How microbes read the map: Effects of implant topography on bacterial adhesion and biofilm formation

Direct observations have clearly shown that biofilm bacteria predominate, numerically and metabolically, in virtually all nutrient-sufficient ecosystems. Therefore, these sessile organisms predominate in most of the environmental, industrial, and medical problems and processes of interest to microbiologists. If biofilm bacteria were simply planktonic cells that had adhered to a surface, this revelation would be unimportant, but they are demonstrably and profoundly different. We first noted that biofilm cells are at least 500 times more resistant to antibacterial agents. Now we have discovered that adhesion triggers the expression of a sigma factor that derepresses a large number of genes so that biofilm cells are clearly phenotypically distinct from their planktonic counterparts. Each biofilm bacterium lives in a customized microniche in a complex microbial community that has primitive homeostasis, a primitive circulatory system, and metabolic cooperativity, and each of these sessile cells reacts to its special environment so that it differs fundamentally from a planktonic cell of the same species.

Biofilms--matrix-enclosed microbial accretions that adhere to biological or non-biological surfaces--represent a significant and incompletely understood mode of growth for bacteria. Biofilm formation appears early in the fossil record (approximately 3.25 billion years ago) and is common throughout a diverse range of organisms in both the Archaea and Bacteria lineages, including the 'living fossils' in the most deeply dividing branches of the phylogenetic tree. It is evident that biofilm formation is an ancient and integral component of the prokaryotic life cycle, and is a key factor for survival in diverse environments. Recent advances show that biofilms are structurally complex, dynamic systems with attributes of both primordial multicellular organisms and multifaceted ecosystems. Biofilm formation represents a protected mode of growth that allows cells to survive in hostile environments and also disperse to colonize new niches. The implications of these survival and propagative mechanisms in the context of both the natural environment and infectious diseases are discussed in this review.

The foreign body reaction composed of macrophages and foreign body giant cells is the end-stage response of the inflammatory and wound healing responses following implantation of a medical device, prosthesis, or biomaterial. A brief, focused overview of events leading to the foreign body reaction is presented. The major focus of this review is on factors that modulate the interaction of macrophages and foreign body giant cells on synthetic surfaces where the chemical, physical, and morphological characteristics of the synthetic surface are considered to play a role in modulating cellular events. These events in the foreign body reaction include protein adsorption, monocyte/macrophage adhesion, macrophage fusion to form foreign body giant cells, consequences of the foreign body response on biomaterials, and cross-talk between macrophages/foreign body giant cells and inflammatory/wound healing cells. Biomaterial surface properties play an important role in modulating the foreign body reaction in the first two to four weeks following implantation of a medical device, even though the foreign body reaction at the tissue/material interface is present for the in vivo lifetime of the medical device. An understanding of the foreign body reaction is important as the foreign body reaction may impact the biocompatibility (safety) of the medical device, prosthesis, or implanted biomaterial and may significantly impact short- and long-term tissue responses with tissue-engineered constructs containing proteins, cells, and other biological components for use in tissue engineering and regenerative medicine. Our perspective has been on the inflammatory and wound healing response to implanted materials, devices, and tissue-engineered constructs. The incorporation of biological components of allogeneic or xenogeneic origin as well as stem cells into tissue-engineered or regenerative approaches opens up a myriad of other challenges. An in depth understanding of how the immune system interacts with these cells and how biomaterials or tissue-engineered constructs influence these interactions may prove pivotal to the safety, biocompatibility, and function of the device or system under consideration.