Gelatin/chitosan/hyaluronan scaffold integrated with PLGA microspheres for cartilage tissue engineering

Poly(lactide-co-glycotide) (PLGA) microspheres integrated into gelatin/chitosan/hyaluronan scaffolds were fabricated by freeze-drying and crosslinking with 1-ethyl-3-(3-dimethyl aminopropyl)carbodiimide. The effects of the microspheres on porosity, density, compressive modulus, phosphate-buffered saline uptake ratio and weight loss of the scaffolds were evaluated. Generally, a scaffold with a higher PLGA content had a lower porosity and weight loss, and a medium uptake ratio, but a larger apparent density and compressive modulus. When the PLGA content was lower than 50%, the PLGA-integrated scaffolds had a similar pore size (approximately 200microm) as that of the control, and as much as 90% of their porosity could be preserved. In vitro chondrocyte culture in the 50% PLGA-integrated scaffold demonstrated that the cells could proliferate and secrete extracellular matrix at the same level as in the control gelatin/chitosan/hyaluronan scaffold.     

Alginate/poly (lactic-co-glycolic acid)/calcium phosphate cement scaffold with oriented pore structure for bone tissue engineering

In this study, the alginate/calcium phosphate cement (CPC) scaffolds with oriented pore structure were fabricated by unidirectional freeze casting and poly (lactic-co-glycolic acid) (PLGA) was used to infiltrate into the macropores to strengthen the scaffolds. By modifying the liquid to powder ratio, the porosity and pore size of the alginate/CPC scaffold could be controlled. At the liquid to powder (L/P) ratio of 3.25, scaffolds possessing open directional macropores and a total porosity of 89.24% could be achieved. The size of the tubule-like macropores could reach 100-200 mum in their radial dimension and more than 1000 mum in the axial one, with macropores well-regulated arrayed. Increasing the L/P ratio would significantly decrease the mechanical strength of alginate/CPC scaffolds. The compressive strength and toughness of scaffolds could be greatly improved via PLGA reinforcement. Three mechanisms of PLGA reinforcement ran as follows: participating in the external load, strengthening the matrix, and patching the defects of CPC pores wall. Alginate/PLGA/CPC scaffold preserved the open directional macropores and might be a potential scaffold for bone tissue engineering.     

Synthesis of macroporous hydroxyapatite scaffolds for bone tissue engineering

A novel method of preparing macroporous hydroxyapatite (HA) by dual-phase mixing was developed: HA slurry and Polymethylmethacrylate (PMMA) resin were mixed together at the volume ratio of 1:1. After pyrolytic removal of the PMMA phase, HA with an open porous structure was obtained. In this way, the porosity of the ceramic was limited to 50%. Attempts to increase the porosity by adding more PMMA resin were confronted with the technical hurdle of sample collapse during the pyrolysis process. To increase the porosity and to improve pore interconnection, an extra foaming step was introduced before the polymerization of PMMA resin. Three foaming agent systems were tried, based on the reactions of citric acid and (bi)carbonate salts: sodium bicarbonate, calcium carbonate, and ammonium bicarbonate. Although all the three foaming agents were able to increase the porosity up to 70%, keeping all the pores interconnected throughout, only ammonium bicarbonate system turned out to be applicable to make HA scaffolds or implants, because both NaHCO(3) and CaCO(3) systems caused alkalic residues in the final ceramic. The porous HA samples were fully characterized by FTIR, XRD, ESEM (EDX), and optical microscopy.     

Fabrication of precision scaffolds using liquid-frozen deposition manufacturing for cartilage tissue engineering

The fused deposition manufacturing (FDM) system has been used to fabricate tissue-engineered scaffolds with highly interconnecting and controllable pore structure, although the system is limited to a few materials. For this reason, the liquid-frozen deposition manufacturing (LFDM) system based on an improvement of the FDM process was developed. Poly(D,L-lactide-co-glycolide) (PLGA) precision scaffolds were fabricated using LFDM from PLGA solutions of different concentrations. A greater concentration of PLGA solution resulted in greater mechanical strength but also resulted in less water content and smaller pore size on the surface of the scaffolds. LFDM scaffolds in general had mechanical strength closer to that of native articular cartilage than did FDM scaffolds. Neocartilage formation was observed in LFDM scaffolds seeded with porcine articular chondrocytes after 28 days of culture. Chondrocytes in LFDM scaffolds made from low concentrations (15-20%) of PLGA solution maintained a round shape, proliferated well, and secreted abundant extracellular matrix. In contrast, the FDM PLGA scaffolds had low cell numbers and poor matrix production because of heavy swelling. The LFDM system offered a useful way to fabricate scaffolds for cartilage tissue-engineering applications.     

