Medical Implants Work Better When You Rough Them Up

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Medical Implants Work Better When You Rough Them Up

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Medical implants ­ from catheters that deliver long-term life support to

joint replacements ­ may work better when their surfaces are on the rough

side, new research suggests.

Newswise ‹ Medical implants ­ from catheters that deliver long-term life

support to joint replacements ­ may work better when their surfaces are on

the rough side, new research suggests.

Implants often have surfaces that soft tissue, such as skin and connective

tissue, cannot attach to, said s von Recum, the study's lead author

and a professor of biomedical engineering at Ohio State University. So the

body in turn forms a tissue capsule around the implant, sealing it off from

the rest of the body.

That seclusion can lead to a variety of serious problems, von Recum said.

For instance, there are more than 300,000 hip and knee replacements each

year in the United States. Such implants usually last for 10 to 12 years

until they become loose and quite painful and need to be replaced.

" Being encased in connective tissue seriously compromises an implant's

function, " von Recum said. " And connective tissue can't tolerate constantly

moving against a foreign object. This friction ­ and ensuing inflammation ­

kills healthy cells and creates a steadily growing capsule of dead tissue. "

Adding texture to an implant's surface ­ the researchers used titanium in

this study ­ increased compatibility with connective tissue cells, called

fibroblasts, considerably.

And while the researchers conducted their experiments using titanium, which

is commonly used to make implants, all implants can benefit from having a

textured surface, von Recum said.

The study appears in a recent issue of the Journal of Biomedical Materials

Research Part A. von Recum conducted the study with Rakhi Jain, a former

doctoral student at Ohio State. von Recum is also the associate dean for

research in veterinary medicine at Ohio State.

The researchers coated disk-shaped polyester wafers with titanium. The disks

were round and about the size of a nickel. Some of the disks were covered

with grooves only several microns deep. Some bone implants currently used

have similar texture, von Recum said, although these grooves tend to be 100

to 200 microns deep and can interlock with hard tissue, such as bone.

" The grooves on our disks were a hundred times smaller than an individual

fibroblast, " von Recum said, adding that the cells attached to the textured

disks by depositing proteins into the grooves.

Fibroblasts from mice were left to grow on both the smooth and textured

disks for three days. At the end of that time, the researchers used

photomicrography ­ taking an image through a confocal microscope ­ to

determine the distance between cell membranes and disk surfaces.

The distance between the fibroblasts and the surface of the textured disks

was immeasurable, suggesting that these cells had adhered to the surface.

Conversely, the researchers could measure the distance ­ although very

small, on the order of nanometers ­ between cell membranes and the surface

of a smooth disk.

" Texturing provided a strong adherence between the surface of a cell and the

surface of a disk, " von Recum said. " That's exactly what we want in an

actual implant. "

That the cells responded so readily to physical changes on the disk surfaces

surprised the researchers.

" Almost everything in the biological world responds primarily to chemical

signals, " von Recum said. " It was astonishing to find that these fibroblasts

responded strongly to mechanical signals on the disk surface. "

Adding texture to implants isn't a new concept; it first gained popularity

in the 1960s.

" The problem with those implants was that the scale of roughness was a

hundred to a thousand times larger than what we've found to be effective, "

von Recum said. " The interface went beyond a layer of connective tissue

cells ­ these old implants essentially became embedded in the body as

connective tissue and bone grew into them. Their removal was nearly

impossible, as it usually resulted in major bone loss in some types of

implants.

" The technique we're proposing ­ and it will be some time before such

implants are made and used ­ doesn't adhere nearly as strongly to the

surrounding tissues, " he continued.

von Recum realized the problems smooth-surfaced implants presented while

working with catheters used for long-term life support.

" Tissue eventually builds up around the area where the smooth plastic of

these catheters enter the skin, " he said. " The area is at risk for infection

and becomes a source of discomfort and possibly mortality ­ people who

depend on a catheter usually can't survive an infection.

" If cells could directly attach to an implant, problems with dead tissue

build up, infections and implant replacements would be far less common. "

Funding for this work was provided in part by Ohio State University.