Tuning and Optimization of Silk Fibroin Gels for Biomedical Applications

Biocompatible and biodegradable porous materials based on silk fibroin (SF), a natural protein derived from the Bombyx mori silkworm, are being extensively investigated for use in biomedical applications including mammalian cell bioprocessing, tissue engineering, and drug delivery applications. In this work, low-pressure, gaseous CO2 is used as an acidifying agent to fabricate SF hydrogels. This low-pressure CO2 acidification method is compared to an acidification method using high-pressure CO2 to demonstrate the effect of CO2 mass transfer and pressure on SF sol-gel kinetics. The effect of SF molecular weight on the sol-gel kinetics is determined using the low-pressure CO2 method. The results from these studies demonstrate that low-pressure CO2 processing proves to be a facile method for synthesizing 3D SF hydrogels. We also determined the effect of SF solution concentration on the morphology and textural properties of SF aerogels. Changing the solution concentration from 2 wt% to 6 wt% yielded a higher surface area (260 to 308 m2/g) and different macro structure, but similar mesopore pore volume and size, and micro structure. Furthermore, we determined the effect of drying method on the morphology and textural properties of SF hydrogels gelled via CO2 acidification. Drying with supercritical carbon dioxide (scCO2) yielded an aerogel surface area five times larger than aerogels that were freeze dried. Moreover, a freeze dried hydrogel initially frozen at -20 °C had pores approximately 10 µm larger than a hydrogel initially frozen at -196 °C. The results presented here also demonstrate the potential of SF aerogels as drug delivery devices for the extended release of ibuprofen, a model drug compound. SF aerogels are loaded with ~21 wt% of ibuprofen using scCO2 at 40 °C and 100 bar. Differential scanning calorimetry of the ibuprofen-loaded SF aerogels indicates that the ibuprofen is amorphous. Scanning electron microscopy and nitrogen adsorption/desorption analysis are used to investigate the morphology and textural properties. Phosphate buffer solution (PBS) soaking studies at 37 °C and pH 7.4 reveal that the SF aerogels do not swell or degrade for up to six hours. In vitro ibuprofen release in PBS at 37 °C and pH 7.4 occurs over a six-hour period when the ibuprofen is loaded in SF aerogel discs with an aspect ratio of ~1.65 (diameter/thickness), whereas the dissolution of the same amount of pure ibuprofen occurs in 15 minutes. Furthermore, the release of ibuprofen from these SF aerogel discs are modeled using the Fu model which indicates that ibuprofen release follows Fickian diffusion for the first 65 wt% of ibuprofen release, and non-Fickian diffusion for the next 25 wt% of ibuprofen release. We also showed that SF aerogel scaffolds support in vitro human foreskin fibroblast cell attachment, proliferation, propagation, and cell seeding of different densities (10x103, 30x103, and 60x103). In summary, we created and characterized a tunable 3D SF aerogel scaffold with potential for applications in drug delivery and tissue engineering applications

Third-Party Liability of Directors and Officers: Reconciling Corporate Personality and Personal Responsibility in Tort

When is a director or of�� cer personally liable in tort to a party who is not the corporation he or she serves? In Canada, there is no clear answer. The law is marked by division both within and between appellate courts, resulting in judgments that are hard to reconcile and verge on arbitrary. This is likely attributable to the mistaken belief that there is a tension between personal liability and corporate personality, as well as the disputed relationship between common law and statutory obligations. To address these challenges, most Canadian courts have followed a threshold corporate law analysis, which seeks to categorize the allegations as either corporate or personal. When applied, this approach often results in directors and of�� cers having immunity with respect to torts they committed in pursuit of the corporation’s interests. Such immunity, however, has no basis in law. Canada’s business corporations statutes do not limit the liability of directors and officers, and implicitly contemplate their exposure to tort claims