Effects of porosity and pore size on in vitro degradation of three-dimensional porous poly(D,L-lactide-co-glycolide) scaffolds for tissue engineering

In vitro degradation of seven three-dimensional porous scaffolds composed of PLGA85/15, a very useful poly(D,L-lactide-co-glycolide), was performed in phosphate-buffered saline solution at 37 degrees C up to 26 weeks, and effects of porosity (80-95%) and pore size (50-450 mum) on the degradation of the scaffolds were investigated. A series of quantities were measured during the degradation processes: molecular weight and its distribution of PLGA; compressive strength and modulus; and weight, dimension, and porosity of scaffolds. In all of cases with different pore morphologies, the degradation processes obeyed a three-stage model. Scaffolds with a higher porosity or a smaller pore size degraded more slowly than and thus outlasted those with a lower porosity or a larger pore size. The effects are both attributed to a wall effect and a surface area effect because the scaffolds with lower porosities or larger pores possess thicker pore walls and smaller surface area, which depress the diffusion of acidic degradation products and thus results in a stronger acid-catalyzed hydrolysis. This work suggests that, in designing a tissue-engineering scaffold composed of PLGA and adjusting its degradation rate, the effects of pore morphologies should be taken into consideration in addition to those of chemical composition and condensed state of raw materials.     

Fabrication and characterization of hydrophilic poly(lactic-co-glycolic acid)/poly(vinyl alcohol) blend cell scaffolds by melt-molding particulate-leaching method

Porous PLGA/PVA scaffolds were fabricated by blending poly(lactic-co-glycolic acid) (PLGA) with polyvinyl alcohol (PVA) to improve the hydrophilicity and cell compatibility of the scaffolds for tissue engineering applications. PLGA/PVA blend scaffolds with different PVA compositions up to 20wt% were fabricated by a melt-molding particulate-leaching method (non-solvent method). The prepared scaffolds were investigated by scanning electron microscopy (SEM), mercury intrusion porosimetry, the measurements of water contact angles and bi-axial tensile strengths, etc. for their surface and bulk characterizations. The scaffolds exhibited highly porous and open-cellular pore structures with almost same surface and interior porosities (pore size, 200-300 microm; porosity, about 90%). The PLGA/PVA blend scaffolds with PVA compositions more than 5% were easily wetted in cell culture medium without any prewetting treatments, which is highly desirable for tissue engineering applications. In vitro cell compatibility of the control hydrophobic PLGA and hydrophilized PLGA/PVA (5wt%) blend scaffolds was compared by the culture of human chondrocytes in the scaffolds and the following analyses by MTT assay and SEM observation. It was observed that the PLGA/PVA blend scaffold had better cell adhesion and growth than the control PLGA scaffold. For in vivo evaluation of tissue compatibility, the scaffolds were implanted into the skull defects of rabbits. The results were evaluated by histology examinations. The PLGA/PVA (5wt%) blend scaffold showed better bone ingrowth into the scaffold and new bone formation inside the scaffold than the PLGA scaffold. It seems that 5% addition of PVA to PLGA to fabricate PLGA/PVA blend scaffolds is enough for improving the hydrophilicity and cell compatibility of the scaffolds.     

