共查询到20条相似文献,搜索用时 109 毫秒
1.
Zhang CY Lu H Zhuang Z Wang XP Fang QF 《Journal of materials science. Materials in medicine》2010,21(12):3077-3083
Nano-hydroxyapatite/poly(l-lactic acid) (nano-HA/PLLA) composites with uniform HA distribution and good mechanical performance were fabricated by a
modified in situ precipitation method, using Ca(OH)2 and H3PO4 as precursors for the synthesis of HA phase. This method has solved the aggregation problem of the nano-sized particles in
the polymer matrix. The X-ray diffraction, Fourier transform infrared spectroscopy, and transmission electron microscopy were
used to characterize the phase composition, chemical interactions and morphology of the composites, while the mechanical properties
were determined by compressive measurements. The results show that the rod-like nano-HA particles synthesized by this method
were uniformly distributed in the PLLA matrix. The compressive strength and Young’s modulus of the composites were greatly
enhanced and reached the values of 155 MPa and 3.6 GPa at 20 wt% HA content, respectively, which are much higher than those
of the reference samples fabricated by direct mixing of PLLA with nano-HA particles. This supports the potential of these
composites for applications in bone tissue engineering and load bearing bone defects repair. 相似文献
2.
Thermally conductive carbon fiber/poly(l-lactic acid) (PLLA) composites were made by using fatty acid amides as binders to form a net-like structure of carbon fibers
in them, aiming at achieving high thermal diffusivity of the composites with a small amount of the fibers and facilitating
their processing without much cost. Infrared thermography analysis of composites with varying the size of carbon fibers and
controlling the solubility parameters of fatty acid amides in them revealed that the composite with 10 wt% of 6 mm-long carbon
fiber and 5 wt% of N,N′-ethylene bis-olearamide had a thermal diffusivity comparable to that of stainless steel (SUS304). This high thermal diffusivity
was due to percolation networks of long carbon fibers bound by the specific low-polarity amide in the composite. 相似文献
3.
Yang C Cheng K Weng W Yang C 《Journal of materials science. Materials in medicine》2009,20(3):667-672
In this paper, hydroxyapatite (HA) particles was modified with long-chain organic silane-Octadecyltrichlorosilane (OTS), and
the modified particles were further used for preparing Poly(l-lactic acid) PLLA/HA porous composite. The modified particles were characterized by means of XRD, FTIR, and XPS techniques.
Both XPS and FTIR results showed that OTS had been combined with HA, and the formation of P–O–Si bond, a covalent bond, on
the HA particle surface was confirmed by XPS. OTS-modified HA particles were used to prepare porous composites by thermally
induced phase separation method. The results showed that the composite had an interconnected pore structure with 100–300 μm
macropores. With OTS dosage increasing during modification, the mechanical properties of PLLA/OTS-modified HA porous composites
increased obviously. These results showed that OTS modification can effectively improve the interface compatibility between
HA surface and PLLA. 相似文献
4.
J. E. Bergsma F. R. Rozema R. R. M. Bos A. W. M. van Rozendaal W. H. De Jong J. S. Teppema C. A. P. Joziasse 《Journal of materials science. Materials in medicine》1995,6(12):715-724
In all patients treated with as-polymerized poly(l-lactide) (PLLA), a welling at the site of implantation was observed after three years of implantation. These swellings seem to be related with degrading PLLA and the formation of particles of high crystallinity. To avoid these complications, poly(96%l-, 4%d-lactide) (PLA96) was developed that possesses lower crystallinity that probably results in a faster and more complete degradation. To study the cause of the swelling of PLLA implants and to study the degradation of PLA96 long-term implantation studies are required. Considering the very slow degradation rate of as--polymerized PLLA, in vitro predegradation was performed at elevated temperatures (90°C) to simulate long-term physiological degradation. In this study a comparison was made between the histopathological reaction to non-degraded and predegraded PLLA, PLA96 and polyethylene (PE) discs implanted subcutaneously in rats. Animals were sacrificed after a postoperative period varying from 4 to 52 weeks. Chemical, light-and electron microscopical analysis and semi-quantitative measurements were performed. Based on the chemical analysis, the degradation rate of PLA96 was higher compared with PLLA. The histological reaction to non-degraded PLLA and PLA96 discs was very mild. The histological reaction to the predegraded implants was qualitatively similar to the reaction to the non-degraded implants, however, quantitatively an increase was noted. A number of predegraded PLLA and PLA96 discs showed an increase of volume with implantation time caused by the formation of fields of polymer debris accompanied by a granulomatous inflammatory reaction. The debris zone was found to consist of both polylactide polymer fragments and small remnants of degenerated cells. From our results it can be concluded that, when compared to PLLA, the degradation of PLA96 is enhanced. Subcutaneously implanted predegraded PLLA and PLA96 discs can induce a swelling similar to that observed with PLLA implants in patients. So, in vitro predegradation followed by in vivo implantation might be used as a model to predict late complications during clinical use. 相似文献
5.
