NIST Tech Beat - April 13, 2006

A new technology for implants that may improve construction or repair of bones in the face, skull and jaw, has been developed by researchers from the American Dental Association Foundation (ADAF) and the National Institute of Standards and Technology (NIST).

Described in recent and upcoming journal articles,* the new technology provides a method for making scaffolds for bone tissue. The scaffold is seeded with a patient’s own cells and is formed with a cement paste made of minerals also found in natural bone. The paste is mixed with beads of a natural polymer (made from seaweed) filled with bone cells. The paste is shaped or injected into a bone cavity and then allowed to harden with the encapsulated cells dispersed throughout the structure. The natural polymer beads gradually dissolve when exposed to the body’s fluids, creating a scaffold that is filled by the now released bone cells.

The cement, a calcium phosphate material, is strengthened by adding chitosan, a biopolymer extracted from crustacean shells. The implant is further reinforced to about the same strength as spongy natural bone by covering it with several layers of a biodegradable fiber mesh already used in clinical practice.

“Bone cells are very smart,” says Hockin Xu, of the ADAF and principal investigator for the project. “They can tell the difference between materials that are bioactive compared to bioinert polymers. Our material is designed to be similar to mineral in bone so that cells readily attach to the scaffold.” The researchers used mouse bone cells in their experiments, but in practice surgeons would use cells cultured from patient samples.

In addition to creating pores in the hardened cement, the natural polymer beads protect the cells during the 30 minutes required for the cement to harden. Future experiments will develop methods for improving the material's mechanical properties by using smaller encapsulating beads that biodegrade at a predictable rate.

NIST and the American Dental Association Foundation have conducted cooperative research on dental and medical materials since 1928. ADAF researchers focus on development of new dental materials, while NIST specializes in the development of improved technologies and methods for measuring materials properties.

The research was funded by the National Institute of Dental and Craniofacial Facial Research, NIST and ADAF.

*E.F. Burgera, H.H.K. Xu and M.D. Weir. Injectable and rapid-setting calcium phosphate bone cement with dicalcium phosphate dihydrate. Journal of Biomedical Materials Research B. April 2006.

H.H.K. Xu, M.D. Weir, E.F. Burguera and A.M. Fraser. Injectable and macroporous calcium phosphate cement scaffold. Biomaterials. In press.

M.D. Weir, H.H.K. Xu, and C.G. Simon, Jr. Strong calcium phosphate cement-chitosan-mesh construct containing cell-encapsulating hydrogel beads for bone tissue engineering, Journal of Biomedical Materials Research A. In press.

When the National Institute of Standards and Technology (NIST) released the final report in October 2005 from its technical investigation of the fires and collapses of the World Trade Center (WTC) towers on Sept. 11, 2001, included were 30 recommendations for improving building and occupant safety derived from the findings. On March 24, 2006, the first 19 proposed changes to model building codes (used as templates for codes legislated, implemented and enforced by state and local jurisdictions) based upon and consistent with the NIST WTC recommendations were submitted to the International Code Council (ICC).

“Taken together, they are a robust, reasonable and appropriate set of advancements and, if adopted, would represent a significant improvement in public safety over current practice,” says WTC Lead Investigator Shyam Sunder.

The 19 proposed changes—submitted by building code experts associated with two ICC committees, the National Institute of Building Sciences and the U.S. General Services Administration—address areas such as increased resistance to building collapse from fire and other incidents, use of spray-applied fire resistive materials (commonly known as “fireproofing”), performance and redundancy of fire protection systems (i.e., automatic sprinklers), elevators for use by first responders and evacuating occupants, the number and location of stairwells, exit path markings, and fuel oil storage/piping.

“NIST welcomes and fully respects the ongoing debate among the professional and building official communities as they consider these proposals for adoption,” Sunder says.

All ICC members will have the opportunity to vote on the proposals at hearings scheduled for this fall. All changes passed, and those which did not pass but for which public comments are received, will then be up for approval—and inclusion in the ICC codes—when ICC government member representatives meet in the spring of 2007.

For more information, including a Web-based system for tracking the progress toward implementing all of the NIST WTC recommendations, visit http://wtc.nist.gov.

Microfluidic Device Tests Fluid Compatibility

A new NIST microfluidic instrument measures the mixing compatibility of complex liquids by observing how drops of one fluid flowing within a "river" of a second fluid change in shape as they travel through channels of various sizes.

