A Magnetic Soft Endoscopic Capsule-Inflated Intragastric Balloon for Weight Management

Overweight and obesity have been identified as a cause of high risk diseases like diabetes and cancer. Although conventional Intragastric Balloons (IGBs) have become an efficient and less invasive method for overweight and obesity treatment, the use of conventional tools such as catheter or endoscope to insert and remove the IGBs from the patient’s body causes nausea, vomiting, discomfort, and even gastric mucous damage. To eliminate these drawbacks, we develop a novel magnetic soft capsule device with gas-filled balloon inflation. The balloon is made from a thin and biocompatible material that can be inflated to a desired volume using biocompatible effervescent chemicals. In addition, both the outer balloon and inner capsule are designed to be soft and chemical resistance. The soft capsule shell is fabricated using scaffold-solvent approach while the outer balloon utilizes a novel fabrication approach for 3D spherical structure. A prototype of the proposed capsule and balloon is given. Experiments are successfully carried out in stimulated gastric environment and fresh porcine stomach to validate the effectiveness and reliability of the proposed approach.


Size estimation for flexible membrane
The flexible PDMS membrane 6 plays an important role for holding and guiding the inner magnet to slide axially the capsule shell. If the membrane is too large, it can cause difficulties for the sliding of inner magnet. In contrast, if the membrane is too small, it is not able to hold the magnet. Therefore, it is necessary to estimate its thickness h and width b in order to provide a rough dimension for the membrane fabrication. Here we apply a pseudo rigid body model for large deformation beam bending under fixed-clamped boundary condition to estimate the flexible membrane size 1 . We choose a symmetric profile for the membrane as shown in Fig. S1. The relation between the applied force Fapplied and its axial deflection  can be described by: where , are the required stiffness of the modelled torsional spring and nonlinear axial spring, respectively. ∆ is the increase of the sliding length. is the stiffness coefficient. is the characteristic radius factor. 0 is the length of original beam. ( ) is the flexural rigidity.
magnet will be very large 2 . In this paper, we choose this threshold is Fthres=0. 6N To find the value of for the PDMS membrane, we need to find . It should be noted that the value for force calculation in Eq. S1 should divide by 4 (for 4 beams). From Eq. S1 to Eq. S4, the value of is 6.1337. Using this value, we can proceed to estimate the membrane thickness/width for the capsule.

(S5)
The inequality from Eq. (S5) will be used for the fabrication process of membrane dimension. For example, if we choose ℎ = 0.2 , then should be less than 0.711mm.

Thickness estimation for the outer balloon
Let 0 is the viscosity of the coating polymer, is the polymer density, is the earth gravity, ∅ is the Zenith angle, and is the radius of the sphere ball. The squared root dependence of the outer layer PDMS thickness for sphere balloon ℎ , on its radius can be expressed as follow 4 : As shown in Fig. S3, if we consider Ecoflex balloon with its thickness 0 and the initial inner and outer radius of 0 and 0 , respectively. Suppose that the Ecoflex material is incompressible. Then its thickness 1 as well as inner radius 1 , outer radius 1 after the Ecoflex balloon is inflated in relation with its initial dimensions can be expressed by 5 : Finally, the thickness 1 of the inflated Ecoflex balloon can be found from the solution of the following equation: From Eq. (S7) and Eq. (S8), the final thickness ℎ for both outer PDMS and inner Ecoflex balloon can be given as: It is noted that the values of 0 is know from the initial sphere ball. For the value 0 , it is easily obtained using the Eq. (S6) for Ecoflex material. The radius 1 can be measured when the Ecoflex balloon is inflated to this size. The value 0 can be derived from Eq. (S6) as follow:

Characterization of external force applied to the outer balloon
The proposed outer balloon is inflated and subsequently tested in a force testing system. It was known that the force per contraction averaged is around 0.2N to 0.65N for the stomach applied to the food or hard capsule 6 . We applied a constant force of around 2.2N to the balloon and put them in solution of simulated gastric acid (pH=1.1-1.3, Sigma Aldrich, USA) for one day. The validation is also carried out for sewing thread balloon using an average force of around 4.2N. As shown in Fig.   S7, the both balloons are able to resist with the applied force and even can resist with a bigger force than the contraction force from the stomach.

Characterization of the inflation and deflation force
We connect the capsule with its inflation and deflation valves to a force measurement system to provide the force information. Because the tip of carbon fibre rod 8 is located 2mm away from the deflation valve, the PDMS membrane 6 has a maximum travel length of 2mm if the deflation valve is not opened. The inflation force is only recorded whenever the inflation valve is opened. This means that only the maximum force to open the inflation valve is considered. For the case of deflation force, we remove the nut 2 to allow the deflation valve can be moved towards the external magnet.
Similar measurement is carried out for the deflation phase where only maximum force is recorded whenever the deflation valve is opened. We carried out five trials for each measurement and the results are shown in Table S1. It can be seen that the maximum force for the inflation and deflation (max) is around 0.5664N. To generate this force, a cylinder permanent magnet with the size of at least 300mm in length and 250mm in diameter is required. This estimated size is obtained using COMSOL Multiphysics 5.0 software for a distance of 50mm between the external cylinder magnet and the inner ring magnet. Both external and inner magnets have the strongest grade of neodymium N52. For a longer distance between the two magnets, see 2 and Figs. S9, S10 for more details.

Soft capsule and balloon in acidic environment
We characterize the chemical resistant of the capsule shell and outer balloon in acidic environment.
The acid chamber is filled with 1.1ml of 60% of citric acid (see Fig. S11 for the detailed injection of the acid into the capsule chamber) and 0.45ml of potassium bicarbonate is placed inside the balloon but outside the acid chamber. We subsequently put the balloon and the capsule into a solution of   Step 2-Insert a needle-syringe with citric acid into the other side of the capsule; Step 3-Inject the acid into the capsule where the air inside will be released out of the capsule via the first needle.

Needle and Syringe
Acid Air out  After using our capsule-balloon Gastric capacity ~1200 ml 7-9 1800 ml [7][8][9] Reduce the stomach size of obese patients from 100ml to 600ml 10,11 Depend on the patient's condition, our capsule-balloons is expected to occupy the stomach space from 150ml to 300ml