Accelerated Degradation Process Research Articles

Injectable, Biomolecule-Responsive Polypeptide Hydrogels for Cell Encapsulation and Facile Cell Recovery through Triggered Degradation.

Injectable hydrogels have been widely investigated in biomedical applications, and increasing demand has been proposed to achieve dynamic regulation of physiological properties of hydrogels. Herein, a new type of injectable and biomolecule-responsive hydrogel based on poly(l-glutamic acid) (PLG) grafted with disulfide bond-modified phloretic acid (denoted as PLG-g-CPA) was developed. The hydrogels formed in situ via enzymatic cross-linking under physiological conditions in the presence of horseradish peroxidase and hydrogen peroxide. The physiochemical properties of the hydrogels, including gelation time and the rheological property, were measured. Particularly, the triggered degradation of the hydrogel in response to a reductive biomolecule, glutathione (GSH), was investigated in detail. The mechanical strength and inner porous structure of the hydrogel were influenced by the addition of GSH. The polypeptide hydrogel was used as a three-dimensional (3D) platform for cell encapsulation, which could release the cells through triggered disruption of the hydrogel in response to the addition of GSH. The cells released from the hydrogel were found to maintain high viability. Moreover, after subcutaneous injection into rats, the PLG-g-CPA hydrogels with disulfide-containing cross-links exhibited a markedly faster degradation behavior in vivo compared to that of the PLG hydrogels without disulfide cross-links, implying an interesting accelerated degradation process of the disulfide-containing polypeptide hydrogels in the physiological environment in vivo. Overall, the injectable and biomolecule-responsive polypeptide hydrogels may serve as a potential platform for 3D cell culture and easy cell collection.

The influence of bioactive additives on polylactide accelerated degradation

Abstract The aim of the research was to study the influence of the bioactive modifiers such as 7 wt.% of micrometric tricalcium phosphate (TCP) and 0.3 wt.% of nanometric hydroxyapatite (HAP) on the accelerated degradation process of composite resorbable implants based on poly(L-lactide) (PLA) matrix. The degradation was assessed on the basis of microstructural, structural and mechanical alterations. The measure of the PLA degradation progress was the gradual decrease in its molecular weight and mechanical strength. As the degradation proceeded, the plastic properties of materials decreased. In the case of composites such changes took place faster, which implies the accelerating influence of modifiers on the degradation process. Moreover, modifiers act as crystallization seeds, accelerating and stimulating the matrix organization and appearance of crystalline areas. The properties of the two composites differ. Adding TCP alone influenced the structural changes in the polymer more significantly than the addition of TCP/HAP, thus affecting the faster degradation.

Stochastic Modeling and Analysis of Multiple Nonlinear Accelerated Degradation Processes through Information Fusion.

Accelerated degradation testing (ADT) is an efficient technique for evaluating the lifetime of a highly reliable product whose underlying failure process may be traced by the degradation of the product’s performance parameters with time. However, most research on ADT mainly focuses on a single performance parameter. In reality, the performance of a modern product is usually characterized by multiple parameters, and the degradation paths are usually nonlinear. To address such problems, this paper develops a new s-dependent nonlinear ADT model for products with multiple performance parameters using a general Wiener process and copulas. The general Wiener process models the nonlinear ADT data, and the dependency among different degradation measures is analyzed using the copula method. An engineering case study on a tuner’s ADT data is conducted to demonstrate the effectiveness of the proposed method. The results illustrate that the proposed method is quite effective in estimating the lifetime of a product with s-dependent performance parameters.

Wood plastic composites weathering: Effects of compatibilization on biodegradation in soil and fungal decay

Material performance testing of wood plastic composites (WPC) requires an efficient evaluation of the resistance against biodegradation. This study investigates the effects of natural weathering on WPC and subsequent material degradation in soil and by fungi. Besides, the effectiveness of using coupling agent (CA) on adhesion of WPC and its influence in degradation was investigated. The WPC composition used was recycled polypropylene - ethylene vinyl acetate/wood flour (70/30 w/w). Four white rot fungi, Trametes villosa, Trametes versicolor, Pycnoporus sanguineus and Fuscoporia ferrea were used in a fungal decay test. For the biodegradation in simulated soil was used respirometric test. Weight loss of all materials, without and with previous natural weathering, was evaluated and surface morphology was examined by scanning electron microscopy (SEM). The results showed that natural weathering accelerated degradation process, influencing the respirometric test and fungal growth. By SEM, it was observed agglomerates of microorganisms, indicating the possible formation of biofilms. The F. ferrea fungus was more effective in surface colonization, with higher weight loss and even the emergence of reproductive structures after the incubation time.

