Hip replacements have a limited life before they too need replacing. This is known in the medical field as revision surgery and it is a source of much pain and inconvenience for the patient. Revision surgery is most often because the underlying bone has deteriorated. Bone needs stress to grow and to maintain strength, yet current hip replacement implants are too stiff - they constrain the affixed bone and prevent it from stretching. The bone around the implant starts to deteriorate and the bond between bone and implant fails.
Titanium, used in orthopaedic implants because it is strong, lightweight and biocompatible, transforms at temperatures above 883°C. The atoms rearrange from a densely-packed structure (called the alpha phase) to one that is loosely-packed (beta phase). Both alpha and beta phases are strong, but the beta phase is half as stiff and has elastic properties closer to that of bone. By adding elements such as tin, niobium and zirconium, our titanium alloy keeps its flexible beta structure at room temperature. If the alloy is then re-heated to 450°C, some alpha phase re-emerges, complicating the microstructure. This makes it more difficult for cracks to progress through the metal, making it less susceptible to fatigue failure. If the amount of alpha is controlled, a metal with good fatigue properties and low-stiffness is made.
To further reduce the stiffness of the implant and match it to that of bone, we use flexible scaffold structures. The scaffolding also allows the bone to grow into the implant, creating a strong bond. These complicated scaffolds are built from thin layers of titanium powder that are melted with a laser, then cooled to solidify. This manufacturing method is called Selective Laser Melting (SLM) and it is like 3D printing. Because SLM is good at producing one-off items, customised implants are possible; the patient’s CAT or MRI scans can be combined with Computer Aided Design to ensure a perfect fit.
My research at the University of Western Australia uses these new materials and advanced manufacturing techniques to try to overcome the main reason why orthopaedic implants fail. If successful, this work will help lead to more durable implants, reducing the need for revision surgery and allowing orthopaedic implants to be used on younger adult patients.
This video was created with friends and family for Gonzolabs "Dance Your Ph.D" 2011 Contest. It illustrates a central part of my research: the effect of the titanium alloy microstructure. The video was created using 2200 photographs because we didn't have a video camera, but also (and more importantly) because stop motion, even though tedious to shoot, is fun.
The music is "Mischa" by unsigned Perth indi-electropop outfit The Transients. Hear more of their music at http://www.thetransients.net
Winner of the Biology category of Dance your PhD 2011 by Science journal.
If you like this video, I'm sure you would also like this other video: vimeo.com/44808911
Research papers: http://www.nature.com/nature/journal/v505/n7485/full/nature12949.html; http://rspb.royalsocietypublishing.org/content/280/1771/20131691.full
Individuals often migrate from their place of origin in a relatively slow pace. As such, related individuals frequently interact. Relatedness between two individuals is defined as the percentage of genes in those two individuals that are identical by common ancestry. My PhD project at University of Oxford focuses on the mechanisms through which relatedness affects sexual interactions of the common fruit fly, Drosophila melanogaster and the red jungle fowl, Gallus gallus.
Our dance depicts the social and sexual behavior of the common fruit fly. Fruit flies are attracted by the smell of rotting fruit where they collect, feed and interact. Males compete against one another for female mates. In addition, males perform a sequence of courtship behaviors. First, they tap and chase the females. Thereafter, they encircle the females while playing a song by vibrating their wings. Then, the males orient themselves at the rear of the females’ abdomen to lick their body. Finally, males attempt copulation. Females can reject the males’ advances with several responses such as flicking of wings and kicking.
This choreography also illustrates how male-male relatedness can reduce the intensity of male-male competition and affect female choice. When two males are related, they are predicted to show less aggression towards each other. Also, females preferentially mate with males that are related to the first mates because there might be immunological and survival costs associated with mating with males that are unrelated to their first mate. Furthermore, we demonstrate the importance of smell in mediating the recognition of relatedness.
This PhD study challenges the traditional ‘stimulus-release’ model of social interaction. Animal social interactions are commonly described as a ‘chain of reciprocal signals’ where each signal is successively ‘released’ by stimuli present in the signal preceding it (Tinbergen). But, how is a signal’s outcome influenced by its dynamic relations to other behaviours in the chain? To study social interactivity, a closed-loop video interface was used to set up live social interaction between male and female pigeons (Columba livia). With this setup we were able to manipulate the dynamics of the interaction and study the role that social dynamics play in behaviour.
For more information about this project, as well as other exciting research about social perception and cognition, check out the BioMotion lab at http://www.biomotionlab.ca/
Shifts in dietary patterns towards a Western-style diet have been accompanied by increased susceptibility to many chronic diseases. It is hypothesized that this may be in part due to changing epigenetic patterns. Epigenetics determines how tightly the DNA is coiled by adding chemical compounds directly to the DNA and the bead-like histone proteins which the DNA wraps around. The tightness of DNA coiling determines which genes are expressed which can affect health and disease. Epigenetic patterns can be modified by the environment, including diet.
My thesis focuses on the effect of consumption of a Western style diet on epigenetic patterns. The first scene depicts a typical lunch time with everyone consuming their favourite processed fast food, which is in contrast to the recommendations of the Dietary Guidelines for Americans through MyPlate. The influence of peer pressure on dietary choices is demonstrated by the throwing out of MyPlate and passing of the fast food.
The second scene takes place inside the nucleus of the cell, with silver DNA wrapped around histone protein dancers. Balloons represent methyl marks which tighten the DNA structure. The pink umbrella represents an acetyl mark, which loosens the DNA structure. Dancing transcription factors can’t bind the tightened DNA at the balloons but they can successfully bind the loosened DNA structure at the umbrella, leading to expression of the green gene. Components of the Western style diet, including pizza, chips and lollipops, come pummeling through the cell and disrupt the epigenetic patterns by moving the balloons and umbrella to different genes. Finally, the transcription factors return to bind the new loosened gene with the umbrella, leading to expression of the red gene.
Inhaled odor molecules bind to receptors located on olfactory sensory neurons in the nasal cavity. The signal from odor receptors is transmitted along the olfactory nerve to the olfactory bulb. The surface of the olfactory bulb is covered with spherical structures called glomeruli, each composed of a bundle of neuronal processes surrounded by cell bodies. Each glomerulus receives input from only one subtype of odor receptor, and each odor activates a unique set of receptors and therefore a unique pattern of glomeruli. I use electrophysiological recordings from rat olfactory bulb slices to examine the functional connections between cells. We hypothesize that an activated glomerulus can inhibit the activation of nearby glomeruli through short axon cells, which connect groups of ten to twenty glomeruli. Lateral inhibition through short axon cells could increase the contrast between similar odors with nearly identical glomerular activation patterns, making it easier for animals to differentiate highly similar odors.
In the dance, I have simplified the system so that each odor sniffed by the dog activates one glomerulus. Each segment starts with the dog inhaling the odor, which is then represented in dance form as a ball that is caught by an odor receptor. The receptor neuron then becomes activated and the odor signal travels along the olfactory nerve to the olfactory bulb where it tags the appropriate glomerulus to activate it. The dancers in each circle represent the glomerular cells activated by the incoming signal, and the dancers that move away from the glomerulus are the short axon cells that inhibit the other glomeruli.