공학석사 학위논문

실리카 섬유를 사용한 폴리라틱 에시드의 기계적

물성과 생체 특성 향상

Effects of silica fibers on the mechanical

and biological properties of Poly (lactic

acid)

2018년 2월

서울대학교 대학원

재료공학부

안 석 우

Effects of silica fibers on the mechanical

and biological properties of Poly (lactic

acid)

지도교수 김현이

이 논문을 공학석사 학위논문으로 제출함

2018년 2월

서울대학교 대학원

재료공학부

안 석 우

안 석 우의 석사 학위논문을 인준함

2018년 2월

위 원 장 안 철 희(인)

부위원장 김 현 이(인)

위 원 선 정 윤(인)

i

Abstract

Effects of silica fibers on the mechanical

and biological properties of Poly (lactic

acid)

Seok Woo Ahn

Department of Materials Science and Engineering

Seoul National University

Resorbable materials for medical implants are a good alternative over

conventional metal implants, because they degrade in the body and

decompose. A secondary operation for removal of the implants after tissue

regeneration is unnecessary in this case. Poly(lactic acid) (PLA), is a good

candidate for resorbable implant materials due to its good biological

properties. However, despites numerous advantages of PLA, PLA’s low

mechanical strength and Young’s modulus compared to metal implants

materials restrict its application in various biomedical area. Consequently,

there were continuous interests in overcoming the insufficient mechanical

properties of PLA without a drastic loss in its general advantages such as

ii

biodegradability and biocompatibility. Among various reinforcing methods,

fiber reinforcing method is advantageous since the orientation of the fibers

can be specified according to different applications. The mechanical strength

of such composites can be highly increased when fibers are aligned parallel to

the force that is being applied. Silica fiber is a good candidate for reinforcing

fibers because of its degradability, high strength and modulus and good

biocompatibility. Surface modification of fibers is an effective method for

enhancing the reinforcing effects of the fibers. There are two types of surface

modifications which were widely used; the use of silane coupling agents and

surface-initiated polymerization. With these methods, adhesion between fibers

and polymer matrix could be improved. As a results, mechanical properties of

composites will be further enhanced.

In this study, we introduced solvent casting, extrusion and injection

molding methods for the fabrication methods of PLA/silica fibers composites.

Then inspired by surface modification, for further improvement in mechanical

properties of PLA/silica fibers composites, two types of surface treatment

were performed on silica fibers’ surfaces; silane treatment and LA-grafting.

With the addition of silica fibers in PLA matrix, elastic modulus significantly

increased. Moreover, after surface treatment, elastic modulus further

increased compared to PLA/untreated silica fibers composites and also tensile

strength increased. Cell viability of the specimens was evaluated with

MC3T3-E1 cells. Cell viability increased with the addition of silica fibers.

iii

The cell viability of PLA/surface treated silica fibers composites also

maintained a value comparable to that of the untreated fiber composites. This

study proved that silica fibers can effectively increase the mechanical

properties and cell viability of PLA. Also, this study demonstrated that silane

treatment and LA-grafting were effective methods for further enhancement of

mechanical properties of PLA while cell viability was maintained.

Keywords: Poly(Lactic acid) (PLA), Composites, Fiber reinforced polymer,

Solvent casting, Extrusion, Injection molding, Mechanical properties, Cell

viabilities

Student number: 2016-20798

iv

Contents

Abstract…………………………………………………………..…ⅰ

Contents…………………………………………………………….ⅳ

List of Figures and Tables…………………………………………ⅵ

Chapter 1. Introduction

Chapter 2. Experimental procedure

2.1. Materials……………………………………………………….7

2.2. Fabrication of PLA/silica fiber composites …………...…7

2.2.1. Surface treatment of silica fibers………………………7

2.2.2. Solvent casting…………………………………………8

2.2.3. Extrusion and injection molding process …………….9

2.3. Surface Characterization of composites …………………10

2.4. Mechanical testing …………………………………………11

2.5. In-vitro biological analysis …………………………………11

Chapter 3. Results and discussions

3.1. Surface characterization of fibers ………………………….16

3.2. Surface observation of composites ………………………….16

3.3. Mechanical properties ……………………………………….17

3.4. In-vitro biological analysis ………………………………….19

v

Chapter 4. Conclusion

Reference……..……………………………………………………….33

Abstract (Korean)…………………………………………………...38

vi

List of figures and tables

Table 1. Weight percentage of each composition of silica fibers.