Accelerated Degradation Process Analysis Based on the Nonlinear Wiener Process with Covariates and Random Effects

It is assumed that the drift parameter is dependent on the acceleration variables and the diffusion coefficient remains the same across the whole accelerated degradation test (ADT) in most of the literature based on Wiener process. However, the diffusion coefficient variation would also become obvious in some applications with the stress increasing. Aiming at the phenomenon, the paper concludes that both the drift parameter and the diffusion parameter depend on stress variables based on the invariance principle of failure mechanism and Nelson assumption. Accordingly, constant stress accelerated degradation process (CSADP) and step stress accelerated degradation process (SSADP) with random effects are modeled. The unknown parameters in the established model are estimated based on the property of degradation and degradation increment, separately for CASDT and SSADT, by the maximum likelihood estimation approach with measurement error. In addition, the simulation steps of accelerated degradation data are provided and simulated step stress accelerated degradation data is designed to validate the proposed model compared to other models. Finally, a case study of CSADT is conducted to demonstrate the benefits of our model in the practical engineering.

Potential application of oil-suspended particulate matter aggregates (OSA) on the remediation of reflective beaches impacted by petroleum: a mesocosm simulation.

This paper presents the oil-suspended particulate matter aggregate (OSA) resulted from the interaction of droplets of dispersed oil in a water column and particulate matter. This structure reduces the adhesion of oil on solid surfaces, promotes dispersion, and may accelerate degradation processes. The effects of the addition of fine sediments (clay + silt) on the formation of OSA, their impact on the dispersion and degradation of the oil, and their potential use in recovering reflective sandy beaches were evaluated in a mesoscale simulation model. Two simulations were performed (21days), in the absence and presence of fine sediments, with four units in each simulation using oil from the Recôncavo Basin. The results showed that the use of fine sediment increased the dispersion of the oil in the water column up to four times in relation to the sandy sediment. There was no evidence of the transport of hydrocarbons in bottom sediments associated with fine sediments that would have accelerated the dispersion and degradation rates of the oil. Most of the OSA that formed in this process remained in the water column, where the degradation processes were more effective. Over the 21days of simulation, we observed a 40% reduction on average of the levels of saturated hydrocarbons staining the surface oil.

Stress conditions in HVDC equipment and routes to in service failure

High voltage equipment designed for DC applications is stressed differently from ac equipment. Most notably, the load conditions of the equipment play a major role in determining the electric field distribution in insulation under dc, due to the temperature dependence of conductivity. Additionally, polarization and space charge phenomena impose a time dependent behavior on the stress distribution. This has major consequences for the way in which degradation of the insulation under dc stress takes place. The nature of the stresses under dc may lead to accelerated degradation processes which could result in early breakdown of the insulation. This paper provides an overview of the stress conditions specific for dc application and highlights via which routes they may lead to failure. The stress distributions in converter transformers and dc cable systems will serve as typical examples.

The impact of inorganic compounds used for protection of wood on cellulose

Abstract Inorganic compounds were often used to protect wood from wood-decaying fungi and insects (e.g. compounds of arsenic, copper, chromium, zinc or boron) or as a retarder of combustion (e.g. ammonium salts, boron compounds). However, their use may accelerate degradation processes, which may show up as worsening of mechanical properties. The study deals with the impact of selected inorganic compounds (sodium chloride, copper sulphate pentahydrate, boric acid and ammonium sulphate) on cellulose. The samples of cellulose impregnated with the said compounds were subject to artificial aging. The cellulose was monitored for weight changes, changes in colour, values of aqueous extract pH, an average polymerization grade, mechanical properties, elementary composition and the content of bound inorganic compounds. The study was meant to identify stability of the used inorganic compounds in the conditions of artificial aging. The results imply that copper sulphate pentahydrate and ammonium sulphate accelerated degradation of cellulose the most. The effect of boric acid lead to larger deterioration of specimens namely in the conditions of dry aging. Sodium chloride had a negligible impact on the course of degradation. Used compounds continue to be at least partly retained in the cellulose specimens even after rinsing.

