Tuning the Poisson's Ratio of Biomaterials for Investigating Cellular Response

Cells sense and respond to mechanical forces, regardless of whether the source is from a normal tissue matrix, an adjacent cell or a synthetic substrate. In recent years, cell response to surface rigidity has been extensively studied by modulating the elastic modulus of poly(ethylene glycol) (PEG)‐based hydrogels. In the context of biomaterials, Poisson's ratio, another fundamental material property parameter has not been explored, primarily because of challenges involved in tuning the Poisson's ratio in biological scaffolds. Two‐photon polymerization is used to fabricate suspended web structures that exhibit positive and negative Poisson's ratio (NPR), based on analytical models. NPR webs demonstrate biaxial expansion/compression behavior, as one or multiple cells apply local forces and move the structures. Unusual cell division on NPR structures is also demonstrated. This methodology can be used to tune the Poisson's ratio of several photocurable biomaterials and could have potential implications in the field of mechanobiology.     

Synthesis and Evaluation of a Molecularly Imprinted Polymer for Solid Phase Extraction of Ethopabate from Chicken Tissue

In this paper the development and evaluation of a molecularly imprinted polymer (MIP) for ethopabate is described. Ethopabate (ETP), 4-acetamido-2-ethoxybenzoic acid methyl ester, is one of the antibiotics which is used as coccidiostat in poultry feeds. In the present study, two widely used functional monomers, methacrylic acid (MAA) and 4-vinylpyridine (4-VP) were compared theoretically and experimentally as the candidates for MIP preparation. Hyperchem software was employed to estimate binding energies between ETP and functional monomers and batch rebinding experiments were performed to study the binding characteristics of the polymers. The results showed that MAA is a better functional monomer to prepare MIP. UV/Vis and NMR spectroscopy were used as two common tools to study the interactions between ETP and MAA in the pre-polymerization mixture. Liquid chromatography experiments showed that the prepared MIP has recognition capability toward ETP in comparison with other structurally related compounds. The ETP-imprinted polymer was further applied for selective solid phase extraction (SPE) of ETP from a chicken tissue sample. The extraction yield of ETP was found to be quantitative (87 ± 3%) and the LOD and LOQ based on 3 and 10 times of the noise of HPLC profile were 0.05 and 0.32 ng ml^?1, respectively. It was confirmed that the binding ability of the prepared MIP for ETP was essentially sufficient in the presence of other compounds coexisting in tissue sample. Therefore, as a selective and efficient solid phase material, ETP-imprinted polymer has a high potential application in the analysis of residues of this antibiotic in chicken tissue samples.     

Synthesis and degradation of agar‐carbomer based hydrogels for tissue engineering applications

Hydrogels studied in this investigation, synthesized starting from agarose and Carbomer 974P, were chosen for their potential use in tissue engineering. The strong ability of hydrogels to mimic living tissues should be complemented with optimized degradation time profiles: a critical property for biomaterials but essential for the integration with target tissue. In this study, chosen hydrogels were characterized both from a rheological and a structural point of view before studying the chemistry of their degradation, which was performed by several analysis: infrared bond response [Fourier transform infrared (FT‐IR)], calorimetry [differential scanning Calorimetry (DSC)], and % mass loss. Degradation behaviors of Agar‐Carbomer hydrogels with different degrees of crosslinkers were evaluated monitoring peak shifts and thermal property changes. It was found that the amount of crosslinks heavily affect the time and the magnitude related to the process. The results indicate that the degradation rates of Agar‐Carbomer hydrogels can be controlled and tuned to adapt the hydrogel degradation kinetics for different cell housing and drug delivery applications. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Engraftment of Prevascularized,Tissue Engineered Constructs in a Novel Rabbit Segmental Bone Defect Model

The gold standard treatment of large segmental bone defects is autologous bone transfer, which suffers from low availability and additional morbidity. Tissue engineered bone able to engraft orthotopically and a suitable animal model for pre-clinical testing are direly needed. This study aimed to evaluate engraftment of tissue-engineered bone with different prevascularization strategies in a novel segmental defect model in the rabbit humerus. Decellularized bone matrix (Tutobone) seeded with bone marrow mesenchymal stromal cells was used directly orthotopically or combined with a vessel and inserted immediately (1-step) or only after six weeks of subcutaneous “incubation” (2-step). After 12 weeks, histological and radiological assessment was performed. Variable callus formation was observed. No bone formation or remodeling of the graft through TRAP positive osteoclasts could be detected. Instead, a variable amount of necrotic tissue formed. Although necrotic area correlated significantly with amount of vessels and the 2-step strategy had significantly more vessels than the 1-step strategy, no significant reduction of necrotic area was found. In conclusion, the animal model developed here represents a highly challenging situation, for which a suitable engineered bone graft with better prevascularization, better resorbability and higher osteogenicity has yet to be developed.     

