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Journal of Materials Science:Materials in MedicineOfficial Journal of the European Societyfor Biomaterials ISSN 0957-4530Volume 25Number 8 J Mater Sci: Mater Med (2014)25:2027-2039DOI 10.1007/s10856-014-5219-z

UV curable lens production usingmolecular weight controlled PEEK basedacrylic oligomer (Ac-PEEK)

Tulay Y. İnan, Emel Yıldız, BirsenKaraca, Hacer Dogan, AlicanVatansever, Muhammed Nalbant &Koray Eken

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UV curable lens production using molecular weight controlledPEEK based acrylic oligomer (Ac-PEEK)

Tulay Y. Inan • Emel Yıldız • Birsen Karaca •

Hacer Dogan • Alican Vatansever •

Muhammed Nalbant • Koray Eken

Received: 29 August 2013 / Accepted: 19 April 2014 / Published online: 6 May 2014

� Springer Science+Business Media New York 2014

Abstract We produced UV curable lenses with proper-

ties blocking short wave UV light. In the UV-curable for-

mulations, we used an oligomer (Ac-PEEK) with another

urethan oligomer (Mw = 2000). Radically active, molec-

ular weight controlled Ac-PEEK was obtained by reacting

2-hydroxyl ethyl methacrylate with molecular- weight-

controlled and isocyanate terminated PEEK (Mn = 4500).

We characterized all synthesized monomer, oligomer and

optical materials with UV/Vis spectrophotometer with

interferogram, elemental analyser, mass spectrophotome-

ter, proton nuclear magnetic resonance, Fourier transform

infrared spectroscopy, thermal gravimetric analyzer, dif-

ferential scanning calorimeter, scanning electron micros-

copy and gas chromatography. Results suggested that

newly synthesized oligomer with the structure of PEEK

absorbs short wave UV-light. Ageing tests [ISO 11979-5,

Ophthalmic implants—intraocular lenses (IOL)—Part 5:

Biocompatibility] performed on the IOL materials were

successful. High contact angle of the obtained lenses sug-

gests that all lenses were hydrophobic and SEM results

revealed that lenses are morphologically homogeneous.

Based on all positive properties just mentioned, we safely

conclude that the lenses produced in this study are very

promising for IOL production.

1 Introduction

An intraocular lens (IOL) is a lens implanted in the eye

used to treat cataracts or myopia. Polymers are becoming

increasingly attractive for a variety of optical applications

such as, lenses, optical circuits, optical fibers, anti-reflec-

tive films and for coatings, optical adhesives, LCD dis-

plays, waveguides, UV-reactive inks, varnishes and IOL [1,

2]. Widely used optical polymers include polymethacry-

lates, polyurethanes, polycarbonates, polystyrene and ure-

thane-acrylates [3].

The sun emits radiation of UV, visible and IR. The

transmitted solar radiation reaches to earth surface as UV-B

radiation (230–300 nm), near UV or UVA radiation

(300–400 nm), visible light (400–700 nm) and near IR

radiation (700–1,400 nm) [4, 5]. An ocular media of a

healthy human transmits near IR and most of the visible

spectrum to the retina, but UV-B radiation is absorbed by

the cornea and does not reach the retina. In infancy, the

human lens freely transmit near UV and visible light above

300 nm, but with further aging, UV radiation from the

environment causes the production of yellow pigments,

florogens within the lens. By age 54 the lens will not

transmit light below 400 nm and transmission of light

between 400 and 500 nm is greatly diminished. As the lens

ages, it continuously develops a yellow color, increasing its

capacity to filter out near UV and blue light. Therefore,

after cataract removal the natural protection provided by

the aged human lens is also removed. Replacing the cata-

ract by an IOL, usually provides UV protection, but blue

light protection is still lacking [6]. Some authors have

T. Y. Inan (&) � E. Yıldız � H. Dogan � A. Vatansever

TUBITAK Marmara Research Center, Chemistry Institute,

41470 Gebze, Kocaeli, Turkey

e-mail: tulayinan2012@gmail.com

B. Karaca

Altcavusoglu Mah., Ozel Cad. Hakkıbey Apt. 13/5 Kartal,

Istanbul, Turkey

M. Nalbant � K. Eken

ANADOLU TIP Teknolojileri A.S., 1. Organize Sanayi Bolgesi

2. Kısım 5. Cadde No: 10 58060, Sivas, Turkey

123

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DOI 10.1007/s10856-014-5219-z

