Melting and crystallization behaviors of biodegradable polymers enzymatically coalesced from their cyclodextrin inclusion complexes

Inclusion complexed (IC) and coalesced biodegradable poly(epsilon-caprolactone) (PCL), poly(L-lactic acid) (PLLA), and their diblock copolymer (PCL-b-PLLA) were achieved by forming ICs between host alpha-cyclodextrin(alpha-CD) and guest PCL, PLLA, and PCL-b-PLLA, followed by removing the alpha-CD host with an amylase enzyme. FTIR spectra of the coalesced polymers reveal that the host alpha-CD can be completely removed, without polymer degradation, by treatment with an amylase enzyme. The melting and crystallization behavior of these CD-IC treated polymers, which are crystallizable, biodegradable, and bioabsorbable, are investigated by differential scanning calorimetry (DSC) and polarized optical microscopy. Results show that coalescence increased the crystallinities of the homopolymers but decreased that of the diblock copolymer. The Avrami exponent (n), derived from both isothermal and nonisothermal crystallization models for homo-PCL and -PLLA and the PCL and PLLA blocks in the diblock copolymer samples coalesced from their ICs, is close to 4, indicating homogeneous crystallization, whereas crystallization of the blocks in the as-synthesized diblock copolymer yields an Avrami exponent around 3, indicating heterogeneous crystallization. All of these results demonstrate that the PCL and PLLA homopolymers and blocks in the IC-coalesced samples are more readily and homogeneously crystallized than those in the as-synthesized samples or their physical blend, even though the level of crystallinity in the IC-coalesced diblock copolymer is significantly lower. Moreover, unlike the as-synthesized diblock copolymer, the crystallization of PCL and PLLA blocks in the IC-coalesced diblock copolymer are not influenced by their covalent connection.     

Blends of aliphatic polyesters. VI. Lipase-catalyzed hydrolysis and visualized phase structure of biodegradable blends from poly(epsilon-caprolactone) and poly(L-lactide)

Phase-separated biodegradable polymer blends were prepared from poly(epsilon-caprolactone) (PCL) and poly(L-lactide) (PLLA), and Rhizopus arrhizus lipase-catalyzed hydrolysis and phase structure of the blend films were investigated. Gravimetry revealed that the lipase-catalyzed hydrolysis of PCL in PCL- and PLLA-rich phases is disturbed by the presence of PLLA. Polarimetry confirmed the occurrence of a predominant hydrolysis of PCL and subsequent removal of the hydrolyzed water-soluble PCL oligomers in the blend films. Gravimetry and gel permeation chromatography of the non-blended PLLA film indicated that R. arrhizus lipase has no catalytic effect on the hydrolysis of PLLA. The phase structure of the blend films could be visualized by selective enzymatic removal of one component and subsequent scanning electron microscopic observation.     

Biodegradable polycarbonate-b-polypeptide and polyester-b-polypeptide block copolymers: synthesis and nanoparticle formation towards biomaterials

The amino poly(trimethylene carbonate)-NHt-Boc (PTMC-NHt-Boc) and poly(epsilon-caprolactone)-NH -Boc (PCL-NHt-Boc) were synthesized by ring-opening polymerization (ROP) of TMC or CL and subsequently deprotected into the corresponding PTMC-NH2 and PCL-NH2. These functional homopolymers were used as macroinitiators for the ROP of gamma-benzyl-L-glutamate N-carboxyanhydride (BLG), consequently, giving the respective diblock copolymers PTMC-b-PBLG and PCL-b-PBLG in almost quantitative yields. The (co)polymers have been characterized by NMR and SEC analyses. DSC and IR studies confirmed the block structure of the copolymers and highlighted a phase separation between the rigid peptide (alpha-helix conformation) and the more flexible polyester segments. The self-assembly and the degradation behaviors of the copolymers depended on the nature of the polyester block and on the copolymer composition. Nanoparticles obtained from PBLG block copolymers were twice smaller ( RH < 100 nm) than those formed from PTMC and PCL homopolymers. Finally, their enzymatic degradation revealed that PTMC nanoparticles degraded faster than those made of PCL.     