聚乳酸-羟基乙酸共聚物/硅酸钙三维多孔骨组织工程支架的构建与性能

BACKGROUND: Some disadvantages exsist in commonly used poly(lactic-co-glycolic acid) (PLGA) scaffolds, including acidic degradation products, suboptimal mechanical properties, low pore size, poor porosity and pore connectivity rate and uncontrollable shape. OBJECTIVE: To construct a scaffold with three-dimensional (3D) pores by adding calcium silicate to improve the properties of PLGA, and then detect its degradability, mechanical properties and biocompatibility. METHODS: PLGA/calcium silicate porous composite microspheres were prepared by the emulsion-solvent evaporation method, and PLGA 3D porous scaffold was established by 3D-Bioplotter, and then PLGA/calcium silicate composite porous scaffolds were constructed by combining the microspheres with the scaffold using low temperature fusion technology. The compositions, morphology and degradability of the PLGA/calcium silicate porous composite microspheres and PLGA microspheres, as well as the morphology, pore properties and compression strength of the PLGA 3D scaffolds and PLGA/calcium silicate composite porous scaffolds were measured, respectively. Mouse bone marrow mesenchymal stem cells were respectively cultivated in the extracts of PLGA/calcium silicate porous composite microspheres and PLGA microspheres, and then were respectively seeded onto the PLGA 3D scaffolds and PLGA/calcium silicate composite porous scaffolds. Thereafter, the cell proliferation activity was detected at 1, 3 and 5 days. RESULTS AND CONCLUSION: Regular pores on the PLGA microspheres and internal cavities were formed, and the PH values of the degradation products were improved after adding calcium silicate. The fiber diameter, pore, porosity and average pore size of the composite porous scaffolds were all smaller than those of the PLGA scaffolds. The compression strength and elasticity modulus of the composite porous scaffolds were both higher than those of the PLGA scaffolds (P < 0.05). Bone marrow mesenchymal stem cells grew well in above microsphere extracts and scaffolds. These results indicate that PLGA/calcium silicate composite porous scaffolds exhibit good degradability in vitro, mechanical properties and biocompatibility.     

Characterization of emulsified chitosan-PLGA matrices formed using controlled-rate freezing and lyophilization technique

This study evaluated the formation of chitosan-50:50 poly-lactic-co-glycolic acid (PLGA) blend matrices using controlled-rate freezing and lyophilization technique (CRFLT). An emulsion system was used in the presence of 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC), a cellular component, as a stabilizer. Blended scaffolds showed an open pore morphology and homogenous interdispersion of PLGA and chitosan. Forming emulsions after dissolving PLGA in chloroform, benzene, or methylene chloride indicated better emulsion stability with benzene and chloroform. Scaffolds formed by freezing at -20, -78, and -196 degrees C from these emulsions showed significant influence of the solvent and freezing temperature on the microarchitecture of the scaffold. By controlling the concentration of chitosan, scaffolds with greater than 90% porosity were attained. Since the two polymers degrade by different mechanisms, formed scaffolds were analyzed for degradation characteristics for 4 weeks in presence of 10 mg/L lysozyme. These results showed no significant difference in the weight loss and dimension changes, as all scaffolds showed significant (a) weight loss and (b) nearly 60% reduction in volume. Further, pH of the incubation media decreased in all the samples. When cellular activity of green fluorescence protein-transfected smooth muscle cells was analyzed, no apparent cytotoxicity was observed. However, the cell spreading area decreased. In summary, these results show promising potential in tissue engineering and drug delivery applications.     

Mechanical and biological properties of hydroxyapatite/tricalcium phosphate scaffolds coated with poly(lactic-co-glycolic acid)

Regeneration of bone, cartilage and osteochondral tissues by tissue engineering has attracted intense attention due to its potential advantages over the traditional replacement of tissues with synthetic implants. Nevertheless, there is still a dearth of ideal or suitable scaffolds based on porous biomaterials, and the present study was undertaken to develop and evaluate a useful porous composite scaffold system. Here, hydroxyapatite (HA)/tricalcium phosphate (TCP) scaffolds (average pore size: 500 μm; porosity: 87%) were prepared by a polyurethane foam replica method, followed by modification with infiltration and coating of poly(lactic-co-glycolic acid) (PLGA). The thermal shock resistance of the composite scaffolds was evaluated by measuring the compressive strength before and after quenching or freezing treatment. The porous structure (in terms of pore size, porosity and pore interconnectivity) of the composite scaffolds was examined. The penetration of the bone marrow stromal stem cells into the scaffolds and the attachment of the cells onto the scaffolds were also investigated. It was shown that the PLGA incorporation in the HA/TCP scaffolds significantly increased the compressive strength up to 660 kPa and the residual compressive strength after the freezing treatment decreased to 160 kPa, which was, however, sufficient for the scaffolds to withstand subsequent cell culture procedures and a freeze–drying process. On the other hand, the PLGA coating on the strut surfaces of the scaffolds was rather thin (<5 μm) and apparently porous, maintaining the high open porosity of the HA/TCP scaffolds, resulting in desirable migration and attachment of the bone marrow stromal stem cells, although a thicker PLGA coating would have imparted a higher compressive strength of the PLGA-coated porous HA/TCP composite scaffolds.     

