Design and fabrication of tubular scaffolds via direct writing in a melt electrospinning mode

Flexible tubular structures fabricated from solution electrospun fibers are finding increasing use in tissue engineering applications. However it is difficult to control the deposition of fibers due to the chaotic nature of the solution electrospinning jet. By using non-conductive polymer melts instead of polymer solutions the path and collection of the fiber becomes predictable. In this work we demonstrate the melt electrospinning of polycaprolactone in a direct writing mode onto a rotating cylinder. This allows the design and fabrication of tubes using 20 μm diameter fibers with controllable micropatterns and mechanical properties. A key design parameter is the fiber winding angle, where it allows control over scaffold pore morphology (e.g. size, shape, number and porosity). Furthermore, the establishment of a finite element model as a predictive design tool is validated against mechanical testing results of melt electrospun tubes to show that a lesser winding angle provides improved mechanical response to uniaxial tension and compression. In addition, we show that melt electrospun tubes support the growth of three different cell types in vitro and are therefore promising scaffolds for tissue engineering applications.     

Preparation and characterization of blended <Emphasis Type="Italic">Bombyx mori</Emphasis> silk fibroin scaffolds

The aim of this study was to compare physical, mechanical and biological properties of 3-dimensional scaffolds prepared from Bombyx mori silk fibroin (SF), fibroin blended with collagen (SF/C), and fibroin blended with gelatin (SF/G) using a freeze-drying technique. The prepared scaffolds were sponge-like structure that exhibited homogeneous porosity with highly interconnected pores. Average pore size of these scaffolds ranged from 65–147 μm. All biodegradable scaffolds were capable of water absorption of 90 %. The degradation behavior of these scaffolds could be controlled by varying the amount of blended polymer. The SF/C and SF/G scaffolds showed higher compressive modulus than that of SF scaffolds which could be attributed to the thicker pore wall observed in the blended constructs. The less crystalline SF structure was observed in SF/G scaffolds as compared to SF/C scaffolds. Thus, the highest compressive modulus was observed on SF/C matrix. To investigate the feasibility of the scaffolds for cartilage tissue engineering application, rat articular chondrocytes were seeded onto the scaffolds. The MTT assay demonstrated that blending collagen or gelatin into SF sponge facilitated cell attachment and proliferation better than SF scaffolds. The blended SF scaffolds possessed superior physical, mechanical and biological properties in comparison to SF scaffolds and showed high potential for application in cartilage tissue engineering.     

Electrospinning of fucoidan/chitosan/poly(vinyl alcohol) scaffolds for vascular tissue engineering

The formation of thrombosis has limited the applications of small diameter vascular in cardiovascular diseases. In order to improve the anticoagulant activities of scaffolds, this study combined fucoidan with CS/PVA and investigated the complete physicochemical and mechanical characterization of the scaffolds to evaluate the feasibility of Fucoidan/CS/PVA scaffolds used in vascular tissue engineering. The SEM graphs show a well defined and interconnected pore structure and the nanofiber diameters are ranging from 341 nm to 482 nm. After immersing in PBS for 5 days, the tensile strength of the crosslinked scaffolds was 722±38 kPa while the elongation at break was 35.5±1.6 %. Besides, added with fucoidan, the scafflolds showed lower rate of plate adhesion (14.75±2.10 %) and markedly prolonged the APTT and TT. Furthermore, owing to the great water uptake ability, sufficient porosity, enhanced drug release and low cytotoxicity, the Fucoidan/CS/PVA scaffolds might be used for vascular tissue engineering with good prospect.     

Influences of Molecular Weights on Physicochemical and Biological Properties of Collagen-Alginate Scaffolds

For tissue engineering applications, biodegradable scaffolds containing high molecular weights (MW) of collagen and sodium alginate have been developed and characterized. However, the properties of low MW collagen-based scaffolds have not been studied in previous research. This work examined the distinctive properties of low MW collagen-based scaffolds with alginate unmodified and modified by subcritical water. Besides, we developed a facile method to cross-link water-soluble scaffolds using glutaraldehyde in an aqueous ethanol solution. The prepared cross-linked scaffolds showed good structural properties with high porosity (~93%) and high cross-linking degree (50–60%). Compared with collagen (6000 Da)-based scaffolds, collagen (25,000 Da)-based scaffolds exhibited higher stability against collagenase degradation and lower weight loss in phosphate buffer pH 7.4. Collagen (25,000 Da)-based scaffolds with modified alginate tended to improve antioxidant capacity compared with scaffolds containing unmodified alginate. Interestingly, in vitro coagulant activity assay demonstrated that collagen (25,000 Da)-based scaffolds with modified alginate (C25-A63 and C25-A21) significantly reduced the clotting time of human plasma compared with scaffolds consisting of unmodified alginate. Although some further investigations need to be done, collagen (25,000 Da)-based scaffolds with modified alginate should be considered as a potential candidate for tissue engineering applications.     

