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Vol. 9. Issue 2.
Pages 2350-2356 (March - April 2020)
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Vol. 9. Issue 2.
Pages 2350-2356 (March - April 2020)
Original Article
DOI: 10.1016/j.jmrt.2019.12.066
Open Access
Dynamic mechanical analysis of polyethylene terephthalate/hydroxyapatite biocomposites for tissue engineering applications
S.A.P. Sughanthya, M.N.M. Ansarib,
Corresponding author
, A. Atiqahb
a Department of Mechanical Engineering, Universiti Tenaga Nasional, 43000 Kajang, Selangor, Malaysia
b Institute of Power Engineering, Universiti Tenaga Nasional, 43000 Kajang, Selangor, Malaysia
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Synthetic biomaterials are widely used for the treatment of diseased or damaged tissue in the field of tissue engineering. Polyethylene terephthalate (PET) is a synthetic thermoplastic engineering polymer with high commercial and industrial interest and has been widely used as implant material in biomedical engineering. Despite that, PET has limited applications due to its high hydrophobicity. Hydroxyapatite (HA) is one of the known biocompatible ceramic for the development of porous scaffolds for bone replacement and tissue engineering due to its resemblance to the mineral constituents of human bones and teeth. Therefore, HA was functionalized into the PET matrix in order to improve the limitation. In this research, PET-HA nano-biocomposite scaffold was electrospun using the electrospinning system. PET and HA were dissolved using trifluoroacetic acid (TFA) and dichloromethane (DCM). The nanofibrous scaffolds were produced at optimum process parameters. The morphology studies were performed using a Scanning Electron Microscope (SEM) and thermomechanical properties were evaluated using Dynamic Mechanical Analysis (DMA). From the morphology analysis, PET-HA nano-biocomposite scaffold which composed of 96% of PET and 4% of HA, has obtained the largest fiber diameter. The DMA analysis showed that the addition of HA improved mechanical properties. However, PET-HA nano-biocomposite scaffold composed of 98% of PET and 2% of HA was preferred as it has the lower value of storage and loss modulus because the application was focusing on the skin where the more flexible scaffold was needed. The PET-HA nano-biocomposite scaffold fabricated has good potential to be used in tissue engineering applications.

Polyethylene terephthalate (PET)
Hydroxyapatite (HA)
Dynamic mechanical analysis (DMA)
Tissue engineering
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The skin is the biggest organ of the body in vertebrates and is made out of the epidermis and dermis with an involved nerve and blood supply [1]. Skin is generally a delicate tissue, covering the whole outer surface and structuring around 15% of the aggregate body mass. Skin is a tissue that is persistently recharged by the expansion and separation of keratinocytes. Skin is made out of three separate layers: hypodermis, dermis and epidermis [2,3]. These three layers assume a vital part in shielding the body from any mechanical harms, for example, injuring. Consistently, a great many individuals need skin graft because of dermal wounds brought about by flame, heat, power, chemicals, bright, atomic vitality, or maladies. A definitive point is to quickly create a build that offers the complete rebuilding of useful skin in a perfect world including the arranged recovery of all the skin extremities and layers with fast vascularisation and scar-free coordination with the encompassing host tissue.

Researchers included in tissue engineering (TE) are seriously researching materials that can repair and replace lost or damaged tissue by initiating the natural regeneration process [4]. In regeneration strategies, biomaterials promote new tissue development by giving a sufficient space (porosity) and a suitable surface to foster and direct cellular attachment, migration, proliferation, and the desired differentiation of particular cell phenotypes all through the scaffold where new tissue formation is required [5–7]. In the field of tissue engineering, it is well known that scaffolds, properly planned regarding structure and properties, assume a vital part to direct and provide support to the growth of cells and additionally their migration around surrounding tissue [8,9]. Some experimental investigations suggest that scaffolds with various compositions provide a suitable platform for cell attachment, proliferation, and cell migration [10].

Biomaterials such as synthetic polymer have a high potential for tissue engineering applications. This is due to its ability to tailor mechanical properties, degradation kinetics, and also bioactivity [11]. Therefore, properties of biomaterial polymer can be enhanced by incorporating mineral polymer fillers (HA) to the main polymer PET which has low bioactivity compared to many other biopolymers such as PLA, PLGA, PCL, etc. [12]. This could improve the overall biocompatibility of the PET-HA nano-biocomposite scaffold.

Hydroxyapatite (HA) is one of the known biocompatible ceramic for the advancement of a porous scaffold for bone substitution and tissue engineering [13,14]. Being a bioactive ceramic HA is generally utilized for different bone repairs and as coatings for the metallic artificial device to enhance their biological properties. Since HA has chemical similarity to the inorganic bone matrix component, synthetic HA displays a strong affinity to host hard tissues [13–15]. Chemical bonding with the host tissue offer HA more significant preferences in clinical applications compared with other bone substitutes, for example, allografts or metallic implants. The main advantages of synthetic HA are its biocompatibility, moderate biodegradability and great osteoconductive and osteoinductive capabilities. The process of coating porous HA scaffold with polymer lining able to mend the mechanical properties in which high interconnectivity and porosity are maintained.

