Tailor-Made Vinylogous Urethane Vitrimers Based on Binary and Ternary Block and Random Copolymers: An Approach toward Reprocessable Materials

Vitrimers are promising reprocessable materials. To tune their properties, microphase separated block copolymers as backbones play an essential role in the thermal and mechanical properties of the resulting nanostructured networks. In this study, various narrow disperse di- and triblock copolymers containing a hydroxyethyl methacrylate block and, for comparison, random copolymers of the same comonomers are synthesized in a controlled manner by photoiniferter reversible addition-fragmentation chain transfer polymerization. Subsequently, the copolymers are modified by acetoacetate groups and cross-linked with diamines. After curing, the di- and triblock copolymer-based vitrimers exhibit excellent thermal and mechanical properties compared to random ones; moreover, their characteristic properties can be adjusted by different types and amounts of diamines. As the transamination reaction is a thermoreversible exchange reaction, the resulting vitrimers are reprocessable and therefore are recyclable materials. The combining of two of these classes of soft materials, namely vitrimers and block copolymers, leads to materials with a broad spectrum of adjustable mechanical properties for various applications with an improved end-of-life management, when compared to permanently crosslinked thermosets.     

Mechanical and microstructural properties of polycaprolactone scaffolds with one-dimensional,two-dimensional,and three-dimensional orthogonally oriented porous architectures produced by selective laser sintering

This article reports on the experimental determination and finite element modeling of tensile and compressive mechanical properties of solid polycaprolactone (PCL) and of porous PCL scaffolds with one-dimensional, two-dimensional and three-dimensional orthogonal, periodic porous architectures produced by selective laser sintering (SLS). PCL scaffolds were built using optimum processing parameters, ensuring scaffolds with nearly full density (>95%) in the designed solid regions and with excellent geometric and dimensional control (within 3–8% of design). The tensile strength of bulk PCL ranged from 10.5 to 16.1 MPa, its modulus ranged from 343.9 to 364.3 MPa, and the tensile yield strength ranged from 8.2 to 10.1 MPa. These values are consistent with reported literature values for PCL processed through various manufacturing methods. Across porosity ranged from 56.87% to 83.3%, the tensile strength ranged from 4.5 to 1.1 MPa, the tensile modulus ranged from 140.5 to 35.5 MPa, and the yield strength ranged from 3.2 to 0.76 MPa. The compressive strength of bulk PCL was 38.7 MPa, the compressive modulus ranged from 297.8 to 317.1 MPa, and the compressive yield strength ranged from 10.3 to 12.5 MPa. Across porosity ranged from 51.1% to 80.9%, the compressive strength ranged from 10.0 to 0.6 MPa, the compressive modulus ranged from 14.9 to 12.1 MPa, and the compressive yield strength ranged from 4.25 to 0.42 MPa. These values, while being in the lower range of reported values for trabecular bone, are the highest reported for PCL scaffolds produced by SLS and are among the highest reported for similar PCL scaffolds produced through other layered manufacturing techniques. Finite element analysis showed good agreement between experimental and computed effective tensile and compressive moduli. Thus, the construction of bone tissue engineering scaffolds endowed with oriented porous architectures and with predictable mechanical properties through SLS is demonstrated.     

Mechanical properties and biocompatibility of melt processed,self-reinforced ultrahigh molecular weight polyethylene

The low efficiency of fabrication of ultrahigh molecular weight polyethylene (UHMWPE)-based artificial knee joint implants is a bottleneck problem because of its extremely high melt viscosity. We prepared melt processable UHMWPE (MP-UHMWPE) by addition of 9.8 wt% ultralow molecular weight polyethylene (ULMWPE) as a flow accelerator. More importantly, an intense shear flow was applied during injection molding of MP-UHMWPE, which on one hand, promoted the self-diffusion of UHMWPE chains, thus effectively reducing the structural defects; on the other hand, increased the overall crystallinity and induced the formation of self-reinforcing superstructure, i.e., interlocked shish-kebabs and oriented lamellae. Aside from the good biocompatibility, and the superior fatigue and wear resistance to the compression-molded UHMWPE, the injection-molded MP-UHMWPE exhibits a noteworthy enhancement in tensile properties and impact strength, where the yield strength increases to 46.3 ± 4.4 MPa with an increment of 128.0%, the ultimate tensile strength and Young's modulus rise remarkably up to 65.5 ± 5.0 MPa and 1248.7 ± 45.3 MPa, respectively, and the impact strength reaches 90.6 kJ/m². These results suggested such melt processed and self-reinforced UHMWPE parts hold a great application promise for use of knee joint implants, particularly for younger and more active patients. Our work sets up a new method to fabricate high-performance UHMWPE implants by tailoring the superstructure during thermoplastic processing.     