View a high resolution version of this image.

Credit line: S.Hudson/NIST

The key to a great party is inviting guests who mix well and don’t instill tension among their fellow revelers. The key to a great detergent, cosmetic, paint or other complex liquid product is pretty much the same—include components that mix well and don’t have high levels of what scientists call “interfacial tension,” a tendency to bead up and pull away from each other.

To help industrial engineers improve their ability to systematically test new product formulations, researchers at the National Institute of Standards and Technology (NIST) have developed a microfluidic instrument that quickly measures interfacial tension.

The instrument is relatively simple and includes a series of channels ranging from 700 micrometers to 50 micrometers wide. Fluids are pumped toward a “T” intersection where drops of one liquid are pinched off and flow along a “river” of the second liquid. As the spherical drops flow through constriction points in the channel, they speed up and elongate. The degree to which the drops stretch out depends on the interfacial tension between the two fluids. High levels of tension exert more pressure on the drops, keeping them more nearly spherical.

Just as the mood of a party goes through stages, the tension between newly mixed liquids can change over time, and the device tracks these changes as the drops move downstream through the channel. A camera captures 100 pictures per second to record the changes, and an algorithm analyzes the data and produces a measurement in approximately 1 second.

Reporting on their work in the March issue of the journal Lab on a Chip, the researchers say they expect that the device will be especially useful to test fresh interfaces for applications with scarce amounts of the fluids to be tested such as custom-synthesized materials from combinatorial chemistry.

Funding for the research was provided by NIST, ICI/National Starch, and Proctor and Gamble.

*J.T. Cabral and S.D. Hudson. Microfluidic approach for rapid multicomponent interfacial tensiometry. Lab on a Chip. March 2006.

Media Contact:
Gail Porter, gail.porter@nist.gov, (301) 975-3392

Materials Declaration Forms Help Meet European Rules

A new standard form and process are available for describing and quantifying hazardous materials in electronics to help companies selling equipment in the European Union meet environmental regulations that take effect July 1. The standard is considered critical in simplifying efforts to comply with the new rules, which could restrict future U.S. electronics exports.

The Materials Declaration Management Standard (IPC-1752) provides a process for tracking and disclosing the amounts of six hazardous materials in electrical and electronic equipment. The standard was developed by IPC, a trade association, with help from the National Institute of Standards and Technology (NIST), the International Electronics Manufacturing Initiative (iNEMI), RosettaNet, and others.

NIST’s contributions included hosting a workshop to gather requirements, modeling the scope of the problem, and developing a process enabling users to submit data in PDF format and export it to a computer readable (XML) form so it can be exchanged with others in the supply chain.

The Restriction of Hazardous Substances, finalized by the European Union in 2003, restricts imports of new electrical and electronic equipment containing lead, mercury, hexavalent chromium, brominated flame retardants, PBBs (polybrominated biphenyls), PBDEs (polybrominated diphenyl ethers) and cadmium. Covered equipment includes household appliances, telecommunication and lighting equipment, tools, toys and sport equipment, and automatic dispensing machines.

The world's official standard for mass—a 115-year-old cylinder of metal—likely will join the meter bar as a museum piece in the near future. Will the standards for electric current, temperature and amount of substance soon follow?

Measurement experts long have planned to replace the kilogram standard—its mass actually fluctuates slightly—with a definition based on an invariable property of nature. The next logical step in the quest for the most precise, consistent and accessible measurements possible is to redefine several more units of the International System of Units (SI), according to a new paper by five eminent scientists from three countries.

The paper, published online April 6 by Metrologia, advocates redefining not only the kilogram but also three more base units of the SI that are not currently linked to true invariants of nature—the ampere, kelvin and mole (used to measure electric current, thermodynamic temperature, and amount of substance, respectively). The paper suggests that all four units be redefined in terms of four different fundamental constants or atomic properties to which precise values would be assigned. A property of nature is, by definition, always the same and can in theory be measured anywhere.

The paper represents the collective opinions of the authors, including one from the University of Reading in the United Kingdom, who heads an influential international metrology committee, as well as three scientists from the U.S. National Institute of Standards and Technology (NIST) and the former director of the Bureau International des Poids et Mesures (BIPM) near Paris.

The paper does not represent the official policy position of any of the authors' three institutions. However, much of the paper echoes, and suggests a practical strategy for implementing, an October 2005 recommendation by the International Committee for Weights and Measures (CIPM).