Plasma for Biomedical

Applications

Presented by

Prof. Sudarsan Neogi

Department of Chemical Engineering

Indian Institute of Technology

Kharagpur

sneogi@che.iitkgp.ernet.in

Presentation outline

• Plasma – introduction

• Salient features of plasma

• Biomedical applications of polymers

• Plasma surface modification of polymers

• Specific biomedical applications of polymers using plasma

• Plasma sterilization

• Latest development

• Summary

Solid

Energy

Liquid

Energy

Gas

Energy

Plasma

Plasma• Plasma – a quasi neutral gas, referred to as fourth state of

matter

• Collection of particles consisting of electrons, ions and excited

atoms and molecules

• Moves in random directions

• Electrically neutral

• Ionization of neutrals sustains the plasma in the steady state

• Natural Plasma – Lightning, all stars including sun

Advantages of plasma treatment

• Alters the surface properties of material without affecting their

bulk property

• Surface modification in a controlled fashion

• Highly cross-linked films irrespective of the surface

geometries

• Formation of multilayer films

• Eco-friendly nature

• The prospect of scaling up

• No water and chemicals required

• Selection of desired chemical pathways

• Minimization of thermal degradation and rapid treatment

Applications of Plasma

• Microelectronics

• Chemical

• Biomedical

Surface properties

Hydrophobicity

Chemical structure

Roughness

Conductivity

Material properties modified by plasma

Effect of plasma on Material surface

Plasma Effect On Surface

Surface modification Induced Grafting Polymerization

Plasma surface activation

Plasma etching

Functionalization

Plasma Surface Activation

• Physical sputtering – Noble gas

• Chemical reaction - O2, H2

• Free radicals created on surface

• Coupling of free radicals with active species in

plasma

• By products - CO2, H2O and low molecular weight

hydrocarbons

Plasma etching

• For the removal of materials from surface

• Selective removal by chemical reactions and/or physical

sputtering

• Cleaning, polishing surfaces, processing plate edges

• Makes the surface rough

• Improves adhesion by increasing surface energy

Functionalization

Reactive plasma gases

Chemical groups

incorporated

Hydroxyl

Carboxyl

Carbonyl

Amino

Peroxyl

Plasma Induced grafting

• Two-step process

• Free radical formation

using inert gas plasma

• Introduction of an

unsaturated monomer

• Improves adhesion

Plasma gases and their applications

Plasma gases Application

Oxidizing gases (O2, air, H2O)

Reducing gases (H2, mixtures

of H2)

Noble gases (Ar, He)

Removal of organics and to

leave oxygen species

Replacement of F or O in

surfaces, removal of oxidation

sensitive materials, conversion

of contaminants to low

molecular weight species

To generate free radicals in

surfaces to cause cross linking

or to generate active sites for

further reaction

Plasma gases and their applications

Plasma gases Application

Active gases (NH3)

Fluorinated gases

Polymerizing gases

To generate amino groups

To make the surface inert and

hydrophobic

Polymerization of layers onto

substrates by direct

polymerization or by grafting

on Ar or He pretreated polymer

surface

Biomaterials

• Biomaterial: Non-viable material

used in a biomedical device intended

to interact with biological systems.

• Biocompatibility: Ability of a

material to perform with an

appropriate host response in a

specific application.

• Blood compatibility: A derivative of

biocompatibility, a complex function

of many parameters including

characteristics of the blood, material

and time.