PEMFC Contamination - Fundamentals and Outlook

PEMFC Contamination - Fundamentals and Outlook

Accelerated Degradation Tests Modeling Based on the Nonlinear Wiener Process with Random Effects

Accelerated degradation tests (ADT) modeling is an important issue in lifetime assessment to the products with high reliability and long lifetime. Among the literature about the accelerated nonlinear degradation process modeling, the current methods did not consider the product-to-product variation of the products with the same type. Therefore, this paper proposes an accelerated degradation process modeling method with random effects for the nonlinear Wiener process. Firstly, we derive the lifetime distribution of the nonlinear Wiener process with random effects. Secondly, the nonlinear Wiener process is used to model the degradation process of a single stress, and the drift coefficient is considered as a random variable to describe the product-to-product variation. Using the random acceleration model, the random effects are incorporated into the constant stress ADT models and the step stress ADT models. Then, a two-step maximum likelihood estimation (MLE) method is presented to estimate the unknown parameters in the degradation models. Finally, a simulation study and a case study are provided to demonstrate the application and superiority of the proposed model.

Step Stress Accelerated Degradation Process Modeling and Remaining Useful Life Estimation

Accelerated degradation process modeling and remaining useful life(RUL) estimation based on Accelerated degradation testing(ADT) are the essential parts of condition based maintenance and health management.Among the literature about the accelerated degradation process modeling,the current methods didn't consider the unit-to-unit variation of the equipment with the same type.Therefore,we present an accelerated degradation process modeling and RUL estimation method based on Wiener process.The Wiener process is used to model the degradation process of a single stress,and the drift coefficient is considered as a random variable to describe the unit-to-unit variation of different equipment.Based on the presented model,the information of reliability and RUL can be obtained.The parameter of the traditional acceleration model is considered as a random variable to describe the unit-to-unit variation of different equipment,and the traditional method turns out to be its special case.Through the step stress ADT data,a two-step maximum likelihood estimation method is presented to estimate the unknown parameters of the presented model.The results of the simulation about the laser degradation show that the presented method performs better than the traditional method and thus can be potentially applied in practice.

Durability of Biodegradable Internal Fixation Plates

In this work prototypes of internal fixation plates of acetabular fractures were developed and manufactured. The injection moulding was used to produce polymeric and composite samples. The plates and paddle-like beam samples made of polylactide and the polymer composite modified with 7 wt. % of tricalcium phosphate were produced. The samples were incubated in physiological fluids for 8 months. During the in vitro tests their durability and mechanical properties were determined. In comparison to the pure polylactide the addition of TCP accelerated degradation process. The degradation of the composite started after about 100 days of incubation, whereas the initial polymer began to degrade about 50 days later. The obtained biodegradable plates revealed sufficient mechanical properties for internal fixation of acetabular fractures for bone joining.

Near-surface geophysical investigations inside the cloister of the historical palace ‘Palazzo dei Celestini’ in Lecce, Italy

Non-invasive geophysical investigations are usually the only way to gain information on subsurface properties that can affect the stability of historical structures and accelerate degradation processes. A combined multi-frequency ground-penetrating radar (GPR) geoelectrical and induced polarization (IP) survey was performed in the cloister of 'Palazzo dei Celestini', Lecce, southern Italy, in order to investigate possible subsurface causes of deterioration. The historical palace was originally a convent connected to the Basilica of 'Santa Croce' and is now the head office of the Province of Lecce Administration and the Prefecture. Built in Pietra Leccese, a fine-grained calcarenite, Santa Croce and Palazzo dei Celestini is the most famous baroque architectural complex of the historical centre of Lecce. The high capillarity of the building material causes deterioration problems especially at some altars of the church and in the lower portion of the walls and pillars of the monumental building. The integrated geophysical survey yielded a detailed description of the shallow stratigraphical and hydro-geological setting of the area and an accurate location of ancient and modern drainage systems. The geophysical information was essential for identifying natural or anthropogenic causes of the local increase in subsoil moisture that could accelerate the degradation process and for developing effective remediation activities.

Soluciones integrales a la problemática de conservación de los acabados arquitectónicos de Mayapán, Yucatán

Mayapán boasts various sculptural and pictorial elements that hold great aesthetic and informative value. Nevertheless, these quite important samples from the Post-classic period, suffer from an accelerated degradation process, mainly due to the constant use of inappropriate refurbishment / restoration materials, specifically synthetic polymers and cement in great quantities.In 2006 a new intervention phase was initiated in Mayapán focused on understanding the complex set of problems that the architectural finishes face while exposed, and on diminishing the greatest damages. New technologies for mural painting conservation have been proposed and experimented as well, with the sole purpose of removing the layers of polymers covering the surface. However, this solution may only be consistent on specific cases; hence, in order to achieve the stone stabilization, a whole and constant maintenance program is required.

