Celebrations and Adventures Away from the Lab
June 27, 2019
Catching up at SB3C
We had an impromptu lunch catching up with current and former lab members at the Summer Biomechanics, Bioengineering and Biotransport Conference at Seven Springs, PA. Sara Bentil is 3 years into her Assistant Professor position at Iowa State and attending her first SB3C. Kristin Myer is newly tenured at Columbia and returning from a sabbatical and Dan Midgett is doing new and cool things at in biomechanics and cardiology at Yale. Along with Arina Korneva and Tracy Ling, it was a great group.
June 5, 2019
Dr. Jiayu Liu
Congratulations to Dr. Jiayu Liu for his successful dissertation defense, “Mechanics-Based Design of Stimuli-Responsive Hydrogel Structures and Devices“. Abstract below.
Stimuli-responsive hydrogels undergo large swelling in response to a wide variety of stimuli, such as temperature, biochemical molecule, pH, electric or magnetic field. Programmable shape changing devices made from stimuli-responsive hydrogels have potentially wide-ranging applications, including drug delivery, soft robotics, and biomedical devices. The current main challenges of advancing stimuli-responsive hydrogel devices into real-life applications are in both the design and fabrication stage. Simple strategies based on mechanics are needed to guide the design of hydrogel devices with complicated shape changes. Traditional fabrication methods such as 2D lithography limits the number of achievable device geometries. The objective of this work is to develop a methodology that covers from constitutive modeling, finite element simulation, mechanics-based design rules, to experimental validation. This hybrid modeling design methodology provides an efficient design framework for stimuli responsive hydrogel structures and devices of functional importance. In the first part of this work, we applied a chemo-mechanical constitutive model to describe the swelling and mechanical behavior of a novel DNA hydrogel (AAm-co-DNA). In order to estimate the elastic modulus of DNA hydrogel that cannot be measured by traditional experimental approach, we used finite element analysis to study the curving of bilayer beams composed of the DNA gel and a passive gel (polyacrylamide, pAAM), and compared the finite element simulations to the experiment result. We further applied the finite element model to investigate the influence of bilayer geometric and material properties on the equilibrium curvature. We used the modified Stoney formula for the curving of film/substrate system to develop a simple design rule for predicting the equilibrium curvature of bilayer gel beams with different dimensions and material properties. In the second part of this work, we report the design, fabrication, and characterization of segmented 3D printed gel tubes composed of an active thermally responsive swelling gel (poly N-isopropylacrylamide, pNIPAM) and a passive thermally nonresponsive gel (pAAM). Using finite element simulations and experiments, we report a variety of primitive shape changes including uniaxial elongation, radial expansion, bending, and gripping based on different segment arrangements of two gels. The assembly of shape-changing primitives could be directly printed and used to achieve complicated tasks. In the final part of this work, we report on the unusual periodic buckling behavior of a 4D printed tubular structure, composed of alternating vertical strips of pNIPAM segments and pAAM segments. The tube design was inspired by the buckled surfaces observed in nature, such as on cacti and euphorbias. We found that the tubes show tunable periodic buckling modes in water at the room temperature, due to the development of compressive stresses in the soft swellable segments induced by the constraint of the stiff non-swellable segments. We developed finite element models to explore the design space and investigate the effects of geometric and material design parameters on the buckling mode. Modeling the swellable segments as the buckling of a bar on an elastic foundation, we derived a bucking parameter that combines the effects of geometry and material properties to predict the transition between different periodic buckling modes and constructed a phase diagram to guide the design of periodic buckling tubes for bioinspired functional gel structures.
May 2, 2019
A small reunion
One of the pleasures of teaching is seeing how well your former students are doing in their new adventures. I ran into JHU ME alumni Bailey Hannon and Martha Whiting, BS 2015 at ARVO. I taught them both in Biosolids and Martha built an essential test fixture for my lab as an REU student. Both were presenting their research and Bailey gave a great talk on using machine learning to automatically count axons. Bailey is a 4th year PhD student in BME at Georgia Tech and Martha is a 3rd year MD student at U. of Maryland.
May 1, 2019
Congratulations to Arina Korneva
Congratulations to Arina Korneva for winning the Members In Training Poster Award Competition for the Glaucoma Section at the 2019 Annual Meeting at ARVO. Arina’s poster was titled “. Well done!
February 11, 2019
Dr. Michelle Chen
Congratulations to Dr. Michelle Chen for her successful dissertation defense, “Mechanochemistry of Collagen Network Remodeling in the Sclera“. Abstract below.