Chitosan composites for bone tissue engineering--an overview

Bone contains considerable amounts of minerals and proteins. Hydroxyapatite [Ca₁₀(PO₄)₆(OH)₂] is one of the most stable forms of calcium phosphate and it occurs in bones as major component (60 to 65%), along with other materials including collagen, chondroitin sulfate, keratin sulfate and lipids. In recent years, significant progress has been made in organ transplantation, surgical reconstruction and the use of artificial protheses to treat the loss or failure of an organ or bone tissue. Chitosan has played a major role in bone tissue engineering over the last two decades, being a natural polymer obtained from chitin, which forms a major component of crustacean exoskeleton. In recent years, considerable attention has been given to chitosan composite materials and their applications in the field of bone tissue engineering due to its minimal foreign body reactions, an intrinsic antibacterial nature, biocompatibility, biodegradability, and the ability to be molded into various geometries and forms such as porous structures, suitable for cell ingrowth and osteoconduction. The composite of chitosan including hydroxyapatite is very popular because of the biodegradability and biocompatibility in nature. Recently, grafted chitosan natural polymer with carbon nanotubes has been incorporated to increase the mechanical strength of these composites. Chitosan composites are thus emerging as potential materials for artificial bone and bone regeneration in tissue engineering. Herein, the preparation, mechanical properties, chemical interactions and in vitro activity of chitosan composites for bone tissue engineering will be discussed.     

Functionalizing cellulose scaffold prepared by ionic liquid with bovine serum albumin for biomedical application

The present study reports the preparation of a cellulose scaffold for tissue engineering directly from cellulose fiber using ionic liquid (IL) by the NaCl leaching method with bovine serum albumin (BSA), which is well known protein utilized for biomedical applications like degradation of polymer, cell attachment and proliferation on scaffold. The 1-n-allyl-3-methylimidazolium chloride (AmimCl) IL was used as a solvent for cellulose. The morphology of the scaffold was studied by scanning electron microscopy (SEM) and the images showed that the pore sizes of the scaffolds were about 200 µm. In addition, the water uptake (WU) and degree of degradation of the cellulose scaffold were measured. Meanwhile, the biocompatibility and bioactivity of the scaffold were determined via 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenytetrazolium bromide (MTT) assay and the Live/Dead viability test. The various results demonstrated the ability of the Mesenchymal stem cells (MSC) to attach to the surface of the scaffolds amplified as percentage of BSA increased in cellulose scaffold.     

Electrospinning and mechanical properties of polymeric fibers using a novel gap-spinning collector

Tissue engineering is an interdisciplinary field which combines the basic principles of life sciences and engineering. One promising idea is the combination of scaffolds and living cells in order to produce new functional tissue. The scaffolds play the role of a microenvironment that guides the cells towards tissue formation and regeneration. One of the most frequently used techniques to produce scaffolds is electrospinning. Tissue engineered constructs have to exhibit physiological and mechanical properties comparable to the native tissue they are intended to replace. To create polymeric fibers with controlled orientation, a cylindrical collector that rotates at a certain speed could be used, creating fibers that run longitudinally. The process of gap-spinning enables the production of specifically aligned fibers. Aim of this study was to develop a novel setup capable of producing multilayered structures with controlled fiber angle. The structural, morphological and mechanical characteristics of the fibers were accessed using scanning electron microscopy and uniaxial tensile tests. Longer pre-stretching led to thinner (in the sub-micron scale), more brittle and less elastic fibers. In a nutshell, the results indicated that fiber mats of desired orientation, fiber diameter and mechanical properties could be produced by controlled gap-spinning with a translational collector.     

