In vitro degradation and release profiles for electrospun polymeric fibers containing paracetanol

In the paper, the poly(D,L-lactide) (PDLLA) and poly(ethylene glycol)-co-poly(D,L-lactide) (PELA) fibers with and without paracetanol drug loading were prepared with an electrospinning method. The morphology of the fibers was observed by scanning electronic microscope (SEM). Their glass transition temperatures (T(g)) were measured with differential scanning calorimetry (DSC). The water contact angle (CA) measurement was also performed to characterize surface properties of fibers. At 37 degrees C in a PBS buffer solution (pH 7.4), in vitro matrix degradation profiles of these fibers were characterized by measuring their weight loss, the molecular weight decrease, and their morphology change. The result showed that the effects of fiber diameter and porosities on the degradation of the electrospun scaffolds might exceed the effects of the molecular weight and the PEG contents, which was different from the polymeric microspheres degradation. In vitro paracetanol release profiles were also investigated in the same condition. The result showed that the drug burst release behaviour was mainly related with the drug-polymer compatibility and the followed sustained release phase depended on polymer degradation.     

Self-accelerated biodegradation of electrospun poly(ethylene glycol)-poly(l-lactide) membranes by loading proteinase K

Proteinase K was successfully loaded inside ultrafine fibers of poly(ethylene glycol)-poly(l-lactide) (PELA) by emulsion electrospinning. A core/shell fiber structure was formed and verified by a transmission electron microscope. In vitro biodegradation of electrospun PELA membranes containing proteinase K (PELA-P) was examined in Tris-HCl buffer solution at pH 8.6 and 37 °C in comparison with electrospun PELA membranes without proteinase K. During biodegradation, mass loss, water absorption, pH value of the incubated buffer, fibrous morphology and thermal properties were monitored. Results suggested that PELA-P membranes degraded significantly faster than PELA membranes. A significant drop in pH value of the buffer after incubation of PELA-P membranes for 1 d was observed, and after 7 d, PELA-P membranes lost their fibrous appearance and masses almost completely. In contrast, electrospun PELA membranes did not show any obvious changes. The obtained electrospun PELA-P membranes exhibited self-accelerated biodegradability and could benefit drug controlled release and tissue regeneration.     

Biodegradable ultrafine fibers with core–sheath structures for protein delivery and its optimization

This study was aimed to design core–sheath‐structured polymeric fibers for protein delivery through emulsion electrospinning to enhance the encapsulation efficiency (EE), structural integrity, and activity retention, and to achieve controllable protein release. Integral core–sheath structure was achieved for electrospun fibers with lysozyme loading efficiency of 93.3% and the specific activity retention (SAR) of 64.6%, while the surface protein content (SP) was as low as 4.2%. The emulsion components were optimized to minimize the burst release and extend the release period, and the release profiles were found to be closely related with the fiber characteristics such as the SPs. An initial burst release as low as 6.2% followed by gradual release for 33 days was indicated from poly(ethylene glycol)‐poly(DL ‐lactide) (PELA) fibers. The gradual protein release was determined by a competition of fiber collapse leading to accelerated release and fiber fusion leading to decelerated release. Dependent on the matrix polymer and protein encapsulated, the degradation behaviors of the fiber matrices were correlated with the release rate and the effective lifetime of the drug release. The core–sheath‐structured ultrafine fibers could protect the structural integrity and bioactivity of encapsulated lysozyme, and an increase in the protective effect was demonstrated for fibers prepared from PELA matrix. Copyright © 2010 John Wiley & Sons, Ltd.     