Surface functionalities for biomaterials

• Biocompatibility

• Blood compatibility

• Reactive groups for attaching

biomolecules

• Compositions promoting cell growth

• Temperature sensitive coatings

• Non-fouling (protein resistant)

coatings

Antibacterial coatings

Controlled drug release

Wettability

Micropatterning

Surfaces strongly adsorbing

proteins

Surface functionalities for biomaterials

Biomedical applications of polymers

Polymers Biomedical applications

Polyethylene Tubes for various catheters, hip

joint, knee joint prostheses

Polypropylene Suture materials, hemodialysis,

blood transfusion bags

PolyTetrafluroethylene Vascular and auditory prostheses,

catheters, tubes

Polyacetals Hard tissue replacement

Polymers Biomedical applications

PMMA Bone cement, intraocular lenses, contact lenses,

fixation of articular prostheses, dentures

Polycarbonate Syringes, arterial tubules, hard tissue replacement,

hemodialyzers, blood pumps, oxygenators

PET Vascular, laryngeal, esophageal prostheses, surgical

sutures, knitted vascular prostheses

Biodegradable polymers Sutures, drug delivery matrix, adhesives, temporary

scaffolding, temporary barrier

Polyurethane Adhesives, dental materials, blood pumps, artificial

hearts and skin and blood contacting devices

Biomedical applications of polymers

Why plasma treatment for biomedical

applications?

• Lack of surface properties

• Surface properties influence cell adhesion

• RF plasma surface modification without affecting their bulk

properties

• Smooth, pinhole free ultra thin film

• Surface tuning

Surface modification of polymeric biomaterials

by RF plasma

• Modifies surface physical and chemical properties without

affecting bulk properties

• Advantageous for the design, development and manufacture of

biocompatible polymers

• Surface modification or by thin-film deposition - protein–

surface interaction and cell adhesion can be optimized for

improving biocompatibility

• RF plasma-treated polymeric biomaterials - Hindering

bacterial adhesion, found wide applications in antimicrobial

coatings.

• Antimicrobial coating on RF plasma-treated polymers can

prevent microbial adherence on the surface, thus preventing

biofilm formation.

Improving biocompatibility/blood compatibility

• Biocompatibility – not an inherent property of a material, but

results from complex interactions between an implant and the

surrounding tissues

• Polymer in biomedical application - should be

biocompatible, should have a low friction coefficient and

hydrophilicity

• Biomaterials selected for mechanical strength or stability in

the body suffer from problems associated with surface-

induced thrombosis

• Thrombosis - initiated by the deposition of a plasma protein

layer on the surface of the implanted biomaterial

• Platelets, fibrin and leukocytes adhere to the deposited protein

• Interaction between the plasma proteins and the surface of the

implant determines the adhesion, activation and spreading of

platelets, activation of coagulation, cell attachment and protein

deposition.

• Polymeric materials - modified to meet the needs of tissue

engineering

• Immobilization of protein with antithrombogenic or

thrombolytic qualities is a way of introducing the

antithrombogenic characteristics on blood-contact materials

• Antithrombogenic materials - heparinated high molecular

weight materials, urokinase immobilized high polymer

materials or plasma-treated high molecular weight materials

• Immobilization of various proteins with antithrombogenic

properties like recombinant hirudin (rHir), thrombomodulin

and human thrombomodulin on polymers

• Vascular grafts - Inner surface of the segmented polyurethane

tube modified by air-plasma treatment holds good as a suitable

substrate

• Improved blood compatibility and enhanced growth of

smooth muscle cells - Polyethyleneterephthalate (PET) films

grafted with acrylic acid using oxygen plasma, immobilized

with insulin, heparin and collagen

• Prevention of platelet aggregation - Polymer-coated encased

stents, facilitating endothelial cell growth on the inner lining of

the stent are used to prevent platelet aggregation

• Plasma treatment - improves the wettability, oxidizes the surface and

enhances endothelial cell growth and cell adhesion on polymer (eg.

