Efficient transfer of human adipose-derived stem cells by chitosan/gelatin blend films

Adipose-derived stem cells (ASCs) are a potential source of abundant mesenchymal stem cells and represent a promising cell-based therapy for tissue damage or degeneration conditions. Previous investigations have demonstrated enhanced therapeutic effects of ASCs in a three-dimensional spheroid culture formulation. In this study, we hypothesize that a composite membrane made of chitosan/gelatin (C/G) is beneficial to facilitate transfer of human ASCs in spheroids. Increasing chitosan content within the blends enhanced the mechanical properties of the sample, including tensile strength and elongation-at-break ratio. Although ASC spheroids developed shortly after seeding on pure chitosan films, increasing gelatin proportion in the C/G blends promoted cell adhesion onto the membranes. We also found that ASCs did not proliferate on chitosan films, but C/G blends of different ratios supported ASC proliferation in the first 4 days of culture. However, ASCs on all C/G blends started to detach from the films to form spheroids after day 4, while ASCs on pure gelatin films remained attached and continued to grow. Gradual gelatin release from the C/G blend films, leading to enriched chitosan content in the blends, probably encouraged ASC detachment and spheroid formation. We placed porous collagen matrix on ASC-seeded C/G blends to simulate the application of ASC-seeded C/G films onto injured tissue and found that a C/G film composed of 75% chitosan could facilitate significantly more cell transfer into the overlying collagen sponge. Therefore, a blend film containing 75% chitosan and 25% gelatin showed promising results to serve as a biomaterial for human ASC-based cell therapy.     

Blending polysaccharides with biodegradable polymers. I. Properties of chitosan/polycaprolactone blends

Blends of polycaprolactone (PCL) and chitosan (CHT) were prepared by casting from a solution. CHT and PCL were dissolved by using acetic acid/water mixtures. Both solutions were slowly mixed to cast blend films containing 10%, 20%, 30%, and 40% by weight of CHT. PCL and CHT form phase separated blends. The phase morphology is in large extent controlled by the casting procedure. Even if casting of the film starts from a clear solution, the solvent composition determines the form in which phase separation takes place and consequently the morphology of the resulting blend after solvent evaporation. The blend containing 20% CHT presents cocontinuous phases. The sample presents a high elastic modulus even at temperatures above melting of PCL. Blends with higher CHT contents consist of disperse PCL domains in a CHT matrix and the contrary occurs in the blend containing 10% CHT in which disperse CHT domains with a network morphology appear inside the spherulites of PCL. In all the blends, the nucleation effect of CHT accelerates the crystallization of PCL from the melt, although in the blends with high CHT contents a part of the PCL mass included in large domains might not be affected by the presence of CHT. The sample containing 20% CHT has a peculiar behavior with respect to the crystallization of PCL, only a small part of PCL crystallizes in isothermal treatments although this fraction crystallizes faster than in the rest of the blends.     

Hybrid hydroxyapatite nanoparticles-loaded PCL/GE blend fibers for bone tissue engineering

In order to augment bone formation, a new biodegradable scaffold system was fabricated using different ratios of hydroxyapatite (HAp) blended with synthetic polymer polycaprolactone (PCL) and natural polymer gelatin (GE) followed by electrospinning method. Three different concentrations of HAp were used in PCL/GE to obtain a blend of 10, 30, and 50% (w/v) HAp–PCL/GE. These HAp-loaded PCL/GE blends were then compared with PCL/GE blends by different mechanical and biological in vitro and in vivo studies to understand the applicability of the system. Scanning electron microscopy, X-ray diffraction analysis, and tensile strength measurement were done to obtain physical properties. Fifty Percent HAp–PCL/GE blends possessed the highest mechanical strength. In vitro cytotoxicity and proliferation of osteoblast cells on the PCL/GE and HAp–PCL/GE scaffolds were examined and shown that addition of HAp in PCL/GE was beneficial by increasing cell viability (>85%) proliferation and cell-surface attachment. Expression of collagen and osteopontin was also found higher in 50% HAp–PCL/GE blends than the others. On the other hand, in vivo bone formation was examined using rat models and increased bone formation was observed in 50% HAp–PCL/GE blends within 6?weeks. Based on the combined results of this study, HAp–PCL/GE membranes were found to hold great promise for use in tissue engineering applications, especially in bone tissue engineering.     

