Hydroxyapatite/TPU/PLA nanocomposites: Morphological, dynamic-mechanical, and thermal study

Vahid Faghihi-Rezaei; Hossein Ali Khonakdar; Vahabodin Goodarzi; Goldis Darbemamieh; Maryam Otadi

doi:10.1515/gps-2022-0087

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Hydroxyapatite/TPU/PLA nanocomposites: Morphological, dynamic-mechanical, and thermal study

Vahid Faghihi-Rezaei , Hossein Ali Khonakdar , Vahabodin Goodarzi , Goldis Darbemamieh and Maryam Otadi

Published/Copyright: November 9, 2022

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From the journal Green Processing and Synthesis Volume 11 Issue 1

Abstract

Nanocomposites based on thermoplastic polyurethane (TPU) and poly lactic acid (PLA) with different weight ratios of 10:90 and 30:70 were prepared by solution method. Hydroxyapatite nanoparticles (n-HA) were used to enhance the physical and mechanical properties of the alloys. To prepare the nanocomposites, the percentages of n-HA varied between 1% and 5%. Different tests were used to investigate the properties of these nanocomposites. Scanning electron microscopy (SEM) analysis, which was used to study the morphology of the blends, showed that there were rough morphologies in between materials, and the results of the mapping test showed that the dispersion of nanoparticles in the polymer matrix was almost good. TGA thermal degradation test showed that the presence of TPU to some extent can affect the thermal stability properties, and with the increase in this material, the thermal properties are strengthened. The crystalline behavior of the samples showed that the presence of TPU and n-HA nanoparticles had negative effects on the crystalline properties. The study of viscoelastic behaviors showed that the presence of TPU enhances the viscous behavior in the sample and decreases the glass transition temperature, while the presence of nanoparticles increases the elastic properties and glass transition temperature. Tensile test showed that the presence of n-HA has a greater effect on the mechanical properties. Dynamic contact angle analysis using water and dimethylformamide (DMF) solvent showed that the existing TPU and n-HA led to major changes in the interaction surface of scaffolds. 3-(4,5-Dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide analysis showed that increasing the amounts of TPU and HA increases cell viability. SEM cell interactions analysis showed that the surfaces of PLA90TPU10H5 and PLA70TPU30H5 samples are very good for the preparation of bone tissue scaffolds. Our findings indicated that the addition of n-HA into PLA/TPU blends could impart new features to the PLA matrix as a promising candidate for bone, cartilage, and tendon tissue engineering.

Keywords: biodegradable; nanocomposite; polylactic acid; hydroxyapatite nanoparticles

1 Introduction

Bone problems resulting from trauma and pathological and physiological analysis of bone are the major problems for global health. The need for bone repair in cranial, oral, maxillofacial and face surgeries, and orthopedics is one of the clinical issues in restorative medicine. Polymer nanocomposites with low cost and easy availability can be used in bone tissue engineering. Bone repair after injury or fracture is a process that requires a set of regular functions to produce new bone, and disruption of these regular functions may cause healing problems [1,2,3].

In bone repair, osteoblasts are responsible for the formation of new bone, and osteoclasts are responsible for bone resorption so that the bone can reach its original structure. Bone defects can be caused by trauma, tumors, and bone diseases, and these defects do not heal on their own. Tissue engineering is emerging as an approach to overcoming this challenge in bone therapy. Bone tissue engineering approaches can be a combination of scaffolding, growth factors, and stem cells to improve damaged tissue function and prevent complications related to the repair of bone and other tissues. The scaffold must have special properties such as physicochemical and mechanical properties to perform cell attachment, proliferation, and maturation to form bone tissue [4,5,6].

