Absorbable sutures natural materials

In general, absorbent sutures are composed of materials that are natural to mammals, such as catgut, and to materials that are either quite susceptible to hydrolysis and/or polymers derived from natural materials such as polyglactin, which is a copolymer of lactic and glycolic acid. Nonabsorbent sutures can be made from natural materials such as cotton, which is a plant material, polymers that range from being hydrophobic to hydrophilic, and steel. 

Sutures remain the most common method of tpproximating the divided edges of tissue (1). Sutures are categorised by size, material, design and behaviour. Absorbable and nonabsorbable materials are further divided into synthetic versus natural products, some of vdiich can be fabricated in braided and/or monofilament form. Non-absorbable sutures have played an important role in the development of surgical procedures, generally made of silk, polyamide, polyester, polypropylene, polyethylene and poly(tetrafluoroethylene) (2). 

An absorbable suture was one that lost a significant portion of its mechanical strength over a period of 2 months > hile a non-absorbable suture was one that maintained a significant portion of its strength longer than 2 months [4]. A suture may lose its toisile strength over a relatively short period of time, but require months or evoi years to absorb completely and be eliminated from the body. The prinuiry mode of degradation for natural materials is enzymolysis, vdiereas for synthetic absorbable materials it is hydrolysis [3]. 

The previous chapter provided a general overview of the properties of materials used for surgical sutures and of the desirable characteristics of such materials. This chapter considers absorbable and nonabsorbable materials in greater detail, looking within each category first at natural materials, and second at synthetic materials. In the section on absorbable materials, natural materials reviewed are ... 

Sutures are also classified according to size. Currently, two standards are used to describe size USP (United States Pharmacopeia) and EP (European Pharmacopeia) (Chu et al., 1997). Appendix 2 at the end of this chapter provides a summary of these. In the USP standard, which is used most commonly, the size is represented by a series combination of two Arabic numbers a zero and any number other than zero, for example, 2-0 (or 2/0). The higher the first number, the finer is the suture material. Sizes larger than 0 (1/0) are denoted by 1,2,3 etc. This standard also varies with the type of suture material. In the EP standard, the code ranges from 0.1 to 10. The corresponding minimum diameter (mm) can be easily calculated by taking the code number and dividing it by 10. The EP standard does not separate natural from synthetic absorbable sutures as does USP. Table 10.A.2 in the Appendix at the end of this chapter outlines USP and EP suture size classification... 

Poly(lactic acid) (PLA) (Fig. 1.16) is an aliphatic polyester polymerised by lactic acid which is made by fermentation of natural raw materials, for example, com starch and sugarcanes. Due to the chiral nature of lactic acid and its effects on the polymer s characteristics, the biodegradability and mechanical properties of PLA can be tailored by varying the proportion of different forms. Meanwhile, PLA can also copolymerise with other monomers or blend with other polymers to improve some properties of the material, eg, flexibility. PLA and PLA-based copolymers are the most popular biodegradable materials for the production of absorbable sutures (Li, 1999) (Fig. 1.16). 

During the healing period, absorbable sutures are replaced by healthy tissue. In general, the tissue response to synthetic absorbable sutures is foreign body in nature. Further, the inflammatory response has been reported by Blomstedt (Blomstedt and Osterberg, 1978) to be less pronounced around suture materials wath low capillarity. 

Whereas most medical uses of polymeric materials require biostability, applications that use the biodegradable nature of some macromolecules have been developed. An example is the use of poly(glycolic acid) and glycolic acid/lactic acid copolymers as absorbable sutures, which go under the trade name Lactomer. 

Poly(glycolic acid) (PGA) is a biodegradable and bioresorbable polyester widely used in biomedical applications. It was first introduced as a material for bioresorbable sutures in the 1970s. PGA has good mechanical strength and a predictable bio-resorbability (i.e., PGA monofilament sutures can be absorbed in the body in about 2—4 weeks depending on their hydrophilic nature), which is a desirable property for... 

Nonabsorbable sutures are divided into natural fibers (silk, cotton, linen), and man-made fibers. The latter include polypropylene, polyanfide, polyester, poly(ether ester), polytetrafluoroethylene (Gore-Tex ), polyvinylidine fluoride (PVDF), and stainless steel. Monofilament Dyloc (from Dynek, Australia) is unusual among synthetic nonabsorbable sutures because it is made from a nonconventional man-made fiber poly(ether ester) (Fig. 10.2). The main types of material for both absorbable and nonabsorbable sutures are discussed in Chapter 11. 

---