Crystallinity assessment and in vitro cytotoxicity of polylactide scaffolds for biomedical applications

Bioresorbable polylactides are one of the most important materials for tissue engineering applications. In this work we have prepared scaffolds based on the two optically pure stereoisomers: poly(l-lactide) (PLLA) and poly(d-lactide) (PDLA). The crystalline structure and morphology were evaluated by DSC, AFM and X-ray diffraction. PLLA and PDLA crystallized in the α form and the equimolar PLLA/PDLA blend, crystallized in the stereocomplex form, were analyzed by a proliferation assay in contact with mouse L-929 and human fibroblasts and neonatal keratinocytes for in vitro cytotoxicity evaluation. SEM analysis was conducted to determine the cell morphology, spreading and adhesion when in contact with the different polymer surfaces. The preserved proliferation rate showed in MTT tests and the high colonization on the surface of polylactides observed by SEM denote that PLLA, PDLA and the equimolar PLLA/PDLA are useful biodegradable materials in which the crystalline characteristics can be tuned for specific biomedical applications.     

Blends of linear and peroxide‐modified branched polylactide for extrusion coating

The purpose of the present work was to improve melt rheological properties of linear poly(L‐lactide) (PLLA) by melt blending with peroxide‐modified branched PLLA for extrusion coating. Peroxide‐modified PLLA, ie, PLLA melt extruded with 0.3 wt% of tert‐Butyl‐peroxybenzoate (TBPB); 2,5‐dimethyl‐2,5‐(tert‐butylperoxy)‐hexane (Lupersol 101 [LOL1]); and benzoyl peroxide was added to linear PLLA in ratios of 5, 15, and 30 wt%. All blends showed increased zero shear viscosity, elastic feature (storage modulus, decreased tan delta), and shear sensitivity. The blends' properties were mostly dependent on the peroxide applied for the modification and, to some extent, on the amount of added peroxide‐modified PLLA. Rheological models suggest that all blend compositions are mainly immiscible. Thermal properties were unchanged; all materials remained amorphous, though the enthalpy of cold crystallization was slightly increased. Extrusion coating on paperboard was conducted with PLLA and peroxide‐modified PLLA blends (90:10). All blends were processable; however, only that made with 2,5‐dimethyl‐2,5‐(tert‐butylperoxy)‐hexane (LOL1) afforded a smooth high‐quality coating surface with improved line speed. Adhesion levels between fibre and plastic and heat seal performance were marginally reduced compared with pure PLLA (3051D). The water vapour transmission measurements with 2,5‐dimethyl‐2,5‐(tert‐butylperoxy)‐hexane (LOL1) showed acceptable water transmission levels, being only slightly higher than for neat PLLA coating.     

Comparison of the degradability of poly(lactide) packages in composting and ambient exposure conditions

The adoption of biodegradable polymeric materials is increasing in food and consumer goods packaging applications, due to concerns about the disposal of petroleum‐based polymers and the increasing cost of petroleum‐based polymer resins. Currently, poly(lactide) (PLA) polymers are the biggest commercially available bio‐based polymeric packaging materials. As the main motivation for adopting biopolymers is environmental, there is a need to address the degradability and environmental performance of biodegradable packages. The aim of this study was to investigate and compare the degradation of two commercially available biodegradable packages made of PLA under real compost conditions and under ambient exposure, using visual inspection, gel permeation chromatography, differential scanning calorimetry and thermal gravimetric analysis. A novel technique to study and track the degradability of these packages under real compost conditions was used. Both packages were subjected to composting and ambient exposure conditions for 30 days, and the degradation of the physical properties was measured at 1, 2, 4, 6, 9, 15 and 30 days. PLA bottles made of 96% l ‐lactide exhibited lower degradation than PLA delicatessen (‘deli’) containers made of 94% l ‐lactide, mainly due to their highly ordered structure and, therefore, their higher crystallinity. The degradation rate changed as the initial crystallinity and the l ‐lactide content of the packages varied. Temperature, relative humidity and pH of the compost pile played an important role in the rate of degradation of the packages. First‐order degradation kinetics and linear degradation trends were observed for both packages subjected to composting conditions. Copyright © 2006 John Wiley & Sons, Ltd.     

