Thermo‐responsive polyurethane hydrogels based on poly(ethylene glycol) and poly(caprolactone): Physico‐chemical and mechanical properties

In this work, we present the synthesis and characterization of chemically crosslinked polyurethanes (PU) composed of poly(ethylene glycol) (PEG) and poly(caprolactone) diol (PCL‐diol), as hydrophilic and hydrophobic segments respectively, poly(caprolactone) triol (PCL‐triol), to induce hydrolysable crosslinks, and hexamethylene diisocyanate (HDI). The syntheses were performed at 45 °C, resulting in polyurethanes with different PEG/PCL‐diol/PCL‐triol mass fractions. All the PUs are able to crystallize and their thermal properties depend on the global composition. The water uptake capacities of the PU increase as the PEG amount increases. The water into hydrogels is present in different environments, as bounded, bulk and free water. The PU hydrogels are thermo‐responsive, presenting a negative dependence of the water uptake with the temperature for PEG rich networks, which gradually changes to a positive behavior as the amount of poly(caprolactone) (PCL) segments increases. However, the water uptake capacity changes continuously without an abrupt transition. Scanning electron microscopy (SEM) analyses of the hydrogel morphology after lyophilization revealed a porous structure. Mechanical compression tests revealed that the hydrogels present good resilience and low recovery hysteresis when they are subject to cycles of compression–decompression. In addition, the mechanical properties of the hydrogels varies with the composition and crosslinking density, and therefore with the water uptake capacity. The PU properties can be tuned to fit for different applications, such as biomedical applications. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43573.     

可注射nHA/PU复合多孔骨修复支架制备及表征

兼具良好孔隙率和原位任意塑形固化的可注射复合多孔骨修复材料在临床不规则骨缺损的治疗方面显示出巨大的优势。本研究通过优化双组分设计,以水为发泡剂制备可注射纳米羟基磷灰石/聚氨酯（nHA/PU）复合多孔支架。利用扫描电子显微镜（SEM）、傅里叶变换红外光谱（FTIR）、X射线衍射（XRD）、力学测试及Gillmore针测试等手段对制备的支架进行结构形貌、化学组成、力学性能和固化时间表征。结果表明,本研究制备的可注射nHA/PU复合多孔支架孔隙率高、孔隙贯通性好,孔径分布在100~700μm,适宜细胞和组织向孔内生长;添加20% nHA显著提高了PU支架的力学强度,但降低了支架的孔隙率;可注射支架在8h固化,适宜临床操作。本研究制备的可注射nHA/PU复合多孔支架在不规则骨缺损修复领域具有较大的应用潜力。     

Properties of some cast polyurethane rubbers prepared from poly-ε-caprolactone polyols and diisocyanates

Polyurethanes were prepared by a one-step method from poly-ε-caprolactone (PCL) diols, diisocyanates, and a triol crosslinking agent (either PCL triol or trimethylolpropane). The influence of composition on mechanical properties was examined. In some formulations the elastomeric properties were lost by crystallization of the PCL segments. The occurrence and rate of crystallization were influenced by the composition and factors such as hydrolytic degradation and oil swelling. In one series of polymers the susceptibility to crystallization could be predicted from the composition. These materials showed melting and glass transitions when examined by differential scanning calorimetry and thermomechanical analysis. The molecular weight of the PCL diol had a greater influence on the glass transition temperature than the diol concentration.     

Three​-dimensional porous poly(ε-caprolactone)/beta-tricalcium phosphate microsphere-aggregated scaffold for bone tissue engineering

In this study, porous scaffolds made of polycaprolactone (PCL)/β-tricalcium phosphate (BTCP) biocomposite were fabricated for bone tissue engineering (BTE) applications. The microsphere-aggregated scaffolds were prepared with various BTCP concentrations (10wt%, 20wt%, 50wt%) by the freeze-drying method. The porosity of obtained microsphere-aggregated scaffolds with various pore sizes was 80–85%, where this value was about 70% for the PCL/BTCP (50) sample with no microsphere formation. The results indicated that adding BTCP has enhanced mechanical strength, and the mineralization of PCL/BTCP composite scaffolds has been increased compared to the pure PCL scaffolds in simulated body fluid (SBF). The adhesion and proliferation of mouse bone marrow mesenchymal stem cells (mMSCs) seeded onto PCL/BTCP scaffolds were enhanced compared to the PCL. In addition, in terms of differentiation, the incorporation of BTCP led to increasing the mineral deposition and alkaline phosphatase activity of mMSCs. The synergistic effect of using microsphere-aggregated scaffolds along with BTCP as a reinforcing agent in PCL biocomposite showed that these porous biocomposite scaffolds have the potential application in BTE.     

