question: What makes medical grade skin adhesive patches so sticky, and how are they able to stay in place for weeks at a time?
comment: Really strong glue chemically bonds to the surfaces it's applied to. Scientists found a glue that chemically mixes with the skin permanently. But it only reacts with the top layer of skin. As your skin cells die off and shed, the chemically bonded cells are shed too. So when the patch comes off, it's not really the glue that wore off, but the skin it bonded to.
passages: PSAs are designed for either permanent or removable applications. Examples of permanent applications include safety labels for power equipment, foil tape for HVAC duct work, automotive interior trim assembly, and sound/vibration damping films. Some high performance permanent PSAs exhibit high adhesion values and can support kilograms of weight per square centimeter of contact area, even at elevated temperatures. Permanent PSAs may initially be removable (for example to recover mislabeled goods) and build adhesion to a permanent bond after several hours or days.
   In contrast with structural adhesives, whose strength is evaluated as lap shear strength, pressure-sensitive adhesives are characterized by their shear and peel resistance as well as their initial tack. These properties are dependent, among other things, on the formulation, coating thickness, rub-down and temperature.
  
  ""Permanent"" pressure-sensitive adhesives are initially pressure-sensitive and removable (for example to recover mislabeled goods) but after hours or days change their properties, by becoming less or not viscous, or by increasing the bond strength, so that the bond becomes permanent.
  
  Section::::Structural and pressure-sensitive adhesives.:Effects of shape.
   Section::::Lifetime.
  
  A pressure-sensitive adhesive will experience a range of conditions throughout its lifetime. These conditions affect one of the following parts of the tape: the surface or the bulk. The surface is merely the part of the tape that is exposed to the environment through the whole of its lifetime. The bulk is everything under the surface of the tape, that is the interactions that occur between the substrate and the adhesive part of the tape.
  
  Section::::Lifetime.:Surface exposure conditions.
   Fugitive glues are frequently used in marketing, where some object—product sample or a return envelope—is glued to another, usually paper, object—a mailing envelope or a magazine. They tend to perform best on smooth, non-porous surfaces. In these applications, fugitive glues are not resealable pressure-sensitive adhesives such as are used on pressure-sensitive tapes or post-it notes, although resealable formulations are available.
  
  Fugitive glues are usually available in hot melt or latex form, with low VOC emissions. They can be also applied in liquid form.
   An adhesive bandage is a small, flexible sheet of material which is sticky on one side, with a smaller, non-sticky, absorbent pad stuck to the sticky side. The pad is placed against the wound, and overlapping edges of the sticky material are smoothed down so they stick to the surrounding skin. Adhesive bandages are generally packaged in a sealed, sterile bag, with a backing covering the sticky side; the backing is removed as the bandage is applied. They come in a variety of sizes and shapes.
  
  Section::::Materials.
   As of 2012, there are no documented or proven examples of sticky-shed from Maxell. TDK has been showing signs as of late of shedding its lubricant in the form of a white powder or white/yellowish goo. This has shown up on the TDK SA and some LX and BX tapes. There have been a few reports of some tape from the current manufacturers ATR and RMGI exhibiting symptoms of sticky-shed. But these may be isolated incidents relating to prototype or single bad batches and are not necessarily indicative of the overall product line integrity.
   Dermotextile
  
  Dermotextile is a natural and visual alternative to cosmetotextile in merging selected skincare active ingredients to different types of support like textiles. With the dermotextile technology, textiles are printed with a continuous controlled release system composed of bio-based microparticles carrying dispersed skincare actives intended for cosmetic, therapeutic, pharmaceutical or medical use. The continuous release system imprinted creates a visual pattern that, with use, will slowly disappear, communicating the efficacy of the transfer onto the skin.
   Section::::Types.:By reactiveness.:Non-reactive.:Contact.
  
  "Contact adhesives" are used in strong bonds with high shear-resistance like laminates, such as bonding Formica to a wooden counter, and in footwear, as in attaching outsoles to uppers. Natural rubber and polychloroprene (Neoprene) are commonly used contact adhesives. Both of these elastomers undergo strain crystallization.
   The release pattern of the microcapsules on cosmetotextiles is triggered by an impact, most likely friction or pressure between the body and fabric, breaking the capsules into fragments and liberating the cosmetic properties.
   Section::::Self-healing polymers and elastomers.:Extrinsic polymer-based systems.:Microcapsule healing.
  
  Capsule-based systems have in common that healing agents are encapsulated into suitable microstructures that rupture upon crack formation and lead to a follow up process in order to restore the materials' properties. If the walls of the capsule are created too thick, they may not fracture when the crack approaches, but if they are too thin, they may rupture prematurely. 
   Polyorthoesters are used as hydrophobic implant materials for drug depots for continuous drug delivery by surface erosion. The active ingredient (which is homogeneously dispersed in a matrix of polyorthoester) should be released as evenly as possible into the human or animal organism over an extended period of time in a zero-order release kinetics. Four classes of polyorthoesters (polyorthoesters type I - IV) are well characterized as biodegradable polymers for drug implants, primarily through work of Jorge Heller (1927-2009).
  
  Section::::Production.
  