The use of polymeric materials in medical engineering is very popular among scientists because these materials with their unique properties can have very amazing effects on scaffolds made from biodegradable materials. On the other hand, these materials have a very high formability and are available at a very low cost, and a variety of methods can be used in the fabrication of various scaffolds with different shapes and morphologies [7,8,9,10]. Among them, the use of poly lactic acid (PLA) polymeric material is one of the best and most widely used materials for use in tissue engineering due to its food and drug administration approvals and also its ease of preparation [11,12]. This material is used in the manufacture of many tissue engineering scaffolds due to its suitable physical and mechanical properties as well as its obvious biological properties [13,14,15]. One of the weaknesses of this material is its brittleness against impact, which greatly increases the possibility of cracking and crushing, therefore, the use of this material in the manufacture of scaffolding used in bone tissue engineering is limited [16,17,18,19]. To solve this problem, soft polymeric materials have been used to increase the flexibility of this material [20,21,22,23,24]. One of the materials that is widely used in medical engineering for making soft tissues is thermoplastic polyurethane (TPU), which is used as a blend, and many efforts and research works have been done on making PLA/TPU blend. Hydroxyapatite (HA) is also widely used in bone repair [25,26,27].

Nofar et al. investigated the rheological behavior of PLA/TPU blend and evaluated its properties. Based on the hard and soft segments of TPU, they studied the melt interaction of this material with PLA macromolecules and obtained interesting results [28].

Kahraman’s research team used an epoxy reactive system to strengthen the interaction between TPU and PLA. In this work, it was shown that the use of a third material to enhance the interaction between these two polymers greatly contributed to the physical and mechanical properties [29]. In another study led by Dong, a nanocomposite based on PLA/TPU and carbon nanotube (CNT) nanoparticles was prepared. They studied the shape memory property of this material and observed that this nanocomposite has special physical and mechanical properties [30]. In another work, Azadi et al. used PLA/TPU blend with graphene oxide nanoparticles and showed that the thermal behavior and creep of this material are interestingly related. They also showed that graphene nanoparticles due to their active surface can have a relatively good interaction with the macromolecules and enhance the mechanical properties of the blend [31]. Yan and colleagues evaluated the physical, mechanical, and shape memory properties of PLA/TPU blends containing multi-walled carbon nanotube nanoparticles. They showed that the modified nanoparticles are well dispersed within the polymer matrix and the presence of these nanoparticles strongly affects the physical and mechanical properties of the blend [32]. Yazdaninia et al. evaluated the thermomechanical properties of PLA/TPU blends containing polyhedral oligomeric silsesquioxane particles and showed that the presence of this material can have many effects on morphology and thermomechanical properties [33].

Based on extensive research and studies conducted on PLA/TPU blend, it was determined that this blend is one of the most widely used materials in the medical industry, and due to the good biocompatibility of PLA and TPU, they can be used in the manufacture of many biocompatible blends in tissue engineering. On the other hand, bioactive nanoparticles such as Hydroxyapatite nanoparticles (n-HA) and bioactive glass can increase the bioactivity of this blend. Because of the specific surface area, surface factors, and the ability to control the porosity of n-HA nanoparticles, it is expected to have a special influence on the properties of the PLA/TPU blends. Therefore, one of the main objectives of this study is to investigate the physical and thermal properties of PLA/TPU blend with different compositions in order to be able to prove the presence of n-HA as an active nanomaterial in this blend and to know the effect of its presence on PLA/TPU properties. The developed nanocomposite exhibited promising potential to be used as vital scaffolds for tissue engineering in the future.

2 Experimental method

2.1 Materials

Materials used in this research are: PLA granules with M _w = 84,000 g·mol⁻¹ from Sigma Aldrich, TPU granules from Merck (Germany), n-HA with fine particle size of 100 nm purchased from Sigma Aldrich, and high-grade dimethylformamide (DMF) and DMSO solvents from Merck (Germany).

2.2 Preparation method

In this study, all samples were prepared as solution. First, a certain amount of polymeric materials were dissolved in DMF and DMSO solvents in a ratio of 30:70 at room temperature for 72 h, then the resulting solution was poured into specified molds and placed in an oven for 48 h. To prepare nanocomposite samples, after preparing the solvents, they were poured into a container and then a certain amount of n-HA was added to them. The samples were then subjected to ultrasonic waves for 15 min using a 100 W ultrasonic device with an amplitude of 0.5 to completely breakdown the formed aggregates. Then, the desired polymer material was weighed and poured into the solution and left for 72 h to obtain a homogeneous solution. Then, the resulting solution was poured into specific molds and placed in the oven. The codes of the prepared samples and the percentage composition of each component are given in Table 1. Figure 1 shows a schematic of the sample preparation process.