Figure 1. Scheme of surface treatment of silica fibers, (A) silane treatment, (B) LA-grafting.

Figure 2. The high resolution of N 1s peaks of ESCA spectra. (A) silane treated silica fibers (B) LA-grafted silica fibers.

Figure 3. The high resolution of C 1s peaks of ESCA spectra. (A) silane treated silica fibers, (B) LA-grafted silica fibers.

Figure 4. FE-SEM images of PLA/silica fibers composites surfaces and EDS patterns of Si element dispersed in PLA matrix. (A) Pure PLA, (B) 10wt%, (C) 20wt%, (D) 30wt%, (E) APTES, (F) LA.

Figure 5. Contact angles depend on (A) fiber contents and (B) surface treatment

Figure 6. Mechanical properties of PLA/silica fibers composites depend on silica fibers contents (A) Elastic modulus, (B) Tensile strength.

Figure 7. Mechanical properties of PLA/silica fibers composites depend on surface treatment. (A) Elastic modulus, (B) Tensile strength.

Figure 8. FE-SEM images of cross sectional area of PLA/silica fibers composites after tensile testing (A) Pure PLA, (B) Untreated, (C) APTES, (D) LA.

Figure 9. CLSM images of MC3T3-E1 cells on (A) Pure PLA, (B) 10wt%, (C) 20wt%, (D) 30wt%

Figure 10. CLSM images of MC3T3-E1 cells on (A) Pure PLA, (B) Untreated, (C) APTES, (D) LA.

Figure 11. The MC3T3-E1 cell viability evaluated by MTS assay with PLA/silica fibers composites after 5 days culturing depending on (A) silica fibers contents, (B) surface treatment.

1

Chapter 1.

Introduction

2

Resorbable materials for medical implants are a good alternative over

conventional metal implants, because they degrade in the body and

decompose. A second operation for removal of the implants after regeneration

of tissue is unnecessary in this case. Poly(L-lactide) (PLA), a typical linear

aliphatic thermoplastic polyester, has been viewed as the most popular

commercial bio-absorbable polymer material because it is biodegradable,

biocompatible, and nontoxic to the human body [1-4]. PLA has been approved

by US Food and drug and widely used in clinical extensive range of

applications, especially for bone-fixation devices used in orthopedics and oral

surgery [5, 6]. Despites numerous advantage of PLA, PLA is still not

satisfactory for processing and application. Especially, its low mechanical

strength and Young’s modulus restrict their application in various biomedical

area [7, 8]. Consequently, there is a continuous interest in overcoming the

insufficient mechanical properties of PLA without a drastic loss in its general

advantages such as biodegradability and biocompatibility [9, 10].

Fibre-reinforced plastics are composite plastics that specifically use

fibre materials to mechanically enhance the strength and elasticity of the

plastics. Comparing to composites which use particles Fibre-reinforced

plastics allow the alignment of the fibres to suit specific design [11, 12]. By

specifying the orientation of fibres, Mechanical strength of composites can be

highly increased when fibres are aligned parallel to the force being applied

3

[12, 13]. Glass fibre-reinforced plastic composites was widely used from

1940s, especially with unsaturated polyesters. Fibre-reinforced composites are

used in diverse fields such as electronic devices and biomedical implant

materials [14]. Especially in the biomedical field, such strengthening method

also has been tried by preparing fiber reinforced composites using several

types of biodegradable fibers incorporated into organic polymer matrix [15,

16].

Silica fiber, one of degradable fibers with high strength and modulus

with good biocompatibility, can be used as a biodegradable reinforcing

material for PLA [17]. Silica has also been widely used as a nanofiller for the

preparation of polymer/silica nanocomposites. It possesses advantages of high

strength and modulus, and good biocompatibility. Since both components are

biodegradable, the composite is also expected to be biodegradable. However,

the main drawback of silica fibers is their hydrophilic nature which result in

low interfacial bonds with the hydrophobic PLA matrix during composite

fabrications. The interphase between the polymer matrix and the nanoparticles

plays a significant role on the mechanical properties of the resulting

composite. Classical composite theory indicates that improved bonding

strength between the polymer matrix and fibers leads to improved mechanical

properties.

