Overview of Manufacturing Processes - Nanotechnology and the Environment - page 34

FiguRe . Example.of.a.micro-injection.molded.medical.implant,.next.to.a.penny.for.scale..
(From.Miniature.Tool.and.Die,.Charlton,.MA,.www.miniaturetool.com..With.permission.)
makers..The.manufacturing.process.must.control.both.the.geometry,.in.terms.of.the.
size,.shape,.and.interconnection.of.components,.and.the.presence.of.conducting.and.
insulating.materials.in.speciic.locations..Injection.molding,.a.very.different.process.
from.lithography,.is.used.to.make.everything.from.large.appliance.and.electronics.
enclosures.to.medical.implants.(Figure.3.1)..For.the.latter,.form.is.represented.by.the.
control.of.the.implant.geometry,.and.function.by.the.necessary.strength,.stiffness,.
and.wear.properties.of.the.material.
3.1.2 l OOking F Orward …l OOking b aCk
Over. the. many. centuries. of. human. development,. the. fabrication. of. products. has.
changed.enormously,.in.terms.of.materials,.tools,.scale,.complexity,.and.degree.of.
human.interaction..However,.these.changes.have.not.been.purely.monotonic.in.their.
progression.. For. example,. early. materials. were. all. “natural. materials”. —. that. is,.
wood.from.trees,.skins.from.animals,.stones.from.the.ground..Although.mixing.of.
materials.to.form.metal.alloys.was.conducted.more.than.4000.years.ago,.remarkable.
advances.have.been.made.in.materials.processing.within.the.most.recent.50.years..
Included.among.these.advances.have.been.discoveries.leading.to.new.“man-made”.
or. synthetic. developments,. such. as. shape. memory. alloys. that. change. shape. at. a.
speciied.temperature,.used.for.applications.as.varied.as.orthodontic.wires,.medical.
insertion. devices,. and. military. actuators;. polymer. ibers. for. ballistic.protection. or.
moisture-wicking.athletic.clothing;.and.semiconductor.materials.that.form.the.core.
of.all.current.electronic.devices..More.recently,.however,.there.has.been.a.return.to.
“natural. materials”. in. efforts. to. create. environmentally. benign. materials. derived.
from.biodegradable.and.renewable.resources.