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2 · ; 1 TGA experiments selected for this study experimental production of PLA organization stand for foam bubble diameter and the phase transition temperature and thermal stability of the TGA experiment manufactured using Perkin Elmer Pyris 1 TGA thermal gravimetric analysis, the use of ceramic crucible, sample mass minimum (1. 00 ± 0. 10) mg, scanning temperature range: 30 ℃ ~ 500 ℃, using high-purity N2 purge and experimental sub-group 2, respectively, process control heating rate 20 ℃ / min and 40 ℃ / min, each PLA materials were selected and saturation pressures of 2,3 and 4MPa PLA foam produced under conditions of four times a TGA experiment, in order to verify the repeatability of experiments,
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tissue engineering is the application of life sciences and engineering principles and technology, research and development with to repair, maintain, and promote human tissue or organ dysfunction and morphological recovery of the biological alternatives. scaffolds for tissue engineering materials can be implanted in vivo, and organization of living cells can be combined and can be degraded and absorbed by the three-dimensional porous three-dimensional structure It is the most basic structure of tissue engineering. the ideal scaffold for tissue engineering of biological materials to a general non-toxic and stable characteristics, but also must have good biocompatibility and tissue compatibility and biodegradation of control absorption rate, while a certain hole density and suitable pore size for cell growth, nutrient exchange and the flow of metabolites to provide enough space. polylactic acid (PLA) is the main raw material for the polymerization of lactic acid polymer, can be used as raw materials for fermentation production of agricultural products and synthetic, have good mechanical properties and physical properties; its metabolism in the human body end product is CO2 and H2O, the intermediate product lactic acid is the body's normal sugar metabolism, showing excellent bio- degradation of absorption, and thermal stability of PLA, the PLA is the U.S. Food and Drug Administration (FDA) approved for human use of the polymer material can be one.
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1.1 PLA foam solid experimental design of this study experimental solid-state system is divided into two parts, foam, CO2 saturation pressure device shown in Figure 1 (a) shows, high-purity CO2 gas saturation ( Nanjing Special Gas Co., Ltd.) to flow from high pressure gas cylinders in the pressure vessel and saturated by the release valve regulating the pressure of CO2 in the pressure vessel, the saturation pressure of the PLA material; temperature foam device shown in Figure 1 (b) shown, after the saturation pressure of the PLA material carried into the foam to the water bath when the water temperature exceeds glass transition temperature, PLA materials will expand and form a porous tissue scaffolds. In this study, L-PLA used raw materials from Shenzhen prone New Material Co., Ltd. to buy, density 1.25 g/cm3, the glass transition temperature of 60 ℃ ~ 65 ℃, the melting temperature of 175 ℃ ~ 185 ℃. raw material sheet thickness 0.4 mm, cylindrical granular material shape, diameter 2.5 mm, height of 3mm. the experiment is as follows: (1) at room temperature, samples of poly lactic acid saturation on the CO2 pressure in the pressurized vessel, the pressure within the pressure vessel through the pressure gauge (minimum scale of 0. 1MP) indicates adjustment; (2) after a certain period of time after the saturation pressure of the sample removed at room temperature and atmospheric pressure desorption to reach equilibrium inside and outside of the foam core; (3) constant temperature water bath sample into a certain time of the foam, to obtain good tissue engineering scaffolds porosity of porous materials due to PLA foam pore density and cell size depends on the CO2 saturation pressure, pressure time, foaming temperature and foaming time and other factors, requiring reasonable conditions to select a different foam scaffold for the production of PLA in this experiment will PLA sheet cut into 20mm × 20mm of sheet 40, and 40 PLA particles prepared materials, they are evenly divided into four groups, in such Table 1 shows the experimental conditions compared foam.
1.2 Experimental results Figure 2 (a) photograph shows the granular material and foaming PLA after the photo (from left to right respectively. raw materials, saturation pressures of 2, 3,4 MPa when the manufacture of foam, and their diameters 7,6,4 · 5mm, height were 7.5, 7,5 mm), shows the original raw materials through the colorless and transparent PLA After the foam into a porous opaque solid foam, the volume increased by 19.6, 13.4, 5.4 times for accurate analysis of the characteristics of PLA foam, with a microscope under these conditions, the production of foam for image capture, measurement The average bubble diameter to the hole as shown in Table 1 the experimental measurements show that the production and, PLA foam tissue scaffolds, the average hole diameter and CO2 saturation pressure,
Salvatore Ferragamo outlet, pressure time and foaming temperature has a direct relationship, it is consistent with homogeneous The basic rules of foam in the low saturation pressure, high pressure foaming temperature and long time, the larger the bubble hole diameter; but when the pressure long enough, when the foam core of becoming saturated, the bubble tends to a hole diameter stable value which saturation pressure of the material properties play a decisive role in the high pressure, CO2 molecules in the gaps between the PLA form more foam core, foam obtained by the high cell density, a small bubble of dense foam hole diameter material experimental bubble foam aperture wide range, from a few to hundreds of μm, for different types of tissues and organs to provide suitable cells the size of the support structure shown in Figure 2 (b) shows the 2MPa saturation pressure, foaming temperature of 85 ℃ PLA tissue scaffolds made of foam scanning electron microscope photographs, it's an average pore size of 300μm.
acid in the body, however, humidity, oxygen and enzymes under the effect of different pore size of scaffold degradation rate will correspondingly accelerated degradation time can be controlled completely in a few months to few years. Therefore, decomposition of PLA scaffold can absorb the time difference between the material basis of theoretical and experimental design in the organizational design of the stent, the growth of different tissues and cells require different pore sizes of materials, and require different biodegradation rate in the actual applications, the pore size is too small foam cell growth and hinder the absorption of scaffolds, but the pore size is too large will reduce the mechanical strength of scaffold material, affecting its structural stability; the same time will reduce the long degradation time of stent materials, the decomposition rate, extend the bracket material is broken down in the body to absorb the time, so in the scaffold design and production needs of a reasonable choice of scaffold pore size and stability of the stand to meet the requirements of different organizations to achieve organizational growth rate and material degradation reasonably match the speed through the tissue engineering scaffold material production and thermal analysis, the scaffolds can be controlled by reasonable experimental production conditions (saturation pressure, foaming temperature, etc.) to obtain different pore size distribution of PLA foam, Stability analysis and achieved by thermal degradation of the estimated time frame the organization.
