Spiders Silk and Silica Composite Could Make New Biomaterial



Spiders Silk and Silica Composite Could Make New Biomaterial

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Bioengineers at Tufts University have created a new fusion protein that for the first time combines the toughness of spider silk with the intricate structure of silica. The resulting nanocomposite could be used in medical and industrial applications, such as growing bone tissue.

“This is a novel genetic engineering strategy to design and develop new ‘chimeric’ materials by combining two of nature’s most remarkable materials -- spider silk and diatom glassy skeletons – that normally are not found together,” said David L. Kaplan, professor and chair of biomedical engineering and director of Tufts’ Bioengineering and Biotechnology Center.

Kaplan, along with his Tufts graduate students and collaborators Carol C. Perry from Nottingham Trent University in England and Rajesh Naik from the Air Force Research Laboratory, released their findings in the paper “Novel Nanocomposites from Spider Silk-Silica Fusion (Chimeric) Proteins” published in the Proceedings of the National Academy of Sciences.

Silica provides structural support to diatoms (single-celled organisms known for their remarkable nanostructural details) while silk proteins from spiders and silkworms are more flexible, stronger and able to self-assemble into readily defined structures. The Tufts researchers were able to design and clone genetic fusions of the encoding genes for these two proteins, and then generate these genetically engineered proteins into nanocomposites at ambient temperatures using only water. In contrast, high temperatures and harsh conditions are typically required by geochemical and industrial synthesis of silica in the laboratory.

Another remarkable detail about the spider silk-silica composite is its size. While past tests using silica have formed silica particles with a diameter between 0.5 and 10 nanometers, the silk-glass composite has a diameter size distribution between 0.5 and 2 nanometers. The smaller, more uniform size will provide better control and more options for processing, which would be “important benefits for biomedical and specialty materials,” according to the research.

Kaplan says this new chimeric protein could lead to a variety of biomedical materials that restore tissue structure and function, including bone repair and regeneration. Other likely applications involve more basic areas of materials science and engineering, including “green chemistry,” which will prevent or reduce pollution.



The research was funded by the National Institutes of Health, the U.S. Air Force Office of Scientific Research and the European Commission.

Silk research spans a decade

Kaplan and his fellow researchers have been working on silks for more than a decade and have focused on these specific spider silk-silica chimeric proteins for about a year.

“We have worked on silks for a long time and we were designing new versions of silks using genetic engineering,” said Kaplan. “Since the diatom and other mineral forming domains had recently been identified in the literature, the silk-silica combination seemed potentially important from a materials perspective.”

In 2002, Kaplan and his team of researchers from Tufts’ School of Engineering and School of Medicine developed a tissue engineering strategy to repair one of the world’s most common knee injuries -- ruptured anterior cruciate ligaments (ACL) -- by mechanically and biologically engineering new ones using silk scaffolding for cell growth. A year later, Kaplan and a postdoctoral fellow at Tufts discovered how spiders and silkworms are able to spin webs and cocoons made of silk and aspects of the spinning process to replicate it artificially.

Tufts University, located on three Massachusetts campuses in Boston, Medford/Somerville, and Grafton, and in Talloires, France, is recognized among the premier research universities in the United States. Tufts enjoys a global reputation for academic excellence and for the preparation of students as leaders in a wide range of professions. A growing number of innovative teaching and research initiatives span all Tufts campuses, and collaboration among the faculty and students in the undergraduate, graduate and professional programs across the University's eight schools is widely encouraged.

Posted June 27th, 2006



Refobacin Plus - A New Antibiotic Bone Cement

Charnley Wear Project

As part of our ongoing program to investigate series of implants in our retrieval collection, the wear characteristics of all Charnley

low friction arthroplasties were analysed. 120 acetabular components were analysed using a coordinate measuring machine.

(we acknowledge Rio Tinto for its use)

Antibiotic bone cements have increased in popularity as a complementary treatment to systemically administered antibiotics for

periprosthetic infection. One successful application of antibiotic bone cement is in the 2-stage revision of infected arthroplasties

using antibiotic-loaded spacers, with the advantage of direct antibiotic delivery to the site of infection.