Design of Plasma Surface‐Activated,Electrospun Polylactide Non‐Wovens with Improved Cell Acceptance

Electrospinning is a versatile technique to generate tissue engineering matrices possessing structural features similar to the extracellular matrix. Biodegradable polylactides are well suited for processing by this technique, but their innate hydrophobicity impairs initial protein adsorption and cell adhesion. In this work, therefore, electrospun poly(L ‐lactide‐co‐D,L ‐lactide) (70/30) non‐wovens are modified with an ultrathin plasma‐polymerized allylamine (PPAAm) coating. Using scanning electron microsocopy (SEM), it is shown that the fiber structure of the non‐woven is not affected by the plasma treatment. X‐ray photoelectron spectroscopy (XPS) and contact angle measurements of PPAAm‐coated non‐wovens confirm the presence of nitrogen and oxygen‐functional groups in the coating and a hydrophilic nature of the coated non‐woven surface. Cell experiments in vitro demonstrate that the PPAAm‐coated surface promotes occupancy of the non‐woven by human MG‐63 osteoblasts accompanied by improved initial cell spreading and filopodia formation along and between the electrospun polylactide fibers. Overall, plasma‐assisted incorporation of amino groups into electrospun polylactone non‐wovens represents a promising approach to tissue engineering scaffolds with improved cell–material interfaces.     

Graphene oxide and hydroxyapatite as fillers of polylactic acid nanocomposites: preparation and characterization

Graphene and its derivatives have attracted great research interest for their potential applications in electronics, energy, materials and biomedical areas. When incorporated appropriately, these atomically thin carbon sheets are expected to improve physical properties of host polymers at extremely small loading. Herein, we report a novel two-step method for the preparation of PLLA/Hap/graphene oxide nanocomposites with augmented mechanical properties when compared to PLLA/Hap and neat PLLA. The presence of graphene oxide (GO) had a positive effect on the dispersion of hydroxyapatite particles on the polymeric matrix contributing for a good homogeneity of the final nanocomposite. PLLA nanocomposites prepared with 30% (w/w) of Hap and 1% (w/w) of GO showed the highest hardness and storage modulus values indicating an efficient load transfer between the fillers and the PLLA matrix. These materials may find interesting biomedical applications as for example bone screws. The following step on the study of these materials will be in vitro tests to access the biocompatibility of these new nanocomposites.     

Multi‐Drug‐Loaded Microcapsules with Controlled Release for Management of Parkinson's Disease

Parkinson's disease (PD) is a progressive disease of the nervous system, and is currently managed through commercial tablets that do not sufficiently enable controlled, sustained release capabilities. It is hypothesized that a drug delivery system that provides controlled and sustained release of PD drugs would afford better management of PD. Hollow microcapsules composed of poly‐l ‐lactide (PLLA) and poly (caprolactone) (PCL) are prepared through a modified double‐emulsion technique. They are loaded with three PD drugs, i.e., levodopa (LD), carbidopa (CD), and entacapone (ENT), at a ratio of 4:1:8, similar to commercial PD tablets. LD and CD are localized in both the hollow cavity and PLLA/PCL shell, while ENT is localized in the PLLA/PCL shell. Release kinetics of hydrophobic ENT is observed to be relatively slow as compared to the other hydrophilic drugs. It is further hypothesized that encapsulating ENT into PCL as a surface coating onto these microcapsules can aid in accelerating its release. Now, these spray‐coated hollow microcapsules exhibit similar release kinetics, according to Higuchi's rate, for all three drugs. The results suggest that multiple drug encapsulation of LD, CD, and ENT in gastric floating microcapsules could be further developed for in vivo evaluation for the management of PD.     

Electrospray Ionization‐Mass Spectrometry Analysis Reveals Migration of Cyclic Lactide Oligomers from Polylactide Packaging in Contact with Ethanolic Food Simulant

Electrospray ionization‐mass spectrometry analysis revealed rapid migration of cyclic oligomers from polylactide (PLA) packaging when stored in contact with 96% ethanol. The mass losses in contact with water, 3% acetic acid, 10% ethanol and isooctane were 3 to 5 times smaller and no migration of cyclic oligomers was observed. The presence of cyclic oligomers in the original PLA films and their solubility in ethanol, thus, explains the rapid mass loss for PLA in contact with ethanolic food simulant. On prolonged ageing no further mass loss was observed in 96% ethanol, whereas mass loss in aqueous food simulants increased because of hydrolysis of PLA matrix or the cyclic oligomers to water‐soluble linear products. The mass losses were generally somewhat smaller for the stereocomplex material compared with the poly‐l ‐lactide materials. Similar trend was observed for solvent uptakes, which is easily explained by the higher degree of crystallinity and stronger secondary interactions in the stereocomplex material. The use of ethanol as a fatty food simulant for PLA materials could, thus, lead to overestimation of the overall migration values. Copyright © 2012 John Wiley & Sons, Ltd.     