Model membrane platforms for biomedicine: case study on antiviral drug development

As one of the most important interfaces in cellular systems, biological membranes have essential functions in many activities such as cellular protection and signaling. Beyond their direct functions, they also serve as scaffolds to support the association of proteins involved in structural support, adhesion, and transport. Unfortunately, biological processes sometimes malfunction and require therapeutic intervention. For those processes which occur within or upon membranes, it is oftentimes difficult to study the mechanism in a biologically relevant, membranous environment. Therefore, the identification of direct therapeutic targets is challenging. In order to overcome this barrier, engineering strategies offer a new approach to interrogate biological activities at membrane interfaces by analyzing them through the principles of the interfacial sciences. Since membranes are complex biological interfaces, the development of simplified model systems which mimic important properties of membranes can enable fundamental characterization of interaction parameters for such processes. We have selected the hepatitis C virus (HCV) as a model viral pathogen to demonstrate how model membrane platforms can aid antiviral drug discovery and development. Responsible for generating the genomic diversity that makes treating HCV infection so difficult, viral replication represents an ideal step in the virus life cycle for therapeutic intervention. To target HCV genome replication, the interaction of viral proteins with model membrane platforms has served as a useful strategy for target identification and characterization. In this review article, we demonstrate how engineering approaches have led to the discovery of a new functional activity encoded within the HCV nonstructural 5A protein. Specifically, its N-terminal amphipathic, α-helix (AH) can rupture lipid vesicles in a size-dependent manner. While this activity has a number of exciting biotechnology and biomedical applications, arguably the most promising one is in antiviral medicine. Based on the similarities between lipid vesicles and the lipid envelopes of virus particles, experimental findings from model membrane platforms led to the prediction that a range of medically important viruses might be susceptible to rupturing treatment with synthetic AH peptide. This hypothesis was tested and validated by molecular virology studies. Broad-spectrum antiviral activity of the AH peptide has been identified against HCV, HIV, herpes simplex virus, and dengue virus, and many more deadly pathogens. As a result, the AH peptide is the first in class of broad-spectrum, lipid envelope-rupturing antiviral agents, and has entered the drug pipeline. In summary, engineering strategies break down complex biological systems into simplified biomimetic models that recapitulate the most important parameters. This approach is particularly advantageous for membrane-associated biological processes because model membrane platforms provide more direct characterization of target interactions than is possible with other methods. Consequently, model membrane platforms hold great promise for solving important biomedical problems and speeding up the translation of biological knowledge into clinical applications.     

Chitosan-Based Scaffold for Mineralized Tissues Regeneration

Conventional bone grafting procedures used to treat bone defects have several limitations. An important aspect of bone tissue engineering is developing novel bone substitute biomaterials for bone grafts to repair orthopedic defects. Considerable attention has been given to chitosan, a natural biopolymer primarily extracted from crustacean shells, which offers desirable characteristics, such as being biocompatible, biodegradable, and osteoconductive. This review presents an overview of the chitosan-based biomaterials for bone tissue engineering (BTE). It covers the basic knowledge of chitosan in terms of biomaterials, the traditional and novel strategies of the chitosan scaffold fabrication process, and their advantages and disadvantages. Furthermore, this paper integrates the relevant contributions in giving a brief insight into the recent research development of chitosan-based scaffolds and their limitations in BTE. The last part of the review discusses the next-generation smart chitosan-based scaffold and current applications in regenerative dentistry and future directions in the field of mineralized tissue regeneration.     

Fabrication of Biocompatible PLGA/PCL/PANI Nanofibrous Scaffolds with Electrical Excitability

Application of electrospun nanofibrous scaffolds has received immense attention in tissue engineering. Fabrication of scaffolds with appropriate electrical properties plays a key role in neural tissue engineering. Since fibers orientation in the scaffolds affects the growth and proliferation of the cells, this study aimed to prepare aligned electrospun conductive nanofibers by mixing 1 %, 10 % and 18 % (w/v) doped polyaniline (PANI) with polycaprolactone (PCL)/poly lactic-coglycolic acid (PLGA) (25/75) solution through the electrospinning process. The fibers diameter, hydrophilicity and conductivity were measured. In addition, the shape and proliferation of the nerve cells seeded on fibers were evaluated by MTT cytotoxicity assay and scanning electron microscopy. The results revealed that the conductive nanofibrous scaffolds were appropriate substrates for the attachment and proliferation of nerve cells. The electrical stimulation enhanced neurite outgrowth compared to those PLGA/PCL/PANI scaffolds that were not subjected to electrical stimulation. As polyaniline ratio increases, electric stimulation through nanofibrous PLGA/PCL/PANI scaffolds results in cell proliferation enhancement. However, a raise more than 10 % in polyaniline will result in cell toxicity. It was concluded that conductive scaffolds with appropriate ratio of PANI along with electrical stimulation have potential applications in treatment of spinal cord injuries.     

