The double porogen approach as a new technique for the fabrication of interconnected poly(L-lactic acid) and starch based biodegradable scaffolds

One of the most widely used fabrication methods of three dimensional porous scaffolds involves compression moulding of a polymer salt mixture, followed by salt leaching. However, the scaffolds prepared by this technique have typically limited interconnectivity. In this study, besides salt particles, an additional polymeric porogen, poly(ethylene oxide), PEO, was added to poly(L-lactic acid), PLLA, to enhance the interconnectivity of the scaffolds. Compression moulded specimens were quenched and put into water, where PEO crystallized and phase separated. Following the leaching of PEO fraction, the permeability and interconnectivity among the macropores formed by salt leaching could be observed. The porosities obtained in the prepared scaffolds were between 76 to 86%. Moreover, the highest porosity of 86% was obtained with minimum fraction of total porogen. The water absorption of the porous scaffolds prepared with PEO could vary between 280 to 450% while water uptake of pure PLLA scaffolds was about 93%. The increase of interconnectivity induced by compounding PLLA with PEO could also be obtained in porous PLLA/starch blends and PLLA/hydroxyapatite composites demonstrating the versatility and wide applicability of this preparation protocol. The simplicity of this organic solvent free preparation procedure of three-dimensional porous scaffolds with high interconnectivity and high surface area to volume ratio holds a promise for several tissue engineering applications.     

具有良好贯通性的颗粒造孔支架的制备及表征

支架孔隙贯通性的研究一直是多孔生物陶瓷的研究重点之一.采用石蜡球作为造孔剂, 在常规的颗粒造孔法制备多孔陶瓷支架的基础上,通过二甲苯处理以便在石蜡球间形成桥联结构, 以扩大颗粒间的接触面积,从而提高多孔陶瓷支架的孔隙贯通性. 借助扫描电镜(SEM)观察陶瓷支架的多孔结构,评价二甲苯处理石蜡球对陶瓷支架孔隙贯通性的改善效果; 采用密度法测定了陶瓷支架的孔隙率并计算其收缩率,并用成骨细胞评价陶瓷支架的细胞相容性. 结果表明,通过二甲苯的处理, 不仅改善了陶瓷支架孔隙的贯通性,而且提高了其孔隙率, 但孔隙率对陶瓷支架的收缩率无明显影响.细胞培养实验显示成骨细胞可进入多孔陶瓷支架内部, 并在材料表面正常生长,贯通性好的多孔陶瓷支架可为成骨细胞生长提供更充分的空间.     

Biodegradable polycaprolactone scaffold with controlled porosity obtained by modified particle-leaching technique

Scaffold with controlled porosity constitute a cornerstone in tissue engineering, as a physical support for cell adhesion and growth. In this work, scaffolds of polycaprolactone were synthesized by a modified particle leaching method in order to control porosity and pore interconnectivity; the aim is to observe their influence on the mechanical properties and, in the future, on cell adhesion and proliferation rates. Low molecular weight PEMA beads with an average size of 200 μm were sintered with various compression rates in order to obtain the templates (negatives of the scaffolds). Then the melt polycaprolactone was injected into the porous template under nitrogen pressure in a custom made device. After cooling and solidifying of the melt polymer, the porogen was removed by selective dissolution in ethanol. The porosity and morphology of the scaffold were studied as well as the mechanical properties. Porosities from 60% to 85% were reached; it was found that pore interconnectivity logically increases with increasing porosity, and that mechanical strength decreases with increasing porosity. Because of their interesting properties and interconnected structure, these scaffolds are expected to find useful applications as a cartilage or bone repair material.     