Oxidative Stress in Obesity: A Critical Component in Human Diseases

Obesity, a social problem worldwide, is characterized by an increase in body weight that results in excessive fat accumulation. Obesity is a major cause of morbidity and mortality and leads to several diseases, including metabolic syndrome, diabetes mellitus, cardiovascular, fatty liver diseases, and cancer. Growing evidence allows us to understand the critical role of adipose tissue in controlling the physic-pathological mechanisms of obesity and related comorbidities. Recently, adipose tissue, especially in the visceral compartment, has been considered not only as a simple energy depository tissue, but also as an active endocrine organ releasing a variety of biologically active molecules known as adipocytokines or adipokines. Based on the complex interplay between adipokines, obesity is also characterized by chronic low grade inflammation with permanently increased oxidative stress (OS). Over-expression of oxidative stress damages cellular structures together with under-production of anti-oxidant mechanisms, leading to the development of obesity-related complications. The aim of this review is to summarize what is known in the relationship between OS in obesity and obesity-related diseases.     

A parallel adaptive finite-element package based on ALBERTA

ALBERTA, a sequential adaptive finite-element toolbox, is being used widely in the fields of scientific and engineering computation, especially in the numerical simulation of electromagnetics. But the nature of sequentiality has become the bottle-neck while solving large scale problems. So we develop a parallel adaptive finite-element package based on ALBERTA, using ParMETIS and PETSc. The package is able to deal with any problem that ALBERT solved. Furthermore, it is suitable for distributed memory parallel computers including PC clusters. In this paper, we present the implementation of the package in detail, and address several key algorithms and strategies of parallelization. Finally, some numerical experiments are given to show the performance and scalability of our package.     

Influence of moving heat source on skin tissue in the context of two-temperature memory-dependent heat transport law

Abstract

Modeling and understanding heat transport and temperature variations within biological tissues and body organs are key issues in medical thermal therapeutic applications, such as hyperthermia cancer treatment. In the present analysis, the bioheat equation is studied in the context of memory responses. The heat transport equation for this problem involving the memory-dependent derivative (MDD) on a slipping interval in the context of three-phase (3P) lag model under two-temperature theory is formulated and is then used to study the thermal damage within the skin tissue during the thermal therapy. Laplace transform technique is implemented to solve the governing equations. The influences of the MDD and moving heat source velocity on the temperature of skin tissues are precisely investigated. The numerical inversion of the Laplace transform is carried out using Zakian method. The numerical outcomes of temperatures are represented graphically. Excellent predictive capability is demonstrated for identification of an appropriate procedure to select different kernel functions to reach effective heating in hyperthermia treatment. Significant effect of thermal therapy is reported due to the effect of delay time and the velocity of moving heat source as well.     

Fabrication of PLGA Based Tissue Engineering Scaffolds via Photocuring and Salt Leaching Techniques

The authors aimed to prepare UV curable porous scaffolds via photo curing and salt leaching techniques. A poly (α -hydroxy ester) based urethane acrylate oligomer was synthesized and a photocurable acrylic based formulation was prepared. Salt particles were introduced to the formulation, which was then poured into cylindrical molds and cured under UV irradiation. Porous scaffolds were obtained after salt leaching. 3T3 cells seeded on the UV cured scaffolds and it was found that cells were well spread on the collagen modified scaffold surface. It can be concluded that the scaffolds provided an effective physical support that allows cell adhesion and proliferation.     

Solvent-Free Fabrication of Tissue Engineering Scaffolds With Immiscible Polymer Blends

A completely organic solvent-free fabrication method is developed for tissue engineering scaffolds by gas foaming of immiscible polylactic acid (PLA) and sucrose blends, followed by water leaching. PLA scaffolds with above 90% porosity and 25–200 µm pore size were fabricated. The pore size and porosity was controlled with process parameters including extrusion temperature and foaming process parameters. Dynamic mechanical analysis showed that the extrusion temperature could be used to control the scaffold strength. Both unfoamed and foamed scaffolds were used to culture glioblastoma (GBM) cells M059 K. The results showed that the cells grew better in the foamed PLA scaffolds. The method presented in the paper is versatile and can be used to fabricate tissue engineering scaffolds without any residual organic solvents.