprolactone) fibers containing bioactive glass nanoparticles (~30 nm). The average thickness of the nanocomposite film and the fibers are 30 μm ± 5 and 300 ± 31 nm, respectively. Electrochemical studies in simulated body fluid and standard immersion corrosion tests have determined that the degradation rate of the magnesium alloy is reduced by two orders of magnitude. Scanning electron microscopy, energy-dispersive X-ray spectroscopy, and X-ray diffraction analyses have shown the formation and precipitation of hydroxyapatite and magnesium hydroxides on the surface of fibrous film after 7 days of incubation. In addition to enhancing the in vitro bioactivity, osteosarcoma and fibroblast cell assays have revealed better cell adhesion and viability on the coated surface. The mechanisms of improved properties are ascribed to the effect of nanocomposite film on the hydrophilicity of the surface and mass transport through the fibrous structure as well as the presence of bioactive nanoparticles.

The Role of H2O2 and K2S2O8 as Oxidizing Agents for Accelerated Corrosion Testing

In this work, the application of hydrogen peroxide (H2O2) and potassium persulfate (K2S2O8) in accelerated corrosion testing was considered. H2O2 is already used as an accelerant in the standard immersion test ASTM G110, and K2S2O8 is an oxidizing agent that shows promise for corrosion testing applications. A Koutecky-Levich approach was used to investigate the cathodic kinetics of both oxidizing agents as well as dissolved oxygen (O2). Cathodic kinetics for O2, H2O2, and S2O82− were faster when measured on a platinum electrode than when measured on an AA2060-T3 electrode. This difference was attributed to the additional limit to cathodic kinetics posed by the protective oxide film on aluminum. H2O2 was a more potent accelerant than K2S2O8 at a concentration of 0.1 M due to the faster cathodic kinetics of H2O2 on aluminum. However, K2S2O8 was more convenient to use in a laboratory setting due to its stability during storage. The severity of tests using K2S2O8 was increased by lowering the solution pH to 2.28. At the low solution pH, cathodic kinetics and extent of attack increased.

Virulence of infectious pancreatic necrosis virus (IPNV) isolates from Mexico.

Infectious pancreatic necrosis virus (IPNV) causes economic losses in Mexican rainbow trout industry. In this study, virulence and genetic fingerprints of Mexican IPNV isolates was investigated for the first time. Two Mexican IPNV isolates were analyzed in rainbow trout fry and the Sp strain was included as high virulence. One of the Mexican IPNV isolate was obtained from diseased fish and the other from fish without clinical signs. The infection was performed using a standardized immersion. Clinical signs were observed at 4 days post infection in fry group infected with strain Sp, two days earlier than in trout infected with IPNV isolates Mexican. Severe lesions were found in 100% of the individuals of Sp group, but only in 25% of each isolated Mexican group. Results suggest that Mexican IPNV isolates are pathogenic, but less virulent than strain Sp. The amino acid motif residues of both Mexican isolates, corresponded to a subclinical disease. Nevertheless, the accumulated motility observed in the field, suggest that other factors play a role in the virulence of the disease.

Poly(l-lactic acid) (PLLA) Coatings with Controllable Hierarchical Porous Structures on Magnesium Substrate: An Evaluation of Corrosion Behavior and Cytocompatibility.

Magnesium (Mg) and its alloys have been intensively explored as the next generation of metallic bone substitutes in past decades, but their rapid corrosion rate in physiological environments is still a great hindrance for further therapeutic applications. In the present study, we attempt to design biodegradable poly(l-lactic acid) (PLLA) coatings on pure Mg substrates (99.99 wt %) with tunable surface morphologies through dip-coating in combination with mixed nonsolvent induced phase separation (Dip-coating-mNIPS) method to regulate their corrosion behavior and biocompatibility. We applied the mixtures of ethanol and hexane as the coagulation baths, and changed the composition of mixed nonsolvent and the concentration of polymer solution to obtain PLLA coatings with different pore sizes and morphologies. Standard electrochemical measurements and immersion tests demonstrated that all PLLA coatings could effectively enhance the corrosion resistance of Mg substrates but that the corrosion behaviors varied among coatings with different surface and inner structures. A systematic investigation of cellular response through MTT assay, LIVE/DEAD staining, cell distribution, and cell attachment indicated that PLLA-coated Mg substrates could enhance cytocompatibility in comparison to pure Mg. In addition, the cellular behaviors were affected by the corrosion activity as well as the surface properties of different PLLA coatings. Our findings illustrated that through the Dip-coating-mNIPS method, the structure of the PLLA membrane on Mg substrates could easily be controlled to regulate the corrosion behaviors and further improve the biocompatibility. This presents great potential in designing functional polymer coatings on Mg-based orthopedic implants to meet specific clinical requirements.

