Mechanical and biological characterization of a porous poly-L-lactic acid-co-ε-caprolactone scaffold for tissue engineering

This article presents a method for making highly porous biodegradable scaffold that may ultimately be used for tissue engineering. Poly(L-lactic-co-1-caprolactone) acid (70:30) (PLCL) scaffold was produced using the solvent casting/leaching out method, which entails dissolving the polymer and adding a porogen that is then leached out by immersing the scaffold in distillated water. Tensile tests were performed for three types of scaffolds, namely pre-wetted, dried, and UV-irradiated scaffolds and their mechanical properties were measured. The prewetted PLCL scaffold possessed a modulus of elasticity 0.92+0.09 MPa, a tensile strength of 0.12+0.03 MPa and an ultimate strain of 23+5.3%. No significant differences in the modulus elasticity, tensile strength, nor ultimate strain were found between the pre-wetted, dried, and UV irradiated scaffolds. The PLCL scaffold was seeded by human fibroblasts in order to evaluate its biocompatibility by Alamar bluew assays. After 10 days of culture, the scaffolds showed good biocompatibility and allowed cell proliferation. However, the fibroblasts stayed essentially at the surface. This study shows the possibility to use the PLCL scaffold in dynamic mechanical conditions for tissue engineering

Aligned poly(L-lactic-co-ε-caprolactone) electrospun microfibers and knitted structure: a novel composite scaffold for ligament tissue engineering

We developed a novel technique involving knitting and electrospinning to fabricate a composite scaffold for ligament tissue engineering. Knitted structures were coated with poly(L-lactic-co-e-caprolactone) (PLCL) and then placed onto a rotating cylinder and a PLCL solution was electrospun onto the structure. Highly aligned 2-μm-diameter microfibers covered the space between the stitches and adhered to the knitted scaffolds. The stress–strain tensile curves exhibited an initial toe region similar to the tensile behavior of ligaments. Composite scaffolds had an elastic modulus (150 ± 14 MPa) similar to the modulus of human ligaments. Biological evaluation showed that cells proliferated on the composite scaffolds and they spontaneously orientated along the direction of microfiber alignment. The microfiber architecture also induced a high level of extracellular matrix secretion, which was characterized by immunostaining. We found that cells produced collagen type I and type III, two main components found in ligaments. After 14 days of culture, collagen type III started to form a fibrous network. We fabricated a composite scaffold having the mechanical properties of the knitted structure and the morphological properties of the aligned microfibers. It is difficult to seed a highly macroporous structure with cells, however the technique we developed enabled an easy cell seeding due to presence of the microfiber layer. Therefore, these scaffolds presented attractive properties for a future use in bioreactors for ligament tissue engineering.

A poly(lactic-co-glycolic acid) knitted scaffold for tendon tissue engineering: an in vitro and in vivo study

We have designed a composite scaffold for potential use in tendon or ligament tissue engineering. The composite scaffold was made of a cellularized alginate gel that encapsulated a knitted structure. Our hypothesis was that the alginate would act as a cell carrier and deliver cells to the injury site while the knitted structure would provide mechanical strength to the composite construct. The mechanical behaviour and the degradation profile of the poly(lactic-co-glycolic acid) knitted scaffolds were evaluated. We found that our scaffolds had an elastic modulus of 750 MPa and that they lost their physical integrity within 7 weeks of in vitro incubation. Autologous rabbit mesenchymal stem cell seeded composite scaffolds were implanted in a 1-cm-long defect created in the rabbit tendon, and the biomechanical properties and the morphology of the regenerated tissues were evaluated after 13 weeks. The regenerated tendons presented higher normalized elastic modulus of (60%) when compared with naturally healed tendons (40%). The histological study showed a higher cell density and vascularization in the regenerated tendons.

A novel bioreactor for ligament tissue engineering

Bioreactors are defined as devices in which biological and/or biochemical processes develop under closely monitored and tightly controlled environmental and operating conditions (e.g. pH, temperature, mechanical conditions, nutrient supply and waste removal). In functional tissue engineering of musculoskeletal tissues, a bioreactor capable of controlling dynamic loading plays a determinant role. It has been shown that mechanical stretching promotes the expression of type I and III collagens, fibronectin, tenascin-C in cultured ligament fibroblasts (J.C.-H. Goh et al., Tissue Eng. 9 (2003), S31) and that human bone marrow mesenchymal stem cells (hBMMSC) – even in the absence of biochemical regulators – could be induced to differentiate into ligament-like fibroblast by the application of physiologically relevant cyclic strains (G. Vunjak-Novakovic et al., Ann. Rev. Biomed. Eng. 6 (2004), 131; H.A. Awad et al., Tissue Eng. 5 (1999), 267; R.G. Young et al., J. Orthop. Res. 16 (1998), 406). Different bioreactors are commercially available but they are too generic to be used for a given tissue, each tissue showing specific mechanical loading properties. In the case of ligament tissue engineering, the design of a bioreactor is still an open question. Our group proposes a bioreactor allowing cyclic traction–torsion on a scaffold seeded with stem cells.