polyurethane) surfaces

• Endothelial cell adhesion - also achieved by ion implantationand

carbon deposition

• PET - reinforced composite in prosthetics shows poor adhesion

• O2 plasma treated PET fibres - improved adhesion in fibre matrix

composite and increased the surface energy

Antimicrobial coating

• Adherence of bacteria to a polymer surface - results in biofilm

formation

• Biofilm - resistance to antibiotics makes the device-associated

infection difficult to treat and necessitates the removal and

replacement of the infected device

• Antibacterial agent is coated on medical polymers to prevent

biofilm formation

• Surface treatment prevents the initial adhesion of bacteria to

the polymer surface or kills the bacteria as they come in

contact with the surface

• Silver ions - possess good antimicrobial properties, anti-

inflammatory properties and enhances healing rates

• Surface properties influencing bacterial adhesion - hydrophobicity,

composition, mechanical properties and morphology

• Both metallic and ionic silver - incorporated into several

biomaterials such as polyurethane, hydroxyapatite, and bioactive

glasses

Tomato fruit at zero time, (a) similar fruit kept for 13 days into a polypropylene bag

fabricated from PP film covered by 12 alternating chitosan/pectin layers in

comparison to similar fruit kept for the same period of time in untreated PP bag (b),

and another one kept in open air (c).