Regulation of biodegradability and drug release behavior of aliphatic polyesters by blending

Polyester blending of poly(epsilon-caprolactone) (PCL) with poly(D, L-lactide) (PLA) and their random copolymers (R(CL/LA)) was found to be a convenient approach to regulate the degradation and drug release behaviors of the polyesters. The blend composition and compatibility both affected its degradation and drug release behavior. A DSC study showed that PCL was compatible with 50:50 poly(CL-CO-D,L-LA) (R(50/50)) but incompatible with 25:75 poly(CL-CO-LA) (R(25/75)) and PLA homopolymer. The hydrolysis experiments indicated that with the same CL/LA segment proportion, compatible blends (PCL/R(50/50)) had higher water content and faster weight loss than incompatible blends (PCL/PLA, PCL/R(25/75)). In the compatible blends the PCL degradation rate was increased while that of R(50/50) was decreased. The controlled release kinetics, diffusion constants, and permeation coefficients of the polymer blends were measured by using northindrone (NTD) as a model. The NTD release rates from the polyester blends increased as the CL unit fraction increased but decreased with increasing the LA unit fraction in the blends. With the same CL/LA unit ratios, the NTD release rate from the compatible blend was slower than that from the incompatible blend. The NTD release from the polyester blend was controlled by the diffusion process in the early stage, but the degradation-caused NTD release was later involved. By tailoring the blend composition to such an extent that the degradation-caused release compensated the decline of the diffusion-caused release, a zero-order NTD release was achieved.     

壳聚糖/聚己内酯共混膜的制备及性能

背景：壳聚糖/聚己内酯共混材料在生物材料领域具有广泛的应用前景,但与蛋白、细胞反应机制尚不明确。 目的：观察壳聚糖/聚己内酯共混膜表面蛋白黏附和细胞活性。 方法：将不同配比的壳聚糖/聚己内酯混合溶液旋转涂膜法成膜。分别通过原子力显微镜、滴形分析仪、石英晶体天平和MTT比色法测量膜的表面形貌、亲疏水性、蛋白吸附和细胞增殖活性。 结果与结论：膜的表面形貌、亲疏水性、蛋白吸附和细胞增殖活性在很大程度上取决于壳聚糖和聚己内酯的质量配比。细胞在壳聚糖膜上具有较好的伸展形态,在聚己内酯膜上具有较高的增殖活性。     

Poly(3-hydroxybutyrate-co-3-hydroxyvalerate)/poly(epsilon-caprolactone) blends for tissue engineering applications in the form of hollow fibers

In this work, hollow fibers to be used as guides for tissue engineering applications were produced by dry-jet-wet spinning of poly(3-hydroxybutyrate-co-3-hydroxyvalerate)/poly(epsilon-caprolactone) (PHBHV/PCL) solutions in chloroform with various weight ratios between the components (PHBHV/PCL 100/0; 80/20; 60/40; 50/50; 40/60; 20/80; 0/100 w/w). Fibers obtained from PHBHV/PCL blends had a low degree of surface and bulk porosity, depending on composition. Physicochemical characterization involving scanning electron microscopy and differential scanning calorimetry (DSC) showed that PHBHV/PCL blends are compatible. Interactions between blend components were studied by Fourier transform infrared total reflectance spectroscopy, DSC analysis, and polarized optical microscopy analysis. Homogeneity of blend composition was assessed by IR-chemical imaging analysis. PHBHV/PCL samples were found to be weakly hydrophilic and their biocompatibility was proved by in vitro tests using mouse fibroblasts. Mechanical properties of PHBHV/PCL blends were investigated by stress-strain tests, showing an increasing ductility of blend samples with increasing PCL amount. Hollow fibers supported fibroblasts attachment and proliferation depending on composition and porosity degree.     