Surface modification is a very effective method for manipulating the

4

surface characteristics. By surface modification, hydrophilic nature of silica

fibers can be reduced for improving the bonding between the hydrophobic

polymer matrix and hydrophilic silica fibers. One approach of surface

modification is the use of a coupling agent. Silane coupling agents are the

most widely used type of coupling agents [18-21]. Silane coupling agents

generally have hydrolysable ends to react with the hydroxyl groups on the

surface of the materials. Thus, the adhesion between hydrophilic material and

hydrophobic polymer matrix was enhanced. For example, (γ-aminopropyl)-

triethoxysilane (APTES) is used to produce HPLC stationary phases as well

as to improve the adhesion between glass and polymers [22, 23].

Another approach is surface-initiated polymerization which is also

called ‘‘grafted from’’ method. It is a technique to form a layer of polymer on

the target surface. Surface-initiated polymerization has been frequently used

for polymerization of active compounds on the material surfaces [24-26].

Jiyeon Choi and Seong Bae cho et al. conducted L-lactide grafting on the

metal surface by applying direct surface-initiated ring-opening polymerization

[27]. The polymerization of L-lactide was propagated by the formation of

initiator, in the presence of proper catalyst and hydroxyl-terminated molecules.

This L-lactide layer significantly reinforced the interfacial adhesion between

hydrophobic PLGA matrix and hydrophilic metal substrate.

In this study, PLA/silica fibers composites were fabricated by using

solvent casting methods, extrusion and injection molding to overcome

5

limitation of PLAs mechanical properties. Moreover, inspired by usage

coupling agent and surface-initiated polymerization, surfaces of silica fibers

were both silane treated and L-lactide grafted by poly-condensation method

for further improvement of the mechanical strength. Fiber characterization,

surface morphology, hydrophilicity, mechanical properties, in vitro cell

viability were Investigated in this study.

6

Chapter 2.

Experimental procedure

7

2.1 Materials

Poly(lactic acid) and silica fibers were purchased from Pureco, Inc.

(Seoul, Korea) and CYC-composites (Chengdu, China), respectively. Average

length and diameter of silica fiber used in this study were approximately 3

mm and 9 μm, respectively. Poly ethylene glycol 200 (PEG) and

dichloromethane (DCM) were purchased from Sigma-Aldrich Korea. PLA

and silica fibers were washed with distilled water and vacuum-dried at 45℃

for 24h prior to use. For surface treatment, 3-aminopropyltriethoxysilane

(3-APTES), Tin(II) 2-ethylhexanoate, (3S)-cis-3,6-Dimethyl-1,4-

dioxane-2,5-dione, and toluene which were used for surface treatment were

also purchased from Sigma-Aldrich Korea.

2.2 Fabrication of PLA/silica fiber composites

2.2.1. Surface treatment of silica fiber: silane treatment and

LA-grafting

Before the chemical surface treatment, the untreated fibers were

rinsed with distilled water at the room temperature to remove impurities of

fibers. Then washed fibers were dried in the oven at 45℃ for 24h.

8

Silane treatment was as follows: 3-aminopropyltriethoxysilane

(3-APTES) was diluted in an aqueous solution of ethanol. The ratio of

3-APTES, distilled water and ethanol were 5v%, 45v%, 50v%, respectively.

Silica fibers were immersed in the solution for 4h at room temperature. After

immersion for 4h, fibers were fully washed with ethanol then dried under

vacuum for 24h at 45℃ to evaporate the remaining ethanol.

