Shaobao Liu

Directed self-assembly of microscale hydrogels by electrostatic interaction

The unique benefit of electrostatic self-assembly of microscale components in solution is demonstrated for the first time. In particular, positive and negative treatment of poly(ethylene glycol) (PEG) facilitates a novel bottom-up assembly approach using electrostatic interaction from microgels with opposite charges. Fundamental investigations of electrostatic interaction of microgels reveal that the contact area of microgels determines the total energy of construct and thus the final patterns. The electrostatic self-assembly approach enables the fabrication of large and complex biological related structures (e.g., multi-layer spheroid) with accurate control. By the design of the microgels, the thickness and number of microgels in each layer can be controlled. Biological investigations of positive and negative treatments of PEG further prove the possibility of using this approach in tissue engineering, regenerative medicine and drug delivery.

Patterning Cellular Alignment through Stretching Hydrogels with Programmable Strain Gradients

The graded mechanical properties (e.g., stiffness and stress/strain) of excellular matrix play an important role in guiding cellular alignment, as vital in tissue reconstruction with proper functions. Though various methods have been developed to engineer a graded mechanical environment to study its effect on cellular behaviors, most of them failed to distinguish stiffness effect from stress/strain effect during mechanical loading. Here, we construct a mechanical environment with programmable strain gradients by using a hydrogel of a linear elastic property. When seeding cells on such hydrogels, we demonstrate that the pattern of cellular alignment can be rather precisely tailored by substrate strains. The experiment is in consistency with a theoritical prediction when assuming that focal adhesions (FAs) would drive a cell to reorient to the directions where they are most stable. A fundamental theory has also been developed and is excellent in agreement with the complete temporal alignment of cells. This work not only provides important insights into the cellular response to the local mechanical microenvironment but can also be utilized to engineer patterned cellular alignment that can be critical in tissue remodeling and regenerative medicine applications.

Analysis of thermal-induced dentinal fluid flow and its implications in dental thermal pain.

OBJECTIVES The initiation of the pain sensation experienced following the thermal stimulation of dentine has been correlated with fluid flow in the dentinal tubules. There may be other mechanisms. METHODS This study examines this possibility using a mathematical model to simulate the temperature and thermal stress distribution in a tooth undergoing thermal stimulation. The results obtained were then used to predict the fluid flow in a single dentinal tubule by considering the deformation of the dentinal tubules and dentinal fluid. RESULTS Deformation of the pulp chamber was observed before a noticeable temperature change was recorded at the dentine-enamel junction. Tubule deformation leads to changes in fluid flow more rapidly than fluid expansion or contraction. This finding agreed with previously reported experimental observations. An initially high rate of outward fluid flow under cooling was found to correspond to short latency neural responses whilst heating was associated with long latency neural responses. CONCLUSION Rapid fluid flow caused by thermal deformation of dentinal tubules may account for the short latency (<1s) activation of mechano-sensitive receptors after of cooling. Long latency (>10s) neural responses could be associated with the activation of thermo-sensitive receptors.

Gradient Mechanical Properties Facilitate Arabidopsis Trichome as Mechanosensor

It has been reported that Arabidopsis thaliana leaf trichome can act as a mechanosensory switch, transducing mechanical stimuli into physiological signals, mainly through a buckling instability to focus external force (e.g., exerted by insects) on the base of trichome. The material and structural properties of trichomes remain largely unknown in this buckling instability. In this report, we mainly focused on material standpoint to explore the possible mechanism facilitating the buckling instability. We observed that the Youngs modulus of trichome cell wall decreased gradually from branch to the base region of trichome. Interestingly, we also found a corresponding decline of calcium concentration on the trichome cell wall. Results of finite element method (FEM) simulation suggested that such a gradient distribution of Youngs modulus significantly promotes force focusing and buckling instability on the base of trichome. It is indicated that Arabidopsis trichome has developed into an active mechanosensor benefiting from gradient cell wall mechanical properties.

Development of a micro-indentation device for measuring the mechanical properties of soft materials

Abstract Indentation is a simple and nondestructive method to measure the mechanical properties of soft materials, such as hydrogels, elastomers and soft tissues. In this work, we have developed a micro-indentation system with high-precision to measure the mechanical properties of soft materials, where the shear modulus and Poissons ratio of the materials can be obtained by analyzing the load–relaxation curve. We have validated the accuracy and stability of the system by comparing the measured mechanical properties of a polyethylene glycol sample with that obtained from a commercial instrument. The mechanical properties of another typical polydimethylsiloxane sample submerged in heptane are measured by using conical and spherical indenters, respectively. The measured values of shear modulus and Poissons ratio are within a reasonable range.

