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Kinetic evaluation of the size-dependent decomposition performance of solvent-free microcellular polylactic acid foams
GePu Guo,QingYu Ma,Fang Wang,Bo Zhao,Dong Zhang
Chinese Science Bulletin , 2012, DOI: 10.1007/s11434-011-4873-5
Abstract: A thermal gravimetric method is described for evaluating the kinetics of cell size-dependent decomposition and lifetime estimation for microcellular tissue engineering scaffolds made of biodegradable polylactic acid (PLA) foams. PLA foam cell sizes from 550 to 20 μm were fabricated experimentally using a solvent-free solid-state foaming technique under saturation pressures from 1 to 5 MPa. The thermal properties of the PLA foams with respect to the cell sizes were measured using thermal gravimetric analysis in a nitrogen atmosphere and the activation energy and pre-exponential factor were derived to evaluate the decomposition kinetics and estimate lifetime. It was found that small cell sizes can be achieved under high saturation pressures and that the thermal stability of PLA decreases after the fabrication process. The cell size-dependent thermal stability and degradation rate indicate that a PLA foam of larger cell sizes has a shorter degradation time, a few tenths that of the PLA raw material, at a temperature of 37°C. The results suggest that it is feasible to optimize fabrication parameters to obtain appropriate cell sizes and lifetimes that satisfy the application requirements for various organs. This study provides the basis for precise scaffold design and quantitative analysis of PLA foams in tissue engineering applications.
Preparation and Characterization of Porous Nano-dHA/PLA/BCP Scaffold
JI Jin-Gou,LI Xi,ZHOU Zhi-Guo,HU Cheng-Bo,XIA Zhi-Ning,HUANG Rui
无机材料学报 , 2009, DOI: 10.3724/sp.j.1077.2009.00480
Abstract: To improve the hydrophilicity and to avoid sharp pH decrease during the degradation of polylactic acid/biphasic calcium phosphate ceramics (PLA/BCP) scaffold in solution, nano calcium deficient hydroxyapatite/polylactic acid/biphasic calcium phosphate (nano-dHA/PLA/BCP) scaffold was prepared by immersing asa2sintered porous BCP scaffold in nano-dHA/PLA mixed solution followed by vacuum drying. The compressive strength of samples was measured by universal test machine. The porosity percentage of samples was investigated by Archimedes method. The surfaces of samples were analyzed by scanning electron microscope (SEM). The watera2retention rate and pH value change of the samples incubating in phosphate buffered solution (PBS) were also studied. The results show that the compressive strength and watera2retention rate of the nanoa2dHA/PLA/BCP scaffold with rougher surface are improved. The pH decrease rate of nano-dHA/PLA/BCP scaffold is slower than that of PLA/BCP scaffolds incubating in PBS, and the surfaces have more bone-like apatite formation when incubating in simulated body fluid (SBF).
Progress on biodegradation of polylactic acid——A Review

Fan Li,Sha Wang,Weifeng Liu,Guanjun Chen,

微生物学报 , 2008,
Abstract: Polylactic acid is a high molecular-weight polyester made from renewable resources such as corn or starch. It is a promising biodegradable plastic due to its mechanical properties, biocompatibility and biodegradability. To achieve natural recycling of polylactic acid, relative microorganisms and the underlying mechanisms in the biodegradation has become an important issue in biodegradable materials. Up to date, most isolated microbes capable of degrading polylactic acid belong to actinomycetes. Proteases secreted by these microorganisms are responsible for the degradation. However, subtle differences exist between these polylactic acid degrading enzymes and typical proteases with respect to substrate binding and catalysis. Amino acids relative to catalysis are postulated to be highly plastic allowing their catalytic hydrolysis of polylactic acid. In this paper we reviewed current studies on biodegradation of polylactic acid concerning its microbial, enzymatic reactions and the possible mechanisms. We also discussed the probability of biologically recycling PLA by applying highly efficient strains and enzymes.
