Saturday, January 25, 2020
Photopolymers for Tissue Engineering Purposes
Photopolymers for Tissue Engineering Purposes DISCUSSSION    Tissue Engineering offers the potential to grow the cartilage in a precise shape and requires minimal operative time. In most of the preliminary studies, a prefabricated mold is used to grow the chondrocytes and obtain a tissue-engineered cartilage. However using the mold techniques is time consuming, does not provide an aesthetic framework for growing the cartilage and there is an uneven growth of cartilage tissue over the framework. 3D CAD manufacturing provides an alternative technique whereby one can accurately fabricate an ear shaped scaffold similar to the normal ear. Approach in scaffold design must be able to create porous structures to attain desired mechanical properties and to produce these structures within arbitrary and complex three-dimensional (3D) anatomical shapes. Material chemistry along with fabrication technique determines the properties that a scaffold can achieve and how cells interact with the scaffold .There are many techniques which are used in additive manufacturing like Stereolithography, Fused deposit modeling, selective laser sintering. Stereolithography exhibits the capability to control the spatial organization of multicellular material compositions with precise porous structures and defined shape according to patient obtained from any medical imaging modality data. In this study, we accomplished stereolithographic fabrication of hybrid scaffolds using visible light excitation by using a commercially available low cost 3D printer. The scaffolds fabricated as such will be suitable as a photo curable material that could offer an ideal environment suitable for cell growth and provide the mechanical support for the regenerative process. The table shows current studies that have made use of photo curable biomaterial that can be used for tissue engineering process.  Figure 6.1 Current studies involving photopolymers for tissue engineering purposes      As explained in the above table there are many studies, which use biodegradable polymers that can be fabricated using the stereolithography technique. However, in most of these studies there are no such combinations of natural and synthetic polymers. Also in many studies, the material has been cross-linked in the lab by using a light source or by a modified/custom made 3D printer. For this study, we decided to use a low cost and a commercially available 3D printer (Formlabs Form 1+) and natural and synthetic available polymers without making any modifications.       PEG is one of the most commonly used synthetic photo polymers for tissue engineering applications. For photo polymerization process the end group of PEG are modified into methacrylates, di acrylates, fumarates,vinyl esters etc and used for the polymerization. The reactivity of vinyl monomers towards free-radical chain polymerization follows this sequence: acrylate à ¢Ã¢â€š ¬Ã… >à ¢Ã¢â€š ¬Ã… vinyl ester ∠¼ vinyl carbonate à ¢Ã¢â€š ¬Ã… >à ¢Ã¢â€š ¬Ã… methacrylate à ¢Ã¢â€š ¬Ã… >à ¢Ã¢â€š ¬Ã… fumarate. Due to the high reactivity rate we have decided to make use of acrylated PEG. Acrylated PEG enables photo polymerization with variable mechanical properties, but by itself, PEG cannot provide an ideal environment for cell growth despite having possessing properties like nontoxicity, low protein adhesion, and nonimmunogenicity. Also PEG does not possess the ability to degrade by itself.      When it comes to biocompatibility issues, natural polymers are generally thought to be advantageous over synthetic hydrogels since natural gels may offer biological property to surrounding cells. Most naturally-derived polymers are either components of natural ECM or provide similar properties that can mimic the ECM properties. One such natural, biocompatible,and biodegradable polymer used to generate hybrid hydrogels is chitosan, an N-deacetylated derivative of the polysaccharide chitin. Although there is a study that shows the photopolymerization of oligomeric chitosan with PEGDA polymeric chitosan has not been successfully polymerized with PEGDA. Chitosan is structurally similar to glycosaminoglycans (GAGs) found in cartilage and is degradable by enzymes in humans. The objective of the study was to get a hybrid copolymer of Chitosan and PEGD which can be 3D printed by stereolithography.        To create the resin we dissolved the chitosan in acetic acid. The acetate anions deprotonate the primary amino groups of chitosan. So it became necessary to dialyze the chitosan solution in a strong basic group solution like a sodium acetate. Dialysis of chitosan solutions in sodium acetate partially neutralizes the protonated primary amino groups. Such partial de-protonation of chitosan enabled mixing of photo initiators for polymerization of PEGDA without quenching the radicals formed by protonated amino groups. Because of the high degree of crosslinking of short chain PEGDA, caused by a higher concentration diacrylate groups compared to long chain PEGDA a commercially available PEGDA 575 was used. In absence of Chitosan the minimum concentration required to create the printable resin was 30% (w/v) . However as shown in table the amount of PEGDA using Chitosan was reduced from 30% to 6-9 % . Once the printable formulation was obtained it was necessary to test the mechanical and cellular properties of these scaffolds. Schematic of cross linked hydrogel with mesh size and crosslinking distance When a hydrogel is kept in the solvent the solvent molecules try to enter inside by the capillary action. As more molecules enter the hydrogel the mesh size à ¯Ã‚  ¸ increases and more of the solvent is absorbed. However, the swelling is not a continuous process and when the capillary forces balances the elastic forces of the network the equilibrium is reached.                                              