Solvent Casting Particulate Leaching Research Articles

ＨＡＰ‐ＰＬＧＡ複合体による顎骨再生への応用に関する実験的研究

This experimental study evaluated bone formation in response to hydroxyapatite-poly (D, L-lactic-coglycolic acid)(HAP-PLGA) composite scaffold in rabbits. HAP-PLGA composite scaffold was prepared by a solvent-casting particulate leaching method. A cylindrical bone defect was created in the tibia of rabbits and was filled with HAP-PLGA composite scaffold and control PLGA scaffold, respectively. Three and 6 weeks after implantion, the implantion sites were evaluated by Micro-focused X-ray computed tomography (micro-CT) and histological analysis. After 3 weeks, bone had infiltrated from the periphery of the defects in both scaffolds, although there was less identifiable bone at the center of the defects. Histological investigations revealed that cortical sites of HAP-PLGA composite scaffold were filled with bone tissue 6 weeks after implantation, whereas those of PLGA scaffold were filled with no bone tissue. Therefore, we conclude that HAP-PLGA composite scaffold enables bone tissue to grow inside. HAP-PLGA composite scaffold may be an ideal scaffold for bone regeneration and bone tissue engineering.

Optimal segmentation of microcomputed tomographic images of porous tissue‐engineering scaffolds

The morphometric properties of the porous tissue-engineering scaffolds play a dominant role in the initial cell attachment and subsequent tissue regeneration. These properties can be derived nondestructively with the use of quantitative analysis of high-resolution microcomputed tomography (microCT) imaging of scaffolds. Accurate segmentation of these acquired images into solid and porous subspaces is critical to the integrity of morphometric analysis. The absence of a single image-processing technique to provide such accurate separability immune to all the intricacies of the acquired data makes this seemingly simple task significantly error prone. Consequently, an optimal segmentation has to be selected by ranking the segmentations produced by a multiplicity of methods. This article proposes a robust, easy-to-implement, unambiguous, signal-processing-based, ground-truth-free, segmentation rating metric that correlates with visual acuity. With the use of this metric it is possible, for the first time, to threshold the data with a wide range of techniques and select automatically the technique that best delineates the acquired image. The proposed solution has been extensively tested on microCT images of scaffolds fabricated with biodegradable poly (propylene fumarate) (PPF) with the use of a solvent casting particulate leaching process. The approaches proposed and the results obtained may have profound implications for accurate image-based characterization of tissue-engineering scaffolds.

Preparation and characterization of bioactive and biodegradable Wollastonite/poly(D,L-lactic acid) composite scaffolds

Composite scaffolds of poly(D,L-lactic acid) (PDLLA) with bioactive wollastonite were fabricated by the conventional solvent casting-particulate leaching method. The pore structures and morphology of the scaffolds were determined by scanning electron microscopy (SEM). The bioactivity of the composites was evaluated by soaking in a simulated body fluid (SBF), and the formation of the hydroxyapatite (HAp) layer was determined by SEM and energy-dispersive spectrometer. The results showed that the wollastonite/PDLLA composites were bioactive as it induced the formation of HAp on the surface of the composite scaffolds after soaking in SBF for seven days. In addition, pH and ion concentration changes of SBF solutions with composite scaffolds were examined. The results showed that the composites could release Ca and Si ions, which could neutralize the acidic degradation by-products of the PDLLA, and stabilize the pH of the SBF solutions between 6.7 and 7.2 within a three-week soaking period. Furthermore, the measurements of the water contact angles suggested that incorporation of wollastonite into PDLLA could improve the hydrophilicity of the composites and the enhancement was dependent on the wollastonite content. All these results suggest that incorporation of wollastonite into PDLLA might be a useful approach for the preparation of composite scaffolds for tissue repair and tissue-engineering applications.

Thermally produced biodegradable scaffolds for cartilage tissue engineering.

A novel process was developed to fabricate biodegradable polymer scaffolds for tissue engineering applications, without using organic solvents. Solvent residues in scaffolds fabricated by processes involving organic solvents may damage cells transplanted onto the scaffolds or tissue near the transplantation site. Poly(L-lactic acid) (PLLA) powder and NaCl particles in a mold were compressed and subsequently heated at 180 degrees C (near the PLLA melting temperature) for 3 min. The heat treatment caused the polymer particles to fuse and form a continuous matrix containing entrapped NaCl particles. After dissolving the NaCl salts, which served as a porogen, porous biodegradable PLLA scaffolds were formed. The scaffold porosity and pore size were controlled by adjusting the NaCl/PLLA weight ratio and the NaCl particle size. The characteristics of the scaffolds were compared to those of scaffolds fabricated using a conventional solvent casting/particulate leaching (SC/PL) process, in terms of pore structure, pore-size distribution, and mechanical properties. A scanning electron microscopic examination showed highly interconnected and open pore structures in the scaffolds fabricated using the thermal process, whereas the SC/PL process yielded scaffolds with less interconnected and closed pore structures. Mercury intrusion porosimetry revealed that the thermally produced scaffolds had a much more uniform distribution of pore sizes than the SC/PL process. The utility of the thermally produced scaffolds was demonstrated by engineering cartilaginous tissues in vivo. In summary, the thermal process developed in this study yields tissue-engineering scaffolds with more favorable characteristics, with respect to, freedom from organic solvents, pore structure, and size distribution than the SC/PL process. Moreover, the thermal process could also be used to fabricate scaffolds from polymers that are insoluble in organic solvents, such as poly(glycolic acid). Cartilage tissue regenerated from thermally produced PLLA scaffold.