Behzad Damadzadeh Hamideh Jabari Mikael Skrifvars Karri Airola Niko Moritz Pekka K. Vallittu 《Journal of materials science. Materials in medicine》2010,21(9):2523-2531
One main application of resorbable poly-l-lactic acid (PLLA) and poly-l-lactic-co-glycolic acid (PLGA) based materials is in medical implants. In this study composites were made from PLLA and PLGA
with hydroxyapatite (HAp) respective β-tricalcium phosphate (β-TCP) fillers. The filler content and particle size were varied,
and the thermal properties as well as the mechanical strength of the composites were investigated. The composites were made
by an extrusion compounding process giving 2–2.5 mm diameter sized profiles. The results verified that the thermal stability
of the composites was reasonable during the optimized compounding conditions. Scanning electron microscopy revealed that the
fillers were well dispersed in the polymer matrices. The mechanical properties were improved by the addition of the fillers.
The optimum mechanical properties for the extruded profiles were obtained with the HAp fillers. The E-modulus was increased
from 3.3 to 4.6 GPa by addition of filler particles (30 wt%) whereas the flexural strength was reduced from 133 to 106 MPa. 相似文献
6.
A hybrid was synthesized by grafting polyhedral oligomeric silsesquioxane (POSS) to multiwalled carbon nanotubes (MWCNTs).
The MWCNT/polymer composites produced using silsesquioxane grafted MWCNTs as a filler had a high electromagnetic interference
shielding effectiveness. Homogeneous dispersion of silsesquioxane grafted MWCNTs occurred throughout the polymer without any
aggregation, while a pristine MWCNT aggregate that integrated several nanotube domains existed in the polymer matrix. A comparative
study of the optical transmittance, electrical, and electromagnetic interference shielding properties of poly(l-lactide) (PLLA)/MWCNT composites based on pristine MWCNTs and silsesquioxane grafted MWCNTs was carried out. A high electromagnetic
interference shielding effectiveness (15–16 dB) was obtained in the 36–50 GHz range at a relatively low filler loading (4
wt%) in the PLLA/silsesquioxane grafted MWCNT composite. 相似文献
7.
Biocompatibility of intraosseously implanted predegraded poly(lactide): an animal study 总被引:1,自引:0,他引:1
J. E. Bergsma R. R. M. Bos F. R. Rozema W. De Jong G. Boering 《Journal of materials science. Materials in medicine》1996,7(1):1-7
During degradation of high molecular weight as-polymerized poly(l-lactide) (PLLA) late complications such as swelling of the subcutaneously implanted bone plates have been observed in patients. However, in the same patients the intraosseously implanted PLLA screws did not give rise to any complications. To investigate a possible difference in the degradation and histological response due to the site of implantation, subcutaneous and intraosseous implantation studies are necessary. In the present study rods of PLLA and a copolymer poly(96l/4d-lactide) (PLA96) and predegraded PLLA and PLA96 were implanted intraosseously in rabbit tibiae. In vitro predegradation at elevated temperatures was used to obtain an enhanced degradation rate to simulate long-term physiological degradation. Animals were sacrificed after a postoperative period varying from 2 to 26 weeks. The predegraded PLLA and PLA96 implants showed a high rate of fragmentation and internalization of particles by macrophages. In the medullary cavity large fields of macrophages and, with the predegraded PLA96 implants, haemorrhages and infiltrates were noted, but no osteolytic changes were observed in the cortical bone. It can be concluded that, based on the disintegration of the implants and the accompanying histological reaction, a reaction similar to that found with subcutaneous implants in former studies had occurred. This indicates that not only the site of implantation, subcutaneous or intraosseous, but a number of other factors will affect the degradation process and the corresponding histological response. 相似文献
8.