Polyurethane toughened polylactide

Summary Brittle polylactide (PLA) was toughened by introducing 5 wt % of a poly(ɛ-caprolactone)(PCL) diol- and triol-based polyurethane (PU) network. The extent of cross-linking of the PU was varied by changing the ratio between diol and triol. The effects of the PU content and its crosslink density on the mechanical properties and the toughness of PU/PLA blends were investigated. Maximum toughness of PU/PLA blends, an order of magnitute higher than that of pure PLA, could be achieved by the use of a proper amount of PU and a proper extent of cross-linking. Received: 17 September 1997/Revised version: 15 December 1997/Accepted: 17 December 1997     

Production, mechanical properties and in vitro biocompatibility of highly aligned porous poly(ε-caprolactone) (PCL)/hydroxyapatite (HA) scaffolds

We produced highly aligned porous poly(ε-caprolactone) (PCL)/hydroxyapatite (HA) scaffolds by unidirectionally freezing PCL/HA solutions with various HA contents (0, 5, 10 and 20 wt% in relation to the PCL polymer) and evaluated their mechanical properties and in vitro biocompatibility to examine their potential applications in bone tissue engineering. All the prepared scaffolds had a highly aligned porous structure, in which the HA particles were uniformly dispersed in the PCL walls. The elastic modulus of the PCL/HA scaffolds significantly increased from 0.12 ± 0.02 to 2.65 ± 0.05 MPa with increasing initial HA content from 0 to 20 wt%, whereas the pore size decreased from 9.2 ± 0.7 to 4.2 ± 0.8 μm. In addition, the PCL/HA scaffolds showed considerably enhanced in vitro cellular responses that were assessed in terms of cell attachment, proliferation and osteoblastic differentiation.     

β-TCP scaffold coated with PCL as biodegradable materials for dental applications

Requirements for an ideal scaffold include biocompatibility, biodegradability, mechanical strength and sufficient porosity and pore dimensions. Beta tricalcium phosphate (β-TCP) has competent biocompatibility and biodegradability, but has low mechanical strength because of its porous structure. Polycaprolactone (PCL) is a biodegradable polymer with elastic characteristics and good biocompatibility. In this study, β-TCP/PCL composites were prepared in different ratio and their morphology, phase content, mechanical properties, biodegradation and biocompatibility were investigated. After coating, surfaces of β-TCP scaffolds were covered with the PCL while some of the pores were partially clogged. The compression and bending strength of β-TCP scaffolds were significantly enhanced by PCL coating. The degradation rate of the scaffold in Tris buffer was reduced with higher content of the PCL coating. MTT and ALP assays showed that the osteoblast cells could proliferate and differentiate on PCL coated scaffolds as well as on bare β-TCP scaffolds. Based on the comprehensive analysis achieved in this study, it is concluded that the β-TCP/PCL composite scaffold fabricated with 40% β-TCP and 5% PCL exhibits optimum properties suitable for dental applications.     

Effect of hexagonal structure nanoparticles on the morphological performance of the ceramic scaffold using analytical oscillation response