Compatibilization effect of poly(epsilon-caprolactone)-b-poly(ethylene glycol) block copolymers and phase morphology analysis in immiscible poly(lactide)/poly(epsilon-caprolactone) blends

The miscibility and phase behavior of two stereoisomer forms of poly(lactide) (PLA: poly (L-lactide) (PLLA) and poly(DL-lactide) (PDLLA)) blends with poly(epsilon-caprolactone)-b-poly(ethylene glycol) (PCL-b-PEG) and PCL-b-monomethoxy-PEG (PCL-b-MPEG) block copolymers have been investigated by differential scanning calorimetry (DSC). The DSC thermal behavior of both the blend systems revealed that PLA is miscible with the PEG segment phase of PCL-b-(M)PEG but is still immiscible with its PCL segment phase although PCL was block-copolymerized with PEG. On the basis of these results, PCL-b-PEG was added as a compatibilizer to PLA/PCL binary blends. The improvement in mechanical properties of PLA/PCL blends was achieved as anticipated upon the addition of PCL-b-PEG. In addition, atomic force microscopy (AFM) measurements have been performed in order to study the compositional synergism to be observed in mechanical tests. AFM observations of the morphological dependency on blend composition indicate that PLA/PCL blends are immiscible but compatible to some extent and that synergism of compatibilizing may be maximized in the compositional blend ratio before apparent phase separation and coarsening.     

Investigation of PLLA/PCL Blends and Paclitaxel Release Profiles

Blends of poly (l-lactide) (PLLA) and poly (ε-caprolactone) (PCL) with and without paclitaxel were prepared via solution casting. DSC analysis as well as SEM analysis of the PLLA/PCL blend solution cast films showed that these blends are all phase separated.%PLLA crystallinity was found to increase with increasing PCL content (up till 15 wt.%). The PCL phase is found to homogeneously disperse in the PLLA matrix as spherical domains where the pore diameters of the PCL domains significantly increased with increasing PCL content. The degradation profiles matched with the slower degrading component PCL rather than PLLA and also increasing PCL content of the blends increased the degradation rate relatively. The increased crystallinity of the PLLA phase with increasing PCL contents confirmed that the degradation occurred through PCL phase. Cell proliferation on PLLA/PCL blends showed that all these blends were suitable for the support of cellular growth. Apoptosis assay with the paclitaxel-loaded PLLA/PCL blends showed an increase in cell death throughout 7 days of incubation where the cell death was increased with increasing PCL contents. This was attributed to the faster release of paclitaxel which was at least partially affected by the faster degradation rate at increasing PCL contents. The paclitaxel release was shown to be degradation controlled in the initial stages followed by a faster diffusion-controlled release in the later stages. These polymer blends were found to be very suitable paclitaxel release agents for which the paclitaxel release times can be altered with the composition of the blend and the film thickness.     

Synthesis of poly(epsilon-caprolactone)-b-poly(gamma-benzyl-L-glutamic acid) block copolymer using amino organic calcium catalyst

A biodegradable two block copolymer, poly(epsilon-caprolactone)-b- poly(gamma-benzyl-L-glutamic acid) (PCL-PBLG) was synthesized successfully by ring-opening polymerization of N-carboxyanhydride of gamma-benzyl-L-glutamate (BLG-NCA) with aminophenyl-terminated PCL as a macroinitiator. The aminophenethoxyl-terminated PCL was prepared via hydrogenation of a 4-nitrophenethoxyl-terminated PCL, which was novelly obtained from the polymerization of epsilon-caprolactone (CL) initiated by amino calcium 4-nitrobenzoxide. The structures of the block copolymer and its precursors from the initial step of PCL were confirmed and investigated by 1H NMR, FT-IR, GPC, and FT-ICRMS analyses and DSC measurements.     