Poly(l-lactic acid)/hydroxyapatite (PLLA/HA) nanocomposite, which combines the properties of PLLA and HA, is suitable to construct scaffold for bone tissue engineering. Its mineralization behavior plays a key role in composite’s property. In this present work, two PLLA/HA composites with porous and compact architecture were fabricated and soaked into simulated body fluid (SBF) at 37 °C for in vitro mineralization, respectively. An attenuated total reflection Fourier transform infrared (ATR FTIR) mapping coupled with principal component analysis was developed to investigate the mineralization kinetics. The FTIR images with an area of 300 × 300 μm2 were collected every 7 days. The results suggest that the mineralization of PLLA/HA composites in SBF follows a zero-order kinetic model, no matter what the architecture is. However, it follows a second-order model when the composite is degraded in phosphate-buffered saline solution based on our previous work. The mechanisms of the in vitro mineralization kinetics in different submersion solutions are discussed. Our results alert researchers that they should choose the mineralization medium cautiously. 相似文献
9.
W. Yan C. Y. Zhang L. L. Xia T. Zhang Q. F. Fang 《Journal of materials science. Materials in medicine》2016,27(8):130
Calcium phosphate ceramics such as synthetic hydroxyapatite and tricalcium phosphate are widely used in the clinic, but they stimulate less bone regeneration. In this paper, nano-hydroxyapatite/poly(l-lactic acid) (nano-HA/PLLA) spindle composites with good mechanical performance were fabricated by a modified in situ precipitation method. The HA part of composite, distributing homogenously in PLLA matrix, is spindle shape with size of 10–30 nm in diameter and 60–100 nm in length. The molar ratio of Ca/P in the synthesized nano-HA spindles was deduced as 1.52 from the EDS spectra, which is close to the stoichiometric composition of HA (Ca/P & 1.67). The compress strength is up to 150 MPa when the HA content increase to 20 %. The in vitro tests indicate that HA/PLLA bio-composites have good biodegradability and bioactivity when immersed in simulated body fluid solutions. All the results suggested that HA/PLLA nano-biocomposites are appropriate to be applied as bone substitute in bone tissue engineering. 相似文献
10.
The enhanced thermal diffusivity and mechanical properties of poly(l-lactic acid) (PLLA) nanocomposites reported here are based on the percolation network formed when PLLA is hybridized with
short carbon fibers (CFs) and functionalized zinc oxide whiskers. The PLLA nanocomposite containing 30 wt% (≈9.5 vol%) ZnO
whiskers and 10 wt% (≈8.1 vol%) CFs had a thermal diffusivity almost as high as that of stainless steel and an insulator-level
electrical resistivity (>1010 Ωm). Modifying the surface of the ZnO whiskers by esterifying them using specific alcohols with long linear alkyl chains
improved the elastic strength and toughness of the nanocomposites significantly. These results suggest that hybridizing PLLA
with short CFs and functionalized ZnO whiskers yields nanocomposites with high thermal diffusivity as well as high electrical
resistivity and excellent mechanical properties. 相似文献
11.
Gerhardt LC Jell GM Boccaccini AR 《Journal of materials science. Materials in medicine》2007,18(7):1287-1298
Titanium dioxide (TiO2) nanoparticles were investigated for bone tissue engineering applications with regard to bioactivity and particle cytotoxicity.
Composite films on the basis of poly(d,l lactid acid) (PDLLA) filled with 0, 5 and 30 wt% TiO2 nanoparticles were processed by solvent casting. Bioactivity, characterised by formation of hydroxyapatite (HA) on the materials
surface, was investigated for both the free TiO2 nanoparticles and PDLLA/TiO2 composite films upon immersion in supersaturated simulated body fluid (1.5 SBF) for up to 3 weeks. Non-stoichiometric HA
nanocrystals (ns-HA) with an average diameter of 40 nm were formed on the high content (30 wt% TiO2) composite films after 2 weeks of immersion in 1.5 SBF. For the pure PDLLA film and the low content composite films (5 wt%
TiO2) trace amounts of ns-HA nanocrystals were apparent after 3 weeks. The TiO2 nanopowder alone showed no bioactivity. The effect of TiO2 nanoparticles (0.5–10,000 μg/mL) on MG-63 osteoblast-like cell metabolic activity was assessed by the MTT assay. TiO2 particle concentrations of up to 100 μg/mL had no significant effect on MG-63 cell viability. 相似文献
12.
