Bioresorbable and bioactive composite materials based on polylactide foams filled with and coated by Bioglass® particles for tissue engineering applications

Poly(DL-lactide) (PDLLA) foams and bioactive glass (Bioglass®) particles were used to form bioresorbable and bioactive composite scaffolds for applications in bone tissue engineering. A thermally induced phase separation process was applied to prepare highly porous PDLLA foams filled with 10 wt % Bioglass® particles. Stable and homogeneous layers of Bioglass® particles on the surface of the PDLLA/Bioglass® composite foams as well as infiltration of Bioglass® particles throughout the porous network were achieved using a slurry-dipping technique. The quality of the bioactive glass coatings was reproducible in terms of thickness and microstructure. In vitro studies in simulated body fluid (SBF) were performed to study the formation of hydroxyapatite (HA) on the surface of the PDLLA/Bioglass® composites, as an indication of the bioactivity of the materials. Formation of the HA layer after immersion in SBF was confirmed by X-ray diffraction and Raman spectroscopy measurements. The rate of HA formation in Bioglass®-coated samples was higher than that observed in non-coated samples. SEM analysis showed that the HA layer thickness rapidly increased with increasing time in SBF in the Bioglass®-coated samples. The high bioactivity of the developed composites suggests that the materials are attractive for use as bioactive, resorbable scaffolds in bone tissue engineering.     

Evaluation of in vitro bioactivity and biocompatibility of Bioglass®-reinforced polyethylene composite

The bioactivity and biocompatibility of Bioglass®-reinforced high-density polyethylene composite (Bioglass®/HDPE) have been evaluated in simulated body fluid (SBF) and by in vitro cell culture, respectively. The formation of a biologically active hydroxy-carbonate apatite (HCA) layer on the composite surface after immersion in SBF was demonstrated by thin-film X-ray diffraction, infrared spectroscopy and scanning electron microscopy, indicating the in vitro bioactivity of Bioglass®/HDPE composites. The HCA layer was formed on the 40 vol% composite surface within 3 days immersion in SBF at a formation rate comparable to those on bioactive glass-ceramics, showing that in vitro bioactivity could be obtained in a composite. Furthermore, the composite was biocompatible to primary human osteoblast-like cells. In comparison with unfilled HDPE and tissue culture plastic control, a significant increase in cellular metabolic activity was found on the composite. Therefore, Bioglass®/HDPE composites have a promising biological response as a potential implant material.     

Novel starch thermoplastic/Bioglass® composites: Mechanical properties, degradation behavior and in-vitro bioactivity

The present research aims to evaluate the possibility of creating new degradable, stiff and highly bioactive composites based on a biodegradable thermoplastic starch-based polymeric blend and a Bioglass® filler. Such combination should allow for the development of bioactive and degradable composites with a great potential for a range of temporary applications. A blend of starch with ethylene–vinyl alcohol copolymer (SEVA-C) was reinforced with a 45S5 Bioglass® powder presenting a granulometric distribution between 38 and 53 m. Composites with 10 and 40 wt % of 45S5 Bioglass® were compounded by twin-screw extrusion (TSE) and subsequently injection molded under optimized conditions. The mechanical properties of the composites were evaluated by tensile testing, and their bioactivity assessed by immersion in a simulated body fluid (SBF) for different periods of time. The biodegradability of these composites was also monitored after several immersion periods in an isotonic saline solution. The tensile tests results obtained indicated that SEVA-C/Bioglass® composites present a slightly higher stiffness and strength (a modulus of 3.8 GPa and UTS of 38.6 MPa) than previously developed SEVA-C/Hydroxylapatite (HA) composites. The bioactivity of SEVA-C composites becomes relevant for 45S5 amounts of only 10 wt %. This was observed by scanning electron microscopy (SEM) and confirmed for immersion periods up to 30 days by both thin-film X-ray diffraction (TF-XRD) (where HA typical peaks are clearly observed) and induced coupled plasma emission (ICP) spectroscopy used to follow the elemental composition of the SBF as function of time. Additionally, it was observed that the composites are biodegradable being the results correlated with the correspondent materials composition.     