PLA-PEG共聚物三维多孔支架的制备及表征

将D,L-丙交酯(D,L-LA)与聚乙二醇(PEG)共聚制备了一系列共聚物,并用IR、GPC和1H-NMR对其进行了表征.在此基础上,采用溶剂浇铸-柱子沥滤技术和层叠技术制备了具有一定空间形状的三维多孔组织工程支架,并研究了致孔剂颗粒尺寸及其用量对多孔支架的孔径、孔隙率的影响.结果表明,PLA-PEG共聚物的分子量随着原料中PEG含量的增加而减小;以PLA-PEG共聚物为原料制备多孔支架时,孔径的大小与致孔剂颗粒尺寸有一定的对应关系,孔隙率随着致孔剂用量的增加而增加;采用层叠技术制备的具有一定形状的三维多孔支架符合组织工程对支架材料的一般要求.     

Inverse Opal Scaffolds and Their Biomedical Applications

Three‐dimensional porous scaffolds play a pivotal role in tissue engineering and regenerative medicine by functioning as biomimetic substrates to manipulate cellular behaviors. While many techniques have been developed to fabricate porous scaffolds, most of them rely on stochastic processes that typically result in scaffolds with pores uncontrolled in terms of size, structure, and interconnectivity, greatly limiting their use in tissue regeneration. Inverse opal scaffolds, in contrast, possess uniform pores inheriting from the template comprised of a closely packed lattice of monodispersed microspheres. The key parameters of such scaffolds, including architecture, pore structure, porosity, and interconnectivity, can all be made uniform across the same sample and among different samples. In conjunction with a tight control over pore sizes, inverse opal scaffolds have found widespread use in biomedical applications. In this review, we provide a detailed discussion on this new class of advanced materials. After a brief introduction to their history and fabrication, we highlight the unique advantages of inverse opal scaffolds over their non‐uniform counterparts. We then showcase their broad applications in tissue engineering and regenerative medicine, followed by a summary and perspective on future directions.     

Design, synthesis and properties of a degradable polyurethane scaffold for meniscus regeneration

Longitudinal lesions in menisci are among the most frequent orthopedic problems of the knee. Repair by simple techniques is only limited to the vascular part of the meniscus. For repair of the avascular part of the meniscus a scaffold, which will assist the body in the formation of new meniscus cell tissue, might be applicable. In this study a biomedical segmented polyurethane with poly(epsilon-caprolactone) as soft segment and 1,4-butanediisocyanate and 1,4-butanediol as uniform hard segments has been synthesised. The material has a micro phase separated morphology and excellent mechanical properties. A porous scaffold was prepared via a combination of liquid-liquid phase separation and salt leaching. The foams prepared combined a very high interconnectivity and porosity with the desired compression modulus. After six months of implantation in the knees of beagles full ingrowth with cells was obtained and it was found that meniscus like tissue had been formed in the scaffold. Moreover, compression behaviour appeared to be comparable to native meniscus tissue.     

Morphology, mechanical properties, and mineralization of rigid thermoplastic polyurethane/hydroxyapatite scaffolds for bone tissue applications: effects of fabrication approaches and hydroxyapatite size

Rigid thermoplastic polyurethane (TPU)/hydroxyapatite (HA) scaffolds were prepared with micro HA (mHA) and nano HA (nHA) particles, respectively, via the thermally induced phase separation method. The effects of solvent and co-solvent, addition of sodium chloride (NaCl) porogen, and HA particle size were studied together with the morphology, compressive properties, and mineralization behavior of the scaffolds. Depending on the solvent, co-solvent, or porogen used, different porous structures were produced. In particular, a ladder-like morphology was obtained when dioxane (Di) was used as the solvent, whereas an interconnected porous structure was obtained by using dioxane and deionized water (DiW) as co-solvents. Rectangular pores with interconnected channels on the pore walls were achieved by using NaCl crystals as porogens. The TPU/nHA scaffolds showed stronger compressive properties than the TPU/mHA scaffolds and the pure TPU scaffolds. The scaffolds prepared using dioxane and water as co-solvents exhibit the greatest compressive modulus. Furthermore, TPU scaffolds with nHA particles had the ability to form bone apatite when soaked in simulated body fluid (SBF). After being soaked in SBF for 3 weeks, the weight percentage of formed apatite in the TPU/nHA-DiW scaffold was 9.2 %wt of the initial TPU content. Preliminary cytotoxicity tests were conducted using NIH 3T3 fibroblast cells. The high survival rate of these cells and the mineralization behavior suggest biocompatibility and high potential of these composites being used in bone tissue engineering applications.     

