Structural characterization and hydrolytic degradation of solid copolymers of d,l-lactide-co-ε-caprolactone by Raman spectroscopy

Enhanced Electrochemical Performance of MWCNT-Assisted Molybdenum-Titanium Carbide MXene as a Potential Electrode Material for Energy Storage Application

Two-dimensional (2D) materials such as MXenes have attracted considerable attention owing to their enormous potential for structural flexibility. Here, we prepared a Mo2TiC2Tx-layered structure from parent Mo2TiAlC2Tx MAX by chemically selective etching of the aluminum layer. The prepared MXene was employed in composite formation with CTAB-grafted multiwalled carbon nanotubes (MWCNTs) to have a structure with improved electrochemical performance. The samples were characterized to analyze the structure, morphology, elemental detection, vibrational modes, and surface chemistry, followed by an electrochemical performance of the Mo2TiC2Tx MXene and MWCNTs@Mo2TiC2Tx composite using the GAMRAY Potentiostat under a 1 M KOH electrolyte. The specific capacitance of pristine Mo2TiC2Tx was 425 F g-1, which was enhanced to 1740 F g-1 (almost 4 times) at 5 mV s-1 due to the increase in active surface area and conductive paths between the MXene sheets. The charge storage mechanism was studied by further resolving the cyclic voltammograms. MWCNTs@Mo2TiC2Tx showed much improved electrochemical performance and reaction kinetics, making it an ideal material candidate for supercapacitor applications.

Visualization of isothermal crystallization and phase separation in poly[(R)-3-hydroxybutyrate]/poly(L-lactic acid) by low-frequency Raman imaging

The visualization of the variation of the inter/intra molecular interaction (C = O⋯CH3) between poly[(R)-3-hydroxybutyrate] (PHB) and poly-L-lactic acid (PLLA) in the PHB/PLLA miscible blend during phase separation and crystallization process was successfully investigated using Raman imaging. Images of the blend were developed using high- and low-frequency Raman spectra acquired during the isothermal crystallization of the blend, and both of them were compared. The low-frequency region allowed to observe the changes in the hydrogen bonds between the molecular chains in the blend during phase separation and crystallization via a band at 75 cm-1 derived from PHB. The imaging results obtained using the band at 75 cm-1 due to hydrogen bonding (C = O⋯CH3) between molecular chains were in good agreement with the results obtained using the C = O stretching band at 1720 cm-1. Herein, we demonstrated that the low-frequency region of the Raman spectrum is more sensitive to detecting the start of the phase separation and crystallization of PHB than the corresponding high-frequency region.

Raman evaluation of the crystallinity degree and composition of poly(L-lactide-co-ε-caprolactone)

In this work, we study two series of the copolymers of L-lactide (LLA) and ε-caprolactone (CL) with the CL molar content of 5, 15, and 30 %. The first series was the commercial semicrystalline granules (Corbion, Netherlands), which we analyzed without any additional modification. The second series was amorphous films, prepared from the granules by hot pressing with the subsequent fast quenching in order to avoid the crystallization. We used Raman spectroscopy in conjunction with the quantum chemical modeling to evaluate the structure of the copolymers. As additional methods, we applied X-ray diffraction (XRD) analysis and differential scanning calorimetry (DSC). The main result of our study is the elaboration of the Raman methods of quantitative analysis of the relative contents of the comonomers and the crystallinity degree of the poly(L-lactide-co-ε-caprolactone). These methods are based on measurements of the ratios of the peak intensities of the poly(L-lactide) (PLLA) bands at 411 and 874 cm-1, the PLLA band at 2947 cm-1 and the poly(ε-caprolactone) band at 2914 cm-1. Raman study shows that growth of the CL content causes the monotonous decrease in the crystallinity degree of PLLA blocks. Density functional theory analysis of LLA decamer in the conformation of helix 103 allows us to assign the PLLA Raman bands. The Raman data on the composition and crystallinity degree of the copolymers correlate very well with the results of XRD and DSC studies, as well as with the information on the composition of the copolymers provided by manufacturer.