Influence of the porosity of hydroxyapatite ceramics on in vitro and in vivo bone formation by cultured rat bone marrow stromal cells 总被引:3,自引:0,他引:3
Okamoto M Dohi Y Ohgushi H Shimaoka H Ikeuchi M Matsushima A Yonemasu K Hosoi H 《Journal of materials science. Materials in medicine》2006,17(4):327-336
The in vitro and in vivo osteoblastic differentiation of rat bone marrow stromal cells (MSCs) was assessed on hydroxyapatite disks with 3 different
porosities: 30%, 50%, and 70% (HA30, HA50, and HA70, respectively). MSCs obtained by 10-day culture of fresh bone marrow cells
were subcultured for 2 weeks on 3 kinds of porous HA disks in the presence and absence of dexamethasone (Dex). After 2 weeks
of subculture, alkaline phosphatase (ALP) activity and osteocalcin production of MSCs/HA composites with Dex were higher than
those without, and increased with increasing porosity. The resultant bone tissue grafts “cultured-bone/HA constructs” were
implanted subcutaneously into the backs of syngeneic rats, and harvested 1, 2, and 4 weeks after implantation. At 1 week,
only cultured-bone/HA70 constructs exhibited expanded bone formation. At 2 and 4 weeks, active osteoblasts and progressive
bone formation were observed morphologically in both cultured-bone/HA50 and HA70 constructs. At 4 weeks, bone tissue was observed
even in cultured-bone/HA30 constructs. ALP activity and osteocalcin production also increased with increasing porosity and
time after implantation. In this in vivo model, different scaffold porosity with similar crystal morphology of the apatite phase demonstrated marked differences in
ability to support osteogenesis by implanted rat MSCs. 相似文献
13.
Chikara Tsutsumi Jun Sakafuji Mai Okada Kazuyuki Oro Kazuaki Hata 《Journal of Materials Science》2009,44(13):3533-3541
Outstanding controlled release materials were developed using statistically random copolymers of l-lactide (l-LA) with ε-caprolactone (CL) using Sn(oct)2 as a catalyst at 150 °C for 24 h without solvent. Preparation of novel controlled release materials was carried out using
useful organic compounds with low boiling points and synthetic random copolymers composed of l-LA and CL as base materials under supercritical carbon dioxide (scCO2). Low-boiling-point compounds such as d-limonene, hinokitiol, and trans-2-hexenal were used. In impregnation experiments using scCO2, the amounts of low-boiling-point compounds increased with an increase in l-LA content. When enzymatic degradation of poly(l-LA-ran-CL) was performed using lipase PS, copolymers with higher CL contents degraded more rapidly than did copolymers with higher
l-LA content. In contrast, enzymatic degradation of copolymers occurred to a higher degree with increased l-LA content in enzymatic degradation by proteinase K. In a controlled release experiment with poly(l-LA-ran-CL) (=73/27), after 400 h of degradation by proteinase K, the remaining weight of the copolymer pellet was 6% and the amount
of d-limonene remaining in the pellet was 15%. 相似文献
14.
The fracture behaviour of injection moulded polyarylamide (PAR) composites containing 30, 50 and 60 wt% glass and 30 wt% carbon fibres has been investigated in both dry and wet states. Kinetics of moisture absorption study revealed that PAR and its composites exhibit Fickian behaviour. The incorporation of short fibres into a PAR matrix has resulted in the reduction of both maximum moisture content (M
m
) and diffusion coefficient (D). The fracture mechanical characterization of the various materials was evaluated by using notched compact tension (CT) specimens. Testing was performed as a function of temperature (T = –40, 20 and 80°C) and crosshead speeds (v = 1 and 1000 mm min–1) on as received (AR) specimens. The influence of water uptake due to the hygrothermal ageing (HA) process on residual fracture performance was also studied. The combined action of moisture-induced plasticization of the PAR matrix and interfacial degradation has been concluded to play a significant role in controlling the fracture behaviour of the (HA) composites. The residual fracture properties of both neat PAR and its composites are almost fully recovered in the case of redrying (RD). Failure mechanisms of both the matrix and the composites, assessed by fractographic studies in a scanning electron microscope (SEM) are discussed. 相似文献
15.