(a) O2 plasma pattern; (b) N2 plasma pattern; (c) NH3-VUV pattern

Plasma for specific Biomedical applications

• Implants

• Bioseparation

• Plasma sterilization

• Biosensors

• Ophthalmology

• Plasma treatments are given to the polymers to achieve the

above-mentioned properties, namely antimicrobial properties

and bio/blood compatibility

Orthopedic implants

• Any material having desirable mechanical properties and

biocompatibility with the bone is used in bone replacement

• Mainly constructed using titanium alloys for strength and lined

with polymers that act as artificial cartilage

• The major obstacle to long-term use of metallic substrates is

bone resorption due to stress shielding, leading to their

degradation after 10–15 years

• Ultra high molecular weight

polyethylene (UHMWPE) and

polytetrafluoroethylene (PTFE) -

used in joint socket

• Polyurethane - in bone joint due

to their excellent wear,abrasion,

corrosion and fatigue resistance

• UHMWPE - used in surgical

replacement of damaged

cartilage in total joint/diseased

joint

• Biocompatibility of UHMWPE - modified by means of cross-

linking, functionalization using various plasmas such as Ar, C2F6,

C2H4, NH4, CH4 and HMDSO, and no cytotoxicity was observed

• Argon and Ar/CH4 plasma-treated samples showed little red

blood cell destruction and thus are more blood compatible

• Carbon-fibre-reinforced polyether ether ketone (PEEK) - treated

by oxygen plasmaand N2/O2 plasma to get better surface

activation for subsequent joining and coating processes, initiation

sites for the formation of calcium phosphate coatings in

supersaturated solutions

Cardiac implants

• Polymers in cardiac implants - as implant leads, artificial

hearts, stents and controlled drug release devices

• Non-biodegradable polymers - polyurethane, silicone rubber,

ethylene vinyl acetate

• Biodegradable polymers - poly(glycoliclactic acid), and high

molecular weight polyanhydride

• Polyurethane matrix synthesized with pore formers and loaded

with ciprofloxacin releases antibiotic at a controlled rate when

coated with n-butyl methacrylate by RF plasma deposition

Dental implants

• Polymethylmethacrylate (PMMA) - used in dental implants as

denture bases, artificial teeth, removable orthodontics, surgical

splinting and aesthetic filling in anterior teeth

• Many other polymers have been explored for several dental

applications such as dentures, crowns, bridges, fillings, mouth

protectors, sutures and implants

• Biofilm formation due to the adhesion of Candida albicans on

PMMA causes denture-induced stomatitis, which is a common

intraoral disease

• Surface loading of histatin 5 - either by

adsorption or chemical cross-linking,

reduces C. albicans biofilm formation

• Modification of PMMA by

copolymerization of methyl methacrylic acid

resulted in twofold increase of the

adsorption of the added amount of histatin 5

per unit surface area

• Amount of histatin adsorption on PMMA

increases more than six times when PMMA

is treated with O2 plasma compared to that

adsorbed onto untreated PMMA

Bio-separation

• Membranes used for biomedical applications should have high

ion/solute permeability, blood compatibility, mechanical

stability and dimensional stability upon swelling

• Hydrophilic composite membranes consisting of acrylic acid

polymer and porous polypropylene with high ion permeability

and dimensional stability were developed by plasma

interpenetrating polymer network techniques

• Deposition of hydrophilic monomers, namely 1-vinyl-2-

pyrrolidone, 2-hydroxyethyl methacrylate (HEMA) and methyl

methacrylate by plasma deposition onto chemical and O2

plasma-treated Nylon 4 membrane

• Plasma deposited polymer layer of dimethylaniline and acrylic

acid on the surface of PET track changed their transport

properties, especially water permeability

• Membranes used for bioseparation are fouled and clogged

when non-specific proteins are adsorbed on it reducing the

thrombogenicity of blood-contacting surfaces or

inhibiting/preventing the non-specific adsorption of protein

surfaces by polymerizing a phospholipid

• Plasma polymerization as pretreatment for phospholipids -

better reduction in platelet adhesion compared to that in

untreated polymer.

Biosensors

• Biosensors require two and three-dimensional microstructured

substrates with a chemically suited surface to mimic the basic

functions of natural tissue

• Chemical micro-patterning of cell culture by plasma

processing allows the introduction of functional groups on the

polymer surface, without affecting its bulk properties

• It enables covalent bonding for fixation and immobilization of

biomolecules on various substrates

• Pulsed RF plasma for polymerization of allylamine - for

successful DNA adsorption and hybridization.

• Micropatterning of amine groups, used in DNA array

technology was achieved with excellent thickness

controllability and uniformity in a relatively short time by

selective deposition of plasma polymerized ethylene diamine

on glass slides

• RF plasma treatment yields a more compatible interface with

biological fluids

• Hydrophobic polypropylene membrane has been made

hydrophilic on one side when treated with ammonia plasma

and coupled to urease to construct a urea sensor, and an

appreciable reduction in the response time has been achieved

Ophthalmology

• Contact lenses - should have high oxygen permeability, good

wettability by tears and resistance to deposition of protein, mucus,

lipid, microorganisms and other foreign substances on the lens

surface

• CF4 plasma-treated PMMA intraocular lens - reduces the

adhesion of proteins, the development of inflammatory cells and

the formation of cellular debris

• Surface modification of silicone with O2 and CO2 plasma - CO2

plasma more suitable for grafting functional groups on the surface

of poly(dimethylsiloxane), since CO2 could be used for a longer

period without causing surface damage, unlike O2 plasma

• Silicone rubber grafted with pHEMA by plasma-induced graft

polymerization - suitable for cell attachment and growth

• Argon RF plasma treatment of polyvinyl alcohol copolymer

hydrogel

Optimal for epithelial cell migration and proliferation

Allows migration, proliferation and synthesis of matrix

and adhesion molecules in vitro

No inflammatory response on the treated surface

PLASMA STERILIZATION

Sterilization

• Emerging application in medical, food and pharmaceutical

industries

• Complete elimination of all types of microorganisms

• Microorganisms normally sterilized

- Bacteria

- Fungi

- Yeast

- Molds

- Spores (most-resistant bacteria)

Importance of sterilization

• Design of medical devices

• To provide a sterile or contaminant-free environment

• Sterility Assessment: SAL (Sterility Assurance Level)

- the probability of a non-sterile product in million containing

a contaminant

• Surgical tools used in brain surgery needs high SAL

• Medical device manufacturers – 10-6 (one in a million devices

may be non-sterile)

• Decontamination of food storage devices

Controversy in commercial sterilizers

• 2 commercial sterilizers – Sterrad®, Plazlyte®

• Sterrad – Hydrogen peroxide + RF plasma(1987)

• Plazlyte – Per acetic acid + MW plasma(1993)

• Both gases have disinfectant properties

• Plasma – used as a detoxifying agent( Krebs et al., 1998)

Is it a plasma sterilizer or chemical sterilizer?