Porous bony scaffolds are utilized to manage the growth and migration of cells from adjacent tissues to a defective position. In the current investigation, the effect of titanium oxide (TiO₂) nanoparticles on mechanical and physical properties of porous bony implants made of polymeric polycaprolactone (PCL) is studied. The bio-nanocomposite scaffolds are prepared with composition of nanocrystalline hydroxyapatite (HA) and TiO₂ powder using the freeze-drying technique for different weight fractions of TiO₂ (0 wt%, 5 wt%, 10 wt%, and 15 wt%). In order to identify the microstructure and morphology of the fabricated porous bio-nanocomposites, the X-ray diffraction (XRD), atomic force microscope (AFM) and scanning electron microscopy (SEM) are employed. Also, the biocompatibility and biodegradability of the manufactured scaffolds are examined by placing them in a simulated body fluid (SBF) for 21 days, their weight and pH changes are measured. The rate of degradation of the PCL-HA scaffold can be controlled by varying the percentage of its constituent components. Due to an increasing growth and activity of bone cells and the apatite formation on the free surface of the fabricated bio-nanocomposite implants as well as their reasonable mechanical properties, they have the potential to be used as a bone substitute. Additionally, with the aid of the experimentally extracted mechanical properties of the scaffolds, the vibrational characteristics of a beam-type implant made of the proposed porous bio-nanocomposites are explored. The results obtained from SEM image indicate that the scaffolds produced by the employed method have high total porosity (70%–85%) and effective porosity. The pore size is obtained between 60 and 200 μm, which is desirable for the growth and propagation of bone cells. Also, it is revealed that the addition of TiO₂ nanoparticles leads to reduce the rate of dissolution of the fabricated bio-nanocomposite scaffolds.     

飞机用不干性聚氨酯密封腻子的研制

以聚醚型聚氨酯树脂为基质制备了不平性密封腻子，讨论了不同原料及用量对树脂性能的影响。制备合适聚氨醋树脂的条件是：聚醚二醇与聚醚三醇结合使用（量比1：1），扩链剂乙二醇与聚醚的量比为0．5：1，异氰酸酯指数0．90。     

Ex Vivo and In Vivo Analyses of Novel 3D-Printed Bone Substitute Scaffolds Incorporating Biphasic Calcium Phosphate Granules for Bone Regeneration

(1) Background: The aim of this study was examining the ex vivo and in vivo properties of a composite made from polycaprolactone (PCL) and biphasic calcium phosphate (BCP) (synprint, ScientiFY GmbH) fabricated via fused deposition modelling (FDM); (2) Methods: Scaffolds were tested ex vivo for their mechanical properties using porous and solid designs. Subcutaneous implantation model analyzed the biocompatibility of PCL + BCP and PCL scaffolds. Calvaria implantation model analyzed the osteoconductive properties of PCL and PCL + BCP scaffolds compared to BCP as control group. Established histological, histopathological and histomorphometrical methods were performed to evaluate new bone formation.; (3) Results Mechanical testing demonstrated no significant differences between PCL and PCL + BCP for both designs. Similar biocompatibility was observed subcutaneously for PCL and PCL + BCP scaffolds. In the calvaria model, new bone formation was observed for all groups with largest new bone formation in the BCP group, followed by the PCL + BCP group, and the PCL group. This finding was influenced by the initial volume of biomaterial implanted and remaining volume after 90 days. All materials showed osteoconductive properties and PCL + BCP tailored the tissue responses towards higher cellular biodegradability. Moreover, this material combination led to a reduced swelling in PCL + BCP; (4) Conclusions: Altogether, the results show that the newly developed composite is biocompatible and leads to successful osteoconductive bone regeneration. The new biomaterial combines the structural stability provided by PCL with bioactive characteristics of BCP-based BSM. 3D-printed BSM provides an integration behavior in accordance with the concept of guided bone regeneration (GBR) by directing new bone growth for proper function and restoration.     

Effect of PCL concentration on PCL/CaSiO3 porous composite scaffolds for bone engineering

