Geckotech uses fractally branching setae for maximum adhesion
Geckotech is a vital and ubiquitous technology throughout virtually all of Terragen Colonized Space. It was one of the first fruits of nanoscale materials technology, and in its most primitive state, dates back to the 1st Century AT.
In the middle 1st Century AT (The early 2000's CE, for students of Old Earth history), researchers studying the climbing methods of geckos, other lizards and insects discovered that the "stickiness" of their feet was due to van der Waals attraction between the tiny setae and the surfaces they were climbing. Using the same principles, but using nanofactured setae with even finer nanostructure, they were able to equal and eventually exceed by over two hundred fold the level of adhesive force per area by using carbon nanotubes to increase the adhesive's surface density. Carbon nanotubes, and in some cases diamondoid or corundumoid, nanohairs remain vital in Class 2 and Class 3 Geckotech to the present day.
Class 1 Geckotech: The first mass-produced geckotech wasn't based on carbon nanotubes, but instead a durable plastic polymer. It possessed a far inferior adhesive strength per area than that of the aforementioned mass-produced nanotube-based geckotech, which was produced later in the 1st Century. The first geckotech made possible a variety of applications, from robots capable of climbing vertical and inverted surfaces, climbing gloves and shoes for sports or military use, to ordinary tape. Predictably, some of the sports purists objected to adhesive climbingware's use. Such geckotech is still used in modern times (though constructed of more durable materials) in applications where stronger adhesion is unneeded. It is known as Class 1 Geckotech and has an adhesive bonding force ranging from fractions of a gram to approximately one kilogram per centimeter squared of adhesive; depending on the needs of the application.
New (at the time) types of clothing, including dress tops and hu swimwear called "bikinis" became possible due to geckotech's creation. Clothing designers of the time made some such clothes no larger than small patches, which only covered skin areas that were taboo in some polities on Old Earth. Zippers, buttons, and a mechanical adhesive called "hook-and-loop tape" were replaced on many clothes by patches of geckotech. This novel way of fastening clothes and linking pieces of cloth together allowed, and where higher technology isn't used still allows, a wide variety of clothing to be pieced together from constituent parts to form highly variable garments. None of the aforementioned types of fasteners became extinct (at least permanently) however. Zippers and buttons are still found on some clothing even in certain ultratech civilizations.
Geckotech-based tape, which appears to have supplanted a tool called "duct tape", is used to carry out makeshift repairs. Indeed, a standing joke in modern times within some polities or meme sets is that some groups (often in the Outer Volumes) use geckotech tape to make critical repairs to their technology.
Class 2 Geckotech was developed later in the 1st Century AT. The advance over Class 1 is due to the adhesive's spatulae* hairs being tipped in carbon nanotubes. This increase in the surface density results in a greater adhesive force per area. Class 2 Geckotech's adhesive force ranges from just over one kilogram per centimeter squared (where Class 1 leaves off) to just below twenty-six kilograms per centimeter squared. Beyond this adhesive force per area, the adhesive cannot self clean if it gets dirty; because it has a stronger bond with dirt particles than surfaces have with the dirt. A stronger adhesive class using Middle-tech level technology for one to few-time use (before requiring cleaning) in dirty environments, or prolonged, repeated use in clean room environments exists. It is known as Clean Use Class Geckotech. Once dirt particles bond to enough of the carbon nanotube hairs' (their technical name is 'capelli') tips, the adhesive becomes totally useless until it is manually cleaned via high pressure air or water jets, which apply a great enough force to the dirt particles to overcome the van der Waals bonding.
Class 3 Geckotech's development began in the 4th Century AT, after the difficulties with dry nano had been overcome. However, it didn't reach its modern potential until hylonano matured. Class 3's setae have a far more complex structure than their Class 2 and 1 predecessors. They consist of hollow, nested, microtech scale diamondoid tubes. The innermost tube is tipped in hairs that are the scale equivalent of Class 2 and 1's spatulae, and like Class 2, the spatulae* are tipped in numerous carbon nanotubes. Class 3's nanotubes are far more numerous per spatula tip than Class 2's, and unlike Class 2's, they in turn end in hundreds of yet smaller nanotubes. The smallest nanotubes, technically known as 'fibre', are 0.4nm in diameter. The nested tube structure of the setae allows them to telescope, lengthening to bring as many of the tiny hairs they bear on their tips into contact with the surface being bonded to. This ability, combined with the far greater density of nanoscale hairs coming in contact with the surface, allows Class 3 to support hundreds of kilograms** per centimeter squared of adhesive area. This increase in adhesive force per area compounds the problem that limits Class 2's adhesive force to less than twenty-six kilograms per centimeter squared. The problem of dirt particles fouling the adhesive by them clinging too strongly to the carbon nanotube hairs to self-clean during use is overcome via the use of a specialized utility fog that cleans particle-fouled hairs. Unlike Class 1 and Class 2 Geckotech, Class 3 requires an energy input beyond that required to simply move, preload and then later peel the adhesive off again. An alternate architecture for Class 3 lacks the telescoping setae, which are replaced by solid pandifico hairs grown biologically and the cleaner-foglets are replaced by bionano and/or synano systems.