冷冻抽提相分离法制备聚乳酸多孔支架

为了制备结构和性能满足骨组织工程支架要求的聚乳酸(PLA)多孔支架材料,采用冷冻抽提相分离法,以1,4-二氧六环和水为混合溶剂,聚乙二醇(PEG)为致孔剂,制得一系列PLA多孔支架,探讨了溶剂组成、PLA浓度、PEG添加量对PLA多孔支架结构和性能的影响,结果表明添加PEG有利于形成多孔三维支架,随着PEG含量的增加,...     

Fabrication of three dimensional polymeric scaffolds with spherical pores

This paper reports polymeric scaffolds with spherical internal macropores and relatively large external dimension. Paraffin spheres with the diameter of several hundred microns were prepared by a suspension technique. Particulate leaching technique based on this kind of spherical porogens was combined with room-temperature compression molding technique to fabricate biodegradable poly(D,L-lactic-co-glycolic acid) (PLGA) porous scaffolds potentially for tissue engineering or in situ tissue induction. The scaffolds exhibited ordered macropores with good pore interconnectivity. The porosity ranged from 80 to 97% adjusted simply by varying porogen content. The foams with porosity around 90% have compressive modulus over 3 MPa and compressive strength over 0.2 MPa. As preliminary cell experiments with 3T3 fibroblasts cultured on the porous scaffolds indicate, the processing procedure of the scaffolds has not brought with problem in cytotoxicity.     

Development of polycaprolactone/chitosan blend porous scaffolds

Polycaprolactone (PCL) and chitosan were blended to fabricate porous scaffolds for tissue-engineering applications by employing a concentrated acetic acid solution as solvent and salt particles as porogen. These scaffolds showed well-controlled and interconnected porous structures. The pore size and porosity of the scaffolds could be effectively modulated by selecting appropriate amounts and sizes of porogen. The results obtained from compressive mechanical measurements indicated that PCL/chitosan could basically retain their strength in their dry state compared to individual components. In a hydrated state, their compressive stress and modulus could be still well maintained even though the weight ratio of chitosan reached around 50 wt%.     

Effects of surfactants on the microstructure of porous ceramic scaffolds fabricated by foaming for bone tissue engineering

A porous scaffold comprising a β-tricalcium phosphate matrix and bioactive glass powders was fabricated by foaming method and the effects of surfactants as foaming agent on microstructure of scaffolds were investigated. Foaming capacity and foam stability of different surfactants in water firstly were carried out to evaluate their foam properties. The porous structure and pore size distribution of the scaffolds were systematically characterized by scanning electron microscopy (SEM) and an optical microscopy connected to an image analyzer. The results showed that the foam stability of surfactant has more remarkable influence on their microstructure such as pore shape, size and interconnectivity than the foaming ability of one. Porous scaffolds fabricated using nonionic surfactant Tween 80 with large foam stability exhibited higher open and total porosities, and fully interconnected porous structure with a pore size of 750-850 μm.     

Poly(HEMA) hydrogels with controlled pore architecture for tissue regeneration applications

The technique for fabrication of soft porous hydrogels, in which both the size and the orientation of inner pores can be controlled, was developed. Three-dimensional hydrophilic gels based on poly[2-hydroxyethyl methacrylate] are designed as scaffolds for regeneration of soft tissues, e.g., nerve tissue. Anisotropic macropores of the size ranging from 10 to 50 μm were formed (1) by using a porogen-leaching method with a solid organic porogen, (2) by phase-separation during gelation in solvent-nonsolvent mixture, or (3) by combination of solid porogen elimination and phase-separation. As a porogen, poly(l-lactide) fibers were applied and consequently washed away under mild conditions to obtain desired spatial orientation of pores. Highly water-swollen polymer gels were characterized with high pressure (low vacuum) scanning electron microscopy (AquaSEM). The morphology of voids remaining after removing the solid PLLA porogen (the macropores) was clearly shown.     

