Biomedical Engineering Reference
In-Depth Information
only optimal performance but also low toxicity and an ideal tissue response. In addition to consid-
ering the long-term biocompatibility of these materials, novel fabrication processes are frequently
required that would provide a suffi cient quantity of the biomaterial in a format that can be delivered
to the site of delivery, which may not be easily accessible for the gastrointestinal tract.
This chapter discusses some of the old and new biomaterials that have been developed for use in
therapeutic strategies to treat disorders associated with the gastrointestinal tract and describes the
fabrication methods involved in their production.
20.2
BIOMATERIALS USED FOR GASTROESOPHAGEAL REFLUX DISEASE
20.2.1 G ASTROESOPHAGEAL R EFLUX D ISEASE
Gastroesophageal refl ux disease (GERD) is one of the most common disorders of the upper gastroin-
testinal tract, with epidemiological studies suggesting that almost 10% of adults in the United States
experience heartburn daily. It is a chronic relapsing disease with 20-25% of patients receiving life-
long medical treatment [2,3]. GERD is most frequently caused by transient or permanent loss of the
barrier function of the lower esophageal sphincter (also termed cardiac sphincter and gastroesopha-
geal sphincter). Moderate to severe cases of GERD that are nonresponsive to medical therapy usu-
ally require antirefl ux surgery. To date, the mainstay of GERD antirefl ux therapy has been achieved
with either open or laparoscopic fundoplication, a surgical procedure in which the upper part of the
stomach is wrapped around the lower part of the esophagus. Due to the morbidity associated with
general anesthesia, bleeding, organ injury, or infection, a move toward the development of mini-
mally invasive endolumenal procedures for GERD has led to studies investigating the use of both
biodegradable and nonbiodegradable materials delivered by endoscopic transoral approach.
20.2.2 S PHINCTER A UGMENTATION U SING B IOMATERIALS
Several endolumenal procedures have been introduced into clinical practice, one of which is lower
esophageal sphincter augmentation via endoscopic implantation of biomaterials. Early studies
investigated the benefi t of injecting bovine dermal collagen into the lower esophagus to bulk the
submucosal tissue and augment the lower esophageal sphincter pressure, but the benefi cial results
were short-lived due to reabsorption of the collagen [4].
20.2.2.1
Ethylene Vinyl Alcohol Copolymer
Better clinical success has been reported with the biocompatible nonresorbable copolymer Enteryx
(Boston Scientifi c Corp, Matick, Massachusetts), which is injected as a nonviscous liquid that rap-
idly forms a spongy solid in situ . Enteryx consists of an injectable solution of 8% ethylene vinyl
alcohol copolymer dissolved in dimethyl sulfoxide. Ethylene vinyl alcohol copolymer (Figure 20.1)
is a semicrystalline polymer derived from the hydrolysis of poly(ethylene- co -vinyl acetate) and is
commercially available in a range of compositions, with a typical vinyl alcohol content of about
55-70 mol%. The vinyl alcohol content determines the melting point ( T m ) of ethylene vinyl alcohol
but is usually in the range of 170-190°C. The glass transition temperature ( T g ) is 45-50°C and is
independent of the vinyl alcohol content. Ethylene vinyl alcohol copolymers absorb large amounts
CH 2
CH 2
CH 2
CH
m
n
OH
FIGURE 20.1 Chemical structure of ethylene vinyl alcohol copolymer. It is a hydrolyzed copolymer of
ethylene and vinyl acetate monomer.
 
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