The Effect of Melanocyte Stimulating Hormone and Hydroxyapatite on Osteogenesis in Pulp Stem Cells of Human Teeth Transferred into Polyester Scaffolds

Presently, tissue engineering is employed in the restoration and repair of tissue defects. Degradable scaffolds, stem cells and stimulating factors are employed in this method. In this study, the effect of melanocyte-stimulating hormone (MSH) and/or hydroxyapatite (HA) on proliferation, osteoblast differentiation, and mineralization of human dental pulp stem cells (hDPSCs) seeded on PLLA-PCL nanofibrous scaffolds was evaluated. For this aim, PLLA-PCL-HA nanofibrous scaffolds were fabricated using electrospinning method. FE-SEM images exhibited that all nanofibers had bead-free morphologies with average diameters ranging from 150–205 nm. Human DPSCs seeded into PLLA-PCL nanofibers were treated with MSH. Cell viability, proliferation, morphology, osteogenic potential, and the expression of tissue-specific genes were assessed by means of MTT assay, FE-SEM, alizarin red S staining, and RT-PCR analysis. hDPSCs exhibited improved adhesion and proliferation capacity on the PLLA-PCL-HA nanofibers treated with MSH compared to other groups (p<0.05). Additionally, PLLA-PCL-HA nanofibers treated with MSH exhibited significantly higher mineralization and alkaline phosphatase activity than other groups. RT-PCR results confirmed that PLLA-PCL-HA nanofibers enriched with MSH could significantly unregulated the gene expression of BMP2, osteocalcin, RUNX2 and DSPP that correlated to osteogenic differentiation (p<0.05). Based on results, incorporation of HA nanoparticles in PLLA-PCL nanofibers and addition of MSH in media exhibited synergistic effects on the adhesion, proliferation, and osteogenesis differentiation of hDPSCs, and therefore assumed to be a favorable scaffold for bone tissue engineering applications.     

Evaluation of procedures to quantify solvent retention in electrospun fibers and facilitate solvent removal

Electrospun fiber scaffolds crafted from polyesters are studied extensively for potential tissue engineering applications. For translation of electrospun fibers into the clinic, the FDA requires analysis and quantification of any organic solvent that may be retained in the fibers since many organic solvents can negatively affect cells and tissues. If a significant amount of solvent is retained, then developing procedures for efficient solvent removal may enhance the clinical potential of these materials. In this study we use fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), and nuclear magnetic resonance spectroscopy (NMR) to analyze solvent retention. A correlative analysis shows that both FTIR and TGA accurately predicted retention of two different solvents (HFP and chloroform) in our electrospun PLLA scaffolds, thus validating these procedures. We also assess the efficacy of various fiber treatment methods to facilitate organic solvent removal and conclude that submersion in 70 % ethanol and heat treatment at 100 °C were the most efficient methods of removing solvent from electrospun PLLA fibers.     

Electrospun PU-PEG and PU-PC hybrid scaffolds for vascular tissue engineering

Produced via electrospinning, polyurethane (PU) scaffolds have always attracted the interest of medical applications due of their unique properties such as good adhesion, biocompatibility and excellent mechanical strength. However, the poor hydrophilicity and hemocompatibility of PU presented a problem during PU’s application in the manufacturing of biomedical materials. We hypothesized that the incorporation of polyethylene glycol (PEG) and phosphatidylcholine (PC) into electrospinning solution of PU could improve the cell affinity and hemocompatibility. This research focused on fabricating hybrid PU-PEG and PU-PC random/aligned scaffolds through electrospinning technique and comparing their properties as a potential biocompatible scaffold for vascular tissue engineering. PC was doped into a PU solution in order to prepare an electrospun scaffold through the electrospinning technology while crosslinked electrospun PUPEG hybrid scaffolds were fabricated by photoinduced polymerization. The contact angle dramatically decreased from 122.3±0.8° to 39.1±0.8° with doping of PC in electrospinning solution while it decreased from 122.3±0.8° to 41.6±0.8° with doping of PEG. Furthermore, the mechanical properties of PU scaffolds were altered significantly by the addition of PC. The hemolysis and cytocompatibility assays demonstrated that these composite scaffolds could potentially be used as a smalldiameter vascular graft.     

