Uwe Gohs

Effect of Electron Beam Irradiation on Biomechanical Properties of Patellar Tendon Allografts in Anterior Cruciate Ligament Reconstruction

Background: Sterilization of anterior cruciate ligament (ACL) allografts is an important prerequisite to prevent disease transmission. However, mechanical tissue properties are compromised by most current sterilization procedures, so that uncompromised sterilization of allografts is difficult to achieve. Hypothesis/Purpose: The aim of this study was to evaluate the effect of the novel electron beam sterilization procedure on the biomechanical properties of human patellar tendon allografts at various irradiation dosages. Electron beam sterilization may be an appropriate alternative to gamma sterilization. Study Design: Controlled laboratory study. Methods: Thirty-two human 10-mm wide bone-patellar tendon-bone grafts were randomized into 4 groups of sterilization with 15, 25, or 34 kGy of electron beam irradiation, respectively. The grafts’ biomechanical properties were evaluated at time zero. Unsterilized grafts functioned as controls. Biomechanical properties were analyzed during cyclic and load-to-failure testing. Results: Strain and cyclic elongation response showed no significant differences between the groups. Electron beam irradiation had no significant effect on stiffness and failure load with the exception of 34 kGy, which resulted in a significant decrease in failure load (1300.6 ± 229.2 N) compared with unsterilized grafts (1630.5 ± 331.1 N). Conclusion: This study showed that electron beam might be an appropriate alternative in sterilization of patellar tendon allografts with minimal effect on mechanical properties of tendon grafts in vitro. Future studies will have to evaluate the effect of the process on the biological properties of allografts in vitro and in vivo. Clinical Relevance: Terminal sterilization of patellar tendon allografts with electron beam irradiation can ensure higher safety of transplanted grafts and hence improve patient safety and acceptance.

Method for Simultaneously Improving the Thermal Stability and Mechanical Properties of Poly(lactic acid): Effect of High-Energy Electrons on the Morphological, Mechanical, and Thermal Properties of PLA/MMT Nanocomposites

Nanocomposites derived from poly(lactic acid) (PLA) and organically modified montmorillonite (oMMT) have been cross-linked by high-energy electrons in the presence of triallyl cyanurate (TAC). The morphology of untreated and cross-linked PLA/MMT nanocomposites was characterized by wide-angle X-ray scattering (WAXS) and transmission electron microscopy (TEM). This treatment can improve both the thermal stability and the glass-transition temperatures of the PLA nanocomposites (e.g., PLA-MMT-TAC 30kGy, 50kGy, and 70kGy) because of the formation of cross-linking structures in the nanocomposites that will considerably reduce the mobility of polymers. Interestingly, at relatively low irradiation doses (e.g., 30 and 50 kGy) a good balance between tensile strength and elongation at break for the PLA nanocomposites could be achieved. These mechanical properties are superior to those of pure PLA. Therefore, combining nanotechnology and electron beam cross-linking is a promising new method of simultaneously improving the mechanical properties (toughness and tensile strength) and thermal stability of PLA.

Rheological, morphological and mechanical investigations on ethylene octene copolymer toughened polypropylene prepared by continuous electron induced reactive processing

We prepared ethylene octene copolymer (EOC) toughened polypropylene (PP) by continuous electron induced reactive processing (EIReP) as well as investigated its rheological, morphological and mechanical properties. A time temperature superposition (TTS) method was utilized in order to investigate the specific thermo-rheological behavior of these PP/EOC blends. At a low concentration of EOC, a reduced blend viscosity was found. In contrast, the blend viscosity increases at higher concentrations of EOC in comparison to virgin PP. The differences in the molecular architecture of EOC and PP as well as the specific interfacial properties of the PP/EOC blend lead to this behavior. In addition, EIReP modified samples showed lower viscosity than their non-modified counterparts. This reduction of the absolute value of complex viscosity was related to the degradation of the PP phase. In EIReP modified samples an enhancement of the storage modulus at low frequencies was attributed to grafting at the interface and crosslinking of the dispersed EOC phases. All investigations of the thermo-rheological properties showed that TTS holds for the EIReP modified and non-modified blends. Using SEM micrographs, the effect of EIReP and blend ratio on the microstructure of toughened PP was studied. Finally, we discussed the origins of the differences of EOC toughened PP in tensile and impact experiments as well as proposed a micro-mechanism based on the investigation of thermal properties and considering molecular effects of EIReP on polymers.

Inactivation Effect of Standard and Fractionated Electron Beam Irradiation on Enveloped and Non-Enveloped Viruses in a Tendon Transplant Model

Background: For increasing allograft tendon safety in reconstructive surgery, an effective sterilization method achieving sterility assurance including viruses without impairing the grafts properties is needed. Fractionated Electron Beam (Ebeam) has shown promising in vitro results. The proof of sufficient virus inactivation is a central part of the process validation. Methods: The Ebeam irradiation of the investigated viruses was performed in an optimized manner (oxygen content < 0.1%, –78 °C). Using principles of a tendon model the virus inactivation kinetics for HIV-2, HAV, pseudorabies virus (PRV) and porcine parvovirus (PPV) were calculated as TCID50/ml and D10 value (kGy) for the fractionated (10 × 3.4 kGy) and the standard (1 × 34 kGy) Ebeam irradiation. Results: All viruses showed comparable D10 values for both Ebeam treatments. For sufficient virus titer reduction of 4 log10 TCID50/ml, a dose of 34 kGy of the fractionated Ebeam irradiation was necessary in case of HIV-2, which was the most resistant virus investigated in this study. Conclusion: The fractionated and the standard Ebeam irradiation procedure revealed comparable and sufficient virus inactivation capacities. In combination with the known good biomechanical properties of fractionated Ebeam irradiated tendons, this method could be a safe and effective option for the terminal sterilization of soft tissue allografts.