Electrospinning and crosslinking of low-molecular-weight poly(trimethylene carbonate-co-L-lactide) as an elastomeric scaffold for vascular engineering

The growth of suitable tissue to replace natural blood vessels requires a degradable scaffold material that is processable into porous structures with appropriate mechanical and cell growth properties. This study investigates the fabrication of degradable, crosslinkable prepolymers of l-lactide-co-trimethylene carbonate into porous scaffolds by electrospinning. After crosslinking by γ-radiation, dimensionally stable scaffolds were obtained with up to 56% trimethylene carbonate incorporation. The fibrous mats showed Young’s moduli closely matching human arteries (0.4–0.8 MPa). Repeated cyclic extension yielded negligible change in mechanical properties, demonstrating the potential for use under dynamic physiological conditions. The scaffolds remained elastic and resilient at 30% strain after 84 days of degradation in phosphate buffer, while the modulus and ultimate stress and strain progressively decreased. The electrospun mats are mechanically superior to solid films of the same materials. In vitro, human mesenchymal stem cells adhered to and readily proliferated on the three-dimensional fiber network, demonstrating that these polymers may find use in growing artificial blood vessels in vivo.

Cross-linked poly(trimethylene carbonate-co-L-lactide) as a biodegradable, elastomeric scaffold for vascular engineering applications

A series of copolymers of trimethylene carbonate (TMC) and l-lactide (LLA) were synthesized and evaluated as scaffolds for the production of artificial blood vessels. The polymers were end-functionalized with acrylate, cast into films, and cross-linked using UV light. The mechanical, degradation, and biocompatibility properties were evaluated. High TMC polymers showed mechanical properties comparable to human arteries (Young’s moduli of 1.2–1.8 MPa and high elasticity with repeated cycling at 10% strain). Over 84 days degradation in PBS, the modulus and material strength decreased gradually. The polymers were nontoxic and showed good cell adhesion and proliferation over 7 days using human mesenchymal stem cells. When implanted into the rat peritoneal cavity, the polymers elicited formation of tissue capsules composed of myofibroblasts, resembling immature vascular smooth muscle cells. Thus, these polymers showed properties which were tunable and favorable for vascular tissue engineering, specifically, the growth of artificial blood vessels in vivo.

Zeta-potential and morphology of electrospun nano- and microfibers from biopolymers and their blends used as scaffolds in tissue engineering

Electrostatic spinning or electrospinning is a fiber spinning technique driven by a high-voltage electric field that produces fibers with diameters in a submicrometer to nanometer range.1 Nanofibers are typical one-dimensional colloidal objects with an increased tensile strength, whose length can achieve a few kilometers and the specific surface area can be 100 m2 g–1 or higher.2 Nano- and microfibers from biocompatible polymers and biopolymers have received much attention in medical applications3 including biomedical structural elements (scaffolding used in tissue engineering,2,4–6 wound dressing,7 artificial organs and vascular grafts8), drug and vaccine delivery,9–11 protective shields in speciality fabrics, multifunctional membranes, etc. Other applications concern superhydrophobic coatings,12 encapsulation of solid materials,13 filter media for submicron particles in separation industry, composite reinforcement and structures for nano-electronic machines.

Surrogate indicators for assessing community resilience

The importance of community resilience to natural disasters is being increasingly recognised. This paper presents an approach for the development of surrogate indicators for comprehensive assessment of community resilience, which is crucial in the context of predicted increase in natural disasters resulting from extreme weather events due to climate change. The use of surrogate indicators is advocated because a comprehensive assessment of community resilience across various thematic areas and associated key areas requires the measurement of a large number of resilience indicators which is not always feasible due to time and resource constraints, To overcome this, researchers tend to use secondary data sources, which are easily available but not always reliable. This highlights the need for surrogate indicators that are easy to measure from reliable primary data sources and are adequate to capture the resilience of a community. Firstly, the paper discusses the two approaches for defining and conceptualising community resilience and the need to account for the complex interrelationships between thematic areas, key areas and resilience indicators and their implications for research. Secondly, a comprehensive framework for the assessment of community resilience is proposed and the difficulties associated with the measurement of overall resilience of the community are discussed. Thirdly, the paper explains a two-step approach to develop surrogate indicators highlighting the necessity and challenges associated with it. Finally, the proposed approach is elaborated with a simple example for better understanding.

Changes to airborne pollen counts across Europe

A progressive global increase in the burden of allergic diseases has affected the industrialized world over the last half century and has been reported in the literature. The clinical evidence reveals a general increase in both incidence and prevalence of respiratory diseases, such as allergic rhinitis (common hay fever) and asthma. Such phenomena may be related not only to air pollution and changes in lifestyle, but also to an actual increase in airborne quantities of allergenic pollen. Experimental enhancements of carbon dioxide (CO) have demonstrated changes in pollen amount and allergenicity, but this has rarely been shown in the wider environment. The present analysis of a continental-scale pollen data set reveals an increasing trend in the yearly amount of airborne pollen for many taxa in Europe, which is more pronounced in urban than semi-rural/rural areas. Climate change may contribute to these changes, however increased temperatures do not appear to be a major influencing factor. Instead, we suggest the anthropogenic rise of atmospheric CO levels may be influential.