Biocompatible and biodegradable polymersome encapsulated hemoglobin: a potential oxygen carrier

This work describes the development of polymersome-encapsulated hemoglobin (PEH) self-assembled from biodegradable and biocompatible amphiphilic diblock copolymers composed of poly(ethylene oxide) (PEO), poly(caprolactone) (PCL), and poly(lactide) (PLA). In the amphiphilic diblock, PEO functions as the hydrophilic block, while either PCL or PLA can function as the hydrophobic block. PEO, PCL, and PLA are biocompatible polymers, while the last two polymers are biodegradable. PEH dispersions were prepared by extrusion through 100 nm pore radii polycarbonate membranes. In this work, the encapsulation efficiency of human and bovine hemoglobin (hHb and bHb) in polymersomes was adjusted by varying the initial concentration of Hb. This approach yielded Hb loading capacities that were comparable to values in the literature that supported the successful resuscitation of hamsters experiencing hemorrhagic shock. Moreover, the Hb loading capacities of PEHs in this study can also be tailored simply by controlling the diblock copolymer concentration. In this study, typical Hb/diblock copolymer weight ratios ranged 1.2-1.5, with initial Hb concentrations less than 100 mg/mL. The size distribution, Hb encapsulation efficiency, oxygen affinity (P 50), cooperativity coefficient (n), and methemoglobin (metHb) level of these novel PEH dispersions were consistent with values required for efficient oxygen delivery in the systemic circulation. Taken together, our results demonstrate the development of novel PEH dispersions that are both biocompatible and biodegradable. These novel dispersions show very good promise as therapeutic oxygen carriers.     

Surface functionalized electrospun biodegradable nanofibers for immobilization of bioactive molecules

A blend mixture of biodegradable poly(epsilon-caprolactone) (PCL) and poly(d,l-lactic-co-glycolic acid)-poly(ethylene glycol)-NH(2) (PLGA-b-PEG-NH(2)) block copolymer was electrospun to produce surface functionalized nanofibers. The resulting nanofibrous mesh with primary amine groups on the surface was applied for immobilization of biologically active molecules using lysozyme as a model enzyme. Lysozyme was immobilized via covalent conjugation by using a homobifunctional coupling agent. The nanofibrous mesh could immobilize a far greater amount of lysozyme on the surface with concomitantly increased activity, primarily due to its larger surface area, compared to that of the solvent casting film. It was also found that the enzyme immobilization process slightly altered thermal and pH-dependent catalytic activity profiles compared to those of native lysozyme. The results demonstrated the surface functionalized electrospun nanofibrous mesh could be used as a promising material for immobilizing a wide range of bioactive molecules.     

Self-assembled micelles of biodegradable triblock copolymers based on poly(ethyl ethylene phosphate) and poly(-caprolactone) as drug carriers

A series of novel amphiphilic triblock copolymers of poly(ethyl ethylene phosphate) and poly(-caprolactone) (PEEP-PCL-PEEP) with various PEEP and PCL block lengths were synthesized and characterized. These triblock copolymers formed micelles composed of a hydrophobic core of poly(-caprolactone) (PCL) and a hydrophilic shell of poly(ethyl ethylene phosphate) (PEEP) in aqueous solution. The micelle morphology was spherical, determined by transmission electron microscopy. It was found that the size and critical micelle concentration values of the micelles depended on both hydrophobic PCL block length and PEEP hydrophilic block length. The in vitro degradation characteristics of the triblock copolymers were investigated in micellar form, showing that these copolymers were completely biodegradable under enzymatic catalysis of Pseudomonas lipase and phosphodiesterase I. These triblock copolymers were used for paclitaxel (PTX) encapsulation to demonstrate the potential in drug delivery. PTX was successfully loaded into the micelles, and the in vitro release profile was found to be correlative to the polymer composition. These biodegradable triblock copolymer micelles are potential as novel carriers for hydrophobic drug delivery.     