Light Scattering Studies on Ternary Polymer Blend Solutions Comprising Poly(hydroxybutyrate)

Summary: We report on light scattering studies of polymer blend solutions in trifluoroethanol (TFE). The polymer blends comprised poly(3‐hydroxybutyrate) (PHB) in combination with poly(ethylene oxide) (PEO) and poly(ε‐caprolactone) (PCL). PHBs of two different molecular masses were used. Relevant quantities were obtained from Zimm plots. All quantities display non‐linear dependencies on blend composition. For the blend system with PEO and PHB of lower molecular mass, we observed a negative excess of the second virial coefficient, which is indicative of the miscibility of the constituents. The opposite is observed for blends with PCL. The situation changes in blends with PEO and PHB of sufficiently high molecular mass. It turns out that PEO is only miscible with PHB of high molecular mass if it is the major component. This can be concluded from both light scattering and viscosity results.

Apparent molecular mass as a function of blend composition for PEO/PHB(1) and PCL/PHB(1) solutions in TFE at 25 °C.     

Polyurethane/polycaprolactane blend with shape memory effect as a proposed material for cardiovascular implants

Shape memory materials have been proposed for cardiovascular stents due to their self-expansion ability. The most ideal way to anchor a stent is using self-expansion in the range of body temperature. This work, for the first time, reports the use of polyurethane/polycaprolactone (PU/PCL) blend as a proposed material for shape memory stents. Polyurethane copolymer based on poly(ε-caprolactone) diol was melt blended with PCL in four different ratios of 20, 30, 40 and 50 wt.% and their shape memory behaviors were examined. All blends except for PU/PCL(80/20) showed shape memory effects with recovery temperatures of around the melting temperature of PCL in the blends. The melting behavior of the PCL in the blends is strongly influenced by composition. Changing the composition of the blend system and crystallization conditions adjusted shape recovery to the range of body temperature for PU/PCL(70/30) blend. The in vitro biocompatibility of PU/PCL(70/30) blend was evaluated in this study using human bone marrow mesenchymal stem cells (hBMSCs). The adhesion, morphology and mitochondrial function were analyzed in order to investigate the cell viability during cell culture on PU/PCL(70/30) blend surface. The results showed that the blend supported cell adhesion and proliferation, which indicated good biocompatibility. Our results suggested that this blend might be a potential material as a stent implant.     

Hollow fibers of poly(lactide-co-glycolide) and poly(ε-caprolactone) blends for vascular tissue engineering applications

At present the manufacture of small-diameter blood vessels is one of the main challenges in the field of vascular tissue engineering. Currently available vascular grafts rapidly fail due to development of intimal hyperplasia and thrombus formation. Poly(lactic-co-glycolic acid) (PLGA) hollow fiber (HF) membranes have previously been proposed for this application, but as we show in the present work, they have an inhibiting effect on cell proliferation and rather poor mechanical properties. To overcome this we prepared HF membranes via phase inversion using blends of PLGA with poly(ε-caprolactone) (PCL). The influence of polymer composition on the HF physicochemical properties (topography, water transport and mechanical properties) and cell attachment and proliferation were studied. Our results show that only the ratio PCL/PLGA of 85/15 (PCL/PLGA85/15) yielded a miscible blend after processing. A higher PLGA concentration in the blend led to immiscible PCL/PLGA phase-separated HFs with an inhomogeneous morphology and variation in the cell culture results. In fact, the PCL/PLGA85/15 blend, which had the most homogeneous morphology and suitable pore structure, showed better human adipose stem cell (hASC) attachment and proliferation compared with the homopolymers. This, combined with the good mechanical and transport properties, makes them potentially useful for the development of small-caliber vascular grafts.     