The primary load-bearing tissue of the eye is the sclera, the eye’s white outer shell. It helps the eye maintain its shape by resisting intraocular pressure and protects the
delicate intraocular structures. The sclera is able to respond to mechanical changes in its environment by self- adapting, a process known as remodeling. This reaction, which alters the microstructure and/or properties of the tissue, is beneficial and clinically important but may also contribute to pathological diseases such as glaucoma and myopia when an imbalance in the remodeling process occurs. It is therefore important to understand the underlying mechanisms that drive the remodeling process, and how it affects tissue microstructure and its mechanical properties. This work focuses on two main parts of the connective tissue microstructure: collagen, which serves as the primary load-bearing component and dominates the anisotropic large-strain mechanical response of the tissue, and glycosaminoglycans (GAGs) which regulate the spacing between collagen fibrils and help determine tissue hydration. The objective of this work is to study the effect of remodeling on mechanical behavior of the posterior sclera. We investigate this through three case studies.
The first part of this work studies the mechanical role of GAGs in the human posterior sclera. Although alterations in mechanical properties and GAG content have been reported in glaucomatous eyes, it is unknown if the change in GAG content directly contributes to the observed changes in mechanical properties. Experimental protocols and novel analysis methods were developed for determining the inflation response of posterior human sclera shells, measured before and after enzymatic GAG degradation. It was shown that GAGs play a measurable role in altering the structure properties and mechanical behavior of the posterior human sclera, likely through their effects on hydration and their interactions with the collagen fibrils.
The second case study investigates how cyclic preconditioning of a collagenous substrate induces material and morphology property changes in collagen fibrils. Experimental studies have shown that repeated cyclic loading of an acellular collagen construct increased collagen stiffness, but did not significantly change fibril anisotropy. A model for the collagen fibril substrate was developed to show that the changes in the collagen anisotropy measured in experiments were insufficient to explain the measured increase in the stiffness of the collagen constructs with cyclic loading. The findings suggest that mechanical loading can induce changes in the stiffness and failure properties of the collagen fibril network through passive chemomechanical processes.
The last part of this work examines the effect of changes in the geometry of the sclera, collagen anisotropic structure, and material properties from glaucoma on the inflation response of the mouse sclera. An inverse finite element method was used to fit model parameters describing fibril properties to the average measured scleral edge displacements of glaucoma and normal mouse eyes. The findings show that changes in collagen fibril material properties are responsible for the observed stiffening effect in glaucoma mouse eyes. The observed structural changes associated with glaucoma did not meaningfully stiffen the mechanical response.
January 19, 2019
Happy New Year
We celebrated the end of 2018 and beginning of 2019 with our annual get together. There was a Battle Ship and Mario Kart face-off between PhD students and postdoc and a 9 year old. Guess who won most of the time. There were also lots of food and a dessert bake off. Vicky Nguyen won with a almond cake, but Michelle Chen and Arina Korneva came in a very close second with a hazelnut cake and delicious brownie like cookies. Clearly everyone at the party was the winner because we all got to eat the desserts.
August 10, 2018
Dr. Jingkai Guo
Congratulations to Dr. Jingkai Guo for his successful dissertation defense, “Modeling the Mechanical Behavior of Soft Active Materials“. Abstract below.
Soft active materials are capable of converting chemical or physical energy into mechanical work in response to various environmental stimuli such as pH, solvent, salt, heat, humidity, electric or magnetic field, and light. These materials are generally inexpensive, lightweight and their properties can be tailored based on requirements of applications. These attractive features give them great potentials in a wide range of applications, such as biomimetic systems inspired from living organisms. The objective of this work was to develop theoretical models that are capable of accurately describing the physical- mechanical behavior of soft active materials. A common set of methods that can be applied to the study of wide range of soft materials was developed. The methods covered different stages of the study, from material characterization to constitutive modeling, from simulation to experiments.
In this work, I focused on three kinds of soft active materials: dielectric elastomers, thermoresponsive gels and shape memory polymers. In the first part of this work, we investigated the temperature dependent viscoelastic behavior of dielectric elastomers and the effects of viscoelasticity on the electro- actuation behavior. We measured the viscoelastic relaxation spectrum of VHB 4905 and applied the results to a discrete multi-process viscoelastic model. The model generally showed good quantitative agreements with experimental measurements in terms of both pure-mechanical and electro-mechanical behaviors of the material. The model was able to qualitatively capture the dependence of the electric breakdown time on voltage and pre-stretch. In the second part of this work, we studied the thermoresponsive bilayer plates with soft and stiff segments that exhibit bidirectional and biaxial curving. We investigated the mechanism underlying the deformation modes through finite element simulation and explored the effects of geometry factors such as the aspect ratio and the segment spacing. In the final part of this work, we developed a constitutive model based on the effective temperature theory that is capable of describing strain hardening behavior in a thermodynamically consistent manner. The model incorporated two mechanisms: one represents the stretching and orientation of the polymer network, which leads to the development of a backstress; the other one represents the molecular reptation, which accounts for the temperature and rate dependence of strain hardening. The model was implemented into finite element programs and was applied to simulate the thermomechanical behavior of polycarbonate. All of the model parameters were determined through standard thermomechanical tests. The simulation results showed good agreements with experiments and the temperature dependence, strain rate dependence and strain state dependence of hardening were quantitatively captured.