Errors in Length-weight Parameters at FishBase.org

Background: FishBase.org is an on-line database of fish related data that has been cited over 1500 times in the fisheries literature. Length-weight relationships in fish traditionally employ the model, W(L) = aL^b^, where L is length and W is weight. Parameters a and b are catalogued by FishBase for a large number of sources and species. FishBase.org detects outliers in a plot of log(a) vs. b to identify dubious length-weight parameters.
Materials and Methods: To investigate possible errors, length-weight parameters from FishBase.org were used to graph length-weight curves for six different species: channel catfish (Ictalurus punctatus), black crappie (Pomoxis nigromacalatus), largemouth bass (Micropterus salmoides), rainbow trout (Oncorhynchus mykiss), flathead catfish (Pylodictis olivaris), and lake trout (Salvelinus namaycush) along with the standard weight curves (Anderson and Neumann 1996, Bister et al. 2000). Parameters noted as “doubtful” by FishBase were excluded. For each species, variations in curves were noted, and the minimum and maximum predicted weights for a 30 cm long fish were compared with each other and with the standard weight for that length. For lake trout, additional comparisons were made between the parameters and study details reported in FishBase.org for 6 of 8 length-weight relationships and those reported in the reference (Carlander 1969) for those 6 relationships. 
Results: In all species studied, minimum and maximum curves produced with the length-weight parameters at FishBase.org are notably different from each other, and in many cases predict weights that are clearly absurd. For example, one set of parameters predicts a 30 cm rainbow trout weighing 44 g. For 30 cm length, the range of weights (relative to the standard weight) for each species are: channel catfish (31.4% to 193.1%), black crappie (54.0% to 149.0%), largemouth bass (28.8% to 130.4%), rainbow trout (14.9% to 113.4%), flathead catfish (29.3% to 250.7%), and lake trout (44.0% to 152.7%). Ten of the twelve extreme curves reference two sources (Carlander 1969 and Carlander 1977). These two sources are used for a total of 100 different species at FishBase.org. In the case of lake trout, comparing the length-weight table at FishBase.org and the cited source (Carlander 1969) revealed that while 5 of 6 total length measurements were incorrectly reported as fork lengths by FishBase.org, all parameters accurately reflected the source. Comparing the length-weight relationships of the source (Carlander 1969) with the table of weights in different length ranges reveals the length-weight parameters in the source are clearly in error. However, FishBase.org also neglects to specify clearly distinguished subspecies and/or phenotypes such as siscowet and humper lake trout.
Conclusion: Length-weight tables at FishBase.org are not generally reliable and the on-line database contains dubious parameters. Assurance of quality probably will require a systematic review with more careful and comprehensive methods than those currently employed. 
&#xa

Push-Pull Control of Motor Output

Inhibition usually decreases input–output excitability of neurons. If, however, inhibition is coupled to excitation in a push–pull fashion, where inhibition decreases as excitation increases, neuron excitability can be increased. Although the presence of push–pull organization has been demonstrated in single cells, its functional impact on neural processing depends on its effect on the system level. We studied push–pull in the motor output stage of the feline spinal cord, a system that allows independent control of inhibitory and excitatory components. Push–pull organization was clearly present in ankle extensor motoneurons, producing increased peak-to-peak modulation of synaptic currents. The effect at the system level was equally strong. Independent control of the inhibitory component showed that the stronger the background of inhibition, the greater the peak force production. This illustrates the paradox at the heart of push–pull organization: increased force output can be achieved by increasing background inhibition to provide greater disinhibition

The impact of technology acceptance and openess to innovaion on software implementation

Senior management decisions to foster innovation and adopt new technology solutions have serious implications for the success of their organization change initiatives. This project examined the issue of senior management decision or reasons of their decision to adopt new Enterprise Resource Planning (ERP) systems as a solution to solve their business problems. This project investigated the degree that perceived ease of use and usefulness of the ERP system influenced decisions made by senior managers to innovate. Roger\u27s diffusion of innovations theory and Davis technology acceptance model theory were used to predict when senior managers were open to innovation, and whether senior managers made decisions to adopt new technological innovations. Out of the 3,000 randomly selected senior managers of small to medium sized organizations in the United States who were invited via emails to participate, 154 completed the online survey. Binary logistic regression analysis on the collected data failed to produce statistically significant support for the claim that perceived ease of use, perceived usefulness, and openness to innovation should impact the senior manager\u27s decision to innovate. The conclusions of this study suggest further research may include a qualitative design to gain a deeper understanding of the underlying reasons, opinions and motivations on the emotive aspects of the decision-making process in the adoption of ERP software innovations. It also offers a positive social change to stakeholders who are potentially affected by technology innovation and adoption by providing empirically validated evidence for causes of senior management technology decisions

Peacemakers Along the DMZ: Non-Self Destruct Landmines in the Republic of Korea

The need for landmines in Korea will remain the same without a change in the terrain or the proximity of either the threat or the enemy, unless we successfully find a viable, fully fielded alternative