Preparation of highly interconnected porous hydroxyapatite scaffolds by chitin gel-casting

In this study, a simple and effective method for producing highly interconnected porous hydroxyapatite (HA) scaffolds was developed by combining gel-casting, particle-leaching and extrusion techniques. Chitin (CT) sol was used to disperse HA particles and wax spheres were introduced as porogens for their excellent deformability. In extrusion process, the accumulated wax spheres in point-to-point contact can transform into surface-to-surface contact by means of the extrusion pressure. Thus, the obtained porous HA scaffolds exhibited an interconnected channel network after leaching out of the porogens. The results showed that the scaffolds prepared by different size of wax spheres exhibited nearly the same volumetric porosity of about 86%, while the compressive strengths decreased as the pore size increased. Therefore, the method developed can be used to effectively tailor the pore size of HA scaffolds while maintaining a high porosity. The highly porous HA scaffolds with excellent interconnectivity are expected to be a promising bone substitute in clinical practice.     

蜡球造孔法制备多孔HA陶瓷支架及其性能优化

组织工程支架的贯通性对其体内生物学表现具有重要影响。采用甲壳素溶胶体系和蜡球造孔剂制备多孔羟基磷灰石(HA)陶瓷支架, 考查在相同模压条件下, 不同浆料/造孔剂比例对多孔HA陶瓷支架的孔隙率、收缩率、贯通性、多孔结构以及抗压强度的影响。结果表明: 该方法可以制备具有高孔隙的多孔HA陶瓷支架, 随着造孔剂比例的增大, 支架的贯通性更好, 当浆料/造孔剂比例为1:1.2时可以得到孔隙率、贯通性、力学性能最优的多孔HA陶瓷支架。     

软骨细胞在聚乳酸支架中的体外生长行为

采用明胶和氯化钠颗粒作为致孔剂,使用溶剂浇铸／颗粒沥滤法制备了高孔隙率、孔间连通和高机械性能的聚乳酸支架,采用软骨细胞体外培养研究了这两种多孔支架对细胞生长性能的影响．结果表明,软骨细胞在以明胶颗粒为致孔剂制备的多孔支架中的相对数量和GAG的分泌量更多,细胞的活性更高。     

Ultra-porous titanium oxide scaffold with high compressive strength

Highly porous and well interconnected titanium dioxide (TiO₂) scaffolds with compressive strength above 2.5 MPa were fabricated without compromising the desired pore architectural characteristics, such as high porosity, appropriate pore size, surface-to-volume ratio, and interconnectivity. Processing parameters and pore architectural characteristics were investigated in order to identify the key processing steps and morphological properties that contributed to the enhanced strength of the scaffolds. Cleaning of the TiO₂ raw powder removed phosphates but introduced sodium into the powder, which was suggested to decrease the slurry stability. Strong correlation was found between compressive strength and both replication times and solid content in the ceramic slurry. Increase in the solid content resulted in more favourable sponge loading, which was achieved due to the more suitable rheological properties of the ceramic slurry. Repeated replication process induced only negligible changes in the pore architectural parameters indicating a reduced flaw size in the scaffold struts. The fabricated TiO₂ scaffolds show great promise as load-bearing bone scaffolds for applications where moderate mechanical support is required.     