聚乙二醇-b-聚乳酸的合成及其电纺形成超细纤维研究

为了提高聚乳酸的亲水性,以辛酸亚锡为催化剂、聚乙二醇单甲醚(mPEG)为大分子引发剂进行丙交酯(LLA)开环聚合,合成聚乙二醇-b-聚乳酸两嵌段共聚物(PELA).以红外光谱1、H核磁共振谱、接触角测试、差热扫描量热分析等方法对PELA的结构及性能进行表征.结果表明,通过调控mPEG与LLA的投料比可以控制PELA的相对分子质量,而随着mPEG组分含量或链长增加,共聚物亲水性增强,但其Tg、Tcc、Tm有所降低.由普通电纺制备PELA超细纤维,并分别由乳液电纺和同轴电纺得到以水溶性聚氧化乙烯(PEO)为芯、PELA为壳的芯/壳结构复合超细纤维(E-PEO/PELA和C-PEO/PELA).扫描电镜和透射电镜结果表明,PELA、E-PEO/PELA和C-PEO/PELA超细纤维形貌良好.随着PELA中mPEG含量的增加,电纺PELA纤维膜的吸水率增强,而由乳液电纺和同轴电纺制备的PEO/PELA芯/壳结构超细纤维膜,亲水性均好于PELA超细纤维膜.     

INVESTIGATION OF POLYDL-LACTIDE-b-POLY（ETHYLENE GLYCOL）-b-POLYDL-LACTIDE MICROSPHERES CONTAINING PLASMID DNA

PolyDL-lactide (PDLLA) and the block copolymer, polyDL-lactide-b-poly(ethylene glycol)-b-polyDL-lactide (PELA) were used as the microsphere matrix to encapsulate plasmid DNA. The PDLLA, PELA, pBR322-1oaded PDLLA and pBR322-1oaded PELA microspheres were prepared by solvent extraction method based on the formation of multiple w1/o/w2 emulsion. The microspheres were characterized by surface morphology, mean particle size, particle size distribution and loading efficiency. The integrity of DNA molecules after being extracted from microspheres was determined by agarose gel electrophoresis. The result suggested that plasmid DNA molecules could retain their integrity after being encapsulated by PELA. The PELA microspheres could prevent plasmid DNA from being digested by DNase. The in vitro degradation and release profiles of plasmid DNA-loaded microspheres were measured in pH - 7.4 buffer solution at 37℃. The in vitro degradation profiles of the microspheres were evaluated by the deterioration in microspheres surface morphology, the molecular weight reduction of polymer, the mass loss of microspheres, the changes of pH values of degradation medium, and the changes of particle size. The in vitro release profiles of the microspheres were assessed by measurement of the amount of DNA presented in the release medium at determined intervals. The release profiles were correlation with the degradation profiles. The release of plasmid DNA from PELA microspheres showed a similar biphasic trend, that is, an initial burst release was followed by a slow, but sustained release.     

Degradation behaviors of electrospun fibrous composites of hydroxyapatite and chemically modified poly(dl-lactide)

It is essential to individually tailor the biodegradability of electrospun fibers and their composites to meet the requirements of specific application. Electrospun poly(dl-lactide) (PDLLA) fibers grafted with functional groups were obtained to induce in situ mineralization of hydroxyapatite (HA), and HA/PDLLA composites were fabricated through hot-pressing of mineralized fibers after layer-by-layer deposition. The degradation behaviors during up to 1 year incubation were clarified for functionalized PDLLA fibers, mineralized HA/PDLLA fibers and hot-pressed composites. The carboxyl and amino groups of electrospun fibers indicated enhancement and alleviation of the autocatalysis effect on the polyester hydrolysis, respectively. The distribution of HA within fiber matrices led quick and strong water absorption, and caused neutralization of the weak acid environment and alleviation of the autocatalysis effect. Due to the location of mineralized HA on the surface of functionalized fibers, significant HA loss and preferential removal of amorphous and low-crystalline apatitic phase were determined during the degradation process. The hot-pressed composites indicated dense structure, small pore size and fusion on the fiber surface, leading significantly lower degradation rate than electrospun fibers and mineralized fibers. Higher degradation rate of matrix polymers and HA loss were shown for hot-pressed composites from mineralized fibers than those from blend electrospun HA/PDLLA fibers. The obtained results should provide solid basis for further applications of functionalized PDLLA fibers, mineralized fibers and fibrous composites in biomedical areas.     