Polyethylene Terephthalate (PET), also known as Dacron, has been widely used as prosthetic vascular grafts and has shown excellent mechanical strength and good biocompatibility. It is a non-biodegradable linear polyester with excellent mechanical properties, which limits the applications for skin in the biomedical field [16]. In general, the high surface is, porosity and interconnectivity of pores within the nonwoven PET matrices ensure good mass transfer and support high cell densities [17]. The addition of HA into PET affects the mechanical properties of the nano-biocomposite. However, the amount of HA addition needs to be optimized. A combination of these two polymers develops a new nano-biocomposite scaffold with improved properties which considered the novelty as it focuses on skin application compared to the common application on hard tissues.

In the present research, the fabrication of nanofibrous composite is studied by the use of a simple method, which is electrospinning and followed by the analysis on the characterization of a nano-biocomposite scaffold produced. Electrospinning is a technique that allows the fabrication of continuous fibres which is similar to the structure of ECM with diameters ranging from several micrometres down to a few nanometers [18–20]. The PET-HA nano-biocomposite scaffold was prepared for skin application which is considered as a novel approach as it is commonly used for hard tissues due to its natural characteristics. The parameters of the process were constant along the entire process of fabricating the fiber mats nano-biocomposite scaffold. The effects of different compositions of PET and HA on the thermomechanical, biocompatibility, physical and morphological properties can be determined throughout this research.


The polyethylene terephthalate (PET) (Recron® PET Resin) was used as a matrix in the nano-biocomposite scaffold. The pellets are solid opaque white components which molecular is 16kgmol−1 was purchased from Recron Malaysia Sdn. Bhd. The material range of the melting point is 240°C–260°C and the relative density is 1.35g/cm3. The value for fine dust is 3mg/m3 while 10mg/m3 for coarse dust according to TRGS 900 (Germany). The hydroxyapatite (HA), white in colour with the average particle size of 2–10μm was used as a reinforcement filler for the nano-biocomposite. It was purchased from Xi’an Shunyi Bio-Chemical Technology Co. LTD, China. The HA powder purity is 99% and the morphology structure is spherical. Two types of solvent were used which are trifluoroacetic acid (TFA) (CF3COOH) from Scharlabs. Spain and dichloromethane (DCM) from Quassi-S Pte.Ltd. DCM molecular weight is 65.05g/mol and TFA density is 1.48g/cm3.

2.2Preparation of PET/HA composite scaffold

The sample was prepared based on solvents mixing. The mixture consisted of 5mL of trifluoroacetic acid (TFA) and 5mL dichloromethane (DCM) were mixed with 1:1 ratio. Then, 1g of polyethylene terephthalate (PET) was inserted into solutions and stirred for 1h so that it can be dissolved under room temperature. Finally, hydroxyapatite (HA) filler was inserted according to the percentage from 0% HA to 4% HA and stirred for another 1h for it to blend homogeneously.

2.3Preparation nanofibrous mat

The nanofibrous mat was prepared using the electrospinning process in which the machine consists of few parts which are DC power supply of regulated high voltage, 1mL syringe needle, metal collector which is rotating and digital syringe pump. The electrospinning process was done under a condition of room temperature and started by filling up the syringe with PET-HA solutions and the needle was fixed to the syringe. The air bubble from the syringe needs to be removed manually where the polymer solution was forced to emerge at the end of the needle. Next, the syringe was fixed to the pump of 1mL/h of flow rate was programmed. An aluminium foil was used to cover up rotating collector in order for fibre to be collected on it so that it will easy to remove the fibres from it for characterization purpose. The distance from the collector and the syringe needle were adjusted to be 10cm.

The needle was connected with high voltage DC power supply, and precautions were taken so that high voltage power supply and the syringe pump not in contact. The regulations of high voltage power supply were done from 10 to 15kV once it’s turned on until the visibility of Taylor’s cone and fluid is pulled to the rotating collector by the charge. The rotating collector was turned on and the electrospinning process was run for 30min until a white sample which is solid occupies the aluminium foil.

2.4Characterization of PET-HA composite

The morphology analysis of the fibres of electrospun PET-HA was done using the Scanning Electron Microscope (SEM) modelled (Hitachi S-3400N). The parameters were a voltage that accelerates 10kV–15kV and 1000× and 5000× magnifications respectively. The dynamic mechanical analysis was done using a Perkin-Elmer Diamond DMA instrument from Seiko Instruments. The scanning was done in tensile mode from the range of 20°C–120°C at 2°C/min. The frequency used was 1Hz and 10μm deformation amplitude (Fig. 1).

Fig. 1.

Schematic representation of skin [2].