Interaction among N-fixing bacteria and AM fungi in Amazonian legume tree ( Schizolobium amazonicum) in field conditions

The Amazon forest has suffered an accelerated degradation process due to cutting to implant agricultural systems, pasture and electricity generation projects and disorganized mining and wood exploitations. The challenge is to develop new technologies for wood production in agroforestry systems. Schizolobium amazonicum is a legume tree, with fast growth and its wood is employed to make furniture. More and more areas have been sowed with S. amazonicum, but this production system is very poor technologically. In the present paper we proposed to evaluate the effect on the plant growth and plant survival of three arbuscular mycorrhizal fungi ( Glomus clarum, Glomus intraradices and Glomus etunicatum) associated with three N-fixing bacteria strains (two Rhizobium sp. and one Burkholderia sp.). Two methods of planting were used: direct sowing or transplantation of seedlings after initial growth in nursery. G. intrarradices was more effective in plant growth when inoculated in seed, and the bacteria strains had no effect when inoculated alone or with AM fungi. However, in seedlings the dual inoculation was more effective. At 210 days Rhi1 and Rhi2 associated with G. clarum or G. etunicatum increase plant growth. At 390 days G. clarum associated with LEM6 or Rhi1 increased most of the parameters evaluated, including biomass and wood production. Direct sowing is the traditional method largely used in the non-tillage areas and was more ineffective. The presence of microorganisms showed significant differences when compared with non-inoculated plant. The results suggested that some microbial combinations were effective in stimulating plant growth, but further experiments need to be carried out to evaluate which N-fixing bacteria and AM fungi is more effective for each planting systems for S. amazonicum.

Grazing and drought reduce cyanobacterial soil crusts in an Australian Acacia woodland

Cyanobacteria-dominant soil crusts are important components of unvegetated interspaces in Australia's semi-arid rangelands. We studied the changes in crust cover and floristics at increasing distances up to 500m from three stock watering points in western Queensland's Mulga bioregion between 2002 and 2005. Sampling times corresponded with pre-drought (2002), drought (2003), early post-drought (2004) and late post-drought (2005) periods. Cyanobacterial cover increased markedly with increasing distance from water, with the largest changes occurring within 200m of water. The change in cover with distance from water was most pronounced before the drought compared with during or after drought. Crust composition also changed in relation to distance from water, and the abundance of three cyanobacteria (Scytonema sp., Stigonema ocellatum, Porphyrosiphon notarissi) was greater away from water. The diversity of crust species increased significantly with distance from water, and was greatest in the late post-drought period. Although cyanobacterial crusts were present close to water (<100m) before the drought, cover close to water had not recovered to pre-drought levels 2 years after drought. Our results indicate that excessive damage by stock trampling has an immediate impact on crusts and reduces their capacity to recover after drought. Changes in the severity or intensity of drought may therefore accelerate degradation processes and compromise the ability of crusts to recover after grazing.

Heterotrophic bacteria abundances in Rodrigo de Freitas Lagoon (Rio de Janeiro, Brazil)

The Rodrigo de Freitas Lagoon (RJ, Brazil) is an important coastal ecosystem that has been submitted to an accelerated degradation process. The aim of this work was to determine the abundance and the spatial distribution of total heterotrophic (by flow cytometry) and cultivated bacteria ("pour plate" method on R2A agar). Another objective was to evaluate the lagoon's influence on water quality of Ipanema and Leblon beaches. Physical and chemical data were acquired too. Sub-superficial water samples were taken monthly, from December 1999 to October 2000. On lagoon, the cultivated bacteria abundance varied from 6.9x10(5) to 5.0x10(7) CFU.100 mL-1. On Ipanema and Leblon beaches, this parameter yielded 1.4x10(5) and 2.8x10(6) CFU.100 mL-1, respectively. Total bacterial abundance varied from 2.9x10(7) to 3.2x10(7) cells.mL-1 on lagoon. On Ipanema and Leblon, this parameter yielded 8.7x10(6) and 1.1x10(7) cells.mL-1, respectively. Two sub-groups were determined with dominance of HNA cells. Samples were added latter to better understand the bacteria present on these environments. Bacterial abundance were analyzed only by flow cytometry and the results varied from 8.3x10(6) to 2.5x10(7) cells.mL-1 on lagoon. On the beach, this parameter yielded 6.9x10(6) cells. mL-1. Two bacterial sub-groups were also observed, with dominance of HNA on lagoon and LNA on the beach. The results showed that the Rodrigo de Freitas Lagoon is an eutrophic ecosystem where the bacterial populations and the physical and chemical parameters do not differ spatially. The data also confirmed that the outflow of the lagoon's polluted waters affect the sanitary conditions of Ipanema and Leblon beaches.