The morphology,mechanical properties and ageing behavior of porous injection molded starch-based blends for tissue engineering scaffolding

One important parameter in the tissue engineering of hard tissues is the scaffold. A scaffold is a support in which cells are seeded and that should create the adequate environment for the cells to attach and proliferate. Furthermore the scaffold should allow the flow of an appropriate culture media, providing nutrients to the cells and simultaneously removing the metabolites resulting from the cells activity. One of the possibilities is to obtain solid foamed structures that will enable the cells to attach, spread into the inner surfaces and start to produce extracellular matrix. Ideally, if the scaffold is produced from a biodegradable material, it should degrade at a pace that is in phase with the formation of the new tissue.In this work it was studied the production of porous structures from biodegradable polymers for use as scaffolds for bone tissue engineering. Two materials were studied, starch compounded with poly(ethylene-vinyl-alcohol) (SEVA-C) and starch with poly(lactic acid) (SPLA). The porous structures were obtained by injection molding with a blowing agent to control the porosity, interconnectivity and degradation rate. In previous attempts, the current starch compounds proved to be very difficult to process by this method. This study includes the characterization of the mechanical properties, water absorption and of the degradation kinetics of the 3-D porous structures.Two starch-based biodegradable 3D porous structures were successfully processed in conventional injection molding and the foaming was obtained by means of the use of a blowing agent. The mechanical properties are very promising as well as the improved degradation kinetics when compared with the synthetic polymers alone, although the degree of porosity and of interconnectivity needs to be improved in further work.     

Processing and degradation behavior of porous magnesium scaffold for biomedical applications

Porous magnesium has the potential to be used as degradable bone scaffolds. In this study, porous magnesium scaffolds were fabricated through powder metallurgy route utilizing spherical naphthalene particle as porogen. Porogen was removed at 120?°C for 24?h followed by sintering at 550?°C for 2?h in argon atmosphere. Micro-computed tomography (micro CT) results indicated that scaffolds have interconnected porous structure with an equivalent pore diameter of nearly 60?µm. Compressive strength of the scaffolds was found in the range of 24?±?4.54?MPa to 184?±?9.9?MPa and decreased with increasing porogen content. In vitro degradation study in phosphate buffered saline (PBS) showed that scaffold degradation behavior was governed by its porosity content. Our results indicate that modulating the porogen content we can tailor the mechanical and degradation behavior of the Mg scaffolds to the application need.     

有机泡沫浸渍法制备多孔生物玻璃支架的研究

选用58S生物活性玻璃粉体为原料,利用预先处理过的聚氨酯泡沫作为模板,制备了一种孔隙率高, 贯通性好,孔径可控的生物玻璃多孔支架. 并通过排水法、X射线衍射（XRD）、扫描电子显微镜（SEM）及傅里叶红外光谱（FTIR）等方法研究和表征了多孔支架的显气孔率、晶相组成、显微形貌和生物活性. 结果表明,浸料一次所得支架的显气孔率为93%左右,浸料二次下降为80%左右;在SBF溶液中,随着时间的延长,材料表面最初形成的颗粒状钙磷化合物逐渐矿化生成叶片状碳酸羟基磷灰石(HCA)层,表明该材料恒温37℃时具有较好的生物矿化性能和生物活性.     

Development and characterisation of a collagen nano-hydroxyapatite composite scaffold for bone tissue engineering

Bone regeneration requires scaffolds that possess suitable mechanical and biological properties. This study sought to develop a novel collagen-nHA biocomposite scaffold via two new methods. Firstly a stable nHA suspension was produced and added to a collagen slurry (suspension method), and secondly, porous collagen scaffolds were immersed in nHA suspension after freeze-drying (immersion method). Significantly stronger constructs were produced using both methods compared to collagen only scaffolds, with a high porosity maintained (>98.9%). It was found that Coll-nHA composite scaffolds produced by the suspension method were up to 18 times stiffer than the collagen control (5.50 ± 1.70 kPa vs. 0.30 ± 0.09 kPa). The suspension method was also more reproducible, and the quantity of nHA incorporated could be varied with greater ease than with the immersion technique. In addition, Coll-nHA composites display excellent biological activity, demonstrating their potential as bone graft substitutes in orthopaedic regenerative medicine.