Evaluations of bioactivity and mechanical properties of poly (?-caprolactone)/silica nanocomposite following heat treatment

Bioactive, Degradable and Tough Hybrids Through Calcium and Phosphate Incorporation

We report the first inorganic/organic hybrids that show outstanding mechanical properties (withstanding cyclic loading) and bone bioactivity. This new hybrid material may fulfil the unmet clinical need for bioactive synthetic bone grafts that can withstand cyclic loading. A SiO2/PTHF/PCL-diCOOH sol-gel hybrid system, that combined inorganic and organic conetworks at the molecular level, previously demonstrated unprecedented synergy of properties, with excellent flexibility and promoted formation of articular cartilage matrix in vitro. Here, for the first time, calcium and phosphate ions were incorporated into the inorganic component of the hybrid network, to impart osteogenic properties. Calcium methoxyethoxide and triethyl phosphate were the calcium and phosphate precursors because they allow for incorporation into the silicate network at low temperature. The hybrid network was characterised with ATR-FTIR, XRD and solid-state Nuclear Magnetic Resonance, which proved calcium and phosphate incorporation and suggested the Ca2+ ions also interacted with PCL-diCOOH through ionic bonds. This resulted in an increased strength (17-64 MPa) and modulus of toughness (2.5-14 MPa) compared to the original SiO2/PTHF/PCL-diCOOH hybrid material (which showed strength of ~3 MPa and modulus of toughness of ~0.35 MPa), while also maintaining the ability to withstand cyclic loading. The presence of calcium and phosphates in the silicate network resulted in a more congruent dissolution of the inorganic and organic co-networks in TRIS buffer. This was shown by the presence of silicon, calcium and phosphate ions along with PCL in the TRIS buffer after 1 week, whereas Ca-free hybrids mainly released PCL with negligible Si dissolution. The presence of calcium and phosphates also enabled deposition of hydroxycarbonate apatite following immersion in simulated body fluid, which was not seen on Ca-free hybrid. All hybrids passed cell cytotoxicity tests and supported preosteoblast cell attachment. The phosphate-free hybrid showed the best mechanical behaviour and supported better cell attachment, spreading and potentially differentiation of cells. Therefore, the SiO2-CaO/PTHF/PCL-diCOOH hybrid represents a promising biomaterial for use in bone regeneration.

Preparation of a non-woven poly(ε-caprolactone) fabric with partially embedded apatite surface for bone tissue engineering applications by partial surface melting of poly(ε-caprolactone) fibers

This article describes a novel method for the preparation of a biodegradable non-woven poly(ε-caprolactone) fabric with a partially embedded apatite surface designed for application as a scaffold material for bone tissue engineering. The non-woven poly(ε-caprolactone) fabric was generated by the electro-spinning technique and then apatite was coated in simulated body fluid after coating the PVA solution containing CaCl₂ ·2H₂ O. The apatite crystals were partially embedded or fully embedded into the thermoplastic poly(ε-caprolactone) fibers by controlling the degree of poly(ε-caprolactone) fiber surface melting in a convection oven. Identical apatite-coated poly(ε-caprolactone) fabric that did not undergo heat-treatment was used as a control. The features of the embedded apatite crystals were evaluated by FE-SEM, AFM, EDS, and XRD. The adhesion strengths of the coated apatite layers and the tensile strengths of the apatite coated fabrics with and without heat-treatment were assessed by the tape-test and a universal testing machine, respectively. The degree of water absorbance was assessed by adding a DMEM droplet onto the fabrics. Moreover, cell penetrability was assessed by seeding preosteoblastic MC3T3-E1 cells onto the fabrics and observing the degrees of cell penetration after 1 and 4 weeks by staining nuclei with DAPI. The non-woven poly(ε-caprolactone) fabric with a partially embedded apatite surface showed good water absorbance, cell penetrability, higher apatite adhesion strength, and higher tensile strength compared with the control fabric. These results show that the non-woven poly(ε-caprolactone) fabric with a partially embedded apatite surface is a potential candidate scaffold for bone tissue engineering due to its strong apatite adhesion strength and excellent cell penetrability. © 2016 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 105A: 1973-1983, 2017.