Surface modification of biodegradable polyesters with fatty acid conjugates for improved drug targeting

We describe a general method for incorporating target ligands into the surface of biocompatible polyester poly(lactic-co-glycolic acid) (PLGA) 50/50 materials using fatty acids. Avidin-fatty acid conjugates were prepared and efficiently incorporated into PLGA. Avidin was chosen as an adaptor protein to facilitate the attachment of a variety of biotinylated ligands. We show that fatty acid preferentially associates with the hydrophobic PLGA matrix, rather than the external aqueous environment, facilitating a prolonged presentation of avidin over several weeks. We successfully applied this approach in both microspheres encapsulating a model protein, bovine serum albumin, and PLGA scaffolds fabricated by a salt-leaching method. Because of its ease, generality and flexibility, this strategy promises widespread utility in modifying the surface of PLGA-based materials for applications in drug delivery and tissue engineering.     

Hydrophilized 3D porous scaffold for effective plasmid DNA delivery

In this study, hydrophilic PLGA/Pluronic F127 scaffolds loaded with a pDNA/PEI-PEG complex were prepared to estimate their potential use as a polymeric matrix for pDNA delivery. The scaffold was fabricated by a novel precipitation/particulate leaching method. The prepared pDNA/PEI-PEG complex-loaded PLGA/Pluronic F127 scaffold exhibited a highly porous (porosity, 93-95%) and open pore structure, as well as hydrophilicity, which can provide the good environment for cell adhesion and growth. The pDNA/PEI-PEG complexes were efficiently loaded into the PLGA/Pluronic F127 scaffold and continuously released from the scaffolds up to ~90% of the initial loading amount over a period of 8 wk, which may lead to continuous gene transfection into human bone marrow mesenchymal stem cells (hBMMSCs). From the in vitro cell culture in the scaffolds for transfection, it was observed that the pDNA/PEI-PEG complex-loaded hydrophilic PLGA/Pluronic F127 scaffold has a higher transfection efficiency of the pDNA/PEI-PEG complexes into hBMMSCs than the hydrophobic PLGA ones. The cell viability associated with the pDNA/PEI-PEG complexes released from the PLGA/Pluronic F127 scaffold was not significantly different from that of the PLGA/Pluronic F127 scaffold without pDNA, indicating its low cytotoxicity, probably due to the sustained release of the pDNA/PEI-PEG complex from the scaffolds. From these results, we could suggest that the pDNA/PEI-PEG complex-loaded hydrophilic PLGA/Pluronic F127 scaffold can be an effective gene delivery system for 3D tissue formation.     

Macroporous biodegradable natural/synthetic hybrid scaffolds as small intestine submucosa impregnated poly(D,L-lactide-co-glycolide) for tissue-engineered bone

—Poly( D , L-lactide-co-glycolide) (PLGA), a biodegradable synthetic polymer, is widely used in a variety of tissue-engineered applications, including drug-delivery systems. However, the PLGA scaffolds, macroporous and three-dimensional structure, are difficult to cell attachment and in-growth due to surface hydrophobicity. In order to introduce in new bioactive functionality from porcine small intestine submucosa (SIS) as natural source for PLGA, we fabricated SIS-powder-impregnated PLGA (SIS/PLGA) hybrid scaffolds. Fabrication parameters, including ratios of SIS, PLGA and salt, were optimized to produce the desired macroporous foam. The scaffolds had a relatively homogeneous pore structure, good interconnected pores from the surface to core region and showed an average pore size in the range 69.23–105.82 μm and over 90% porosity. The SIS/PLGA scaffolds degraded with a rate depending on the contents of the SIS. After the fabrication of the SIS/PLGA hybrid scaffolds the wettability of the scaffold was greatly enhanced, resulting in uniform cell seeding and distribution. So, it was observed that BMSC attachment to the SIS/PLGA scaffolds increased gradually with increasing SIS contents. Scaffolds of PLGA alone and SIS/PLGA were implanted subcutaneously under dorsal skin of athymic nude mouse to observe the osteoconductivity. It was found from the result that the effects of the SIS/PLGA scaffolds on bone formation are stronger than control PLGA scaffolds. In summary, the SIS/PLGA scaffolds have osteoconductive effects to allow remodeling and replacement by osseous tissue.     