Fast Degradable and Thermally Conductive Silicone Rubber Vitrimer with Low Dielectric and UV-Shielding Properties

Silicone rubbers are widely employed in various fields such as electronics, electrical engineering, mobile communications, aerospace, and automotive industries. However, silicone rubbers are typically challenging to reprocess and degrade. Moreover, with the advancement of technology, higher demands are placed on its thermal conductivity and dielectric properties. In this study, diglycidyl ether terminated polydimethylsiloxane is cured by 4,4′-dithiodibutyric acid which contains dual dynamic covalent disulfide and ester bonds with triazobicyclodecene as the ester exchange catalyst to prepare silicone rubber vitrimers (SRVs) through a casting method. The SRVs demonstrate a relatively higher intrinsic thermal conductivity of 0.26 W (m⁻¹ K⁻¹) compared to ≈0.20 W (m⁻¹ K⁻¹) of conventional silicone rubber. Besides, the SRVs exhibit very low and stable dielectric constant and dielectric loss at both low and high frequencies (X-band). The lowest dielectric constant and dielectric loss tangent at 10 GHz are 2.75 and 0.0650, respectively. Besides, the dual dynamic covalent bonds enable the SRVs to have excellent reprocessability and fast degradability. Moreover, the SRVs reveal UV-shielding capability, as the transmittance of the SRVs is 0% from 200 to 400 nm of UV light.     

Finite element analysis of a four-unit all-ceramic fixed partial denture

All-ceramic restorations are known to be prone to brittle fracture. However, a previously performed in vitro study indicates that four-unit fixed partial dentures (FPDs) with a zirconia framework are sufficiently strong to withstand occlusal forces in the posterior region. The aim of this study was to determine the stress distribution in such a four-unit FPD made of yttria-stabilized polycrystalline tetragonal zirconia (Y-TZP), under an occlusal load. A three-dimensional finite element model was constructed and a stress analysis performed with a force of 1630 N applied at the centre of the middle connector area. The location of maximum tensile stress according to finite element analysis coincided with the fracture origin of all 10 specimens fractured within the previous in vitro study. The maximum tensile stress in the area of the middle connector amounted to 633 MPa. It increased with the load being applied from the oral towards the buccal side (648 MPa) and decreased with the load being applied from the buccal towards the oral side (570 MPa). These stresses are of the same order as the flexural strength of Y-TZP, determined under standardized test conditions to be 600–1000 MPa. The model presented is intended to be used for further investigations, including thermally induced stresses during veneering.     

Non‐Volatile Glycerin Gel Enhanced by Sub‐5 nm Particles with Super Elasticity,Recoverability, and High Temperature Resistance

A gel material that can be applied to industry needs to fulfill two requirements: excellent mechanical properties and high temperature resistance. Previous research developed a hydrogel enhanced by sub‐5 nm particles, with excellent mechanical properties. While its application in the open environment is still limited by the volatilization of inner moisture, in this research, a non‐volatile gel (NV gel) enhanced by 5‐nm spherulites is manufactured. The NV gel remains stable after staying at 90 °C for 24 h. Meanwhile, being enhanced by sub‐5 nm nanospherulites, the NV gel shows good mechanical properties: with 200 ppm nanoparticle content, the tensile strength reaches 814 kPa and the compressive stress is 173.41 MPa at a recoverable 99% strain. The high temperature resistance is characterized by thermogravimetric analysis (TGA) and mechanical testing after thermal treatment. Transmission electron microscopy, scanning electron microscopy, Fourier transform infrared spectroscopy, time of flight secondary ion mass spectrometry, and thermogravimetric analysis are used to evaluate the microstructure of NV gel. Possessing non‐volatile and good mechanical properties at the same time, this NV gel becomes very suitable for fulfilling the application requirement as an engineering material.     