Simulated gastrointestinal digestion of polylactic acid (PLA) biodegradable microplastics and their interaction with the gut microbiota

The accumulation of microplastics (MPs) in the environment as well as their presence in foods and humans highlight the urgent need for studies on the effects of these particles on humans. Polylactic acid (PLA) is the most widely used bioplastic in the food industry and medical field. Despite its biodegradability, biocompatibility, and "Generally Recognized As Safe" (GRAS) status, recent animal model studies have shown that PLA MPs can alter the intestinal microbiota; however, to date, no studies have been reported on the possible gut and health consequences of its intake by humans. This work simulates the ingestion of a realistic daily amount of PLA MPs and their pass through the gastrointestinal tract by combining the INFOGEST method and the gastrointestinal simgi® model to evaluate possible effects on the human colonic microbiota composition (16S rRNA gene sequencing analysis) and metabolic functionality (lactic acid and short-chain fatty acids (SCFA) production). Although PLA MPs did not clearly alter the microbial community homeostasis, increased Bifidobacterium levels tended to increase in presence of millimetric PLA particles. Furthermore, shifts detected at the functional level suggest an alteration of microbial metabolism, and a possible biotransformation of PLA by the human microbial colonic community. Raman spectroscopy and field emission scanning electron microscopy (FESEM) characterization revealed morphological changes on the PLA MPs after the gastric phase of the digestion, and the adhesion of organic matter as well as a microbial biofilm, with surface biodegradation, after the intestinal and colonic phases. With this evidence and the emerging use of bioplastics, understanding their impact on humans and potential biodegradation through gastrointestinal digestion and the human microbiota merits critical investigation.

All-natural environmentally degradable poly (butylene terephthalate-co-caprolactone): A theoretical and experimental study of its degradation properties and mechanisms

The design and production of materials with excellent mechanical properties and biodegradability face significant challenges. Poly (butylene terephthalate-co-caprolactone) copolyesters (PBTCL) is obtained by modifying the engineering plastic polybutylene terephthalate (PBT) with a simple one-pot process using readily biodegradable ε-caprolactone (ε-CL). The material has mechanical properties comparable to those of commercial biodegradable copolyester PBAT. Besides, this copolyester exhibited remarkable degradability in natural environments such as soil and ocean, for example, PBTCL1.91 lost >40 % of its weight after 6 months of immersion in the Bohai Sea. The effect and diversity of specific microorganisms acting on degradation in the ocean were analyzed by 16 s rDNA gene sequencing. Theoretical calculations such as Fukui function and DFT, and experimental studies on water-soluble intermediates and residual matrixes produced after degradation, confirmed that the insertion CL units not only act as active sites themselves susceptible to hydrolysis reactions, but also promote the reactivity of ester bonds between aromatic segments. This work provides insight for the development of novel materials with high performance and environmental degradability.

Raman Study of Block Copolymers of Methyl Ethylene Phosphate with Caprolactone and L-lactide

We present an in-depth analysis of Raman spectra of novel block copolymers of methyl ethylene phosphate (MeOEP) with caprolactone (CL) and L-lactide (LA), recorded with the excitation wavelengths of 532 and 785 nm. The experimental peak positions, relative intensities and profiles of the poly(methyl ethylene phosphate) (PMeOEP), polycaprolactone (PCL) and poly(L-lactide) (PLA) bands in the spectra of the copolymers and in the spectra of the PMeOEP, PCL and PLA homopolymers turn out to be very similar. This clearly indicates the similarity between the conformational and phase compositions of PMeOEP, PCL and PLA parts in molecules of the copolymers and in the PMeOEP, PCL and PLA homopolymers. Experimental ratios of the peak intensities of PMeOEP bands at 737 and 2963 cm^-1 and the PCL bands at 1109, 1724 and 2918 cm^-1 can be used for the estimation of the PCL-b-PMeOEP copolymers chemical composition. Even though only one sample of the PMeOEP-b-PLA copolymers was experimentally studied in this work, we assume that the ratios of the peak intensities of PLA bands at 402, 874 and 1768 cm^-1 and the PMeOEP band at 737 cm^-1 can be used to characterize the copolymer chemical composition.

Following Polymer Degradation with Nanodiamond Magnetometry

Degradable polymers are widely used in the biomedical fields due to non-toxicity and great biocompatibility and biodegradability, and it is crucial to understand how they degrade. These polymers are exposed to various biochemical media in medical practice. Hence, it is important to precisely follow the degradation of the polymer in real time. In this study, we made use of diamond magnetometry for the first time to track polymer degradation with nanoscale precision. The method is based on a fluorescent defect in nanodiamonds, which changes its optical properties based on its magnetic surrounding. Since optical signals can be read out more sensitively than magnetic signals, this method allows unprecedented sensitivity. We used a specific mode of diamond magnetometry called relaxometry or T1 measurements. These are sensitive to magnetic noise and thus can detect paramagnetic species (gadolinium in this case). Nanodiamonds were incorporated into polylactic acid (PLA) films and PLA nanoparticles in order to follow polymer degradation. However, in principle, they can be incorporated into other polymers too. We found that T1 constants decreased gradually with the erosion of the film exposed to an alkaline condition. In addition, the mobility of nanodiamonds increased, which allows us to estimate polymer viscosity. The degradation rates obtained using this approach were in good agreement with data obtained by quartz crystal microbalance, Fourier-transform infrared spectroscopy, and atomic force microscopy.