[CLC ] R318. 08 [Document code] A [Article ID] 1001-4616 (2010) 04-0048-05
3 Conclusion In this paper, traditional tissue engineering scaffold material in organic solvent residues, the use of CO2 saturation pressure and temperature of the solid foam foam technology, biodegradable materials, PLA carried out under different conditions of tissue scaffolds made of foam, obtained with different cell density and pore size distribution of PLA foam, experiments have measured their wide aperture range (a few μm to several hundred μm), cell growth to meet the requirements of different organizations,
Beats By Dre Studio, while application of thermogravimetry on PLA foam for thermal analysis and comparison and PLA materials, experimental results show that, PLA material through the foam, its hot decreased stability, decomposition temperature decreases; with lower saturation pressure, PLA foam foam stent diameter increased, reducing the number of foam,
vibram five fingers outlet, its decomposition temperature increased, while the degradation at room temperature, extended in this paper's findings for different types of tissue engineering scaffold materials and cell diameter, and the precise control of scaffold degradation characteristics to provide a new detection method.
2 PLA foam TGA
1 material preparation
2.2 TGA measurements Figure 3 (a) and (b) gives the PLA, respectively, the bubble in raw materials and the heating rate of 20 ℃ / min and 40 ℃ / min, the thermal re- curve seen at 300 ℃ to 400 ℃ range of memory in a process of rapid weight loss, PLA breaks down quickly, without a secondary decomposition process, completely decomposed in the gasification completely into CO2 and H2O, without leaving any residue, This feature proved entirely suitable for making tissue PLA scaffolds with good biodegradability and absorption in the same heating speed, PLA highest decomposition temperature of raw materials, with the saturation pressure increases, the foam density, cell pore size decreases, the decomposition temperature decreases, while from the beginning to the complete decomposition decomposition decomposition of time longer. under different heating rate TG curve shape similar to the same trend at different temperature conditions, thermal decomposition of the sample sequence no change, indicating that the PLA scaffold material and have similar degradation characteristics; but as the heating rate increased, a corresponding increase in their decomposition temperature, TG curves move to high temperatures through TG curve analysis can be, under different production conditions The resulting PLA foams with different thermal stability. PLA raw material because there is no foam, which links to the highest degree of molecular bonds, so the best stability; through high-pressure gas saturation pressure, CO2 molecules into the PLA molecules free space, the greater the saturation pressure, PLA foam core in the more, the more the formation of foam, bubble wall thickness decreased, PLA molecular link key to minimize, reduce the thermal stability, decomposition temperature decreases, although high-temperature weight loss for the PLA stents was less affected, but the degradation kinetic theory can use the TG curve degradation time estimates obtained by calculating the temperature of 37 ℃, saturated 3, 4 and 4.7 MPa pressure of the PLA stent 5% weight loss raw materials and the degradation time was 2.5 E10, 9.2 E10, 1.3 E11, 1.5 E11 and 6.5 E12min, visible PLA decomposition of raw material and stent materials have a very different time, the time gap to 200 times more visible case of body temperature and high-aperture small foam cell density has a longer degradation time frame due to the degradation of the TG experiment time is estimated in N2 environment, PLA scaffold degradation time is longer.
[Keywords] tissue engineering scaffolds, polylactic acid, solid foam method, TG
porous scaffolds produced by the current method phase separation, particle precipitation solution casting technique, fiber bonding method (non-woven mesh method) and the supercritical gas foaming method, etc. separated from the particle precipitation and solution casting technique requires large amounts of organic solvent remaining in the polymer Organic solvents will destroy the biological activity of cells and tissue, reducing the biological compatibility of biological scaffolds. fiber bonding method requires a high temperature, high temperature will destroy the activity of biological molecules. supercritical gas foaming method requires high-pressure gas, through the rapid cooling the foam buck the growth, the method has the inherent instability of the results difficult to control foam in recent years developed gas-solid foam technology is a physical foaming process, do not use any organic solvents, foam process simple, easy to control parameters, the results are stable foam; production of PLA tissue scaffold physical and chemical characteristics and stability, can be used in the production of tissue engineering scaffolds. tissue engineering scaffolds need to have the right foam density and pore size, they decided to the material's mechanical properties and tissue growth characteristics. thermogravimetric analysis (TGA) is in the process control temperature with the heat balance for material quality and temperature relationship of a technology that can accurately measure the quality of material changes and changes rate, in analytical chemistry, polymers, synthetic materials are widely used due to different cell density and pore size of the organization stand PLA foam composition of CO2 and the proportion of different, but also determines the material's physical and chemical properties, so can be achieved by TGA foam tissue scaffold pore size and thermal stability and degradation time of the analysis in this study design a CO2 system, solid-state foaming experiments, micro-organization of the PLA stent foam materials to obtain a good distribution of foam scaffold for tissue engineering, and through the TGA experiment with different hole diameter of the PLA foam foam material under different heating rate thermal stability analysis.
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