“…non-toxic gas mixture which does not have any disinfectant

property by themselves and they should sterilize only under the

applied electric field”

- Alexander Fridmann, Low temperature plasmas Vol 2

Requirements of a sterilization process

• Highly efficient

• Operate at/near ambient temperatures

• Short treatment times

• Non-toxic

• Minimal substrate damage

• Compatible to wide range of materials

Latest developments

IN

Plasma sterilization

Micro plasma

• Plasma needle – being confined in narrow

spaces (10 - 500 µm)

• Stable operation – non-thermal plasma

• Site-specific treatment – Dental, corneal

infections

FE-DBD – Floating electrode-Dielectric

Barrier Discharge

Floating electrode

(Human hand/ animal organ)

Dielectric Barrier Discharge

electrode

(Insulated electrode)

Gregory Fridman, 2006

Plasma-assisted blood coagulation

+ Saphenous vein cut for mouse

+ Continuous bleeding

+ 15 sec DBD treatment

+ Stops bleeding

+ Blood vessel remains sealed

+ No visible/microscopic damage

Plasma-assisted blood coagulation

(Continued)

• FE-DBD plasma promote blood clot formation for patients

suffering from clotting disorders

Biofilm treatment

• 10 min exposure kills 100% biofilm (hazardous) formation using

RF high-pressure cold plasma jet

Nina et al., IEEE Transactions on Plasma Science, (2006) 34, 1304 - 9

Other important applications

• In wound healing, the tissue damage should be minimized as

well as wounds need to be sterilized to prevent bacterial

invasion

• Treatment in melanoma skin cancer, ulcers, burns

• Treating corneal infections – In vivo test in rabbit eyes showed

strong bactericidal effect without tissue damage

• Treatment of tumor cells

RF plasma applied to human skin

• Atmospheric pressure RF plasma can be safely applied to

human skin treatment without electrical and thermal damage

S Y Moon et al., Thin solid films, (2009) 517, 4272-4275

Summary

• RF plasma treatment of polymeric biomaterials has been a topic of

extensive investigations pertaining to a wide range of applications

• Biomaterials, which have permanent contact with the body and

tissues, require unique surface properties like surface free energy,

hydrophilicity and specific surface morphology, for improved

cell/protein adhesion on the polymer surface

• Ability to modify a surface in a controlled way, deposition of cross-

linked films on complex geometries, formation of multilayer films,

rapidity, sterility and the prospect of scaling-up are the salient

features of RF plasma processing that makes it suitable for

biomedical applications

• RF plasma treatment produces three major effects on biomaterials:

surface modification, grafting and film deposition

• Surface modification improves adhesion, enhances surface

wettability and spreading, and reduces surface friction

• Antimicrobial coatings on RF plasma-treated biopolymers can

prevent microbial adherence on polymer surface, thus preventing

biofilm formation

• Either by surface modification or by thin-film deposition, protein–

surface interactions and cell adhesion can be optimized for

improving biocompatibility

• Modified polymeric biomaterials are widely used in implants,

bioseparation, biosensors and ophthalmology

• Possibility of fast and low temperature sterilization minimizing

the substrate damage especially for heat sensitive materials

• Atmospheric plasma sterilization for live tissue treatment

• Plasma needle – site-specific treatment

• A possible solution for the future medical industry

Plasma Treatment Operating conditions

• Gas (Ar) flow rate : 10 sccm

• Reactor Pressure : 12.5 mTorr

• Power : 30 –50 W

• Exposure time : 3 –7 mins

Various Doses

SL.No Etch

Time

Etch

Power

1 3 30

2 4 50

3 5 30

4 6 50

5 7 30

DEVELOPMENT OF AN ANTIMICROBIAL

IUD BY VACUUM PLASMA ETCH

METHOD

Deposition of Nanosize/ Picosize particles of

RISUG® over IUDs

by Vacuum Plasma Etch Method

Uncoated Copper T Coated Copper T

Surface morphology study

Uncoated Untreated Polyethylene Uncoated Plasma treated Polyethylene

RISUG® Coated T, 6 mins at 50 WPlasma Treated T, 6 mins at 50 W

ATOMIC FORCE MICROSCOPY IMAGES

Untreated polyethylene

Plasma treated RISUG®

drug coated polyethylene

Plasma treated PE

(6 mins, 50 W)

Microencapsulated Effervescent

Vaginal Drug Delivery System.