The mechanisms by which the antibiotic is released from the bone cement (PMMA) is still largely undefined. It is believed the

antibiotic is first released directly from the surface and subsequently flows from interconnecting voids and cracks through the

cement rather than by a diffusion process.

Refobacin Plus (Biomet) contains gentamicin and is essentially a high viscosity bone cement, but has an initial low viscosity to

allow for vacuum mixing and adequate delivery.

1. Elution Studies

Static and dynamic tests were performed on hand and vacuum

mixed cement samples to determine gentamicin release over time.

Refobacin Plus was compared with CMW3 Gentamicin (De

Puy), which is currently used with the RPH hip spacer.

The findings are summarised as follows:

? For CMW3, there is an initial burst release of gentamicin

(first day) with minimal release there after.

? Refobacin also has a burst release of gentamicin in the first

24 hours but, in contrast to CMW3, the gentamicin steadily

releases over a long period. The concentration of

gentamicin after 8 weeks is ~9 times higher than the

concentration after 1 day and ~16 times higher than CMW3.

? Vacuum-mixed Refobacin showed better gentamicin release

than the hand-mixed samples.

? The dynamic elution tests showed similar trends with

greater release of gentamicin from Refobacin compared to

CMW3.

2. Mechanical Tests (ISO 5833)

The mechanical properties of Refobacin Plus were determined

using shear, compression and bending tests. Results were

compared with previous laboratory studies and published

values of other cements.

In summary, Refobacin bone cement has excellent elution

characteristics and is superior to CMW3 for both the total

amount of gentamicin release and the time over which the

release occurs. The mechanical properties of Refobacin Plus

compare favourably to other bone cements. We are currently

evaluating this cement for use in the RPH Hip Spacer.



-- very good

New composite materials being developed as bone implants

Published: 03 August 1999

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Dr Matt Trau A University of Queensland research group is developing new composite materials for surgical bone implants, to widen the range of options available to patients and surgeons.

The worldwide market for such materials is $1 billion a year and growing as the population ages.

The research group led by Dr Matt Trau of the University's Chemistry Department aims to develop an ideal implant material which will possess equivalent mechanical properties to natural bone, allowing the patient to be immediately mobile after surgery. The work targets an implant to be completely resorbed gradually by the body as new natural bone tissue replaces it.

Dr Trau is one of seven recipients of the inaugural University of Queensland Foundation Research Excellence Awards announced at Brisbane Customs House on August 3.

He said bone was a dynamic organ capable of self-regeneration following injury. In some cases, however, defects were too large for natural repair and therefore required the implantation of autografts, allografts or other synthetic materials to facilitate the healing process. Although current therapies were successful in many cases, they all had their associate problems such as limited supply of bone from other parts of the body in the case of autografts, disease transmission for allografts and fatigue failure of artificial bone cement and metal implants.

"Given the low density and extraordinary mechanical properties of bone, the design of materials for surgical bone implants presents and incredible challenge for the materials chemist," he said.

"Within our research group we have recently developed methods to produce porous bone implant materials based on Biopol polymer/ceramic composites. The external shape, porosity and mechanical properties of these implants can be easily tailored to suit any particular patient.

"Biopol polymers are a new generation of polyester thermoplastics which are produced by bacteria. Given their biological origin, these polymers are completely biocompatible and biodegradable within the human body. Our current work aims to significantly improve the strength of such implants by reinforcing the polymer with a nanostructured ceramic material."

Since arriving at the University in 1997, Dr Matt Trau has established a strong and vibrant research group within the Chemistry Department.

The research interests of the group focus around the creation of the novel nanostructured biomaterials. Current Australian Research Council-funded programs also include artificial human tissue engineering and the development of devices for rapid DNA sequencing and combinatorial drug screening. Dr Trau said his $80,000 award would directly support these research projects.

In the brief period since establishment, the group has raised research funds in excess of $945,000 ($848,778 of these monies awarded to Dr Trau and co-collaborators), generated significant quality publications (one in Nature and two Langmuir articles) and three patents.