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speculated that the spectral transmission characteristics of

the ideal. IOL would approximate that of the adult crys-

talline lens. Thus the logic to replace the natural human

crystalline lens with an IOL that approximates its UV

absorption properties could be extended to the replacement

of the crystalline lens by an IOL capable of attenuating

blue light filtration as well [7, 8].

The use of conventional yellow dyes such as commer-

cially available 4-phenylazophenol (Solvent Yellow 7);

2-(20-methyl)-phenylazo-4-methylphenol (Solvent Yellow

12), in IOLs to block blue light is not desirable because

these dyes are not bound to the lens material and thus may

leach out of the IOL after it is inserted in the eye. These

dyes also cause problems in the manufacture of the poly-

mer lenses in the extraction step since solvent may remove

non-bonded dye from the lens [9].

Alcon Laboratories, Inc. has developed polymerizable

yellow dye which is soluble in radically active acrylic

monomers and manufactured the AcrySof Natural IOL to

approximate the UV and blue-light attenuating properties

of the human crystalline lens. This IOL contains a cova-

lently bound chromophore that absorbs light in the

400–500 nm range, adding this light protection to that

already provided in the UV range [10].

UV curing offers manufacturers many benefits such as

lower energy consumption, less environmental pollution

and very rapid curing [1–3]. In general, liquid monomers

and oligomers are mixed with a small percent of photo-

initiators, and then exposed to UV energy. In a very short

times like seconds, the products inks, coatings or adhesives

instantly harden. Depending on the specific application,

nonreactive additives such as pigments, adhesion promot-

ers, and surface active agents may be used in formulations.

Oligomers are the major ingredients in these formulations

because they govern the mechanical properties of the UV-

cured materials, [1–3, 10–14] Most of the oligomers con-

tain methacrylate, vinyl or ally acrylate functionality since

this type of unsaturation provides the highest response to

light.

One of the best high temperature, high performance

engineering thermoplastics are poly(arylene ether ketone)s

and their copolymers because of their superior combination

of chemical, physical, and mechanical properties. High

melting and glass transition temperatures, wide range of

attainable crystallinities, excellent chemical resistance are

some of the useful properties of these kind of polymers. In

addition, they also have good processability to produce

various forms in specific applications such as molded parts,

composites, fibers, films, coatings, and adhesives [15].

IOL implantation is one of the most satisfying advances

of medicine. Millions of individuals with visual disability

or frank blindness from cataracts had and continue to have

benefit from this procedure. It has been reported by oph-

thalmologists that the modern cataract-IOL surgery is safe

and complication-free most of the time. In the mid-1980s,

IOLs were evolving rapidly, but now most techniques,

lenses and surgical adjuncts now allow to achieve the basic

requirement for successful IOL implantation [16]. UV-

transmittance, extraction with saline solution and hexane,

hydolytic stability and photostability tests etc. are known as

biocompatibility tests according to ISO 11979-5 (Oph-

thalmic implants—IOL—Part 5: Biocompatibility). There

are also other factors that should be taken into account

before the commercialization of the lenses. ISO 11979-7

standart mainly deals with the clinical variables like best

spectacle corrected visual acuity (BSCVA); refraction;

intraocular pressure; corneal status; iritis; IOL decentra-

tion; IOL tilt; IOL discoloration; IOL opacity; cystoid

macular oedema; hypopyon; endophthalmitis; pupillary

block; retinal detachment; status of anterior and posterior

capsule and additional variables that can be studied in the

clinical investigations.