Macroporous biodegradable natural/synthetic hybrid scaffolds as small intestine submucosa impregnated poly(D,L-lactide-co-glycolide) for tissue-engineered bone

Poly(D,L-lactide-co-glycolide) (PLGA), a biodegradable synthetic polymer, is widely used in a variety of tissue-engineered applications, including drug-delivery systems. However, the PLGA scaffolds, macroporous and three-dimensional structure, are difficult to cell attachment and in-growth due to surface hydrophobicity. In order to introduce in new bioactive functionality from porcine small intestine submucosa (SIS) as natural source for PLGA, we fabricated SIS-powder-impregnated PLGA (SIS/PLGA) hybrid scaffolds. Fabrication parameters, including ratios of SIS, PLGA and salt, were optimized to produce the desired macroporous foam. The scaffolds had a relatively homogeneous pore structure, good interconnected pores from the surface to core region and showed an average pore size in the range 69.23-105.82 microm and over 90% porosity. The SIS/PLGA scaffolds degraded with a rate depending on the contents of the SIS. After the fabrication of the SIS/PLGA hybrid scaffolds the wettability of the scaffold was greatly enhanced, resulting in uniform cell seeding and distribution. So, it was observed that BMSC attachment to the SIS/PLGA scaffolds increased gradually with increasing SIS contents. Scaffolds of PLGA alone and SIS/PLGA were implanted subcutaneously under dorsal skin of athymic nude mouse to observe the osteoconductivity. It was found from the result that the effects of the SIS/PLGA scaffolds on bone formation are stronger than control PLGA scaffolds. In summary, the SIS/PLGA scaffolds have osteoconductive effects to allow remodeling and replacement by osseous tissue.     

Three-dimensional duck’s feet collagen/PLGA scaffold for chondrification: role of pore size and porosity

Abstract

An ideal tissue-engineered scaffold must provide sufficient porosity to allow free movement of cells, nutrients, and oxygen for proper cell growth and further maintenance. Owing to variation in pore sizes and shapes of as-fabricated scaffold, the amount of oxygen available for the cells attached to the scaffold and transfer of by-products and excrement will be different, which ultimately results in cell activity. Thus, optimizing pore size and porosity of a scaffold for a specific tissue regeneration are one of the key highlights, which should be considered while designing a scaffold as well as choosing a specific cell type. In this study, three-dimensional (3D) scaffolds based on blends of duck’s feet collagen (DC) and poly (lactic-co-glycolic acid) (PLGA) with different pore sizes i.e. 90–180, 180–250, 250–355 and 355–425 μm were prepared using solvent casting/salt leaching approach and examined its effects on chondrification. The morphological analysis of the as-fabricated scaffolds was performed using SEM for studying porosity and pore size. The cell proliferation and gene expression were investigated after culturing costal chondrocytes on each scaffolds using 3-(4, 5-dimethylthiazol-2-yl)-2,5 diphenyltetrazolium bromide (MTT) assay and qRT-PCR. Histological staining of in vivo implants was performed in nude mice as models. The biological evaluation showed a pore-size dependent chondrification at different time points. Especially, the 355–425 μm DC/PLGA scaffold showed a highest positive impact on maintenance of cell proliferation, costal chondrocyte phenotype and increased glycosaminoglycan accumulation than the other groups. These results indicated that DC/PLGA scaffolds with pore size ranging from 250 to 425 μm can be considered as highly-suitable constructs for enhanced chondrification.     

Beneficial effect of hydrophilized porous polymer scaffolds in tissue-engineered cartilage formation