In vitro characterization of chitosan-gelatin scaffolds for tissue engineering

Recently, chitosan–gelatin scaffolds have gained much attention in various tissue engineering applications. However, the underlying cell–matrix interactions remain unclear in addition to the scaffold degradation and mechanical characteristics. In this study, we evaluated (i) the degradation kinetics of chitosan and chitosan–gelatin scaffolds in the presence of 10 mg/L of lysozyme for dimensional stability, weight loss, and pH changes for a period of 2 months, (ii) tensile and compressive properties of films and scaffolds in wet state at 37 °C, (iii) viability of fibroblasts and human umbilical vein endothelial cells (HUVECs) on scaffolds, and (iv) the alteration in cell spreading characteristics, cytoskeletal actin distribution, focal adhesion kinase (FAK) distribution and PECAM-1 expression of HUVECs under static and 4.5, 8.5, 13 and 18 dyn/cm² shear stress conditions. Degradation results showed that gelatin-containing chitosan scaffolds had faster degradation rate and significant loss of material than chitosan. Mechanical properties of chitosan are affected by the addition of gelatin although there was no clear trend. Three-dimensional chitosan and chitosan–gelatin scaffolds supported fibroblast viability equally. However, chitosan membranes decreased cell-spreading area, disrupted F-actin and localized FAK in the nucleus of HUVECs. Importantly, the lowest shear stress tested (4.5 dyn/cm²) for 3 h washed away cells on chitosan suggesting weak cell adhesion. In the blends, effect of gelatin was dominant; actin and FAK distribution were comparable to gelatin in static culture. However, at higher shear stresses, presence of chitosan inhibited shear-induced increase in cell spreading and weakened cell adhesive strength. No significant differences were observed in PECAM-1 expression. In summary, these results showed significant influence of blending gelatin with chitosan on scaffold properties and cellular behavior.     

Characterization of Poly(ε-caprolactone)/Polyfumarate Blends as Scaffolds for Bone Tissue Engineering

There is considerable interest in the design of polymeric biomaterials that can be used for the repair of bone defects. In this study, we used ultrasound to prepare a compatibilized blend of poly(ε-caprolactone) (PCL) and poly(diisopropyl fumarate) (PDIPF). The formation of post-sonication inter-polymer coupling products was verified by SEC analysis of a blend with azo-labeled PDIPF. We also analyzed the physicochemical and mechanical properties of the compatibilized blend. When compared to PCL alone, the PCL/PDIPF blend showed no difference in its resistance as evaluated by the elastic modulus, although it did show a 50% decrease in ultimate tensile stress (P < 0.05) and an 84% decrease in elongation-at-break (P < 0.05). However, the mechanical properties of this blend were comparable to those of trabecular bone. We next evaluated biocompatibility of the PCL/PDIPF blend, and of homo-polymeric PCL and PDIPF films for comparison, with UMR106 and MC3T3E1 osteoblastic cells. Osteoblasts plated on the compatibilized blend adhered and proliferated more than on either homo-polymer, showed a greater number of cellular processes with a better organized actin cytoskeleton and expressed more type-I collagen and mineral, both markers of osteoblast phenotype. These results support the hypothesis that this new compatibilized blend could be useful in future applications for bone regeneration.     

Isothermal Crystallization Kinetics of Poly(ε‐caprolactone) with Tetramethyl Polycarbonate and Poly(styrene‐co‐acrylonitrile) Blends Using Broadband Dielectric Spectroscopy

Summary: Phase behavior and isothermal crystallization kinetics of poly(ε‐caprolactone) (PCL) blends with tetramethyl polycarbonate (TMPC) and poly(styrene‐co‐acrylonitrile) with 27.5 wt.‐% acrylonitrile content have been investigated using broadband dielectric spectroscopy and differential scanning calorimeter. An LCST‐type phase diagram has been observed for PCL/SAN blend while all the different blend compositions of PCL/TMPC were optically clear without any phase separation structure even at high temperatures up to 300 °C. The composition dependence of T_gs for both blends has been well described by the Gordon‐Taylor equation. The phase diagram of PCL/SAN was theoretically calculated using the Flory‐Huggins equation considering that the interaction parameter is temperature and composition dependent. The equilibrium melting point of PCL depressed in the blend and the magnitude of the depression was found to be composition dependent. The interaction parameters of PCL with TMPC and SAN could not be calculated from the melting point depression based on Nishi‐Wang approach. The isothermal crystallization kinetics of PCL and in different blends was also investigated as a function of crystallization temperature using broadband dielectric spectroscopy. For pure PCL the rate of crystallization was found to be crystallization temperature (T_c) dependent, i.e., the higher the T_c, the lower the crystallization rate. The crystallization kinetics of PCL/TMPC blend was much slower than that of PCL/SAN at a constant crystallization temperature. This behavior was attributed to the fact that PCL is highly interacted with TMPC than SAN and consequently the stronger the interaction the higher the depression in the crystallization kinetics. It was also attributed to the different values of T_g of TMPC (191 °C) and SAN (100 °C); therefore, the tendency for crystallization decreases upon increasing the T_g of the amorphous component in the blend. The analysis of the isothermal crystallization kinetics was carried out using the theoretical approach of Avrami. The value of Avrami exponent was almost constant in the pure state and in the blends indicating that blending simply retarded the crystallization rate without affecting the crystallization mechanism.