Preparation and characterization of a novel electrospun spider silk fibroin/poly(D,L-lactide) composite fiber

In the paper, we successfully prepared spider silk fibroins (Ss)/poly( d, l-lactide) (PDLLA) composite fibrous nonwoven mats for the first time to the best of our knowledge. The morphology of the fibers was observed by a scanning electron microscope (SEM) and transmission electron microscope (TEM). The secondary structure change of the spidroin before and after electrospinning was characterized using Fourier transform infrared spectroscopy (FT-IR). Herein, a qualitative analysis of the conformational changes of the silk protein was performed by analyzing the FT-IR second-derivative spectra, from which quantitative information was obtained via the deconvolution of the amide I band. A mechanical test was carried out to investigate the tensile strength and the elongation at break. A water contact angle (CA) measurement was also performed to characterize surface properties of the fibers. The cytotoxicity of electrospun PDLLA and Ss-PDLLA nonwoven fibrous mats was evaluated based on a CCL 81(Vero) cells proliferation study. The results showed that the hydrophilic and mechanical property of the composite fiber were improved by introducing spidroin.     

Controlled enzymatic degradation of poly(?-caprolactone)-based copolymers in the presence of porcine pancreatic lipase

Poly(?-caprolactone) (PCL) has been extensively studied for biomedical use due to its outstanding biocompatibility. Well-defined random and block copolymers based on PCL such as poly(?-caprolactone-r-2,2-dimethyltrimethylene carbonate) (PCD), poly[(?-caprolactone-r-2,2-dimethyltrimethylene carbonate)-b-PEG-b-(?-caprolactone-r-2,2-dimethyltrimethylene carbonate)] (PECD) and poly[MPEG-b-(?-caprolactone-r-2,2-dimethyltrimethylene carbonate)] (MPECD) containing 5.0-8.5 mol% 2,2-dimethyltrimethylene carbonate (DTC) and 15.9-18.3 mol% polyethylene glycol (PEG) or polyethylene glycol monomethyl ether (MPEG) have been synthesized by using lanthanum tris(2,6-di-tert-butyl-4-methylphenolate) as catalyst. Their crystallization properties, thermal behaviors, hydrophilicities and degradation properties depend on the tunable microstructures and morphologies. It is found for the first time that porcine pancreatic lipase (PP lipase) can effectively catalyze the degradation of PCD electrospun mats (EMs) with 92.0% weight loss within 7 days while it shows no detectable effect on PCL EMs. Surface erosion mechanism is proposed in the enzymatic degradation systems, and the high proportion of amorphous domain of PCD contributes to its fast degradation rate according to the degradation product analyses. The enzymatic degradation rates of PCD EMs with porous structures and huge surface areas are higher than those of compression molding films (CMFs). Introducing PEG segment improves the hydrophilicity of PCD but decreases the degradation rate. A PEG segment enrichment process on the surface is addressed, which prevents the contact of PP lipase with PCD segments in the PEG-involved electrospun fiber. PECD and MPECD exhibit different mechanical strengths and contact angles, but similar degradation profiles. This study provides a practical example for tunable biodegradation of polyesters by designing the materials' bulk structures and/or surface morphologies.     