Biomanufacturing versus Superficial Cell Seeding: Simulation of Chondrocyte Proliferation in a Cylindrical Cartilage Scaffold  [PDF]
Mohammad Izadifar
International Journal of Tissue Engineering , 2013, DOI: 10.1155/2013/407047
Abstract: Local volume averaging approach was used for modeling and simulation of cell growth and proliferation, as well as glucose transfer within a cylindrical cartilage scaffold during cell cultivation. The scaffold matrix including the nutrient solution filling spaces among seeded cell colonies was treated as a porous medium. Applying differential mass balance of cells and glucose to a representative elementary volume of the scaffold, two diffusional mass transfer models were developed based on local volume averaged properties. The derived governing equations take into account time-dependent glucose diffusion, glucose consumption by cells, cell migration, apoptosis, and cell reproduction within the scaffold. Since the volumetric fraction of cells in the scaffold relies on cell growth, which strongly depends on glucose concentration in the scaffold, the governing equations were solved simultaneously using implicit finite difference method and Gauss-Seidel technique. Simulation results showed that cell volumetric fraction of the scaffold can reach about 45% after 50 days if a culture medium with a glucose concentration of 45?kgm?3 is used. Also, simulation results indicate that more uniform and higher average cell volume fraction of the scaffold can be obtained if biomanufacturing-based cell seeding is used across the scaffold rather than cell seeding on the scaffold surface. 1. Introduction Nowadays tissue engineering has extensively attracted the attention of researchers to the development of biological substitutes for repairing or maintaining damaged tissues. Principally three therapeutic strategies which can be adopted for treating a damaged tissue are (i) implantation of precultivated cells; (ii) implantation of preassembled tissues which have been regenerated in vitro; (iii) implantation of biocompatible and biodegradable scaffolds containing live cells for in situ regeneration. In the third strategy, live cells and growth factors are incorporated in a degradable scaffold which is implanted in the damaged tissue where growth of both tissue cells and cells in the scaffold promotes tissue healing [1]. A cell-scaffold can be made of natural materials such as chitosan, collagen, and glycosaminoglycans or synthetic materials such as polyglycolic acid (PGA), polylactic acid (PLA), and polycaprolactone (PCL) by means of a biomanufacturing fabrication method. The scaffold features must satisfy some crucial conditions. The porosity of the scaffold should be sufficiently high to facilitate cell growth, cell migration, and nutrient transfer as well as transport of
Novel Biodegradable Porous Scaffold Applied to Skin Regeneration  [PDF]
Hui-Min Wang, Yi-Ting Chou, Zhi-Hong Wen, Zhao-Ren Wang, Chun-Hong Chen, Mei-Ling Ho
PLOS ONE , 2013, DOI: 10.1371/journal.pone.0056330
Abstract: Skin wound healing is an important lifesaving issue for massive lesions. A novel porous scaffold with collagen, hyaluronic acid and gelatin was developed for skin wound repair. The swelling ratio of this developed scaffold was assayed by water absorption capacity and showed a value of over 20 g water/g dried scaffold. The scaffold was then degraded in time- and dose-dependent manners by three enzymes: lysozyme, hyaluronidase and collagenase I. The average pore diameter of the scaffold was 132.5±8.4 μm measured from SEM images. With human skin cells growing for 7 days, the SEM images showed surface fractures on the scaffold due to enzymatic digestion, indicating the biodegradable properties of this scaffold. To simulate skin distribution, the human epidermal keratinocytes, melanocytes and dermal fibroblasts were seeded on the porous scaffold and the cross-section immunofluorescent staining demonstrated normal human skin layer distributions. The collagen amount was also quantified after skin cells seeding and presented an amount 50% higher than those seeded on culture wells. The in vivo histological results showed that the scaffold ameliorated wound healing, including decreasing neutrophil infiltrates and thickening newly generated skin compared to the group without treatments.
