Absorbable sutures have the benefit over non absorbable sutures of not requiring removal. The chitosan salts are biocompatible and biodegradable making them useful as absorbable haemostats. Suturing of buccal incision is recommended with absorbable suture material. The rectus fascia is closed with monofilament absorbable suture. The layers of tissue in the knee are stitched together, usually with absorbable sutures. The wound is closed with a single absorbable suture or with adhesive strips. PGA suture is classified as a synthetic, absorbable, braided multifilament. The first known absorbable sutures were made of the intestines of sheep. Occasionally, absorbable sutures can cause inflammation and be rejected by the body rather than absorbed. The skin can be closed with suture which may be visible or invisible (absorbable). It is often used in conjunction with the absorbable suture Monocryl. The following table compares some of the most common absorbable sutures. Catgut has largely been replaced by synthetic absorbable polymers such as Vicryl and polydioxanone. The first synthetic absorbable was based on [[polyvinyl alcohol]] in 1931. The light saturation point is the maximum amount of photons absorbable by a plant species.