Post-polymerization Methods Research Articles

Scalable enzymatic polymerization and low-temperature post-polymerization of poly(butylene succinate): Process parameters and application

Poly(butylene succinate) is a semicrystalline bio-based and biodegradable polymer with good processability. However, using metal-based transesterification catalysts during chemical synthesis can be a drawback, especially for the biomedical and food packaging sector. An alternative approach was herein employed, using immobilized Candida antarctica Lipase B as a biocatalyst in a solvent-free process to synthesize PBS in line with green chemistry. The key process parameters (reaction temperature, pressure, time) were studied regarding the prepolymer’s molecular weight, thermal properties, and morphology. Thanks to the process's simplicity, scaling up followed, and a quantity of 20 g of PBS (Mn¯ 1700 g·mol−1) was received, thus filling the relevant gap in the open literature. The scaled-up grade was subsequently submitted to different sustainable post-polymerization methods (SSP, melt post-polymerization) to increase the molecular weight while maintaining the green character of the final product. The post-polymerized PBS (Mn¯ 3000 g·mol−1) was used as a carrier for the naturally occurring antioxidant flavonoid naringin. The release profile of naringin from the PBS nanocarrier was assessed, proving the enzymatically synthesized and upgraded PBS an effective matrix for high-purity encapsulation systems for the first time.

Influence of the postpolymerization type and time on the flexural strength and dimensional stability of 3D printed interim resins

Statement of problemThe mechanical strength of 3-dimensionally (3D) printed interim resins is unclear but influenced by printing parameters. Evidence regarding standardization of the postpolymerization type and time for 3D printed interim resins is sparse. PurposeThe purpose of this in vitro study was to evaluate the influence of postpolymerization type and time on flexural strength and dimensional stability of 3D printed resins for interim restorations. Material and methodsA total of 288 bars were 3D printed (Form 2; Formlabs, stereolithography—SLA, 50 µm, 30 degrees), (25×2×2 mm; International Organization for Standardization—ISO 4049:2019) abraded and randomly divided into 9 groups (n=30) according to postpolymerization (Ultraviolet device—UV; Microwave with water—MWA; Microwave without water—MW) and time (15, 20, and 30 minutes for UV; and 5, 8, and 10 minutes for MW and MWA). Each bar was then measured with digital calipers at 11 points for length, thickness, and width before and after postpolymerization to analyze dimensional stability. The flexural strength was then measured (σ; 980.6 N, 1 mm/minute) and the fractured surfaces were analyzed with scanning electron microscopy. The σ (MPa) data were evaluated by using a 2-way analysis of variance (ANOVA) and the Tukey honestly significant difference (HSD) pairwise comparisons test (α=.05). Dimensional stability data (mm) were analyzed by using the Kruskal-Wallis test and Dwass-Steel-Critchlow-Fligner multiple comparisons. The Weibull analysis was performed with σ data. ResultsThe 2-way ANOVA revealed that all factors and their interaction were significant for σ (P<.001). The UV groups presented the highest σ values, being statistically higher than all MW and MWA groups. The Weibull analysis revealed that postpolymerization UV groups found the highest values regarding the characteristic strength, although the MW 8-minute group (13.71) found the highest value for the Weibull modulus. Furthermore, the Kruskal-Wallis test revealed that only the postpolymerization factor was significant for dimensional stability (P<.001). The postpolymerization microwave groups found greater expansion variations at all times, with the MW 8-minute group (0.78 ±0.54) presenting the greatest variation in dimensional stability. ConclusionsUV was determined to be the most suitable type of postpolymerization for interim printed resin among the postpolymerization methods, regardless of the application time. The postpolymerization MW groups found greater variations in dimensional stability.

Post-polymerization of three-dimensional printing resin using a dental light curing unit

