Team:SCU-China/Hardware

Hardware

Overview

Hardware: Antibacterial and deodorant insoles

Goal: To provide suitable media for our E. coli strains t to meet the needs of bacterial growth, mass transfer and biosafety.

Achievement: One super absorbent polymer hydrogel and two kinds of hydrogels with high mechanical strength were synthesized and a serials of material performance tests (Mechanical Strength tests, Equilibrium Swelling Rate test, Water retention tests, Biocompatibility test) were conducted. Three different types insoles’ prototypes were designed and made. Also, the feedback of the insoles were collected from the users and involved in the improvement of the insoles.

Hardware devices: there different type insole prototypes.

Details

Introduction

This year, our team project aimed at designing an innovative insole called "Comfootable" to prevent foot odor and foot infection of microorganisms by two strains of engineered E.coli. Compared with the conventional chemical treatment, biological method shows high specificity and long effectiveness. Yet, the traditional bacterial media was limited to be used as the substrate of our insole for it’s low mechanical strength and poor water retention ability. Also，present materials used in the insoles also were not suitable to culture bacteria. To address these problems to manage our innovative insole, we synthesized several new types of hydrogels (Nano Composite hydrogels and Double Network hydrogels.) having a good performance on water absorption, water retention, mechanical strength and biocompatibility. In addition, we designed and produced some innovative insoles and constantly improve them with the help and feedback of our users.

Design

Material

Agar/PAAm DN gel

Agar/PAM DN hydrogels were synthesized using a one-pot, heating-cooling-photopolymerization method. all reactants of AM (7 mol L1, 4.9756 g), agar (17mgmL1, 0.17 g),initiator HMP (0.4 mol%ofAM, 0.0639g), and crosslinker MBA (0.028 mol% of AM, 3.02 mg) were added into a tube. After three cycles of degassing, 10 mL of degassed water were added. The tube was then sealed under N2 protection and heated up to 95 1C to dissolve agar in a water bath, forming a transparent precursor solution. Then, the solution was injected into a glass mold with a 1 mm thick PTFE spacer and gradually cooled down to room temperature. During the cooling process, agar formed the first physically crosslinked network via physically-associated agar helical bundles. Once the first agar network was formed, the agar gel and other unreacted species in the same pot were photo-polymerized for B1 hour using UV light (wavelength: 365 nm, intensity: 8 W, UVP,CA)to form the second chemically cross-linked network of PAM that interpenetrates with the first agar network. Gels were removed from the molds afterwards and sealed with a plastic wrap to keep moisture before tensile testing. Unlike the conventional two or multiple-step methods, this one-pot process takes only 1–2 hours to complete DN gels. Agar single network (SN) hydrogels and PAM SN hydrogels were prepared using the modified one-pot method. Agar SN gels were synthesized using the heating up-and-cooling down process without involving photo-polymerization, while PAM SN hydrogels were directly synthesized using the photo-polymerization method. We also prepared the Agar/PAM DN and SN parent gels at different concentrations of AM, agar, initiator, and crosslinker to examine their effects on the mechanical and antifouling properties.

Double Network hydrogel

Insole model

Insole 1

Insole 1 has a resin based skeleton with Polyurethane sponge crammed in the hole of it. The resin skeleton support most of the weight of the feet. While the Polyurethane sponge acts as the mix solid-liquid culture media of the engineered E.coli. When force is applied on the insole, the skeleton will deform slightly , therefore the solution containing the cecropin XJ will be squeezed out to kill the bacteria on people’s feet, which is efficient for mass transferring.

Figure. Resin skeleton of insole 1.

Figure. Schematic diagram of insole 1.

But in human practice part, many people refused to try it in public. Some roommates of the one who’s responsible for human practice tried this all said that it’s not very comfortable. So we have the new edition of insole: insole 2. Visit Human Practice Part for more information.

Insole 2

Insole 2 is a hydrogel based insole. The principle part is a whole foot shape insole made by one type hydrogel containing the nutrients required by the growth of bacteria . Two strains are mixed together in the insole system to grow.

It’s the optimized of insole I and it looks more advanced in shape. People who wear it feel more comfortable. Visit Human Practice Part for more information about it.

Figure. Hydrogel main body of insole 1.

Figure. Schematic diagram of insole 2.

Insole 3

Insole 3 also has a hydrogel based main part. Yet, it is divided into two different parts to realize different functions. The first part locates in the areas where most force apply when people are moving,like the sole ,heel and the toe. In this area, high mechanical strength gel containing bacteria lysis solution made the skeleton, with the particle of super absorbent polymers ( SAP particle) on the top gap of it. These SAP particles swelled with culture solution can provide enough nutrients for the bacterial growth. The first type E.coli witch can produce Cecropin XJ grow on the surface of the SAP particles.when temperature beyond the critical value, it will lyse to release the Cecropin to realize the antibacterial function. The other area of the insole consists of the another hydrogel contain less water with the second type E.coli grow on it can absorb the foot sweat of people to reach the goal of both deodorant and arefaction.