Mechanical characteristics and water stability of silt solidified by incorporating lime, lime and cement mixture, and SEU-2 binder

Abstract Silt has a poor geotechnical performance. In this study, an investigation on silt solidification was performed by incorporating lime, mixture of lime and cement (LC), and a self-developed lab-made binder (named SEU-2 binder). The properties of solidified silt cured in standard curing and immersion curing for 7, 28 and 90 days, respectively, were determined in relation to unconfined compressive strength (UCS) and water stability. The solidification mechanism was further analyzed by the technologies of scanning electron microscope (SEM) and X-ray diffraction (XRD) analysis. Results revealed that the UCS of lime solidified silt had an optimum value when the dosage of lime was 8%, while the UCS of LC and SEU-2 binder solidified silt increased with an increase of LC and SEU-2 binder content. The water stability coefficient (WSC) of lime solidified silt increased first and then stabilized, whereas the WSC of LC solidified silt hardly changed with water curing time. However, WSC of SEU-2 binder solidified silt has insignificant change with SEU-2 binder content. With the increase of binder content, the WSC of lime solidified silt increased first and then decreased, and the WSC of LC solidified silt hardly changed. However, for SEU-2 binder solidified silt, WSC showed no obvious correlation with SEU-2 binder content. Generally, SEU-2 binder solidified silt had superior mechanical properties relative to that solidified by lime or LC, which can be further explained by SEM and XRD analyses.

Studies on the bioactive flavonoids isolated from Azadirachta indica

Two novel natural metabolites, 3-O-butyl-(-)-epicatechin (1) and 3-O-butyl-(-)-epigallocatechin (2), as well as several known substances, (−)-epicatechin (3), (+)-gallocatechin (4), (−)-epigallocatechin (5), azadirachtin A (6), trilinolein (7) and octadecanoic acid-tetrahydrofuran-3,4-diyl ester (8), were isolated from the bark of Azadirachta indica. The structures of all compounds were established by comprehensive and comparative spectroscopic analysis of NMR and ESI-HRMS data. The new metabolites 1 and 2 represent one of the few examples of natural compounds with a butyl ether group moiety. The acaricidal activity of the compounds was tested using a standard Shaw larval immersion assay. All the compounds, except 7, possess a LD50 value less than or equal to 7.2 mM.

Effect of Chelating Additive on Pore Structure and Mechanical Property of Mortar under Different Curing Conditions

Effect of chelating additive on microstructure, hydration products and mechanical property of mortar under different curing conditions was investigated. The microstructure was tested by nuclear magnetic resonance and scanning electron microscope. And the chemical composition of hydration products was analyzed by X-ray diffraction. The compressive strength was measured under different curing conditions at different curing age, including standard curing, water immersion, seawater immersion and salt mist curing. After curing for 28 days in water, compared to control mortar, the reduction ratio of harmful pores whose size larger than 0.1μm in mortar with chelating additive (CA mortar) was 14.6%, followed by 8.9%, 9.2% and 2.9% which was under standard curing, seawater immersion and salt mist curing, respectively. From the scanning electron microscope image, there were more needle-like and bar-like crystals in CA mortar making it more compact, which was mainly calcium silicate hydrate through component analysis. Besides, the raising percentage of compressive strength of CA mortar under water immersion is 28.6% compared to control mortar at the age of 28 days, followed by 26.8%, 21.8% and 16.3% which was under standard curing, seawater immersion and salt mist curing, respectively. The results indicate that chelating additive can enhance compactness and compressive strength of cement-based materials especially under water immersion by promoting the formation of calcium silicate hydrate.

