Where does adhesion collide?

In surface science and materials engineering, adhesion is the interfacial bonding that holds two surfaces together when they are brought into contact, resisting their separation. Johnson, Kendall, and Roberts's 1971 Surface energy and the contact of elastic solids showed how the surface energy of the contacting bodies produces an attractive force that enlarges the contact area beyond what the applied load alone would give, setting the modern account of the work of adhesion. The strength of a joint is read from the force needed to peel or pull it apart, and a break is called adhesive when it runs along the interface or cohesive when it runs through one of the materials. The referent is a physical bond between two solid surfaces, measured in energy per unit area or peel force, not a cell sticking to its neighbours, a scar joining two organs, or a one-sided contract.[1]

Unit

A physical bond between two surfaces, as work of adhesion in energy per unit area or as peel force

Recovery means

For elastic solids the contact can be reversible, springing apart once the pulling force exceeds the adhesive force, though real engineered joints often fail permanently

Measured by

Quantified by peel, pull-off, and lap-shear tests, and by the work of adhesion inferred from contact mechanics and surface energy

In cell biology, adhesion is the binding of a cell to other cells or to the extracellular matrix, mediated by families of adhesion molecules such as cadherins, integrins, and selectins. Gumbiner's 1996 Cell adhesion: the molecular basis of tissue architecture and morphogenesis set out how these receptors organise cells into tissues, transmit signals across the membrane, and drive the movements of development. Here adhesion is a specific, receptor-mediated recognition event that can be switched on and off, not the passive contact of two inert surfaces. The referent is a molecular attachment between living cells, assayed by which molecules bind and how firmly cells resist detachment, and it is unrelated to a peeled joint, a surgical scar, or a contract.[2]

Unit

A receptor-mediated attachment of a cell to other cells or to the extracellular matrix

Recovery means

Adhesion is dynamic and reversible: cells release and reform contacts as their receptors are regulated, which lets them migrate and rearrange

Measured by

Assessed by adhesion assays that count bound cells or measure the force to detach them, and by identifying the cadherins, integrins, or selectins involved

In surgery and medicine, adhesions are abnormal fibrous bands of scar tissue that form between organs or tissue surfaces that are normally separate, most often after abdominal surgery, infection, or inflammation. Arung, Meurisse, and Detry's 2011 Pathophysiology and prevention of postoperative peritoneal adhesions reviewed how injury to the peritoneum disturbs the balance between fibrin deposition and breakdown, so that fibrin bridges persist and mature into collagenous bands. Such adhesions can distort anatomy and are a leading cause of bowel obstruction, chronic pain, and infertility. The referent is unwanted scar tissue that pathologically joins structures inside the body, counted by its clinical consequences, not a designed bond, a molecular receptor, or a legal document.[3]

Unit

A fibrous band of scar tissue abnormally joining tissues or organs

Recovery means

Not applicable: mature adhesions rarely resolve on their own and usually require surgical division, which itself risks forming new adhesions

Measured by

Identified at surgery or on imaging and graded by extent and density, and studied through their complications such as rates of bowel obstruction

In contract law, a contract of adhesion is a standardised agreement drafted by the party with superior bargaining power and offered to the other on a take-it-or-leave-it basis, with no real opportunity to negotiate its terms. Kessler's 1943 Contracts of adhesion: some thoughts about freedom of contract named the form and warned that mass-produced standard contracts let a dominant firm legislate private terms behind the language of free agreement. Courts respond by construing ambiguities against the drafter and by refusing to enforce terms that are unconscionable or beyond the weaker party's reasonable expectations. The referent is a legal instrument defined by unequal bargaining and imposed terms, and it borrows the word adhesion only as a metaphor for one side merely adhering to what the other wrote.[4]

Unit

A standardised take-it-or-leave-it contract whose terms are set by the stronger party

Recovery means

Not applicable

Measured by

Not measured numerically: identified by courts from the drafting process and unequal bargaining, and policed through doctrines of construction and unconscionability