Influence of electron beam irradiation on physicochemical properties of poly(trimethylene carbonate)

Electron beam (EB) irradiation of poly(trimethylene carbonate) (PTMC), an amorphous, biodegradable polymer used in the field of biomaterials, results in predominant cross-linking and finally in the formation of gel fraction, thus enabling modification of physicochemical properties of this material without significant changes in its chemical structure. PTMC films (M_w: 167-553 kg mol⁻¹) were irradiated with different doses using an electron accelerator. Irradiation with a standard sterilization dose of 25 kGy caused neither significant changes in the chemical composition of the polymer nor significant deterioration of its mechanical properties. Changes in viscosity-, number-, weight-, and z-average molecular weights of PTMC for doses lower than the gelation dose (D_g) as well as gel-sol analysis and swelling tests for doses above D_g indicate domination of cross-linking over degradation. EB irradiation can be considered as an effective tool for increasing the average molecular weight of PTMC and sterilization of PTMC-based biomaterials.     

Effect of gamma‐irradiation sterilization on the physical and mechanical properties of a hybrid wound dressing

A wound dressing should ideally provide an optimal healing environment which enables rapid healing. It should maintain a moist environment at the wound surface, allow gas exchange, act as a barrier to microorganisms, remove excess exudates and afford mechanical protection to the wound. A new bioresorbable hybrid wound dressing which combines a poly(DL‐lactic‐co‐glycolic acid) porous top layer with a spongy collagen sublayer was developed and studied. The top layer contained the antibiotic drug gentamicin for controlled release to the wound site. It is of very high importance to use an appropriate sterilization process for this special new wound dressing, which will not have a deleterious effect on its function. Our investigation therefore focused on the effects of gamma‐irradiation sterilization (10, 25, 35 and 50 kGy) on the structure properties of this wound dressing. The physical and mechanical properties were of the wound dressings were affected by the gamma irradiation because of a combination of chain scission and crosslinking of the collagen layer mainly. The weight loss and water vapor transmission rate were increased, while the water uptake was decreased with the increase in the irradiation dose. The changes were small when doses of 10 or 25 kGy were applied at room temperature. The gamma‐irradiation resulted in stronger but more brittle wound dressings. These trends were smaller when the sterilization process was carried out in liquid nitrogen. Our research shows that gamma‐sterilization process is feasible for our new concept of hybrid wound dressings and optimal conditions can be chosen. Copyright © 2016 John Wiley & Sons, Ltd.     

Changes of porous poly(ε-caprolactone) bone grafts resulted from e-beam sterilization process

The most important mechanical feature of poly(ε-caprolactone) (PCL) foams applied in bone tissue engineering as a scaffold, has been investigated as a function of irradiation dose. Radiation is proposed for the sterilization of the polymer before the implantation. Polycaprolactone scaffold foams were obtained by combination of compression molding and particulate leaching techniques. The porogen was changed in the range 74–96 w% and the irradiation dose was varied from 25 to 150 kGy. Our results show that yield strength is not a function of radiation dose, but is rather influenced by the porosity, while the critical strain is mainly dependent on the dose. All these together mean that the modulus of the elasticity of PCL foams is dependent on both the porosity and the dose.     

PEGylated poly(ester amide) elastomer scaffolds for soft tissue engineering

Biodegradable synthetic elastomers with tunable mechanical and physicochemical properties remain attractive materials for soft tissue engineering. We have recently synthesized novel poly(1,3‐diamino‐2‐hydroxypropane‐co‐glycerol sebacate)‐co‐poly(ethylene glycol) (APS‐co‐PEG) biodegradable elastomers. This class of PEGylated elastomers has widely tunable mechanical and degradation properties compared wtih currently available biodegradable elastomers. To further investigate the biological application of this class of elastomers, we fabricated hybrid APS‐co‐PEG/polycaprolactone (PCL) porous scaffolds by electrospinning. The fiber morphology, chemical composition, mechanical properties, degradability, and cytocompatibility of hybrid APS‐co‐PEG/PCL electrospun scaffolds were characterized. These scaffolds exhibited a wide range of mechanical properties and similar cytocompatibility to PCL scaffolds. Importantly, PEGylation inhibited platelet adhesion on all APS‐co‐PEG/PCL electrospun scaffolds when compared with PCL and APS/PCL scaffolds, suggesting a potential role in mitigating thrombogenicity in vivo. Additionally, APS‐25PEG/PCL scaffolds were found to be mechanically analogous to human heart valve leaflet and supported attachment of human aortic valve cells. These results reveal that hybrid APS‐co‐PEG/PCL scaffolds may serve as promising constructs for soft tissue engineering, especially heart valve tissue engineering. Copyright © 2017 John Wiley & Sons, Ltd.     