Silane treatment was followed by a LA-grafting as follows: Prior to

LA-grafting, three times of recrystallization process were performed with

(3S)-cis-3,6-Dimethyl-1,4-dioxane-2,5-dione for purifying L-lactide. Tin(II)

2-ethylhexanoate which was used as catalyst was dissolved in 200mL of

toluene under nitrogen atmosphere. Then, 5g of purified L-lactide and 10g of

silane treated fibers were added into catalyst mixed toluene. The mixture was

stirred at 80℃ for 24h. After reaction, the fibers were fully washed with

methanol and dried under vacuum for 48h at 45℃.

Silane treated and LA grafted fibers were characterized using X-ray

photoelectron spectroscopy (XPS) (AXIS SUPRA, Kratos, U.K).

2.2.2. Solvent casting

The PLA was firstly dissolved in dichloromethane at a ratio of 10

9

wt%. After PLA was fully melted in dichloromethane, PEG which was used

as surfactant was added to PLA solution at a ratio of 1.5ml: 180ml. Then,

silica fibers were mixed with PLA solution at a ratio of 10 wt%, 20 wt%, 30

wt%, respectively. Surface treated silica fibers also were mixed with PLA

solution at a ratio of 20 wt%. Mixtures of silica fibers and PLA solution were

stirred for 24h. After stirring, the mixtures were poured on glass chalet at

room temperature to evaporate dichloromethane for 24h. Fully dried mixtures

were washed with distilled water and dried in vacuum oven for 24h at 65℃

2.2.3. Extrusion and injection molding process

Solvent casted composites were crushed with mechanical mixer for

extrusion process. Then, washed with distilled water. In order to remove

absorbed moisture and to prevent void formation, washed PLA/ silica fibers

composites were dried at 65℃ under vacuum for 24h before processing. A

uniform temperature of 160℃ was maintained during extrusion process.

After extrusion process, composites were also crushed with mechanical mixer.

Then, composites were washed with distilled water again and dried in vacuum

oven for 24h at 65℃ prior to injection molding process.

With extruded and fully dried composites, injection molding was

10

carried out on the injection molding machine with four temperature zones.

The nozzle temperature was 100℃ and towards to hopper, two zones

temperatures were 140℃ and 175℃, respectively. Lastly, The hopper

temperature was set at 160℃. Samples were molded for tensile tests as dog

bone shape.

2.3 Surface Characterization of composites.

The morphology of surface and cross section of the composites was

observed by field-emission scanning electron microscope (FE-SEM,

JSM-6300F, JEOL, Tokyo, Japan). A platinum coating with 300 second with

7mA was coated on composites surfaces. Accelerating voltage of 20kV was

used to collect FE-SEM images for the composite specimens. The atomic

composition of each sample was investigated by energy dispersive

spectrometry placed in SEM.

The hydrophilicity was determined by water contact angle

measurements (goniometer, Phoenix 300) in air, which were carried out using

a sessile drop method-based measuring system (n = 3).

11

2.4 Mechanical testing

A mechanical testing machine (5582, Instron Corp., Danvers, MA)

was used to measure the tensile properties. The strain was measured using a

model extensometer. Crosshead speed of 1mm/min were used for testing pure

PLA and composites. All results presented are the average values of three

samples.

2.5 in-vitro biological analysis

The in vitro biocompatibility of the samples was evaluated with MC3T3-E1

cells (ATCC, CRL-2593; Rockville, MD). All the samples were sterilized by

ethanol and dried. Then, fully dried samples were treated with UV light. All

the samples were immersed in ethanol for 3h and dried in vacuum at 60℃ for

1 day. Then, the samples were treated with UV light for 1hr prior to in vitro

biological analysis. The pre-incubated cells were seeded onto the samples at a

density of 3×104 cells/ml for the cell attachment test and 3×104 cells/ml for

cell proliferation test. For cell culturing the alpha minimum essential medium

(a-MEM, LM008-53, WELGENE Inc., Korea), supplemented with 10% fatal

bovine serum (FBS, Gibco Inc., YS) and 1% Pen Strep, was used as the

culturing medium, and the cells were incubated in a humidified incubator with

12

5% CO2 at 37℃

After 6h of incubation, the surface images of cell attachment on the each

sample were observe by a confocal microscope. Cell proliferation was

observed with 3 samples (n=3) by an MTS assay after 5 days of culturing.

