Soft tissue substitute

In the biomedical area, SPHs and SPH composites can be used to make various biomedical devices, such as artificial pancreas, artificial cornea, and artihcial skin, articular cartilage, soft tissue substitutes, cell growth substrates in tissue engineering, burn dressings, surgical augmentation of the female breast, or hemoperfusion in blood detoxification and in the treatment of uremia. 

Polyelectrolytes have been widely investigated as components of biocompatible materials. Biomaterials come into contact with blood when used as components in invasive instruments, implant devices, extracorporeal devices in contact with blood flow, implanted parts of hard structural elements, implanted parts of organs, implanted soft tissue substitutes and drug delivery devices. Approaches to the development of blood compatible materials include surface modification to give blood compatibility, polyelectrolyte-based systems which adsorb and/or release heparin as well as polyelectrolytes which mimic the biological activity of heparin. 

The development of biomechanical models derived from continuum formulations for transport of water and charged species in porous media has been carried out for various soft tissues [1-3] and implemented using finite element models (FEMs) [4-8], Such models provide quantitative views of the response of these complex structures that is especially useful in the study of orthopedic, vascular, ocular, and soft tissue substitutes developed by tissue engineering. In this paper a formulation and FEM are described that incorporate and extend these works in a very general model that identifies physical material properties and allows transient analyses of both natural and artificial soft tissue structures. 

Besides the promising use of BASYC in experimental vascular surgery we see the possibility for the application of BC as a soft-tissue substitution material in various medical fields because of its extraordinary properties. 

Salinas et al. [90] prepared CaO-SiOj-PDMS hybrid materials and their in vitro bioactivity was assessed by immersion into simulated body fluid (SBF). Due to their bioactivity and good mechanical properties, these materials could be used for soft tissue substitution or for coating metallic implants to damp the differences in rigidity of metal and bone. 

Gallium, like mercury, is liquid at room temperature, but unlike mercury is much less hazardous. Its most interesting use is as a visualization tool of soft tissues and bone lesions in radiography. Industrial applications include use in high temperature thermometers, metal alloys, and as a substitute for mercury in arc lamps. 

Parameters for transfer of uranium into and out of bone were assumed to be proportional to those of alkaline earth elements such as calcium (the U02 ion can substitute for the Ca "" ion at bone surfaces). Age-specific bone turnover rates developed for a generic alkaline-earth model (ICRP 1993) were incorporated into the uranium model to predict distribuhon to the tissues. As a result of this change, a greater proportion of uranium distributes to bone and a lesser proportion to soft tissues at ages under 25 years, compared to adults. 

In 1982 selective retention of phenolic PCB metabolites was first observed in the intraluminal uterine fluid of pregnant mice after administration of CB-31, using whole body autoradiography and subsequent chemical analysis [36]. Administration of CB-77 to pregnant mice resulted in a dramatic accumulation of a phenolic metabolite in fetal soft tissue [191]. The retained metabolite was shown to be 4-OH-3,3, 4, 5-tetraCB and localized in the blood in both the fetus and in adult mice [73], A metabolism study of the structurally related CB-105 in mice showed significant retention of the para-substituted hydroxylated metabolite 4-OH-CB-107 in blood [71]. The 4-OH-CB 107 was also shown to be retained in blood from rats administered Aroclor 1254 [39], and was observed at high levels in blood and brain tissue from rat fetuses exposed in utero [192],... 

When there is adequate sunlight, no dietary source of the vitamin is required. Indeed, an argument can be made that the calciferols are not normal components of the diet. In the United States, it is added to milk, other dairy products, and dairy substitutes. Fish is about the only natural food source. Cholecal-ciferol is produced in the body from endogenously synthesized 7-dehydrocholecalciferol (Fig. 8.10). Consistent with a hormone model, excess amounts of cholecalcdferol can result in excess calcium uptake from the intestinal tract, leading to calcification of soft tissues. 

Most mutations of p53 genes are somatic missense mutations involving amino acid substitutions in the DNA binding domain. The mutant forms of p53 are misfolded proteins with abnormal conformations and the inability to bind to DNA, or they are less stable. Individuals with the rare disorder Li-Fraumeni syndrome, (an autosomal dominant trait) have one mutated p5 > gene and one normal p53 gene. These individuals have increased susceptibility to many cancers, such as leukemia, breast carcinomas, soft-tissue sarcomas, brain tumors, and osteosarcomas. 

Calcium phosphate A family of calcium phosphate ceramics including aluminum calcium phosphate, ferric calcium phosphate, hydroxyapatite and tricalcium phosphate (TCP), and zinc calcium phosphate which are used to substitute or augment bony structures and deliver drugs. Glass-ceramics A glass crystallized by heat treatment. Some of those have the ability to form chemical bonds with hard and soft tissues. Bioglass and Ceravital are well known examples. 

Since the 1950s, polyethylene (PE) has been applied in surgery. At that time after PE implantation, only formation of so-called granulated tissue around a polymer was found, that is a weak response of the body to the implant. PE is not widely used for the substitution of soft tissues, but it is an important substitute for bone tissues, i.e. the head of the hip bone and other elements of the pelvis bones. The wear resistance property of low pressure PE makes its application in bone tissue substitution. HOPE can be widely used in pelvic prostheses [54]. 

The use of nanocellulose has been suggested in different areas of medicine as substitute of blood vessels and linfatics (Yamanaka et al. 1990 Klemm et al. 2003) substitute of hollow internal organs as ureter, trachea, and digestive tract (Yamanaka et al. 1990 Klemm et al. 2003 Ono et al. 1989) cuff for reconstruction of nerves (Klemm et al. 2003) substitute of duramater (Oster et al. 2003 Damien et al. 2005) substitute of the abdominal wall, skin, subcutaneous tissue, articulation, cartilage, and reinforcement of areas of decreased resistance in the abdominal wall, esophagus, and intestinal tube (Ono et al. 1989) threads (Roberts et al. 1986) and agent for increases in soft tissue, reconstruction of the pelvic... 

To mimic the mechanical behavior of the native tissue is a basic assumption to facilitate the biointegration and function of the substitute. Incorporation of fibers to the biomaterial matrix opens the way to inhomogeneity, anisotropy, nonlinearity, and viscoelasticity features. Provided that interfacial binding between matrix and fibers in the composite goes on, mechanical properties could be tailored by varying the amount and orientation of fibers embedded, to suit the purpose applications, whether it s related to hard or soft tissue substimtes. Individual fibers, no matter how small and isolated compared to fibrous structure, could affect mechanical properties. To be effective, fibers principal direction should be considered and controlled. 

Hydroxyapatite (Hench, 1993), /3-tricalcium phosphate (Wilson, 1993), Bioglass (Hench, 1991) and Glass Ceramics A-W (Yamamuro, 1993 Kokubo, 1991) are typical inorganic materials that can directly bond to bone tissues when embedded in human bodies. They have already been used as bone-substitutes in clinics. Such tissue-bonding property is denoted as bioactivity and is exceptional because it is only found for a limited kind of materials (Ohtsuki, 1991, 1992) and the rest of all materials, i.e., metals, ceramics, and polymers are not bioactive. However, those ceramic materials are far from ideal tissue substitutes since their fracture toughness is lower than that ofhuman cortical bone, and too hard to be applied to soft tissue replacement. Hence, they find a limited range of use. 

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