à ¯Ã‚  ¸Ãƒ ¯Ã¢â€š ¬Ã‚ à ¯Ã¢â€š ¬Ã‚ ½Ãƒ ¯Ã¢â€š ¬Ã‚ Q1/3 * (ÃŽ ³2)1/2 where Q =swelling ratio and   Î ³ = distance between two crosslinking points. As evident from the figure and the equation there is a direct relation between the swelling ratio and mesh size. As the amount of the PEGDA concentration increases, the degree of the crosslinking has increased. Highly cross-linked hydrogels will have a tighter structure, and will swell less compared to the same hydrogels with lower crosslinking ratios. Crosslinking hinders the mobility of the polymer chain and hence lowers the swelling ratio.   As evident from Fig the mechanical modulus of the hydrogel was inversely related to the swelling ratio. As the ratio of PEGDA increased from 5 to 15, the elastic modulus increased by approximately seven times in both LMWC and HMWC Chitosan. As the swelling ratio decreases the increased resistance of the hydrogel contributes to the increase in Youngs modulus. Diluted PEGDA, without chitosan, at 30% (w/v) had the highest stiffness with a compression modulus of 1125  ± 68.05 kPa (Mean  ± SD). It was observed that the gel was capable of recovering to its original length following even with a 50% strain deformation.It is evident that increasing the ratio of the initiator will increase the crosslinking density which will reduce the mesh size and in turn increase the modulus of the hydrogel.As evident from the swelling ratio the hybrid hydrogel had a higher swelling ratio than pure PEGDA which led to higher pore size which was proved with the SEM Imaging side
Friday, January 17, 2020
Cramming: Time and Long Term Memory
Universal Vice: Cramming â€Å"Whoops! It's the night before the big exam, and you haven't done a lick of studying all semester. Looking back on it, you know that you should have been hitting the books all those nights you were watching television, but there's nothing you can do about it now. Don't throw in the towel yet, though–it's time to get cramming. †How often do you do this? Most common among high school and college-aged students, cramming is often used as a means of memorizing and the practice of working intensively to absorb large volumes of informational material in short amounts of time.It is a widely-used study skill performed in preparation of an examination or other performance-based assessment. Best stated by H. E. Gorst in his book, The Curse of Education, â€Å"as long as education is synonymous with cramming on an organized plan, it will continue to produce mediocrity. †Students are often forced to cram after improper time utilization or in ef forts to understand information shortly before being tested. Improper time management is usually the cause for last-minute cramming sessions, and many study techniques have been developed to help students succeed in lieu of cramming.Generally considered as a negative study technique, cramming is becoming more and more common among students at the secondary and post-secondary level, not mentioning those who are as young as five years old. Pressure to perform well in the classroom and to engage in extracurricular activities in addition to other responsibilities often results in this kind of study habit, cramming. According to W. G. Sommer, â€Å"students in a university system often adapt to the time-constraints that are placed upon them in college, and often use cramming to perform well on tests†.In his article, Procrastination and Cramming: How Adept Students Ace the System, he states, â€Å"Many students outwardly adapt to this system, however, engage in an intense and priv ate ritual that comprises five aspects: calculated procrastination, preparatory anxiety, climactic cramming, nick-of-time deadline-making, and a secret, if often uncelebrated, victory. These adept students often find it difficult to admit others into their efficient program of academic survival. †Students have crammed for decades. What most of us don’t know is how many use this study strategy.The lit review in the article references a collection of studies that puts the percentage somewhere between 25 and 50. In this research sample, 45 percent were on the agree side of a scale that measured the extent of cramming. These are some of the very pragmatic questions explored empirically by the researchers: How widespread is cramming among students? Do students think cramming is an effective study strategy? Does cramming work, as in how does it affect course grades? And the really bottom line questions: How effective is cramming in the long run?What’s the impact on le arning and retention? Czarina Isabel F. de Leon, a freshman college student of University of the Philippines – Diliman states, â€Å"I believe that many students cram all the time. Maybe, this is due to lack of knowledge with regards to time management and discipline. But honestly speaking, I can say that cramming helps me in some way. I don’t know if it’s just me who feels that cramming stimulates my brain cells more. It seems like I am able to formulate more ideas and to absorb more information whenever I cram for some of my school works and tests.In spite of this, I don’t think that cramming has affected my grades that much because there are so many factors that can influence class marks. If I were to choose from cramming and not cramming, I would definitely choose the latter. This is because I know for a fact that if I wouldn’t cram, I’m sure that my work is clearly done and not just scrapped from somewhere. I do believe that cramming p roduces risky works, in such a way that a person who crams is not sure whether he did his job well or not. Perhaps the question that most needs addressing is this one: How come some exams can be mastered so successfully by students who’ve prepared by cramming? You might think it’s just a problem with multiple-choice exams. Not so. In this study and others, the amount of cramming students reported was not a function of exam type. Are teachers testing too much recall on their exams? It might be interesting to go through an exam and see how many questions can be answered with material you could memorize but not understand at all or well.Cramming is often discouraged by educators because the hurried coverage of material tends to result in poor long-term retention of material. In a 2007 study conducted by University of South Florida psychologist Doug Rohrer, it was determined that last minute studying reduces retention of material and may hinder the learning process in the long term. There is a biological reason for this. The problem is that cramming information places it into our brains in short term storage. This is where you put everyday information that is not really worth remembering.In order to learn we have to transfer information into long term memory. Once there, you can retrieve it far easier over a longer period of time. All information are processed in the brain and stored in short term memory. The problem is that these information sort of overloads the brain and are not kept for very long. Can you remember every single event that happened to you in a given day? Think of the literal thousands of bits of information you are exposed to every day. It's not necessary to remember it all, so the brain dumps it after a time.Can you remember what you had for breakfast the day before yesterday? What shirt you wore? How much lunch cost? How many steps there are in preparing for exams? No. What makes you think you will remember some factoid from clas s that you never heard of before? Sure you may remember it for a day or two, but that's it. Only when you make an effort to remember something repeatedly do you transfer that information into the other kind of memory, long term memory. Cramming fails because you’re relying on short term memory.In spite of these facts, cramming will always be an option for those who need to accomplish a large amount of task in a short period of time. Like any other vices, cramming can be very addictive and may supply us what we need for now, but we may not benefit from it for a long period of time. Since it is continuously done by most of us nowadays, not only by students but also by some adults as well, avoiding it will be very difficult for all of us. It’s like a universal vice that most of us used to live with and it can be applicable for everyone.Cramming is a vice that will forever be present in this world – it may be lessened but will never be eradicated, especially for stu dents like me. â€Å"While cramming probably won't get you an â€Å"A,†it can definitely save you from an â€Å"F. †So suck it up and get ready for a long, hard night. And vow to be a better student from now on. †Works Cited: â€Å"Cramming (education) -. †Wikipedia, the free encyclopedia. Web. 27 Sept. 2009. . Pangilinan, Candy. â€Å"Candidly  » Cramming and homecoming. †PEP. ph: The Number One Site for Philippine Showbiz | Home. 2 Dec. 2007. Web. 27 Sept. 2009. . â€Å"How to Cram for a Test – wikiHow. †WikiHow – The How-to Manual That You Can Edit. Web. 27 Sept. 2009. . Weimer, Maryellen. â€Å"Key Questions about Cramming  «. †Teaching Professor. 02 Dec. 2008. Web. 27 Sept. 2009. . â€Å"Cramming – Definition of cramming at YourDictionary. com. †Dictionary Definitions, Sentence Examples, Synonyms and More. Web. 27 Sept. 2009. . â€Å"Cram – Definition of cram verb (LEARN) from Cambr idge Dictionary Online: Free English Dictionary and Thesaurus. Cambridge Dictionary Online: Free English Dictionary and Thesaurus – Cambridge University Press – Cambridge Dictionaries Online – Cambridge University Press. Web. 27 Sept. 2009. . Handy, Edna Wells. â€Å"Why Students Fail. †Autoredirect to main site. Web. 27 Sept. 2009. . â€Å"The dangers of cramming for exams. †PSU BMB. Web. 27 Sept. 2009. . Weinberg, Tamar. â€Å"How to Cram for Exams – How To – Lifehacker. †Lifehacker, tips and downloads for getting things done. 02 Mar. 2008. Web. 27 Sept. 2009. . de Leon, Czarina Isabel . Personal Interview. 14 October 2009.