Background/PurposeIn vat photopolymerization, post-polymerization of the three-dimensional (3D) printing resin is necessary to ensure the optimum physical properties of the printed objects. This study aimed to evaluate the potential use of a handheld polywave light-emitting diode (LED) dental light-curing unit (LCU) for post-polymerizing 3D printed resins by measuring the microhardness and biaxial flexural strength of the post-polymerized resin. Material and methods3D printed 1- and 2-mm-thick disks were irradiated with a dental LCU at 3200 mW/cm2. Post-polymerization was repeated either on one side from the top surface: two cycles (T2), four cycles (T4), and eight cycles (T8), or on both sides from the top and bottom surfaces: one cycle (T1B1), two cycles (T2B2), and four cycles (T4B4) for each side. The microhardness and biaxial strength of the disks were compared to those post-polymerized by a conventional desktop polymerizing unit (PC) and those without post-polymerization (NC). ResultsMicrohardness of the disks varied between the top and bottom surfaces of the 1-mm and 2-mm-thick disks, depending on the post-polymerization methods. T8 and T4B4 produced comparable microhardness on the top surface to PC for both thicknesses. In contrast, PC, T2B2, and T4B4 exhibited the highest microhardness on the bottom surface. Except for NC, the 1-mm-thick disks had a higher biaxial flexural strength than the 2-mm-thick disks. T4B4 resulted in the highest biaxial flexural strength for both thicknesses, which was comparable to that of the desktop polymerizing unit. ConclusionThe microhardness and biaxial flexural strengths of the post-polymerized 3D-printed disks increase with polymerization time. With sufficient polymerization from both sides, the polywave LCU has the potential to be a viable alternative to desktop polymerization units.

Can postpolymerization for 3D-printed interim restorations be improved?

Statement of problemPostpolymerization methods influence the properties of 3-dimensionally (3D) printed materials. Nevertheless, it is a time-consuming step that could lead dentists to avoid the chairside use of 3D printing. Information assessing the impact of different postpolymerization workflows on flexural strength and color stability is sparse. PurposeThe purpose of this in vitro study was to analyze the impact of different postpolymerization methods on the flexural strength and color stability of 3D-printed resins used for interim restorations. Material and methodsThree resin materials: CT (Cosmos Temp; Yller Biomaterials), DT (Denture Teeth; Formlabs), and CB (C&B MFH; NextDent) were submitted to 4 methods of postpolymerization: a Form Cure polymerization chamber (FC) (Form Cure; Formlabs), a broadband LED device (Valo Grand; Ultradent Products, Inc) operating at 1000 mW/cm2 for 2 different polymerization times (40 seconds/V40 or 120 seconds/V120), and a custom-made polymerization chamber with a 24 W UV LED Strip (CC). The specimens were assessed for flexural strength using an universal testing machine immediately after polymerization or after 10 000 thermal cycles, and the color stability was evaluated using a spectrophotometer at baseline, after 7 days in dark, dry storage at 37 °C and after 24 hours of artificial aging in water at 60 °C. The data were evaluated using 3-way ANOVA (flexural strength) and 3-way repeated measurements ANOVA (color stability), followed by the Tukey HSD test (α=.05). ResultsFlexural strength showed significant differences for resin, postpolymerization method, time, and for the interaction between all effects. CT showed the highest overall flexural strength, while DT showed the lowest. In general, V120 produced specimens with higher flexural strength. Thermocycling did not reduce flexural strength except for CB polymerized with FC and V120, and DT polymerized with V40. For color stability, significant differences were found for resin, postpolymerized method, time, and for the interaction between all effects. The highest ΔE values were observed for DT polymerized using V40 after artificial aging. The lowest values were observed for the same resin but polymerized using V120 after 7 days in dark, dry storage at 37 °C. ConclusionsPostpolymerization with the broadband LED device for 120 seconds can produce specimens with higher flexural strength values and higher color stability when compared with the other postpolymerization workflows tested in this study.

Miniemulsion polymerization-formulated poly(fluorene-alt-6-(2-ethylhexyl)-[1,2,5]thiadiazole[3,4-f]benzotriazole) for cancer cell imaging