This article mainly deals with the IOL material; new

material (Ac-PEEK) usage to block short wave UV-lights

and its production in laboratory scale ve biocompatibility

tests for the lenses. For this aim, UV-curable lens with short

wave UV-blocking properties was obtained by using

Ac-PEEK and Ac-PEEK was synthesized by reacting

2-hydroxyl ethyl methacrylate (HEMA) and molecular

weight controlled isocyanate terminated PEEK (Mn = 4500).

Obtained lenses tested according to ISO 11979-5 and very

encouraging results were obtained.

2 Materials and methods

2.1 Materials

Polyetherpolyol (propylene oxide polyhydric alcohol,

Vladimir Chemical Plant) was dried under vacuum before

use. Its hydroxyl content was determined to be 1, 65 mg

KOH/g [17]. 5-tert-butyl isophthalic acid (TBIPA,

Amoco), Bisphenol A (BisA, Dow Chemical), sodium

carbonate (Riedel-de Haen), methanol, toluene, hydroqui-

none, hexane, MgSO4 (Aldrich), 2-2-dimethoxy-2-pheny-

lacetophenone (IRGACURE 651, BASF), dimethyl

sulfoxide (DMAc, Riedel-de Haen), fluorobenzene (Mal-

linckrodt), AlCl3 (Merck AG), HCl (Merck AG), dichlo-

romethane (Merck AG), sodium sulphate (Merck AG),

KOH (Merck AG) and dibutyltin dilaurate (DBTDL,

Merck), Isobornyl methacrylate (IBoMA, Sartomer),

Phenoxy ethyl methacrylate (PEM, Polyscience), metha-

crylic acid (MAK, Merck) toluene diisocyanate (TDI, Ba-

yer) were used without further purification.

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2.2 Methods

2.2.1 Synthesis of monomers

2.2.1.1 Synthesis of 5-tert-butyl-isophthaloyl chloride (TB

IPC) This monomer was obtained by following the pre-

viously reported method with 98 % yield as shown in

Scheme 1 [18].

2.2.1.2 Synthesis of 5-tert-butyl-1, 3-bis-(4-fluorobenzoyl)

benzene (tBuFBB) This is in Scheme 2 [18].

2.3 Synthesis of oligomers

2.3.1 Synthesis of molecular weight controlled OH

terminated PEEK synthesis

Poly(arylene ether) (PEEK) was prepared by the conden-

sation of 5-tert-butyl-1,3 bis(4-hydroxybenzoyl) benzene

with bisarylhalides via nucleophilic aromatic substitution

reaction [19, 20] (Table 1). The amounts of bisphenol,

bisarylhalide, were controlled using Carothers equation and

they were charged into the 100 ml reaction flask with

K2CO3 equipped with a Dean Stark trap, a condenser, a

thermometer, and a magnetic stirrer and N2 inlet. Reactions

were carried out in DMAc at 140 �C for 8 h and toluene

was used as the azeotropic agent. The reaction temperature

was maintained at 170 �C for further 5 h. After removal of

toluene, the reaction mixture was allowed to cool to room

temperature; the viscosity of the mixture was reduced with

additional DMAc, and then filtered to remove the inorganic

salts. Polymer solution was precipitated from methanol/

water mixture. Light colored polymer was washed with

water and dried at 105 �C for 12 h under vacuum.

2.3.1.1 Synthesis of isocyanate terminated PEEK Isocy-

anate terminated PEEK (Ac-PEEK) was prepared from

molecular weight controlled OH terminated PEEK and TDI

as shown in Scheme 3I.

2.3.2 Prepolymer (oligourethane methacrylate, OUMA)

synthesis

Synthesis of the oligourethane methacrylate (OUMA) was

synthesized by using HEMA and isocyanate terminated

PEEK as shown in Scheme 3II. Poliol (20.00 g, OH num-

ber = 54, 4 mg KOH/g) was charged into flame-dried three-

necked 250-ml round-bottom flask equipped with a nitrogen

inlet and a dropping funnel. DBTDL (0.08 % by weight) was

added into the reaction flask as a catalyst and the flask were

stirred by a mechanical stirrer. The reaction temperature was

kept between 30 and 40 �C with a temperature-controlled

water bath for 15 min. TDI (3, 41 g, 0.0196 mol) was added

dropwise to the reaction mixture over a period of 1 h. The

reaction temperature was increased to 50 �C for 2 h. Then,

2.6 g HEMA (0.0199 mol) was added to the reaction med-

ium at 50 �C and the reaction was completed after 2 h.