Figure. Hydrogel main body of insole 3 with slipsole.

Figure. Hydrogel main body of insole 3 with foot arch support.

Figure. Schematic diagram of insole 3.

Stretch goals

1) smart antibacterial & deodorant gel paste

2) Effluent disposal network.

Results 1

(1) Super absorbent polymer (SAP）

1) Swelling test

Figure 1. Equilibrium Swelling Ratio(ESR) of SAP in different solutions.

Figure 1. Shows that Super absorbent polymer Sodium polyacrylate(PAANa) has huge potential to absorb liquid. Though ESR of SAPs decreased from 413.8 in pure water to 52.7 in LB due to ion effect, it’s enough for our insole design.

2) Water retention of SAP

Figure 2. Water retention of SAP in room temperature(RT).

Figure 3. Water retention of SAP in 55℃.

Whether in room temperature(RT) or high temperature(55℃）,the SAPs presented much lower rate of water lose. SAPs still had about 15% water content while the control became completely dry, indicating the strong water retention ability of SAPs.

Results 2

The poly-crylamide/agar double network hydrogel is coded as“Axay”, in which “A” represents the acrylamide,“x” stands for the molar percentage of acrylamide（AAm）monomer content in the hydrogel. And “a” represents the “agar”, “y”stands for the agar concentration mg/ml. In addition, the ratio of photoinitiator to monomer was fixed as 1mol%, and the ratio of crosslinker to monomer was fixed as 0.028mol%.

(1) MECHANICAL STRENGTH TESTS.

Abstract:

Using a simple one-pot, heating-cooling-photopolymerization method, we have successfully synthesized new type hydrogels with high mechanical properties , like cartilage and natural rubber, of stiffness (elastic modulus) , strength ( failure tensile stress ), and toughness , excellent extensibility and a unique free-shapeable property (formation of many complex shapes). Which not only fulfilled the basic ends of insoles, but also provided a wild range hydrogels with controllable stiffness and toughness to meet the needs of personal customized “Comfootable” insoles.

1) The polyacrylamide Single network hydrogel was totally transparent, becoming opaque and darker with the increasing of agar concentration.

Fig. Formation of agar medium and A3 DN gels with agar concentrations at 3, 7, 13, 17, 23, 27 mg/mL.

2) Compared with the brittle traditional agar medium easily crushed under finger compression, agar/PAAm DN gel shows high stiffness and good recovery.

Fig. Finger compression of traditional agar medium and A5a17 DN gel. (a) traditional agar medium, (b) A5a17 DN gel.

3) High stiffness of DN gel compared with soft PAAm SN gel.

Fig. Finger compression of A5 DN gel. (a) A5 SN, A5a7 DN, A5a17 DN, A5a27 DN gels (from left to right). (b) Finger compression of A5 SN gel. (C) Finger compression of A5a7 DN gel.

Compressive test

Dependence of Compressive Elastic Modulus on Acrylamide Concentrations.

the stiffness (elastic modulus)of polyacrylamide single gels depended strongly on acrylamide concentration, increasing proportionally to acrylamide concentration.

Fig. Effect of acrylamide concentrations on the polyacrylamide single gels

Dependence of Compressive Elastic Modulus on Acrylamide and Agar Concentrations.

Agar concentrations affected the stiffness(elastic modulus)of agar/PAAm DN hydrogels in varying degrees. As the whole, the stiffness increased with agar concentrations. And can achieve high stiffness at the agar concentrations of 17mg/ml or above.

Fig. Effect of agar concentrations on the DN gels at the feeding concentration of AAm (a) 3mol/L, (b)5mol/L, (c)7mol/L.

Dependence of Elastic Modulus and Toughness on Agar and Acrylamide Concentrations.

Fig. Stiffness and toughness of DN gels with varies acrylamide concentrations at the feeding concentrations of agar 27mg/ml.

According to the figure, stiffness (elastic modulus) increased linearly with acrylamide concentration all through. Yet the toughness first grew rapidly with the acrylamide concentration, and then slowed down at the point of acrylamide 5mol/L.

Fig. Stiffness and toughness of DN gels with varies agar concentrations at the feeding concentration of AAm 5 mol/L.

Both stiffness and toughness increased proportionally with the agar concentrations and achieved an pretty high value at the agar concentration of 17mg/mL and above, which was comparable to cartilage and natural rubber.

Fig. Photographs demonstrating how different DN gels sustain a high compression. (a) A3a3 DN gel, (b) A5a7 DN gel.