Porous polycaprolactone (PCL)-coated calcium silicate (CaSiO₃) composite scaffolds were successfully prepared by 3D gel-printing (3DGP) and vacuum impregnation technology in this study. The effect of different PCL concentration on porous CaSiO₃ scaffolds prepared by 3DGP technology was studied. The composition and morphological characteristics of PCL/CaSiO₃ scaffolds were tested by using fourier transform infrared spectroscopy (FTIR), scanning electron microscope (SEM), and energy dispersive spectrometer (EDS) analysis. PCL coating amount on the scaffolds surface was calculated by thermogravimetric analysis (TGA). Compressive strength was tested by a universal testing machine, and degradability was tested by immersing the scaffolds in a simulated body fluid (SBF). The results show that PCL coating thickness increased from 7.29 μm to 12.2 μm, and the compressive strength of the corresponding composite scaffolds increased from 17.15 MPa to 24.12 MPa following with PCL concentration increasing from 7.5% to 12.5%. When the porous composite scaffolds were immersed in SBF for 28 days, the degradation ratio was 1.06% (CaSiO₃), 1.63% (CaSiO₃-7.5PCL), 1.81% (CaSiO₃-10PCL) and 1.55% (CaSiO₃-12.5PCL), respectively. It is obviously that PCL/CaSiO₃ composite scaffolds, which are suitable for bone growth in bone repair engineering, are beneficial to improve the mechanical properties and biodegradability of pure CaSiO₃ scaffolds.     

Hemocompatible polyurethane/gelatin-heparin nanofibrous scaffolds formed by a bi-layer electrospinning technique as potential artificial blood vessels

In this paper, a scaffold, which mimics the morphology and mechanical properties of a native blood vessel is reported. The scaffold was prepared by sequential bi-layer electrospinning on a rotating mandrel-type collector. The tubular scaffolds (inner diameter 4 mm, length 3 cm) are composed of a polyurethane (PU) fibrous outer-layer and a gelatin-heparin fibrous inner-layer. They were fabricated by electrospinning technology, which enables control of the composition, structure, and mechanical properties of the scaffolds. The microstructure, fiber morphology and mechanical properties of the scaffolds were examined by means of scanning electron microscopy (SEM) and tensile tests. The PU/gelatin-heparin tubular scaffolds have a porous structure. The scaffolds achieved a breaking strength (3.7±0.13 MPa) and an elongation at break (110±8%) that are appropriate for artificial blood vessels. When the scaffolds were immersed in water for 1 h, the breaking strength decreased slightly to 2.2±0.3 MPa, but the elongation at break increased to 145±21%. In platelet adhesion tests the gelatin-heparin fibrous scaffolds showed a significant suppression of platelet adhesion. Heparin was released from the scaffolds at a fairly uniform rate during the period of 2^nd day to 9^th day. The scaffolds are expected to mimic the complex matrix structure of native arteries, and to have good biocompatibility as an artificial blood vessel owing to the heparin release.     

Fabrication of co‐continuous poly(ε‐caprolactone)/polyglycolide blend scaffolds for tissue engineering

The apparent inability of a single biomaterial to meet all the requirements for tissue engineering scaffolds has led to continual research in novel engineered biomaterials. One method to provide new materials and fine‐tune their properties is via mixing materials. In this study, a biodegradable powder blend of poly(ε‐caprolactone) (PCL), polyglycolide (PGA), and poly(ethylene oxide) (PEO) was prepared and three‐dimensional interconnected porous PCL/PGA scaffolds were fabricated by combining cryomilling and compression molding/polymer leaching techniques. The resultant porous scaffolds exhibited co‐continuous morphologies with ～50% porosity. Mean pore sizes of 24 and 56 μm were achieved by varying milling time. The scaffolds displayed high mechanical properties and water uptake, in addition to a remarkably fast degradation rate. The results demonstrate the potential of this fabrication approach to obtain PCL/PGA blend scaffolds with interconnected porosity. In general, these results provide significant insight into an approach that will lead to the development of new composites and blends in scaffold manufacturing. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42471.     

Surface‐engineered hydroxyapatite nanocrystal/ poly(ε‐caprolactone) hybrid scaffolds for bone tissue engineering