Repetitive cleavage of elastomeric membrane via controlled interfacial fracture

Here, we report a method of fabricating thin layer of polydimethylsiloxane (PDMS), with a thickness in the range of 60-80 nm, which can be repeatedly generated (more than 10 times) from the same block of PDMS via controlled interfacial fracture. The thin layers can be transferred to various substrates by peeling off from the bulk PDMS. The cleavage is attributed to the built-in stress at the fracture interface due to plasma treatment, resulting in the repetitive formation of the thin membranes, with no residue from processing, and with a surface roughness of ∼5 nm. We were able to demonstrate transferred patterns with controlled thickness by varying the oxygen plasma treatment conditions and the composition of bulk PDMS stamp. Using the method, we achieved residual-free patterns with submicrometer resolution for applications in biomolecule array templates.

Hydroxyapatite formation on sol-gel derived poly(ε-caprolactone)/bioactive glass hybrid biomaterials

Investigation of novel biomaterials for bone regeneration is based on the development of scaffolds that exhibit bone-bonding ability, biocompatibility, and sufficient mechanical strength. In this study, using novel poly (ε-caprolactone)/bioactive glass (PCL/BG) hybrids with different organic/inorganic ratios, the effects of BG contents on the in vitro bone-like hydroxyapatite (HA) formation, mechanical properties, and biocompatibility were investigated. Rapid precipitation of HA on the PCL/BG hybrid surfaces were observed after incubating in simulated body fluid (SBF) for only 6 h, as confirmed by scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), Fourier-transform infrared spectroscopy (FTIR), and inductively coupled plasma atomic emission spectroscopy (ICPS). The ICPS elemental analysis results were further analyzed in terms of the Ca(2+) and PO4(3-) which were consumed to form the apatite layer. The results revealed that the rate and total amount of HA deposition decreased with an increase in PCL content. The compressive modulus and strength of the PCL/BG hybrids increased with the decrease in PCL content. The highest values were achieved at the lowest PCL content (10 wt %) and were around, 90 MPa and 1.4 GPa, respectively. To evaluate the cytotoxicity of PCL/BG bioactive hybrids, MC3T3-E1 osteoblast-like cells were cultured for up to 72 h. Our data indicated that whereas initial cell attachment was marginally lower than the control tissue culture poly styrene (TCPS) surface, the hybrid materials promoted cell growth in a time-dependent manner. Cell viability within the different PCL/BG hybrid samples appeared to be influenced by compositional differences whereby higher PCL contents correlated with slight reduction in cell viability. Taken together, this study adds important new information to our knowledge on hydroxyapatite formation, mechanical properties, and cytotoxic effects of PCL/BG hybrids prepared by the sol-gel process using a tertiary glass composition and may have considerable potential for bone tissue regeneration applications.

Osteoconductive and degradable electrospun nonwoven poly(epsilon-caprolactone)/CaO-SiO2 gel composite fabric

A nonwoven ceramic/polymer composite fabric composed of randomly mixed bioactive and fast degradable CaO-SiO(2) gel fibers and biodegradable poly(epsilon-caprolactone) (PCL) fibers is prepared with a simultaneous electrospinning method for potential use as bone grafting materials. A 17% PCL solution is prepared using 1,1,3,3-hexafluoro-2-propanol as the solvent, whereas the CaO-SiO(2) gel solution is prepared via a condensation reaction following the hydrolysis of tetraethyl orthosilicate. PCL and CaO-SiO(2) gel solutions are spun simultaneously with two separate nozzles. As controls, pure PCL and CaO-SiO(2) gel nonwoven fabrics are also made by the same methods. The three nonwoven fabrics were exposed to simulated body fluid for 1 week and resulted in the deposition of a layer of apatite crystals on the surfaces of both the CaO-SiO(2) gel and PCL/CaO-SiO(2) gel composite fabrics, but not on the PCL fabric. A tensile strength test showed that the fracture behavior of the CaO-SiO(2) gel fabric was brittle, that of the PCL fabric was ductile-tough, and that of the PCL/CaO-SiO(2) gel composite fabric was intermediate between that of the CaO-SiO(2) gel and PCL fabrics. Our in vivo tests showed that the CaO-SiO(2) gel and PCL/CaO-SiO(2) gel composite fabrics had good osteoconductivity and fast degradation rates in calvarial defects of New Zealand white rabbits within 4 weeks, in contrast to the pure PCL fabric. Together, these results suggest that the composite fabric composed of PCL and CaO-SiO(2) gel fibers must have a great potential for use in applications such as bone grafting because of its good osteoconductivity and adequate mechanical properties.

