Materials Today Communications
Volume 16, September 2018, Pages 264-273
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Hybrid electrospun fibers based on TPU-PDMS and spherical nanohydroxyapatite for bone tissue engineering

https://doi.org/10.1016/j.mtcomm.2018.06.013Get rights and content

Highlights

  • Novel electrospun scaffolds based on TPU-PDMS blend and spherical nanohydroxyapatite.

  • Scaffolds reveal superior physico-mechanical and biological properties with nanohydroxyapatite addition.

  • Hybrid biomaterial suitable for orthopedic tissue interfaces.

Abstract

The present work deals with the preparation and characterization of hybrid electrospun fibres of thermoplastic polyurethane/polydimethylsiloxane (TPU-PDMS) and spherical nanohydroxyapatite (nHap) for bone tissue engineering applications. The fiber morphology with interconnected pore network, hydrophilicity, and mechanical properties of electrospun compatibilized blends were markedly influenced by the presence of nHap. The nHap based nanocomposites showed improvement in static and dynamical mechanical properties. Furthermore, the tensile strength was increased by 150% with the addition of 5 wt% of nHap in TPU-PDMS blend due to its superior morphology. The enhancement in the dispersion of nHap in TPU-PDMS blend matrix even at higher concentration was confirmed by FESEM, and Micro-CT analysis. Morphology of MTT (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide) assay using human osteoblast-like cells (MG-63) proved all the scaffolds were non-cytotoxic. The TPU-PDMS scaffold with 5 wt% nHap showed the best performance regarding the cell viability, SBF bioactivity and hemocompatibility which makes its applicability in the fabrication of living bony constructs, especially for bone tissue interfaces.

Introduction

Electrospinning is an emerging technique that allows fabrication of fibrous scaffolds with well-defined architecture, controlled pore size, fiber diameter and topography which favors cell growth and closely resembles the in vivo like architecture of the extracellular matrix [1]. Numerous natural, as well as the synthetic polymers have been electrospun into fibrous scaffold for various tissue engineering applications. Tissue engineering evolved as a promising approach for restoring the damaged tissue and organ [2]. The attractive features of electrospinning is the capability to produce a wide range of fiber morphologies by controlling various material and process parameters [[3], [4], [5], [6], [7]].

The search for biomaterials is always welcomed in the material world due to its unique features to utilize as implants. Among those, biodegradable material follows a time-dependent sacrificial approach, bioactive materials like bioglass and hydroxyapatite reveals an enhanced activity towards the cell growth and biostable materials act as a stable support for the tissues [[8], [9], [10], [11], [12], [13], [14], [15]]. Much attempt has been invested in the progress of biomaterials for the repair or replacement of hard tissue. Because of the excellent biocompatibility and bioactivity of the bioceramics, they have been successfully used for hard tissue replacement. Among the bioactive ceramics, synthetic hydroxyapatite with the chemical composition of Ca10(PO4)6(OH)2 has been broadly studied as the bone replacement material [[16], [17], [18]]. Since polymers are the most extensively used alloplastic materials and have applications in both bone and soft-tissue reconstruction and augmentation, by the effective utilization of biocompatible polymers as matrices for the nanohydroxyapatite, we can attain a better medium to deliver nanohydroxyapatite. The most suitable way of achieving this is through blend polymers so that it possesses synergistic features.

Thermoplastic polyurethane (TPU) and polydimethylsiloxane (PDMS) elastomers have been tried as the best combination for various biostable applications in the biomedical field [4,[19], [20], [21], [22], [23]]. Due to the excellent physico-mechanical properties and biocompatibility of TPU, it is widely accepted for biomedical applications [4,[24], [25], [26]]. Polydimethylsiloxane (PDMS) elastomers are considered as the best biocompatible synthetic polymers because of its excellent biostability, biocompatibility, physiological inertness, higher temperature resistance, and oxidative stability. The nanocomposites of TPU-PDMS blend matrix based on nanohydroxyapatite were previously introduced by solvent casting technique [27]. The selection of individual blend matrices with improved properties along with its synergy drives the blends suitable for this particular function. Since TPU and PDMS are immiscible, compatibilization is essential for avoiding phase separation. The compatibilization of TPU and PDMS using EMA as compatibilizer was previously studied by our group and optimized at different blend ratios by solution mixing and melt mixing technique [28]. The selection of processing technique is crucial here while considering the biomechanical properties. For tissue engineering application, electrospinning technique was most preferred while considering the physical parameters such as porosity which drives the cell growth [29]. Even though the TPU has a strong history in electrospinning application, PDMS is a novel material to this field. Electrospinning of PDMS is a big challenge due to its lower molecular weight and uncrosslinked state. This can be solved by using the compatibilized blend solution. The TPU–PDMS compatibilized blend was previously reported with its better biocompatibility as compared to pristine TPU even with very low proportion of PDMS [19].

The aim of the study is to introduce nHap particles in a biostable medium fabricated for the easier delivery of nHap particles to regenerate the damaged tissues. In this work, the nHap based TPU-PDMS compatibilized blend nanocomposites prepared by electrospinning technique were used, which can offer unique performance in orthopedic tissue interfaces especially in the osteo-chondral interfaces. Due to the presence of soft PDMS, flexible TPU and osteoconductive nanohydroxyapatite, it can mimic the structure and function of soft-to-hard tissue junctions of bone-cartilage interfaces.

Section snippets

Materials

The medical grade Thermoplastic Polyurethane, TEXIN RxT85 A, with number average molecular weight Mn 80,000 was provided by Bayer Material Science, India. PDMS, a liquid grade silicone rubber was supplied by Momentive Specialty Chemicals Inc. (India). Ethylene-methyl acrylate copolymer (EMA), OPTEMA TC-120 was procured from M/s Exxon Chemicals Inc. USA. Solvent Tetrahydrofuran (THF) of analytical grades was supplied by Merck, Germany. Calcium nitrate (Ca(NO3)2.4H2O), diammonium hydrogen

Scaffold characterization

For analyzing the morphology of the original scaffolds as well as the scaffolds after 3 and 7 days of cell culture, a FESEM (Field Emission Scanning Electron Microscope, MERLIN with Tungsten filament; Carl ZEISS, SMT, Germany) with the accelerating voltage set to 15 kV was utilized. The elemental mapping was also carried out using FESEM of simulated body fluid (SBF) immersed scaffolds for apatite growth confirmation. Microcomputed Tomography (GE Phoenix Vtomex-s) was used for porosity

Field emission scanning electron microscopy (FESEM)

The challenge of electrospinning of PDMS based matrix was overcome using the compatibilization effect of EMA in TPU-PDMS matrix. The TPU-PDMS blend and the nanocomposites exhibited a non-uniform porous beaded architecture and the morphology of T70P30 blend and its nanocomposite at 5 wt% were given in Fig. 1. The porous beads were formed due to the combined effect of the difference in extensibility of individual polymer chains and the difference in volatility of the solvent from polymer chains

Summary and conclusion

In summary, electrospun fibrous scaffolds using TPU-PDMS compatibilized blend and its nanocomposites based on nHap were fabricated and characterized for their physical and biological properties. The scaffolds exhibited porous beaded morphology with interconnected pore network with nHap incorporation. The addition of osteoconductive nHap significantly improved the overall mechanical properties and cell response of the scaffolds. The in vitro bioactivity using SBF depicted that the nanocomposites

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