Pyrogallic acid‐PLGA conjugate as new biodegradable material suitable for final sterilization by irradiation

This paper reports the feasibility to prepare a biodegradable material stable to γ‐irradiation by grafting of poly(lactide‐co‐glycolide) with pyrogallic acid (PLGA‐g‐PA) and ferulic acid (PLGA‐g‐FA) in mild condition. Only the grafting procedure with PA did not modify molecular weight (Mw) of the starting polymer and PLGA‐g‐PA showed antioxidant properties. The polymer degradation in pH 7.4 phosphate buffer saline (PBS) was mainly governed by a random chain scission mechanism according to a first‐order reaction. The irradiation at the dose of 25 kGy caused only a very slight decrease of Mw and the degradation patterns of the non‐irradiated and irradiated material were superimposable. PLGA‐g‐PA resulted a promising material to develop biodegradable drug delivery systems which would be sterilizable in the final container. Copyright © 2010 John Wiley & Sons, Ltd.     

Thermal Degradation of Poly(ε-caprolactone), Poly(L-lactic acid) and their Blends with Poly(3-hydroxy-butyrate) Studied by TGA/FT-IR Spectroscopy

Summary: The thermal degradation behavior of poly(ε-caprolactone) (PCL) and poly(L-lactic acid) (PLA) have been studied in different environment. It was found that these polymers undergo completely different degradation processes in nitrogen and oxygen atmosphere. In oxygen environment PCL and PLA mainly decompose to CO₂, CO, water and short-chain acids. In nitrogen atmosphere PCL releases 5-hexenioc acid, CO₂, CO and ε-caprolactone, whereas PLA decomposes to acetaldehyde, CO₂, CO and lactide. The polymer blends of poly(3-hydroxybutyrate) (PHB) with PCL and PLA decompose similar to the individual homopolymers with crotonic acid as the initial decomposition product of PHB.     

Calorimetric and Dielectric Study of the Segmented Biodegradable Poly(ester‐urethane)s Based on Bacterial Poly[(R)‐3‐hydroxybutyrate]

Two series of segmented poly(ester‐urethane)s were synthesized from bacterial poly[(R)‐3‐hydroxybutyrate]‐diol (PHB‐diol), as hard segments, and either poly(ε‐caprolactone)‐diol (PCL‐diol) or poly(butylene adipate)‐diol (PBA‐diol), as soft segments, using 1,6‐hexamethylene diisocyanate as a chain extender. The hard‐segment content varied from 0 to 50 wt.‐%. These materials were characterized using ¹H NMR spectroscopy and GPC. The polymers obtained were investigated calorimetrically and dielectrically. DSC showed that the T_g of either the PCL or PBA soft segments are shifted to higher temperatures with increasing PHB hard‐segment content, revealing that either the PCL or PBA are mixed with small amounts of PHB in the amorphous domains. The results also showed that the crystallization of soft or hard segments was physically constrained by the microstructure of the other crystalline phase, which results in a decrease in the degree of crystallinity of either the soft or hard segments upon increase of the other component. The dielectric spectra of poly(ester‐urethane)s, based on PCL and PHB, showed two primary relaxation processes, designated as α_S and α_H, which correspond to glass–rubber transitions of PCL soft and PHB hard segments, respectively. Whereas in the case of other poly(ester‐urethane)s, derived from PBA and PHB, only one relaxation process was observed, which broadens and shifts to higher temperature with increasing PHB hard‐segment content. It was concluded from these results that our investigated materials exhibit micro‐phase separation of the hard and soft segments in the amorphous domains.     

Study of enzymatic degradation of microbial copolyesters consisting of 3-hydroxybutyrate and medium-chain-length 3-hydroxyalkanoates

Enzymatic degradation of poly(3-hydroxybutyrate-co-3-hydroxyalkanoates) (PHBA) biopolyester consisting of 3-hydroxybutyrate (HB) and 15 mol% medium-chain-length 3-hydroxyalkanoates (HA) was studied using a polyhydroxyalkanoates (PHA) depolymerase produced by Ralstonia pickettii T1. It was found that PHBA films did not lose their weight after 25 h of depolymerase treatment. In contrast, three commercially available PHAs including poly-3-hydroxybutyrate (PHB), poly(3-hydroxybutyrate-19 mol% 3-hydroxyvalerate) (PHBV) and poly(3-hydroxybutyrate-19 mol% 3-hydroxyhexanoate) (PHBHHx) lost 75%, 94% and 39% of their original weights. Slow degradation of PHBA was also confirmed by the absence of HA monomers, dimers or trimers as degradation products in their depolymerase solution compared with abundance of degradation products released by the other three PHAs under the same condition. Surface erosion of PHBA was only observed after 48 h of enzymatic treatment compared with those of PHB, PHBV and PHBHHx which already had obvious surface changes after 7.5 h of same treatment. Although the crystallinities of PHB, PHBV, PHBHHx and PHBA were in the order PHB > PHBV > PHBHHx > PHBA valued at 55.8%, 47.8%, 45.9% and 40.9%, respectively, the order of degradability was PHBV > PHB > PHBHHx > PHBA. It can be proposed that PHA enzymatic degradation using this depolymerase was structure related: longer side-chain PHA including PHBHHx and PHBA was less favorable for the depolymerase degradation, longer the side chain, less the biodegradation.     