Three dimensional (3D) porous poly(L-lactic acid) (PLLA) scaffolds were fabricated using a modified gas foaming method whose effervescent porogens were a mixture of sodium bicarbonate and citric acid. To improve chondrocyte adhesion, the scaffolds were then hydrophilized through oxygen plasma treatment and in situ graft polymerization of acrylic acid (AA). When the physical properties of AA-grafted scaffolds were examined, the porosity and pore size were 87 approximately 93% and 100 approximately 300 microm, respectively. The pore sizes were highly dependent on the varying ratios (w/w) between porogen and polymer solution. Influenced by their pore sizes, the compressive moduli of scaffolds significantly decreased with increasing pore size. The altered surface characteristics were clearly reflected in the reduced water contact angles that meant a significant hydrophilization with the modified polymer surface. Electron spectroscopy for chemical analysis (ESCA) and time-of-flight secondary ion mass spectrometer (ToF-SIMS) also confirmed the altered surface chemistry. When chondrocytes were seeded onto the AA-grafted PLLA scaffolds, cell adhesion and proliferation were substantially improved as compared to the unmodified scaffolds. The benefit of the modified scaffolds was clear in the gene expressions of collagen type II that was significantly upregulated after 4-week culture. Safranin-O staining also identified greater glycosaminoglycan (GAG) deposition in the modified scaffold. The AA-grafted porous polymer scaffolds were effective for cell adhesion and differentiation, making them a suitable platform for tissue-engineered cartilage.     

The effect of porosity on drug release kinetics from vancomycin microsphere/calcium phosphate cement composites

The influence of porosity on release profiles of antibiotics from calcium phosphate composites was investigated to optimize the duration of treatment. We hypothesized, that by the encapsulation of vancomycin-HCl into biodegradable microspheres prior admixing to calcium phosphate bone cement, the influence of porosity of the cement matrix on vancomycin release could be reduced. Encapsulation of vancomycin into a biodegradable poly(lactic co-glycolic acid) copolymer (PLGA) was performed by spray drying; drug-loaded microparticles were added to calcium phosphate cement (CPC) at different powder to liquid ratios (P/L), resulting in different porosities of the cement composites. The effect of differences in P/L ratio on drug release kinetics was compared for both the direct addition of vancomycin-HCl to the cement liquid and for cement composites modified with vancomycin-HCl-loaded microspheres. Scanning electron microscopy (SEM) was used to visualize surface and cross section morphology of the different composites. Brunauer, Emmett, and Teller-plots (BET) was used to determine the specific surface area and pore size distribution of these matrices. It could be clearly shown, that variations in P/L ratio influenced both the porosity of cement and vancomycin release profiles. Antibiotic activity during release study was successfully measured using an agar diffusion assay. However, vancomycin-HCl encapsulation into PLGA polymer microspheres decreased porosity influence of cement on drug release while maintaining antibiotic activity of the embedded substance.     

Electrospun PLGA nanofiber scaffolds for articular cartilage reconstruction: mechanical stability, degradation and cellular responses under mechanical stimulation in vitro

We investigated the potential of a nanofiber-based poly(DL-lactide-co-glycolide) (PLGA) scaffold to be used for cartilage reconstruction. The mechanical properties of the nanofiber scaffold, degradation of the scaffold and cellular responses to the scaffold under mechanical stimulation were studied. Three different types of scaffold (lactic acid/glycolic acid content ratio = 75 : 25, 50 : 50, or a blend of 75 : 25 and 50 : 50) were tested. The tensile modulus, ultimate tensile stress and corresponding strain of the scaffolds were similar to those of skin and were slightly lower than those of human cartilage. This suggested that the nanofiber scaffold was sufficiently mechanically stable to withstand implantation and to support regenerated cartilage. The 50 : 50 PLGA scaffold was degraded faster than 75 : 25 PLGA, probably due to the higher hydrophilic glycolic acid content in the former. The nanofiber scaffold was degraded faster than a block-type scaffold that had a similar molecular weight. Therefore, degradation of the scaffold depended on the lactic acid/glycolic acid content ratio and might be controlled by mixing ratio of blend PLGA. Cellular responses were evaluated by examining toxicity, cell proliferation and extracellular matrix (ECM) formation using freshly isolated chondrocytes from porcine articular cartilage. The scaffolds were non-toxic, and cell proliferation and ECM formation in nanofiber scaffolds were superior to those in membrane-type scaffolds. Intermittent hydrostatic pressure applied to cell-seeded nanofiber scaffolds increased chondrocyte proliferation and ECM formation. In conclusion, our nanofiber-based PLGA scaffold has the potential to be used for cartilage reconstruction.     