Deformation of rutting due to temperature change from recycle of hot-mix asphalt with crumb rubber

The cover layer of the pavement can be functioned as a structural layer or non-structural layer. Improvement of road surface conditions is done by overlay with additional layers above it or stripping the surface layers of the road. Reclaimed Asphalt Pavement (RAP) or asphalt stripping results into a new problem of aggregate asphalt waste. Utilization of material from the pavement surface layer can reduce environmental pollution and can save maintenance cost. Research has been done by knowing the content of asphalt and gradation of aggregate from stripping asphalt through the extraction process. A few modified asphalts as Asbuton Retona Blend-55 (Asbuton-R) and fresh aggregates have been added to obtain the aggregate bitumen mixture on the specification type of Asphalt Concrete Wearing Coarse (ACWC) mixture. Crumb Rubber (CR) of used tire rubber has been added to the new aggregate and mixed with the old asphalt mixture, and then added asphalt modified Asbuton-R. Crumb rubber (CR) of 0.5%, 1%, 1.5% and 3% were added to each variation of asphalt content ranging from 1.5%; 2%; and 4%. The result of the recycled aggregate asphalt mixture was tested with Marshall Standard and Marshall Immersions on the optimum Asbuton-R content. The deformation resistance of pavement mixture to weather changes has been simulated using Wheel Tracking Machine (WTM) at 26° C, 30° C, 35° C. The results showed that RAP content of more than 80% can still be utilized in the recycling process. The asphalt pavement mixture resistance to rutting deformation due to temperature change, with the addition of 1.5% of optimum Asbuton-R content has shown an increase.

Solubility analysis of elastomers in a bio-based lubricant using Hansen parameters

The solubility of automotive elastomers, namely, silicone rubber (VMQ), flouroelastomer (FKM) and ethylene-propylene-diene monomer (EPDM) in Jatropha bio-based lubricant (bio-oil), an engine mineral oil (EMO) and a blend of the bio-oil with EMO, respectively, was analyzed by using the Hansen solubility method. In addition, an experimental compatibility analysis, consisting on standard immersion tests and measurements of changes in mass, volume, hardness and tensile and tear strengths, was conducted to complement and validate the results obtained using the Hansen method. The Hansen method was found to be in good agreement with the compatibility tests and provided an appropiate description of the dissolution/degradation behavior of the seals upon exposure to the lubricants. Finally, it was found that FKM was the most compatible in the three lubricants, while EPDM was very prone to dissolution/degradation in EMO and B20, and VMQ in the bio-oil.

Establishment of a multi-acaricide resistant reference tick strain (IVRI-V) of Rhipicephalus microplus

Tick-borne diseases is a global threat and tick resistance to commonly used acaricides is a growing problem, thus calling for improved resistance monitoring tools. To aid in monitoring of resistance in field tick populations, a resistant colony of Rhipicephalus microplus was characterized with the aim to establish a reference multi-acaricide resistant tick strain. Using a standardized adult immersion test, the Lethal Concentration(LC)50 values for deltamethrin, cypermethrin, fenvalerate and diazinon against the laboratory selected resistant tick (LSRT) strain were determined as 306.7 ppm, 2776.9 ppm, 30262.1 ppm and 9458.7 ppm. Relative to the susceptible IVRI-I tick strain, the LSRT strain showed 4.78- and 5.84-fold increases in activity of esterases, a 6-fold increase for monooxygenases and a 2.24 fold increase for glutathione S-transferase. In the acetylcholinesterase 2 gene, 22 single nucleotide polymorphisms (SNPs) were identified in the LSRT strain. Four of these SNPs lead to amino acid substitutions and were consistently found in resistant field populations in India. A C190A mutation in the domain II S4-5 linker region of sodium channel gene resulting in a L64I amino acid substitution was recorded in the LSRT strain. Monitorable indicators for the maintenance of the strain, designated as the reference IVRI-V tick strain and representing the first established multi-acaricide resistant tick strain in India, were identified.

High-frequency (10-100 MHz) ultrasound instrumented forceps for precision cancer surgery

A critical issue for surgery of soft tissue cancers is ensuring removal of all malignant tissue while conserving as much unaffected tissue as possible. A minimally invasive, in vivo technique for detecting residual cancer in surgical margins or metastatic cancer in lymph nodes would significantly improve the precision and efficacy of cancer surgery. The objective of this project was to develop ultrasound instrumented “smart” forceps to guide surgeons during operations, to provide instant diagnostic information, and to enable more precise and complete resection of malignant tissue. The device was based on Martin forceps, modified to include two ultrasonic sensors (polyvinylidene difluoride) at the tips of the forceps, a tissue thickness sensor (rotary potentiometer), sensor wires, and a spring to control the manual stiffness of the forceps. A high-frequency pulser-receiver was used to excite the transmitting sensor at 50 MHz and amplify through-transmission signals from the receiving sensor. The forceps were tested with agarose phantoms embedded with polyethylene microspheres of different diameters (58-550 μm) to vary attenuation. Testing included standard 50-MHz immersion transducers for comparison. The results showed that the forceps’ performance was equal to standard transducers, with comparable sensitivity for attenuation and superior accuracy for wave speed.