Effect of Graphene Addition on Polycaprolactone Scaffolds Fabricated Using Melt-Electrowriting

Melt-electrowriting (MEW) is an emerging method that combines electrospinning and extrusion printing, allowing the fabrication of micron-scale structures suitable for tissue engineering. Compared to other additive fabrication methods, melt-electro written structures can offer more appropriate substrates for cell culture due to filament size and mechanical characteristics of the fabricated scaffolds. In this study, polycaprolactone (PCL)/graphene composites were investigated for fabrication of micron-size scaffolds through MEW. It was demonstrated that the addition of graphene can considerably improve the processability of PCL to fabricate micron-scale scaffolds with enhanced resolution. The tensile strength of the scaffold prepared from PCL/graphene composite (with only 0.5 wt.% graphene) was proved significantly (by more than 270%), better than that of the pristine PCL scaffold. Furthermore, graphene was demonstrated to be a suitable material for tailoring the degradation process to avoid undesirable bulk degradation, rapid mass loss and damage to the internal matrix of the polymer. The findings of this study offer a promising route for the fabrication of high-resolution scaffolds with micron-scale resolution for tissue engineering.

Ultra-Short Laser Surface Properties Optimization of Biocompatibility Characteristics of 3D Poly-ε-Caprolactone and Hydroxyapatite Composite Scaffolds

The use of laser processing for the creation of diverse morphological patterns onto the surface of polymer scaffolds represents a method for overcoming bacterial biofilm formation and inducing enhanced cellular dynamics. We have investigated the influence of ultra-short laser parameters on 3D-printed poly-ε-caprolactone (PCL) and poly-ε-caprolactone/hydroxyapatite (PCL/HA) scaffolds with the aim of creating submicron geometrical features to improve the matrix biocompatibility properties. Specifically, the present research was focused on monitoring the effect of the laser fluence (F) and the number of applied pulses (N) on the morphological, chemical and mechanical properties of the scaffolds. SEM analysis revealed that the femtosecond laser treatment of the scaffolds led to the formation of two distinct surface geometrical patterns, microchannels and single microprotrusions, without triggering collateral damage to the surrounding zones. We found that the microchannel structures favor the hydrophilicity properties. As demonstrated by the computer tomography results, surface roughness of the modified zones increases compared to the non-modified surface, without influencing the mechanical stability of the 3D matrices. The X-ray diffraction analysis confirmed that the laser structuring of the matrices did not lead to a change in the semi-crystalline phase of the PCL. The combinations of two types of geometrical designs-wood pile and snowflake-with laser-induced morphologies in the form of channels and columns are considered for optimizing the conditions for establishing an ideal scaffold, namely, precise dimensional form, mechanical stability, improved cytocompatibility and antibacterial behavior.

Kinetic degradation and biocompatibility evaluation of polycaprolactone-based biologics delivery matrices for regenerative engineering of the rotator cuff

Whereas synthetic biodegradable polymers have been successfully applied for the delivery of biologics in other tissues, the anatomical complexity, poor blood supply, and reduced clearance of degradation byproducts in the rotator cuff create unique design challenges for implantable biomaterials. Here, we investigated lower molecular weight poly-lactic acid co-epsilon-caprolactone (PLA-CL) formulations with varying molecular weight and film casting concentrations as potential matrices for the therapeutic delivery of biologics in the rotator cuff. Matrices were fabricated with target footprint dimensions to facilitate controlled and protected release of model biologic (Bovine Serum Albumin), and anatomically-unhindered implantation under the acromion in a rodent model of acute rotator cuff repair. The matrix obtained from the highest polymeric-film casting concentration showed a controlled release of model biologics payload. The tested matrices rapidly degraded during the initial 4 weeks due to preferential hydrolysis of the lactide-rich regions within the polymer, and subsequently maintained a stable molecular weight due to the emergence of highly-crystalline caprolactone-rich regions. pH evaluation in the interior of the matrix showed minimal change signifying lesser accumulation of acidic degradation byproducts than seen in other bulk-degrading polymers, and maintenance of conformational stability of the model biologic payload. The context-dependent biocompatibility evaluation in a rodent model of acute rotator cuff repair showed matrix remodeling without eliciting excessive inflammatory reaction and is anticipated to completely degrade within 6 months. The engineered PLA-CL matrices offer unique advantages in controlled and protected biologic delivery, non-toxic biodegradation, and biocompatibility overcoming several limitations of commonly-used biodegradable polyesters.