RELEASE OF IBUPROFEN FROM PEG-PLLA ELECTROSPUN FIBERS CONTAINING POLY(ETHYLENE GLYCOL)-b-POLY(α-HYDROXY OCTANOIC ACID) AS AN ADDITIVE

<正>Poly(α-hydroxy octanoic acid) was first used as an additive for the preparation of electrospun ultra-fine fibers of poly(ethylene glycol)-b-poly(L-lactide)(PEG-PLLA).Ibuprofen was loaded in the electrospun ultra-fine fibers.The results from environmental scanning electron microscopy(ESEM),wide angle X-ray diffraction(WAXD) and differential scanning calorimetry(DSC) demonstrated that ibuprofen could be perfectly entrapped in the fibers electrospun from PEG-PLLA usingα-hydroxy octanoic acid or PEG-b-poly(α-hydroxy octanoic acid)(PEG-PHOA) as additives.Compared with electrospun PEG-PLLA fibers which entrapped 20 wt%ibuprofen,the PEG-PLLA electrospun fibers containing PEG-PHOA exhibited integral and robust after 1 week incubated in 37℃,pH 7.4 phosphate buffer solution with 10μg/mL proteinase K.Compared with electrospun fibers without PEG-PHOA,the concentration of proteinase K in release media had less effect on the release rate of ibuprofen.An unique release profile was found from PEG-PLLA fiber after the incorporation of PEG-PHOA. Enzyme degradation experiments demonstrated that PEG-PHOA but notα-hydroxy octanoic acid monomer was the crucial factor for integrity maintenance of the electrospun fibers,which may be due to the enzyme degradation tolerance property of the PEG-PHOA polymer additive.     

Novel biodegradable polymers as gene carriers

This study investigated two new biodegradable polymers as gene controlled-released coatings for gene transfer. Poly(ethylene glycol)-co-poly(D,L-lactic acid) (PELA) and poly(ethylene glycol)-co-poly(lactic acid)-co-poly(glycolic acid) random copolymer (PELGA) were synthesized and used as microspheres matrices with encapsulated plasmid pCH110. The plasmid loading efficiency, cytotoxicity, transfection efficiency and in vitro degradation and release profiles of microsphere complexes were evaluated in details. The biodegradable polymers showed high DNA loading efficiency and low cytotoxicity as gene controlled-released coatings, and the poly(ethylene glycol) (PEG) contents of polymer matrices influenced the diameter, loading efficiency and transfection efficiency of plasmid DNA within the microspheres. The average diameters of PELA and PELGA microspheres were between 0.5 and 1.5 microm, and the plasmid loading efficiency was 62 and 73% for PELA and PELGA microspheres with 10% PEG content, respectively. In vitro testing showed a gradual release profile of DNA from polymeric matrices. The polymers/DNA microspheres had high transfection efficiency and early gene expression and maintenance of gene expression level for up to 96 h, although transfection efficiency were slightly lower than that of liposome in the initial 24 h. The biodegradable polymeric materials possess potential superiority as gene carriers.     

Annealing Effect on Electrospun Polymer Fibers and Their Transformation into Polymer Microspheres

Electrospinning is a simple and convenient technique to produce polymer fibers with diameters ranging from several nanometers to a few micrometers. Different types of polymer fibers have been prepared by electrospinning for various applications. Among different post‐treatment methods of electrospun polymer fibers, the annealing process plays a critical role in controlling the fiber properties. The morphology changes of electrospun polymer fibers under annealing, however, have been little studied. Here we investigate the annealing effect of electrospun poly(methyl methacrylate) (PMMA) fibers and their transformation into PMMA microspheres. PMMA fibers with an average size of 2.39 μm are first prepared by electrospinning a 35 wt% PMMA solution in dimethylformamide. After the electrospun fibers are thermally annealed in ethylene glycol, a non‐solvent for PMMA, the surfaces of the fibers undulate and transform into microspheres driven by the Rayleigh instability. The driving force of the transformation process is the minimization of the interfacial energy between the polymer fibers and ethylene glycol. The sizes of the microspheres fit well with the theoretical predictions. Longer annealing times are found to be required at lower temperatures to obtain the microspheres.     

