Morphological effects of porous poly-D,L-lactic acid/hydroxyapatite scaffolds produced by supercritical CO2 foaming on their mechanical performance

A novel supercritical CO2 foaming technique was used to fabricate scaffolds of controllable morphology and mechanical properties, with the potential to tailor the scaffolds to specific tissue engineering applications. Biodegradable scaffolds are widely used as temporary supportive structures for bone regeneration. The scaffolds must provide a sufficient mechanical support while allowing cell attachment and growth as well as metabolic activities. In this study, supercritical CO2 foaming was used to prepare fully interconnected porous scaffolds of poly-D,L-lactic acid and poly-D,L-lactic acid/hydroxyapatite. The morphological, mechanical and cell behaviours of the scaffolds were measured to examine the effect of hydroxyapatite on these properties. These scaffolds showed an average porosity in the range of 86%–95%, an average pore diameter of 229–347 µm and an average pore interconnection of 103–207 µm. The measured porosity, pore diameter, and interconnection size are suitable for cancellous bone regeneration. Compressive strength and modulus of up to 36.03 ± 5.90 and 37.97 ± 6.84 MPa were measured for the produced porous scaffolds of various compositions. The mechanical properties presented an improvement with the addition of hydroxyapatite to the structure. The relationship between morphological and mechanical properties was investigated. The matrices with different compositions were seeded with bone cells, and all the matrices showed a high cell viability and biocompatibility. The number of cells attached on the matrices slightly increased with the addition of hydroxyapatite indicating that hydroxyapatite improves the biocompatibility and proliferation of the scaffolds. The produced poly-D,L-lactic acid/hydroxyapatite scaffolds in this study showed a potential to be used as bone graft substitutes

Effect of initial relative density on the post-liquefaction behaviour of sand

Understanding the behaviour of soils under cyclic/dynamic loading has been one of the challenging topics in geotechnical engineering. The response of liquefiable soils has been well studied however, the post liquefaction behaviour of sands needs better understanding. In this paper, the post liquefaction behaviour of sands is investigated through several series of multi-stage soil element tests using a cyclic Triaxial apparatus. Four types of sand were used where the sands were first liquefied and then monotonically sheared to obtain stress-strain curves. Results of the tests indicate that the stress-strain behaviour of sand in post liquefaction phase can be modelled as a bi-linear curve using three parameters: the initial shear modulus ( ), critical state shear modulus ( ), and post-dilation shear strain ( ) which is the shear strain at the onset of dilation. It was found that the three parameters are dependent on the initial relative density of sands. Furthermore, it was observed that with the increase in the relative density both and increase and decreases. The practical application of the results is to generate p-y curves for liquefied soil

A practical method for construction of p-y curves for liquefiable soils

In practice, analysis of laterally loaded piles is often carried out using a “Beam on Non-linear Winkler Foundation method” whereby the lateral pile-soil interaction is modelled as a set of non-linear springs (also known as p y curves). During seismic liquefaction, the saturated sandy soil changes its state from a solid to a thick fluid like material (solid suspension), which in turn alters the shape of the p-y curve. Typically, p-y curves for non-liquefied soil looks like a convex curve with initial stiff slope which reduces with pile-soil relative displacement (y). However, recent research conclusively showed that p-y curve for liquefied soil has a different shape, i.e., upward concave with near-zero initial stiffness (due to the loss of particle to particle contact) up to a certain displacement (y), beyond which the stiffness increases due to reengaging of the sand particles. This paper presents a practical method for construction of the newly proposed p-y curves along with an example

Experimental study of roll-formed aluminium lipped channel beams in shear

Use of aluminium sections as primary load bearing members has recently expanded considerably in the building industry. Aluminium as a new constructional material has several advantages in building structures including corrosion resistance, durability, high strength-to-weight ratio, reduced cost of transportation and ease of erection and fabrication. The popularity of aluminium structures has attracted attention regarding the efficiency and design of many sections, and roll-formed lipped channel beam (LCB) is one of these commonly used sections. However, aluminium LCBs are prone to shear buckling failures due to its increased web slenderness and low elastic modulus compared to steel. Hence an experimental study was conducted to investigate the shear behaviour of LCBs and to verify the current design rules to accurately predict the shear strengths. Shear tests have been conducted using ten different generally available roll-formed aluminium LCBs. The test sections were loaded at mid-span at the shear centre until failure. The results obtained from the tests were then compared with the predictions using the current shear design rules in the Australian/New Zealand standards and Eurocodes for both aluminium structures and cold-formed steel structures as their shear behaviour are quite similar. This paper presents the details and results of this experimental study and comparison with shear design rules based on current design rules