Near-infrared (NIR) conjugated polymer nanoparticles (CPNPs) possesses advantages for bioimaging because of their merits in low autofluorescence interference, good biocompatibility, large light extinction coefficient, improved photostability, and facile functionalization capability. Different from conventional post-polymerization methods for fabricating NIR CPNPs, like nanoprecipitation, emulsion and solvent evaporation/miniemulsion, and self-assembly, herein, an efficient one-pot strategy by in-situ miniemulsion polymerization is demonstrated to synthesize CPNPs for NIR fluorescence imaging of cancer cells. Via adjusting the donor-acceptor strength, the new CP, poly(fluorene-alt-6-(2-ethylhexyl)-[1,2,5]thiadiazole[3,4-f]benzotriazole) (PFTA), show absorption and emission maximum at 648 nm and 730 nm, respectively, which is much more red-shifted than its counterpart, poly(fluorene-alt-benzo-2,1,3-thiadiazole) (PFBT). DFT calculation demonstrates that the repeating unit of PFTA has a smaller dihedral angel to 33.2° and much reduced energy gap to 2.46 eV, as compared to that of PFBT NPs. Importantly, through controlling surfactant concentrations from 40 g·L−1 to 2.5 g·L−1 during the miniemulsion polymerization, the particles size can be accordingly changed from even 88 to 210 nm. Furthermore, the particles show extinction coefficient of 2.82 × 104 M−1·cm−1at 648 nm, photoluminescence quantum yields c.a. 2.4% and fluorescence lifetime c.a. 1.26 ns, respectively. Moreover, the PFTA NPs exhibit biocompatibility, good colloidal stability and bright fluorescence signals to clearly pinpoint breast cancer cells, with a trend that smaller NP size, higher cellular uptake. This work demonstrates the promise of miniemulsion polymerization as a facile method to fabricate NIR CPNPs for bioimaging.

Postpolymerization of a 3D-printed denture base polymer: Impact of post-curing methods on surface characteristics, flexural strength, and cytotoxicity

ObjectiveThis study investigated the influence of postpolymerization of a three-dimensional (3D) printed denture base polymer. The effect of post-curing methods on surface characteristics, flexural strength, and cytotoxicity was evaluated. MethodsA total of 172 specimens were additively manufactured using one denture base material (V-Print dentbase, VOCO) and further post-cured by different light-curing devices, including Otoflash G171 (OF), Labolight DUO (LL), PCU LED (PCU), and LC-3DPrintbox (PB), respectively. Polymethyl methacrylate resin (PalaExpress Ultra) was used as a reference (REF). Afterward, surface topography was observed using scanning electron microscopy, and surface roughness was measured (n = 6). Furthermore, flexural strength was tested (n = 20). Cytotoxicity was evaluated by the extract and direct contact tests. The data were analyzed using the Kolmogorov-Smirnov test and one-way ANOVA followed by Tukey's multiple comparisons and Kruskal-Wallis tests (p < 0.05). ResultsThe different post-curing methods applied did not significantly influence surface topography and roughness (Ra). Meanwhile, specimens post-cured by PCU (162.3 ± 44.16 MPa) and PB (171.2 ± 34.41 MPa) showed significantly higher flexural strength than those post-cured by OF (131.3 ± 32.87 MPa) and REF (131.2 ± 19.19 MPa), respectively. Additionally, various post-curing methods effectively decreased the cytotoxic effects of 3D-printed denture base polymer. ConclusionsDifferent post-curing methods did not significantly alter the Ra values of the 3D-printed denture base material. However, flexural strength was significantly affected by the postpolymerization methods, which might be attributed to the different wavelengths of post-curing devices. In addition, various postpolymerization methods reduced the cytotoxic effects of the 3D-printed denture base polymer. Clinical significanceFlexural strength of additively manufactured denture bases depends on the postpolymerization strategy. Therefore, an appropriate post-curing method is required to optimize the flexural strength of 3D-printed denture materials.

Influence of postpolymerization methods and artificial aging procedures on the fracture resistance and flexural strength of a vat-polymerized interim dental material