Table 1

Code and percentage composition of all prepared samples

Sample codes	PLA (wt%)	TPU (wt%)	n-HA (wt%)
PLA100	100	—	—
TPU100	—	100	—
PLA90TPU10	90	10	—
PLA70TPU30	70	30	—
PLA90TPU10H1	90	10	1
PLA90TPU10H3	90	10	3
PLA90TPU10H5	90	10	5
PLA70TPU30H1	70	30	1
PLA70TPU30H3	70	30	3
PLA70TPU30H5	70	30	5

Figure 1

Sample preparation method in this research.

2.3 Characterization

2.3.1 Fourier transform infrared (FTIR) analysis

This technique is used to identify the types of chemical bonds and interactions created between the materials in the samples. This test was performed on an FTIR spectrometer (Borker Model, Germany) in radiant mode and at a wavenumber from 500 to 4,000 cm⁻¹.

2.3.2 Scanning electron microscopy (SEM)-mapping test

To perform this test, a Philips SEM (the Netherlands) was used. All samples were coated with gold and platinum for 20 min and then placed on the device probe and the images were evaluated and tested at different magnifications. The dispersion of n-HA in the samples was determined by mapping test to identify calcium and phosphate elements.

2.3.3 Dynamic mechanical thermal analysis (DMTA) analysis

This test is used to measure the viscoelastic properties of the samples. Samples with specified dimensions were placed in the DMTA Model X in tensile mode and the test was performed at a frequency of 1 Hz in a temperature range of −80°C to 100°C and at a rate of 3°C·min⁻¹, and storage modulus, loss modulus, and loss factor were reported.

2.3.4 TGA analysis

This test was used to identify the degree of thermal stability in the samples and all samples were analyzed using Q1000. The rate of heating was 10°C·min⁻¹, and the test was performed in air atmosphere and the amount of samples in each test was considered to be 5 mg. The test was performed from room temperature to 600°C.

2.3.5 Dynamic contact angle analysis

The hydrophilicity and hydrophobicity properties of samples were identified by measuring the water and DMF contact angle on the surface of the samples in the sessile drop mode. In this method, a solvent droplet with a size of 4 µL according to ASTM D7334 standard was placed on the dry sample surface at 37°C. Then, the position of the droplet at different times was imaged using a Gausou digital microscope.

2.3.6 Differential scanning calorimetry (DSC) analysis

This test was performed for all samples by Q1000 in nitrogen atmosphere and cooling and heating diagrams were obtained at a rate of 10°C·min⁻¹. The amount of samples used was 5 mg and was placed in an aluminum pan.

2.3.7 Tensile test

This analysis was done for all samples using an INSTRUN instrument with a 50 t load cell. All samples have the same dimensions and the test was performed at a strain rate of 10 mm·min⁻¹.

2.3.8 In vitro analysis

To evaluate the cell response to the surface of samples, cell viability was conducted through 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay. Treatment of the samples’ surface was performed to explore the effect of modification on the cell viability of samples. All sample pieces were washed in phosphate buffered saline (PBS) solution (pH 7.4) and incubated with Dulbecco’s modified Eagle medium and 10% fetal bovine serum in 96-well plates overnight to remove any trace of ethanol. Afterward, mouse embryo fibroblast cells (L929) were seeded on all specimens (5,000 cells·well⁻¹) and incubated at 37°C, 95% air, and 5% CO₂ condition. After 1, 3, and 5 days of cell culture, all the scaffolds were turned into fresh wells, and the MTT solution was added to the well, the well plates were incubated for 3 h at 37°C in the dark. The absorbance of the MTT solution was evaluated at 570 nm with a spectrophotometer device. The morphology of the adhesion cells was determined by SEM. After 5 days in the culture medium, the samples were removed from the plate, and the cells that failed to adhere to the scaffold were separated by washing with PBS solution. The adherent cells were fixed with 4% glutaraldehyde solution, and finally, cell scaffolds were coated with a thin layer of gold to prepare for SEM.

