Biomimetics and Biomimicry in Engineering

Posts Tagged ‘porous materials’

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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Materials Research Exchange 2018

In Knowledge Transfer, Seminars and Keynotes on 2018/05/08 at 10:14 am

We spoke at the UK Advanced Material Research & Investor Showcase event in London on 13th March. The event, organised by EPSRC, Innovate UK and KTN, and supported by DSTL, was aimed at materials scientists and engineers who work at the research:industry:academia interface in the UK. It was a fabulous opportunity to learn more about the facilities the UK plcs and Universities have for materials processing and characterization, and also to find out more about the ongoing projects co-sponsored by Innovate UK.

We were invited to present our ongoing project in collaboration with FAR UK Ltd, ‘L3:An Integrated approach towards zero net emissions via lightweight manufacturing’, which is researching how to achieve weight reduction in composites (i.e. fibre-reinforced polymers) without sacrificing mechanical performance, and using a cost effective manufacturing process.

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The process under development is one that has the ability to use lower cost composite materials and is inherently near-zero waste, both in its production strategy and also because it does not use environmentally damaging materials.

The process makes porous polymeric structures where the inherent loss of mechanical properties is mitigated by the addition of fibres (initially glass and carbon, expected to be replaced by naturally derived fibres in the near future).  Additionally, the microstructure of the pores and the orientation of the fibres can be controlled in-situ using external means such as sonication and magnetic fields.

This project is allowing us to move forward towards the realisation of topology optimisation and its true implementation for composite manufacturing processes.

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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

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

Functionally-Tailored Cellular Structures

In Publications, Seminars and Keynotes on 2018/01/10 at 1:41 pm

Many applications in science and engineering can benefit from the control of porosity
gradients. Producing heterogeneous materials allows the properties of that material to
be tailored more specifically to the requirements, reducing resource consumption and
weight. A designed microstructure is able to produce similar strength and stiffness values to a homogenous material at a reduced weight by removing discontinuities between phases where stress concentrations occur.

Joe Holt, researcher of the Multifunctional materials Lab, studying at the EPSRC Centre for Doctoral Training in Embedded Intelligence and co-sponsored by FAR UK Ltd, has presented our work on functionally tailored cellular structures via topology optimisation.

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A tailored cellular structure is realised by topology optimisation of a volume loaded
in compression. The optimisation is set-up to incorporate a full spectrum of densities
of the parent material, as to simulate a cellular solid of varying density. The resulting
structure is produced by ultrasound sonication of a polyurethane foam system during
the foam rise. Targeted sonication power and frequency allows the manipulation of
density in specific regions, producing a finished structure with a density profile representing the results of the topology optimisation.

Snowflakes

In Comment on 2017/12/21 at 12:56 pm

Wilson A. Bentley (1865-1931). This gentleman studied the formation of snowflakes under varied conditions of temperature, pressure and relative humidity.

With rather low-tech scientific apparatus (i.e. a simple microscope and rudimentary equipment to control temperature, pressure and % humidity), he created hundreds, if not thousands, of snow crystals. He coined the sentence “no two snowflakes are the same”.

If it is snowing where you are now, look out of the window and pay attention to the snowflakes. It is not that all the different snowflakes that you see falling from the sky are all absolutely unique and different. His claim means that, under specific atmospheric and physical conditions (i.e. T, P, %hum, altitude, etc), one and only one type of snow crystal will form, and then fall onto the ground.

These images are original photographs taken by Bentley himself using his microscope. The crispness of the images is breathtaking and the beauty of the fractals extraordinary. Enjoy! For example, when snowflakes crystallises with the shape of a tube or a needle, fall to the ground and form a layer of snow on a mountain, that layer may be the precursor in the formation of avalanches.

Bentley’s pioneering work has helped geophysicists and engineers understand ice formations and how to prevent catastrophes. However, there are many questions still unsolved! Snowflakes grow as thin plates, but if the temperature varies only a few degrees, they evolve into long thin crystals. No one knows why.

This last image belongs to a collection from SnowCrystals.com and a beautiful classification of the different types of snowflakes can be seen here.

Lab diaries: Multifunctional microstructures

In Comment on 2017/12/12 at 1:18 pm

We have created new structures that provide comfortable accommodation for bone-forming cells. We seeded them, puffed up their pillows, fed them with their favourite food and drink and waited. The other day we went to check on them. This one looks particularly pleased!

Mock up

When we fixed the cells we found this shape, decorated with eyes (prob debris from the desiccating chemicals) which we have decorated with a tie

We are functionalising surfaces to tune them to chemical bio markers and embedding intelligence to create active structures and welcoming new homes for cell cultures. Attention to detail: we even decorate their sitting spaces with flowers

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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.

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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.

Removing mass with maths

In Comment on 2017/11/14 at 3:02 pm

We are creating lightweight materials by removing mass from where it is not needed and adding it to places subjected to high loads and strains. It is Drawing with Maths

“[The Universe] is written in the language of mathematics, and its characters are triangles, circles and other geometrical figures, without which it is humanly impossible to understand a single word of it” —Galileo Galilei, The Controversy on the Comets, 1618

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.

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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.