Editor’s note: Science Scan is a roundup of recently published biotechnology-relevant research.

It takes nimble fingers to tie surgical sutures in the confined space of a laparotomy. Along comes a biodegradable surgical thread that tightens up automatically, once sewn into the body. The same technology may someday allow surgeons to implant devices in a temporarily compressed form, which would expand to permanent shape once inside. Other thermoplastic materials exist, but this “smart suture,” its inventors say, is the first that can break down and reabsorb in the body.

An online Sciencexpress report in Science dated April 25, 2002, reports the innovation under the title: “Biodegradable, elastic shape memory polymers for potential biomedical application.” Its two co-authors are at the Institute for Technical and Macromolecular Chemistry in Aachen, Germany, and in the chemical engineering department at the Massachusetts Institute of Technology in Cambridge.

The Science paper describes “a group of degradable, thermoplastic polymers, which are able to change their shape after prompting by an increase in temperature. Their shape memory capability,” the paper adds, “enables bulky implants to be placed in the body through small incisions, or to perform complex mechanical deformations automatically.” It points out, for starters, that “the introduction of biodegradable implant materials, as well as minimally invasive surgical procedures, in medicine has significantly improved health care within the last few decades.”

As a demonstrator model of their concept in biomedical applications, the authors fashioned a smart suture, and tried it four times in albino rats. The animals were sacrificed and shaved, and an incision made through the belly tissue and abdominal muscle. The wound was lightly sutured, using a standard surgical needle. The shape memory effect was actuated by raising the temperature to 41 degrees Celsius.

“This feasibility study,” the Science article concludes, “suggests that this type of material has the potential to influence how implants are designed, and could enable new surgical devices in the future.”

Historical postscript: Just 20 years ago, in 1982, Britain’s Imperial Chemical Industries Ltd. farmed out some of its research on a bacterially made biodegradable plastic. The material, polyhydroxybutyrate, was synthesized by a soil bacterium, Alcaligenes eutropus. The bug-made polymer had mechanical properties similar to those of the petrochemically produced chemical, but cost more to make. Nonetheless, both a British and an American firm took on ICI’s off-site offer, and announced they would try to make surgical pins and sutures out of A. eutropus’ output.

Hair-Raising Research Locates Hidden Site Of Stem Cells In Mouse Melanocyte Follicles

Stem cells, which have the capacity to self-renew and generate differentiated progeny, are maintained, it is thought, in a specific environment known as a niche. The site of this hideout remains largely obscure for most stem cell systems. Now molecular geneticists and dermatologists at Kyoto University shine a light into this darkness. An article in Nature dated April 25, 2002, reports their finding under the title “Dominant role of the niche in melanocyte stem-cell fate determination.”

Melanocyte stem cells reside in the bulge area part, where the arrector pili muscle attaches to the hair follicle’s outer root sheath. Bundles of these smooth muscle fibers act to pull the hairs erect, causing goose bumps in humans, but increasing depth of fur coats in most mammals. With the help of transgenic mice, the Japanese researchers tracked down the niche harboring the stem cells that give rise to the pigment-producing cells of the melanocytes. These pigment cells which color hair and skin proliferate and differentiate in lockstep with the hair regeneration cycle.

The lower permanent portion of mouse hair follicles was the only population in this region, the co-authors note, that “fulfills the criteria for stem cells, namely being immature, slow cycling, self-maintaining and [having] full competence in regenerating progeny on activation at early anagen [the first fine fuzz of hair renewal].” A salient finding “demonstrated that a portion of amplifying stem cell progeny can migrate out from the niche and retain sufficient self-renewing capability to function as stem cells after repopulation into vacant niches.”

Adverting from rodents to humans, they conclude: “The re-pigmentatation process we observed strongly suggests that human melanoblasts are the stem cell source for hair matrix melanocytes and for epidermal melanocytes. Indeed, the pigmentation pattern is reminiscent of the recovery process of human vitiligo, an acquired disease characterized by loss of melanocytes.”

Differences In Homo sapiens/Plasmodium falciparum Suggest Antimalarial Drug Target

A newly discovered misfit in how drugs against malaria work on the redoubtable Plasmodium falciparum parasites and their human hosts maps a new route to new drugs. Antimalarial antifolate compounds, e.g. pyrimethamine, have been used successfully against the disease for half a century, but no one fully understood how they take down the parasite without harming the patient. Experts attributed the agent’s efficacy to host-parasite differences in drug binding.

At the University of Washington in Seattle, scientists now report studies of a likely key drug target the enzyme dihydrofolate reductase-thymidylate synthase (DHFR-TS). Their paper in Science, dated April 19, 2002, bears the title: “Divergent regulation of dihydrofolate reductase between malaria parasite and human host.” In both host and parasite, the messenger RNA for producing more of that enzyme is bound to the enzyme itself. The paper’s authors found that when drug binds to enzyme in humans, the mRNA is released, allowing the body to up its output of DHFR-TS. In parasites, that drug binds to a different site on the enzyme. No mRNA is released, and the pathogen can’t make more DHFR-TS in its own defense.

An accompanying “Perspective,” titled “When the host is smarter than the parasite,” concludes: “With a little planning, we should be able to exploit our mammalian sophistication to develop potent antiparasitic drugs.”