Microwave‐assisted synthesis and characterization of biodegradable block copolyesters based on poly(3‐hydroxyalkanoate)s and poly(D,L‐lactide)

Microwave (MW)‐assisted ring‐opening polymerization (ROP) provides a rapid and straightforward method for engineering a wide array of well‐defined poly(3‐hydroxyalkanoate)‐b‐poly(D,L ‐lactide) (PHA‐b‐PLA) diblock copolymers. On MW irradiation, the bulk ROP of D,L ‐lactide (LA) could be efficiently triggered by a series of monohydroxylated PHA‐based macroinitiators previously produced via acid‐catalyzed methanolysis of corresponding native PHAs, thus affording diblock copolyesters with tunable compositions. The dependence of LA polymerization on temperature, macroinitiator structure, irradiation time, and [LA]₀/[PHA]₀ molar ratio was carefully investigated. It turned out that initiator efficiency values close to 1 associated with conversions ranging from 50 to 85% were obtained only after 5 min at 115 °C. A kinetic investigation of the MW‐assisted ROP of LA gave evidence of its “living”/controlled character under the experimental conditions selected. Structural analyses and thermal properties of biodegradable diblock copolyesters were also performed. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Novel block copolymers of atactic PHB with natural PHA for cardiovascular engineering: Synthesis and characterization

Low-molecular weight macroinitiators derived from natural poly(3-hydroxyalkanoates) (PHAs), which contain olefinic and activated by 18-crown-6 ether carboxylic end groups, were used in anionic ring opening polymerization (ROP) of racemic β-butyrolactone and new diblock copolymers of selected PHAs (PHB, PHBV, PHO) with atactic poly[(R,S)-3-hydroxybutyrate] (a-PHB) were obtained. These novel copolymers were characterized using ¹H NMR, GPC and DSC. Hydrolytic degradation studies of selected copolymers were also performed. Finally, the suitability of these polymeric materials for cardiovascular engineering and as blend compatibilizers was demonstrated.     

Mechanical, thermal and degradation properties of poly(d,l-lactide)/poly(hydroxybutyrate-co-hydroxyvalerate)/poly(ethylene glycol) blend

The mechanical, thermal and biodegradable properties of poly(d,l-lactide) (PDLLA), poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) and poly(ethylene glycol) (PEG) blends were studied. The influence of PEG on the tensile and impact strengths of the blends was investigated. The results showed that the toughness and elongation at break of the PDLLA/PHBV (70/30) blends were greatly improved by the addition of PEG, and the notched Izod impact strength increased about 400% and the elongation at break increased from 2.1% to 237.0%. The thermal and degradation properties of the blends were investigated by differential scanning calorimeter (DSC) and thermogravimetric analyzer (TGA), it was found that the thermal stability of PHBV in the presence of PDLLA was improved. The degradation test showed that the addition of PEG could notably accelerate the biodegradation of the blends in the soil at room temperature, and the mass loss is about 20% after 30 days of the storage.     

Synthesis of PHB nanoparticles from optimized medium utilizing dairy industrial waste using Brevibacterium casei SRKP2: A green chemistry approach

Polyhydroxyalkanoates (PHAs) are natural, biodegradable polymers accumulated by bacteria under nutritional exhausted condition where carbon source is in excess. A gram positive bacterium (designated strain SRKP2) that potentially accumulated polyhydroxybutyrate (PHB) was isolated from dairy industrial waste. From its morphological and physiological properties and nucleotide sequence of its 16S rRNA, it was suggested that strain SRKP2 was similar to Brevibacterium casei. PHAs were synthesized from a medium containing dairy waste, yeast extract and sea water. The synthesized PHAs were characterized by FT-IR as Polyhydroxybutyrate (PHB). Response surface methodology was applied to optimize the production of PHB. From the optimized medium the yield of PHB was found to be 2.940 g/L. Here we report the direct use of dairy waste and sea water as potential sources for the production of PHB. Produced PHB was used to synthesize nanoparticles using solvent displacement technique.     