Impact of rain on daily bus ridership : a Brisbane case study

Weather is one of the most significant elements affecting transit ridership on a daily basis. Until now, there has been limited focus in the literature investigating this issue. Adverse weather conditions impact travellers in choosing travel mode and route, travel schedule, and trip making itself. This paper explores the relationship between adverse weather and transit ridership by analysing the correlation between daily bus ridership and daily precipitation for a three-year period from 2010 to 2012. It is observed from the analysis that wet weather has varying impacts on daily bus ridership. Overall, rainfall negatively affects the daily bus ridership in this region. Morning peak-hours and weekend ridership were found more sensitive to rain than entire day’s ridership and weekdays. The study also found a negative correlation between the morning-peak precipitation level and the daily bus ridership, which suggests that a small amount of morning peak-hours rain reduces a significant amount bus ridership for the whole day. The analysis also confirms that summer rain has the most significant effect on ridership compared with the other three seasons. The study findings will contribute to enhancing the fundamental understanding of traveller behaviours, particularly mode choice behaviour under adverse weather conditions.

Innovative methods for assessing viability of diversification into new markets : a study based on an engineering consultancy

This study resulted in the development of a decision making tool for engineering consultancies looking to diversify into new markets. It reviewed existing decision tools used by contractor's entering new markets to develop a bespoke tool for engineering consultants to establish more rigor around the decision making process rather than rely purely on the intuition of company executives. The tool can be used for developing medium and long term company strategies or as a quick and efficient way to assess the viability of new market opportunities when they arise. A combination of Delphi and Analytical Hierarchy Process was selected as the basis of the decision theory.

Vocational education in science, technology, engineering and maths (STEM) : Curriculum innovation through school industry partnerships

Governments have recognised that the technological trades rely on knowledge embedded traditionally in science, technology, engineering and mathematics (STEM) disciplines. However, there is substantial evidence that students are turning away from these subjects in schools because the school curriculum is seen as irrelevant, with clear implications for not just vocational education but also higher education. In this paper, we report preliminary findings on the development of two curricula that attempt to integrate science and mathematics with workplace knowledge and practices. We argue that these curricula provide educational opportunities for students to pursue their preferred career pathways. These curricula were co-developed by industry and educational personnel across three industry sectors, namely, mining industry, aerospace and wine tourism. The aim was to provide knowledge appropriate for students moving from school to the workplace as trade apprentices in the respective industries. The analysis of curriculum and associated policy documents reveals that the curricula adopt applied learning orientations through teaching strategies and assessment practices which focus on practical skills. However, although key theoretical science and maths concepts have been well incorporated, the extent to which knowledge deriving from workplace practices is included varies across the curricula. The extent to which applications of concepts are included in the models depends on a number of factors not least the relevant expertise of the teacher as a practitioner in the industry. Our findings highlight the importance of teachers having substantial practical industry experience and the role that whole school policies play in attempts to align the range of learning experiences with the needs of industry.

Conceptual and thematic analysis of policies and guidelines on engineering asset management of different states in Australia

The role of government in developing policies and guidelines for asset management is becoming increasingly important especially in view of ageing infrastructure and increasing financial risks for building infrastructure. This paper reviews policies and guidelines developed by Australian state authorities against industry developed principles. It utilizes the software program Leximancer to; a) produce conceptual visualisations of the key themes and concepts embedded within state-wide policies and guidelines, and b) systematically compare the differing asset management foci between states. The analyses reveal mixed results in terms of policy priorities and guidelines for managing assets at a strategic level across states. This paper outlines a rigorous analytical methodology to inform specific policy changes.

Critical factors for sustainable reconstruction of post natural disasters

While scientists are still debating the level of climate change impact to new weather patterns, there have been some devastating natural disasters worldwide in the last decade. From cyclones to earthquakes and from Tsunamis to landslides, these disasters occur with formidable forces and crushing effects. As one of the most important arrangements to erase the negative influence of natural disasters and help with the recovery and redevelopment of the hit area, reconstruction is of utmost importance in light of sustainable objectives. However, current reconstruction practice confronts quite a lot of criticisms for focusing on providing short-term necessities. How to conduct the post disaster reconstruction in a long-term perspective and achieve sustainable development is thereby a highlight for industry practice and research. This paper introduced an on-going research project which is aimed at establishing an operational framework for improving sustainability performance of post disaster reconstruction by identifying critical sustainable factors and exploring their internal relationships. The research reported in this paper is part of the project. After a comprehensive literature review, 17 potential critical sustainability factors for post disaster reconstruction were identified. Preliminary examination and discussion of the factors was conducted.