Cultured cells reacted with 3-(4,5-dimethylthiazol-2-yl)-5-(3-carboxy-

methjoxyphenyl)-2-(4-sulfophenyl)-2H-tetrazolium (MTS, Promega, Madison,

WI, USA) for mitochondrial reduction.

13

Table 1. Weight percentage of each composition of silica fibers.

14

Figure 1. Scheme of surface treatment methods of silica fibers, (A)

silane treatment, (B) LA-grafting.

15

Chapter 3.

Results and Discussions

16

3.1 Surface characterization of fibers: silane treatment

and LA-grafting.

Figure 2. and Figure 3. show high resolution analysis of the bond

energy spectrum of N1s and C1s measured after both silane treatment and

LA-grafting. Since N signal was observed at both silane treated and

LA-grafted fibers, this is due to the presence of 3-APTES on silica fibers

surface. Then, in high resolution analysis of the bond energy spectrum of C1s,

the considerable difference in C-O bond and C=O peaks between silane

treated fibers and LA-grafted fibers was observed. After LA-grafting, C-O

and C=O signals were clearly shown compared to just silane treated silica

fibers. These signals came from C-O and C=O bonds which is existed in

L-lactide. This result is evident that the L-lactide was well grafted on silica

fibers’ surfaces after LA-grafting methods.

3.2. Surface observation of composites.

PLA/silica fiber composites with 0, 10, 20, 30 wt% were successfully

fabricated. And also composites with both silane treated and LA-grafted silica

fibers were fabricated with 20wt%. The SEM images of the surfaces in Figure

4. show that silica fibers are reasonably well distributed in the PLA matrix.

17

And also there are no apparent defects in the matrix on composites surface. As

fibers can be observed in SEM images, all composites produced by injection

molding had fibers that were aligned to a reasonable degree parallel to

injection molding direction. Fibers alignment was generated by shear force

which was applied during injection molding process. Alignment of fibers help

to further improve the mechanical properties of composites to align direction.

The hydrophilicity of the PLA/silica fibers composites was examined

by measuring the incident contact angle, as shown in Figure 5. (n=3). The

contact angle of the bare PLA substrate was about 90 degrees. With increasing

content of silica fibers in PLA matrix, the contact angle decreased steadily and

the 30wt% of PLA/silica fiber composites exhibited a value of about 60

degrees. Contact angle of composites with surface treated fibers decreased

slightly, there were no statistically significant differences with untreated one.

3.3 Mechanical properties

The tensile strength test was performed with three samples of each

composition to see reinforcing effects of silica fiber; 0wt%, 10wt%, 20wt%,

30wt%. The elastic modulus and tensile strength were determined by

analyzing the stress versus strain curve of each specimen. Figure 6. shows the

elastic modulus and tensile strength of the composites with different content

18

of silica fibers. The elastic modulus of the pure PLA is approximately 3.3GPa.

Compared to pure PLA, elastic modulus of the composites significantly

increased with the addition of silica fibers into PLA. The 30wt% PLA/silica

fiber composite had an average elastic modulus value of 5GPa, which is

approximately 1.5 times larger than that of the pure PLA. But in case of

tensile strength, it was hard to see reinforcing effects of silica fibers. There

was no statistically significant difference in tensile strength value between

pure PLA and composites.

Also tensile strength test with composites which fibers were surface

treated to observe surface treatment effects on mechanical strength of

composites. The elastic modulus and tensile strength also were determined by

analyzing the stress versus strain curve of each specimen. Figure 7. shows the

elastic modulus and tensile strength of the composites with different surface

treatment methods. Content of silica fibers was fixed with 20wt%. The elastic

modulus of the PLA is approximately 3.3GPa. Comparing to pure PLA,

elastic modulus of the composites significantly increased with both silane

treatment and LA-grafting methods. Elastic modulus of the composites which

fibers were silane treated is about 5.7GPa, which is higher value than 30wt%

of untreated silica fiber composites. Moreover, Elastic modulus further

increased to 7.5GPa with LA-grafting method, which is approximately 2.3

times larger than that of the pure PLA. Tensile strength was also slightly

19

increased.

