Thermoplastic Poly Ether Urethane Research Articles

Evaluation of 3D-printed bolus for radiotherapy using megavoltage X-ray beams

A radiotherapy bolus is a tissue-equivalent material placed on the skin to adjust the surface dose of megavoltage X-ray beams used for treatment. In this study, the dosimetric properties of two 3D-printed filament materials, polylactic acid (PLA) and thermoplastic polyether urethane (TPU), used as radiotherapy boluses, were investigated. The dosimetric properties of PLA and TPU were compared with those of several conventional bolus materials and RMI457 Solid Water. Percentage depth-dose (PDD) measurements in the build-up region were performed for all materials using 6 and 10 MV photon treatment beams on Varian linear accelerators. The results showed that the differences in the PDDs of the 3D-printed materials from the RMI457 Solid Water were within 3%, whereas those of the dental wax and SuperFlab gel materials were within 5%. This indicates that PLA and TPU 3D-printed materials are suitable radiotherapy bolus materials.

Reexamination of the microphase separation in MDI and PTMG based polyurethane: Fast and continuous association/dissociation processes of hydrogen bonding

Microphase separation and hard segment packing in polyurethanes remain areas of active research interest in order to optimize their performances. In this work, a commercial thermoplastic polyetherurethane (1180A, BASF) is used as a model system to investigate the packing of hard segments during microphase separation. Although DSC studies show several transitions during heating and cooling, no crystal structure is detected by XRD. Nevertheless, these endothermic and exothermic peaks should belong to the complicate hard/soft segment interaction and related structures. Time and temperature dependent FTIR spectra prove fast hydrogen bonding association/dissociation phenomena in the current system. We infer that such fast process can induce loosely or irregular packing of hard segments during cooling. On the other hand, the continuous change of degree of microphase separation with temperature implies different hard domain structures and stabilities at different temperatures. At high temperature, only hard domains with large size and compactly packed segments can survive. This is because the thermodynamic stability of hard domains is decided by the strength of hydrogen bonding and the size of hard domain, similar with classical description of ‘nucleation’. Morphological information obtained by fitting the SAXS curves proves the validity of the above model. Moreover, the significant difference in mechanical properties before and after thermal treatment can be explained by the microstructure model.

Effect of dose and temperature on the physical properties of an aliphatic thermoplastic polyurethane irradiated with an electron beam

The electron beam irradiation of a fully aliphatic thermoplastic polyetherurethane was carried out in air at doses ranging from 50 to 4000 kGy at room temperature and 100 °C and a dose rate of 5.1 kGy min−1. The effects of the irradiation on the chemical structure and the physical properties were studied. Gel was obtained already at the lower dose, increasing to almost 100% gel at the higher dose, with cross-linking predominating over chain scission. FTIR and DSC measurements proved that both, soft segment and hard segment, were affected by irradiation. Mechanical properties were adversely affected by irradiation mainly due to the cross-linking produced in the amorphous part of the material. Irradiation temperature did not have any significant effect except at the highest dose of 4000 kGy.

Fibroblastic response and surface characterization of O2-plasma-treated thermoplastic polyetherurethane

Injection-molded samples of thermoplastic polyetherurethane (TPU) were treated with low-temperature oxygen plasma for different processing times in order to enhance cellular attachment for a gastric implant. Its effects were investigated by contact angle measurement, surface topography, cytotoxicity and cell colonization tests. No significant changes were found in the surface roughness of plasma treatment with plasma treatment time of less than 5 min. Longer treatment showed significantly higher surface roughness. It seems that there was a link between the changes in contact angle and enhanced cell growth on the treated surface, although only for the range up to plasma treatment times of 3 min. Prolonged treatment times did not cause any major changes in the water contact angle, but strongly improved the number of growing cells on the surface. Plasma treatment for 3–7 min led to a twofold increase in the number of cells compared to untreated samples and did not significantly alter the WST-1 nor worsened the lactate dehydrogenase activity compared to the control. Thus, it appears that O2 plasma treatment is a suitable surface modification method for a gastric implant made of TPU in order to improve surface cell attachment where 3–7 min is the recommended treatment time.

Effect of different γ‐irradiation doses on cytotoxicity and material properties of porous polyether‐urethane polymer

Biomaterials respond to sterilization methods differently. Steam sterilization might decrease the performance of thermoplastic polyether-urethane (TPU); however, the effect of different gamma-radiation doses on this polymer is contradictory in present literature. The purpose of this study was to investigate the differences between irradiative doses in comparison with steam sterilization on a porous TPU scaffold produced by a new processing method. No significant differences in the surface chemical structure were found with attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR) analysis when comparing with the sterilization methods. The molecular weight (M(w)) had a net increase from 11.5 +/- 0.039 to 13.2 +/- 0.072 kDa by gamma-sterilization from 10 to 60 kGy. The samples that were irradiated (>60 kGy) had also an increase in polydispersity index (PDI; 1.45 +/- 0.007) in comparison with the nonsterile ones (1.31 +/- 0.017), which indicate branching. Liquid chromatography/mass spectroscopy (LC/MS) analysis showed that there was a correlation between the concentration of the breakdown product, methyl dianiline, and cytotoxicity. The concentration of this compound was found to be four times higher in steam-sterilized sample (1.3 +/- 0.01 ppb) compared with that of the polymer sample gamma-sterilized at 10 kGy (0.3 +/- 0.01 ppb). The cytotoxicity of TPU was found to decrease with higher radiation doses, and was significantly higher for the steam-sterilized samples. It is recommended that TPU produced with the described foaming method should be sterilized by gamma-irradiation at 25 kGy or higher doses.

MuCell® technology for injection molding: A processing method for polyether-urethane scaffolds

MuCell® injection molding technology which takes supercritical carbon dioxide as blowing agent was used as processing method to generate porous samples made of thermoplastic polyether-urethane. The influence of processing parameters on the morphology of the porous structures was examined by mercury intrusion porometry and image analysis. An increase in injection speed and content of CO2 in the polymer melt decreased pore sizes whereas an increase in the percentage of weight reduction increased pore sizes. Polyether-urethane samples with porosities of 70% and pore sizes from 184 to 1102 μm were observed. Interconnective pore sizes ranged from 40 to 275 μm.

Biostability of polyether-urethane scaffolds: A comparison of two novel processing methods and the effect of higher gamma-irradiation dose

This article deals with enzyme-induced biodegradation behavior of thermoplastic polyether-urethane (TPU). Porous scaffolds were processed by a new foaming method applied in hot pressing and injection molding. The scaffolds were subsequently gamma sterilized. The samples were incubated with cholesterol esterase (CE) for 28 days to simulate an enzymatic degradation order to assess polymer biostability. The main focus of degradation products was the most toxic one: methylene dianiline (MDA). LC/MS was used to separate the breakdown products and to identify possible MDA amounts. The results showed that (a) the hot-pressed sample released an MDA amount almost twice as large (0.26 ng +/- 0.008) as that of the injection-molded samples (0.15 ng +/- 0.003) after incubation with enzyme activity in the physiological range, and (b) a tenfold increase in CE activity revealed considerably higher MDA amounts (7540.0 ng +/- 0.004). This enzyme concentration is physiologically unlikely, however, but may occur for extreme high inflammation behavior. Even for extremely high levels of CE enzyme, the scaffold will not discharge MDA above toxic levels. The injection-molded samples sterilized at 25 kGy seem to represent the most promising processing method. Therefore, the new injection-molding foaming process of polyether-urethane can be considered appropriate for use as a biomaterial.