A review on degradation mechanisms of polylactic acid: Hydrolytic,photodegradative, microbial,and enzymatic degradation

Recently, thoughtful disagreements between scientists concerning environmental issues including the use of renewable materials have enhanced universal awareness of the use of biodegradable materials. Polylactic acid (PLA) is one of the most promising biodegradable materials for commercially replacing nondegradable materials such as polyethylene terephthalate and polystyrene. The main advantages of PLA production over the conventional plastic materials is PLA can be produced from renewable resources such as corn or other carbohydrate sources. Besides, PLA provides adequate energy saving by consuming CO₂ during production. Thus, we aim to highlight recent research involving the investigation of properties of PLA, its applications and the four types of potential PLA degradation mechanisms. In the first part of the article, a brief discussion of the problems surrounding use of conventional plastic is provided and examples of biodegradable polymers currently used are provided. Next, properties of PLA, and (Poly[L-lactide]), (Poly[D-lactide]) (PDLA) and (Poly[DL-lactide]) and application of PLA in various industries such as in packaging, transportation, agriculture and the biomedical, textile and electronic industry are described. Behaviors of PLA subjected to hydrolytic, photodegradative, microbial and enzymatic degradation mechanisms are discussed in detail in the latter portion of the article.     

A two-parameter parsimonious bathtub model for the analysis of system failure times with illustrations to reliability data

In this study, a two-parameter, upper-bounded probability distribution called the tau distribution is introduced and its applications in reliability engineering are presented. Each of the parameters of the tau distribution has a clear semantic meaning. Namely, one of them determines the upper bound of the distribution, while the value of the other parameter influences the shape of the cumulative distribution function. A remarkable property of this new probability distribution is that its probability density function, survival function, hazard rate function (HRF), and quantile function can all be expressed in terms of its cumulative distribution function. The HRF of the proposed probability distribution can exhibit an increasing trend and various bathtub shapes with or without a low and long-flat phase (useful time phase), which makes this new distribution suitable for modeling a wide range of real-world problems. The constraint maximum likelihood estimation, percentile estimation, approximate Bayesian computation, and approximate quantile estimation computation are proposed to calculate the unknown parameters of the model. The suitability of the estimation methods is verified with the aid of simulation and real-world data results. The modeling capability of the tau distribution was compared with that of some well-known two- and three-parameter probability distributions using two data sets known from the literature of reliability engineering: time between failures data of a machining center, and time to failure of data acquisition system cards. Based on empirical results, the new distribution may be viewed as a viable competitor to the Weibull, Gamma, Chen, and modified Weibull distributions.     

Longitudinal modelling and control of a flapping-wing micro aerial vehicle

A simulation model, flight-dynamics oriented, of a flapping-wing micro aerial vehicle (MAV) is presented here. The model, based on animal flapping flight, integrates the aerodynamic forces computed along each wing to determine the global motion of the MAV with respect to an inertial reference frame. After some analytic simplifications, and taking into account the periodic nature of the system inputs, an averaged model is derived, and a simple, nonlinear closed-loop control law is designed for the dynamics along the vertical and pitch axis, allowing an efficient stabilization of the naturally unstable model.     

Effects of brown rice and white rice on expression of xenobiotic metabolism genes in type 2 diabetic rats

Xenobiotics constantly influence biological systems through several means of interaction. These interactions are disturbed in type 2 diabetes, with implications for disease outcome. We aimed to study the implications of such disturbances on type 2 diabetes and rice consumption, the results of which could affect management of the disease in developing countries. In a type 2 diabetic rat model induced through a combination of high fat diet and low dose streptozotocin injection, up-regulation of xenobiotic metabolism genes in the diabetic untreated group was observed. Xenobiotic metabolism genes were upregulated more in the white rice (WR) group than the diabetic untreated group while the brown rice (BR) group showed significantly lower expression values, though not as effective as metformin, which gave values closer to the normal non-diabetic group. The fold changes in expression in the WR group compared to the BR group for Cyp2D4, Cyp3A1, Cyp4A1, Cyp2B1, Cyp2E1, Cyp2C11, UGT2B1, ALDH1A1 and Cyp2C6 were 2.6, 2, 1.5, 4, 2.8, 1.5, 1.8, 3 and 5, respectively. Our results suggest that WR may upregulate these genes in type 2 diabetes more than BR, potentially causing faster drug metabolism, less drug efficacy and more toxicity. These results may have profound implications for rice eating populations, constituting half the world's population.     

Antioxidant Property Enhancement of Sweet Potato Flour under Simulated Gastrointestinal pH

Sweet potato is known to be rich in healthful antioxidants, but the stability of its antioxidant properties under gastrointestinal pH is very much unknown. Hence, this study aimed to evaluate the changes in antioxidant properties (total contents of phenolics and flavonoids as well as antioxidant activity) of sweet potato flour (SPF) under simulated gastrointestinal pH conditions. It was found that the yield of SPF crude phenolic extract increased from 0.29 to 3.22 g/100 g SPF upon subjection to gastrointestinal pH conditions (p < 0.05). Also elevated significantly were the total phenolic content (TPC), total flavonoid content (TFC) and antioxidant activity of SPF (p < 0.05). In summary, the antioxidant properties of SPF were enhanced under gastrointestinal pH conditions, suggesting that SPF might possess a considerable amount of bound phenolic and other antioxidative compounds. The antioxidant properties of SPF are largely influenced by pH and thus might be enhanced during the in vivo digestive process.     

Neuroprotective Effects of Germinated Brown Rice against Hydrogen Peroxide Induced Cell Death in Human SH-SY5Y Cells

The neuroprotective and antioxidative effects of germinated brown rice (GBR), brown rice (BR) and commercially available γ-aminobutyric acid (GABA) against cell death induced by hydrogen peroxide (H(2)O(2)) in human neuroblastoma SH-SY5Y cells have been investigated. Results show that GBR suppressed H(2)O(2)-mediated cytotoxicity and induced G0/G1 phase cell cycle arrest in SH-SY5Y cells. Moreover, GBR reduced mitochondrial membrane potential (MMP) and prevented phosphatidylserine (PS) translocation in SH-SY5Y cells, key features of apoptosis, and subsequent cell death. GBR exhibited better neuroprotective and antioxidative activities as compared to BR and GABA. These results indicate that GBR possesses high antioxidative activities and suppressed cell death in SH-SY5Y cells by blocking the cell cycle re-entry and apoptotic mechanisms. Therefore, GBR could be developed as a value added functional food to prevent neurodegenerative diseases caused by oxidative stress and apoptosis.     

Microstructure of copolymers of vinylidene cyanide,methacrylonitrile and acrylonitrile with methyl α acetoxyacrylate,a captodative monomer

Summary Copolymers of vinylidene cyanide (1a) methacrylonitrile (1b) and acrylonitrile (1c) with a captodative monomer, methyl acetoxyacrylate were synthesized by radical copolymerization and their microstructures were studied by ¹³C NMR spectroscopy.The copolymer of 1a with methyl -acetoxyacrylate (2) has mostly an alternating structure but the copolymers of 1b and 1c with 2 are rather statistical. The measurement of their reactivity ratios for these two reactions is in agreement with the proposed structures.