Early Recognition of the PCL/Fibrous Carbon Nanocomposites Interaction with Osteoblast-like Cells by Raman Spectroscopy

Poly(ε-caprolactone) (PCL) is a biocompatible resorbable material, but its use is limited due to the fact that it is characterized by the lack of cell adhesion to its surface. Various chemical and physical methods are described in the literature, as well as modifications with various nanoparticles aimed at giving it such surface properties that would positively affect cell adhesion. Nanomaterials, in the form of membranes, were obtained by the introduction of multi-walled carbon nanotubes (MWCNTs and functionalized nanotubes, MWCNTs-f) as well as electro-spun carbon nanofibers (ESCNFs, and functionalized nanofibers, ESCNFs-f) into a PCL matrix. Their properties were compared with that of reference, unmodified PCL membrane. Human osteoblast-like cell line, U-2 OS (expressing green fluorescent protein, GFP) was seeded on the evaluated nanomaterial membranes at relatively low confluency and cultured in the standard cell culture conditions. The attachment and the growth of the cell populations on the polymer and nanocomposite samples were monitored throughout the first week of culture with fluorescence microscopy. Simultaneously, Raman microspectroscopy was also used to track the dependence of U-2 OS cell development on the type of nanomaterial, and it has proven to be the best method for the early detection of nanomaterial/cell interactions. The differentiation of interactions depending on the type of nanoadditive is indicated by the ν(COC) vibration range, which indicates the interaction with PCL membranes with carbon nanotubes, while it is irrelevant for PCL with carbon nanofibers, for which no changes are observed. The vibration range ω(CH2) indicates the interaction for PCL with carbon nanofibers with seeded cells. The crystallinity of the area ν(C=O) increases for PCL/MWCNTs and for PCL/MWCNTs-f, while it decreases for PCL/ESCNFs and for PCL/ESCNFs-f with seeded cells. The crystallinity of the membranes, which is determined by Raman microspectroscopy, allows for the assessment of polymer structure changes and their degradability caused by the secretion of cell products into the ECM and the differentiation of interactions depending on the carbon nanostructure. The obtained nanocomposite membranes are promising bioactive materials.

Degradation Behavior of Polymers Used as Coating Materials for Drug Delivery-A Basic Review

The purpose of the work was to emphasize the main differences and similarities in the degradation mechanisms in the case of polymeric coatings compared with the bulk ones. Combined with the current background, this work reviews the properties of commonly utilized degradable polymers in drug delivery, the factors affecting degradation mechanism, testing methods while offering a retrospective on the evolution of the controlled release of biodegradable polymeric coatings. A literature survey on stability and degradation of different polymeric coatings, which were thoroughly evaluated by different techniques, e.g., polymer mass loss measurements, surface, structural and chemical analysis, was completed. Moreover, we analyzed some shortcomings of the degradation behavior of biopolymers in form of coatings and briefly proposed some solving directions to the main existing problems (e.g., improving measuring techniques resolution, elucidation of complete mathematical analysis of the different degradation mechanisms). Deep studies are still necessary on the dynamic changes which occur to biodegradable polymeric coatings which can help to envisage the future performance of synthesized films designed to be used as medical devices with application in drug delivery.

Composites Based on Poly(Lactic Acid) (PLA) and SBA-15: Effect of Mesoporous Silica on Thermal Stability and on Isothermal Crystallization from Either Glass or Molten State

Several composites based on an L-rich poly(lactic acid) (PLA) with different contents of mesoporous Santa Barbara Amorphous (SBA-15) silica were prepared in order to evaluate the effect of the mesoporous silica on the resultant PLA materials by examining morphological aspects, changes in PLA phases and their transitions, and, primarily, the influence on some final properties. Melt extrusion was chosen for the obtainment of the composites, followed by quenching from the melt to prepare films. Completely amorphous samples were then attained, as deduced from X-ray diffraction and differential scanning calorimetry (DSC) analyses. Thermogravimetric analysis (TGA) results demonstrated that the presence of SBA-15 particles in the PLA matrix did not exert any significant influence on the thermal decomposition of these composites. An important nucleation effect of the silica was found in PLA, especially under isothermal crystallization either from the melt or from its glassy state. As expected, isothermal crystallization from the glass was considerably faster than from the molten state, and these high differences were also responsible for a more considerable nucleating role of SBA-15 when crystallizing from the melt. It is remarkable that the PLA under analysis showed very close temperatures for cold crystallization and its subsequent melting. Moreover, the type of developed polymorphs did not accomplish the common rules previously described in the literature. Thus, all the isothermal experiments led to exclusive formation of the α modification, and the observation of the α’ crystals required the annealing for long times at temperatures below 80 °C, as ascertained by both DSC and X-ray diffraction experiments. Finally, microhardness (MH) measurements indicated a competition between the PLA physical aging and the silica reinforcement effect in the as-processed amorphous films. Physical aging in the neat PLA was much more important than in the PLA matrix that constituted the composites. Accordingly, the MH trend with SBA-15 content was strongly dependent on aging times.