To achieve novel polymer/bioceramic composite scaffolds for use in materials for bone tissue engineering, we prepared organic/inorganic hybrid scaffolds composed of biodegradable poly(ε‐caprolactone) (PCL) and hydroxyapatite (HA), which has excellent biocompatibility with hard tissues and high osteoconductivity and bioactivity. To improve the interactions between the scaffolds and osteoblasts, we focused on surface‐engineered, porous HA/PCL scaffolds that had HA molecules on their surfaces and within them because of the biochemical affinity between the biotin and avidin molecules. The surface modification of HA nanocrystals was performed with two different methods. Using Fourier transform infrared, X‐ray diffraction, and thermogravimetric analysis measurements, we found that surface‐modified HA nanocrystals prepared with an ethylene glycol mediated coupling method showed a higher degree of coupling (%) than those prepared via a direct coupling method. HA/PCL hybrid scaffolds with a well‐controlled porous architecture were fabricated with a gas‐blowing/particle‐leaching process. All HA/PCL scaffold samples exhibited approximately 80–85% porosity. As the HA concentration within the HA/PCL scaffolds increased, the porosity of the HA/PCL scaffolds gradually decreased. The homogeneous immobilization of biotin‐conjugated HA nanocrystals on a three‐dimensional, porous scaffold was observed with confocal microscopy. According to an in vitro cytotoxicity study, all scaffold samples exhibited greater than 80% cell viability, regardless of the HA/PCL composition or preparation method. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

3D Composite scaffolds using strontium containing bioactive glasses

In this study, it was aimed to fabricate and characterize three-dimensional composite scaffolds derived from Sr-doped bioactive glass for bone tissue engineering applications. The scaffolds were fabricated by using polymer foam replication technique and coated with gelatin to be able to improve the properties of them. The porous scaffolds were successfully synthesized using optimized process parameters. Both coated and uncoated scaffolds favored precipitation of calcium phosphate layer when they were soaked in simulated body fluid (SBF). Gelatin coating improved the mechanical properties of the scaffold and also it did not change the bioactive behavior of the scaffold. It was observed that there was a good pore interconnectivity maintained in the scaffold microstructure. Results indicated that scaffolds can deliver controlled doses of strontium toward the SBF medium. That is the determinant for bone tissue regeneration, as far as strontium is known to positively act on bone remodeling.     

Effect of the diisocyanate structure and the molecular weight of diols on bio‐based polyurethanes

Bio‐based polyurethanes (PU) containing poly(ε‐caprolactone) diol (PCL) and hydroxyl telechelic natural rubber (HTNR) were synthesized. The effect of the diisocyanate structure and the molecular weights of diols on the mechanical properties of PU were investigated. Three different molecular structures of diisocyanate were employed: an aliphatic diisocyanate (hexamethylene diisocyanate, HDI), an aromatic diisocyanate (toluene‐2,4‐diisocyanate, TDI) and a cycloalkane diisocyanate (isophorone diisocyanate, IPDI). Two molecular weights of each diol were selected. When HDI was employed, a crystalline PU was generated while asymmetrical structures of TDI and IPDI provided an amorphous PU. The presence of crystalline domains was responsible of a change in tensile behavior and physical properties. PU containing TDI and IPDI showed a rubber‐like behavior: low Young's modulus and high elongation at break. The crystalline domains in PU containing HDI acted as physical crosslinks, enhancing the Young's modulus and reducing the elongation at break, and they are responsible of the plastic yielding. The crystallinity increased the tear strength, the hardness and the thermal stability of PU. There was no significant difference between the TDI and IPDI on the mechanical properties and the physical characteristics. Higher molecular weight of PCL diol changed tensile behavior from the rubber‐like materials to the plastic yielding. Thermal and dynamic mechanical properties were determined by using DSC, TGA and DMTA. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Preparation and characterization of new nano-composite scaffolds loaded with vascular stents

In this study, vascular stents were fabricated from poly (lactide-ɛ-caprolactone)/collagen/nano-hydroxyapatite (PLCL/Col/nHA) by electrospinning, and the surface morphology and breaking strength were observed or measured through scanning electron microscopy and tensile tests. The anti-clotting properties of stents were evaluated for anticoagulation surfaces modified by the electrostatic layer-by-layer self-assembly technique. In addition, nano-composite scaffolds of poly (lactic-co-glycolic acid)/polycaprolactone/nano-hydroxyapatite (PLGA/PCL/nHA) loaded with the vascular stents were prepared by thermoforming-particle leaching and their basic performance and osteogenesis were tested in vitro and in vivo. The results show that the PLCL/Col/nHA stents and PLGA/PCL/nHA nano-composite scaffolds had good surface structures, mechanical properties, biocompatibility and could guide bone regeneration. These may provide a new way to build vascularized-tissue engineered bone to repair large bone defects in bone tissue engineering.     

