Browsing by Author "Jin, Tao"
Now showing 1 - 4 of 4
Results Per Page
Sort Options
Item Computational modeling of fibrous biological tissues and bio-inspired materials(2016-09-23) Jin, Tao; Stanciulescu, IlincaMany bio and bio-inspired materials are composed of fiber network structures embedded in ground matrices and can be categorized as fibrous biomaterials. Understanding the structure-function relationship of these materials provides insight into the pathophysiology of various diseases, such as arteriosclerosis, and advances many biomedical applications, such as artificial heart valves. Combining numerical methods with experimental technologies is effective for investigating these relationships. A new computational framework is proposed to simulate the mechanical behavior of fibrous biomaterials. First, the microscopic fiber structure is synthetically generated via a random walk algorithm and incorporated into finite element (FE) simulations based on the embedded fiber approach. The material parameters involved in the generation of these fiber structures have physical or geometric interpretations and can potentially be obtained from experiments. The element residual and stiffness matrix are then derived via a variational approach. Moreover, FE simulations can be easily combined with the Monte Carlo method to consider the material structure randomness and describe the material average behavior. Since the number of degrees of freedom of the discretized system remains unchanged, the proposed framework maintains the computational efficiency of FE simulations while taking into consideration the material microscopic structure. Poly(ethylene glycol) diacrylate (PEGDA) hydrogel is one bio-inspired material used for tissue engineered heart valves. As an example of applying the proposed framework, various factors including pattern ratio, orientation, and waviness can be numerically investigated for their influence on the mechanical behavior of patterned PEGDA hydrogels. Moreover, a (toe-heel-linear) three-region stress-strain relationship typically exhibited by biological tissues is depicted by properly tuning the hydrogel properties. Studying these properties provides input for better hydrogel design. Arterial walls are another example of biological tissues that can effectively use the proposed framework. Structure-function relationships of different arterial wall layers are examined by using layer-specific experimental data. Material structures like fiber dispersion caused by fiber angular distribution and waviness are both considered. Additionally, the material parameters used in the proposed framework can be linked to phenomenological parameters in the homogenized modeling approach. By linking these parameters, it is possible to calculate the phenomenological parameters directly from the quantities measured in experiments.Item Computational modeling of the arterial wall based on layer-specific histological data(Springer, 2016) Jin, Tao; Stanciulescu, IlincaArterial walls typically have a heterogeneous structure with three different layers (intima, media, and adventitia). Each layer can be modeled as a fiber-reinforced material with two families of relatively stiff collagenous fibers symmetrically arranged within an isotropic soft ground matrix. In this paper, we present two different modeling approaches, the embedded fiber (EF) approach and the angular integration (AI) approach, to simulate the anisotropic behavior of individual arterial wall layers involving layer-specific data. The EF approach directly incorporates the microscopic arrangement of fibers that are synthetically generated from a random walk algorithm and captures material anisotropy at the element level of the finite element formulation. The AI approach smears fibers in the ground matrix and treats the material as homogeneous, with material anisotropy introduced at the constitutive level by enhancing the isotropic strain energy with two anisotropic terms. Both approaches include the influence of fiber dispersion introduced by fiber angular distribution (departure of individual fibers from the mean orientation) and take into consideration the dispersion caused by fiber waviness, which has not been previously considered. By comparing the numerical results with the published experimental data of different layers of a human aorta, we show that by using histological data both approaches can successfully capture the anisotropic behavior of individual arterial wall layers. Furthermore, through a comprehensive parametric study, we establish the connections between the AI phenomenological material parameters and the EF parameters having straightforward physical or geometrical interpretations. This study provides valuable insight for the calibration of phenomenological parameters used in the homogenized modeling based on the fiber microscopic arrangement. Moreover, it facilitates a better understanding of individual arterial wall layers, which will eventually advance the study of the structure–function relationship of arterial walls as a whole.Item Direct triplet sensitization of oligothiophene by quantum dots(Royal Society of Chemistry, 2019) Xu, Zihao; Jin, Tao; Huang, Yiming; Mulla, Karimulla; Evangelista, Francesco A.; Egap, Eilaf; Lian, TianquanEffective sensitization of triplet states is essential to many applications, including triplet–triplet annihilation based photon upconversion schemes. This work demonstrates successful triplet sensitization of a CdSe quantum dot (QD)–bound oligothiophene carboxylic acid (T6). Transient absorption spectroscopy provides direct evidence of Dexter-type triplet energy transfer from the QD to the acceptor without populating the singlet excited state or charge transfer intermediates. Analysis of T6 concentration dependent triplet formation kinetics shows that the intrinsic triplet energy transfer rate in 1[thin space (1/6-em)]:[thin space (1/6-em)]1 QD–T6 complexes is 0.077 ns−1 and the apparent transfer rate and efficiency can be improved by increasing the acceptor binding strength. This work demonstrates a new class of triplet acceptor molecules for QD-based upconversion systems that are more stable and tunable than the extensively studied polyacenes.Item Numerical investigation of the influence of pattern topology on the mechanical behavior of PEGDA hydrogels(Elsevier, 2017) Jin, Tao; Stanciulescu, IlincaPoly(ethylene glycol) diacrylate (PEGDA) hydrogels can be potentially used as scaffold material for tissue engineered heart valves (TEHVs) due to their good biocompatibility and biomechanical tunability. The photolithographic patterning technique is an effective approach to pattern PEGDA hydrogels to mimic the mechanical behavior of native biological tissues that are intrinsically anisotropic. The material properties of patterned PEGDA hydrogels largely depend on the pattern topology. In this paper, we adopt a newly proposed computational framework for fibrous biomaterials to numerically investigate the influence of pattern topology, including pattern ratio, orientation and waviness, on the mechanical behavior of patterned PEGDA hydrogels. The material parameters for the base hydrogel and the pattern stripes are directly calibrated from published experimental data. Several experimental observations reported in the literature are captured in the simulation, including the nonlinear relationship between pattern ratio and material linear modulus, and the decrease of material anisotropy when pattern ratio increases. We further numerically demonstrate that a three-region (toe-heel-linear) stress–strain relationship typically exhibited by biological tissues can be obtained by tuning the pattern waviness and the relative stiffness between the base hydrogel and pattern stripes. The numerical strategy and simulation results presented here can provide helpful guidance to optimize pattern design of PEGDA hydrogels toward the targeted material mechanical properties, therefore advance the development of TEHVs.