Evaluation of ⁶⁰Co-gamma radiosterilization on Chinese medicines with HPLC/FTIR

The aim of this study was to evaluate the effect of radiosterilization on 30 Chinese medicines using γ‐rays from the isotope ⁶⁰Co. Two groups of Chinese medicines, non‐treated and dry samples, were treated using a ⁶⁰Co irradiation source at the doses 0, 3, 6 and 9 kGy. After storage for 3 months, characterizations of chemical compounds and functional groups were performed by high‐performance liquid chromatography (HPLC) and Fourier transform infrared spectroscopy. The results of radiosterlization showed that nearly all of the medicines were decontaminated under the dose of 9 kGy. In most samples, chemical compounds and functional groups were not altered by the irradiation treatment. However, minor changes were found in the molecular structures of 14 medicines under the reported ‘safety dose’ (10 kGy). The drying process before irradiation could decrease the chemical changes caused by γ‐rays to 50%. The HPLC analysis of nine medicines revealed minor changes at a dose of 3 kGy. The findings in this study provide important information that may suggest the need for a re‐evaluation of the reported safety dose. Therefore, further investigation may be warranted to insure the safety of γ‐radiosterlization of Chinese medicines. Copyright © 2010 John Wiley & Sons, Ltd.     

Effect of soy protein isolate on the thermal, mechanical and morphological properties of poly (-caprolactone) and corn starch blends

The development of biodegradable polymers is considered to be a good alternative to decrease the volume of the plastic waste disposed into the environment every year. The use of natural polymers as raw materials to develop polymer blends and composites has increased the demand for renewable sources such as starch and soy protein.In this work, the authors prepared and characterized the thermal, mechanical and morphological properties of blends based on poly (-caprolactone) and modified corn starch, with added soy protein isolate (SPI) and sorbitol. All samples were processed by extrusion in a single-screw extruder and hot pressing. It was observed that the addition of modified corn starch and SPI were responsible for the reduction of thermal and mechanical properties of the materials, compared to pristine PCL. However, with increasing amounts of SPI and the reduction of starch incorporated into the samples, their properties tend to recover. The insertion of soy protein isolate in the formulations was done with the aim of balancing the C/N ratio of the blend, which plays a key role in the biodegradation process of these materials.     

Brush Type Copolymers of Poly(3-hydroxybutyrate) and Poly(3-hydroxyoctanoate) with Same Vinyl Monomers via “Grafting From” Technique by Using Atom Transfer Radical Polymerization Method

Brush type graft copolymers of poly(3-hydroxybutyrate) (PHB) and poly(3-hydroxyoctanoate) (PHO) with methylmethacrylate, (MMA), styrene, (S), and n-butylmethacrylate, (n-BuMA) were obtained by using Atom Transfer Radical Polymerization Method, (ATRP), via “grafting from” technique. Firstly PHB and PHO were chlorinated by passing chlorine gas through their solution in CHCl₃/CCl₄ (75/25 v/v) mixture and CCl₄, respectively, in order to prepare chlorinated PHB, PHB-Cl, and chlorinated PHO, PHO-Cl, with different chlorine contents. The determination of the chlorine content in chlorinated poly(3-hydroxyalkanoate) (PHA-Cl) was performed by the Volhard Method. Then ATRP of vinyl monomers was initiated by using PHA-Cl as macroinitiators in the presence of cuprous chloride (CuCl)/2,2′-bipyridine complex as catalyst, at 90 °C in order to obtain brushes containing PHAs. The polymer brushes were fractionated by fractional precipitation methods and the γ values calculated from the ratio of the volume of nonsolvent (methanol) and the volume of solvent (chloroform) of brushes varied between 0.82 and 6.50 depending on the composition of brushes. The polymer products were characterized by gel permeation chromatography (GPC), ¹H NMR, FTIR, thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) techniques.     

