Biomimetics and Biomimicry in Engineering

Posts Tagged ‘Publications’

How pore morphology impacts stiffness

In Publications on 2018/05/15 at 10:52 am

Our most recent study on how pore size, morphology and orientation have an effect on stiffness of a porous alloy has been published in the Journal of Materials Engineering and Performance.

Our article ‘Effect of Pore Size, Morphology and Orientation on the Bulk Stiffness of a Porous Ti35Nb4Sn Alloy‘ describes how the metal foams of a titanium alloy were designed to study porosity as well as pore size and shape independently. These were manufactured using a powder metallurgy/space-holder technique that allowed a fine control of the pore size and morphology; and then characterized and tested against well-established models to predict a relationship between porosity, pore size and shape, and bulk stiffness. Among the typically used correlations, existing power-law models were found to be the best fit for the prediction of macropore morphology against compressive elastic moduli, outperforming other models such as exponential, polynomial or binomial.

The new coefficients reported in this study contribute toward a design tool that allows the tailoring of mechanical properties through porosity macrostructure. The results show that, for the same porosity range, pore shape and orientation have a significant effect on mechanical performance and that they can be predicted. Conversely, pore size has only a mild impact on bulk stiffness.

Pore_morphology_mech_props

The full article can be found here

The DOI is https://doi.org/10.1007/s11665-018-3380-0

 

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A manufacturing protocol for the production of biocompatible porous catalysts

In Publications, Seminars and Keynotes on 2018/02/09 at 2:23 pm

Mohammad Alqahtani, researcher of the Multifunctional Materials Lab, is conducting research to develop a new manufacturing method and testing protocol for the fabrication of biocompatible catalyst-carrier for controlled drug delivery. The carrier could be used as a prodrug activation agent when implanted in cancerous tissues in the human body. When orally-ingested drugs are deployed into the area under treatment through the blood stream, the catalyst could activate the prodrugs and these affect the area by releasing anticancer treatment. In this research, a titanium-based carrier was used to manufacture the medical device due to their biocompatibility and non cytotoxicity.

In a feasibility study, the samples were made as porous carriers.  Porous materials have larger surface area than solid materials. Therefore, when the contact area between the drug and the carrier increases this has a potency effect on the effectiveness of the drug.

His work has been presented recently

20170608_ma_poster-wolfsonconf1.jpg

This work is a continuation of the research work already presented here and published here and here.

Mechanical behaviour that mimics that of cortical and trabecular bones

In Publications on 2017/11/30 at 11:22 am

We have published our most recent results on how porosity and pore size affect both mechanical properties and biological response of osteoblastic cells on titanium porous structures.

Working with volumetric porosities that match those of cortical and trabecular bone, we finely controlled the pore size in the substrate with the aim to assess how a variation in pore size can tailor mechanical properties (i.e. stiffness and strength). Furthermore, we report how we could establish regressions that would allow us to create a design tool based on porosity, so it would return the desired mechanical properties values.

From a bioengineering viewpoint, the results from this study showed that scaffolds with the lowest pore range (45-106um) presented the largest number of cells attached in the early days  (day 1 and  3) indicating this microarchitecture was the best indicated for cell attachment. Pore range >300 mm exhibited the most favourable conditions for cell proliferation, surpassing those on the control samples. The viability of scaffolds with pore size 212-300um was the poorest, indicating these scaffolds do not promote cell proliferation for osteosarcoma osteoblasts due to the distance the cells had to span.

Proliferation_supplementary

Proliferation data from the osteoblasts on titanium porous (A,B 1-4) and non-porous (Ti) normalised to the previous timepoint of culture (in/in-1, n=3, 7, 12); as it appears in https://www.ncbi.nlm.nih.gov/pubmed/28532024

The study can be found here in the Materials Science and Engineering C: Materials for Biological Applications.

Engineered foams for wheelchair seating

In Publications on 2017/11/08 at 10:39 am

We have published the results arising from our studies on open cell polymeric foams that can be tailored so that they support those who are bed bound or wheelchair users providing them with general well being and alleviating pressure points.

Avoiding pressure points, managing sores and permitting air permeability are the three main design specifications that clinicians aim to when choosing a cushion. In addition to that, a functional cushion, such as those who support lateral movements (e.g. leaning sideways to grab a glass of water and be helped to return to your initial position without compromising one’s stability) and protect from vibration and impacts (e.g. dropping off a curb), are the focus of our research project.

The Multifunctional Materials Lab and clinicians from the NHS have studied how we can help their clinician colleagues understand cushion performance and therefore aid them with the prescription of these to patients and users.