Aberration-corrected cryoimmersion light microscopy

Cryogenic fluorescent light microscopy of flash-frozen cells stands out by artifact-free fixation and very little photobleaching of the fluorophores used. To attain the highest level of resolution, aberration-free immersion objectives with accurately matched immersion media are required, but both do not exist for imaging below the glass-transition temperature of water. Here, we resolve this challenge by combining a cryoimmersion medium, HFE-7200, which matches the refractive index of room-temperature water, with a technological concept in which the body of the objective and the front lens are not in thermal equilibrium. We implemented this concept by replacing the metallic front-lens mount of a standard bioimaging water immersion objective with an insulating ceramic mount heated around its perimeter. In this way, the objective metal housing can be maintained at room temperature, while creating a thermally shielded cold microenvironment around the sample and front lens. To demonstrate the range of potential applications, we show that our method can provide superior contrast in Escherichia coli and yeast cells expressing fluorescent proteins and resolve submicrometer structures in multicolor immunolabeled human bone osteosarcoma epithelial (U2OS) cells at [Formula: see text]C.

Relationship between electrochemical processes and environment-assisted crack growth under static and dynamic atmospheric conditions

AbstractEnvironment-assisted cracking (EAC) of aluminum alloys in corrosive atmospheres is a significant maintenance and safety issue. EAC is influenced by the interaction of stress, environment, and microstructure. Atmospheric conditions and corrosion kinetics are dynamic due to diurnal cycles and changing operating conditions. Temperature, relative humidity, and surface contaminants interact to control thin-film electrolyte properties. Within a crack, the separation of the anode and cathode may occur due to concentration gradients between the crack tip, mouth, and external surface. Conventional immersion testing is not well suited to study factors and interactions leading to atmospheric EAC because the bulk electrolyte conditions for immersion testing are different from the thin-film properties. Additionally, standard three-electrode immersion measurements are not well suited to directly investigate the variation and distribution of cathodic and anodic currents on a sample surface and within an EAC crack. In this work, atmospheric electrochemical tests have been conducted using a segmented, multielectrode sensor with an artificial crevice to quantify local, dynamic anodic and cathodic current distributions. These tests are compared to EAC growth rate measurements. Maximum EAC growth rates are observed when high cathodic current is measured at the tip of artificial crevices, suggesting a hydrogen embrittlement mechanism.

Ab initio calculations of the electronic structure and specific optical features of β-LiNH4SO4 single crystals

In the present work complex experimental and theoretical studies of electronic and optical properties for β-lithium-ammonium sulfate crystals of good optical quality are performed using the X-ray photoelectron spectroscopy (XPS) and X-ray emission spectroscopy (XES). Standard immersion and spectroscopic techniques accompanied by the theoretical quantum-chemical calculations in the density functional theory (DFT) framework were applied. Calculations of band structure and related properties were carried out within a framework of local density and generalized gradient approximations as well as hybrid B3LYP functionals. The energy levels features and their origin are established from the DFT calculations and they were ferified by XPS and XES measurements. Theoretical and experimental refractive indices dispersions along the principal crystallographic directions (nx, ny and nz) as well as birefringence dispersion (Δnx, Δny and Δnz) in the visible spectral range are obtained. It was found a closeness of nx and ny curves for the titled crystals. More precise birefringence examining predicts their intersection at λ ≈ 190 nm.

