Surgical implants environment

The ASTM F 1185 designation specifies chemical and crystallographic requirements for hydroxyapatite applied to the surfaces of surgical implants. Elemental analyses for calcium and phosphorus will confirm the expected stoichiometry of hydroxyapatite. The calcium and phosphorus contents will be determined by a suitable method such as ion chromatography. A quantitative X-ray diffraction analysis will determine a hydroxyapatite content of at least 95%. The concentration of deleterious trace elements such as arsenic, cadmium, mercury and lead will be assessed for hydroxyapatite derived from natural resources. The analysis of other trace elements may be required, based on the conditions, apparatus or environments specific to the manufacturing techniques and raw materials. Inductively coupled plasma/mass spectroscopy (ICP/MS), atomic absorption (AAS) or the... 

Soft tissue responses to biomaterials for medical devices are generally viewed from the inflammation and wound healing perspectives and are usually considered as parts of the tissue or cellular host responses to injury. Placement of a biomaterial or medical device in the soft tissue environment involves injection, insertion, or surgical implantation, all of which injure the tissues or organs involved. Early host responses are dynamic and change with time (Table 2.1). It is important to consider this time variable in determining the host response or biocompatibility of a material. 

This experience was based on the merging of the CT data of the temporal bone and those obtained by the computer-aided design files of the medical devices, both transferred to a VR environment to achieve a simulation of the surgical implantation procedure. 

Developing of surgical implants confronts major problems because human bodies have extremely complex environments. They could be identified as having the most horrible environmental situation on earth. In addition different human bodies have different environmental requirements. Thus what can survive in one body usually does not survive in other bodies. This type of reaction requires extensive R D to ensure that a medical product can survive and meet its requirements in all human or specific bodies. 

Arfsten, D.P., Bekkedal, M., Wilfong, E.R., et al., 2005. Study of the reproductive effects in rats surgically implanted with depleted uranium for up to 90 days. J. Toxicol. Environ. Health Part A 68, 967-997. 

The major limitation of titanium is its chemical reactivity with other materials at elevated temperatures. This property has necessitated the development of nonconven-tional refining, melting, and casting techniques consequently, titanium alloys are quite expensive. In spite of this reactivity at high temperature, the corrosion resistance of titanium alloys at normal temperatures is unusually high they are virtually immune to air, marine, and a variety of industrial environments. Table 11.10 presents several titanium alloys along with their typical properties and applications. They are commonly used in airplane structures, space vehicles, surgical implants, and in the petroleum and chemical industries. 

When an implant is surgically inserted into the human body, the internal environment is greatly disturbed. Haematomas are likely to collect around the implant, resulting in a lowered pH. Laing observed pH values as low as 4-0 in healing wounds. The low pH usually persists until the haematomas are reabsorbed after several weeks ... 

Clinical observations have suggested that the organ environment can influence the response of tumors to therapy. For example, in women with breast cancer, lymph node and skin metastases are more sensitive to chemotherapeutic intervention than metastases in either the lung or the bone (34). Similarly, orthotopic implantation of human tumor cells from surgical specimens into nude mice has shown that colon carcinomas injected into the wall of the colon, results in more clinically relevant outcomes then subcutaneously injected colon carcinomas. Orthotopic implanta-... 

After resolving the issue of matrix design, the next step was to determine a desirable anatomical location. Several considerations were used in determining possible implant sites. The first is the size of the implant and the requirement that it be placed in juxtaposition to well-vascularized tissue. A transplant matrix constructed as a porous sheet-like structure could be at most 200 mm thick, based on estimates of nutrient transport limitations (66). The size of a device required to replace about 5% of the mass of an adult liver would then be about 0.5 m2. Surgical trauma must be avoided when implanting the device, because such trauma produces fibrin clots and hematoma formation around the wounded area, which creates a poor environment for cell survival. Also, the implant may behave better if supplied by the portal circulation rather than the systemic, because the portal circulation contains potential hepatotrophic factors. For these reasons, the mesentery—the vascularized membrane which secures the intestines—was selected as the best potential site (Fig. 15). 

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