Sternberg K Kramer S Nischan C Grabow N Langer T Hennighausen G Schmitz KP 《Journal of materials science. Materials in medicine》2007,18(7):1423-1432
In this study, absorbable polymer stent coatings for localized drug delivery based on poly(l-lactide) (PLLA) and cyclosporine A (CsA) were developed and tested in vitro. Metallic stents were coated with different compositions
of PLLA/CsA (70/30, 60/40, 50/50% w/w) and β-sterilized. The specimens were used to assess the drug release kinetics with
HPLC. Sterilization influenced polymer degradation was measured with GPC. Mechanical integrity of the stent coatings was studied
with SEM. The interconnection of the coated stents with a balloon-catheter was characterized by the measurement of stent dislodgment
force. A migration assay was used to determine the inhibitory effect of the model drug CsA on smooth muscle cell (SMC) migration.
The release of CsA was established over time periods up to 24 days in sodium chloride solution and in porcine blood plasma.
An inhibition of SMC migration (max. 26–33%) was found for CsA concentrations of 4 × 10−5 to 4 × 10−7 mol/l. Marked molecular weight reduction (70–80%) of the PLLA matrix occurred after β-sterilization. We also observed a substantial
decrease of in vitro degradation time. The maintenance of the mechanical integrity of the polymer coating during crimping
and dilation of the specimens could be verified, and a sufficient stent dislodgment force of 0.8–0.9 N was measured. 相似文献
16.
对用于骨折内固定的β-偏磷酸钙晶须/左旋聚乳酸(β-CMPW/PLLA)复合材料在体外降解过程中强度的变化、 分子量和微观形貌进行了初步研究。结果表明: 在人体模拟体液(SBF)中浸泡, 前8周材料的强度变化较小, 25wt%β-CMPW/75wt%PLLA降解20周后的抗压强度值仍高达103MPa; 45wt%β-CMPW/55wt%PLLA降解12周后抗压强度约为初始值的88%。扫描电镜图表明, 随降解时间的延长, 因聚乳酸溶解而在样品中形成孔洞。在降解周期内, SBF溶液的pH值随β-CMPW/PLLA降解时间的延长基本保持稳定。凝胶渗透色谱检测结果表明, PLLA的数均相对分子质量和重均相对分子质量随降解时间的延长而降低, 降解20周后数均相对分子质量约为20万, 重均相对分子质量下降了32%。 相似文献
17.
Density (ρ) and ultrasonic velocity (u) values of amino acids l-alanine, l-proline, l-valine, and l-leucine in 2M aqueous KCl and 2M aqueous KNO3 solutions have been measured as a function of amino acid concentration at different temperatures (298.15 K, 303.15 K, 308.15 K,
313.15 K, 318.15 K, and 323.15 K). Using the ρ and u data, partial molal volume () and partial molal isentropic compressibility () values have been computed. The increase in partial molal volume with temperature has been attributed to the volume expansion
of hydrated zwitterions. The and values of l-alanine, l-proline, l-valine, and l-leucine in 2M aqueous KCl and KNO3 solutions have been found to be larger than the corresponding values in water. The larger partial molal volumes of l-alanine, l-proline, l-valine, and l-leucine in 2M aqueous KCl and KNO3 solutions have been ascribed to the formation of ‘zwitterion-K+/Cl−/NO3−’ and ‘K+/Cl−/NO3−–water dipole’ aggregates in solutions. The formation of these entities in solutions causes the release of water associated
with zwitterions to the bulk water. The larger partial molal compressibilities of l-alanine-/l-proline-/l-valine-/l-leucine–2M aqueous KCl/KNO3 solutions than the corresponding values in water have been attributed to the formation of ‘zwitterion–ion’ and ‘ion–water
dipole’ incompressible entities in solutions. 相似文献
18.
Bioactive ceramic/bioresorbable plastic composites have been expected as materials for the bone fracture fixations which have
more biocompatibility than monolithic bioresorbable plastics. Many studies have been conducted on these materials. Most studies,
however, focused on the mechanical properties under static loading. In the actual usage, these materials are loaded dynamically.