Inhibition of 3‐D Tumor Spheroids by Timed‐Released Hydrophilic and Hydrophobic Drugs from Multilayered Polymeric Microparticles

First‐line cancer chemotherapy necessitates high parenteral dosage and repeated dosing of a combination of drugs over a prolonged period. Current commercially available chemotherapeutic agents, such as Doxil and Taxol, are only capable of delivering single drug in a bolus dose. The aim of this study is to develop dual‐drug‐loaded, multilayered microparticles and to investigate their antitumor efficacy compared with single‐drug‐loaded particles. Results show hydrophilic doxorubicin HCl (DOX) and hydrophobic paclitaxel (PTX) localized in the poly(dl ‐lactic‐co‐glycolic acid, 50:50) (PLGA) shell and in the poly(l ‐lactic acid) (PLLA) core, respectively. The introduction of poly[(1,6‐bis‐carboxyphenoxy) hexane] (PCPH) into PLGA/PLLA microparticles causes PTX to be localized in the PLLA and PCPH mid‐layers, whereas DOX is found in both the PLGA shell and core. PLGA/PLLA/PCPH microparticles with denser shells allow better control of DOX release. A delayed release of PTX is observed with the addition of PCPH. Three‐dimensional MCF‐7 spheroid studies demonstrate that controlled co‐delivery of DOX and PTX from multilayered microparticles produces a greater reduction in spheroid growth rate compared with single‐drug‐loaded particles. This study provides mechanistic insights into how distinctive structure of multilayered microparticles can be designed to modulate the release profiles of anticancer drugs, and how co‐delivery can potentially provide better antitumor response.     

Stereocomplex block copolymer micelles: core-shell nanostructures with enhanced stability

Monodisperse stereocomplex block copolymer micelles were obtained through the self-assembly of equimolar mixtures of poly(ethylene glycol)-block-poly(l-lactide) and poly(ethylene glycol)-block-poly(d-lactide) in water. These micelles possessed partially crystallized cores and mean hydrodynamic diameters ranging from 31 to 56 nm, depending on the lactide content. They exhibited kinetic stability and redispersion properties superior to micelles prepared with isotactic or racemic polymers alone. This study demonstrates the advantages of stereocomplex formation in the design of stabilized water-soluble nanoparticles.     

Layer-by-Layer crystallization of enantiomeric poly(lactide)s

Poly(lactide)s stereocomplex ultrathin film with controlled structure at a molecular level was able to be prepared by stepwise assembly using the stereocomplex interaction. Pure stereocomplex crystal can be easily obtained by using this technique. When the substrates pre-coated with the stereocomplex assembly were immersed into solution of poly(L-lactide) or poly(D-lactide) for a long time, each polymer was homogeneously deposited on the substrates. The enantiomer was epitaxially crystallized on the stereocomplex film. The XRD pattern of the films showed similar characteristic peaks of the stereocomplex, indicating that the crystallization was influenced by conformation of polymer at the substrate. This is the first case of the epitaxially growth of polymers on the structurally regulated surface. These films had high degree of crystallinity although the assemblies did not undergo a crystallization process. This method was considered to be a general method that can be applied to other polymers, which able to form stereocomplex.     

改性纳米MgO/PLLA复合薄膜的制备及性能

为了改善左旋聚乳酸(PLLA)的降解性,采用溶液共混法将PLLA和MgO纳米颗粒(MgO-NPs)进行复合,制备了一种具有良好力学性能的骨修复复合材料.结果显示:改性MgO纳米颗粒(g-MgO-NPs)在PLLA基体中的分散效果及界面结合性比未改性的好.4%(质量比)g-MgO-NPs的添加量使薄膜的拉伸强度从10.6 MPa增大到30.1 MPa,断裂伸长率从71%减小为59%,并使薄膜降解后的pH值趋于稳定,基本接近生理盐水的pH值.由此表明:g-MgO-NPs在一定程度上能改善聚乳酸复合膜的降解性及其力学性能.     