There are cracks in the middle of the cylinder column of A3a3 DN gel after high compression of 90% strain. While the A5a7 DN gel in perfect condition and recovery immediately after extreme compression of 95% strain.

Tensile test

1) Tensile stress-strain curves of agar/PAAm DN gels

Fig. Effect of agar concentrations in the first network on mechanical properties of agar/PAAm DN gels at the feeding concentrations of AAm (a) 3 mol/L, (b) 5mol/L, (c) 7 mol/L.

Figure shows that at a low AAm concentration of 3 mol/L (a), the tensile stress of DN gels increased from 0.15-0.6MPa. At higher AAm concentrations, DN gels prepared exhibited high mechanical stress of 0.4-0.9MPa at AAm 5mol/L(b) and 0.3-1.2MPa at AAm 7mol/L(C),indicating that the increase of the AAm concentration can enhance the fracture stress of DN gels. Besides, the failure tensile stress was generally improved with the increase of agar concentrations at AAm concentrations of 3 mol/L. However, it presented another pattern at high AAm concentration. Instead of increasing all the time, there was an turning point at the agar concentration of 17mg/mL, where both reached the maxium tensile stress of 0.87MPa (b), 1.25MPa (c).Then, we specifically examined the effects of AAm concentrations on the mechanical properties at the feeding concentration of agar 17mg/L.

Figure. Effect of AAm concentrations on the mechanical properties at the feeding concentration of agar 17mg/L.

Figure shows that the fracture tensile stress improved with the increase of AAm concentration

under 7 mol/L. Above that, it fell down. A7a17 DN gel presented the peak value of 1.25MPa, while the next one was 0.87MPa of A5a17 DN gel.

Table 1. Mechanical properties of agar/PAAm DN gels with various agar and acrylamide concentrations.

The results of orthogonal tests presented above shows the tensile strain of the DN gel varied from 8-22 mm/mm. And the effect of agar and acrylamide concentrations on toughness shows similar tendency as the fracture tensile stress. A5a17 DN gel possessed both the maximum fracture tensile strain and toughness.

4) Effect of sodium alginate on the mechanical properties of agar/PAAm gels.

Table 2. Mechanical properties of agar/PAAm gels with various acrylamide concentrations at the feeding concentration of agar 17 mg/mL.

Fig. Photograph of A7a17S0.2 TN gel tensile test with fracture tensile strain of 27.644mm/mm.

Table 2 shows the mechanical strength of gels at the agar concentration of 17mg/L. It should be pointed out that when 0.2mg/mL SA(Sodium Alginate) was added into the mix aqueous solution of agar and acrylamide, the mechanical strength of the A7a17 gel was highly enhanced with the maximum tensile stress of 27.64 mm/mm (Fig)and the maximum toughness of 92108.1J/m^3, indicating that proper amount sodium alginate can form the semi-interpenetrating network to help dissipate the energy applied.

Results 3

BIOCOMPATIBILITY TESTS

Fig. Photographs of biocompatibility tests of agar/PAAm gels. A7 SN gel and A7a27 gel medium(a), excited by ultraviolet(b), A7a17 gel and A7a17S0.2 gel medium(c),excited by ultrabiolet(d).

The results of the Inhibition Ring Test s showed that there were not significant difference between experimental group and the control, indicating that the new type hydrogels we synthesized is biocompatible to be used as the main body material of our insoles.

SWELLIING TESTS

Fig. Effect of agar concentration on ESR of agar/PAAm gels. (a) ESR of dry gels in pure water. (b) ESR of swelling gels in pure water. (c) ESR of dry gels in LB. (d) ESR of swelling gels in LB.

Figure shows that the Equilibrium of Swelling Ratio (ESR) of the dry gels in pure water varied from 8-16(a), in LB varied from 6-18(c). While the ESR of swelling gels in pure water varied from 0.5-3(b), in LB varied from 0.5-3(d). The relatively high ESR of dry gels indicated the huge potential of the hydrogel based insoles to absorb the nutrients, while the less ESR of swelling gels prevent the insoles from out of use for huge swelling deforming.

Results 4

(4)Insoles

1) insole 1

Figure. Photographs of insole 1. (a) resin skeleton of insoel 1. (b) whole 4 layers of insole 1.

2) insole 2

Figure. Photographs of mould and main body of hydrogel based insole 2.

3) insole 3

Figure. Photographs of insole 3 (a) mould of insoel 3 with slipsole. (b) main body of insole 3 with slipsole .(c) mould and hydrogel main body of insole 3 with foot arch support.

Personal customized insoles

The unique free- shapeable property of of our agar/PAAm DN gels enabled the personal customized shape insoles, like the insole with slipesole(a) for people who want higher height, or the insoles with foot arch support(b) for people with flatfoot. While two different type insoles——the summer type and winter type provided alternative choice for people to choose in different season, which improved the user experience greatly.