What is TPU: Full Form /material and Organo-Floromica Nanocomposites for Biomedical Applications

introduction

Thermoplastic polyurethane (TPU) are linear, segmented block copolymers consisting of hard and soft segments.

 Rigid segments are composed of diisocyanate and short chain

Expansion molecules such as diols or diamines are rigid and highly polar. Hydrogen bonding within the hard segment of the TPU acts as a reinforcing association.

On the other hand, soft segments consist of long, linear flexible polyether or polyester chains that interconnect two rigid segments. In short,

Hard segments act as multidimensional tie points acting as both physical crosslinks.

 While soft sections mainly affect the elastic properties of TPU

Demonstrates physical properties comparable to medical grade polyether-based TPU

Materials such as Palethane™ 80A and is now widely accepted as one of the most biostable of all commercial TPUs.

 Our previous work shows that elast-

Eon E5-325 TPU can be tailored to provide advantageous mechanical properties by?

Incorporation of organically modified smectic nanosilicates. we found the best

Surface modification was achieved with the most hydrophobic/dual surfactant system TPU nanocomposites with OrganoFloromica

Modified with DODMAC/CC was then selected for further evaluation on biostability.

 To safely use these PDMS/PHMO-based TPU nanocomposites in humans

biological systems, assessment of mechanical performance under specific conditions and

Considering the environmental impact is also necessary, TPU nanocomposites have to be exposed in human bodily fluids.

 Closely mimic the in vitro tests in liquid media. Physicochemical conditions and temperature are required for "screening" of this TPU

Nanocomposites for end use in implantable devices, and before costly

In vivo tests in appropriate animal models.

 It is especially important for this task. To assess time-dependent dynamic mechanical integrity by employing fatigue testing. fatigue

is a failure mechanism that occurs when a material is subjected to or repeats a cyclic load

Tension .

In this communication, the in vitro mechanical properties of PDMS/PHMO TPU

Reported and compared nanocomposites incorporating organofluoromica

Commercial silicone elastomer (Nusil Med 4860). The samples have been subjected to

Physical in vitro conditions by immersing host TPU and nanocomposite samples in

saline solution at 37 °C. An in vitro fatigue test was performed to estimate the potential

Long-term improvement of in vivo performance of TPU nanocomposites for implants

Application.

Material TPU

 

Supply of Thermoplastic Polyurethane (TPU) AorTech Biometerials Pty Ltd (VIC,

Australia). This TPU is commercially known as the ElastEon™ E5-325

g/mol poly(dimethylsiloxane) (PDMS) and 700 g/mol poly(hexamethylene oxide) (PHMO)

A soft segment mixed in the 98:2 (w/w) ratio, and a hard segment which is alternately composed of 4,4'-

Methylene diphenyl diisocyanate (MDI) and 1,4 butanediol (BDO) sequences. Difficult

The volume concentration is 32.5 wt%. Nusil Med 4860 is a medical grade elastomer which has a

Two-part silicon system in 1:1 mixing ratio (Part A:B). Part A contains 30wt% amorphous

silica, while Part B is a 5 wt% dimethyl, methylhydrogen siloxane copolymer. when it

The two components are mixed, causing Nusil Med 4860 to cure rapidly 5 minutes at 165 C

Presence of platinum catalyst. This material was supplied by CochlearTM Ltd and is

Commercially available from Nusil (via EIM Medical Consulting Pvt Ltd, NSW, Australia).

Somasif ME100 (ME) was a synthetic fluoromica (tetrasilicic trioctahedral fluoromica)

Supplied by Kobo Products, Inc. ((NJ, USA). It is a fine white powder with average

Platelet length is about 650 nm. This Floromica surface was modified with a double Modification system (75% dimethyldioctadecylammonium chloride (DODMAC) and 25%

Choline chloride to obtain 'hydrophobic organo-fluoromica') as nanofiller for this study.

This dual surface modified Fluoromica (Organo-Floromica) was chosen in this study because

This has resulted in the best mechanical performance when involved in

TPU due to its hydrophobic characteristic which can provide a more favorable TPU-nanophiler

chit chat.

TPU Methods

High Energy Milling Process for Organo-fluoromica (MED-C)

High energy milling was performed on Organo-Floromica using the Netzsch laboratory mill

Type LABSTAR LS1. 0.4 mm yttrium-stabilized zirconium oxide (ZrO2) grinding beads

Worked as milling media. Milling in an ethanol/water mixture 1:1. was done on

Ratio. The organo-silicate was melted for 2 h to reduce its particle size from ~650nm to

~250 nm. The milled MED-C suspension is then separated by centrifugation a . was separated using

Beckman Coulter Allegra X-15 Benchtop Centrifuge 3 . with a rotation speed of 4750 rpm for

minutes, and later washed off with MilliQ water. washed soil dried up

overnight at 60 C in an oven and ground by jet milling prior to nanocomposite processing.

Preparation of TPU Nanocomposite Sheets

E5-325 TPU was used as the matrix material in this study. Two-Hour Milled Organoflorica

(MED-C (2HM) was used as the nanofillers. E5-325 TPU nanocomposite containing MED-C

(2HM) was prepared with 2 wt% nanofiller structure using melt processing (MP).

way. In a later discussion, these nanocomposites were described as 2MED-C. referred to as

(2HM). A number denotes 2 wt% organosilicate loading in TPU. first two letters

represent the nanosilicate used (ME = Somasif ME 100) and the last two letters (D–C) represent

Dual DODMAC/CC surface modification. characters in parentheses; (2HM) denoted

Nanofiller size reduction process of 2 h high energy milling. E5-325 TPU

The nanocomposites were prepared by melting TPU pellets with 2 wt% organo-.