Novel bioresorbable and bioactive composites based on bioactive glass and polylactide foams for bone tissue engineering

Bioresorbable and bioactive tissue engineering scaffolds based on bioactive glass (45S5 Bioglass®) particles and macroporous poly(DL-lactide) (PDLLA) foams were fabricated. A slurry dipping technique in conjunction with pretreatment in ethanol was used to achieve reproducible and well adhering bioactive glass coatings of uniform thickness on the internal and external surfaces of the foams. In vitro studies in simulated body fluid (SBF) demonstrated rapid hydroxyapatite (HA) formation on the surface of the composites, indicating their bioactivity. For comparison, composite foams containing Bioglass® particles as filler for the polymer matrix (in concentration of up to 40 wt %) were prepared by freeze-drying, enabling homogenous glass particle distribution in the polymer matrix. The formation of HA on the composite surfaces after immersion in phosphate buffer saline (PBS) was investigated to confirm the bioactivity of the composites. Human osteoblasts (HOBs) were seeded onto as-fabricated PDLLA foams and onto PDLLA foams coated with Bioglass® particles to determine early cell attachment and spreading. Cells were observed to attach and spread on all surfaces after the first 90 min in culture. The results of this study indicate that the fabricated composite materials have potential as scaffolds for guided bone regeneration.     

Bioactivity of degradable polymer sutures coated with bioactive glass

Novel bioactive materials have been prepared by coating violet resorbable Vicryl sutures with a bioactive glass powder derived from a co-precipitation method. Two techniques have been chosen for the composite preparation: pressing the sutures in a bed of glass powder and slurry-dipping of sutures in liquid suspensions of bioactive glass powders. The uniformity and thickness of the coatings obtained by the two methods were compared. The bioactivity of the sutures with and without bioactive glass coating was tested by soaking in an inorganic acellular simulated body fluid (SBF). The composite sutures were characterised by XRD, SEM and FTIR analyses before and after soaking in SBF solution to assess the formation of hydroxyapatite on their surfaces, which is a qualitative measure of their bioactivity. The possible use of bioactive sutures to produce tissue engineering scaffolds and as reinforcement of resorbable calcium phosphates is discussed.     

Biodegradable polyurethane composite scaffolds containing Bioglass® for bone tissue engineering

Five types of solid and porous polyurethane composites containing 5–20 wt.% of Bioglass® inclusions were synthesized. Porous structures were fabricated by polymer coagulation combined with the salt-particle leaching method. In-vitro bioactivity tests in simulated body fluid (SBF) were carried out and the marker of bioactivity, e.g. formation of surface hydroxyapatite or calcium phosphate layers upon immersion in SBF, was investigated. The chemical and physical properties of the solid and porous composites before and after immersion in SBF were evaluated using different techniques: Fourier Transform Infrared Spectroscopy (FTIR), Differential Scanning Calorimetry (DSC), Dynamic Mechanical Analysis (DMA) and Thermogravimetric Analysis (TGA). Moreover the surface structure and microstructure of the composites was characterised by Atomic Force Microscopy (AFM) and Scanning Electron Microscopy (SEM), respectively. Mercury intrusion porosimetry, SEM and microtomography (μCT) were used to determine pore size distribution and porosity. The fabricated foams exhibited porosity >70% with open pores of 100–400 μm in size and pore walls containing numerous micropores of <10 μm. This pore structure satisfies the requirements for bone tissue engineering applications. The effects of Bioglass® addition on microstructure, mechanical properties and bioactivity of polyurethane scaffolds were evaluated. It was found that composite foams showed a higher storage modulus than neat polyurethane foams. The high bioactivity of composite scaffolds was confirmed by the rapid formation of hydroxyapatite on the foam surfaces upon immersion in SBF.     