2.3.9 Hydrocatalytic degradation analysis

This analysis was performed in PBS solution and all samples with specific dimensions were first weighed and then placed in a shaker incubator at 37°C for 60 days. Then, at different intervals, all samples were dried and weighed. Finally, their weight loss percentage was calculated according to Eq. 1:

(1) Weight loss ( % ) = W 0 − W t W 0 × 100

where W ₀ and W _t are the initial weight and weight at time t in each analysis interval, respectively.

3 Results and discussion

3.1 SEM results

SEM analysis was used to study the morphology of the studied samples. Figure 2 shows the cross-sectional morphology of PLA90TPU10 and PLA70TPU30 blend specimens at two different magnifications. The cross-sectional morphology of the PLA90TPU10 sample in Figure 2a and b shows that there is a relatively good interaction between the two polymeric materials because the main functional groups present in the two polymers cause weak interactions between them. Figure 2c and d shows the inside morphology of the PLA70TPU30 sample. As stated, with the increase in TPU in the sample, the TPU structures clearly show themselves, that is, with the increase in the weight percentage of TPU, the degree of compatibility in this polymer sample decreases and more phase separation is observed. This has been observed in previous articles and reports [20,21,22].

Figure 2

SEM analysis results for pure blend samples: (a and b) PLA90TPU10 and (c and d) PLA70TPU30.

Figure 3 shows the surface morphology of nanocomposite blend samples with different percentages of n-HA. Figure 3a–c shows the morphology of nanocomposite samples with different percentages of HA (1–3 wt%) in PLA90TPU10 blend. These figures show that the presence of n-HA has a significant role in changing the morphology of the samples and the nanoparticles have been able to be placed between the layers of these two polymers, which increase the degree of interaction between them to some extent. In previous works, it was reported that the presence of nanoparticles can have a great effect on the compatibility between two polymers, which is also seen in this work [30,31,32].

Figure 3

SEM analysis results for nanocomposite blend samples: (a) PLA90TPU10HA1, (b) PLA90TPU10HA3, (c) PLA90TPU10HA5, (d) PLA70TPU30HA1, (e) PLA70TPU30HA3, and (f) PLA70TPU30HA5.

Also, morphological changes in PLA70TPU30 blend sample with different weight percentages of n-HA are shown in Figure 3d–f. These images also show that the presence of more n-HA can greatly contribute to better morphology and compatibility between these two polymers.

Mapping test was used to detect the elements of calcium and silicon to investigate the dispersion of n-HA in the studied samples. The results are shown in Figure 4. The images show that the dispersion of n-HA in the polymer matrix is relatively good. Figure 5 shows the dispersion of nanoparticles in the polymer matrix for the PLA70TPU30 sample. These images prove that the dispersion of nanoparticles has improved with the increase in TPU phase.

Figure 4

Mapping analysis of samples: PLA90TPU10HA1 (a, a′, a″), PLA90TPU10HA3 (b, b′, b″), and PLA90TPU10HA5 (c, c′, c″).

Figure 5

Mapping analysis of samples: PLA70TPU30HA1 (a, a′, a″), PLA70TPU30HA3 (b, b′, b″), and PLA70TPU30HA5 (c, c′, c″).

3.2 TGA results

TGA test was used to investigate the thermal stability of nanocomposites and the effect of nanoparticles on the thermal degradation of blends. The results are shown in Figure 6. Figure 6a shows the thermal stability of pure and blend samples. This figure shows that the degradation onset temperature in the PLA sample is much higher than that in TPU, but over time the thermal stability in the TPU sample increases due to the formation of charcoal and resistance to heat penetration. Figure 6b shows the thermal stability changes for the PLA90TPU10 blend sample and its nanocomposites. This figure shows that the onset temperature of degradation in the nanocomposite sample with 5 wt% of nanoparticles occurred earlier than the other samples. This may be due to the poor dispersion of nanoparticles, the accumulation of nanoparticles, the creation of hot spots, and earlier degradation in the sample. In the sample with 3 wt% nanoparticles, thermal stability is increased due to better dispersion of nanoparticles in the polymer matrix. Figure 6c shows the thermal degradation for PLA70TPU30 sample and its nanocomposites. It can be seen that the presence of 5 wt% nanoparticles increased the thermal stability more than other samples. Perhaps the higher presence of TPU in the samples caused the better dispersion of nanoparticles and possibly by adjusting the viscosity between these two polymers, the dispersion of nanoparticles in the polymer matrix was improved.