Electrospun PLGA nanofiber scaffolds for articular cartilage reconstruction: mechanical stability,degradation and cellular responses under mechanical stimulation in vitro

We investigated the potential of a nanofiber-based poly(DL-lactide-co-glycolide) (PLGA) scaffold to be used for cartilage reconstruction. The mechanical properties of the nanofiber scaffold, degradation of the scaffold and cellular responses to the scaffold under mechanical stimulation were studied. Three different types of scaffold (lactic acid/glycolic acid content ratio = 75 : 25, 50 : 50, or a blend of 75 : 25 and 50 : 50) were tested. The tensile modulus, ultimate tensile stress and corresponding strain of the scaffolds were similar to those of skin and were slightly lower than those of human cartilage. This suggested that the nanofiber scaffold was sufficiently mechanically stable to withstand implantation and to support regenerated cartilage. The 50 : 50 PLGA scaffold was degraded faster than 75 : 25 PLGA, probably due to the higher hydrophilic glycolic acid content in the former. The nanofiber scaffold was degraded faster than a block-type scaffold that had a similar molecular weight. Therefore, degradation of the scaffold depended on the lactic acid/glycolic acid content ratio and might be controlled by mixing ratio of blend PLGA. Cellular responses were evaluated by examining toxicity, cell proliferation and extracellular matrix (ECM) formation using freshly isolated chondrocytes from porcine articular cartilage. The scaffolds were non-toxic, and cell proliferation and ECM formation in nanofiber scaffolds were superior to those in membrane-type scaffolds. Intermittent hydrostatic pressure applied to cell-seeded nanofiber scaffolds increased chondrocyte proliferation and ECM formation. In conclusion, our nanofiber-based PLGA scaffold has the potential to be used for cartilage reconstruction.     

Hybrid coating of hydroxyapatite and collagen within poly(D,L-lactic-co-glycolic acid) scaffold

To improve the cell-affinity of biodegradable polymer scaffold, coating hydroxyapatite (HA) or collagen on the surface of polymer materials seemed to be a strategy to combine both advantages of them. The objective of this study was to develop a novel method to introduce HA and collagen inside polymer scaffold uniformly. HA and collagen suspension was mixed with paraffin microspheres, and molded to form a composite sample. After the sample was dried, HA/collagen composite was left among and on the surface of paraffin microspheres. Poly(D,L-lactic-co-glycolic acid) (PLGA) (50/50) solution was cast into the inter-space of the paraffin microspheres and dried. Afterwards, the paraffin was dissolved and removed, HA/collagen was transferred to the surface and even inside of the pore wall of PLGA scaffolds. Collagen fibers and HA particles which were inlaid inside the PLGA pore wall could help to enhance the coating strength between HA/Col coating and the pore wall surface of the PLGA scaffold. The scaffolds with HA/Col coating were expected to exhibit desirable properties in bone tissue engineering.     

The nanocomposite scaffold of poly(lactide-co-glycolide) and hydroxyapatite surface-grafted with l-lactic acid oligomer for bone repair

Nanohydroxyapatite (op-HA) surface-modified with l-lactic acid oligomer (LAc oligomer) was prepared by LAc oligomer grafted onto the hydroxyapatite (HA) surface. The nanocomposite of op-HA/PLGA with different op-HA contents of 5, 10, 20 and 40 wt.% in the composite was fabricated into three-dimensional scaffolds by the melt-molding and particulate leaching methods. PLGA and the nanocomposite of HA/PLGA with 10 wt.% of ungrafted hydroxyapatite were used as the controls. The scaffolds were highly porous with evenly distributed and interconnected pore structures, and the porosity was around 90%. Besides the macropores of 100–300 μm created by the leaching of NaCl particles, the micropores (1–50 μm) in the pore walls increased with increasing content of op-HA in the composites of op-HA/PLGA. The op-HA particles could disperse more uniformly than those of pure HA in PLGA matrix. The 20 wt.% op-HA/PLGA sample exhibited the maximum mechanical strength, including bending strength (4.14 MPa) and compressive strength (2.31 MPa). The cell viability and the areas of the attached osteoblasts on the films of 10 wt.% op-HA/PLGA and 20 wt.% op-HA/PLGA were evidently higher than those on the other composites. For the animal test, there was rapid healing in the defects treated with 10 and 20 wt.% op-HA/PLGA, where bridging by a large bony callus was observed at 24 weeks post-surgery. There was non-union of radius defects implanted with PLGA and in the untreated group. This was verified by the Masson’s trichrome staining photomicrographs of histological analysis. All the data extrapolated that the composite with 10 and 20 wt.% op-HA exhibited better comprehensive properties and were the optimal composites for bone repairing.