Comparative characterization of decellularized renal scaffolds for tissue engineering

Native extracellular matrix (ECM) provides scaffolds for tissue engineering with natural architecture and biochemical composition. Maintaining the native ECM in decellularized tissues provides cues for cells, which promote their tissue specific arrangement and function. Several approaches have been used to decellularize ECM from the kidney in order to reestablish renal tissue but their comparability is hampered because methods for decellularization and assessment of ECM vary widely. Therefore, we applied a standardized immersion protocol to decellularize porcine kidney tissue with three detergents Triton X-100, SDS and sodium deoxycholate (SDC) at variable temperatures. For comparative analysis decellularization efficacies, structural preservation, composition and cell attachment and viability were analyzed. Structural ECM-conservation is strongly dependent on decellularization temperature, while preservation of glycosaminoglycans (GAG), collagens and cytokines was affected by the detergents used. GAG and collagens were best maintained by 1% SDS at 4 °C, whereas cytokines were best maintained in 1% SDC at 4 °C. Viability and attachment of human induced pluripotent stem cell derived renal precursor cells were best in SDC-ECM and thus not associated with the degree of GAG and collagen maintenance but the cytokine preservation. Based on structural and functional characteristics, we developed a scoring system that allows intra- and inter-study comparison of decellularization strategies. Application of the scoring system to our experimental data showed that decellularization with 1% SDS at 4 °C provided the highest structural and composition scores, while 1% SDC at 4 °C had lower structural and composition but a significantly better cell performance score. Inclusion of multiple published studies in the scoring matrix for comparison identified the highest structural and composition scores when decellularization was performed with SDS at low concentration, for a short period of time and at low temperature. Furthermore, the scoring system indicated that cell attachment and viability cannot be concluded from any other parameter and should therefore always be included in evaluation of decellularization strategies.

Investigation of the effects of palm biodiesel dissolved oxygen and conductivity on metal corrosion and elastomer degradation under novel immersion method

The aim of this work was to investigate the compatibility of fuel delivery materials with palm biodiesel fuel under novel immersion method which simulated diesel engine operation. For this, a two-stage investigation was conducted. In the first stage, the effects of biodiesel dissolved oxygen concentration and conductivity value on fuel delivery materials degradation under standard immersion were determined as a baseline study. In the second stage, modified immersion investigations which simulated the deterioration of biodiesel under common rail diesel engine operation (CRDE) were carried out to ascertain the compatibility present between fuel delivery materials and palm biodiesel. Palm biodiesel dissolved oxygen and conductivity were found to adversely affect both copper corrosion and nitrile rubber (NBR) degradation. The copper corrosion rate and NBR volume change increased by 9% and 13%, respectively due to 22.5% increase in the conductivity. In contrast, the copper corrosion rate and NBR volume swelling reduced by 91% and 27%, respectively due to 96% reduction in the dissolved oxygen concentration. Copper corrosion and NBR degradation were found to be lowered by up to 93% and 85%, respectively under modified immersion as compared to standard immersion. This study has inferred that good compatibility is present between fuel delivery materials and biodiesel under CRDE operation.

A systematic comparison of biodegradation behavior of absorbable metal: in standardized immersion, arterial bioreactor and in vivo study