Controlled Drug Release from Biodegradable Polymer Matrix Loaded in Microcontainers Using Hot Punching

Microcontainers are reservoir-based advanced drug delivery systems (DDS) that have proven to increase the bioavailibity of the small-molecule drugs, targeting of biomolecules, protection of vaccines and improved treatment of Pseudomonas aeruginosa. However, high-throughput loading of these micron-sized devices with drug has been challenging. Hot punching is a new technique that is a fast, simple and single-step process where the microdevices are themselves used as mold to punch biocompatible and biodegradable drug-polymer films, thereby loading the containers. Here, we investigate the effect of hot punching on the drug distribution as well as drug release from the loaded drug-polymer matrices. Zero-order sustained drug release is observed for the model drug Furosemide embedded in biodegradable polymer, Poly-ε-caprolactone, which is attributed to the unique spatial distribution of Furosemide during the loading process.

Relationship between the Young's Modulus and the Crystallinity of Cross-Linked Poly(ε-caprolactone) as an Immobilization Membrane for Cancer Radiotherapy

Cancer is a leading cause of death in the world. In cancer radiotherapy, immobilization membranes composed of cross-linked poly(ε-caprolactone) (PCL) are utilized for patient positioning. A higher-dimensional stability of the membrane is urgently required to facilitate more accurate radiation dose delivery. It is extremely important to establish the relationship between the degree of crystallinity and the Young's modulus (E) because it determines the mechanical properties and can be modulated by crystallinity. When two components of the membrane with different strains are in contact, a gradient region adjacent to the interface is formed and confirmed by attenuated total reflection infrared microscopy. Atomic force microscopy (AFM) and Raman spectroscopy are used to scan the same area in the gradient region (14 µm × 14 µm) to characterize E and crystallinity (X Raman), respectively. This co-localized method ensures the accuracy of the relationship. Finally, 1764 AFM measurement data are processed and 49 pairs of E-X Raman data are obtained. The regression curve shows that E monotonically increases with X Raman. The nonlinearity of the curve may be attributed to the α-relaxation and cross-linking of PCL chains. The chemical structure of this material significantly impacts the mechanical properties, thus requiring future investigation.

Preparation of electrospun nanofibers with desired microstructures using a programmed three-dimensional (3D) nanofiber collector

The traditional electrospinning process produces dense two-dimensional (2D) nanofiber (NF) sheets that limit cell infiltration and proliferation. Our previous study demonstrated that 3D NF sheets could be formed on an NF collector surface mounted with multiple movable needles through the corona discharge. In this study, we developed a programmed electrospun 3D NF collector. It can precisely control the moving speed of NF collector during electrospinning; thereby fabricating 3D NFs with desired microstructures (pore size, pore volume, and interconnectivity). Four types of polycaprolactone (PCL) 3D NF matrices with different microstructures can be obtained concurrently on the NF collector surface, which are set by different forward moving speed of the NF collector device: NF-zero (no move, as control), NF-low (0.085 mm/min), NF-mid (0.158 mm/min) and NF-high (0.232 mm/min). A linear increase of the NF sheet thickness (from 0.21 mm to 0.91 mm) was recorded with accelerating collector movement. Quantitative analysis using scanning electron microscopy (SEM), micro-computed tomography (μ-CT), and confocal laser scanning microscopy (CLSM) showed a monotonic increase of pore size and porosity with the increase of collector moving speeds. The collector movement also impacted the crystallinity and mechanical properties of the NFs. When prepared at high collector speed, the NFs showed improved proliferation and differentiation (p < .05) of pre-osteoblastic MC3T3 cells compared to the NFs from the static collector. A programmed NF collector device allows for the reproducible, precise and continuous fabrication of 3D NFs with tailorable geometry and microstructures. This simple, controllable, one-step process could promote the clinical translation of electrospun NFs in tissue engineering and regenerative medicine.

