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Model Description

The HGS consists of a cylindrical latex chamber that simulates the stomach compartment, and four conveyor belts that periodically impinge a series of Teflon rollers upon its wall to mimic the antral contraction wave activity of the stomach wall (Fig. 7.1). The system operates inside an insulated chamber maintained at 37 °C, while facilitating the delivery of gastric juices and emptying of simulated digesta in a continuous and controlled manner.

Gastric Compartment

The stomach is represented by a 5.7 L cylindrical vessel (20 cm high and 10.2 cm diameter) that ends in the form of a conic frustum (13 cm height and 2.5 cm final diameter).

Made of latex rubber, the gastric compartment sits straight up, wrapped onto a stainless steel ring (10.2 cm high and 15.2 cm diameter) that is supported by four

Fig. 7.1 Human gastric simulator. (1) Motor (2) Gastric compartment (3) Mesh bag (4) Simulating secretion tubes (5) Teflon roller set (6) Conveying belt (7) Insulated chamber. From Kong and Singh (2010)

diametrically opposed legs welded to the base. The open end of the container provides a simple way for loading food materials into the unit and for sampling of the simulated digesta during the process.

Gastric Motility

With the primary goal of mimicking the physical processes driving food disintegration, the HGS was designed to reproduce the motor activity of the antral contraction waves (ACWs) along the distal region of the stomach.

The dynamics of the ACWs along the lower part of the cylindrical vessel is mimicked by a mechanical drive system. Four conveyor rubber belts move along the height of the gastric compartment at 90° from each other.

Each belt is supported by four 0.95 cm pulleys, which attached to a low-carbon steel plate are moved by a drive shaft (1.27 cm diameter brass rod) connected to a 115 V Stir-Pak Heavy-Duty Mixer head (model R-50002-10, Cole-Parmer) motor. A StirPak controller (model R-50002-02, Cole-Parmer) is used to allow for speed adjustments within the range of 2–180 rpm. Power is transmitted from one drive shaft to another via two bevel gears coupled at a 90° angle.

Each timing belt (0.95 cm wide) carries three sets of equally spaced Teflon rollers located every 20 cm of each other. Each set of rollers consists of two wide Teflon wheels (1.27 cm diameter, 0.9 mm long) placed together through an aluminium rod, that is secured to the belt by a male threaded screw (0.2 cm diameter, 1.5 cm long). As the belt moves, rollers start impinging the compartment wall (at about two-thirds of its total height). As the rollers propagate down, they replicate the increasing compression pattern of the ACWs by getting successively closer to the rollers on the opposite belt. The closer the rollers, the higher the compression forces.

To avoid possible interference between neighbouring rollers as they get further down the bottom of the gastric compartment, the lower pulleys closer to the compartment are placed at two different levels, with one pair of opposite pulleys located 3.0 cm higher than the other pair.

In order to simulate the motility pattern of the ACWs, the drive system is set to impose three propagating contractions per minute (with one finishing while another commences). If desired, this propagation speed can be changed by simply adjusting the rpm of the driving shaft. The force imposed by the rollers on the simulated digesta can be controlled by adjusting the distance between opposite rollers through the screw engagement depth inside the aluminium rod.

Gastric Emptying

To simulate the sieving effect of the pylorus, a polyester mesh bag (pore size of 1.5 mm) is used to line the inner surface of the gastric compartment and prevent larger particles from emptying the compartment. At the end of the trial, the mesh can be easily taken out through the open top section of the compartment, facilitating the removal and analysis of the remaining digesta.

The rate of gastric emptying is controlled by means of a peristaltic pump (Masterflex Pump Controller 7553-50/7090-42 Pump, Cole-Parmer, Chicago, Ill., U.S.A.) connected to the bottom of the gastric compartment through a 0.32 cm plastic tube.

Gastric Secretions

Simulated gastric juices are delivered at about 10–15 cm from the bottom of the compartment through five polyethylene tubes (I.D. 0.86 mm) uniformly distributed between the mesh bag and the latex wall.

The delivery rate of the simulated gastric juice into the compartment is controlled by a mini peristaltic pump (Model 3385, VWR, Scientific, Rochester, N.Y., U.S.A.) and a control valve placed on a 6.4 mm plastic tube that later on divides into five tubes going into the compartment. The flow rate of the simulated secretion can be adjusted between 0.03 and 8.2 mL/min.

It is noteworthy that while it is possible to control the release of gastric juices during the simulated processes, there are no mechanisms in place to automatically adjust this gastric response to the specific composition and volume of simulated digesta.

Temperature Control

The system is placed inside an insulated plastic foam chamber, where two 60 W light bulbs and a mini-fan are installed to maintain the system operating at uniform and constant temperature of 37 °C. The operation of the bulbs is automatically controlled by a thermostat (Model T675A 1516, Honeywell, Honeywell Inc., Minneapolis, Minn., U.S.A.).

 
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