The results from our study have been published in the Medical Engineering and Physics Journal and in the Assistive Technology Journal .

The International Standard that regulates developments in this topic is the ISO16840-2:2007, which is currently under revision. We are hoping our work to inform their work and assist in their revisions for the replacement ISO 16840-2.

iso_replacement

 

Porosity and pore size effect on the properties of sintered Ti35Nb4Sn alloy scaffolds and their suitability for tissue engineering applications

In Publications on 2017/11/03 at 11:04 am

Our most recent results on the importance of tailoring porosity engineered materials for cell regeneration are to be published in the Journal of Alloys and Compounds.

Porous scaffolds manufactured via powder metallurgy and sintering were designed for their structure (i.e. pore size and porosity) and mechanical properties (stiffness, strength) to be controlled and tailored to mimic those of human bone. The scaffolds were realised to fulfill three main objectives:

(i) to obtain values of stiffness and strength similar to those of trabecular (or spongy) bone, with a view of exploiting these as bone grafts that permit cell regeneration,

(ii) to establish a relationship between stiffness, strength and density that allows tailoring for mass customisation to suit patient’s needs; and

(iii) to assess alloy cytotoxicity and biocompatibility via in vitro studies.

The results obtained using a very low stiffness alloy (Ti35Nb4Sn) further lowered with the introduction of nominal porosity (30–70%) with pores in the ranges 180–300 μm and 300–500 μm showed compatibility for anatomical locations typically subjected to implantation and bone grafting (femoral head and proximal tibia). The regression fitting parameters for the linear and power law regressions were similar to those found for bone specimens, confirming a structure favourable to capillary network formation. Biological tests confirmed non-cytotoxicity of the alloy.

Scaffolds of porosity nominal 50%vol and pore range 300–500 μm performed best in the adhesion and propagation assays due to a good balance between surface area and pore cavity volume.

Graphical abstract for https://doi.org/10.1016/j.jallcom.2017.10.026

Study on bio-mechanical properties of porosity scaffolds tailored for cell regeneration, https://doi.org/10.1016/j.jallcom.2017.10.026

A pre-view of the article appears on Journal of Alloys and Compounds, Volume 731, 15 January 2018, Pages 189-199, https://doi.org/10.1016/j.jallcom.2017.10.026.

 

The effect of pore size and porosity on mechanical properties and biological response of porous titanium scaffolds

In Publications on 2017/10/27 at 8:49 am

The Multifunctional Materials Lab has recently published our results on porosity tailored titanium scaffolds. The results were very interesting and demonstrated there is more to what the eye can see in a first pass: cells are extremely sensitive to cavities and ‘think’ about whether they should bridge a gap or simply fill the hole.

Our article can be found here

The effect of pore size and porosity on elastic modulus, strength, cell attachment and cell proliferation was studied for Ti porous scaffolds manufactured via powder metallurgy and sintering. Porous scaffolds were prepared in two ranges of porosities so that their mechanical properties could mimic those of cortical and trabecular bone respectively. Space-holder engineered pore size distributions were carefully determined to study the impact that small changes in pore size may have on mechanical and biological behaviour. The Young’s moduli and compressive strengths were correlated with the relative porosity. Linear, power and exponential regressions were studied to confirm the predictability in the characterisation of the manufactured scaffolds and therefore establish them as a design tool for customisation of devices to suit patients’ needs. The correlations were stronger for the linear and the power law regressions and poor for the exponential regressions. The optimal pore microarchitecture (i.e. pore size and porosity) for scaffolds to be used in bone grafting for cortical bone was set to < 212 μm with volumetric porosity values of 27–37%, and for trabecular tissues to 300–500 μm with volumetric porosity values of 54–58%. The pore size range 212–300 μm with volumetric porosity values of 38–56% was reported as the least favourable to cell proliferation in the longitudinal study of 12 days of incubation.

https://doi.org/10.1016/j.msec.2017.03.249

Cells are sensitive to small changes in pore size and some are even detrimental to their proliferation. https://doi.org/10.1016/j.msec.2017.03.249

Published in Materials Science and Engineering: C, Volume 77, 1 August 2017, Pages 219-228, https://doi.org/10.1016/j.msec.2017.03.249

Mathematical modelling of sonicated bubbles

In Publications on 2017/05/31 at 5:10 pm

One possible manufacturing method for bone scaffolds used in regenerative medicine involves the acoustic irradiation of a reacting polymer foam to generate a graded porosity. Sonication of foams have been our focus of research for many years now as this technology allows the porosity tailoring of cellular materials.