Safety Evaluation of a Bioglass–Polylactic Acid Composite Scaffold Seeded with Progenitor Cells in a Rat Skull Critical-Size Bone Defect  [PDF]
Karam Eldesoqi, Dirk Henrich, Abeer M. El-Kady, Mahmoud S. Arbid, Bothaina M. Abd El-Hady, Ingo Marzi, Caroline Seebach
PLOS ONE , 2014, DOI: 10.1371/journal.pone.0087642
Abstract: Treating large bone defects represents a major challenge in traumatic and orthopedic surgery. Bone tissue engineering provides a promising therapeutic option to improve the local bone healing response. In the present study tissue biocompatibility, systemic toxicity and tumorigenicity of a newly developed composite material consisting of polylactic acid (PLA) and 20% or 40% bioglass (BG20 and BG40), respectively, were analyzed. These materials were seeded with mesenchymal stem cells (MSC) and endothelial progenitor cells (EPC) and tested in a rat calvarial critical size defect model for 3 months and compared to a scaffold consisting only of PLA. Serum was analyzed for organ damage markers such as GOT and creatinine. Leukocyte count, temperature and free radical indicators were measured to determine the degree of systemic inflammation. Possible tumor occurrence was assessed macroscopically and histologically in slides of liver, kidney and spleen. Furthermore, the concentrations of serum malondialdehyde (MDA) and sodium oxide dismutase (SOD) were assessed as indicators of tumor progression. Qualitative tissue response towards the implants and new bone mass formation was histologically investigated. BG20 and BG40, with or without progenitor cells, did not cause organ damage, long-term systemic inflammatory reactions or tumor formation. BG20 and BG40 supported bone formation, which was further enhanced in the presence of EPCs and MSCs. This investigation reflects good biocompatibility of the biomaterials BG20 and BG40 and provides evidence that additionally seeding EPCs and MSCs onto the scaffold does not induce tumor formation.
Manufacture of Partially Biodegradable Composite Materials Based on PLA-Tires Powder: Process and Characterization  [PDF]
Carlos Rolando Rios-Soberanis,Shuchi Wakayama,Takenobo Sakai,José de los ángeles Rodriguez-Laviada,Emilio Pérez-Pacheco
International Journal of Polymer Science , 2013, DOI: 10.1155/2013/514951
Abstract: This research work focuses on the processability and mechanical characterization of blends of polylactic acid (PLA) and tire (elastomeric part). Wasted tires used as filler in the PLA matrix were reduced by two different processes (thermal shock and pyrolysis) in order to acquire the solid residuals in powder to be characterized and compared. Elastomeric solids obtained from scraped tires were used as filler in the PLA matrix and mixed in a Brabender 60?cc mixer at different concentrations ranging from 0% to 60% of filler volume fraction. The blend was laminated, and then samples were obtained in order to undertake mechanical properties at tension and Izod impact tests. A fully detailed analysis on the solid powders by Differential Scanning Calorimeter (DSC), thermogravimetric analysis (TGA), infrared analysis (IR), and scanning electron microscopy analysis (SEM) identified them as a rich source of carbon. Blends were characterized thermally and mechanically showing a direct effect due to the tire nature (thermoset rubber) and concentration. Fracture mechanisms were also identified. 1. Introduction In recent years, there has been widespread interest in the manufacture of products from recycled materials. Among the advantages of doing this is the fact that material recycling makes the technology more economically and environmentally attractive [1]. Particularly among the waste materials in the advancement of civilization, waste tires are a major concern, because the amount of waste tires is increasing more and more due to the increasing demand for tires, and because of their short lifetime, it is therefore necessary to develop methods for recycling waste tires. A number of approaches have been proposed to make use of the large amount of waste rubber; one of them is like biopolymer. Biopolymers are expensive and have either property or processing limitations [2]. Most durable bioresins available in the markets are based on PLA. Biopolymers are made from PLA blended with polymers like polycarbonate (PC), polypropylene (PP), acrylonitrile butadiene styrene (ABS), high impact polystyrene (HIPS), polyethylene terephthalate (PET), and poly(methyl methacrylate) (PMMA). Fillers, fibers, and additives are also added to the blends to prevent degradability, increase processability, reduce brittleness and speed crystallization. In order to overcome disadvantages, such as poor mechanical properties of polymers from renewable resources, or to offset the high price of synthetic biodegradable polymers, various blends and composites have been developed over the last
Polylactic Acid (PLA) Composite Films Reinforced with Wet Milled Jute Nanofibers  [PDF]