Figure 6

TGA test for all studied samples: (a) pure and blend samples, (b) PLA90TPU10 nanocomposites, and (c) PLA70TPU30 nanocomposites.

3.3 DSC results

The DSC test was performed for all samples by cooling, the results of which are shown in Figure 7. Figure 7a shows the DSC test results for pure and blend samples. This figure shows that PLA polymer has a crystalline structure and TPU has a lower crystal structure due to its rubber structure. In the PLA90TPU10 sample, it is observed that with the presence of TPU, the melting peak intensity is somewhat reduced compared to the PLA melting peak intensity. In the PLA70TPU30 sample, it is also observed that the presence of TPU can be a barrier against melting and reduce the intensity of PLA melting peak. Figure 7b shows the crystallization changes in blend samples and nanocomposites based on PLA90TPU10. This figure shows that very little change has been observed in the crystallinity diagrams of the samples and the presence of TPU has had very negative effects on PLA crystallinity. On the other hand, the presence of nanoparticles has not been able to improve the crystallization behavior, and perhaps the presence of better nucleation has reduced the crystallization temperature to some extent.

Figure 7

Cooling and crystallization diagrams of all samples studied and obtained from DSC: (a) pure and blend samples, (b) PLA90TPU10 nanocomposites, and (c) PLA70TPU30 nanocomposites.

But in Figure 7c, the changes in the crystal diagrams for PLA70TPU30-based blend samples are more tangible and more visible. In this case, it is observed that in the PLA70TPU30H5 sample, the peak area for the PLA sample has increased, which may be due to the presence of nanoparticles and their positive effect on the rapid formation of crystals. On the other hand, it is observed that the presence of nanoparticles caused a further decrease in the crystallization temperature in the samples. Table 2 also shows the changes in the crystallinity value for all samples.

Table 2

Crystallization data obtained from DSC test

Samples	Enthalpy of melting (J·g⁻¹)	Crystallization temperature (°C)
PLA100	50.39	152.70
TPU100	12.00	150.67
PLA90TPU10	48.67	153.09
PLA70TPU30	29.68	153.06
PLA90TPU10H1	44.40	156.60
PLA90TPU10H3	44.58	153.79
PLA90TPU10H5	40.59	153.31
PLA70TPU30H1	37.81	156.08
PLA70TPU30H3	38.84	154.65

3.4 Mechanical analysis

DMTA test was used to evaluate the viscoelastic behavior of the samples. In this test, the elastic and viscous behaviors of the samples are analyzed in such a way that we can have a correct and logical judgment on them. In Figure 8, the storage modulus behavior of all samples is analyzed. Figure 8a shows the changes in the storage modulus for pure and blend samples. In this figure, it can be seen that the storage modulus of PLA is higher than the storage modulus of other materials due to its higher elastic behavior and higher stiffness, and TPU has a lower modulus due to its rubber-like behavior. By blending these two polymers together, it is clear that the use of certain amounts of TPU in PLA can change the viscoelastic behavior and create a material that has better behavior.

Figure 8

Study of storage module of: (a) pure and blend samples, (b) PLA90TPU10, and its nanocomposites, and (c) PLA70TPU30 and its nanocomposites.

In the following, the behavior of the viscoelastic properties of the prepared nanocomposites is evaluated in order to analyze the behavior of these samples more accurately. Figure 8b shows the changes in the storage module for PLA90TPU10 and its nanocomposites. It is clear that the presence of nanoparticles in the samples has caused an increase in mechanical properties. By increasing the amount of n-HA, the elastic part of the samples is strengthened and shows high mechanical properties.