Dr Trau obtained his PhD in physical chemistry from the University of Melbourne in 1992 and joined the University of Queensland two years ago.

He has won many academic prizes and scholarships including the Dow Chemical (Australia) Ltd scholarship in Chemistry (1985, 1986), the G.S. Caird Scholarship (Major) in Chemistry (1986), a British Council Postgraduate Bursary (Travel Scholarship) (1991), a Fulbright Postdoctoral Scholarship to the United States of America (1993-96) and the MITI Visiting Scientist, Electrotechnical Laboratory, Tsukuba Research Centre in Japan (1998).

In 1998, he was a member of the Queensland Government's "Biotechnology Mission to the US", with a workshop on "The Future of Biotechnology in Australia" held at Harvard University.

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|Engineering Composites Properties |

|Composite materials include some of the most advanced engineering materials today.  The addition of high strength fibers to a polymer |

|matrix can greatly improve mechanical properties such as ultimate tensile strength, flexural modulus, and temperature resistance. |

|Examples are illustrated in the table below. |

|Typical Values of Filled and Unfilled Polymers for Injection Molding |

|  |

|Ultimate Tensile |

|Strength (MPa) |

|Flexural Modulus (GPa) |

|Deflection Temperature at |

|1.8 MPa load (°C) |

| |

| |

|Unfilled |

|With 30% Glass Fiber |

|Unfilled |

|With 30% Glass Fiber |

|Unfilled |

|With 30% Glass Fiber |

| |

|Polyetheretherketone |

|90 |

|150 |

|4 |

|10 |

|160 |

|285 |

| |

|Polyphenylene Sulfide |

|70 |

|140 |

|5 |

|11 |

|120 |

|260 |

| |

|Epoxy |

|70 |

|150 |

|2.5 |

|25 |

|175 |

|200 |

| |

|Phenolic |

|60 |

|90 |

|3 |

|20 |

|180 |

|250 |

| |

|Thermoset Polyester |

|60 |

|140 |

|3 |

|8 |

|130 |

|220 |

| |

|ABS |

|40 |

|90 |

|2.5 |

|7 |

|90 |

|110 |

| |

| |

|Additives can also be included in polymers for reasons other than thermo-mechanical property improvements.  For example, graphite, |

|PTFE, or molybdenum disulfide are added to polymers as lubricants to lower the coefficient of friction or wear rate in tribological |

|applications such as bearings or slide plates. |

|MatWeb has entries for well over 8000 polymers, including both thermoplastics and thermosets, which have been reinforced through the |

|addition of glass fiber, carbon fiber, aramid fiber, wood, or mineral reinforcements.  Not all of these are cutting edge products; |

|some merely include inexpensive inorganics such as calcium carbonate or talc as a way of achieving improved dimensional stability in |

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|Since the vast majority of polymer-based composites are generally processed and sold as polymers, MatWeb has categorized them |

|according to the base resin in our material property data search tools.  Some manufacturers of composite materials do not even |

|disclose the identity or quantity of reinforcing fibers for competitive reasons. |

|MatWeb has other structural composite materials in addition to filled polymers.  For example, you can find 'Metal Matrix Composite' |

|listed in the "Nonferrous Metal' section of our Material Type Search or 'Composite Fibers' and 'Composite Core Material' listed under |

|'Other Engineering Materials'. |

|A good strategy to find the composite material of choice for your application from the MatWeb Property Search is to pick a category |

|such as polymers, thermoset, or epoxy and specify a minimum tensile strength or flexural modulus from the property field.  Two MatWeb |

|materials categories on our Search and Index page that explicitly target composites are 'Carbon Fiber/Thermoset Composite' and |

|'Composite SMC' (Sheet Molding Compound).  SMCs consist of polymer resin and reinforcing agent (glass or carbon fiber) produced and |

|sold in continuous sheets.  SMCs, usually thermoset-based, often have longer fibers and higher fiber content than composites produced |

|for injection molding or extrusion.  This can result in a stronger and stiffer product, but the ability to form complex shapes from |

|SMCs is limited is limited. |

| |

| |

| |



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