Temporal Sequence of Inflammation and Wound Healing

Inflammation is generally defined as the reaction of vascularized living tissue to local injury. Inflammation serves to contain, neutralize, dilute, or wall off the injurious agent or process. In addition, it sets into motion a series of events that may heal and reconstitute the implant site through replacement of the injured tissue by regeneration of native parenchymal cells, formation of fibroblastic scar tissue, or a combination of these two processes (11,12).

The sequence of events following implantation of a drug delivery system, medical device, or biomaterial is illustrated in Figure 1. The size, shape, and chemical and physical properties of the biomaterial and/or the physical dimensions and properties of the prosthesis or device may be responsible for variations in the intensity and time duration of the inflammatory and wound-healing processes. Thus, intensity and/or time duration of inflammatory reaction responses may characterize the biocompatibility of a biomaterial, medical device, or drug delivery system.

In general, the biocompatibility of a material with tissue has been described in terms of the acute and chronic inflammatory responses and of the fibrous capsule formation that are seen over various time periods following implantation. Histologic evaluation of tissue adjacent to implanted materials as a function of implant time has been the most commonly used method of evaluating the biocompatibility. Classically, the biocompatibility of an implanted material has been described in terms of the morphologic appearance of the inflammatory reaction to the material. However, the inflammatory response is a series of complex reactions involving various types of cells, the densities, activities, and functions of which are controlled by various endogenous and autocoid mediators. The simplistic view of the acute inflammatory response progressing to the chronic inflammatory response may be misleading with respect to bio-compatibility studies and an understanding of the inflammatory response to implants. Studies using the cage implant system show that monocytes and macrophages are present in highest concentrations when neutrophils are also at their highest concentrations, that is, the acute inflammatory response (27,28). Neutrophils have short lifetimes—hours to days—and disappear from the exudate more rapidly than macrophages, which have lifetimes of days to weeks to months. Eventually, monocytes become the predominant cell type in the exudate, resulting in a chronic inflammatory response. Monocytes rapidly differentiate into macrophages, the cells principally responsible for normal wound healing in the foreign body reaction (Fig. 2). Classically, the development of granulation tissue has been considered to be a part of chronic inflammation, but because of unique tissue-material interactions, it is preferable to differentiate the foreign body reaction—with its varying degree of granulation tissue development, including macrophages, fibroblasts, and capillary formation— from chronic inflammation.

FIGURE 2 In vivo transition from blood-borne monocyte to biomaterial adherent monocyte/ macrophage to FBGC at the tissue/biomaterial interface. Little is known regarding the indicated biologic responses that are considered to play important roles in the transition to FBGC development. Abbreviation: FBGC, foreign body giant cell.

FIGURE 2 In vivo transition from blood-borne monocyte to biomaterial adherent monocyte/ macrophage to FBGC at the tissue/biomaterial interface. Little is known regarding the indicated biologic responses that are considered to play important roles in the transition to FBGC development. Abbreviation: FBGC, foreign body giant cell.

How To Reduce Acne Scarring

How To Reduce Acne Scarring

Acne is a name that is famous in its own right, but for all of the wrong reasons. Most teenagers know, and dread, the very word, as it so prevalently wrecks havoc on their faces throughout their adolescent years.

Get My Free Ebook


Post a comment