Completion of the reaction was confirmed with the disap-

pearance of the characteristic –NCO peak at 2,275 cm-1 in

the Fourier transform infrared spectroscopy (FTIR) spec-

trum and also free % TDI analysis.

2.4 Preparation of the UV-curable IOLs

for characterization

UV-curable acrylated urethane recipes were prepared by

mixing OUMA and Ac-PEEK oligomers with IBoMA,

PEM as the reactive diluents and the photoinitiator (IR-

GACURE 651) homogeneously. The amount of the acrylic

monomer was varied from 10 to 40 wt%, the amount of the

Ac-PEEK was ranged from 0.4 to 1.5 wt% and the

photoinitiator (IRGACURE 651) concentration was kept

constant at 0.019 m/L on the basis of the final formulation

(Table 2). Lenses were prepared by pouring the viscous

liquid formulations onto a quartz mould. Finally, the

mixture was irradiated for 210 s under high pressure UV

lamp (OSRAM-300W). The adequate exposure time for

curing was previously determined by following the disap-

pearance of the unsaturated methacrylate bands and gel

contents of the films obtained by extracted samples.Scheme 1 Synthesis of TBIPC

Scheme 2 Synthesis of

tBuFBB

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2.5 Characterizations

Proton nuclear magnetic resonance (1H NMR) spectra

were taken in DMSO-d6 using TMS as internal reference

and were recorded by a Bruker NMR Spectrometer

(500 MHz). FTIR spectra were taken on a Perkin Elmer

Spectrum One FTIR Spectrometer. Differential scanning

calorimetry (DSC) analyses were performed at a heating

rate of 10 �C/min under nitrogen atmosphere using Perkin

Elmer Jade DSC. Reported values were obtained from a

second heating after a quick cooling of the first run.

Thermogravimetric data were obtained between 30 and

900 �C, under nitrogen, with a heating rate of 10 �C/min

using a Thermogravimetric Analyzer Perkin Elmer Pyris 1.

For elemental analysis, Thermo Finnigan Flash EA 1112

Series (Strada Rivoltana 20090 Rodano) was used. Mass

spectrophotometer (MS) studies were performed at 70 eV

with Fision VG ZabSpec gas chromatography (GC–MS).

The UV transmission spectra of the samples were obtained

by using Scinco NEOSYS-2000 UV/Vis spectrophotome-

ter. Morphologies of the lenses were studied under a

scanning electron microscope (JEOL 6335F; SEM). For all

the mentioned characterizations at least two samples were

used.

Contact angle (CA) measurements were performed

using saline solution (9 g/l sodium chloride) with Kruss

DSA 100 Model Contact Angle equipment. Biological

safety of the samples named as extractables and hydrolytic

stability tests were evaluated according to ISO 11979-5

[21], UV-transmittance according to ISO 11979-2. For this

characterization 3–5 lenses were used.

3 Results and discussion

3.1 Molecular weight controlled PEEK (OH-PEEK)

and acyrlic terminated PEEK (Ac-PEEK)

The reaction scheme of the molecular weight controlled

isocyanate terminated PEEK is shown in Table 2 and

characterization results are given below. Number average

molecular weight of the NCO-terminated PEEK was aimed

to be 5,000 g/mol. But obtained molecular weight was

determined to be as 4,300 g/mol. For this characterization

two replicates were used.

Overlayed FTIR spectrums of pristine OH-terminated

PEEK and Ac-PEEK are given in Fig. 1. The absorption

peaks at 3,065 cm-1 is aromatic C–H stretching, 2,962 cm-1

is aliphatic C–H stretching, 1,744 and 1,797 cm-1 is C=O

stretching, 1,045 cm-1 C–O–C stretching and 1,366 cm-1

shows C–H propane bending.