Fluoromica using a Hake Riomax OS twin screw extruder (Thermo Scientific, USA).

The extrudate was pelleted and dried at ~70 °C for approximately 20 h before being

Compression molded. Compression molding was performed using a hydraulic press. a couple

Brass plates were used, with a rectangular cavity in the bottom plate. molds were

The pellets are heated to 185 °C before being added. I. was "pre-pressed" at 1 kPa for

min, followed by 5 kPa for 0.5 min. pressure released to remove further air

The bubbles were then pressed to the samples at 7.5 kPa for 0.5 min. samples were

Cooled to a pressure of about 140 °C using undisturbed controlled water flow

Pressure. Plaques approximately 1 mm thick were drawn and then sutured off

under vacuum at 85 °C for approximately 5 h and left for at least one week before aging

test.

in vitro fatigue test

To obtain sensible in vitro results, the test was performed in an environment

Cells containing phosphate buffered saline (PBS) solution (pH ~ 7.4). In addition, 0.02%

Sodium azide was added to the solution to slow the growth of micro-organisms, and the test was

Performed in 37 °C conditions, which approximates the temperature of the human body. test samples

The environmental chambers were air-conditioned for at least 30 min before proceeding.

mechanical test. Dumbbell samples that were perforated with an ASTM D-638-M-3 dye were employed for each test. A cyclic tensile load of 500 N was applied axially at 0.2 Hz

10,000 cycles. A cyclic strain amplitude of 50% was applied, and the test was recorded using

A sinusoidal waveform and a 50 ms data acquisition rate. The hysteresis was calculated on

Up to 125% from the 5th cycle using the equation below.

Transmission electron microscopy (TEM) analysis

TEM analysis was performed to observe the dispersion of organofloromica platelets throughout

TPU Matrix. Thin sections of about 80 nm thickness were cut using diatoms

Diamond Knife on Leica Ultracut UC6FCS Cryogenic Ultramicrotome Between -80 and -

110 °C to ensure that the polymers were rigid. 2.3M. Sections were raised using a loop of

Mounted on sucrose and 200 mesh copper grid (ProSciTech, Australia). grid installed

on droplets of deionized water and then transferred through five washes. the grids were then

Allowed to air dry in self-closing forceps before sawing. The sample was tested at a high level

Magnification (93000×) on the operation of a Technai F30 FEG TEM (FEI Company, The Netherlands)

Further images were captured at 300 kV with a Direct Electron LC1100 lens-coupled 4k × 4k

CCD camera system.

Results And Discussion

In vitro (in PBS, 37 °C) fatigue properties of silicone elastomer (MED 4860), virgin TPU

and TPU nanocomposite

In this work, fatigue test was performed to determine the behavior of the material

Body fluid under fluctuating load, 37 °C. Since long-term stability is important in vivo

For biomedical use, the deformation and properties change due to fatigue behavior must be

also be addressed. It turns out that TPU has an elastic part which

stores and returns energy, and a viscous part that captures and returns energy

heat . At 37 °C, the soft segments are above their glass transition temperature and provide

Materials have their elastic behavior, while rigid sections are below their glass or melt transition

Thought to control temperature and plastic deformation, high modulus and tensile

strength. This unique TPU morphology conforms to the deformation and evolves with this

It is believed to be the primary source of hysteresis and cyclic softening. hysteresis is a

Measurement of energy absorbed or dissipated during any cycle of loading or unloading when

The material is subjected to repeated loading. Most TPUs show hysteresis characteristic,

and it can be attributed to many factors such as non-affine conformation, irreversible

Orientation of the hard domain, plastic deformation and energy loss of the hard domain

The hard domain is caused by orientation. TPU breakdown and repair

Mesophase morphology is responsible for stress-softening during cyclic loading

(Mullin effect) and hysteresis loss. This may in some way contribute to the reduction

mechanical integrity . The area between two curves is the energy which is not

comes back but is converted into heat. Hysteresis can give information about the degree of loop fatigue.

. Modification of the hysteresis loop along the cycle is associated with strain variation

over time, which depends on the cyclic stability of the test material. major revision

At high cyclic loads indicating cyclic softening or reduction in the hysteresis loop

in mechanical power. For a comparison of the cyclic effect, the hysteresis loop . happens from

The cycle numbers of 5, 100, 1000 and 10,000 were obtained from the stress–strain curves.

during the fatigue test and they are presented in Figure 1.

TPU Conclusion

Our preliminary studies on in vitro fatigue show promising properties of E5-325 TPU

Nanocomposite (2MED-C (2HM)), which has potential for further development for biomaterials.

When subjected to in vitro conditions, 2MED-C (2HM) shows the highest fatigue strength

Achieving the highest maximum stress value at both low and high cyclic loading (up to 10,000 cycles).

Well-dispersed and exfoliated organofloromica platelets can act as nano-barriers.

Increased fatigue resistance. The data reported here are evidence that well-engineered nanofillers

The systems can aid in the performance of the TPU under an environment of environmental challenge. if carefully

formulated, this nanofiller can have a positive effect on viscoelastic properties such as creep and

In addition to fatigue, ultimate tensile strength and tear strength. However, early in vitro

Fatigue testing was done as a proof-of-concept phase, the results obtained from this study should

provide a useful measure of predicting the E5-325 TPU nanocomposite biostability, which is . essential for

Development and design of future biomedical TPU nanocomposites. Thus, these conclusions can be qualified

Further investigation of in vitro and in vivo mechanical properties and stability under diverse

Environmental aging for a complete investigation on the biostability and biocompatibility of this

Nanocomposite System.