Nanoparticle technology in bone tissue engineering

Nanotechnology has been increasingly utilized to enhance bone tissue engineering strategies. In particular, nanotechnology has been employed to overcome some of the current limitations associated with bone regeneration methods including insufficient mechanical strength of scaffold materials, ineffective cell growth and osteogenic differentiation at the defect site, as well as unstable and insufficient production of growth factors to stimulate bone cell growth. Among the tremendous technologies of nanoparticles in biological systems, we focus here on the three major nanoparticle research areas that have been developed to overcome these limitations and disadvantages: (a) the generation of nanoparticle-composite scaffolds to provide increased mechanical strength for bone graft, (b) the fabrication of nanofibrous scaffolds to support cell growth and differentiation through morphologically-favored architectures, and (c) the development of novel delivery and targeting systems of genetic material, especially those encoding osteogenic growth factors. These nanoparticle-based bone tissue engineering technologies possess a great potential to ensure the efficacy of clinical bone regeneration.

Bioactivity improvement of poly(epsilon-caprolactone) membrane with the addition of nanofibrous bioactive glass

Nanofibrous glass with a bioactive composition was added to a degradable polymer poly(epsilon-caprolactone) (PCL) to produce a nanocomposite in thin membrane form ( approximately 260 microm). The bioactivity and osteoblastic responses of the nanocomposite membrane were examined and compared with those of a pure PCL membrane. Glass nanofibers with diameters in the range of hundreds of nanometers were added to a PCL solution at 20 wt.%, and the mixture was stirred vigorously and air dried. The obtained nanocomposite membrane showed that many chopped glass nanofibers formed by the mixing step were embedded uniformly into the PCL matrix. The nanocomposite membrane induced the rapid formation of apatite-like minerals on the surface when immersed in a simulated body fluid. Murine-derived osteoblastic cells (MC3T3-E1) grew actively over the nanocomposite membrane with cell viability significantly improved compared with those on the pure PCL membrane. Moreover, the osteoblastic activity, as assessed by the expression of alkaline phosphatase, was significantly higher on the nanocomposite membrane than on the pure PCL membrane. The currently developed nanocomposite of the bioactive glass-added PCL might find applications in the bone regeneration areas such as the guided bone regeneration (GBR) membrane.

Effect of acidic degradation products of poly(lactic-co-glycolic)acid on the apatite-forming ability of poly(lactic-co-glycolic)acid-siloxane nanohybrid material

The effect of poly(lactic-co-glycolic) acid (PLGA) degradation products on the apatite-forming ability of a PLGA-siloxane nanohybrid material were investigated. Two PLGA copolymer compositions with low and high degradability were used in the experiment. The PLGA-siloxane nanohybrid materials were synthesized by end-capping PLGA with acid end-groups using 3-isocyanatopropyl triethoxysilane following the sol-gel reaction with calcium nitrate tetrahydrate. Two nanohybrid materials that had different degradability were exposed to simulated body fluid (SBF) for 1-28 days at 36.5 degrees C. The low degradable PLGA hybrid showed apatite-forming ability within 3 days of incubation while the high degradable one did not within 28 days testing period. The results were explained in terms of the acidity of the PLGA degradation products, which could directly influence on the apatite dissolution.

