Journal of Biomimetics, Biomaterials and Tissue Engineering Vol. 3

Abstract: The mechanical model of a number of biological tissues is a membrane, i.e., a sheetlike structure with small thickness, where deformation and stress can be described locally in two dimensions. Many bio-membranes, particularly if subjected to large mechanical loads, present a fibrous structure, with stiff fibers, sometimes with preferential orientations, embedded in a more compliant matrix. Among this tissues are, e.g., the arterial walls, the amniotic membrane, and the skin. The stiff fibers, typically made of collagen, are initially wrinkled and they follow the deformation of the embedding matrix without contributing to the mechanical response until they are fully distended. In this paper, the response of a fibrous membrane is described in the framework of hyperelasticity, with aim to the implementation in an existing finite element code. A micro-mechanical recruitment model, based on the statistical distribution of the activation stretch of the collagen fibers is introduced, leading to the definition of a simple form of the strain-energy function, depending on physically well-defined parameters. After some validation tests performed in homogeneous strain conditions, an application to the study of the stress field around circular holes in large deformation is presented, showing the capabilities of the proposed model.

Abstract: Following a polyelectrolytical complex reaction, alginate/poly(L-Arginine)-chitosan ternary complex microcapsules were prepared by coating poly(L-Arginine) and chitosan as membrane materials on calcium alginate beads, which were produced by a high-voltage electrostatic droplet generator. The influences on the diameter and uniformity of the calcium alginate beads were studied, and the optimum operating parameters were selected to produce microcapsules. The in vitro drug release behavior and pH stimuli-response of alginate/poly(L-Arginine)-chitosan ternary complex microcapsules were investigated. In comparison with alginate/chitosan microcapsules, alginate/poly(L-Arginine) microcapsules and their corresponding double-membrane microcapsules, alginate/poly(L-Arginine)-chitosan microcapsules released the macromolecular drug in a more sustained and stable way. It was found that they released 85.7% of the bovine erythrocytes hemoglobin (Hb) in 85 hours by approximate first-order kinetics in pH 6.8 PBS. While in a pH 1.0 HCl solution, only 9.6 % of the Hb was released in the first half hour and then the drug release shifted to a flat stage, which indicated that the alginate/poly(L-Arginine)-chitosan microcapsules possessed a pH stimuli-response property. The results suggest that the alginate/poly(L-Arginine)-chitosan ternary complex microcapsules might be a potential colon-targeted drug delivery system for the encapsulation of proteins.

Abstract: Functionally graded materials (FGMs) can be found naturally in many biological structures, for example bamboo and the mollusc shell. They are defined as having a compositional or microstructural gradient, for example the gradation in fibre content in bamboo stems. A continuous bulk functionally graded material has the potential to be an ideal orthopaedic implant for load bearing applications. Due to the fabrication complexities involved in the production of these continuous bulk functionally graded materials, commercialisation and fabrication are still proving to be a challenge to researchers worldwide. This paper presents an overview of the redesigned novel commercially viable process known as the Impeller-Dry-Blending (IDB) process. Results presented in this paper of fabricated functionally graded materials illustrate the potential of IDB to produce continuous bulk functionally graded materials consisting of either compositional or porosity concentration changes. The successful fabrication of these continuous bulk functionally graded materials at such a low cost clearly demonstrates the commercial viability of the IDB process.

Abstract: With new applications in the area of diagnostics, drug discovery and genetics, the need for Biological Micro-Electro-Mechanical Systems (BioMEMS) has increased tremendously in the last decade. Especially, surface stress-based BioMEMS has been investigated extensively in the recently years. In this paper, a new BioMEMS is proposed, which can be used to detect cells. It consists of microfluidics, square membrane and a fiber optic interferometer. The square membrane as the crucial and sensitive part includes three layers, self-assembled monolayer (SAM), gold and substrate material. Based on the BioMEMS, some fundamental study has been done, especially for the membrane due to its crucial role in the whole system. The finite element (FE) method has been used to study the membrane with different substrates. By the fundamental study, some important conclusions have been acquired: (1) The square membrane will reach maximal deflection at different ratio values (P: membrane size) to different substrates; (2) To a certain substrate, such as PDMS, the ratio making the membrane reach maximal deflection is different to dissimilar PDMS layer thickness; (3) If young’s modulus (E) of the substrate is too small, separation may happen between the gold layer and substrate layer when the gold size becomes smaller.

Abstract: There has been much recent activity in the research area of nanoparticles and nanocrystalline materials, in many fields of science and technology. This is due to their outstanding and unique physical, mechanical, chemical and biological characteristics. Recent developments in biomineralization have demonstrated that nano-sized particles play an important role in the formation of the hard tissues of animals. It is well established that the basic inorganic building blocks of bones and teeth of mammals are nano-sized and nanocrystalline calcium orthophosphates (in the form of apatites) of a biological origin. In mammals, tens to hundreds of nanocrystals of biological apatite are found to combine into self-assembled structures under the control of bio-organic matrixes. It was also confirmed experimentally that the structure of both dental enamel and bones could be mimicked by an oriented aggregation of nano-sized calcium orthophosphates, determined by the biomolecules. The application and prospective use of nano-sized and nanocrystalline calcium orthophosphates for clinical repair of damaged bones and teeth are also known. For example, a greater viability and a better proliferation of various cells were detected on smaller crystals of calcium orthophosphates. Furthermore, studies revealed that the differentiation of various cells was promoted by nano-sized calcium orthophosphates. Thus, the nano-sized and nanocrystalline forms of calcium orthophosphates have the potential to revolutionize the field of hard tissue engineering, in areas ranging from bone repair and augmentation to controlled drug delivery devices. This paper reviews the current state of knowledge and recent developments of various nano-sized and nanocrystalline calcium orthophosphates, covering topics from the synthesis and characterization to biomedical and clinical applications. This review also provides possible directions of future research and development.

Abstract: In recent years, research into three-dimensional (3-D) scaffolds for tissue engineering has become an important topic. To avoid biological rejection, there are many biocompatible materials being developed for in vitro cultivation of autologous cells for implantation into the human body. The 3-D structures of scaffolds are not easily observed using traditional optical or electron microscopes, which only allow examination of the surfaces of samples or ultra thin films, and often require complicated pre-treating processes. The high-brilliance synchrotron radiation (SR) hard X-ray is an emerging technique to acquire tomography. This study involves the successful reconstruction of 3-D images and the animation of the structure of a collagen scaffold. The images were obtained using synchrotron radiation hard X-ray images, which eliminates the need for embedding and microtoming. SR hard X-ray imaging is a non-destructive technique, which has demonstrated a high spatial resolution and transmission, enabling the morphology of osteoblasts adhered on the inner surfaces of the collagen scaffolds to be captured. It is a convenient facility to obtain 3-D tomography images for biomaterial studies. This is the first study to observe the 3-D structures of collagen scaffolds and aquire detailed images of osteoblast attachment on the scaffold, by utilization of third-generation SR hard X-ray radiography.