Dielectric constant, ε′, of pure PCL, blends of PCL/TMPC = 80/20 and PCL/SAN = 80/20 as a function of crystallization time at 47 °C and 1 kHz.     

Wall stress reduction in abdominal aortic aneurysms as a result of polymeric endoaortic paving

Polymeric endoaortic paving (PEAP) may improve endovascular repair of abdominal aortic aneurysms (AAA) since it has the potential to treat patients with complex AAA geometries while reducing the incidence of migration and endoleak. Polycaprolactone (PCL)/polyurethane (PU) blends are proposed as PEAP materials due to their range of mechanical properties, thermoformability, and resistance to biodegradation. In this study, the reduction in AAA wall stress that can be achieved using PEAP was estimated and compared to that resulting from stent-grafts. This was accomplished by mechanically modeling the anisotropic response of PCL/PU blends and implementing these results into finite element model (FEM) simulations. We found that at the maximum diameter of the AAA, the 50/50 and 10/90 PCL/PU blends reduced wall stress by 99 and 98%, respectively, while a stent-graft reduced wall stress by 99%. Our results also show that wall stress reduction increases with increasing PEAP thickness and PCL content in the blend ratio. These results indicate that PEAP can reduce AAA wall stress as effectively as a stent-graft. As such, we propose that PEAP may provide an improved treatment alternative for AAA, since many of the limitations of stent-grafts have the potential to be solved using this approach.     

Multilayer composite scaffolds with mechanical properties similar to small intestinal submucosa

Use of biodegradable scaffolds to engineer new tissues has become an attractive option in various transplantation protocols. In particular, small intestinal submucosa (SIS) has generated immense interest in various tissue engineering applications because of its diverse favorable properties. However, it is a natural matrix, which leads to problems in large-scale preparations and contains sample to sample heterogeneity. In this study, we explored the formation of synthetic matrix mimicking the characteristics of the SIS. Three-dimensional composite structures were developed by sandwiching 50:50 PLGA film between porous chitosan matrices. The outer chitosan layers provide biological activity while the inner PLGA layer provides mechanical strength. PLGA films were initially perforated at 1 cm distance, and the porous chitosan matrix was formed sequentially on each side by controlled rate freezing and lyophilization technique at -80 degrees C. Scanning electron microscopy analysis showed a layered microarchitecture with chitosan filling the perforations of PLGA membrane. Urea permeability studies confirmed that the perforations were filled (negligible urea transfer across composite over 8 h). Tensile strength analysis showed that the matrices formed using 160 kDa PLGA had sufficient break stress ( approximately 4.5 MPa). Degradation analysis over 8 weeks in the presence of 10 mg/L lysozyme showed a 50% decrease in total weight and an 80% decrease in PLGA molecular weight. When cellular adhesion and actin distribution of mouse embryonic fibroblasts were evaluated, for 7 days, cells showed their typical spindle shape and redistribution of actin fibers on composite matrices. Viability studies and MMP-2/MMP-9 activity showed that the cells were viable and functional, similar to tissue culture plastic. Further, canine bladder smooth muscle cells also showed similar cell adhesion and spreading on the composite matrix. In summary, composite structures mimicking SIS were constructed and show potential as a tissue engineering material.     