On the other hand, Figure 8c shows the changes in the storage modulus for the PLA70TPU30 sample and its nanocomposites. As can be seen, the presence of nanoparticles has a good effect on the physical and mechanical properties of samples. In these samples, it can be seen that due to the use of higher amounts of TPU, the storage modulus is lower than the storage modulus of other samples. The increase in nanoparticles due to better dispersion and better interaction with the polymer matrix has caused a further increase in the mechanical properties of the samples.

Changes in the viscosity behavior of all samples based on the tan δ parameter are shown in Figure 9. In this figure, the behavior of the samples can be evaluated according to the height and width of the peaks. Figure 9a shows the tan δ changes in pure and blend samples. In this figure, it is clear that the glass transition temperature for pure PLA sample is much higher than that for TPU sample, which is related to the glass behavior of PLA relative to TPU. On the other hand, by blending these two polymers with different ratios, the glass transfer temperature will be different for the samples and for the sample with more TPU, the glass transfer temperature will be lower.

Figure 9

tan δ vs temperature curves of: (a) pure and blend samples, (b) PLA90TPU10 and its nanocomposites, and (c) PLA70TPU30 and its nanocomposites.

Figure 9b shows the tan δ changes in the PLA90TPU10 sample and its nanocomposites. The presence of nanoparticles increases the glass transition temperature and 5% by weight of HA in the sample causes a further increase in the glass transition temperature due to the immobility of the polymer chains. Figure 9c shows the tan δ changes in the PLA70TPU30 sample and its nanocomposites. It is clear that more nanoparticles have been able to further increase the glass transition temperature.

Mechanical analysis of the studied samples was performed in strain-stress mode and their results are presented in Figure 10. From Figure 10a, it can be seen that the addition of TPU to PLA reduces the mechanical properties, which can be related to the rubbery like nature of TPU. On the other hand, the mechanical properties of nanocomposite samples are shown in Figure 10b. From this figure it can be seen that the addition of nanoparticles has a good effect on the mechanical properties, and with the increase in the amount of nanoparticles in the polymer blend, there is a huge impact on the mechanical behavior. This phenomenon can be related to the presence of nanoparticles and good interaction with all pairs of blends as well as good dispersion in the matrix texture.

Figure 10

Mechanical analysis: (a) blend samples and (b) their nanocomposites.

3.5 Contact angles analysis

The reaction between molecular water and the surface of scaffolds was analyzed by contact angle analysis in dynamic mode and their results are presented in Figure 11. In this figure, it can be pointed out that all samples were studied under dynamic contact angle analysis for 45 s. All collected angles were analyzed and are presented in Figure 11a; in this figure it can be seen that the rate of angle reduction of the samples is very low. This observation is related to the low hydrophilicity of the samples. Therefore, this analysis was performed by DMF solvent as a good organic solvent to clear the role of hydrophobicity properties of the samples. This analysis was performed and their results are presented in Figure 12. Based on the observed results, it can be seen that all samples showed good behavior against organic solvent.

Figure 11

Contact angle analysis of the studied samples: (a) images of all samples in different modes and (b) results of all samples.

Figure 12

Contact angles of the studied samples for DMF solvent: (a) PLA100, (b) TPU100, (c) PLA90TPU10, (d) PLA70TPU30, (e) PLA90TPU10HA1, (f) PLA90TPU10HA3, (g) PLA90TPU10HA5, (h) PLA70TPU30HA1, (i) PLA70TPU30HA3, and (j) PLA70TPU30HA5.

3.6 In vitro study

The MTT analysis of the selected samples is presented in Figure 13. In this study, it can be seen that these selected samples show good cell compatibility and are suitable for application in cell study and scaffold manufacturing.

Figure 13

MTT analysis of the studied samples (S3 – PLA90TPU10, S4 – PLA70TPU30, S7 – PLA90TPU10H5, and S10 – PLA70TPU30H5).

According to the MTT analysis, the interactions between cells and scaffolds were investigated and their results are presented in Figure 14. In this figure, it can be observed that the increase in the amount of TPU and HA in the scaffolds increases cell attachment and the interaction properties between the cells and surfaces. On the other hand, it can be concluded that the addition of HA nanoparticles to the scaffolds increases cell amount on the scaffold surfaces.