Biosynthesis and characterization of polyhydroxyalkanoate block copolymer P3HB-b-P4HB

Polyhydroxyalkanoates (PHA) synthesis genes phbC and orfZ cloned from Ralstonia eutropha H16 were transformed into beta-oxidation weakened Pseudomonas putida KTOY08ΔGC, a mutant of P. putida KT2442. The recombinant P. putida strain termed KTHH06 was able to produce a short-chain-length PHA block copolymer consisting of poly(3-hydroxybutyrate) (P3HB) as one block and poly(4-hydroxybutyrate) (P4HB) as another block. One-dimensional and two-dimensional nuclear magnetic resonance (NMR) clearly indicated the polymer was a diblock copolymer consisting of 20 mol % P3HB as one block and 80 mol % P4HB as another one. Differential scanning calorimetric (DSC) showed that P3HB block melting temperatures (T(m)) in the block copolymer P3HB-b-P4HB was shift to low temperature compared with homopolymer P3HB and a blend of P3HB and P4HB. The block copolymer with a number average molecular weight of 50000 Da and a polydispersity of 3.1 demonstrated a better yield and tensile strength compared with that of its related random copolymer and blend of homopolymers of P3HB and P4HB.     

Sulfonamide-based pH- and temperature-sensitive biodegradable block copolymer hydrogels

Novel pH- and temperature-sensitive biodegradable poly(epsilon-caprolactone-co-lactide)-poly(ethylene glycol) (PCLA-PEG) block copolymers were synthesized with oligomeric sulfamethazine (OSM) end groups (OSM-PCLA-PEG-PCLA-OSM). Aqueous solutions of these block copolymers have shown sol-gel transition behavior upon both temperature and pH changes under physiological conditions (37 degrees C, pH 7.4). The sol-gel transition of these block copolymer solutions was fine-tuned by controlling the PEG length, the hydrophobic to hydrophilic block ratio (PCLA/PEG), and the molecular weight of the sulfamethazine oligomer. Since changes in temperature do not induce gel formation in this pH- and temperature-sensitive block copolymer solution, this hydrogel can be employed as an injectable carrier using a long guide catheter into the body. In addition, the pH of the block copolymer solution showed no change following PCLA degradation over 1 month, and no indication of gel collapse was observed on addition of buffer solution. As such, these properties make the OSM-PCLA-PEG-PCLA-OSM hydrogel an ideal candidate for use as an injectable carrier for certain protein-based drugs known to denature in low-pH environments.     

Impact of silicone-based block copolymer surfactants on the surface and bulk microscopic organization of a biodegradable polymer,poly(epsilon-caprolactone)

Two amphiphilic AB block copolymers, containing a highly compatible poly(epsilon-caprolactone) (PCL) block connected to a poly(dimethylsiloxane) (PDMS) block having a low surface energy, are synthesized and characterized in terms of their dispersion in a presynthesized PCL matrix. X-ray photoelectron spectroscopy, contact angle measurements, atomic force microscopy, and optical microscopy are used to describe the evolution of the surface chemical composition, as well as the surface and bulk morphology of the PCL/copolymer blends as a function of the nature and weight surface free energy and the dispersion of the copolymers in the blends, leading to important modifications of the bulk and the surface morphology. These differences are interpreted in terms of the impact of the block copolymers on the semicrystalline polymer structure and related properties in the prospect of using the surfactants to improve the synthesis of PCL in supercritical CO(2).     

Macromolecular design of aliphatic polyesters with maintained mechanical properties and a rapid, customized degradation profile

An innovative type of triblock copolymer that maintains and even increases the mechanical properties of poly(l-lactide) (PLLA) and poly(ε-caprolactone) (PCL) with a controlled, predictable, and rapid degradation profile has been synthesized. Elastic triblock copolymers were formed from the hydrophobic and crystalline PLLA and PCL with an amorphous and hydrophilic middle block of poly(but-2-ene-1,4-diyl malonate) (PBM). The polymers were subjected to degradation in PBS at 37 °C for up to 91 days. Prior to degradation, ductility of the PLLA-PBM-PLLA was approximately 4 times greater than that of the homopolymer of PLLA, whereas the modulus and tensile stress at break were unchanged. A rapid initial hydrolysis in the amorphous PBM middle block changed the microstructure from triblock to diblock with a significant reduction in ductility and molecular weight. The macromolecular structure of the triblock copolymer of PLLA and PBM generates a more flexible and easier material to handle during implant, with the advantage of a customized degradation profile, demonstrating its potential use in future biomedical applications.     