金属氧化物对PLLA降解性能的影响

将分别添加微量金属氧化物CaO、MgO、ZnO 的生物可降解聚酯聚乳酸(PLLA)薄膜放入陕西当地土壤的提取液中进行微生物兹化反应,以研究薄膜中金属氧化物对PLLA降解性能的影响,并通过红外光谱中官能团吸收强度的变化,表征了其降解前后的化学结构。研究结果表明：添加金属氧化物的PLLA在陕西当地土壤的提取液中能够降解,添加微量的 CaO、MgO加快了PLLA的降解速度,而添加ZnO对PLLA 的降解没有太大影响。用显微镜对降解前后膜的观察发现：纯 PLLA 薄膜降解后的膜表面变得明显粗糙,有显著的微生物侵蚀痕迹;而添加微量金属氧化物的薄膜中,由于均匀分散金属氧化物的存在,导致降解后膜表面出现了更大的缺陷和侵蚀痕迹。     

Synthesis and characterization of biodegradable poly(l-lactide)/layered double hydroxide nanocomposites

This study reports the preparation and physical properties of biodegradable nanocomposites fabricated using poly(l-lactide) (PLLA) and magnesium/aluminum layered double hydroxide (MgAl-LDH). The MgAl-LDH with molar ratio of Mg/Al = 2 were synthesized by the co-precipitation method. In order to improve the chemical compatibility between PLLA and LDH, the surface of LDH was organically-modified by polylactide with carboxyl end group (PLA–COOH) using ion-exchange process. Then, the PLLA/LDH nanocomposites were prepared by solution intercalation of PLLA into the galleries of PLA–COOH modified LDH (P-LDH) in tetrahydrofuran solution. Both X-ray diffraction data and Transmission electron microscopy images of PLLA/P-LDH nanocomposites indicate that the P-LDHs are randomly dispersed and exfoliated into the PLLA matrix. Mechanical properties of the fabricated 1.2 wt.% PLLA/P-LDH nanocomposites show significant enhancements in the storage modulus when compared to that of neat PLLA. Adding more P-LDH into PLLA matrix induced a decrease in the storage modulus of PLLA/P-LDH nanocomposites, probably due to the excessive content of PLA–COOH moleculars with low mechanical properties. The thermal stability and degradation activation energies of the PLLA and PLLA/P-LDH nanocomposites can also be discussed.     

Crystallization and thermal behaviour of optically pure polylactides and their blends

Lactic acid based polymers of medical grade were crystallized under isothermal and non-isothermal conditions from the melt. Optically pure enantiomeric polylactides, Poly(L-lactide) (PLLA) and Poly(D-lactide) (PDLA), are found to crystallize as crystalline form. PLLA/PDLA blends were prepared by a melt mixing process and during solidification yielded both lower melting homocrystallites and higher melting stereocomplex crystallites. The effects of isothermal and non-isothermal crystallization conditions on developed polymorphism and degree of crystallinity are evaluated for PLLA/PDLA blends.     

Graphene Oxide/Polymer‐Based Biomaterials

Since its discovery in 2004, derivatives of graphene have been developed and heavily investigated in the field of tissue engineering. Among the most extensively studied forms of graphene, graphene oxide (GO), and GO/polymer‐based nanocomposites have attracted great attention in various forms such as films, 3D porous scaffolds, electrospun mats, hydrogels, and nacre‐like structures. In this review, the most actively investigated GO/polymer nanocomposites are presented and discussed, these nanocomposites are based on chitosan, cellulose, starch, alginate, gellan gum, poly(vinyl alcohol) (PVA), poly(acrylamide), poly(?‐caprolactone) (PCL), poly(lactic acid) (PLLA), poly(lactide‐co‐glycolide) (PLGA), gelatin, collagen, and silk fibroin (SF). The biological and mechanical performance of such nanocomposites are comprehensively scrutinized and ongoing research questions are addressed. The analysis of the literature reveals overall the great potential of GO/polymer nanocomposites in tissue engineering strategies and indicates also a series of challenges requiring further research efforts.

     

Electrospun magnetic poly(l-lactide) (PLLA) nanofibers by incorporating PLLA-stabilized Fe3O4 nanoparticles