3Results and discussion3.1Characteristics analysis

Fig. 2 shows SEM images of the microstructure of PET-HA composites at 0%, 1%, 2%, 3%, 4%. In general, the electrospun fibres with copolymers often offer polymeric materials enhancement which includes the thermal stability tailoring, mechanical strength and barrier of properties. It often relates that the use of copolymers improves the electrospun scaffold performances compared to homopolymers [21]. The increase in the average fibre diameter of electrospun PET-HA composite due to the increase in HA percentage is part of the increment of the polymer solution conductivity. The more the jet carries charges, the higher the force of elongation applied to the jet under the electrical field. It was known that fibres tension dependent on the excess charges self-repulsion on the jet. Besides that, by adding HA into the polymer solution increases the concentration of the total polymer and eventually causes an increment in the viscosity. By adding more HA, the viscosity increases and promotes polymer jet fast solidification and high resistance of the bending instability [22]. According to Cannella et al. [23], the mechanical behaviour is affected more by the porosity compared to additive manufacturing.

Fig. 2.

SEM image of nano-biocomposite scaffold at 3000× mag (a) PET-HA 0, (b) PET-HA 1 (1% wt.), (c) PET-HA 2 (2% wt.), (d) PET-HA 3 (3% wt.) and (e) PET-HA 4 (4% wt.).


The changes of storage modulus (E’), loss modulus (E”), and damping factor (Tan δ) in pure PET-HA and PET-HA composites on heating from DMA testing as shown in Fig. 3. All the samples had a transition temperature range where E’ suddenly decreased, whereas E” and tan δ sharply changed with the increasing temperature. The peak of the modulus curve or the peak of the tan δ curve is employed to identify the Tg. Fig. 3c shows that the Tg of pure PET and PET-HA composites at 0%, 1%, 2%, 3% and 4%. It can be observed that the composites with HA have higher damping factor compared to the pure PET matrix. Fibre composites interface effect can be explained clearly in damping curves. The Tan δ peak value lies almost at the same temperature for all composites with HA compared to the pure PET. It was stated that the higher the value of Tan δ peak, the greater the molecular mobility degree [24].

Fig. 3.

(a) Storage modulus (E’), (b) loss modulus (E”) and (c) damping factor (Tan δ) in pure PET-HA and PET-HA composites measured by DMA testing.


Fig. 3b displays the effect of temperature on the loss modulus (E”) of PET-HA nano-biocomposite scaffold. Loss modulus (E”) refers to the “plasticity” of a material, it is a measure for the ability of a material to follow deformation without breaking. It can be seen that loss modulus (E”) value increases as the temperature increases in the glassy region. The Tg value obtained from the loss modulus was found to be lower than the curve of Tan δ. The value of the loss modulus for all composites decreases at the rubbery stage and finally the melting stage. The loss modulus range for PET-HA 2 is more preferable compared to other nano-biocomposites scaffolds as the application focusing on the skin where lower loss modulus is needed. According to Ahmad et al. [21], a material being more elastic is due to the storage modulus value. The incorporation of the PET fibre imposed a high degree of restriction which supports efficient stress transfer throughout the fibre/matrix interface.

The effect of temperature on the storage modulus of PET-HA nano-biocomposite scaffold as shown in Fig. 3a. Storage modulus (E’) refers to the elasticity (stiffness) of a material and is proportional to the energy that is stored during one period under load. It can be observed that all the composites obtained maximum storage modulus (E’) value at the glassy region due to the characteristics of the main polymer which is PET has good luminous transmittance, high birefringence and excellent mechanical strength. In the vicinity of the Tg, a sharp decrease in storage modulus (E’) value was observed which indicates that the composites are going through glass/rubbery transition. The PET-HA 2 nano-biocomposite scaffold is better as it has low storage modulus because the focus of this research is mainly for skin application. Skin application scaffold requires low stiffness value [25,26].


The PET-HA nano-biocomposites scaffolds with different ratios have a high impact on the fibre diameter. The fibre diameter increases as the composition of HA increases. All the nano-biocomposites scaffolds obtained the maximum storage modulus (E’) value at the glassy region, loss modulus (E”) value increases as the temperature increases at the glassy region and the nano-biocomposite with HA have higher damping factor compared to the pure PET nano-biocomposite scaffold. However, PET-HA 2 nano-biocomposite scaffold was preferred as it has a lower value of storage and loss modulus because the application is focusing on the skin where the more flexible scaffold is needed. This research should be furthered so that it can be elucidated and recognize in different composite materials prospects for the application of tissue engineering. In order to achieve those targets, a study on different mechanical properties, for instance, the flexural and tensile strength, can be done where the mechanical stability and viability of the material can be evaluated. Study on water absorption and also the test on simulated body fluid (SBF) absorption under environment characterization which helps in evaluating the effect of PET-HA composite to the environment, can also be carried out.

Conflict of interest

The authors declare that there is no conflicts of interest.


The experimental work was conducted at Tissue Engineering Centre, Hospital Universiti Kebangsaan Malaysia (HUKM), Universiti Tenaga Nasional, iRMC & UNITEN R&D Sdn. Bhd. for support. Also, the Department of Mechanical Engineering and Institute of Power Engineering, UNITEN.

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Journal of Materials Research and Technology

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