Thursday, January 9, 2020
Crickets and Their Reaction to Different Stimuli, Light,...
CRICKETS AND THEIR REACTION TO DIFFERENT STIMULI, LIGHT, SOUND, AND TOUCH Introduction According to Dorothea Kohstall-Schnell and Heribert Gras, Nicklaus, R found in his study most insects have fine hairs and/ or other structures for detecting movement such as wind and sound. (Activity of Giant Interneurones and other Wind-Sensitive Elements of the Terminal Ganglion in the Walking Cricket. Kohstall-Schnell, D. Gras, H. 1994).The cricket is equipped with these hair sensory structures. According to Dorothea Kohstall-Schnell and Heribert Gras, Palka, J. and Olberg, R found these structures trigger sensory cells and the message then passes through neurons to reach the terminal ganglion. (Activity of Giant Interneurones and other†¦show more content†¦There will also be a control group, a set of crickets in the same environment with the same stimuli, just not on ice. Once the cricket’s soil has reached 53.6 degrees Fahrenheit, measured with a thermometer, the first stimuli, light, is brought in. Light will be flashed on/ off with strobe light on high of the phone flashlight for 45 sec. Then record how many times the crickets jump, and rate their movement on a scale of 1-5. This rating is done collaboratively and decided upon as a group. The crickets will then sit for 2 more minutes without a stimulus. Once the two minutes is up the first and second stimuli will be used. The flash light and a noise (alarm sound on phone on high), these two stimuli will be present for 45seconds. Then record how many times the crickets jump as a whole, and rate their movement on a scale of 1-5.The crickets will then again sit for 2 minutes without stimuli. Lastly bring in all 3 stimuli. Throughout the 45 seconds the crickets will be presented with flashing light, sound, and motion (wind from a fan turned on its highest notch). 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Wednesday, January 1, 2020
Analysis Of Movie Rain Man By Barry Morrow And Ronald Bass
â€Å"246 Toothpicks†Whitt Johnson Denver School of Nursing â€Å"246 Toothpicks†According to the Centers for Disease Control (CDC), it is estimated that one in 68 children are affected with autism spectrum disorder (Baio, 2010). Children diagnosed with this disorder eventually grow into adults who need similar care and attention they required earlier in life. The focus of this paper is the 1988 movie â€Å"Rain Man†, a story written by Barry Morrow and Ronald Bass, directed by Berry Levinson, cast played by Dustin Hoffman as Raymond Babbitt â€Å"Rain man†and Tom Cruse as brother, Charlie Babbitt. The National Institutes of Neurological Disorders and Stroke (Autism Spectrum Disorder Fact Sheet, 2015) state that autism â€Å"refers to a group of complex neurodevelopmental disorders characterized by repetitive and characteristic patterns of behavior and difficulties with social communication†. Savant autism is a rare and extraordinary form of autism characterized by deep, thorough knowledg e of one particular subject or area of interest. Our character, Raymond Babbitt, is one of those rare savant autistic individuals. Raymond Babbitt, a now 57 year old male with an impeccable memory, lacks the skills to connect socially has been living with being an â€Å"idiot savant†or a â€Å"high functioning autistic savant†(Rain Man, 1988) all his life. He has been institutionalized at Walbrook Institute since a young age. Dr. Brunner, Raymond’s doctor, states to Charlie early in the movie, â€Å"routines andShow MoreRelatedDeveloping Management Skills404131 Words  | 1617 PagesLine 58 Understanding and Appreciating Individual Differences Important Areas of Self-Awareness 61 Emotional Intelligence 62 Values 65 Ethical Decision Making and Values 72 Cognitive Style 74 Attitudes Toward Change 76 Core Self-Evaluation 79 SKILL ANALYSIS 84 Cases Involving Self-Awareness 84 Communist Prison Camp 84 Computerized Exam 85 Decision Dilemmas 86 SKILL PRACTICE 89 Exercises for Improving Self-Awareness Through Self-Disclosure 89 Through the Looking Glass 89 Diagnosing Managerial Characteristics
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