Highly porous polycaprolactone scaffolds doped with calcium silicate and dicalcium phosphate dihydrate designed for bone regeneration

Polycaprolactone (PCL), dicalcium phosphate dihydrate (DCPD) and/or calcium silicates (CaSi) have been used to prepare highly porous scaffolds by thermally induced phase separation technique (TIPS). Three experimental mineral-doped formulations were prepared (PCL-10CaSi, PCL-5CaSi-5DCPD, PCL-10CaSi-10DCPD); pure PCL scaffolds constituted the control group. Scaffolds were tested for their chemical-physical and biological properties, namely thermal properties by differential scanning calorimetry (DSC), mechanical properties by quasi-static parallel-plates compression testing, porosity by a standard water-absorption method calcium release, alkalinizing activity, surface microchemistry and micromorphology by Environmental Scanning electronic Microscopy (ESEM), apatite-forming ability in Hank Balanced Saline Solution (HBSS) by Energy Dispersive X-ray Spectroscopy (EDX) and micro-Raman, and direct contact cytotoxicity. All mineral-doped scaffolds released calcium and alkalinized the soaking medium, which may favor a good biological (osteogenic) response. ESEM surface micromorphology analyses after soaking in HBSS revealed: pure PCL, PCL-10CaSi and PCL-10CaSi-10DCPD kept similar surface porosity percentages but different pore shape modifications. PCL-5CaSi-5DCPD revealed a significant surface porosity increase despite calcium phosphates nucleation (p < 0.05). Micro-Raman spectroscopy detected the formation of a B-type carbonated apatite (Ap) layer on the surface of PCL-10CaSi-10DCPD aged for 28 days in HBSS; a similar phase (but of lower thickness) formed also on PCL-5CaSi-5DCPD and PCL; the deposit formed on PCL-10CaSi was mainly composed of calcite. All PCL showed bulk open porosity higher than 94%; however, no relevant brittleness was observed in the materials, which retained the possibility to be handled without collapsing. The thermo-mechanical properties showed that the reinforcing and nucleating action of the inorganic fillers CaSi and DCPD improved viscoelastic properties of the scaffolds, as confirmed by the increased value of storage modulus and the slight increase in the crystallization temperature for all the biomaterials. A detrimental effect on the mechanical properties was observed in samples with the highest amount of inorganic particles (PCL-10CaSi-10DCPD). All the scaffolds showed absence of toxicity, in particular PCL-10CaSi-10DCPD. The designed scaffolds are biointeractive (release biologically relevant ions), nucleate apatite, possess high surface and internal open porosity and can be colonized by cells, creating a bone forming osteoblastic microenvironment and appearing interesting materials for bone regeneration purposes.

Biocompatibility and biodegradation properties of polycaprolactone/polydioxanone composite scaffolds prepared by blend or co-electrospinning

Electrospun polymer scaffolds are regarded as an ideal tissue engineering scaffold due to similar morphological properties with the native extracellular matrix. Among these, polycaprolactone is widely used to fabricate electrospun fibrous scaffolds due to its excellent biocompatibility, good mechanical properties, and ease of manufacture. However, its low biodegradation rate has a negative influence on its application in tissue engineering scaffold. To address this issue, this study prepared hybrid scaffolds composed of polycaprolactone and polydioxanone (a fast-degrading polyether-ester) via either the blend or co-electrospinning. Subsequently, the structural characteristics, mechanical strength, in vitro/vivo degradation, cellularization, and vascularization of two kinds of hybrid scaffolds were evaluated to decide which method is more suitable for producing tissue engineering scaffolds. The incorporation of polydioxanone increased the mechanical strength of both composite scaffolds. Moreover, co-electrospun scaffolds exhibited improved hydrophilicity compared to blend scaffolds. The results of in vitro and in vivo degradation studies showed that the degradation rate of both composite scaffolds was faster than that of neat polycaprolactone scaffolds due to the incorporated polydioxanone component. Especially in co-electrospun scaffolds, the fast degradation of polydioxanone fiber gave rise to larger pore size, thus leading to faster cellularization and better vascularization compared to blend scaffolds. Therefore, co-electrospinning was demonstrated to be superior to blend electrospinning for the preparation of composite scaffolds. Co-electrospun polycaprolactone–polydioxanone scaffolds may be promising candidates for tissue engineering.

In vitro Bioactivity of Poly(∊-Caprolactone)-Apatite (PCL-AP) Scaffolds for Bone Tissue Engineering: The Influence of the PCL/AP Ratio

Porous poly(∊-caprolactone) (PCL) is used as long-term bioresorbable scaffold for bone tissue engineering. The bone regeneration process can be enhanced by addition of carbonated apatites (AP). This study was aimed at evaluating the influence of the PCL/AP ratio on the in vitro degradation and bioactivity of PCL-AP composites. To this purpose, PCL-AP samples were synthesised with the following PCL/AP weight/weight ratios: 50/50, 60/40 and 75/25.