Thermal gravimetric analyzer (TGA) termograms of the

pristine OH-terminated PEEK and Ac-PEEK are given inTa

ble

1C

hem

ical

stru

ctu

reo

fth

eP

EE

Ko

lig

om

er

Co

de

Bis

ph

eno

lD

ihal

og

ene

Rep

eati

ng

un

it

PE

EK

OH

HO

HQ

CC

CH

3CH

3H

3C

OO

FF

TB

FB

B

CC

CH

3CH

3H

3C

OO

OO

OH n

HO

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Fig. 2 and Table 3. The first weight loss that occurred

between 150 and 300 �C can be attributed to the decom-

position of acrylic groups in Ac-PEEK. Introducing acrylic

functionality decreased first decomposition temperature of

the prepolymer. The second weight loss occurred over the

temperature range between 600 and 900 �C could be

ascribed to the decomposition of PEEK molecules. The

results indicate that the thermal stabilities of these Ac-

PEEK samples are sufficiently high to meet the require-

ments of optical materials.

Figure 3 shows the DSC thermograms of the pristine

OH-terminated PEEK and Ac- PEEK. DSC results showed

that the glass transition temperature (Tg) of pure pristine

OH-terminated PEEK was 157.7 �C and acrylic terminated

PEEK was 150 �C. Introducing acrylic functionality

decreased Tg of the polymer.

3.2 Synthesis of OUMA

FTIR spectrum of the OUMA is given in Fig. 4.

a) Isocyanate (–N=C=O) asymmetric stretching peak

appeared at 2,270 cm-1 disappeared at the end of the

reaction.

b) Stretching vibration band of characteristic –NH band

appeared at 3,337 cm-1.

c) Carbonyl (C=O) (Amide I band), stretching vibration

band at 1,720 cm-1 and carbonyl (C=O) stretching

vibration band for methacrylate were appeared at the

same region.

d) –NH deformation and –CON stretching vibration

band (Amide II band) appeared at 1,539 cm-1

Isocyanate terminated PEEK oligomer

(I)

(II)

Scheme 3 I Synthesis of isocyanate terminated PEEK, II synthesis of OUMA

Table 2 UV-curable formulations

Materials PEEK0 PEEK04 PEEK075 PEEK15

OUMA 46.6 46.6 46.6 46.6

PEM 22.4 22.0 22.0 20.9

IBoMA 29.8 29.8 29.8 29.8

AC-PEEK (Mw) – 0.4 0.75 1.5

MAK 1.1 1.1 1.1 1.1

IRGACURE 651 (m/l) 0.019 0.019 0.019 0.019

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show-CNH bands which is the indication of the

occurrence of the urethane reaction and disappearance

of the isocyanate groups.

a-b Unsaturated esters (–C=C–COO) of methacrylate

groups characterized as:

a) Appearance of –CH2 bending and stretching at 950

and 820 cm-1 respectively.

b) Appearance of –C=C vibration at 1,640 cm-1.

c) Appearance of less characteristic –CH2 and –CH

stretching vibration at 3,090–3,000 cm-1 are the

indications of the methacrylate groups.

1H NMR spectrum of the OUMA is given in Fig. 5. 1H

NMR (200 MHz, CDCl3) d (ppm): 1.6 (6H, s, CH3), 3.16 (16

H, m, (CH2)4), 4.07 (4H, t, CH2 -NH), 4.22 (4H, t, CH2-O),

5.2 (2H, s, NH), 5.6 and 6 (4H, =CH2). 1H NMR spectra of

urethane ether were consistent with its chemical structure.

3.3 UV-cured lens characterizations

3.3.1 FTIR characterization

Overlayed FTIR spectrum of the UV-cured lens with Ac-

PEEK and without acrylated Ac-PEEK is given in Fig. 6.