Vijay Baheti,Jiri Militky,S. Z. Ul Hassan
Conference Papers in Science , 2013, DOI: 10.1155/2013/738741
Abstract: In the present study, waste jute fibers formed in textile industries were wet pulverized to nanoscale using high energy planetary ball milling. The rate of refinement of uncleaned jute fibers having noncellulosic contents was found slower than the cleaned jute fibers. This behavior is attributed to the strong holding of fiber bundles by noncellulosic contents which offered resistance to the defibrillation during wet milling. In addition, the pulverization of fibers in the presence of water prevents the increase in temperature of mill which subsequently avoided the sticking of material on the milling container. After three hours milling, the diameter of nanofibers was observed around 50?nm. In the further stage, obtained nanofibers were incorporated under 1?wt%, 5?wt%, and 10?wt% loading into polylactic acid composite films. The potentials of jute nanofibers were investigated for improvement in mechanical and barrier properties of films. The maximum improvement in mechanical properties was observed in case of 5?wt% composite film where Young’s modulus was increased to 3.3?GPa from 1.0?GPa as compared with neat PLA film. 1. Introduction The demand for textiles has increased significantly in the last decade due to the rise in the living standards of people. However, increased demands of textiles also brought the challenges to dispose significant amount of wastes, generated during the processing and end of life textile materials [1, 2]. In recent years, research on recycling and reuse of textile wastes, instead of landfilling or incineration, has gained a lot of importance due to the increased awareness of environmental concerns. Traditionally, textile wastes have been converted to individual fiber stage through cutting, shredding, carding, and other mechanical processes. The fibers are then rearranged into products for applications in garment linings, household items, furniture upholstery, automotive carpeting, automobile sound absorption materials, carpet underlays, building materials for insulation and roofing felt, and low-end blankets [1, 2]. However, recent increased competition and reduced profit margins of such industries have forced the researchers to find alternative more profitable applications of textile wastes. One such interesting way is to separate the nanofibrils or nanocrystals from the textile wastes and subsequently incorporate them into high performance functional products. The lists of the previous literature articles have reported the remarkable mechanical properties of cellulose nanofibers in the range of 130–160?GPa that resulted
Flexural Properties of Long Bamboo Fiber/ PLA Composites  [PDF]
Shinji Ochi
Open Journal of Composite Materials (OJCM) , 2015, DOI: 10.4236/ojcm.2015.53010
Abstract: This paper describes the flexural properties of biodegradable composites made using natural fiber and biodegradable plastics. Biodegradable composites were fabricated from bamboo fiber bundles and PLA (polylactic acid) resin. In this research, effect of molding temperature and fiber content on flexural properties of bamboo fiber reinforced composites was investigated. The flexural strength of this composite increased with increasing fiber content up to 70%. The flexural strength of composites decreased at molding temperature of 180°C. Biodegradable composites possessed extremely high flexural strength of 273 MPa, in the case of molding temperature of 160°C and fiber content of 70%.
Development of structure and properties during thermal calendering of polylactic acid (PLA) fiber webs
eXPRESS Polymer Letters , 2008, DOI: 10.3144/expresspolymlett.2008.7
Abstract: Due to its thermoplastic and biodegradable nature, poly(lactic acid) (PLA) holds good promise in its increasing use in the form of fibers for medical, agricultural, apparel, upholstery, hygiene, and other applications. Most of the research being done on PLA fibers is to understand their production by melt spinning, solution spinning, and the structure-property relationships during fiber formation. Nonwovens are one of the important forms of the materials into which PLA polymer can be converted to create many useful products. Thermal bonding is the most widely used bonding technique employed to impart strength, and other useful characteristics to the nonwovens. However, there is limited research done to study the behavior of PLA fibers during thermal bonding of nonwovens. Hence the research was carried out to investigate the thermal bonding of nonwovens made from PLA staple fibers. The PLA fibers were carded and then calendered at different temperatures. The webs were characterized for their structure and properties. The observed results are discussed with respect to the investigated processing conditions.
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