Fibrous capsule

To be biocompatible is to interact with all tissues and organs of the body in a nontoxic manner, not destroying the cellular constituents of the body fluids with which the material interfaces. In some appHcations, interaction of an implant with the body is both desirable and necessary, as, for example, when a fibrous capsule forms and prevents implant movement (2). 

Interactions at surfaces and interfaces also play an essential role in the design and function of clinical implants and biomedical devices. With a few recent exceptions, implants do not attach well to tissue, and the resulting mobility of the tissue-implant interface encourages chroitic inflammation. The result can be a gathering of platelets at the site, leading to a blood clot or to the formation of a fibrous capsule, or scar, around the implant (Figure 3.3). 

Vacant , F.X. PHEMA as a fibrous capsule-resistant breast prosthesis. Blast. Reconstr. Surg., 113, 949, 2004... 

In vivo biocompatibility was assessed through subcutaneous implantation in Sprague-Dawley rats. PLGA was used as a control polymer. PGS and PLGA implants with the same surface area/volume ratio were implanted in dorsal subcutaneous pockets. A fibrous capsule around PGS (45 pm thick after 35 days implantation) appeared later than that around PLGA (140 pm thick after 14 days implantation). After 60 days of implantation, the implant was completely absorbed with no signs of granulation or scar formation. ... 

Like the in vitro studies, the in vivo degradation of the TMC-CL copolymers containing 89% CL showed no change in shape or size after one year. As the degradation of the TMC-CL copolymers was so slow, a mature fibrous capsule remained throughout the year. Histological results of the TMC-CL copolymers were similar to those obtained from TMC-DLLA or other commonly used biodegradable polymers. 

Goreish HH, Lewis AL, Rose S, Lloyd AW. The effect of phosphorylcholine-coated materials on the inflammatory response and fibrous capsule formation in vitro and in vivo observations. Journal of Biomedical Materials Research A 2004, 68, 1-9. 

The major factors impacting sensor performance, whatever the physiological basis, are the degree of local vascularity and the loss of functional microvessels, together with the eventual presence and thickness of a fibrous capsule. Continued inflammation and collagen deposition eventually reach an equilibrium state, and the thickness of the fibrous capsule has been proposed as an index of biocompatibility.32 The thickness and vascularity of the capsule depend on the size, surface texture, and porosity of the implant.33-35... 

Polyurethanes have also been employed as outer sensor membranes. Yu et al. evaluated the biocompatibility and analytical performance of a subcutaneous glucose sensor with an epoxy-enhanced polyurethane outer membrane.15 The membrane was mechanically durable and the resulting sensors were functional for up to 56 days when implanted in the subcutaneous tissue of rats. Despite the improved sensor lifetime, all of the polyurethane-coated sensors were surrounded by a fibrous capsule, indicating an enduring inflammatory response that is undesirable due to the aforementioned effects on analytical sensor performance. To date, the clinical success of most passive approaches has been rather limited. It is doubtful that one passive material alone will be capable of imparting long-term (i.e., weeks to months) biocompatibility for in vivo use due to the extremely dynamic nature of the wound environment. 

We now turn to an anatomical description of lymph nodes. The lymph node is surrounded by a thick, fibrous capsule and is subdivided into compartments by trabeculae. Inside the capsule is the subcapsular or marginal sinus, which forms the entry point of lymphatic fluid into the node, via the afferent vessel. The lymph node cortex, which lies beneath the subcapsular sinus, is the location of the primary and secondary lymphoid follicles. The primary follicles are comprised of B-lymphocytes. An immune response stimulates B-cells to replicate and differentiate, converting the primary follicle into a secondary follicle or germinal center, surrounded by a zone of small lymphocytes. The paracortex surrounds the germinal centers and primary follicles and contains mostly T-lymphocytes. The medulla is composed of medullary cords, consisting of macrophages and plasma cells, and medullary sinuses. The medullary vessels include the arteries and veins, and the afferent and efferent lymphatic vessels, respectively, deliver the lymphatic fluid into and out of the lymph node. 

Fig. 11.6. Hymenolepis nana section of a cysticercoid in the intestinal villus of a mouse 96 h p.i. No fibrous capsule is formed, but marked eosinophilia develops.

Fig. 16 Light microscopic images of tissue capsule surrounding titanium implants with a DNA and poly-D-lysine complex coating. After 12 weeks of implantation, all implants were surrounded by a relatively mature fibrous capsule without the presence of inflammatory cells at the implant interface. Reprinted with permission from [126]...

Lymphadenopathy is most often not clinically manifested however, bright yellow plaques and a cholesterol ester content 100-fold higher than normal have been documented for both normal-size and enlarged lymph nodes in Tangier patients. Biopsies of bone marrow and the affected tissues have revealed many foam cells that are smaller than those observed in lipid storage diseases. In addition, these cells contain sudanophilic deposits which are not membrane-bound, as is the case for lysosomal storage diseases. Foam cells have also been found in otherwise normal skin, ureters, renal pelvises, tunica albuginea (white fibrous capsule) of testicles, mitral and tricuspid valves, and aorta, coronary, and pulmonary arteries. 

Potentials of the order of 15000—20000 volts were measured on these particles. A discharge of such potentials suffices to initiate the LOX. Dust can be minimized by moistening the adsorbent with 20—25% of water or by providing special capsules for the expl. Good results were obtained by using briquetted fibrous vegetable matter, peat, straw, wood pulp and the like as adsorbents. Such briquets did not produce dust when dropped from a height of 25m. The brisance of the LOX made of such briquets was only 3—4% less than that of ordinary LOX... 

The perivascular fibrous capsule (R Glisson, 1654) commences in the hepatic porta as a tree-like branching framework of connective tissue surrounding the interlobular vessels. It also surrounds the central hepatic vein and its small tributaries, which are joined to the parenchyma by radial fibres as well as being established in the portal tracts. This prevents a suction-induced collapse of the venous vessels as a result of respiration-dependent negative pressure in the pleural cavity. The perivascular connective tissue, known as Glisson s capsule, extends fine secondary trabeculae into the parenchyma. They contain the intralobular biliary, lymphatic and blood capillaries. 

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