Vibrational IR and Raman spectroscopies coupled to thermogravimetry (TG) and differential scanning calorimetry (DSC) were used to investigate the in vitro degradation mechanism in different media: 0.01 M NaOH solution (pH = 12), saline phosphate buffer at pH 7.5 (SPB), esterase in SPB and simulated body fluid (SBF) at pH 7.5. The latter medium was used to evaluate the bioactivity of the composites. A control PCL sample was analysed before the addition of the AP component.

As regards the untreated samples, the method of synthesis utilised for preparing the composite was found to enhance the crystallinity degree. The AP component revealed to be constituted of a B-type carbonated hydroxyapatite with a 3% carbonate content. After 28 days of treatment, the samples showed different degradation patterns and extents depending on the degradation medium, the starting PCL crystallinity and composite composition. Weight measurements, Raman and TG analyses revealed deposition of an apatitic phase on all the composites immersed in SBF. Therefore, all the samples displayed a good bioactivity; the sample which showed the most pronounced apatitic deposition was 50/50, i.e. that containing the highest amount of AP.

Catalytic metal-based systems for controlled statistical copolymerisation of lactide with a lactone

A comprehensive survey of the recent developments of metal-based catalysts for the ROcoP of lactide with another lactone is presented.

Synthesis, stereocomplex crystallization and homo-crystallization of enantiomeric poly(lactic acid-co-alanine)s with ester and amide linkages

α-Hydroxy acid and α-amino acid-derived poly(l-lactic acid-co-l-alanine)s and poly(d-lactic acid-co-d-alanine)s with different alanine unit contents were synthesized and their stereocomplex crystallization and homo-crystallization were investigated.

Doxycycline-loaded coaxial nanofiber coating of titanium implants enhances osseointegration and inhibits Staphylococcus aureus infection

Few studies have been reported that focus on developing implant surface nanofiber (NF) coating to prevent infection and enhance osseointegration by local drug release. In this study, coaxial doxycycline (Doxy)-doped polycaprolactone/polyvinyl alcohol (PCL/PVA) NFs were directly deposited on a titanium (Ti) implant surface during electrospinning. The interaction of loaded Doxy with both PVA and PCL NFs was characterized by Raman spectroscopy. The bonding strength of Doxy-doped NF coating on Ti implants was confirmed by a stand single-pass scratch test. The improved implant osseointegration by PCL/PVA NF coatings in vivo was confirmed by scanning electron microscopy, histomorphometry and micro computed tomography (μCT) at 2, 4 and 8 weeks after implantation. The bone contact surface (%) changes of the NF coating group (80%) is significantly higher than that of the no NF group (<5%, p < 0.05). Finally, we demonstrated that a Doxy-doped NF coating effectively inhibited bacterial infection and enhanced osseointegration in an infected (Staphylococcus aureus) tibia implantation rat model. Doxy released from NF coating inhibited bacterial growth up to 8 weeks in vivo. The maximal push-in force of the Doxy-NF coating (38 N) is much higher than that of the NF coating group (6.5 N) 8 weeks after implantation (p < 0.05), which was further confirmed by quantitative histological analysis and μCT. These findings indicate that coaxial PCL/PVA NF coating doped with Doxy and/or other drugs have great potential in enhancing implant osseointegration and preventing infection.

Determining conformational order and crystallinity in polycaprolactone via Raman spectroscopy

Raman spectroscopy is a popular method for non-invasive analysis of biomaterials containing polycaprolactone in applications such as tissue engineering and drug delivery. However there remain fundamental challenges in interpretation of such spectra in the context of existing dielectric spectroscopy and differential scanning calorimetry results in both the melt and semi-crystalline states. In this work, we develop a thermodynamically informed analysis method which utilizes basis spectra - ideal spectra of the polymer chain conformers comprising the measured Raman spectrum. In polycaprolactone we identify three basis spectra in the carbonyl region; measurement of their temperature dependence shows that one is linearly proportional to crystallinity, a second correlates with dipole-dipole interactions that are observed in dielectric spectroscopy and a third which correlates with amorphous chain behavior. For other spectral regions, e.g. C-COO stretch, a comparison of the basis spectra to those from density functional theory calculations in the all-trans configuration allows us to indicate whether sharp spectral peaks can be attributed to single chain modes in the all-trans state or to crystalline order. Our analysis method is general and should provide important insights to other polymeric materials.

β-Pyridylenolate zinc catalysts for the ring-opening homo- and copolymerization of ε-caprolactone and lactides

Eleven zinc β-quinolylenolates with varying substituents have been synthesized, and some of these complexes are excellent catalysts for the ring-opening homo- and copolymerization of ε-CL and LAs.