Melt Spinning of Poly(3‐hydroxybutyrate) for Tissue Engineering Using Electron‐Beam‐Irradiated Poly(3‐hydroxybutyrate) as Nucleation Agent

Electron-beam-irradiated poly(3-hydroxybutyrate) was used as a nucleating agent for poly(3-hydroxybutyrate) in a melt-spinning process. Molecular data and thermal properties of the irradiated samples were determined. The thermal properties of the nucleated melts were determined to assess the influence of the nucleation agents, and then spinning tests were carried out. Thermal and textile properties of the spun fibers were also determined. Estimations of the improvement of the crystallization in the spinline and of the inhibition of secondary crystallization in the fibers from the use of the described blood-compatible nucleation agents are given.

Variable structural colouration of composite interphases

Variable structural colouration results in brilliant colour changes in nature, due to the interaction of light with periodic photonic nanostructures. We report the observations of variable structural colouration from red, orange, yellow to green in a composite interphase region. By overlapping graphene nanoplatelets (GNPs) with ordered and disordered features using a special deposition approach, unique “fish scale” like structures are achieved. Variable structural colouration is observed through the mechanical tuning of fine parallel multilayers. Moreover, the method with incorporated variable structural colouration and electrical sensing functionality brings a first valuable step towards danger rating and the early warning of microcracks prior to a material’s failure, using a few colours for addressing danger, alarm and safety in a “traffic light” system.

Functionalized allylamine polyphosphate as a novel multifunctional highly efficient fire retardant for polypropylene

In this study, an efficient novel allylamine polyphosphate (AAPP) as a flame retardant (FR) crosslinker is used to improve the thermal stability of flame retarded polypropylene (PP) composites under electron beam treatment. First, a multifunctional AAPP has been designed and synthesized via a simple ion exchange reaction of the common ammonium polyphosphate (APP). AAPP was mixed with PP via a twin-screw extruder to prepare a series of flame retarded PP composites. Afterwards these composites were irradiated with high energy electrons in order to increase their thermal stability. The results showed an increased LOI value of PP/AAPP composites and effective melt dripping resistance in the UL-94 test in comparison with traditional PP/ammonium polyphosphate (APP) composites. Moreover, CC data like the heat release rate (HRR), total heat release (THR), smoke production rate (SPR), and total smoke production (TSP) showed that AAPP had a much better contribution to the flame retardation of PP than APP. Besides, AAPP provided an excellent quality of char residue in the combustion stage due to its P–N–C and P–O–C structures. Moreover, the environment-friendly electron beam technology was an efficient approach to improve the thermal stability of these multifunctional flame retarded PP composites without the use of additional stabilizers. This innovative idea may be expanded to other polymer systems to develop high performance polymer composites by environment-friendly electron beam technology.

Process induced morphology of irradiated HD-PE

The preparation of cross-linked polyethylene with high energy electrons is a well-known and used method to change material properties [1-6]. A new developed technique called “Electron induced reactive processing” simultaneously combines polymer modification with high energy electrons and melt mixing processes [7-13]. In the case of polyethylene, this novel technique leads to exceptional mechanical properties. Definitely, these properties depend on the molecular architecture as well as the morphological characteristics of polyethylene after the electron treatment.In this work we concentrate on the morphological changes of high density polyethylene generated by using state of the art high energy electron treatment in the solid state compared with high density polyethylene modified with the electron induced reactive processing.

Online Structural-Health Monitoring of Glass Fiber-Reinforced Thermoplastics Using Different Carbon Allotropes in the Interphase

An electromechanical response behavior is realized by nanostructuring the glass fiber interphase with different highly electrically conductive carbon allotropes like carbon nanotubes (CNT), graphene nanoplatelets (GNP), or conductive carbon black (CB). The operational capability of these multifunctional glass fibers for an online structural-health monitoring is demonstrated in endless glass fiber-reinforced polypropylene. The electromechanical response behavior, during a static or dynamic three-point bending test of various carbon modifications, shows qualitative differences in the signal quality and sensitivity due to the different aspect ratios of the nanoparticles and the associated electrically conductive network densities in the interphase. Depending on the embedding position within the glass fiber-reinforced composite compression, shear and tension loadings of the fibers can be distinguished by different characteristics of the corresponding electrical signal. The occurrence of irreversible signal changes during the dynamic loading can be attributed to filler reorientation processes caused by polymer creeping or by destruction of electrically conductive paths by cracks in the glass fiber interphase.

Surface Characterization of Electron Irradiated Polymer Brushes

Abstract Polymer brushes are representing a versatile tool to adjust and control surface phenomena like wetting, adsorption and adhesion. Moreover, certain complementary surface modification methods can support improving their intended applications. A promising strategy is the combination of the grafting-to method under initiator and solvent free conditions with an additional electron-beam irradiation step which can lead to polymer brushes with high-selective properties. The experiments were focused on the investigation of the surface reactions taking place during the dose-dependent irradiation of the thin polymer brush layers with the aim to modify their properties. A comprehensive and detailed study of the initiated functionalization reactions associated with their influence on the alteration of surface properties of different homo and binary polymer brush layers was performed using sensitive surface characterization techniques such as XPS, contact angle measurements, and ellipsometry.