Preparation of Bioactive Poly(Lactic-Co-Glycolic)Acid and Silica Gel Fibers Mixed Non-Woven Fabric

Poly(lactic-co-glycolic)acid and silica gel fibers mixed non-woven fabric was made by electro-spinning method for the potential application as a bone grafting material. The silica gel, the source material for electro-spinning, was prepared by the hydrolysis of tetraethyl orthosilicate in the presence of calcium salt, water, hydrochloric acid and ethanol. Poly(lactic-co-glycolic)acid solution was prepared by dissolving it in the hexafluoroisopropanol. Then, they were transferred to two separate syringes which were connected to the high voltage supply generating a high electric field between the spinneret and the ground collecting drum. The silica gel containing calcium and poly(lactic-co-glycolic)acid solution were spun together under the electric field of 2 ㎸/㎝. The FE-SEM observations showed that the silica gel and poly(lactic-co-glycolic)acid fibers were mixed together completely and its handling property was much improved compared to that of the non-woven silica gel fabric. After soaking in the SBF for 1 week, low crystalline apatite crystals were also observed to occur on the silica fiber surfaces first and then they were also observed to occur on the poly(lactic-co-glycolic)acid fiber surfaces. From the results, it can be concluded that the poly(lactic-co-glycolic)acid and silica gel fibers mixed non-woven fabric made by electro-spinning method has a bioactivity. It means it has a potential to be used as a bone grafting material because of its apatite-forming ability, high surface area to volume ratio and high porosity.

Comparativein vitro andin vivo studies using a bioactive poly(ɛ-caprolactone)-organosiloxane nanohybrid containing calcium salt

Comparative in vitro and in vivo studies were conducted using a bioactive poly(epsilon-caprolactone)-organosiloxane nanohybrid containing calcium, which was prepared by sol-gel method. The behavior of human bone marrow stromal cells (hBMSCs) during in vitro osteogenic differentiation were evaluated on poly(epsilon-caprolactone)-organosiloxane nanohybrid and poly(epsilon-caprolactone)-organosiloxane nanohybrid coated with apatite, which mimicked in vivo events. hBMSCs cultured on tissue culture plates (TCPs) were used as a control. For comparative studies, in vivo testing was also conducted using poly(epsilon-caprolactone)-organosiloxane nanohybrid and poly(epsilon-caprolactone)-organosiloxane nanohybrid coated with apatite in the diaphyseal bone defects of rabbit tibiae. Initial attachments and early proliferations of hBMSCs onto poly(epsilon-caprolactone)-organosiloxane with or without the apatite layer were comparable those onto TCPs. However, the late proliferation and the osteogenic differentiation activities on poly(epsilon-caprolactone)-organosiloxane nanohybrid were significantly lower than the hybrid coated with apatite or TCPs. These results were caused by the delayed detachment of hBMSCs induced by the upward growth of spire-shaped apatite granules on the flat apatite layer through mixed nucleation (heterogeneous and homogeneous nucleation) and growth of apatite crystals during cell culture. However, the poly(epsilon-caprolactone)-organosiloxane nanohybrid showed excellent osteoconductivity as same as poly(epsilon-caprolactone)-organosiloxane nanohybrid coated with apatite in vivo even though the cell testing results in vitro were poor. This discrepancy can be explained by the difference in initial degree of supersaturation of apatite in cell culture medium and buffering ability between cell culture medium and body fluid with respect to calcium, which directly affects the nucleation mechanism of apatite crystals and the morphology of grown apatite granules. These findings imply that much attention is required and an optimal method should be used to assess cell responses in vitro. Our results suggest that precoating the apatite layer before in vitro testing is desirable for bioactive materials that release calcium quickly and in large amount because this treatment can more closely mimic in vivo events.

Bioactive composite materials for tissue engineering scaffolds

Synthetic bioactive and bioresorbable composite materials are becoming increasingly important as scaffolds for tissue engineering. Next-generation biomaterials should combine bioactive and bioresorbable properties to activate in vivo mechanisms of tissue regeneration, stimulating the body to heal itself and leading to replacement of the scaffold by the regenerating tissue. Certain bioactive ceramics such as tricalcium phosphate and hydroxyapatite as well as bioactive glasses, such as 45S5 Bioglass, react with physiologic fluids to form tenacious bonds with hard (and in some cases soft) tissue. However, these bioactive materials are relatively stiff, brittle and difficult to form into complex shapes. Conversely, synthetic bioresorbable polymers are easily fabricated into complex structures, yet they are too weak to meet the demands of surgery and the in vivo physiologic environment. Composites of tailored physical, biologic and mechanical properties as well as predictable degradation behavior can be produced combining bioresorbable polymers and bioactive inorganic phases. This review covers recent international research presenting the state-of-the-art development of these composite systems in terms of material constituents, fabrication technologies, structural and bioactive properties, as well as in vitro and in vivo characteristics for applications in tissue engineering and tissue regeneration. These materials may represent the effective optimal solution for tailored tissue engineering scaffolds, making tissue engineering a realistic clinical alternative in the near future.