Magnetic poly(l-lactide) (PLLA)/Fe₃O₄ composite nanofibers were prepared with the purpose to develop a substrate for bone regeneration. To increase the dispersibility of Fe₃O₄ nanoparticles (NPs) in the PLLA matrix, a modified chemical co-precipitation method was applied to synthesize Fe₃O₄ NPs in the presence of PLLA. Trifluoroethanol (TFE) was used as the co-solvent for all the reagents, including Fe(II) and Fe(III) salts, sodium hydroxide, and PLLA. The co-precipitated Fe₃O₄ NPs were surface-coated with PLLA and demonstrated good dispersibility in a PLLA/TFE solution. The composite nanofiber electrospun from the solution displayed a homogeneous distribution of Fe₃O₄ NPs along the fibers using various contents of Fe₃O₄ NPs. X-ray diffractometer (XRD) and vibration sample magnetization (VSM) analysis confirmed that the co-precipitation process had minor adverse effects on the crystal structure and saturation magnetization (Ms) of Fe₃O₄ NPs. The resulting PLLA/Fe₃O₄ composite nanofibers showed paramagnetic properties with Ms directly related to the Fe₃O₄ NP concentration. The cytotoxicity of the magnetic composite nanofibers was determined using in vitro culture of osteoblasts (MC3T3-E1) in extracts and co-culture on nanofibrous matrixes. The PLLA/Fe₃O₄ composite nanofibers did not show significant cytotoxicity in comparison with pure PLLA nanofibers. On the contrary, they demonstrated enhanced effects on cell attachment and proliferation with Fe₃O₄ NP incorporation. The results suggested that this modified chemical co-precipitation method might be a universal way to produce magnetic biodegradable polyester substrates containing well-dispersed Fe₃O₄ NPs. This new strategy opens an opportunity to fabricate various kinds of magnetic polymeric substrates for bone tissue regeneration.     

<Emphasis Type="Italic">In vitro</Emphasis> properties of PLLA screws and novel bioabsorbable implant with elastic nucleus to replace intervertebral disc

The suitability of two different implant types for the replacement of the intervertebral disc was studied in vitro. Self-reinforced poly-L-lactide (SR-PLLA) screws Ø 4.5 mm were studied 24 weeks in vitro and cylindrical implants with elastic nucleus made of poly(L/D)lactide 96/4, poly(L/DL)lactide 70/30, Bioactive Glass n:o 13–93 and Polyactive^® 1000PEOT70PBT30 were studied 15 weeks in vitro. The cylindrical implant mimics the size and shape of the intervertebral disc. During the in vitro, there were no changes in compression properties with either implant types. The screws had sufficient modulus for intervertebral ossification in the canine model and the cylindrical implant showed also sufficient mechanical properties. These results suggest that both implant types could be used in clinical testing.     

Inside Front Cover: Conducting‐Polymer Nanotubes for Controlled Drug Release (Adv. Mater. 4/2006)

Martin and co‐workers report on p. 405 that nanotubes formed from the conducting polymer poly(3,4‐ethylenedioxythiophene) (PEDOT), as shown on the inside cover, can be used for the controlled release of anti‐inflammatory drugs. The fabrication process includes electrospinning of a biodegradable polymer, either poly(L ‐lactide) or poly(lactide‐co‐glycolide), into which the required drug is incorporated, followed by electrochemical deposition of the conducting polymer around the drug‐loaded electrospun nanofibers. Drug release from the nanotubes is achieved by external electrical stimulation of the nanotubes.     

Self‐Adjusting,Polymeric Multilayered Roll that can Keep the Shapes of the Blood Vessel Scaffolds during Biodegradation

A self‐adjusting, blood vessel‐mimicking, multilayered tubular structure with two polymers, poly(ε‐caprolactone) (PCL) and poly(dl ‐lactide‐co‐glycolide) (PLGA), can keep the shape of the scaffold during biodegradation. The inner (PCL) layer of the tube can expand whereas the outer (PLGA) layers will shrink to maintain the stability of the shape and the inner space of the tubular shape both in vitro and in vivo over months. This approach can be generally useful for making scaffolds that require the maintenance of a defined shape, based on FDA‐approved materials.     

β-磷酸三钙/聚L-乳酸与大鼠骨膜成骨细胞复合骨修复材料的研究

采用溶液浇铸-模压成型-沥滤方法制备了β-TCP/PLLA多孔支架材料, 将支架材料与大鼠骨膜成骨细胞复合获得新型组织工程骨修复材料. 通过抗压强度及压缩模量的表征研究了支架材料的力学性能; 采用SEM观测、MTT法、碱性磷酸酶活性及骨钙素分泌量检测细胞复合材料的体外成骨特性; 通过裸鼠肌袋种植, 以组织学方法评价细胞复合材料的异位成骨能力. 结果表明: β-TCP/PLLA多孔支架材料孔隙率可调, 孔径为100～00μm, 孔道相互贯通; 材料抗压强度和压缩模量随孔隙率的增大而降低, β-TCP复合PLLA后材料的力学性能高于同孔隙率的纯PLLA多孔材料; 复合支架材料适宜骨膜成骨细胞粘附和生长, 无细胞毒性; 骨膜成骨细胞复合β-TCP/PLLA支架材料的体外成骨特性良好, 且具有体内异位成骨能力.