Effect of nanoparticulate bioactive glass particles on bioactivity and cytocompatibility of poly(3-hydroxybutyrate) composites

This work investigated the effect of adding nanoparticulate (29 nm) bioactive glass particles on the bioactivity, degradation and in vitro cytocompatibility of poly(3-hydroxybutyrate) (P(3HB)) composites/nano-sized bioactive glass (n-BG). Two different concentrations (10 and 20 wt %) of nanoscale bioactive glass particles of 45S5 Bioglass composition were used to prepare composite films. Several techniques (Raman spectroscopy, scanning electron microscopy, atomic force microscopy, energy dispersive X-ray) were used to monitor their surface and bioreactivity over a 45-day period of immersion in simulated body fluid (SBF). All results suggested the P(3HB)/n-BG composites to be highly bioactive, confirmed by the formation of hydroxyapatite on material surfaces upon immersion in SBF. The weight loss and water uptake were found to increase on increasing bioactive glass content. Cytocompatibility study (cell proliferation, cell attachment, alkaline phosphatase activity and osteocalcin production) using human MG-63 osteoblast-like cells in osteogenic and non-osteogenic medium showed that the composite substrates are suitable for cell attachment, proliferation and differentiation.     

Development of a composite based on hydroxyapatite and magnesium and zinc‐containing sol–gel-derived bioactive glass for bone substitute applications

In the present study, a bioceramic-based composite was prepared by sintering compacts made up of mixtures of hydroxyapatite (HA) and sol–gel-derived bioactive glass (64SiO₂-26CaO-5MgO-5ZnO) (based on mol%) powders. HA powder was mixed with different concentrations of the glass powders up to 30 wt.%. The effect of adding bioactive glass powder to HA matrix, on the mechanical properties of the composite was assessed by compression test. The specimen with the highest compressive strength was chosen to be immersed in simulated body fluid (SBF) to study apatite forming ability and dissolution behavior. It was found that compressive strength of the specimen was decreased 65% after maintaining in the SBF for 14 days. X-ray diffraction (XRD) showed prevalence of HA and β-TCP related peaks. Also, the surface morphology of the composite was observed using scanning electron microscopy (SEM). The study of degradation behavior revealed Si release capability of this composite. Biological evaluations in vitro confirmed the composite studied could induce osteoblast-like cells' activities.     

Tensile strength of pine needles and their feasibility as reinforcement in composite materials

A feasibility study concerning the use of pine needles from Maritime Pine (Pinus pinaster) trees as reinforcement in composite materials has been presented in this paper with the tensile strength being investigated for a total of 150 specimens at three gauge lengths, namely 50, 75 and 100 mm. In order to calculate the tensile strength for each specimen, a correlation was obtained between the cross-sectional area and external dimensions of the individual pine needles. The mean value of the tensile strength was noted to vary only slightly between 33.4 MPa for the 50 mm gauge length and 31.4 MPa for the 100 mm case with a minimum and maximum of 15 and 65 MPa, respectively. Analysis of the data using the standard Weibull model indicated the Weibull strength to vary between 33.5 and 36.0 MPa whereas the Weibull modulus varied between approximately 3.5 and 4.5. Further analysis using the Weibull model indicated the presence of a bimodal strength distribution at each gauge length that was consistent with the presence of two distinct flaw populations operating within the pine needles. Overall, it was concluded that the strength of the pine needles was sufficient for inclusion in polymer matrix composites subject to low stress or non-load bearing applications such as fibreboard and thermal or acoustic insulation.     

In vitro bioactivity, cytocompatibility, and antibiotic release profile of gentamicin sulfate-loaded borate bioactive glass/chitosan composites

