Normal wound healing compared to healing within porous Dacron implants.

This study examined the hypothesis that healing within porous implants differs from that in normal connective tissue. Special attention was given to extracellular components including collagen, reticular fibers, and ground substance, and to enzymes associated with activated macrophages. Using Dacron velour and the rabbit as host, the healing of normal connective tissue and that of the tissue/implant interface were histologically compared 10 and 28 days postimplantation. The results exhibited significant differences between connective tissue healing, implant capsule formation, and granulation tissue generation. The healing of connective tissue and implant capsule formation were essentially complete at 28 days. However, tissue inside the implant was qualitatively different and did not significantly change between 10 and 28 days. It was characterized by macrophages and giant cells, a predominantly acid mucopolysaccharide ground substance, and qualitatively fewer and less well defined collagen and reticular fibers were observed than in normal wound healing. Thus we conclude that the connective tissue inside Dacron velour does not resemble normal connective tissue after 10 or 28 days of healing. Furthermore, the collagen never fully matures into orderly bundles, a phenomenon which may be related to an altered mucopolysaccharide composition and a diminished reticular network. The lysosomal enzymatic activity of the macrophages and perhaps the giant cells at the tissue/implant interface may be linked to these differences.

Some aspects of macrophage behavior at the implant interface.

The macrophage plays a pivotal role in both wound healing and cellular response to implants, including percutaneous devices. Within twenty-four hours macrophages were found in close contact with the implant surface. Eventually fibroplasts and connective tissue proliferate, and finally the implant will be encapsulated. The presence of macrophages is essential for the activation of collagen synthesis by fibroplasts . Implant shape and surface can profoundly affect macrophage behavior. At rough implant surfaces macrophages with giant cells are present for many months with the possibility of chronic granulomatous reactions. Superior tissue compatibility should be associated with smooth, well contoured implants with no acute angles.

Ultrastructural observations of cells at the interface of a biodegradable polymer: Polyglactin 910.

Transmission electron microscopy was used to study the ultrastructure of cells at the interface with an implanted biodegradable polymer, Polyglactin 910. Various stages of implantation were observed from 1 day to 63 days, when absorption of the polymer was essentially complete. Events occurring at the interface include initial adhesion of macrophages on the implant surface; phagocytosis of wound debris; and subsequent erosion, invasion, and phagocytosis of the polymer by macrophages and giant cells. A vascular perfusion technique for fixation of the polymer sites implanted in soft tissue is also described.

Biologic response to sutures.

Whenever a foreign object is implanted in living tissue, a cellular response occurs. Sutures usually produce a mild response that varies in character with different materials. The cellular and tissue reaction can be evaluated by both morphologic and enzyme histochemical approaches. Such studies assist in understanding suture absorption and the degree of inertness in tissues associated with the various suture materials. In addition, the in vivo measurement of breaking strength retention provides information on suture safety. Such studies also assist in the development of improved suture materials for various surgical applications.

The biologic and physical criteria for suture selection in cataract surgery.

This paper has disucssed histochemical, physical, and clinical considerations involved in proper suture selection for cataract surgery. Guidelines are proposed so that the surgeon can employ a standard method for evaluating each suture's performance. Accordingly, the surgeon can select the proper proper suture to satisfy his needs regardless of his operative technique.

Tissue response to implanted polymers: the significance of sample shape.

Studies were designed to demonstrate the need for standardization of shape of samples used as implants to evaluate histotoxicity of polymer materials. Six medical-grade polymers (polypropylene, polyethylene, polyurethane, silicone rubber, poly(vinyl chloride), and Teflon) were extruded as rods with circular-, triangular-, and pentagonal-shaped cross sections, and were implanted in rat gluteal muscles for 14 days. Evaluation of the tissue response was assessed by quantitating cellular lysosomal acid phosphatase enzyme activity by using microspectrophotometry. All triangular-shaped implants showed the highest enzyme activity and cellular response; pentagon shapes showed less, and circular rods showed the lowest activity. The results demonstrate the need for standard sample shape for valid comparative studies of tissue response to implanted polymers.

Polyglactin 910 suture absorption and the role of cellular enzymes.

Enzyme histochemical procedures for both hydrolase and oxidoreductase enzyme activity were applied to cryostat sections of polyglactin 910 suture implant sites. Sutures were implanted either solely in tissue or in a combination of in vitro incubation followed by implantation in vivo for total time periods of seven to 56 days. Suture absorption rates were also measured. It is concluded from the results that neither cellular nor enzyme activity is necessary for the degradation and absorption of polyglactin 910 sutures. This conclusion is based on similar absorption rates for sutures implanted solely in vivo and sutures treated in vitro and then implanted in tissue to give equivalent time spans. There were strong indications, however, that the products of suture hydrolysis are probably metabolized through the oxidative enzyme systems of cells adjacent to the suture. This mechanism of polyglactin 910 suture absorption is quite different from that observed and reported for catgut absorbable sutures.

The rabbit ear chamber: a unique in vivo model for the continuous observation of implanted biomaterials.

The rabbit ear chamber provides a unique system for viewing an in vivo environment from outside the body. The plastic chamber, modified for our use, is described. Once surgically implanted into the ear of a Laboratory Lop rabbit, a thin tissue bed which grows between the layers of the chamber can be viewed through the microscope. The absorption of biomaterials placed into the chamber can then be observed as a dynamic process.

An approach to the numerical quantitation of acute tissue response to biomaterials.

The hydrolytic enzyme activity associated with the tissue reaction to implanted polyvinyl chloride rods containing graded concentrations of an organotin stabilizer was quantitated by microphotometry of tissue sections. The procedure was more sensitive to the effects of the additive than the usual histologic evaluation. It is considered that this type of approach offers a sensitive and objective index to supplement the more subjective morphologic observations in judging the acute histotoxicity of implants.