Biodegradable electrospun mat: Novel block copolymer of poly (p‐dioxanone‐co‐L‐lactide)‐block‐poly(ethylene glycol)

Ultrafine fibers of a laboratory‐synthesized new biodegradable poly(p‐dioxanone‐co‐L ‐lactide)‐block‐poly(ethylene glycol) copolymer were electrospun from solution and collected as a nonwoven mat. The structure and morphology of the electrospun membrane were investigated by scanning electron microscopy, differential scanning calorimetry (DSC), wide‐angle X‐ray diffraction (WAXD), and a mercury porosimeter. Solutions of the copolymer, ranging in the lactide fraction from 60 to 80 mol % in copolymer composition, were readily electrospun at room temperature from solutions up to 20 wt % in methylene chloride. We demonstrate the ability to control the fiber diameter of the copolymer as a function of solution concentration with dimethylformamide as a cosolvent. DSC and WAXD results showed the relatively poor crystallinity of the electrospun copolymer fiber. Electrospun copolymer membrane was applied for the hydrolytic degradation in phosphate buffer solution (pH = 7.5) at 37 °C. Preliminary results of the hydrolytic degradation demonstrated the degradation rate of the electrospun membrane was slower than that of the corresponding copolymers of cast film. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 1955–1964, 2003     

Electrospun poly(l-lactide)-grafted hydroxyapatite/poly(l-lactide) nanocomposite fibers

Composite fibers composed of poly(l-lactide)-grafted hydroxyapatite (PLA-g-HAP) nanoparticles and polylactide (PLA) matrix were prepared by electro-spinning. Environmental scanning electron microscope (ESEM) and transmission electron microscopy (TEM) were employed to investigate the morphology of the composite fibers and the distribution of PLA-g-HAP nanoparticles in the fibers, respectively. At a low content (∼4 wt%) of PLA-g-HAP, the nanoparticles dispersed uniformly in the fibers and the composite fibrous mats exhibited higher strength properties, compared with the pristine PLA fiber mats and the simple hydroxyapatite/PLA blend fiber mats. But when the content of PLA-g-HAP further increased, the nanoparticles began to aggregate, which resulted in the deterioration of the mechanical properties of the composite fiber mats. The degradation behaviors of the composite fiber mats were closely related to the content of PLA-g-HAP. At a low PLA-g-HAP content, degradation may be delayed due to the reduction of autocatalytic degradation of PLA. When PLA-g-HAP content was high, degradation rate increased because of the enhanced wettability of the composite fibers and the escape of the nanoparticles from fiber surfaces during incubation.     

Encapsulation of proteinase K in PELA ultrafine fibers by emulsion electrospinning: preparation and in vitro evaluation

The aims of this study were to encapsulate water-soluble bioactive agents into biodegradable hydrophobic polymers via emulsion electrospinning for drug delivery and tissue engineering applications and propose a simple and facile method to evaluate the bioactivity of the encapsulated protein. Proteinase K was selected as a model protein to be incorporated into poly(ethylene glycol)-poly(l-lactide) (PELA) ultrafine fibers. Core–shell structured fibers with single core or multi-core were observed. In vitro release study showed that after a burst release at the early stage, a sustained release was achieved, indicating that proteinase K was incorporated inside ultrathin fibers successfully. Results of in vitro incubation in Tris–HCl buffer at pH?8.6 and 37?°C revealed that electrospun PELA membranes containing proteinase K (PELA-P) showed obvious morphological changes, large mass loss, and slight decreases in melting temperature, melting enthalpy and relative molecular mass in 7 days. Additionally, a significant drop in pH value of the buffer after incubation of the PELA-P membrane was also observed. These findings clearly showed that encapsulation of water-soluble bioactive agents inside hydrophobic polymers could be achieved by emulsion electrospinning without compromising their bioactivity.     