Figure 8. shows the morphologies of the fractured cross-sectional

SEM images of composites following the tensile strength. In images of

Composites with untreated silica fibers, clear circular shape sites which fibers

were pulled out could be found. In contrast, composites with silane treated

and LA-grafted fibers, clear voids were hard to found compared to untreated

fiber composites. And many fibers with surface treatment were broken at the

fracture surface compared that untreated fibers were just pulled out. It

suggested that bonding strength between fibers and PLA matrix was enhanced

by surface treatment.

3.4 In vitro biological analysis

The initial biological responses of the samples were studied through

osteoblast attachment to the PLA/silica fibers composites. Cell attachment

images are shown in Figure 9. and Figure 10. The degree of attachment

increased with addition of silica fibers. Cells that were cultured on pure PLA

were characterized by needle-shaped and poor attachment to the surface.

However, with the PLA/silica fiber composites, cells were more securely

attached to the surfaces with filopodia extensions and flattening of the cells.

In Figure 10, cells were also spread out on the surface of composites with

20

surface treated fibers.

The cell proliferation data for samples cultured for 5 days is shown in

figure 11. After 5 days, the cell viability of composites had a significant

difference compared to pure PLA. The amount of cell proliferation for

composites increased with the addition of silica fibers. And also, the amount

of cell proliferation for composites with surface treated silica fibers was

appeared at high values similar with composites with untreated silica fibers.

In both cell attachment and proliferation test results showed that

biocompatibility increased with the addition of silica fibers and that no signs

of cytotoxicity are present. Cellular responses affected on the surface of

materials; surface roughness, component, charge and hydrophobicity. Silica is

well-known its biocompatible properties. Therefore, Silica fibers enhanced

osteo-conductivitiy of the PLA. These results suggest that the silica fibers are

promising reinforcing materials of PLA in the realm of biomedical

application.

21

Figure 2. The high resolution of N 1s peaks of ESCA spectra. (A)

silane treated silica fibers (B) LA-grafted silica fibers.

22

Figure 3. The high resolution of C 1s peaks of ESCA spectra. (A) silane

treated silica fibers, (B) LA-grafted silica fibers.

23

Figure 4. FE-SEM images of PLA/silica fibers composites surfaces and

EDS patterns of Si element dispersed in PLA matrix. (A) Pure PLA,

(B) 10wt%, (C) 20wt%, (D) 30wt%, (E) APTES, (F) LA.

24

Figure 5. Contact angles depend on (A) fiber contents and (B) surface

treatment.

25

Figure 6. Mechanical properties of PLA/silica fibers composites depend

on silica fibers contents (A) Elastic modulus, (B) Tensile strength.

26

Figure 7. Mechanical properties of PLA/silica fibers composites depend

on surface treatment. (A) Elastic modulus, (B) Tensile strength.

27

Figure 8. FE-SEM images of cross sectional area of PLA/silica fibers

composites after tensile testing (A) Pure PLA, (B) Untreated, (C)

APTES, (D) LA.

28

Figure 9. CLSM images of MC3T3-E1 cells on (A) Pure PLA, (B)

10wt%, (C) 20wt%, (D) 30wt%

29

Figure 10. CLSM images of MC3T3-E1 cells on (A) Pure PLA, (B)

Untreated, (C) APTES, (D) LA.

30

Figure 11. The MC3T3-E1 cell viability evaluated by MTS assay with

PLA/silica fibers composites after 5 days culturing depending on (A)

silica fibers contents, (B) surface treatment.

31

Chapter 4.

Conclusion

32

In our experiment, PLA/Silica fibers composites with 0, 10, 20,

30wt% were successfully produced with solvent casting, extrusion and

injection molding. Moreover, silica fibers were surface treated for further

enhancement of mechanical properties of PLA/silica fibers composites. In

XPS analysis, we could observe both silane treatment and LA-grafting were

well performed. Then composites which fibers were surface treated with

20wt% were also successfully fabricated. The elastic modulus of the

composites showed that the composite can be strengthened with the addition

of silica fibers. But comparing to elastic modulus, the tensile strength of the

composites cannot be enhanced by untreated silica fibers. With surface treated

silica fiber, the elastic modulus of the composites highly increased in both

silane treated and LA-grafted silica fibers composites. Especially, with

LA-grafting methods, elastic modulus increased approximately 2.3 times

larger than that of PLA. Tensile strength also slightly increased by surface

treatment of silica fibers. Moreover, in vitro biological properties also

enhanced with the addition silica fibers because of silica fibers’ better

biocompatibility compared to PLA. Then, cell viability did not decrease by

surface treatment of fibers. Since mechanical properties and cell viability

increased with the addition of silica fibers, PLA/silica fibers composites can

be considered as the potentially applicable materials in biomedical fields.