Borate bioactive glass-based composites have been attracting interest recently as an osteoconductive carrier material for local antibiotic delivery. In the present study, composites composed of borate bioactive glass particles bonded with a chitosan matrix were prepared and evaluated in vitro as a carrier for gentamicin sulfate. The bioactivity, degradation, drug release profile, and compressive strength of the composite carrier system were studied as a function of immersion time in phosphate-buffered saline at 37 °C. The cytocompatibility of the gentamicin sulfate-loaded composite carrier was evaluated using assays of cell proliferation and alkaline phosphatase activity of osteogenic MC3T3-E1 cells. Sustained release of gentamicin sulfate occurred over ~28 days in PBS, while the bioactive glass converted continuously to hydroxyapatite. The compressive strength of the composite loaded with gentamicin sulfate decreased from the as-fabricated value of 24 ± 3 MPa to ~8 MPa after immersion for 14 days in PBS. Extracts of the soluble ionic products of the borate glass/chitosan composites enhanced the proliferation and alkaline phosphatase activity of MC3T3-E1 cells. These results indicate that the gentamicin sulfate-loaded composite composed of chitosan-bonded borate bioactive glass particles could be useful clinically as an osteoconductive carrier material for treating bone infection.     

Characterisation of the bioactive behaviour of sol–gel hydroxyapatite–CaO and hydroxyapatite–CaO–bioactive glass composites

The fabrication and characterization of sol–gel derived hydroxyapatite–calcium oxide (HAp–CaO) material is investigated focusing on the effect of the addition of a bioactive glass on the material bioactive behaviour through the fabrication of a novel HAp–CaO (70 wt.%)–bioactive glass (30 wt.%) composite material. The bioactive behaviour of the materials was assessed by immersion studies in Simulated Body Fluid (SBF) and the alterations of the materials surfaces after soaking periods in SBF were characterized by Scanning Electron Microscopy (SEM) and Fourier Transform Infrared Spectroscopy (FTIR). A brittle and weakly crystalline carbonate hydroxyapatite (HCAp) layer was found to develop on the surface of all samples, few hours after immersion in SBF, confirming the high bioactivity of the material. Alterations of the morphology of the developed HCAp layer, which led to a more compact structure, were observed on the surface of composite samples after 7 days of immersion in SBF. The presence of the CaO phase seems to accelerate the formation of HCAp, while the bioactive glass affects both the morphology and cohesion of the developed layer.     

Bioactive evaluation of 45S5 bioactive glass fibres and preliminary study of human osteoblast attachment

Bioactive glass fibres can be used as tissue engineering scaffolds. In this investigation, the bioactive response of 45S5 glass fibres was assessed in simulated body fluid (SBF). Preliminary attachment of osteoblasts to the fibre surface was assessed, as were the fibre tensile strength and fracture toughness. Fourier transform infrared spectroscopy (FTIR) analysis revealed that hydroxyapatite (HA) was formed on the fibres' surface after 2-4 days in SBF. Raman micro-spectroscopic analysis was used to monitor development of the HA layer during immersion. A correlation was found between increase in intensity of the PO4(3-) peak near 964cm(-1) and appearance of crystalline HA (P-O bending peaks) using FTIR. Such results are encouraging for in situ bioactivity monitoring, as Raman spectra are insensitive to the presence of water, unlike FTIR. Average tensile strength of 45S5 fibres (79 microm diameter) was 340+/-140 MPa. Fracture toughness, determined using fracture surface analysis, was 0.7+/-0.1 MPa m1/2. Confocal microscopy revealed osteoblasts attached and spread along the fibres after 15-90 min culture. Scanning electron microscopy analysis showed that cells with filopodia and dorsal ruffles remained attached after 14 days in culture. These results are encouraging, as cell adhesion is an important first step prior to proliferation and differentiation.     

Tensile strength of glass fibres with carbon nanotube–epoxy nanocomposite coating

A study has been made of a concept of ‘healing’ coatings applied onto the brittle fibre surface to reduce the stress concentrations and thus to improve the reinforcing efficiency in a composite. Coatings made from neat epoxy and carbon nanotube (CNT) reinforced epoxy nanocomposite were applied onto the individual glass fibres as well as rovings. It is shown that the 0.3 wt.% CNT–epoxy nanocomposite coating gave rise to a significant increase in tensile strength of the single fibre for all gauge lengths, better than the neat epoxy coating. The results on glass fibre roving also indicated a clear beneficial effect of nanocomposite impregnation on tensile strength. The rovings impregnated with the CNT nanocomposite exhibited a more uniform strength distribution and higher strengths than those impregnated with the neat epoxy. The changes in prevailing failure mechanisms influenced by the epoxy and nanocomposite coatings have been identified.     