A multilayered scaffold of a chitosan and gelatin hydrogel supported by a PCL core for cardiac tissue engineering

A three-dimensional scaffold composed of self-assembled polycaprolactone (PCL) sandwiched in a gelatin–chitosan hydrogel was developed for use as a biodegradable patch with a potential for surgical reconstruction of congenital heart defects. The PCL core provides surgical handling, suturability and high initial tensile strength, while the gelatin–chitosan scaffold allows for cell attachment, with pore size and mechanical properties conducive to cardiomyocyte migration and function. The ultimate tensile stress of the PCL core, made from blends of 10, 46 and 80 kDa (Mn) PCL, was controllable in the range of 2–4 MPa, with lower average molecular weight PCL blends correlating with lower tensile stress. Blends with lower molecular weight PCL also had faster degradation (controllable from 0% to 7% weight loss in saline over 30 days) and larger pores. PCL scaffolds supporting a gelatin–chitosan emulsion gel showed no significant alteration in tensile stress, strain or tensile modulus. However, the compressive modulus of the composite tissue was similar to that of native tissue (～15 kPa for 50% gelatin and 50% chitosan). Electron microscopy revealed that the gelatin–chitosan gel had a three-dimensional porous structure, with a mean pore diameter of ～80 μm, showed migration of neonatal rat ventricular myocytes (NRVM), maintained NRVM viability for over 7 days, and resulted in spontaneously beating scaffolds. This multi-layered scaffold has sufficient tensile strength and surgical handling for use as a cardiac patch, while allowing migration or pre-loading of cardiac cells in a biomimetic environment to allow for eventual degradation of the patch and incorporation into native tissue.     

The biodegradability of polyester blends

Blends of poly(epsilon-caprolactone) (PCL) and poly(L-lactic acid) (PLLA) with polyglycolic acid-co-L-lactic acid (PGLA) were prepared by three methods: compression moulding, coprecipitation, and solvent evaporation of a methylene chloride-in-water emulsion of the polymers. The rates of hydrolytic chain scission of each component of the blends were determined by deconvolution of GPC traces of samples maintained in phosphate buffer, pH 7.4, 37 degrees C, for up to 3000 h. The observed rates were dependent on the method of blending. For compression moulded blends, the rate of chain scission of PGLA was decreased and that of PCL and PLLA increased. A corresponding delay in the onset of weight loss was also observed. There was no evidence of blend miscibility.     

Gel casting of resorbable polymers. 2. In-vitro degradation of bone graft substitutes.

Gel cast microporous materials produced from: slow resorbing, poly(L-lactide); fast resorbing, 50:50 poly(DL lactide coglycolide); and blends of these polymers have been characterized by weight loss, compression testing and thermal analysis after immersion in phosphate buffered saline (37 degrees C, pH 7.4) for times up to 6 months. Increasing weight loss and reduction in compressive properties with immersion time were measured. Blending reduces the rate of weight loss and material shrinkage relative to the copolymer. Thermal analysis of degraded samples revealed evidence of reorganization of the crystalline phase in poly(L-lactide) and a crystalline component in the 50:50 copolymer, estimated at 5-7% of the original material content, which is probably responsible for gel formation. Thermograms of the blend are effectively a superposition of thermograms of the individual components. Gel casting shows potential for varying the resorption rate, form stability and compressive properties of micro/macroporous bone graft substitutes.     