Raman Line Imaging of Poly(ε-caprolactone)/Carbon Dioxide Solutions at High Pressures: A Combined Experimental and Computational Study for Interpreting Intermolecular Interactions and Free-Volume Effects

In the present study, a Raman line-imaging setup was employed to monitor in situ the CO2 sorption at elevated pressures (from 0.62 to 7.10 MPa) in molten PCL. The method allowed the quantitative measurement of gas concentration in both the time-resolved and the space-resolved modes. The combined experimental and theoretical approach allowed a molecular level characterization of the system. The dissolved CO2 was found to occupy a volume essentially coincident with its van der Waals volume and the estimated partial molar volume of the probe did not change with pressure. Lewis acid-Lewis base interactions with the PCL carbonyls was confirmed to be the main interaction mechanism. The geometry of the supramolecular complex and the preferential interaction site were controlled more by steric than electronic effects. On the basis of the indications emerging from Raman spectroscopy, an equation of state thermodynamic model for the PCL-CO2 system, based upon a compressible lattice fluid theory endowed with specific interactions, has been tailored to account for the interaction types detected spectroscopically. The predictions of the thermodynamic model in terms of molar volume of solution have been compared with available volumetric measurements while predictions for CO2 partial molar volume have been compared with the values estimated on the basis of Raman spectroscopy.

Three-Dimensional Printing of Bone Extracellular Matrix for Craniofacial Regeneration

Tissue-engineered approaches to regenerate bone in the craniomaxillofacial region utilize biomaterial scaffolds to provide structural and biological cues to stem cells to stimulate osteogenic differentiation. Bioactive scaffolds are typically comprised of natural components but often lack the manufacturability of synthetic materials. To circumvent this trade-off, we 3D printed materials comprised of decellularized bone (DCB) matrix particles combined with polycaprolactone (PCL) to create novel hybrid DCB:PCL scaffolds for bone regeneration. Hybrid scaffolds were readily printable at compositions of up to 70% bone by mass and displayed robust mechanical properties. Assessments of surface features revealed both collagenous and mineral components of bone were present. Qualitative and quantitative assessments showed increased surface roughness relative to that of pure PCL scaffolds. These findings correlated with enhanced cell adhesion on hybrid surfaces relative to that on pure surfaces. Human adipose-derived stem cells (hASCs) cultured in DCB:PCL scaffolds without soluble osteogenic cues exhibited significant upregulation of osteogenic genes in hybrid scaffolds relative to pure PCL scaffolds. In the presence of soluble phosphate, hybrid scaffolds resulted in increased calcification. The hASC-seeded scaffolds were implanted into critical-sized murine calvarial defects and yielded greater bone regeneration in DCB:PCL scaffolds compared to that in PCL-only at 1 and 3 months post-transplantation. Taken together, these results demonstrate that 3D printed DCB:PCL scaffolds might be effective for stimulating bone regeneration.

Copolymerization of l-lactide and ε-caprolactone catalyzed by mono-and dinuclear salen aluminum complexes bearing bulky 6,6′-dimethylbipheyl-bridge: random and tapered copolymer

Mono- and dinuclear salen aluminum complexes bearing a racemic 6,6′-dimethyl-biphenyl bridge could efficiently catalyze the copolymerization of l-LA and ε-CL in the melt, producing practically random and tapered copolymers, respectively.

Antimicrobial electrospun poly(ε-caprolactone) scaffolds for gingival fibroblast growth

This study discusses the value of polymer electrospun materials in three-dimensional (3D) scaffolds and antibacterial wound dressings for potential dental applications.

Melt electrospinning of poly(lactic acid) and polycaprolactone microfibers by using a hand-operated Wimshurst generator

A conventional melt electrospinning setup usually needs a large, heavy high-voltage power supply and cannot work without a plug (electricity supply). In this article, we report a new melt electrospinning setup based on a small hand-operated Wimshurst generator, which can avoid electrical interference between the high-voltage spinning system and the heating system, and make the setup very portable and safe. Poly(lactic acid) (PLA) and polycaprolactone (PCL) fibers with diameters of 15-45 μm were fabricated successfully by using this apparatus. Experimental parameters such as the rotational speed of the generator handle (a half turn to two turns per second) and the spinning distance (2-14 cm) were investigated. In addition, PLA and PCL fibers were directly melt-electrospun onto a pork liver, and the temperature and adhesiveness of the deposited fibers were studied. The results indicate that the apparatus and melt-electrospun polymer microfibers may be used in dressing for wound healing.