A microstructural examination of apatite induced by Bioglass® in vitro

Bioglass®, a clinically used bone graft material, has been tested in vitro in a simulated body fluid (SBF) up to four weeks. Apatite crystals were not only found to form on its surface but also in the reaction solutions. The apatite crystals have been examined by high-resolution transmission electron microscopy (TEM). The crystals formed in the solutions appear identical in morphology and structure with those formed on the Bioglass® surface. It may be that the soluble Si in the solution serves as the nucleating site for the apatite crystal or that apatite nuclei are released from the Bioglass® surface to the solution resulting in crystal growth.     

Spark plasma sintering of sol-gel derived 45S5 Bioglass®-ceramics: Mechanical properties and biocompatibility evaluation

This work aims to find an efficient sintering technique and optimal sintering conditions of a novel sol-gel derived Bioglass®-ceramic powder so as to achieve much improved mechanical properties compared to conventional Bioglass®. To this end, the spark plasma sintering (SPS) technique was for the first time used to densify the sol-gel derived Bioglass®-ceramic powder. It was found that the sol-gel derived Bioglass®-ceramics sintered with the SPS technique at 950 °C for 15 min had a high Young's modulus value of ~ 110 GPa, which was comparable to that of compact bone and significantly higher than the maximal value achieved by the conventional heat treatment. Moreover, the Bioglass®-ceramic compacts sintered with SPS released alkaline ions slowly and as a result, these highly densified Bioglass®-ceramics exhibited better cytocompatibility at the early stage of cell culture testing, compared to the conventional Bioglass®. Hence, the SPS technique is recommended to be used in the process of sol-gel derived Bioglass®-ceramics and its tissue engineering scaffolds.     

Plasma spraying of zirconia-reinforced hydroxyapatite composite coatings on titanium: Part II Dissolution behaviour in simulated body fluid and bonding degradation

The change of phase, morphology and bond strength of plasma sprayed hydroxyapatite (HA) coating and ZrO2/HA composite coatings immersed in simulated body fluid (SBF) for various periods of time was studied. X-ray diffractometry (XRD) and scanning electron microscopy (SEM) were used to identify the phase and observe the morphology of the coating surface before and after immersion. In addition, inductively coupled plasma emission spectroscopy (ICP) was used to measure the ion release rate of coatings in SBF for various periods of time. Observation of the morphology by SEM shows that the composite coating with the addition of ZrO2 in HA significantly reduced the dissolution rate of impurity phases in simulated body fluid. The argument was supported by measurement of Ca2+ ion concentration in SBF. During plasma spraying, less OH- ions were lost in a ZrO2-containing composite coating. This factor, together with the reduced effective surface of the ZrO2-containing HA coating, were attributed to the reduced dissolution rate of the composite coatings. All the plasma sprayed coatings degraded after immersion in SBF owing to dissolution of constituents in the coating, however, the addition of ZrO2 in HA improved the bonding strength of HA coating after immersion in SBF.     

Mechanical and in vitro performance of apatite–wollastonite glass ceramic reinforced hydroxyapatite composite fabricated by 3D-printing

In situ hydroxyapatite/apatite–wollastonite glass ceramic composite was fabricated by a three dimensional printing (3DP) technique and characterized. It was found that the as-fabricated mean green strength of the composite was 1.27 MPa which was sufficient for general handling. After varying sintering temperatures (1050–1300°C) and times (1–10 h), it was found that sintering at 1300°C for 3 h gave the greatest flexural modulus and strength, 34.10 GPa and 76.82 MPa respectively. This was associated with a decrease in porosity and increase in densification ability of the composite resulting from liquid phase sintering. Bioactivity tested by soaking in simulated body fluid (SBF) and In Vitro toxicity studies showed that 3DP hydroxyapatite/A–W glass ceramic composite was non-toxic and bioactive. A new calcium phosphate layer was observed on the surface of the composite after soaking in SBF for only 1 day while osteoblast cells were able to attach and attain normal morphology on the surface of the composite.     