  Section::::Production.:1st generation polyorthoester (POE I).
   Section::::Application.:Environmental factors.
   That being said, in order to avoid delamination, selection of an adhesive tape needs to be based upon the conditions that the tape will experience over its lifetime. This selection process will reduce the chains of adhesive tape degradation and failure occurring during the lifetime of the tape though there is not guarantee that this process will completely avoid the possibility.
  
  Section::::Lifetime.:Effects on recycling.
   Recent studies have started to question the nature of the microcapsules’ shells and their toxicity impact or possible allergy reactions on humans. Because shell residues and excessive irregular amounts of substance are left on the skin surface after liberation, micro-encapsulation is more and more preferred for applications that are not in direct contact with human body, while the dermotextile technology, using natural based micro-particles as cosmetic carriers instead of microcapsules, is slowly taking over the skincare field.
   In the Langer lab, Karp was inspired by another lab's publication in "Nature" that described adhesives based on the way that gecko's feet stick to surfaces; he and Langer applied for funding from NSF to make medical adhesives based on geckos, and received the funding.
   The interplay of molecular scale mechanisms and hierarchical surface structures is known to result in high levels of static friction and bonding between pairs of surfaces . Technologically advanced adhesive devices sometimes make use of microstructures on surfaces, such as tightly packed periodic posts. These are biomimetic technologies inspired by the adhesive abilities of the feet of various arthropods and vertebrates (most notably, geckos). By intermixing periodic breaks into smooth, adhesive surfaces, the interface acquires valuable crack-arresting properties. Because crack initiation requires much greater stress than does crack propagation, surfaces like these are much harder to separate, as a new crack has to be restarted every time the next individual microstructure is reached.
   Various innovative approaches and engineered materials are used to keep in line with requirements. Some designs apply sticking based on vacuum in addition to high friction and softness (see e.g. micro-suction tapes).
  
  Other development includes designs that find inspiration in nature, especially in animals that are able to climb walls and ceilings such as geckos, 
  
  various species of insects
  
  , tree frogs
  
  , or chameleons.
   Surface factors such as smoothness, surface energy, removal of contaminants, etc. are also important to proper bonding.
  
  PSAs are usually designed to form a bond and hold properly at room temperatures. PSAs typically reduce or lose their tack at low temperatures and reduce their shear holding ability at high temperatures; special adhesives are made to function at high or low temperatures.
  
  Section::::Structural and pressure-sensitive adhesives.
   Section::::Mucoadhesives in drug delivery.:Dosage Forms.
  
  Section::::Mucoadhesives in drug delivery.:Dosage Forms.:Tablets.
  
  Tablets are small, solid dosages suitable for the use of mucoadhesive coatings. The coating may be formulated to adhere to a specific mucosa, enabling both systemic and targeted local administration. Tablets are generally taken enterally, as the size and stiffness of the form results in poor patient compliance when administered through other routes.
  
  Section::::Mucoadhesives in drug delivery.:Dosage Forms.:Patches.
   However, the substrate can still be affected by humidity and UV exposure if the substrate is applied in an environment that it was not designed for. For instance, one could get substrate failure by using a tape that was made to be used in a desert in a place such as Florida. The difference in temperature might not be very large, but there is a huge difference in humidity. Any environmental effect on the substrate is dependent on the identity and purpose of the substrate.
  
  Section::::Lifetime.:Mechanical wear.
   Section::::Applications.:Tissue scaffolding.
   Section::::Physics.:Wear.:Rubbing Wear or Fretting.
  
  The rubbing wear occurs in systems subject to more or less intense vibrations, which cause relative movements between the surfaces in contact with the order of the nanometer. These microscopic relative movements cause both adhesive wear, caused by the displacement itself, and abrasive wear, caused by the particles produced in the adhesive phase, which remain trapped between the surfaces. This type of wear can be accelerated by the presence of corrosive substances and the increase in temperature.
  
  Section::::Physics.:Wear.:Erosion Wear.
   Application of the patch tests takes about half an hour, though many times the overall appointment time is longer as the provider will take an extensive history. Tiny quantities of 25 to ~150 materials (allergens) in individual square plastic or round aluminium chambers are applied to the upper back. They are kept in place with special hypoallergenic adhesive tape. The patches stay in place undisturbed for at least 48 hours. Vigorous exercise or stretching may disrupt the test.
   Billy Bunter is glued into a chair with seccotine in The Magnet #100 (1910).
  
  In the C.S. Lewis novel "That Hideous Strength" (1945) a character is described as having a cigarette "seccotined" to her lip.
  
  In the E. Nesbit novel "The Story of the Amulet" (1906) a broken saucer would never be the same again even if bits were joined "with Seccotine or the white of an egg."
   Some types are commonly used in sports to add a non-slip wrapping to things which must be gripped, such as tennis racquets, and hockey and lacrosse sticks, because of their rough texture and removability leaving little residue.
  
  Section::::History.
  
  Primitive surgical tape, or "sparadrapum" probably consisted of strips of cloth impregnated with some type of plaster or sticky gum, which was applied over gauzes or wound dressings to hold them in place. Plaster casts over fractures were sometimes called "Spanish dressings"
  
raw_presuppositions: Medical grade skin adhesive patches are very sticky and strong enough to remain in place for weeks.
raw_corrections: It is not only the strength of the adhesive patch, but the chemical reaction it has with the skin of it's user that causes it's strong bond.