July 9, 2018
Congratulations to Tracy
Tracy Ling wins first place in Masters Level Paper (Poster) Competition at the World Congress in Biomechanics in Dublin, Ireland. Here is a picture of her winning poster in the lab. This has been a good year for Tracy. She also won a travel award to give a podium presentation at ARVO in Honolulu, Hawaii in 2018. Tracy is currently a PhD student in the Lab working on biomechanics of the mouse optic nerve head.
May 22, 2018
Congratulations to Dr. Dan Midgett
April 24, 2018
Dr. Dan Midgett
Congratulations to Dr. Dan Midgett for his successful dissertation defense, “Measuring the Full-Field Inflation Response of the Optic Nerve Head“. Abstract below.
The optic nerve head (ONH) is the region where the retinal ganglion cell (RGC) axons travel through the eye wall and bundle to form the the optic nerve. The lamina cribrosa (LC) and the peripapillary sclera (PPS) are the primary load-bearing structures of the ONH, supporting the RGCs and maintaining the pressure gradient between the intraocular and intracranial pressures. The LC is comprised of a network of collagen beams that wrap around the RGC bundles as they insert through the eye wall. The PPS is the stiff, thick portion of the posterior sclera that surrounds the LC. In the disorder known as glaucoma significant remodeling occurs in the tissues of the ONH, with changes in the collagen, elastin, and glycosaminoglycan (GAG) microstructure. This is associated with visual field loss and the death of RGC axons. While the mechanisms leading to vision loss remain unknown, glaucoma is commonly associated with older age and the level of intraocular pressure (IOP). A current hypothesis asserts that damage to the RGC axons is incurred mechanically through IOP-induced strains within the LC. If this hypothesis is correct, then the biomechanics of the LC and PPS are major contributing factors to the susceptibility of individuals to glaucoma damage. The objective of this work is to measure the three-dimensional (3D), pressure-induced deformation of the LC and PPS, and to investigate how the pressure-induced strains within the LC and PPS vary with region, age, LC shape, and GAG content.
We developed an ex vivo inflation test for the human posterior sclera, designed to measure the deformation of the ONH due to applied changes in the pressure within 21 eyes with no history of glaucoma. The pressure was varied between 5 and 45 mmHg, and images of the collagen and elastin within the LC and PPS were acquired using second harmonic generation (SHG) and two-photon fluorescence (TPF). Digital volume correlation (DVC) was used to calculate the deformation of the elastin and collagen between pressures, and analytical methods were developed to calculate the 3D strain fields within the LC and PPS at the resolution of the collagen beams within the LC (< 1μm). This study revealed heterogeneous strain fields with many localized regions of high strain. We found that the LC strains were smaller in older eyes and in the nasal quadrant, and larger on the periphery of the LC. We showed that this pattern of strain was consistent with the patterns of early glaucoma damage. Interactions between the LC and the PPS were also observed, with many eyes experiencing regions of compressive radial strain in the PPS adjacent to the LC. We also observed a significant reduction in the strains of the LC after the degradation of the majority of sGAGs within the LC and sclera. This demonstrates that the presence of sGAGs has a significant effect on the on the biomechanics of the ONH. This method was similarly applied to measure the IOP-induced deformation of the ONH within mouse eyes. Strains within the mouse LC were primarily nasal-temporal in magnitude and were significantly reduced after 1-3 days of chronic IOP elevation. LC strains were also smaller in older mice. We conclude that there are significant regional and individual variations in the susceptibility of the LC and PPS to strain induced through pressure. These variations may contribute to individual susceptibility to glaucoma.
December 10, 2017
Lab Mug Design
We held a contest to design our lab mug. It was inspiring to see all of your creative design. Tracy Ling’s design won a close vote. But since there were so many great ideas, I combined a few of the top vote getters to come up with the final mug design.
- “Who, what, where, why, Nguyen”: a pronunciation guide and description of the Lab’s scientific inquiry – Tracy Ling.
- The colorful orb in the middle of the diamond is an eye and the surrounding “N” depicts a polymer backbone, representing the Lab’s 2 areas of research -Tracy Liu.
- The red curve is actual data for the stress-strain curve of polycarbonate. It illustrates the difficult journey of a PhD student – Jingkai Guo.