4000.0 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 450.0

cm-1

%T

OH-PEEK

Acrylic-PEEK

Fig. 1 FTIR spectrums of the

molecular weight controlled OH

and Ac-PEEKs

Fig. 2 TGA termograms of the

molecular weight controlled OH

and Ac-PEEKs

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Even in Ac-PEEK concentrations of 1.5 wt%, some dif-

ferences were observed in the spectrum. The absorption

peaks of aromatic C–H stretching at 3,065 cm-1 was

observed at 2,955 cm-1 and aliphatic C–H stretching

2,962 cm-1 was observed at 2,874 cm-1. Appearence of

the peaks at 1,477, 1,390, 968 and 842 cm-1 also another

indications of Ac-PEEK in the structure

3.3.2 Thermal characterizations by TGA and DSC studies

TGA curves of UV-cured lenses without Ac-PEEK

(PEEK0) and with Ac-PEEK (PEEK15) are given in Fig. 7.

Lenses were heated up to 900 �C at heating rate of 10 �C

min-1 under N2. 1.5 wt% addition of Ac-PEEK has not an

important effect on lens but the results indicate that the

thermal stabilities of the produced lenses are sufficiently

high to meet the requirements of optical materials.

Figure 8 shows the DSC of the lenses without Ac-PEEK

(PEEK0) and with Ac-PEEK (PEEK15). It showed that the

glass transition temperature (Tg) of PEEK0 was -21 �C

and PEEK15 was -25 �C. Introducing 1.5 wt% PEEK

decreased the Tg of the lens due to higher molecular weight

of the Ac-PEEK.

It is difficult to suggest a strong relation between the

content of Ac-PEEK content and the thermal properties for

the UV-cured formulations.

3.3.3 UV-transmittance

UV/Vis spectra of freshly prepared lenses and hydrolyti-

cally tested as well as protected from exposure to light be

recorded according to ISO 11979-2 using a calibrated

Scinco NEOSYS-2000 UV/Vis spectrophotometer in the

range of 300–1,100 nm [19]. Finally, the record spectra of

the differently treated optical materials were compared to

each other to identify potential influences of exposure to

light upon the transmittance of the lenses. The obtained

results are given in Figs. 9 and 10. Increasing Ac-PEEK

content and applying hydrolytic stability test to the lenses

increased blocking ability of the lenses produced (Fig. 9).

3.3.4 Extraction with saline solution and hexane

One of the important property for IOL’s is the extraction of

the lenses in different mediums. UV-cured lenses were

extracted over a period of 72 h at 37 �C with saline solu-

tion (9 g/l sodium chloride) and n-hexane according to ISO

11979-5 [13], then saline solution extracts and n-hexane

extracts of the investigated samples were detected by using

GC/MS chromatography.

Based upon the results obtained with extractables test

according to ISO 11979-5 it can be concluded that:

• The transmission spectra of the optical material

extracted with saline solution and n-hexane showed

no differences as compared to the spectrum of the

Table 3 TGA results of OH-PEEK and Acr-PEEK

Sample Tg (�C) Thermooxidative stability values (�C)

5 % Weight

loss

50 %

Weight loss

% wt

resudue

OH-PEEK 157.7 500 610 46

Acr-PEEK 150 150 600 43

Fig. 3 DSC termograms of the

molecular weight controlled OH

and Ac-PEEKs

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corresponding negative control optical materials

(untreated optical material).

• The GC/MS sensitivity of was \0.5 ppm and no

product-related peaks were detected in the GC/MS

fingerprint chromatogram of the tested saline solution

extracts and the n-hexane extracts of the investigated

optical materials as compared to the chromatograms of

the negative control (untreated saline solution/pure

n-hexane).

3.3.5 Hydrolytic stability

Hydrolytic stability is another important characterization

method for the IOL production. The test was performed

according to the ISO 11979-5 in saline solution. Test per-

formed for 20 days at 100 �C. UV-transmittances of the

lenses are given in Fig. 10 and saline solution extracts of

the investigated samples were detected by using GC/MS

chromatography. The GC/MS sensitivity was \0.5 ppm

4000.0 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 450.01.3

5

10

15

20

25

30

35

40

45

50

55

60

65

70

75

80

85

89.4

cm-1

%T

Fig. 4 FTIR spectrum of the

OUMA

Fig. 5 NMR spectrum of the

OUMA

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and no product-related peaks were detected in the saline

solution extracts of the investigated optical materials as

compared to the chromatograms of the negative control

(untreated saline solution). Photograph of the tested sam-

ples also are given in Fig. 11a. Introducing lenses to the

hydrolytic stability test increased the blocking ability of the

lenses to the low UV light and also color of lenses changed

from white to yellow same as the original lenses in the eye.