Modeling Corrosion Processes for Alloy 22 Waste Packages

ABSTRACTThe proposed waste package design for the disposal of high-level radioactive waste at the potential repository at Yucca Mountain, Nevada, consists of an outer container made of Alloy 22, a corrosion resistant Ni-Cr-Mo-W alloy, surrounding an inner container made of Type 316 nuclear grade stainless steel. Models to assess the influence of waste package degradation modes on the overall system performanceconsider uniform and localized corrosion processes. Based on measurements of passive anodic current density, the uniform aqueous corrosion rate of Alloy 22 is estimated to be slow, and long waste package lifetimes are projected in the absence of conditions that promote accelerated degradation processes. The initiation of localized corrosion is possible in chloride-containing waters with low concentrations of inhibiting oxyanions such as nitrate. Although propagation rates for localized corrosion are typically orders of magnitude greater than the passive uniform corrosion rates, the maximum penetration depth of localized attack may be limited to depths significantly less than the container thickness as a result of stifling andarrest of localized corrosion.

The in vitro hydrolysis of poly(ester urethane)s consisting of poly[( R)-3-hydroxybutyrate] and poly(ethylene glycol)

This paper reports the study of the complete degradation process for a series of newly synthesized multi-block poly(ester urethane)s consisting of poly[( R)-3-hydroxybutyrate] (PHB) as hard and hydrophobic block and poly(ethylene glycol) (PEG) as soft and hydrophilic segment. The initial stages of degradation of the poly(PHB/PEG urethane)s were monitored by carrying out the degradation experiments at pH 7.4 and 37 °C. The weight loss of the copolymer films was traced, and the degraded copolymer films were characterized by GPC, 1H NMR, TGA, and SEM. The induction phase of the polymer degradation was characterized by a random chain scission of the ester backbone bonds of the PHB segments and an insignificant decline in the weight of the polymer films. An accelerated degradation process was carried out at pH 11.5 and 37 °C to investigate the long-term degradation behaviour. The characterization of the degraded polymer films was similar to that for the experiment at pH 7.4. In addition, the water-soluble degradation products were characterized by GPC, 1H NMR, and FTIR. The main components of the water-soluble degradation products were found to be PEG blocks (monomeric up to quadmeric), 3-hydroxybutyric acid, and crotonic acid. It was found that the copolymer incorporating the highest amount of PEG degraded at the highest rate of all the copolymers studied. The complete degradation of the poly(PHB/PEG urethane)s was monitored using a combination of the physiological and accelerated hydrolytic degradation.

The Inhibition of Early N-Glycan Processing Targets TRP-2 to Degradation in B16 Melanoma Cells

Tyrosinase-related protein-2 (TRP-2) is a DOPAchrome tautomerase catalyzing a distal step in the melanin synthesis pathway. Similar to the other two melanogenic enzymes belonging to the TRP gene family, tyrosinase and TRP-1, TRP-2 is expressed in melanocytes and melanoma cells. Despite the increasing evidence of its efficiency as a melanoma antigen, little is known about the maturation and intracellular trafficking of TRP-2. Here we show that TRP-2 is mainly distributed in the TGN of melanoma cells instead of being confined solely to melanosomes. This, together with the plasma membrane occasional localization observed by immunofluorescence, suggest the TRP-2 participation in a recycling pathway, which could include or not the melanosomes. Using pulse-chase experiments we show that the TRP-2 polypeptide folds in the endoplasmic reticulum (ER) in the presence of calnexin, until it reaches a dithiothreitol-resistant conformation enabling its ER exit to the Golgi. If N-glycosylation inhibitors prevent the association with calnexin, the TRP-2 nascent chain undergoes an accelerated degradation process. This process is delayed in the presence of proteasomal inhibitors, indicating that the misfolded chain is retro-translocated from the ER into the cytosol and degraded in proteasomes. This is a rare example in which calnexin although indispensable for the nascent chain folding is not required for its targeting to degradation. Therefore TRP-2 may prove to be a good model to document the calnexin-independent retro-translocation process of proteasomally degraded proteins. Clearly, TRP-2 has a distinct maturation pathway from tyrosinase and TRP-1 and possibly a second regulatory function within the cell.