SMA acid

Effervescent mixture

Plasma treatment

Vaginal fluid

Effervescence

starts

CO2 liberationPressure increase

Our Idea

Plasma Treatment

Radio frequency plasma in M-PECVD-1A [S] instrument designed by MILMAN Thin Solid Films.

Flow rate of 10 sccm, Pressure 175 mT, DC bias 112V, Radio Frequency 13.56 MHz and Argon Plasma were maintained.

Sample Code Power (W) Initial Temp in C

Final temp in C

Time in mins

1 30 26.7 35.3 5

2 40 25.7 36.2 5

3 50 25.1 36.4 5

4 60 23.8 36.8 5

5 70 22.1 35.9 5

FT IR data

4000 3800 3600 3400 3200 3000 2800 2600 2400 2200 2000 1800 1600 1400 1200 1000 800 600

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

1.1

1.2

1.3

1.4

1.5

absorb

ance

wave number

encapsulated effervescence product

plasma treated encapsulated effervescence product

styrene maleic acid

citric acid

4000 3800 3600 3400 3200 3000 2800 2600 2400 2200 2000 1800 1600 1400 1200 1000 800 600

0.00

0.05

0.10

0.15

0.20

0.25

0.30

0.35

0.40

Y A

xis

Title

X Axis Title

encapsulated effervescence product

plasma 30 W

plasma 40 W

plasma 50 W

plasma 60 W

plasma 70 W

1) Negligible change in chemistry on plasma treatment.

2) O-H stretch of the alcohols in citric acid have disappeared in the encapsulated product suggesting encapsulation.

SEM Data

No plasma treatment Power 30 W

Power 40 W Power 50 W

Power 60 W Power 70 W

Plasma treatment causes surface roughness in the form of pits crevices and pores.

Honeycomb arrangement has been observed in certain situations.

Pulsing Plasma Treatment

Pulsing plasma in M-PECVD-1A [S] instrument designed byMILMAN Thin Solid Films.

Flow rate of 25 sccm, Pressure of 275 mT, Frequency of 20kHz, 70 % duty cycle and Argon Plasma were maintained.

Sample Code

Voltage (V) Initial Temp in C

Final temp in C

Time in mins

1 400 22.8 24.4 5

2 500 25.1 26.5 5

FT IR data

4000 3800 3600 3400 3200 3000 2800 2600 2400 2200 2000 1800 1600 1400 1200 1000 800 600

0.00

0.01

0.02

0.03

0.04

0.05

0.06

0.07

0.08

absorb

ance

wave number

Encapsulated no plasma

plasma 500 V

plasma 400 V

No change in the chemistry of the sample

Differential Scanning Calorimetry

No change on plasma treatment.

Different from the pure drug molecule

Position [°2Theta]

20 30 40 50 60 70 80 90

Counts

0

20

40

60 ENCAP

Position [°2Theta]

20 30 40 50 60 70 80 90

Counts

0

20

40

60

plasma

Peak

no

2 θ d spacingCount

1 30.741 2.9061 47

2 31.937 2.8000 61

3 45.626 1.9867 35

Peak

no

2 θ d spacingCount

1 30.475 2.9309 46

2 31.671 2.8229 71

3 45.626 1.9867 44

Encapsulated product

Plasma treated Encapsulated product

XRD data

Plasma treatment does not cause any change to the crystal structure.

SEM Data

Well defined pits and pores on the surface.

Formation of arrays of pits.