Preparation and characterization of biodegradable PLA polymeric blends

The purpose of this study was to fine-tune the mechanical properties of high molecular-weight poly-L-lactic acid (PLLA), especially to increase its toughness without sacrificing too much of its original strength. Besides of its long degradation time, PLLA is usually hard and brittle, which hinders its usage in medical applications, i.e., orthopedic and dental surgery. Some modifications, such as the addition of plasticizers or surfactants/compatibilizers, are usually required to improve its original properties. PDLLA can degrade quickly due to its amorphous structure, thus shortening the degradation time of PLLA/PDLLA blends. Blends of biodegradable poly-L-lactic acid (PLLA) and poly-DL-lactic acid (PDLLA) or polycaprolactone (PCL), in addition to a third component, the surfactant-a copolymer of ethylene oxide and propylene oxide, were prepared by blending these three polymers at various ratios using dichloromethane as a solvent. The weight percentages of PLLA/PDLLA (or PCL) blends were 100%/0%, 80%/20%, 60%/40%, 50%/50%, 40%/60%, 20%/80% and 0%/100%, respectively. Physical properties such as the crystalline melting point, glass transition point (T(g)), phase behavior, degradation behavior, and other mechanical properties were characterized by thermogravimetric analysis, differential scanning calorimetry (DSC), infrared spectroscopy, gel permeation chromatography, and dynamic mechanical analysis (DMA). DSC data indicate that PLLA/PDLLA blends without the surfactant had two T(g)'s. With the addition of the surfactant, there was a linear shift of the single T(g) as a function of composition, with lower percentages of PLLA producing lower glass transition temperatures indicating that better miscibility had been achieved. DMA data show that the 40/60 PLLA/PDLLA blends without the surfactant had high elastic modulus and elongation, and similar results were observed after adding 2% surfactant into the blends. The 50/50 PLLA/PDLLA/2% surfactant blend had the highest elastic modulus, yield strength, and break strength compared with other ratios of PLLA/PDLLA/2% surfactant blends. The elongation at break of 50/50 PLLA/PDLLA was similar to that of PLLA. Again, the elongation at break of 50/50 PLLA/PDLLA/2% surfactant was almost 1.2-1.9 times higher than that of 50/50 PLLA/PDLLA and PLLA. Elongation of PLLA increased with the addition of PCL, but the strength decreased at the same time. In conclusions, adding PDLLA and surfactant to PLLA via solution-blending may be an effective way to make PLLA tougher and more suitable to use in orthopedic or dental applications.     

Blending polysaccharides with biodegradable polymers. II. Structure and biological response of chitosan/polycaprolactone blends

Blends of polycaprolactone (PCL) and chitosan (CHT) were prepared by casting from the mixture of solutions of both components in suitable solvents. PCL, and CHT, form phase separated blends with improved mechanical properties and increased water sorption ability with respect to pure PCL. The morphology of the system was investigated by scanning electron microscopy (SEM), atomic force microscopy (AFM) and confocal microscopy. Dispersed domains of CHT in the semicrystalline PCL matrix were found in samples with less than 20% CHT but cocontinuous phase morphologies are found in blends with 20% or more CHT. This feature was corroborated by the temperature dependence of the elastic modulus measured by dynamic mechanical properties as a function of temperature. It was observed that for those blends above 20 wt% CHT, the mechanical stability of the system was kept even after melting of the PCL phase. Primary human chondrocytes were cultured on the different substrates. Cell morphology was studied by SEM and the viability and proliferation was investigated by the colorimetric MTT assay. Different protein conformations were found by AFM on CHT and PCL samples which were related to the biological performance of the substrates. Hydrophilicty of the material is not directly related to the biological response and the sample with 20 wt% CHT shows better results than the other blends with respect to chondrocyte viability and proliferation. However, the results obtained in the blends are worse than in pure PCL. It seems to be correlated with the surface energy of the different blends rather than hydrophilicity.     

Elastomeric biodegradable polyurethane blends for soft tissue applications

Four biodegradable polyurethane blends were made from segmented polyurethanes that contain amino acid-based chain extender and diisocyanate groups. The soft segments of these parent polyurethanes were either polyethylene oxide (PEO) or polycaprolactone (PCL) diols. The blends were developed to investigate the effect of varying soft segment compositions on the overall morphological, mechanical, and degradative properties of the materials, with a view to producing a family of materials with a wide range of properties. The highly hydrophilic PEO material was incorporated to increase the blend's susceptibility to degradation, while the PCL polyurethane was selected to provide higher moduli and percent elongations (strains) than the PEO parent materials can achieve. All four blends were determined to be semi-crystalline, elastomeric materials that possess similarly shaped stress-strain curves to that of the PCL-based parent polyurethane. As the percent composition of PEO polyurethane within the blend increased, the material became weaker and less extensible. The blends demonstrated rapid initial degradation in buffer followed by significantly slower, prolonged degradation, likely corresponding to an initial loss of primarily PEO-containing polymer, followed by the slower degradation of the PCL polyurethane. All four blends were successfully formed into three-dimensional porous scaffolds utilizing solvent casting/particulate leaching methods. Since these new blends possess a range of mechanical and degradation properties and can be shaped into three-dimensional objects, these materials may hold potential for use in soft tissue engineering scaffold applications.