An ideal tissue engineering scaffold must be designed from a polymer with an adequate degradation rate. The processing technique must allow for the preparation of 3-D scaffolds with controlled porosity and adequate pore sizes, as well as tissue matching mechanical properties and an appropriate biological response. This communication revises recent work that has been developed in our laboratories with the aim of producing 3-D polymeric structures (from starch-based blends) with adequate properties to be used as scaffolds for bone tissue engineering applications. Several processing methodologies were originally developed and optimised. Some of these methodologies were based on conventional melt-based processing routes, such as extrusion using blowing agents (BA) and compression moulding (combined with particulate leaching). Other developed technologies included solvent casting and particle leaching and an innovative in situ polymerization method. By means of using the described methodologies, it is possible to tailor the properties of the different scaffolds, namely their degradation, morphology and mechanical properties, for several applications in tissue engineering. Furthermore, the processing methodologies (including the blowing agents used in the melt-based technologies) described above do not affect the biocompatible behaviour of starch-based polymers. Therefore, scaffolds obtained from these materials by means of using one of the described methodologies may constitute an important alternative to the materials currently used in tissue engineering. D
The properties of moulded plastic products are dependent on the processing technology used in their manufacture and in particular on the structural morphology resulting from the thermomechanical environment imposed on the melt. This paper investigates these phenomena, through the moulding of polyethylene using different methods and the subsequent testing of the mechanical properties of the products. A unified approach is presented to describe the behaviour of the products based on knowledge of the thermomechanical conditions imposed during processing. A linear medium density polyethylene was processed using rotational moulding, compression moulding, and injection moulding in order to achieve different thermomechanical conditions (i.e. shear rates and cooling rates). The processing conditions used were typical of those in common use in the respective industries. The moulded parts were mechanically tested in order to determine the tensile, flexural, and impact properties. These measurements were performed both on samples corresponding to the entire thickness of the moulding and on slices taken from across the section of the mouldings. The mechanical tests were complemented with density measurements, to assess the crystallinity across the wall thickness, and polarised light microscopy, to characterise the mouldings' microstructure. It is shown that the type of dependence of the mechanical performance on the thermomechanical conditions imposed during processing is similar for the three moulding techniques used.
The properties of moulded plastic products are dependent on the processing technology used in their manufacture and in particular on the structural morphology resulting from the thermomechanical environment imposed on the melt. This paper presents a unified approach to describe the behaviour of the products based on knowledge of the thermomechanical conditions imposed during processing. A linear medium density polyethylene has been processed using rotational moulding, compression moulding, and injection moulding in order to achieve different thermomechanical conditions (i.e. shear rates and cooling rates). The processing conditions used were typical of those in common use in the respective industries. The moulding parts were mechanically tested to determine the tensile, flexural, and impact properties. These measurements were performed both on samples corresponding to the entire thickness of the moulding and on slices taken from across the section of the mouldings. On the basis of these measurements, two models were developed. One is based on laminate theory, in which, from a knowledge of the mechanical properties of the individual layers through the wall thickness, it is possible to predict the tensile and flexural properties of the full thickness moulding. The other is an empirical model that predicts the tensile modulus of a plastic part as a function of two thermomechanical indices. It is shown that the type of dependence of the mechanical performance on the thermomechanical conditions imposed during processing is similar for the three moulding techniques used. A good agreement is achieved between the experimental data and those predicted by the thermomechanical model. It is also shown that via the combined use of the thermomechanical indices concept and the laminate analysis, good predictions of the mechanical behaviour of plastic mouldings with complex microstructures can be achieved. It is proposed that this approach could provide a very valuable addition to existing melt flow simulation packages. This would enable not only processing conditions to be optimised but the properties of the end product could be predicted.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations鈥揷itations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.