Event Abstract Back to Event A systematic comparison of biodegradation behavior of absorbable metal: in standardized immersion, arterial bioreactor and in vivo study Juan Wang1, 2*, Lumei Liu2*, Yeoheung Yun2* and Nan Huang1* 1 Southwest Jiaotong University, Dept. of Materials Science and Engineering, China 2 North Carolina Agricultural & Technical State University, NSF Engineering Research Center for Revolutionizing Metallic Biomaterials, United States Introduction: Absorbable metals have been widely tested in various in vitro environments to evaluate their biodegradation as vascular stent materials[1]. However, there exists a gap between in vivo and in vitro test results. A key step is to identify the relevant biochemical and biophysical microenvironments in test-systems. The purpose of this study was to establish an appropriate methodology for accurate and standardized determinations of degradation parameters in the pre- and post- endothelialization stage after stent implantation, which plays a vital part in predicting the fate of magnesium (Mg)-based stent. Materials and Methods: As-drawn Mg wires of 99.9% purity with a length of 10 mm and a diameter of 250 μm (Goodfellow, USA) were used. In the standardized immersion test, Mg wires were immersed in DMEM solution according to the standard protocol ASTM-D1141-98[2]. The LumeGen bioreactor (TGT DynaGen® Series, USA) as a vascular bioreactor was chosen to stimulate physiological aortal conditions (Fig. 1a). Each porcine abdominal aorta with a diameter of ~8 mm and a length of 5 cm was mounted into a chamber with a flow rate of 100 ml/min and a pulse pressure of 80-120 mmHg (Fig. 1b). In aortal in vivo test, rat abdominal aortas were used for implantation. Two Mg segments were symmetrically implanted into the lumen and wall of each aorta in the bioreactor or in vivo tests (Fig. 1c). Samples were analysed by X-ray computed tomography (CT). Fig. 1.(a) Photograph of bioreactor. Mg wires in the wall and lumen of a porcine aorta in the chamber (b) and rat aorta in vivo (c). Results and Discussion: One of two Mg wires exposed on the lumen and contacted the circulating medium to simulate a pre-endothelialization stage. The other Mg wire was embedded under the intima to simulate a post-endothelialization stage. The degradation product volumes, residual Mg volumes and average degradation rates were calculated utilizing the CT data. In Fig. 2, in vivo degradation was slower than in vitro degradation both in the standardized static and flow bioreactor conditions. In terms of the aortal bioreactor, flow convection on the lumen surface severely accelerated Mg degradation due to the increase of mass transfer, fluid shear stress and pulsatile stress, compared with low Mg degradation rate in the wall. In the aortal in vivo model, the degradation rate of Mg wire in the wall was faster than that in the lumen, and calcification was observed around Mg surrounding tissue. The degradation of Mg wire in the wall (diffusion limited region) was accelerated, which may result in the decrease of local pH from lysosome. Fig. 2. Volume ratios of residual Mg and corrosion products in the static no aorta, and the aortal lumen and wall of the bioreactor and in vivo conditions for 3-day. Conclusions: First-time investigation of degradation testing in the aortal bioreactor revealed that hydrodynamics plays a dominant role on the degradation. The established porcine aortal bioreactor and rat aortal in vivo model are expected to provide a better understanding of degradation mechanism of absorbable metallic stents. NIH grant (1SC3GM113728-01); NSF-ERC for revolutionizing metallic biomaterials (NSF-0812348); National Natural Science Foundation of China under Grant (81330031); Thanks Prof. Deling Kong, Dr. Zhihong Wang and Ms. Yifan Wu from Nankai University for in vivo test.

The use of multiple pseudo-physiological solutions to simulate degradation behavior of pure Fe: towards a standard static immersion test

The use of multiple pseudo-physiological solutions to simulate degradation behavior of pure Fe: towards a standard static immersion test

The use of multiple pseudo-physiological solutions to simulate the degradation behavior of pure iron as a metallic resorbable implant: a surface-characterization study.

Understanding the interactions of a pure iron surface with biological elements, such as ions and proteins in an aqueous medium, is essential for an accurate in vitro assessment of corrosion patterns. In fact, the synergy of chlorides, carbonates, phosphates and complex organic molecules present in the body environment is a key factor affecting both in vivo and in vitro degradation of materials, especially iron and its alloys. The aim of this work was the assessment of degradation patterns of pure iron in 5 commercial pseudo-physiological solutions by a thorough study of degraded surface chemistry and morphology. It also provides a methodological basis to understand the short-term degradation mechanism of degradable iron depending on the surrounding physiological media. The standard static immersion corrosion test was modified to adapt the procedure to pseudo-physiological solutions. After a 14-day static immersion test, the surfaces of samples were investigated by scanning electron microscopy, stylus profilometry and atomic force microscopy techniques. The chemistry and phase composition of the degraded layers were evaluated, respectively, by X-ray photoelectron spectrometry and X-ray diffractometry. The morphology and composition of the degradation layers were found to be different for the test-solutions: for phosphate-rich solutions, the formation of an adherent passive layer was found; degradation mechanisms related to general corrosion were predominant for all the other solutions. In conclusion, the chemical composition of the used medium plays a fundamental role in the degradation pattern of pure iron, so that direct comparisons of solutions with different ion concentrations, as reported in the literature, need to be carefully assessed.

4H-SiC P<sup>+</sup>N UV Photodiodes for Space Applications

Spectral sensitivity measurements versus temperature have been carried out on irradiated SiC p+n photodiodes, fabricated using two different doping processes: Aluminium standard implantation and Boron plasma immersion ion implantation. The spectral sensitivity of Al doped photodiodes increase for incident wavelength higher than 270 nm, and are very stable below. Boron doped irradiated photodiodes show a general increase of the photoresponse for all wavelengths. In both cases, an hysteresis effect is observable when with the temperature. Results are presented and discussed.