Enzyme-catalyzed degradation of poly(l-lactide)/poly(?-caprolactone) diblock, triblock and four-armed copolymers

Poly(l-lactide)/poly(?-caprolactone) diblock, triblock and four-armed copolymers with the same monomer feed ratio (50/50) were synthesised by two step ring opening polymerisation of successively added ?-caprolactone and l-lactide, using isopropanol, ethylene glycol, or pentaerythritol as initiator and zinc lactate as co-initiator. The resulting copolymers were characterised by ¹H NMR, DSC, SEC, and FT-IR, which confirmed the blocky characteristic of the copolymers. Solution cast films were allowed to degrade at 37 °C in the presence of proteinase K, and the degradation was monitored by gravimetry, DSC, SEC, ¹H NMR and ESEM. The effects of chain structure, block length and crystallinity on the degradation are discussed. The four-armed block copolymer degrades the most rapidly, while the diblock copolymer exhibited the slowest degradation rate. The difference was related to the crystallinity depending on both the molecular structure and block length. Little compositional or molar mass changes were obtained during degradation, which strongly supports a surface erosion mechanism, in agreement with ESEM observations.     

Degradable Polymers. IV. Degradation of Aliphatic Thermoplastic Block Copolyesters

Three block copolymers of poly(ethylene succinate) and poly(tetramethylene glycol) with about 20, 54, and 59 mol% polyether have been prepared and subjected to hydrolytic degradation at 37°C. The sample containing 59 mol% showed drastic changes in the properties after 3 months of degradation, whereas the other samples exhibited only minor changes. The tensile strength was completely lost, the molecular weight had decreased to 7% of the original value, and the crystallinity (measured as heat of fusion) had more than doubled. IR and ¹H-NMR analyses showed that the rates of release of the different polymeric blocks varied throughout the period of hydrolytic degradation. Fibers of the block copolymer poly(ethylene succinate)/poly(tetramethylene glycol) with poly(tetramethylene glycol) fractions ranging from 20 to 50 mol% have been analyzed by ¹³ C NMR to determine the molecular weights of the PES blocks and by reflection IR, ESCA, and SEM to investigate the surface composition. The molecular weights of the polyester blocks were inversely proportional to the mol% of polyether, and the values were in agreement with theoretical calculated values. The surface concentration of the polyether was found to be higher than that in the bulk and also independent of the mol% polyether in the range of study. A degradation mechanism is proposed which involves a combined effect of surface erosion and hydrolytic attack on the ester linkages connecting the amorphous polyether and the crystalline polyester blocks.     

Surface properties and enzymatic degradation of end-capped poly(l-lactide)

Surface properties and enzymatic degradation of poly(l-lactide) (PLLA) end-capped with hydrophobic dodecyl and dodecanoyl groups were investigated by means of advancing contact angle (θ_a) measurement, quartz crystal microbalance (QCM) and atomic force microscopy (AFM). The θ_a values of end-capped PLLA films were larger than those of non-end-capped PLLA films, suggesting that the hydrophobic dodecyl and dodecanoyl groups were segregated on the film surface. The weight changes of end-capped PLLA thin films during enzymatic degradation in the presence of proteinase K were monitored by using a QCM technique. The relatively fast weight loss of PLLA film occurred during first few hours of degradation, followed by a decrease in the erosion rate. The erosion rate of PLLA films at the initial stage of degradation was dependent on the chain-end structure of PLLA molecules, and the value decreased with an increase in the amount of hydrophobic functional groups. The surface morphologies of PLLA thin films before and after degradation were characterized by AFM. After the enzymatic degradation, the surface of non-end-capped PLLA films was blemished homogeneously. In contrast, the end-capped PLLA thin films were degraded heterogeneously by the enzyme, and many hollows were formed on the film surface. From these results, it has been concluded that the introduction of hydrophobic functional groups at the chain-ends of PLLA molecules depressed the erosion rate at the initial stage of enzymatic degradation.     