In-situ formation of biodegradable hydrogels by stereocomplexation of PEG-(PLLA)8 and PEG-(PDLA)8 star block copolymers

Eight-arm poly(ethylene glycol)-poly(L-lactide), PEG-(PLLA)(8), and poly(ethylene glycol)-poly(D-lactide), PEG-(PDLA)(8), star block copolymers were synthesized by ring-opening polymerization of either L-lactide or D-lactide at room temperature in the presence of a single-site ethylzinc complex and 8-arm PEG (M(n) = 21.8 x 10(3) or 43.5 x 10(3)) as a catalyst and initiator, respectively. High lactide conversions (>95%) and well-defined copolymers with PLLA or PDLA blocks of the desired molecular weights were obtained. Star block copolymers were water-soluble when the number of lactyl units per poly(lactide) (PLA) block did not exceed 14 and 17 for PEG21800-(PLA)(8) and PEG43500-(PLA)(8), respectively. PEG-(PLA)(8) stereocomplexed hydrogels were prepared by mixing aqueous solutions with equimolar amounts of PEG-(PLLA)(8) and PEG-(PDLA)(8) in a polymer concentration range of 5-25 w/v % for PEG21800-(PLA)(8) star block copolymers and of 6-8 w/v % for PEG43500-(PLA)(8) star block copolymers. The gelation is driven by stereocomplexation of the PLLA and PDLA blocks, as confirmed by wide-angle X-ray scattering experiments. The stereocomplexed hydrogels were stable in a range from 10 to 70 degrees C, depending on their aqueous concentration and the PLA block length. Stereocomplexed hydrogels at 10 w/v % polymer concentration showed larger hydrophilic and hydrophobic domains as compared to 10 w/v % single enantiomer solutions, as determined by cryo-TEM. Correspondingly, dynamic light scattering showed that 1 w/v % solutions containing both PEG-(PLLA)(8) and PEG-(PDLA)(8) have larger "micelles" as compared to 1 w/v % single enantiomer solutions. With increasing polymer concentration and PLLA and PDLA block length, the storage modulus of the stereocomplexed hydrogels increases and the gelation time decreases. Stereocomplexed hydrogels with high storage moduli (up to 14 kPa) could be obtained at 37 degrees C in PBS. These stereocomplexed hydrogels are promising for use in biomedical applications, including drug delivery and tissue engineering, because they are biodegradable and the in-situ formation allows for easy immobilization of drugs and cells.     

Synthesis, properties, and light-induced shape memory effect of multiblock polyesterurethanes containing biodegradable segments and pendant cinnamamide groups

Novel multiblock polyesterurethanes containing crystalline hard and amorphous soft segments and pendant cinnamamide moieties were designed and synthesized via a two-step polyaddition reaction using N,N-bis(2-hydroxyethyl) cinnamamide (BHECA), biodegradable poly(l,l-lactide) (PLLA), and poly(ε-caprolactone) (PCL) diols as raw materials and hexamethylene diisocyanate (HDI) as coupling agent and characterized by (1)H NMR, FTIR, UV, DSC, tensile and photomechanical tests, and so on. The copolymers behaved as typical thermoplastic elastomers and showed satisfactory thermal and mechanical properties. They also exhibited light-induced shape memory effect (LSME) at room temperature on exposure to light stimuli. The pendant cinnamamide groups work as photoresponsive molecular switches and provide the polymer with LSME via reversible [2 + 2] cycloaddition cross-linking. The strain fixity (R(f)) increases with the content of BHECA and the strain recovery (R(r)) increases with the content of PLLA. The R(f) reaches 50% at a BHECA content of 20 wt % and the R(r) reaches >95% at PLLA content of 50 wt %.     