Fibroblast culture on surface-modified poly (glycolide-co-ε-caprolactone) scaffold for soft tissue regeneration

Novel porous matrices made of a copolymer of glycolide (G) and ε-caprolactone (CL) (51 : 49, Mw 103 000) was prepared for tissue engineering using a solvent-casting particulate leaching method. Poly(glycolide-co-ε-caprolactone) (PGCL) copolymer showed a rubber-like elastic characteristic, in addition to an amorphous property and fast biodegradability. In order to investigate the effect on the fibroblast culture, PGCL scaffolds of varying porosity and pore size, in addition to surfacehydrolysis or collagen coating, were studied. The large pore-sized scaffold (pore size >150 μm) demonstrated a much greater cell adhesion and proliferation than the small pore-sized one. In addition, the higher porosity, the better the cell adhesion and proliferation. The surface-hydrolyzed PGCL scaffold showed enhanced cell adhesion and proliferation compared with the unmodified one. Type I collagen coating revealed a more pronounced contribution for increased cell interactions than the surface-hydrolyzed one. These results demonstrate that surface-modified PGCL scaffold can provide a suitable substrate for fibroblast culture, especially in the case of soft tissue regenerations.

Release of bioactive human growth hormone from a biodegradable material: Poly(ε‐caprolactone)

We have characterized the biodegradable material poly(ϵ-caprolactone) (PCL) as a delivery system for recombinant human growth hormone (hGH). Two contrasting methods for the manufacture of the biomaterial were investigated: namely, solvent casting and solvent casting particulate leaching; the latter yielded porous PCL discs. The degree of porosity, which was assessed by scanning electron microscopy, could be controlled by incorporating selected concentrations of particulate sodium chloride during the manufacturing process. Bioactive hGH released from the PCL preparations was quantified with a highly sensitive and precise bioassay which was based upon hGH activation of rat lymphoma Nb2 cells. Eluates obtained from control discs of PCL which had not been loaded with hGH proved to be nontoxic when tested on these cells. The release of bioactive hGH from hormone-loaded nonporous discs of PCL was found to be a direct function of the initial hormone loading dose. Increased porosity of the discs manufactured by solvent casting particulate leaching increased the delivery of hGH from discs which had been immersion loaded. However, hGH release after surface loading was independent of porosity. Hormone concentrations were also assessed by immunoassay so that the ratios of bio- to immunoactivity (B:I ratio) of the hormone release could be determined. We found that the B:I ratio of the hormone after release from unstored discs was identical to that of the hormone prior to its incorporation into the PCL, demonstrating that the mild incorporation procedures utilized had not adversely affected the structural integrity of the hormone. However, if the hormone-loaded discs were stored at 37°C prior to elution, the B:I ratios of the hGH released decreased indicating that this compromised the bioactive site. © 1998 John Wiley & Sons, Inc. J Biomed Mater Res, 40, 204–213, 1998

Release of bioactive human growth hormone from a biodegradable material: poly(epsilon-caprolactone).

We have characterized the biodegradable material poly(epsilon-caprolactone) (PCL) as a delivery system for recombinant human growth hormone (hGH). Two contrasting methods for the manufacture of the biomaterial were investigated: namely, solvent casting and solvent casting particulate leaching; the latter yielded porous PCL discs. The degree of porosity, which was assessed by scanning electron microscopy, could be controlled by incorporating selected concentrations of particulate sodium chloride during the manufacturing process. Bioactive hGH released from the PCL preparations was quantified with a highly sensitive and precise bioassay which was based upon hGH activation of rat lymphoma Nb2 cells. Eluates obtained from control discs of PCL which had not been loaded with hGH proved to be nontoxic when tested on these cells. The release of bioactive hGH from hormone-loaded nonporous discs of PCL was found to be a direct function of the initial hormone loading dose. Increased porosity of the discs manufactured by solvent casting particulate leaching increased the delivery of hGH from discs which had been immersion loaded. However, hGH release after surface loading was independent of porosity. Hormone concentrations were also assessed by immunoassay so that the ratios of bio- to immunoactivity (B:I ratio) of the hormone release could be determined. We found that the B:I ratio of the hormone after release from unstored discs was identical to that of the hormone prior to its incorporation into the PCL, demonstrating that the mild incorporation procedures utilized had not adversely affected the structural integrity of the hormone. However, if the hormone-loaded discs were stored at 37 degrees C prior to elution, the B:I ratios of the hGH released decreased indicating that this compromised the bioactive site.