December 10, 2017
Lab Holiday Party
Celebrating another year and saying farewell to 3 lab members. Zheng Jia left to start a faculty position in Zhejiang University, China. Ran Shi will be returning to Beijing Institute of Technology after 1 year as visiting student, and Hai Dong will be moving to UIUC to start another postdoc. Thank you for all your hard work. Best wished on your new adventure.
July 29, 2017
Lab Summer BBQ
Chilling in the backyard with good food and good conversation before the start of another academic year. Thanks all for your hard work.
July 25, 2017
Annual Meeting of the Society of Engineering Science, Boston, MA
The lab was well represented at conference at Northeastern U. by Hai Dong, Jingkai Guo and Zheng Jia who gave a 40 invited talk on growth and remodeling. It was also great seeing Sarah Bentil giving a talk as a professor.
June 20, 2017
Summer Biomechanics, Bioengineering, Biotransport Conference, Tucson, AZ
A reunion with Kristin Myers and her group in the beautiful Tucson desert. Michelle and Elizabeth were busy at the poster session and Dan had a great talk in the Ocular Biomechanics session.
May 7, 2017
ARVO 2017, Baltimore MD
Tracy Ling’s first conference. Both Dan and Tracy did a great job presenting their posters. Nearly 3 hours of nonstop talking. Not a simple feat.
December 10, 2016
Holiday Party 2016
Thank you all for another wonderful year!
We held our first Christmas Cookie Baking Contests. Everyone baked their recipes (or some online recipe found the night before) and brought them to share. We all inspected, tasted, and voted for the best tasting and best looking cookie. It was a close race, as all the cookies were delicious! The winners are Tracy Ling’s swirled cookie (A) for the prettiest cookie and Michelle Chen’s apple pie-let (C) for the most delicious treat.
Yankee Swap Gift Exchange
Puzzle – “Things I ate as a kid”
May 4, 2016
ARVO Annual Meeting, Seattle
Dan presented a fabulous poster at ARVO. He was talking nonstop from 10:30-1:30 pm. Congratulations to Dan!
March 25, 2016
Farewell Lunch For Bahram and Barbara
Congratulations to Barbara for her successful Thesis Defense and Bahram for his new job at Baxter.
March 17, 2016
APS March Meeting in Baltimore
Jingkai and Michelle both gave excellent talks on modeling amorphous polymers and mechanochemistry of collagen. It was Michelle’s first conference talk!
December 13, 2015
Holiday Party 2015
Thank you all for you another great year.
October 21, 2015
21st Annual James F. Bell Lecture in Continuum Mechanics
Introducing my PhD advisor, Huajian Gao, as the 2015 Bell Lecturer was a treat
July 5, 2015
Summer in Zurich
May 20, 2015
Congratulations to James Teasley BSMS ’15 and Martha Whiting BS ’15!
PhD Hooding Ceremony
Congratulation to Rui Xiao ’15 and Theresa Tonge ’15 on their graduation. Baptiste Coudrillier ’14 made a belated appearance.
Lunch at Cafe Azafran
Another year has ended and summer is on the horizon. We gathered for lunch to celebrate, catch up with Baptiste, and wish Rui well in his new adventure.
February 27, 2015
Dinner, Word Thief, and a new group picture
January 9, 2015
Congratulations Rui, Dissertation Defense Party
October 24, 2014
Congratulations Theresa, Dissertation Defense Party
July 19, 2014
Summer Party 2014, Legos Party
July 9, 2014
June 25, 2014
Vicky’s Tenure Celebration
May 16, 2014
International Workshop on Multiscale Mechanobiology, Hong Kong
May 14, 2014
IUTAM Mechanics of Soft Active Materials, Haifa, Israel
July 10, 2013
Summer Party 2013, Farewell to Baptiste
June 17, 2013
Mary is Leaving MIT, Mary Boyce’s Farewell Celebration, Boston, MA
May 28, 2013
Congratulations Baptiste! Dissertation Defense Party
March 20, 2013
Applied Physics Society Meeting, Baltimore, MD
December 19, 2012
Holiday Party 2012, Gingerbread Holiday
June 19, 2012
Summer Bioengineering Conference, Farjardo, Puerto Rico
February 6, 2012
December 17, 2011
Holiday Party 2011, Biggest gathering yet
November 12, 2011
International Mechanical Engineering Congress and Exposition 2011 Denver, CO
June 20, 2011
Summer Bioengineering Conference 2011, Farmington, PA
May 21, 2011
Summer Party 2011, Break out the Bocce
May 22, 2010
Summer Party 2010, Inaugural BBQ
June 22, 2009
Summer Bioengineering Conference, Lake Tahoe, CA
January 12, 2009