In this study, effects of strain rate on the mechanical properties of tricalcium phosphate/poly(l-lactide) (TCP/PLLA) composites were investigated experimentally and analytically. The TCP/PLLA composites containing three
different TCP contents (5, 10 and 15 wt.%) were prepared by injection molding. In order to characterize the mechanical properties,
tensile and compressive tests were conducted. The results of tensile tests indicated that the Young’s moduli of composites
increased with increasing TCP contents. For each TCP contents, tensile Young’s modulus kept constant up to strain rate of
10−1/s. On the other hand, tensile strength increased with increasing strain rate. The effect of strain rate became larger with
decreasing TCP contents, which means the strain rate dependency of the PLLA is more effective than that of TCP. From the results
of compressive tests, similar results with tensile tests were obtained. That is, compressive Young’s modulus kept constant
up to strain rate of 10−1/s and the 0.2% proof stress increased with increasing strain rate. In order to predict the mechanical behavior of TCP/PLLA
composites, the micro-damage mechanics was proposed. In this analysis, 3-phases particle reinforced composites, which include
the intact particles, damaged particles and matrix, are assumed. The elastic constants are calculated with micromechanics
based on the analyses by Eshelby and Mori and Tanaka. Only the debonding between particle and matrix are assumed as the damage.
The nonlinearity in the stress-strain behavior of matrix PLLA is also considered. The debonding particles are assumed as voids.
Void formation is calculated based on the energy criterion. The energy release rate associated with void formation was estimated
by fitting the analytical results with the experimental results of the composites with 15 wt.% TCP contents for each strain
rate. Then the analytical results for the composites with 5 and 10 wt.% TCP contents were compared with the experimental results.
The analytical tensile stress-strain curves are in good agreement with experimental results. It is also clarified that the
energy release rate associated with void formation increased with increasing strain rate. 相似文献
19.
Xu Y Fu W Li G Shi J Tan H Hu K Cui F Lin Q Zhang X 《Journal of materials science. Materials in medicine》2012,23(4):1119-1128
In this study, we have fabricated an artificial ureter by transplantation of in vitro-expanded urothelial cells onto an in
vivo-prefabricated capsular stent using tissue engineering methods. Spiral poly (l-lactic acid) (PLLA) stents were transplanted into the subcutaneous of Wistar rats for a period of 1, 2 or 3 weeks to induce
the formation of connective tissue capsules on their surfaces. The capsular PLLA stents were then decellularized and further
recellularized with bladder epithelial cells to fabricate artificial ureters. The results showed that the entrapped cells
in all capsules remained continuously proliferation and lined up in continuous layers. In addition, the urothelial cells on
the capsular stents with an embedding period of 2 or 3 weeks showed higher proliferative viability compared with the cells
on the stents with an embedding time of 1 week (P < 0.05). The results of the study indicated that the prefabricated capsular stents could serve as alternative cell carriers
for tissue engineered ureters, especially with embedding time from 2 to 3 weeks. 相似文献
20.
Bioactive ceramics attracts much attention as materials for bone implants, because of their high biocompatibility. For example, hydroxyapatite (HA) has bone-bonding ability through a bone-like apatite layer in body environment and β-tricalcium phosphate (β-TCP) has a high bioresorbability in body environment. In addition, HA/β-TCP composites has the characteristics of both HA and TCP. However, it is difficult to sinter the composite, so that MgO has been used as a sintering agent. In the present study, effects of MgO addition on sintering calcium phosphate ceramics and composites were investigated. In order to evaluate the effect of MgO on the composites, HA, HA/β-TCP(30wt%), and HA/β-TCP(50wt%) with 1wt% MgO were prepared and characterized. To clarify the role of MgO on sintering of calcium phosphate ceramics, HA, β-TCP, and α-TCP with different TCP content (0, 1, 2, 3, 4, and 5 wt%) were also prepared. The results suggest that MgO addition densified HA/β-TCP composites and gave higher strength composites. The results of monolithic calcium phosphate ceramics indicated MgO addition was effective on β-TCP and α-TCP, not on HA. The maximum content of Ca atom in β-TCP displaced with Mg atoms in MgO might be 24 atm%. 相似文献