Biomedical Engineering Reference
In-Depth Information
biomaterials, such as collagen, represents a major clinical problem and appears to be encouraged by
glutaraldehyde cross-linking. To overcome this problem, further chemical pretreatment of implants
with biphosphonates has been proposed as a way of inhibiting calcifi cation of the implants by
interfering with crystal growth that prevents accumulation of calcium [40]. However, with each
additional treatment stage, collagen becomes less like the original endogenous extracellular matrix
material, which is its major attribute. Furthermore, as the collagen gradually degrades over time,
the implant fails to conserve its volume, meaning repeat injections are usually necessary [41,42].
Besides leading to additional patient discomfort, this may also be clinically unsuitable for some
patients as approximately 3% of patients treated with bovine collagen show allergic reactions pre-
venting retreatment [43,44].
20.4.2.3
Zirconium Dioxide Microspheres
Durasphere (Carbon Medical Technologies, St. Paul, Minnesota) is another microsphere-type bulk-
ing agent that has been studied over short- and long-term periods in patients with an internal anal
sphincter defect refractory to conservative management [45]. Durasphere consists of biocompatible
and nonimmunogenic zirconium dioxide microspheres coated in pyrolytic carbon and suspended in
a water-based carrier gel containing β-glucan. Although the size of microspheres ranges from 251
to 300 µm, which is considered to be approximately three times the migration threshold of 80 µm,
microsphere migration has been reported to be visible on x-ray in some patients treated for stress
urinary incontinence [46]. It has been suggested that the density of the bulk material (zirconium diox-
ide, 5.89 g/cm
3
), which is much higher than the density of the surrounding soft tissue (approximately
1 g/cm
3
), may account for the microsphere migration described [32].
20.5
BIOMATERIALS AND LAPAROTOMY PROCEDURES
20.5.1 I
NTRA
-A
BDOMINAL
A
DHESIONS
Adhesions are fi brous connections between tissues that occur as a result of tissue injury taking place
during abdominal and pelvic surgery, radiation to abdominal or pelvic areas, or certain diseases,
such as endometriosis. Postoperative intra-abdominal adhesions are a very common consequence
of abdominal and pelvic surgery. Their formation is a major cause of morbidity, accounting for
60-70% of the all small bowel obstruction cases in the Western world [47]. Small bowel obstruc-
tion, as a result of adhesions, can cause abnormal orientation of the intestine, leading to strangula-
tion and intestinal necrosis, with a high risk of morbidity and mortality. As a consequence of the
common and serious nature of adhesions, there is an intensive area of biomaterials research devoted
to developing materials that will prevent this condition. Therefore, the materials highlighted in this
section do not form an exhaustive list, rather an indication of the type of materials that have been
tested past and present.
20.5.2 B
IOMATERIALS
TO
P
REVENT
I
NTRA
-A
BDOMINAL
A
DHESIONS
The most common objective in preventing adhesion formation using biomaterials has been to sepa-
rate surgically traumatized internal tissue surfaces. Since the beginning of the twentieth century,
many barrier materials, including silicones, polyvinyl pyrrolidine, oiled silk, and silver or gold foil,
have been developed and tested in preclinical models, but most have been noneffective or have been
found to exacerbate the problem [48].
20.5.2.1
Hyaluronic Acid-Based Biomaterials
The most effective barrier developed and tested in a prospective randomized clinical trial is a bio-
resorbable membrane called Seprafi lm (Genzyme Corporation, Cambridge, Massachusetts),
which is composed of chemically modifi ed hyaluronic acid (sodium hyaluronate) and