Synthesis, characterization, and morphology studies of biodegradable amphiphilic poly[(R)-3-hydroxybutyrate]-alt-poly(ethylene glycol) multiblock copolymers

Novel biodegradable amphiphilic alternating block copolymers based on poly[(R)-3-hydroxybutyrate] (PHB) as biodegradable and hydrophobic block and poly(ethylene glycol) (PEG) as hydrophilic block (PHB-alt-PEG) were successfully synthesized through coupling reaction. Their chemical structures have been characterized by using gel permeation chromatography, (1)H nuclear magnetic resonance, and Fourier transform infrared spectroscopy. Differential scanning calorimetry (DSC) analysis revealed that both PHB and PEG blocks in PHB-alt-PEG block copolymers can crystallize to form separate crystalline phase except in those with a short PEG block (M(n) 600) only PHB crystalline phase has been observed. However, due to the mutual interference from each other, the melting transition of both PHB and PEG crystalline phases shifted to lower temperature with lower crystallinity in comparison with corresponding pure PHB and PEG. The crystallization behavior of PHB block and PEG block has also been studied by X-ray diffraction, and the results were in good agreement with those deduced from DSC study. The surface morphologies of PHB-alt-PEG block copolymer thin films spin-coated on mica have been visualized by atomic force microscopy with tapping mode, indicating formation of laterally regular lamellar surface patterns. Static water contact angle measurement revealed that surface hydrophilicity of these spin-coated thin films increases with increasing PEG block content.     

Self-assembly of polypeptide-containing ABC-type triblock copolymers in aqueous solution and its pH dependence

Self-assembling of novel biodegradable ABC-type triblock copolymer poly(ethylene glycol)-poly(L-lactide)-poly(L-glutamic acid) (PEG-PLLA-PLGA) is studied. In aqueous media, it self-assembles into a spherical micelle with the hydrophobic PLLA segment in the core and the two hydrophilic segments PEG and PLGA in the shell. With the lengths of PEG and PLLA blocks fixed, the diameter of the micelles depends on the length of the PLGA block and on the volume ratio of H(2)O/dimethylformamide (DMF) in the media. When the PLGA block is long enough, morphology of the self-assembly is pH-dependent. It assembles into the spherical micelle in aqueous media at pH 4.5 and into the connected rod at or below pH 3.2. The critical micelle concentration (cmc) of the copolymer changes accordingly with decreasing solution pH. Both aggregation states can convert to each other at the proper pH value. This reversibility is ascribed to the dissociation and neutralization of the COOH groups in the LGA residues. When the PLGA block is short compared to the PEG or PLLA block, it assembles only into the spherical micelle at various pH values.     

Syntheses and physical characterization of new aliphatic triblock poly(L-lactide-b-butylene succinate-b-L-lactide)s bearing soft and hard biodegradable building blocks