The effects of PCL diol molecular weight on properties of shape memory poly(ε-caprolactone) networks

Shape memory poly(ε-caprolactone) (PCL) networks with different molecular weights of PCL diol were prepared via thiol–ene reaction in this work. The highly efficient thiol–ene reaction ensured a uniform distribution of PCL chains between crosslinker, contributing well-defined network architecture with good mechanical and shape memory properties. ¹H NMR spectra were used to confirm that PCL diol was completely converted into acrylate-terminated PCL. Gel content experiment and Fourier-transform infrared showed that almost all samples exhibited virtually the complete crosslinking network due to the highly selective thiol–ene reaction between acrylate-terminated PCL and tetrathiol crosslinker. Differential scanning calorimetry and X-ray diffraction tests revealed that the melting temperature and crystallinity of the prepared PCL networks by using high molecular weight of PCL diol displayed a higher result compared to ones using low molecular weight. The dynamic mechanical analyzer results revealed that the storage modulus of the network dropped evidently across the thermal transition, these characteristics of the PCL network indicated that all exhibited a good shape memory effect. The shape fixing ability was kind of being affected by the PCL diol molecular weight, while the shape recovery ratio of all samples can almost reach 99% irrespective of the length of PCL diol. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47055.     

Synthesis,characterization, and cytotoxicity of PCL–PEG–PCL diacrylate and agarose interpenetrating network hydrogels for cartilage tissue engineering

Hydrogels are suitable biomaterials for cartilage tissue engineering due to the excellent ability to retain water to provide suitable environment for the tissue, however, the insufficient mechanical properties often prevent their wider applications. The objective of this study was to fabricate biocompatible hydrogels with good mechanical performance, high-water content, and porous microstructure for cartilage regeneration. Photocrosslinked hydrogels are one of the most widely used systems in tissue engineering due to the superior mechanical properties. In this study, block copolymer, poly(ε -caprolactone)-poly(ethylene)-poly(ε -caprolactone) diacrylate (PCL–PEG–PCL; PEC), was prepared by ring-opening polymerization, and PEC hydrogels were made through free radical crosslinking mechanism. Agarose network is chosen as another component of the hydrogels, because of the high-swelling behavior and cartilage-like microstructure, which is helpful for chondrocytes growth. Interpenetrating networks (IPN) were fabricated by diffusing PEC into agarose network followed by photo-crosslinking process. It was noted that incorporating PEC into the agarose network increased the elastic modulus and the compressive failure properties of individual component networks. In addition, high-swelling ratio and uniform porosity microstructures were found in the IPN hydrogels. IPN and PEC showed low cytotoxicity and good biocompatibility in elution test method. The results suggest promising characteristics of IPN hydrogels as a potential biomaterial for cartilage tissue engineering.     

Exceptionally flame-retardant flexible polyurethane foam composites: synergistic effect of the silicone resin/graphene oxide coating

A facile strategy was developed to fabricate flexible polyurethane (PU) foam composites with exceptional flame retardancy. The approach involves the incorporation of graphene oxide (GO) into a silicone resin (SiR) solution, which is then deposited onto a PU foam surface via the dip-coating technique and cured. Fourier-transform infrared spectroscopy, scanning electron microscopy, and Raman spectroscopy measurements demonstrated that the SiR and GO were successfully coated onto the PU skeleton and the intrinsic porous structure of the PU foam remained intact. The effects of SiR and GO on the mechanical and thermal stability and flame retardancy of PU composites were evaluated through compression tests, thermogravimetric analysis, vertical combustion tests, and the limiting oxygen index. The measurement results revealed that the composites (PU@SiR-GO) showed superior flame retardancy and thermal and mechanical stability compared to pristine PU or PU coated with SiR alone. The mechanical and thermal stability and the flame-retardant properties of the PU composites were enhanced significantly with increasing GO content. Based on the composition, microstructure, and surface morphology of PU@SiR-GO composites before and after combustion tests, a possible flame-retardance mechanism is proposed. This work provides a simple and effective strategy for fabricating flame-retardant composites with improved mechanical performance.