Photograph of the control sample is given in Fig. 11b.

The following results for hydrolytic stability were

obtained for the different investigations:

• The hydrolysis of the optical materials caused insig-

nificant mass changes.

• No extractable organic substances were found in the

several analyzed hydrolysates.

• No relevant differences were observed in the transmis-

sion spectrum of the optical material after the hydro-

lytic treatments.

• The SEM investigation exhibited no ultra structural

modifications of the treated optical material in com-

parison to the untreated reference lens.

• Color of the lenses with Ac-PEEK changed from white

to yellow after hydrolytic stability test like our natural

lenses changed by the age. The colour of control lenses

did not changed.

Based upon these results and the testing procedures

requested in ISO 11979-5 it can be concluded that the

hydrolytic stability of the investigated optical materials

could be confirmed.

Fig. 6 FTIR spectrum of the lenses without Ac-PEEK (PEEK0) and with Ac-PEEK (PEEK15)

Fig. 7 TGA termograms of

the lenses with and without

Ac-PEEK

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Fig. 8 DSC termograms of the lenses with and without Ac-PEEK

Fig. 9 UV-transmittance of

the lenses with and without

Ac-PEEK

Fig. 10 UV-transmittance of

the Ac-PEEK based lenses

before and after hydrolytic

stability test

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3.3.6 Photostability

Photostability is another important characterization method

for the IOL production. The test was performed according

to the ISO 11979-5 in saline solution. The aim of this study

was to investigate the influence of ultraviolet/visible (UV/

Vis) light exposure on a foldable IOL.

Fifteen IOLs, stored in a saline solution, were exposed

to UV radiation as described in ISO 11979-5, Annex B,

using a radiation source (Xenon arc lamp) in order to

simulate an in vivo exposure time of 20 years.

After the exposure to light, UV/Vis spectra of IOLs

exposed to light as well as protected from exposure to light,

were recorded according to ISO 11979-2 using a calibrated

UV/Vis spectrophotometer in the range of 300–1100 nm.

Finally, the recorded spectra of the differently treated IOLs

were compared to each other in order to identify potential

influences of exposure to light upon the transmittance of

the lenses.

Furthermore, the used saline solutions were investigated

for potential leachable substances (organic origin) which

may have been released from the lens material into the

surrounding saline solutions during exposure to light. The

analyses of the saline solutions were carried out using GC

coupled with a mass selective detector.

UV-transmittances of the lenses and also control lenses

before and after test were the same as given in Fig. 9 and

saline solution extracts of the investigated samples were

detected by using GC/MS chromatography. The GC/MS

sensitivity was \0.5 ppm and no product-related peaks

were detected in the saline solution extracts of the AC-

PEEK based optical materials compared to the chromato-

grams of the negative control (untreated saline solution).

Photographes of the tested samples are given in Fig. 12a.

Introducing lenses to the photostability test did not change

the colour of the lens. Photograph of the control sample is

given in Fig. 12b.

The investigation of the photostability of the investi-

gated IOLs from Ac-PEEK gave the following results:

1. Appearance The IOLs exposed to light showed no

discoloration and were transparent, the negative con-

trol lenses (IOLs protected from exposure to light)

remained colorless and transparent.

2. Transmission spectra The transmission spectra of the

IOLs exposed to light showed same light transmission

over the investigated wavelength range as compared to

the spectra of the negative controls (IOLs protected

from exposure to light). The UV light adsorption in the

exposed IOLs indicated that the IOL material was not

damaged due to the light exposure.