Statement of problemThe influence of postpolymerization methods and artificial aging procedures on the fracture resistance and flexural strength of additively manufactured interim polymers remains unclear. PurposeThe purpose of this in vitro study was to evaluate the effect of the conditions (dry and water- and glycerin-submerged) and time (25, 30, 35, 40, and 45 minutes) of postpolymerization methods with and without artificial aging procedures on the fracture resistance and flexural strength of an additively manufactured interim material. Material and methodsBar specimens (25×2×2 mm) were manufactured from an interim resin (NexDent C&B MFH N1) with a 3-dimensional printer (NexDent 5100) as per the manufacturer’s recommendations. Three groups were created based on the postpolymerization condition: dry (D group) and submerged in a container with water (W group) or glycerin (G group) inside the ultraviolet polymerization machine (LC-3DPrint Box). Each group was divided into 5 subgroups (D1 to D5, W1 to W5, and G1 to G5) depending on the polymerizing time (25, 30, 35, 40, and 45 minutes) (n=20). Each subgroup was divided into nonaged and aged subgroups. The aged groups were treated in a mastication simulator. Fracture strength was measured on a universal testing machine. The flexural strength was calculated as per International Organization for Standardization (ISO) 10477-2018. The Kolmogorov-Smirnov test demonstrated that data were normally distributed. The 3-way ANOVA test was used to analyze the data (α=.05). ResultsA significant main effect was found on the fracture strength analysis for each of the 3 factors: postpolymerization condition (F[2, 449]=81.00, P<.001), treatment duration (F[4, 449]=2.84, P=.024), and aging procedure (F [1, 449] =7.62, P=.006). The only significant 2-way interaction was between postpolymerization condition and treatment duration (F[8, 449]=3.12, P=.002). Furthermore, a significant main effect was found on the flexural strength for each of the 3 factors including postpolymerization condition (F[2, 449]=82.55, P<.001), treatment duration (F[4, 449]=2.85, P=.024), and artificial aging procedure (F[1, 449]=6.72, P=.010). The only significant 2-way interaction was between postpolymerization condition and treatment duration (F[8, 449]=3.33, P=.001). Dry postconditions at 25 minutes and nonaged procedures obtained the significantly highest fracture resistance and flexural strength values. ConclusionsPostpolymerization conditions and duration time affected the fracture resistance and flexural strength of the additively manufactured interim material assessed. Artificial aging procedures significantly decreased the fracture resistance and flexural strength of the additively manufactured interim dental material.

Effects of water boiling, microwave, and water bath post-polymerization on mechanical properties of acrylic denture resins

Acrylic restorations in the mouth are exposed to strong occlusal forces. Their mechanical properties depend on the type and method of their polymerization. The aim of this study is a comparative analysis of mechanical properties (flexural strength and modulus of elasticity) of acrylic materials before and after the post-polymerization treatments (water boiling, microwave irradiation and water storage). The study included denture base resins, as well as an acrylate for orthodontic appliances impregnated with aesthetic beads. Flexural strength, modulus of elasticity and the deflection were measured immediately after polymerization, after a hot and microwave post-polymerization and after immersion in a water bath at the temperature of 37?C. The applied post-polymerization methods resulted in an increase in flexural strength and modulus of elasticity relative to the initial values for all tested materials. Being aware of the reduction in fracture risk of dental prosthesis after a proposed post-polymerization procedure, it could be used in all clinical situations where there is an increased risk of damage to dentures.

Effect of inorganic fillers and post-polymerization methods in experimental composites

Effect of inorganic fillers and post-polymerization methods in experimental composites

Preliminar study on the influence of two post-polymerization methods for two composite laboratory systems

Preliminar study on the influence of two post-polymerization methods for two composite laboratory systems

Effect of autoclave postpolymerization treatments on the fracture toughness of autopolymerizing dental acrylic resins

IntroductionMicrowave and water bath postpolymerization have been suggested as methods to improve the mechanical properties of heat and autopolymerizing acrylic resins. However, the effects of autoclave heating on the fracture properties of autopolymerizing acrylic resins have not been investigated. PurposeThe aim of this study was to assess the effectiveness of various autoclave postpolymerization methods on the fracture properties of 3 different autopolymerizing acrylic resins. MethodsForty-two specimens of 3 different autopolymerizing acrylic resins (Orthocryl, Paladent RR and Futurajet) were fabricated (40×8×4mm), and each group was further divided into 6 subgroups (n=7). Control group specimens remained as processed (Group 1). The first test group was postpolymerized in a cassette autoclave at 135°C for 6 minutes and the other groups were postpolymerized in a conventional autoclave at 130°C using different time settings (5, 10, 20 or 30 minutes). Fracture toughness was then measured with a three-point bending test. Data were analyzed by ANOVA followed by the Duncan test (α=0.05). ResultsThe fracture toughness of Orthocryl and Paladent-RR acrylic resins significantly increased following conventional autoclave postpolymerization at 130°C for 10 minutes (P<.05). However, the fracture toughness of autoclave postpolymerized Futurajet was not significantly different than its control specimens (P<.05). The fracture toughness of Futurajet was significantly less than Paladent RR and Orthocryl specimens when autoclaved at 130°C for 10 minutes. ConclusionsWithin the limitations of this study, it can be suggested that autoclave postpolymerization is an effective method for increasing the fracture toughness of tested autoploymerized acrylic resins.