Kinetic modelling and bifurcation analysis of chemomechanically miniaturized gels under mechanical load

Chemomechanically responsive gels, with great potential applications in the fields of smart structures and biomedicines, present autonomously oscillatory deformation driven by the Belousov-Zhabotinsky chemical reaction. The dynamic behavior of the responsive gels is obviously affected by the external mechanical load. This approach proposed a kinetic model with an ordinary differential equation to describe the oscillatory deformation of the gels under the mechanical load. Then the periodic solutions and phase diagrams of the oscillation are obtained using the improved Runge-Kutta and shooting methods. The results demonstrated that bifurcations are typically existent in the system and the characters of the oscillatory deformation regularly depend on the mechanical load as well as the concentration of reactants and the stoichiometric coefficient of chemical reaction. This development is supposed to promote the practical applications of the chemomechanically responsive gels.Graphical abstract

The protective effects of acupoint gel embedding on rats with myocardial ischemia-reperfusion injury

Aims: Prevention and treatment of myocardial ischemia‐reperfusion (I/R) injury has for many years been a hot topic in treating ischemic heart disease. As one of the most well‐known methods of complementary and alternative medicine, acupuncture has attracted increasing interest in preventing myocardial I/R injury due to its remarkable effectiveness and minimal side effect. However, traditional acupuncture approaches are limited by cumbersome execution, high labor costs and inevitable pain caused by frequent stimulation. Therefore, in this work, we aimed to develop a novel acupoint gel embedding approach and investigated its role in protecting against myocardial I/R injury in rats. Main methods: Gels were embedded at bilateral Neiguan (PC6) points of rats and their protective effects against myocardial I/R injury evaluated in terms of changes in histomorphology, myocardial enzymology, antioxidant capacity, anti‐inflammatory response, and anti‐apoptosis of cells. Key findings: We found that the approach of acupoint gel embedding could significantly reduce myocardial infarcted size, repair pathological changes, mitigate oxidative stress damage and inflammatory response, as well as inhibit apoptosis of cardiomyocytes. Such cardioprotective effects were found to be associated with Notch‐1/Jagged‐1 signaling pathway. Significance: The proposed approach of acupoint gel embedding has advantages in continuous acupoint stimulation, dosing controls, and no side effects in the course of treatment, as well as in reducing the pain caused by frequent acupuncture. It can form an alternative therapy to not only protect against myocardial I/R injury but also hold great potential in treating other diseases in the future.

Intracellular Microfluid Transportation in Fast Growing Pollen Tubes

Fast tip growth of pollen tubes is a process of fundamental importance in sexual plant reproduction. In this chapter, physical models were developed to analyze the hydrodynamics and the advection–diffusion dynamics of fountain streaming in pollen tubes. It is demonstrated that the unique properties of fountain streaming contribute to the fast tip growth of pollen tubes by regulating the gradients of turgor pressure and cell wall materials. Simple experiments confirm that the tip shape and growth rate of pollen tubes are influenced by the changes in turgor pressure gradients as induced by drought stress. Both the analytical and the numerical methods presented in this chapter provide mechanistic insights for the understanding of the sexual reproduction and infertility of flowering plants under normal conditions and drought stress.

Thermal Pain in Teeth: Heat Transfer, Thermomechanics and Ion Transport

Thermal pain in tissues of the body can result from a broad range of stimuli, both direct (e.g., temperature changes) and indirect (e.g., chemical and thermomechanical effects). Heating and cooling stimuli are seemingly similar, in the sense that both are transduced through the same pathway, down to the level of thermally sensitive ion channels in nociceptors. However, the perception induced by them can be quite different. For example, cold foods are known to produce more rapid and sharper pain sensations in teeth than hot foods. These seemingly disparate phenomena can be explained through coupled models of heat transfer, ion transport and thermomechanics. Such models have important implications for a broad range of clinical therapies. We present here one set of such models, and provide as an example their application to a better understanding of thermal pain in teeth.