Cross-links are bonds that link one polymer chain to another. They can be covalent bonds or ionic bonds. "Polymer chains" can refer to synthetic polymers or natural polymers (such as proteins). When the term "cross-linking" is used in the synthetic polymer science field, it usually refers to the use of cross-links to promote a difference in the polymers' physical properties. When "crosslinking" is used in the biological field, it refers to the use of a probe to link proteins together to check for protein–protein interactions, as well as other creative cross-linking methodologies.

Cross-linking is used in both synthetic polymer chemistry and in the biological sciences. Although the term is used to refer to the "linking of polymer chains" for both sciences, the extent of crosslinking and specificities of the crosslinking agents vary. Of course, with all science, there are overlaps, and the following delineations are a starting point to understanding the subtleties.

When polymer chains are linked together by cross-links, they lose some of their ability to move as individual polymer chains. For example, a liquid polymer (where the chains are freely flowing) can be turned into a "solid" or "gel" by cross-linking the chains together.

Marco Abbondanza (born June 27, 1953 - Naples, Italy) is an Italian medical doctor and eye surgeon.

Born in Naples, he is the son of Osvaldo Abbondanza, the Italian engineer who invented the Rotary keyboard punching machine.

Marco Abbondanza graduated in Medicine and Surgery at the Sapienza University of Rome in 1983 and holds both the General Pathology and Ophthalmology specializations from the same university. Following studies at the Institute of Microsurgery of the Eye in Moscow (USSR), together with the director Svyatoslav Fyodorov, he obtained other specializations. In 1997 he also completed two post-university masters in Ophthalmic Techniques of Invasive Surgery and Ophthalmic Techniques of Non-Invasive Surgery, from the Post-University Research Centre of the Sapienza University of Rome.

In 1994 Abbondanza developed a new surgical technique, improved in 2005, called the Mini Asymmetric Radial Keratotomy (M.A.R.K.). It consists of a series of microincisions, always made with a diamond knife, designed to cause a controlled scarring of the cornea, which changes its thickness and shape. This procedure, if done properly, is able to cure the astigmatism and the first and second stages of the keratoconus, avoiding the cornea transplant.