In vitro ageing and degradation of PEG-PLA diblock copolymer-based nanoparticles

Diblock copolymers composed of poly(oxy-ethylene) (POE) and poly(dl-lactic acid) segments were synthesized by anionic polymerization of d,l-lactide using the oxyanion formed by reaction of the monohydroxyl monomethoxy-poly(ethylene glycol) on sodium hydride. For comparison, a similar copolymer was prepared by using tin octoate to catalyze the lactide polymerization. The copolymers were used to make nanoparticles, which were stored at 4 °C. After a few months under these storage conditions, a dramatic decrease of the poly(ethylene glycol) content was observed, however, the mean diameter of the nanoparticles was not affected. The degradation of the nanoparticles was investigated in vitro under conditions selected to mimic physiological conditions. Changes of characteristics were monitored by ¹H NMR, SEC, DLLS and CZE on nanoparticles and/or on the degradation by-products dissolved in the ageing medium. According to their nanometric dimensions, the microparticles degraded very slowly and there was no difference in behaviour between the sodium hydride and the stannous octoate-derived copolymers.     

Hydrolytic degradation and thermal properties of linear 1-arm and 2-arm poly(dl-lactic acid)s: Effects of coinitiator-induced molecular structural difference

“Linear” 1-arm and 2-arm poly(dl-lactide) [i.e., poly(dl-lactic acid), or PDLLA] polymers with relatively low number-average molecular weights (M_n in the range 0.2-6 × 10⁴ g mol⁻¹) were synthesized using ring-opening polymerization of dl-lactide initiated with tin(II) 2-ethylhexanoate (i.e., stannous octoate) and coinitiators of dl-lactic acid and ethylene glycol (these PDLLA polymers are hereafter abbreviated as 1-DL and 2-DL, respectively). Their glass-transition properties were monitored by differential scanning calorimetry, and their hydrolytic degradation was investigated using gravimetry and gel permeation chromatography. The results of the present study indicate that the coinitiator-induced molecular structural difference of the terminal groups, the chain directional change, the incorporated coinitiator moiety as an impurity in the middle of the molecule, and the molecular weight each affect both the hydrolytic degradation behavior and rate, and the glass-transition properties of the “linear” 1-DLs and 2-DLs. The glass-transition temperature (T_g) values were higher for the 2-DLs than for the 1-DLs, indicating low chain mobility and a strong inter-chain interaction of 2-arm PDLLA. However, the coinitiator-induced molecular structural difference did not produce a difference in the excess free volume of the end groups between the 1-DLs and 2-DLs, despite the difference produced in the terminal groups. On the other hand, although the hydrolytic degradation of the 1-DLs and 2-DLs proceeds via bulk erosion, significant surface erosion also occurs in the 2-DLs. This should have caused a larger weight loss and lower decrease rate of M_n of the 2-DLs compared to those of the 1-DLs. Moreover, the results of the present study indicate that in 2-arm PDLLA selective chain cleavage at the terminal ester groups or second ester groups from the chain terminals, which are induced by two terminal hydroxyl groups, is the significant hydrolytic degradation route. However, the random cleavage of ester groups, irrespective of their position, is the main hydrolytic degradation route.     

Dual Electrospun Supramolecular Polymer Systems for Selective Cell Migration

Dual electrospinning can be used to make multifunctional scaffolds for regenerative medicine applications. Here, two supramolecular polymers with different material properties are electrospun simultaneously to create a multifibrous mesh. Bisurea (BU)‐based polycaprolactone, an elastomer providing strength to the mesh, and ureido‐pyrimidinone (UPy) modified poly(ethylene glycol) (PEG), a hydrogelator, introducing the capacity to deliver compounds upon swelling. The dual spun scaffolds are modularly tuned by mixing UPyPEG hydrogelators with different polymer lengths, to control swelling of the hydrogel fiber, while maintaining the mechanical properties of the scaffold. Stromal cell derived factor 1 alpha (SDF1α) peptides are embedded in the UPyPEG fibers. The swelling and erosion of UPyPEG increase void spaces and released the SDF1α peptide. The functionalized scaffolds demonstrate preferential lymphocyte recruitment proposed to be created by a gradient formed by the released SDF1α peptide. This delivery approach offers the potential to develop multifibrous scaffolds with various functions.