Evaluations of a Novel Bioactive and Degradable Poly(Ɛ-Caprolactone) Hybrid Material Containing Silanol Group and Calcium Salt as a Bone Substitute

Bioactive poly(e-caprolactone)-siloxane hybrid material was newly developed and its in vitro and in vivo evaluations were made for the potential application as a bone substitute. The polymer precursor, triethoxysilane end capped poly(e-caprolactone) was prepared by the reaction with a,w-hydroxyl poly(e-caprolactone) and 3-isocyanatopropyl triethoxysilane with 1,4-diazabicyclo [2,2,2] octane as a catalyst and toluene as a solvent. The triethoxysilane end capped poly(e-caprolactone) was hydrolyzed and condensed to yield a hybrid sol-gel material. The gelation was carried out for 1 week at ambient condition in a covered Teflon mold with a few pinholes and then dried under vacuum at room temperature for 48 h. Its bioactivity was evaluated by examining the apatite formation on its surface in the SBF and its osteoconductivity was assessed in the tibia of white rabbit. The hybrid material showed apatite-forming ability in the SBF within 1 week soaking. Besides, new bone was formed on the surface of a cylindrical shaped specimen with no histologically demonstrable intervening non-osseous tissue after 6 weeks implantation. There was no evidence of inflammation or foreign body reaction. From the results, it can be concluded that this newly developed hybrid material has osteoconductivity and is likely to be used for the application as a bone graft substitute.

Evaluation of a Chitosan Nano-Hybrid Material Containing Silanol Group and Calcium Salt as a Bioactive Bone Graft

A bioactive chitosan-siloxane nano-hybrid material was newly developed and evaluated for the potential application as a bone graft material. The chitosan which can be dissolved in organic solvent was synthesized by the reaction with phtalic anhydride (Ph-Chitosan) and it was then reacted with 3-isocyanatopropyl triethoxysilane (Si-Chitosan) in dimethylformamide. Following this, the Si-Chitosan was hydrolyzed and condensed to yield a hybrid sol-gel material (Si-O-Chitosan). The gelation was carried out for 1 week at ambient condition in a covered Teflon mold with a few pinholes and then dried under vacuum at room temperature for 48 h. The bioactivity of the chitosan nano-hybrid material was evaluated by examining the apatite forming ability in the simulated body fluid (SBF). The surface microstructure and functional groups of the specimen was analyzed by field emission scanning electron microscopy and Fourier transformed infrared spectroscopy, respectively. The crystal phases of the specimen before and after the bioactivity testing were analyzed by thin film X-ray diffractometry. Newly developed chitosan nano-hybrid material showed apatite-forming ability in the SBF within 1 week soaking and this ability was believed to come from the silanol group formed on the surface of Si-O-Chitosan and calcium salt which increased the ionic activity product of apatite in the SBF.

Effect of Silica Content in the PMMA/Silica Nano-Composite on the Mechanical Properties and Growth Behavior of Calcium Phosphate Crystals during Cell Culture

The effect of silica content in the PMMA/silica nano-composite on the mechanical properties and the growth behavior of apatite crystals were investigated. The PMMA/silica nano-composites with different silica content were synthesized through the sol-gel reaction with triethoxysilane end-capped PMMA and tetraethyl orthosilicate (TEOS). The compressive strength showed its maximum value when the content of TEOS was 20 wt% while the elastic modulus showed its maximum value when the content of TEOS was 60 wt%. The growth behavior of the apatite crystals following the cell culture showed different response according to the silica content. As increasing the TEOS content, the shape of the apatite crystals changed from globule-like structure to fiber-like one.