Figure 14

SEM of cell attachment surface of the studied samples: (a) PLA90TPU10, (b) PLA70TPU30, (c) PLA90TPU10HA5, and (d) PLA70TPU30HA5.

3.7 Hydrocatalytic degradation analysis

Degradation behavior of the selected samples in PBS environment was analyzed and their results are presented in Figure 15. In these results, it can be seen that all samples have a declining behavior because all materials are biodegradable. Due to this behavior, the presence of TPU in PLA increases the mass loss rate of samples. Also, the addition of HA nanoparticles increases the amount of mass loss over time. These results can be attributed to the increased interactions between water molecules and the polymerized surface of the scafolds.

Figure 15

Hydrocatalytical degradation process of the selected samples.

4 Conclusion

In this research, biocompatible polymer nanocomposites based on PLA, TPU, and n-HA were prepared by solution method. Therefore, to test the properties of the prepared samples, various tests such as SEM, Mapping, TGA, DSC, and DMTA were used. The results of SEM analysis showed that the morphology of the prepared samples is highly incompatible, and the presence of nanoparticles can cause relative compatibility. Mapping test showed that the dispersion of nanoparticles in the matrix is suitable and the presence of TPU can be more effective in better dispersion of nanoparticles. TGA test also showed that in samples with lower TPU, lower amount of n-HA had a positive effect on the thermal degradation process and in samples with higher TPU, higher nanoparticles had a better effect on TGA diagram. DSC test also showed that the crystallization in the samples decreased with the presence of TPU, and n-HA had a positive effect on reducing the crystallization temperature in the samples. On the other hand, changes in the viscoelastic behavior of the samples were performed using DMTA test and the results showed that the presence of TPU reduces the storage modulus of the samples, and the presence of nanoparticles could partially compensate for the loss in the samples’ modulus. Also, based on the results of tan δ, it was found that the glass transition temperature for the samples decreases with the increase in the amount of TPU, and increases with the presence of nanoparticles, which is due to the restriction in the movement of polymer macromolecules. The tensile test results showed that the presence of n-HA has a huge impact on the tensile and modulus of the studied samples. Dynamic contact angle analysis using water and DMF solvent showed that the existence of TPU and n-HA led to major changes on the interaction surface of the scaffolds and these analyses are very prominent for PLA70TPU30 and its nanocomposites. MTT analysis performed on PLA90TPU10, PLA70TPU30, PLA90TPU10H5, and PLA70TPU30H5 samples showed that cell viability is suitable on the surface of PLA90TPU10H5 and PLA70TPU30H5 samples. SEM cell interaction analysis showed that the surface of PLA90TPU10H5 and PLA70TPU30H5 samples are very good for the preparation of bone tissue scaffolds. Our findings indicated that the addition of n-HA into PLA/TPU blends could impart new features to the PLA matrix as a promising candidate for bone, cartilage, and tendon tissue engineering. Moreover, these novel nanocomposites can be used for other tissue regenerations and still more studies can be done on these developed systems.

Funding information: Authors state no funding involved.
Author contributions: Vahid Faghihi-Rezaei: software, visualization, writing – original draft, conceptualization, validation, formal analysis, and investigation; Hossein Ali Khonakdar: conceptualization, validation, investigation, resources, and writing – review and editing; Vahabodin Goodarzi: conceptualization, validation, formal analysis, and investigation; Goldis Darbemamieh: software, visualization, writing, resources, conceptualization, validation, formal analysis, and investigation; Maryam Otadi: software, data curation, methodology, visualization, and investigation.
Conflict of interest: Authors state no conflict of interest.
Data availability statement: The data that support the findings of this study are available from the corresponding author upon reasonable request.

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Received: 2022-07-16

Revised: 2022-09-28

Accepted: 2022-10-05

Published Online: 2022-11-09

This work is licensed under the Creative Commons Attribution 4.0 International License.

Articles in the same Issue

https://doi.org/10.1515/gps-2022-0087

Keywords for this article

biodegradable; nanocomposite; polylactic acid; hydroxyapatite nanoparticles

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