Marine Biopolymers as Bioactive Functional Ingredients of Electrospun Nanofibrous Scaffolds for Biomedical Applications

Marine biopolymers, abundantly present in seaweeds and marine animals, feature diverse structures and functionalities, and possess a wide range of beneficial biological activities. Characterized by high biocompatibility and biodegradability, as well as unique physicochemical properties, marine biopolymers are attracting a constantly increasing interest for the development of advanced systems for applications in the biomedical field. The development of electrospinning offers an innovative technological platform for the production of nonwoven nanofibrous scaffolds with increased surface area, high encapsulation efficacy, intrinsic interconnectivity, and structural analogy to the natural extracellular matrix. Marine biopolymer-based electrospun nanofibrous scaffolds with multifunctional characteristics and tunable mechanical properties now attract significant attention for biomedical applications, such as tissue engineering, drug delivery, and wound healing. The present review, covering the literature up to the end of 2021, highlights the advancements in the development of marine biopolymer-based electrospun nanofibers for their utilization as cell proliferation scaffolds, bioadhesives, release modifiers, and wound dressings.     

Fabrication and surface modification of melt-electrospun poly(D,L-lactic-co-glycolic acid) microfibers

In this study, biodegradable poly(D,L-lactic-co-glycolic acid) (PLGA) fibers were prepared by a melt-electrospinning and treated with plasma in the presence of either oxygen or ammonia gas to modify the surface of the fibers. The effects of processing parameters on the melt-electrospinning of PLGA were examined in terms of fiber morphology and diameter. Among the processing parameters, the spinning temperature and mass flow rate had a significant effect on the average fiber diameter and its distribution. The water contact angle of melt-electrospun PLGA fibers decreased significantly from 123 ° to 55 ° (oxygen plasma treatment) or to 0 ° (ammonia plasma treatment) by plasma treatment for 180 sec, while their water content increased significantly from 2.4 % to 123 % (oxygen plasma treatment) or to 189 % (ammonia plasma treatment). Ammonia gas-plasma enhanced the surface hydrophilicity of PLGA fibers more effectively compared to oxygen gas-plasma. X-ray photoelectron spectroscopy analysis supported that the number of polar groups, such as hydroxyl and amino groups, on the surface of PLGA fibers increased after plasma treatment. Overall, the microfibrous PLGA scaffolds with appropriate surface hydrophilicity and fiber diameter could be fabricated by melt electrospinning and subsequent plasma treatment, without a significant deterioration of fiber structure and dimensional stability. This approach of controlling the surface properties and structures of fibers could be useful in the design and tailoring of novel scaffolds for tissue engineering.     

Effects of PLGA nanofibrous scaffolds structure on nerve cell directional proliferation and morphology

Electrospinning has been recognized as an efficient technique for the fabrication of neural tissue engineering scaffolds. Many approaches have been developed on material optimization, electrospinning techniques, and physical properties of scaffolds to produce a suitable scaffold for tissue engineering aspects. In this study, structural properties of scaffolds were promoted by controlling the speed of fiber collection without any post-processing. PLGA scaffolds, in two significantly different solution concentrations, were fabricated by the electrospinning process to produce scaffolds with the optimum nerve cell growth in a desired direction. The minimum, intermediate and maximum rate of fiber collection (0.4, 2.4, 4.8 m/s) formed Random, Aligned and Drown-aligned fibers, with various porosities and hydrophilicities. The scaffolds were characterized by fiber diameter, porosity, water contact angle and morphology. Human nerve cells were cultured on fiber substrates for seven days to study the effects of different scaffold structures on cell morphology and proliferation, simultaneously. The results of MTT assay, the morphology of cells and scaffold characterization recommend that the best structure to promote cell direction, morphology and proliferation is accessible in an optimized hydrophilicity and porosity of scaffolds, which was obtained at the collector linear speed of 2.4 m/s.     