Fig. 11 a Photographs of the lenses after hydrolytic stability test for

20 days at 100 �C. b Photographs of the control lenses after

hydrolytic stability test for 20 days at 100 �C

Fig. 12 a Photographs of the Ac-PEEK based lens after photostability test. b Photographs of the control lens after after photostability test

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3. Organic leachables In the saline solution of the IOLs

exposed to light, no leachable organic substances could

be identified, which were not present in the saline

solution containing IOLs which were not exposed to

light.

Based upon these findings it can be concluded that the

exposure to light had no negative effect on the transmission

properties of the lenses, no differences in the UV/Vis

transmission were observed between the spectra of the

IOLs exposed to light as compared to the spectra of the

corresponding negative control IOLs. Furthermore, the

chemical stability of the IOLs was not negatively influ-

enced by the exposure to light, compared to the saline

solutions of the negative control IOLs.

Therefore, it is concluded that the investigated lenses

were stable against ultraviolet/visible light exposure as

described in ISO 11979-5.

Table 4 Contact angle results the lenses

Contact angle results (in saline solution, �)

PEEK0 PEEK04 PEEK075 PEEK15

81.0 81. 6 83.9 84.0

Ac-PEEK0

Ac-PEEK15

Ac-PEEK15 After Hydolytic stability

BA

C D

E F

Fig. 13 SEM results of the

lenses. a PEEK0(X12),

b PEEK15(X5000),

c PEEK15(X12), d (PEEK15

(X5000) e PEEK15(X12) after

hydrolytic stability test,

f PEEK15(X2500) after

hydrolytic stability test

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3.3.7 Contact angle

Contact angle is a measure of surface properties of mate-

rials and change in contact angle means change in their

surface chemistry. PEEK is intrinsically hydrophobic;

contact angle results of the all produced lenses are obtained

to be around 80 �C as given in Table 4. Cross linking is an

effective method to change morphology and surface

properties of the polymeric materials. We tested effect of

Ac-PEEK ratio on the surface properties of the lenses in

cross linked structure. All the lenses tested are homoge-

neous; there is no difference between the surface and bulky

matrix of the lenses in terms of chemical composition.

Therefore, based on this change, it is possible to say that

the addition of the Ac-PEEK is effective.

3.3.8 SEM analysis

A series of lenses were prepared by using UV-curing sys-

tem from 0.4 to 1.5 wt% Ac-PEEK contents. Figure 13a, b

(PEEK0), Fig. 13c, d (PEEK15) and Fig. 13 e, f (PEEK15/

After hydrolytic stability test) show surface images of the

lenses. Homogeneous lenses were obtained and the addi-

tion of Ac-PEEK didn’t change the morphology. White

regions in the SEM images as shown with white arrow

were due to the presence of NaCl in saline solution.

4 Conclusions

This study demonstrates how an UV curable IOL lens was

obtained by using the acrylic terminated molecular weight

controlled Ac-PEEK with amounts ranging from 0.4 to

1.5 wt% in UV-curable formulations being sufficient to obtain

short wave UV-light blocking properties. Ac-PEEKs based

lenses have promising results by looking at the UV-trans-

mittance, hydrolytic stability, extraction, photostability, con-

tact angle, SEM, and thermal characterization results. These

lenses showed that Ac-PEEK has UV light blocking effect for

short wave even they are used in concentrations of as low as

1.5 wt%. Contact angle of the lenses showed that all lenses are

hydrophobic and SEM results revealed that lenses are mor-

phologically homogeneous. Ageing test results also reveals

that these lenses change colour to yellow without extractable

matter and also may help blue light filtration as well.

As a result, in the very near future it may be possible to

have oligomers with wide range UV-blocking properties in

the main oligomer structure without using extra UV-blocker.

Acknowledgments This work is financially supported by Anadolu

Tıp. A. S. The authors thank Nevin Bekir, Zekayi Korlu and Mustafa

Candemir for their valuable technical assistance in laboratory and Dr.

Erkan ERTURK for NMR operation. Operation of SEM was possible

with help of Cem Berk.

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