Preparation and in vitro bioactivity of poly(d,l-lactide) composite containing hydroxyapatite nanocrystals

The nano-sized hydroxyapatite (n-HA) was incorporated into poly(d,l-Lactide) (PDLLA) to form a bioactive and biodegradable composite for application in hard tissue replacement and regeneration. Thin film of PDLLA composite containing 20 mass% of n-HA fillers was successfully developed through integration of solvent co-blending and hot pressing techniques. firstly, n-HA and PDLLA were chemically synthesized, respectively, then mixed together and homogeneously dispersed in N,N-dimethyl formamide(DMF) solvent, finally, the dried blended hybrid containing PDLLA matrix and n-HA fillers was put into the mould and compacted by hot-pressing machine under 8 MPa pressure at 110 °C for 15 min. In vitro studies were conducted using the simulated body fluid(SBF). Composite specimens were soaked in SBF from 1 day to 21 days prior to surface analysis. Results obtained from scanning electron microscopy(SEM) examination, Energy dispersive X-ray detector(EDX) analysis and X-ray diffraction (XRD) analysis showed that a layer of non-stoichiometric apatite formed within 7 days on HA/PDLLA composite surface after its immersion in SBF, demonstrating moderate in vitro bioactivity of n-HA/PDLLA composite, though a moderate rate of apatite formation in SBF was found on initial stage of immersion periods for n-HA/PDLLA composite, compared to the other biomaterial composite. This type of composite film exhibited certain desirable bioactive characteristics, and they are promising bone candidates to develop novel bioactive composites for biomedical application.     

标距和应变率对Kevlar49单束拉伸力学性能的影响

为探究Kevlar 49单束的尺寸效应及应变率敏感性, 首先, 利用MTS万能试验机对不同标距(25、50、100、150、200和300 mm)的Kevlar 49单束进行了准静态(应变率为1/600 s-1)拉伸测试; 然后, 利用Instron落锤冲击系统对标距为25 mm的试样进行了动态(应变率为40~160 s-1)拉伸测试; 最后, 利用Weibull模型进行统计分析, 量化了不同标距和应变率下Kevlar 49单束拉伸强度的随机变化程度。结果表明: Kevlar 49单束的拉伸力学性能与标距和应变率有相关性; 拉伸强度随标距的增加而减小, 但随应变率的增加而增大; 峰值应变和韧性均随标距和应变率的增加而减小; 提取的Weibull参数可用于数值模拟及工程应用。      

Interfacial properties and microfailure degradation mechanisms of bioabsorbable fibers/poly-l-lactide composites using micromechanical test and nondestructive acoustic emission

Interfacial properties and microfailure degradation mechanisms of the bioabsorbable composites for implant materials were investigated using micromechanical technique and nondestructive acoustic emission (AE). The tensile strength of absorbable fibers with hydrolysis was analyzed statistically using either uni- or bimodal Weibull distribution. As hydrolysis time increased, the tensile strength, the modulus and the elongation of poly(ester-amide) (PEA) and bioactive glass fibers decreased, whereas those of chitosan fiber almost did not change. Interfacial shear strength (IFSS) between bioactive glass fiber and poly-l-lactide (PLLA) was much higher than PEA or chitosan fiber/PLLA systems using dual matrix composite (DMC) specimen. The decreasing rate of IFSS was the fastest in bioactive glass fiber/PLLA composites whereas that of chitosan fiber/PLLA composites was the slowest. Work of adhesion, W_a between bioactive glass fiber and PLLA was the highest, and the wettability results were consistent with the IFSS. AE energies of PEA fiber decreased gradually, and their distributions became narrower than those in the initial state with hydrolysis time. In case of bioactive glass fiber, AE energies in tensile failure were much higher than those in compression. In addition, AE parameters at the initial state were much higher than those after degradation under both tensile and compressive tests. Interfacial properties and microfailure degradation mechanisms can be important factors to control bioabsorbable composite performance.