33

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초록

흡수성 임플란트 의료용 생체 재료는 기존의 금속 임플란트

보다 우수한 재료이다. 흡수성 임플란트 의료용 생체 재료는 생분해

성을 가지고 있어 조직 재생 후 임플란트를 제거하기위한 2 차 수

술이 필요하지 않다. Poly (lactic acid) (PLA)는 우수한 생체적합

성으로 인해 이러한 흡수성 임플란트 재료에 적합한 재료이다. 그러

나 금속 임플란트 재료에 비해 PLA는 낮은 기계적 강도 및 영률을

가지고 있어 다양한 의료 분야에서의 사용이 제한된다. 이러한 이유

로 인해, PLA의 생분해성 및 생체 적합성과 같은 장점을 크게 상실

하지 않으면서 PLA의 기계적 성질을 향상시키는데 지속적인 연구

가 진행되어왔다. 고분자의 기계적 성질을 향상시키는 다양한 방법

중에서, 섬유 보강 방법은 상이한 용도에 따라 섬유의 배향을 조절

할 수 있는 장점을 가지고있다. 섬유의 배향과 가해지는 힘이 평행

하게 존재할 때 섬유 보강 고분자의 기계적 강도는 크게 증가한다.

다양한 섬유 중에서 실리카 섬유는 생분해성, 고강도, 높은 영률 및

우수한 생체 적합성으로 인하여 PLA의 기계적 물성을 강화시키는

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데 적합한 섬유이다. 또한 고분자내에서 섬유의 효과적인 기계적 물

성을 향상 효과를 위해 섬유의 표면 개질 방법이 있다. 널리 사용되

는 두 가지 유형의 표면 개질 방법으로 실란 커플링제의 사용과 표

면 개시 중합의 방법이 있다. 이러한 방법으로 섬유와 고분자 매트

릭스 사이의 접착 성을 향상시켜, 복합 재료의 기계적 성질을 더욱

향상시킬 수 있다. 본 연구에서는 PLA / 실리카 섬유 복합 재료의

제조를 위해 용매 제거, 압출 및 사출 성형 방법을 도입했다. 또한

표면 개질 방법에 영감을 받아 PLA / 실리카 섬유 복합 재료의 기

계적 성질을 더욱 향상시키기 위해 실리카 섬유 표면에 실란 처리

와 LA-grafting의 두 가지 표면 처리를 진행하였다. PLA에 실리카

섬유를 첨가 함에 따라 탄성 계수가 상당히 증가했고. 표면 처리 후,

탄성 계수는 PLA / 처리되지 않은 실리카 섬유 복합체에 비해 더욱

증가하였으며, 인장 강도 또한 증가하였다. 복합체의 세포 생존율은

MC3T3-E1 세포로 평가하였다. 세포 생존율은 실리카 섬유의 첨

가 함에 따라 증가하였다. PLA / 표면 처리 된 실리카 섬유 복합체

의 세포 생존율은 처리되지 않은 섬유 복합체와 비슷한 수치를 유

지했다. 이 연구로 실리카 섬유가 PLA의 기계적 성질 및 세포 생존

율을 효과적으로 증가시킬 수 있음을 확인했다. 또한 실리카 섬유의

표면 개질을 통해 세포 생존율을 유지하면서 PLA의 기계적 성질을

40

더욱 향상시킬 수 있었음을 확인했다.

주요어: 폴리라틱에시드, 복합체, 섬유 강화 수지, 용매 제거법, 압출,

사출 성형, 기계적 성질, 세포 생존율

학번: 2016-20798