20060117_1500_B2_red

Sonicated foam (energy received from the left) with a marked gradation in porosity

We have joined forces with Prof Mulholland’s team (Dr Barlow and Dr Bradley) at Strathclyde University and worked on a mathematical model of a non-reacting process in order to develop theoretical confirmation of the influence of the acoustic signal on the polymer foam.

The model describes single bubble growth in a free rising, nonreacting polymer foam irradiated by an acoustic standing wave and incorporates the effects of inertia. Investigations are carried out to explore the influence of inertia on the bubble volume, fluid pressure and the stress tensors of the foam, and to explore the effect of fluid viscosity and acoustic pressure amplitude on the final bubble volume, and the curing time. A key result is that increasing the applied acoustic pressure is shown to result in a reduced steady state bubble volume, indicating that ultrasonic irradiation has the potential to produce tailored porosity profiles in cellular materials such as bioengineering scaffolds and light-weight structures.

Our work has been compiled as a paper recently published in the Journal of Non-Newtonian Fluid Mechanics and can be found here (Open Access).

Applying International Standards to manage comfort

In Publications on 2017/03/01 at 6:46 pm

Have you ever seen the seat testing device at IKEA? We have used a very similar one in our study.

ikea_durability_test

IKEA durability test

Open cell polymeric foams can be tailored so that the support provided and the level of stability is customised to people’s needs. For those who are bed bound or wheelchair users the selection of a cushion can improve their health and general well being. Avoiding pressure points, managing sores and permitting air permeability are the three main design specifications that patients and clinicians aim to when choosing a cushion. In addition to that, a functional cushion, such as those who support lateral movements (e.g. leaning sideways to grab a glass of water and be helped to return to your initial position without compromising one’s stability) and protect from vibration and impacts (e.g. dropping off a curb), are the focus of our last research project.

My team and I have had the privilege to work with the biomechanics and physiotherapists at the SMART Centre at Astley Ainslie Hospital in Edinburgh to study how we can help their clinician colleagues understand cushion performance and therefore aid them with the prescription of these to patients and users.

The results from our study have been presented at the PMG 2012 Conference and recently published by the Assistive Technology journal (free e-prints can be collected here). This has allowed us to interact with the community that is preparing the new version of the ISO16840-2:2007 which will regulate developments in this area.

 

Empowering resilient communities

In Publications on 2017/02/06 at 10:58 pm

We have created low-cost housing solutions for the local community in Pabal (India). Those people have a lot of ingenuity but not a lot of money to buy expensive building materials. Only the transport to their villages would cost them a significant amount.

But they have a wealth of natural resources. And amongst them, they have bamboo, a fascinating multifunctional material, ideal for structure-erecting, wind-loading and vibration-proofing due to its heterogeneous porous structure and high shear modulus.

bamboo_microstructure

Bamboo: macro and microstructure

We have helped them to build those modular huts by providing them with a set of instructions that are universal and accessible to all, no matter the mother tongue, ability or building skills. In this way they are prepared to adapt and be resilient to the threats posed by natural forces and climate change hazards (e.g. floods, pluvial, wind, earth tremors) and reinforce their coping strategy as a resilient community.

In the process of developing those instructions we have learnt a lot from the Information Design community. There is so much lo learn about user-centric design, cognitive load and the language of actions, perspectives and colours to convey instructions and allow self-guidance. I deeply thank them for having mentored us.

Our work can be read here and directly on the Information Design Journal site

idj_22-1_pb

Information Design Journal 2016 volume 22 no. 1

 

Making sense of standardisation

In Publications on 2013/11/18 at 12:27 am

Standardisation is that useful process that allows us engineers to share a common ‘plane of reference’ on which to base our conversations. It is useful to know that a material (say, a slab of titanium) has the same mechanical properties when it is measured in Loughborough, Sydney, Lima or Granada.

But sometimes standardisation goes too far on the other extreme. The over-translation from observation to technical definitions might turn an ISO norm into a document that is no longer useful for practical purposes. This is particularly risky when ISO norms attempt to tabulate and measure in ‘softer’ areas such as healthcare and rehabilitation.

In a piece of work recently published here, my colleagues from the NHS Scotland SMART Centre and we have restated some practical insight to an ISO norm that guides the characterisation of wheelchair cushions for a better guidance to prescription by clinicians.

Our work has been well received by the practising community and we look forward to continue working with them.

Ref: Hollington J., Hillman S.J., Torres-Sanchez C., Boeckx J., Crossan N., “ISO 16840-2:2007 load deflection and hysteresis measurements for a sample of wheelchair seating cushions”, Medical Engineering & Physics, in press. DOI:10.1016/j.medengphy.2013.10.010