Assessing the mechanical,phase inversion,and rheological properties of poly-[(R)-3-hydroxybutyrate-co-(R)-3-hydroxyvalerate] (PHBV) blended with poly-(l-lactic acid) (PLA)

Poly-(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) and poly-(l-lactic acid) (PLA) have attracted much interest in recent years since they are biodegradable, thus can replace synthetic non-degradable materials. In this study, improvements of PHBV, mechanical, phase inversions, and rheological properties were investigated after blending with PLA in varying ratio’s. Three different blends of commercially available PLAs with 92–98% l-lactide units and one grade of PHB with 5% valerate content were blended using a micro-compounder at 175 °C. The composition of PHBV in blends ranged from 50% to 80%. With the addition of PLA, increases in the flexural strength and elastic modulus were observed for several blends, while minor to no changes were detected in the elongation at break and tensile strength as compared to pure PHBV material. Like many conventional plastics, the complex viscosity decreased with increasing rotational frequency due to decreasing entanglements and molecular weight. The complex viscosity with respect to time was very stable for the blends, but no improvements in the PHBV viscosity were observed with the addition of PLA at 170 °C. Three phase inversion models were used to predict the continuity of the blends, and the results showed both dual- and PLA-continuity phase for the blends. In summary, the mechanical results showed improvements in the tensile and flexural properties, while the rheological observation showed minor improvements in the complex viscosity for numerous concentrations.     

Photodegradation of biodegradable polyesters: A comprehensive study on poly(l-lactide) and poly(?-caprolactone)

The photodegradation of melt-crystallized and amorphous-made poly(l-lactide) (PLLA-C and PLLA-A, respectively) and cast-crystallized poly(?-caprolactone) (PCL) was investigated comprehensively for the periods up to 200 h using gel permeation chromatography, differential scanning calorimetry, tensile testing, and polarization optical microscopy. The photodegradation of PLLA and PCL films proceeds via a bulk erosion mechanism, indicating that UV penetrates the specimens with no significant reduction in its intensity, irrespective of the chemical structure and the crystallinity of biodegradable polyesters. The photodegradability of PCL chains was higher than that of PLLA chains. This strongly suggests that the chemical structure of the two sequential groups adjacent to the ester oxygen rather than the density of ester group is crucial to determine the photodegradability of biodegradable polyesters. Although PLLA chains are photodegradable even in the crystalline regions, their photodegradability is lower than that in the amorphous regions. The significant increase in weight-average molecular weight (M_w)/number-average molecular weight (M_n) was observed for PLLA-A and PCL films, even when the decrease in M_n by UV irradiation was small. Most of the tensile properties of PLLA and PCL films remained unchanged during UV irradiation, while solely the elongation at break of PCL film significantly decreased. This result reflects that among the tensile properties the elongation at break was most sensitive to the change in molecular characteristics of biodegradable polyesters by UV irradiation. The contrast between bright and dark parts of Maltese crosses remained unchanged for the spherulites in PLLA-C and PCL films even after UV irradiation for 200 h. This result exhibits that the cleaved fraction of the tie chains was too low to cause the traceable disorientation of lamellae.     

Curcumin‐loaded biodegradable polyurethane scaffolds modified with gelatin using 3D printing technology for cartilage tissue engineering

We described the curcumin‐loaded biodegradable polyurethane (PU) scaffolds modified with gelatin based on three‐dimensional (3D) printing technology for potential application of cartilage regeneration. The printing solution of poly(ε‐caprolactone) (PCL) triol (polyol) and hexamethylene diisocyanate (HMDI) in 2,2,2‐trifluoroethanol was printed through a nozzle in dimethyl sulfoxide phase with or without gelatin. The weight ratio of HMDI against PCL triol was varied as 3, 5, and 7 in order to evaluate its effect on the mechanical properties and biodegradation rate. A higher ratio of HMDI resulted in higher mechanical properties and a lower biodegradation rate. The use of gelatin increased the mechanical properties, biodegradation rate, and curcumin release due to the surface cross‐linking, nanoporous structure, and surface hydrophilicity of the scaffolds. In vitro study revealed that the released curcumin enhanced the proliferation and differentiation of chondrocyte. The 3D‐printed biodegradable PU scaffold modified with gelatin should thus be considered as a potential candidate for cartilage regeneration.     

Thermal and mechanical properties of poly(3-hydroxybutyrate-co-3-hydroxyvalerate) plasticized by biodegradable soybean oils

The effects of soybean oil (SO) and epoxidized soybean oil(ESO) as biodegradable plasticizers for poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) were studied using thermal and mechanical analyses. PHBV/SO and PHBV/ESO blends were prepared by evaporating solvent from blend solutions. The levels of additive in the blend varied from 5% to 30%. As a plasticizer for PHBV, ESO was more effective than SO in depression of the glass transition temperature as well as in increasing the elongation at break and the impact strength of the films with increasing levels of additive. Biodegradation of the plasticized PHBV films was carried out by accelerated compost method. The degradation rates of the blend films with SO or ESO were found to be faster than that of PHBV film. From the thermogravimetric analysis, it was found that the thermal reaction between the epoxide groups of ESO and PHBV fragments with carboxylic chain ends, occurred during the degradation of PHBV/ESO blends.