This study presents chemical syntheses and physical characterization of a new aliphatic poly(L-lactide-b-butylene succinate-b-L-lactide) triblock copolyester with soft and hard biodegradable building blocks. First, poly(butylene succinate) (PBS) prepolymers terminated with hydroxyl functional groups were synthesized through melt polycondensation from succinic acid and 1,4-butanediol. Further, a series of new PLLA-b-PBS-b-PLLA triblock copolyesters bearing various average PLLA block lengths were prepared via ring opening polymerization of L-lactide with the synthesized hydroxyl capped PBS prepolymer (Mn = 4.9 KDa) and stannous octanoate as the macroinitiator and catalyst, respectively. By means of GPC, NMR, FTIR, DSC, TGA, and wide-angle X-ray diffractometer (WAXD), the macromolecular structures and physical properties were intensively studied for these synthesized PBS prepolymer and PLLA-b-PBS-b-PLLA triblock copolyesters. 13C NMR and GPC experimental results confirmed the formation of sequential block structures without any detectable transesterification under the present experimental conditions, and the molecular weights of triblock copolyesters could be readily regulated by adjusting the feeding molar ratio of L-lactide monomer to the PBS macroinitiator. DSC measurements showed all single glass transitions, and their glass transition temperatures were found to be between those of PLLA and PBS, depending on the lengths of PLLA blocks. It was noteworthy that the segmental flexibilities of the hard PLLA blocks were found to be remarkably enhanced by the more flexible PBS block partner, and the PBS and PLLA building blocks were well mixed in the amorphous regions. Results of TGA analyses indicated that thermal degradation and stabilities of the PLLA blocks strongly depended on the average PLLA block lengths of triblock copolyesters. In addition, FTIR and WAXD results showed the coexistence of the assembled PLLA and PBS crystal structures when the average PLLA block length became larger than 7.8. These results may be beneficial for this new biodegradable aliphatic triblock copolyester to be applied as a potential biomaterial.     

L-Phe end-capped poly(L-lactide) as macroinitiator for the synthesis of poly(L-lactide)-B-poly(L-lysine) block copolymer

A poly(L-lactide)-b-poly(Nepsilon-(Z)-L-lysine) (PLLA-b-PZLys) block copolymer was synthesized through the ring-opening polymerization of Nepsilon-(Z)-lysine-N-carboxyanhydride using L-Phe-terminated PLLA as a macroinitiator. The L-Phe-terminated PLLA was prepared through a novel three-step process. First, the hydroxyl-terminated PLLA was synthesized through the ring-opening polymerization of L-lactide initiated by n-butanol under the existence of tin(II) ethylhexanoate. Subsequently, the complete capping of the hydroxyl end group of PLLA with BOC-L-Phe was achieved by using a mixed anhydride of BOC-L-Phe under the catalysis of 4-(1-pyrrolidinyl) pyridine. Finally, the free amino end group was obtained by removal of the t-butoxycarbonyl group through trifluoroacetic acid treatment under anhydrous condition. All these treatments were conducted under mild conditions, thus avoiding the breakdown of the PLLA backbone. Poly(L-lactide)-b-poly(L-lysine) block copolymer was produced after deprotection treatment of PLLA-b-PZLys. The structure of the block copolymer was confirmed by 1H NMR, IR, and GPC. Adjustment of the ratio of the NCA monomer to the macroinitiator could control the chain length of the PLys block.     

Investigation of biodegradability and cellular activity of PCL/PLA and PCL/PLLA electrospun webs for tissue engineering applications

Biodegradability and cellular activity are key performance indicators that should be prioritized for tissue engineering applications. Biopolymer selection, determination of necessary structural properties, and their synergistic interactions play an active role in obtaining the expected biodegradability and biological activity from scaffolds. In this study, it is aimed to produce electrospun webs with improved biocompatibility by blending polycaprolactone (PCL) with polylactic acid (PLA) and poly-l -lactide (PLLA), and examine the effect of biopolymer selection and blend ratio on the biodegradability and cellular activity of surfaces. In this context, fibrous webs are produced from PCL/PLA and PCL/PLLA blends with a weight ratio of 80/20 and 50/50 and pure polymers of PCL, PLA, and PLLA by electrospinning method and subjected to morphological and biological analyses. The biodegradation tests are carried out hydrolytically while the cell viability and cell proliferation analyses are performed with adult human primary dermal fibroblasts and human umbilical endothelial cells (HUVECs). The results show that the fiber diameters of the fabricated webs ranged from 0.747 to 1.685 μm. At the end of the 5th month, it is observed that the biodegradation rates of the webs blended 50% with PLA and PLLA, in comparison to PCL ones, increase from 3.7% to 13.33% and 7.69%, respectively. On the other hand, cell culture results highlight that the addition of 20% PLA and PLLA improves the cellular activity of both cell types, but increased PLA or PLLA ratio in PCL webs has a negative effect as it makes the structure stiff and brittle.