The advantages of geckotech adhesive over other mechanisms such as suction, interlocking, magnetic, chemical and static adhesives are: Unlike suction adhesion, which cannot function in a vacuum, and can only function slightly in low-pressure environments, geckotech adhesive can attach with its full force irrespective of the presence or not of an atmosphere. However, geckotech cannot adhere to tetrafluoroethylene compounds or omniphobic-coatings. Neither can chemical, magnetic or interlocking. Therefore, provided an atmosphere or hydrosphere exists to exert a pressure on the vacuum cup, suction adhesion does have minor functionality in modern civilization.
Interlocking adhesives, while used in certain applications, sometimes in hybrid with geckotech, cannot adhere to atomically flawless surfaces. Geckotech, however, can adhere to atomically smooth as well as very rough surfaces due to its bonding mechanism and the various scales of hairs that bend to adapt to irregular surfaces.
Magnetic adhesion is only effective on metallic elements such as iron, cobalt and nickel.
For use in locomotion, chemical adhesives are impracticable above the scale of small insects or synsects. Synsects, beyond the first, lab bound, pre-geckotech prototypes of the 1st Century AT, have never employed chemical adhesives in order to adhere to the surfaces they navigate. Small insects and other organisms only evolved chemical adhesives for locomotive use because they were (and for the organisms that haven't been gengineered to posses superior geckotech, still are) functional enough to provide a survival advantage.
Electrostatic adhesion is far too weak for most macroscopic applications. Where electrostatic adhesion could be used it isn't, due to the far superior bonding strength per area of geckotech. Electrostatic adhesion isn't functional in environments with a heavy electrical charge in the atmosphere, in highly humid environments and underwater (and other fluids). Geckotech adhesive isn't affected by any of these.
Capillary adhesion, like electrostatic, is far too weak to be of use at scales larger than insects or small amphibians. It, like chemical adhesives, evolved on animals as a "good enough" trait. That is, good enough for their survival.
Due to geckotech's need to bring as many of its nanoscopic hairs in contact with a surface as possible, often setae are not mounted on a flat, flexible substrate, but instead on the tips of larger hairs. In some cases, such hairs are mounted on the tips of yet larger hairs and so forth. The technical names of the two hair scales larger than setae are technically known as 'aiguille' and 'spoletta'. They increase the number of bending scales the adhesive has, which allows the geckotech that possesses them (and in some cases, even larger hairs) the ability to adapt to macroscopically very rough surfaces.
Geckotech adhesive is used for virtually endless applications throughout Terragen Civilization, therefore this article, which is intended to be of reasonable brevity, can only mention a tiny fraction of them:
The applications that touch the lives of the largest numbers of beings within Terragen Civilization are those that employ geckotech as a locomotion aid. Countless clades, non-sophont beings and mechanisms possess geckotech engineered, gengineered or neogened into them as one of their traits. Sophont bionts rarely posses Class 1 Geckotech; instead they bear Class 2, bionano or synano based variants of Class 3 that were first developed in the Zoeific Biopolity. The same holds true for vecs, cyborgs, nanoborgs and other semi- to fully-non-biological beings. Excluding some cyborgs, if these non-biological beings possess Class 3 Geckotech, it is rarely fully bionano based. Such adhesive appendages are useful in gravity environments for climbing vertical and navigating inverted surfaces without falling. In ultra-low or zero gravity environments, they are useful for temporary holdfasts and/or to allow, for whatever reason, the ability to move in a manner analogous to that of beings in gravity environments.
Geckotech-bearing appendages are useful for grasping objects without the need to wrap digits, arms, tentacles, pseudopodia or other manipulatory appendages around the object. For example: certain clades of cephalopod ancestry have been gengineered to employ geckotech inside their "suckers".
Predictably, setae have been convergently evolved by xenorganisms on many worlds. Artifacts from extinct xenosophont civilizations have been found that incorporate adhesives indistinguishable from Terragen geckotech. It is likely that most of these civilizations studied organisms, perhaps even themselves, in order to understand the underlying principles involved for their creation of "geckotech" instead of arriving at the idea via trial and error.
The term 'spatulae' originates from the fact that on naturally evolved Old Earth animals such as geckos and anoles, this scale of hair ends in a spatula-like tip. This isn't true of Class 2 and 3 Geckotech, as previously described. However, Class 1, while not always, is sometimes engineered to this structure.
* Class 3, and lower classes as well, are only able to bear their limit in weight if the surface they are bonding to can bear this weight as well. Some materials, such as crumbling limestone, shale, flaky plant bark and lichen, aren't capable of supporting the same, or even close to the same, weight as materials such as less-weathered limestone, sandstone, granite, diamondoid, metals, alloys and plastics.