Self-assembled peptides: characterisation and in vivo response

The fabrication of tissue engineering scaffolds is a well-established field that has gained recent prominence for the in vivo repair of a variety of tissue types. Recently, increasing levels of sophistication have been engineered into adjuvant scaffolds facilitating the concomitant presentation of a variety of stimuli (both physical and biochemical) to create a range of favourable cellular microenvironments. It is here that self-assembling peptide scaffolds have shown considerable promise as functional biomaterials, as they are not only formed from peptides that are physiologically relevant, but through molecular recognition can offer synergy between the presentation of biochemical and physio-chemical cues. This is achieved through the utilisation of a unique, highly ordered, nano- to microscale 3-D morphology to deliver mechanical and topographical properties to improve, augment or replace physiological function. Here, we will review the structures and forces underpinning the formation of self-assembling scaffolds, and their application in vivo for a variety of tissue types.     

Uniaxially well-aligned nanofiber arrays fabricated by electrospinning with a stable and low moving velocity jet

Aligned fibers in micro-/nano-scale have attracted more attention especially in tissue engineering field because cells can orientation growth along the fiber. However, it is still a huge technological challenge in achieving it as a result of the inherent bending instability of an electrospinning jet. Herein, we report a novel and simple spinning approach, in which low dielectric constant of dioxane was judiciously used as solvent for spinning dope, to obtain electrospinning jet with low induced charge, therefore eliminating electrically and aerodynamically driven bending instability, and forming a stable and low forward-moving velocity jet longer than 100 cm. This consequently allows for readily collecting and fabricating individual fibers, well-aligned ultrafine fiber arrays over large areas. Our approach has proved to be effective in preparing well-aligned ultrafine fibers from biodegradable poly(D, L-lactic acid) with different molecular mass, natural polymer acetyl cellulose and synthesized non-biodegradable polymer polystyrene.     

Ultrasound-mediated preparation and evaluation of a collagen/PVP-PCL micro- and nanofiber scaffold electrospun from chloroform/ethanol mixture

In this study, to improve the cellular biocompatibility of PVP-PCL micro- and nanofiber scaffold, a novel electrospun collagen/PVP-PCL micro- and nanofiber scaffold was sucessfully prepared assisted by ultrasonic irradiation using chloroform/ethanol mixtures as solvent. The micro- and nanofibers of the electrospun PCL-PVP scaffolds still presented compact inter-fiber entanglement and three-dimensional netlike network with some certain range of pore space after introducing collagen. The incorporated collagen phase was dispersed as inclusions within the electrospun fibers, and then could be easily released by immersing the scaffold in Hanks simulated body fluid. Meanwhile, the integral triple helix structure of collagen could be maintained after blending with the PVP-PCL mixture due to the weak intermolecular interactions. Furthermore, the suitable mechanical and degradation properties of the PVP-PCL scaffold were still reserved after introducing collagen, and the introduction of collagen could further promote the thermostability of the PVP-PCL scaffold. Above all, the collagen/PVP-PCL scaffold showed no cytotoxicity, better cell proliferation, and improved viability of primary fibroblasts than the PVP-PCL scaffold. In conclusion, blending collagen with the PVP-PCL mixture in this study has potential for promoting the biocompatibility of PVP-PCL micro- and nanofiber scaffolds for tissue engineering.     

Molecular dynamics simulation of the adsorption of polymer chains on CNTs,BNNTs and GaNNTs

Molecular dynamics simulations are used here to study the adsorption of polymer chains on the nanotube surface. Considering three nanotubes, including carbon, boron nitride and gallium nitride nanotubes, the effect of nanotube types on the polymer/nanotube interactions are investigated. Aramid, poly(phenylene sulfide), poly(phenylene oxide) and polycarbonate are selected as the polymer chains. It is seen that the π-stacking of these polymer chains results in large interaction energy between the nanotubes and polymer chains. Comparing the interaction energies between different polymer chains and nanotubes, it is shown that boron nitride nanotubes can reinforce polymer matrices more effectively than carbon and gallium nitride nanotubes. Besides, the effect of temperature on the polymer/nanotube interaction is studied. It is shown that the polymer chains have more expanded shapes at larger temperature which leads to more π-π interactions and larger interaction energies.