Effect of Autoclave Postpolymerization Treatments on the Fracture Toughness of Autopolymerizing Dental Acrylic Resins

Microwave and water bath postpolymerization have been suggested as methods to improve the mechanical properties of heat and autopolymerizing acrylic resins. However, the effects of autoclave heating on the fracture properties of autopolymerizing acrylic resins have not been investigated. The aim of this study was to assess the effectiveness of various autoclave postpolymerization methods on the fracture properties of 3 different autopolymerizing acrylic resins. Forty-two specimens of 3 different autopolymerizing acrylic resins (Orthocryl, Paladent RR and Futurajet) were fabricated (40x8x4mm), and each group was further divided into 6 subgroups (n=7). Control group specimens remained as processed (Group 1). The first test group was postpolymerized in a cassette autoclave at 135°C for 6 minutes and the other groups were postpolymerized in a conventional autoclave at 130°C using different time settings (5, 10, 20 or 30 minutes). Fracture toughness was then measured with a three-point bending test. Data were analyzed by ANOVA followed by the Duncan test (α=0.05). The fracture toughness of Orthocryl and Paladent-RR acrylic resins significantly increased following conventional autoclave postpolymerization at 130°C for 10 minutes (P<.05). However, the fracture toughness of autoclave postpolymerized Futurajet was not significantly different than its control specimens (P<.05). The fracture toughness of Futurajet was significantly less than Paladent RR and Orthocryl specimens when autoclaved at 130°C for 10 minutes. Within the limitations of this study, it can be suggested that autoclave postpolymerization is an effective method for increasing the fracture toughness of tested autoploymerized acrylic resins.

Synthesis and Characterization of Water‐Soluble Conjugated Glycopolymer for Fluorescent Sensing of Concanavalin A

A neutral polyfluorene derivative that contains 20 mol% 2,1,3-benzothiadiazole (BT) is synthesized by Suzuki cross-coupling polymerization. A cationic conjugated polymer A and an alpha-mannose-bearing polymer B are subsequently obtained through different post-polymerization methods. As a result of the charged pendant groups or sugar-bearing groups attached to the polymer side chains, both A and B show good water-solubility. The titration of Concanavalin A (Con A) into polymer aqueous solution leads to different fluorescent responses for polymers A and B. Polymer A does not show any obvious fluorescence change upon interaction with Con A, whereas polymer B shows fluorescence increase in BT emission intensity when Con A is added. This is because of the specific interaction between alpha-mannose and Con A, which induces polymer aggregation, and then facilitates energy transfer from the phenylene-fluorene segments to the BT units. A practical calibration curve ranging from 1 nM to 250 nM is obtained by correlating the changes in BT emission intensity with Con A concentration. The advantage of polymer B-based Con A macromolecular probe is that it shows signal increase upon Con A recognition, which is significantly different from other conjugated polymer-based fluorescence quenching assays.

Acrylic removable appliances: Comparative evaluation of different postpolymerization methods

In orthodontics, the polymeric part of removable orthodontic appliances could be a hazard for patients because high residual monomer contents can lead to allergic reactions. In addition, water uptake, color stability, and mechanical properties are influenced by the degree of conversion. The aim of this investigation was to evaluate the effectiveness of different postpolymerization methods on the properties of removable orthodontic appliance resins. A total of 300 rectangular specimens (5 postpolymerization groups: 20 per group) were manufactured of Orthocryl (n = 100, Dentaurum, Ispringen, Germany), Palapress (n = 100, Heraeus-Kulzer, Wehrheim, Germany), and Pro Base Cold (n = 100, Ivoclar-Vivadent, Schaan, Liechtenstein). The first 2 postpolymerization groups were postcured in a stove (10 minutes at 40 degrees C or 80 degrees C). The third resin group was postcured in a microwave at 600W for 5 minutes, and the fourth polymer group was postcured in a microwave at 600W for 10 minutes. Twenty conventionally cured samples (cold-curing under pressure: water bath 40 degrees C, 25 minutes, 2.2 bar) were the control group. Water sorption, fracture toughness, and Vickers hardness were measured. Fracture toughness and Vickers hardness of the resins are slightly increased after curing. Heat as a secondary curing method decreases water uptake of resins used for removable orthodontic appliances. Heat postpolymerization appears to improve the properties of removable orthodontic appliance resins.