Novel Bisphosphonated Methacrylates: Synthesis,Polymerizations, and Interactions with Hydroxyapatite

Five novel methacrylates containing either bisphosphonate ( 1 and 2 ), bisphosphonic acid (3), carboxylic acid (4) , or both bisphosphonic and carboxylic acid together (5) , are synthesized. The monomers 1 and 2 are synthesized by the reactions of tetraethyl 1‐hydroxyethane‐1,1‐diyl­diphosphonate with ethyl α‐bromomethacrylate and tert‐butyl α‐bromomethacrylate; the same procedure fails with tetraethyl hydroxy(phenyl)methylenediphosphonate. 1 is converted to 3 by hydrolysis with trimethylsilyl bromide (TMSBr), and 2 is converted to 4 by hydrolysis with trifluoroacetic acid (TFA). Monomer 5 is obtained by hydrolysis of 2 first with TMSBr and then with TFA. The hydrolytic stability, the properties of the copolymerizations with commercial dental monomers, and HAP interactions make these monomers promising candidates for dental adhesives.

     

Synthesis and Property of an Organosilicon Polyurethane Acrylate Prepolymer Containing Disulfide Bonds for Photopolymerization

Photocurable organosilicon polyurethane acrylate materials combine the merits of both polyurethane and organosilicon and have become the most widely used class of photocurable resins due to the advantages of easy preparation and performance tunability, but they suffer from serious volume shrinkage and difficult degradation. In this article, an organosilicon polyurethane acrylate prepolymer (SSiPUA) containing disulfide bonds is designed and synthesized. The prepolymer exhibits good ability to photopolymerize and reduce the volume shrinkage. The final double bond conversion (DBC) of the system with SSiPUA reaches 92%, and the volume shrinkage is decreased to 4.9% that is much less than that (13.9%) without SSiPUA. Besides, with the increase of SSiPUA content within a certain range, the hydrophobicity, heat resistance, the tensile strength, and the elongation at break of the photocured films gradually increase. The water contact angle, initial decomposition temperature, the tensile strength, and the elongation at break reach up to 93°, 282 °C, 1.8 MPa, and 576.2%, respectively. However, the glass transition temperature is reduced with the increase of SSiPUA content owing to the excellent flexibility of polysiloxane chain segments. More significantly, the SSiPUA containing disulfide bonds endows the photocured film with good degradation properties.     

Influence of preparation techniques to the strength of the bone–cement interface behind the flange in total knee arthroplasty

IntroductionRecent clinical studies show an increased risk of femoral loosening in high-flexion TKA. Loosening seems to occur behind the anterior flange, which is covering both cancellous bone and cortical bone. It is important to optimize the interface strength between cement and both bone types to increase femoral component fixation. This study was performed to determine the cement–cortical bone interface strength for different preparation techniques.Material and methodsA pure tensile and shear force was applied to interface specimens. The cortical surface area was prepared in three different ways: (1) Unprepared cortical bone with periosteum; (2) Periosteum removed and cortical bone roughened with a rasp; (3) Periosteum removed and three Ø3.2 mm holes drilled through the cortex. A reference group was added with a cancellous bone surface.ResultsThe interface tensile strength of Group 1 was 0.06 MPa and the shear strength was 0.05 MPa. For Group 2, respectively 0.22 MPa and 1.12 MPa. For Group 3, respectively 1.15 MPa and 1.77 MPa. For cancellous bone a tensile strength of 1.79 MPa and a shear strength of 3.85 MPa were measured.ConclusionThe strength of the cement–cancellous bone interface is superior to the cement–cortical bone interface. The preferred preparation technique of the cortical bone is to remove all the periosteum and drill holes through the cortex within the footprint of the anterior flange, to prevent cortical weakening.Clinical relevanceUltimately, the proposed preparation technique will lead to longer implant survival, particularly for prostheses which are used in the high-flexion range.     

Cytoxicity,dynamic and thermal properties of bio-based rosin-epoxy resin/ castor oil polyurethane/ carbon nanotubes bio-nanocomposites

In order to prepare bio-nanocomposites with no-cytotoxicity, the rosin-based epoxy resin (MPAER) and castor oil-based polyurethane (COPU) were synthesized and carbon nanotubes (CNTs) was used to enhance the properties of curing MPAER/COPU materials. The curing reaction, dynamic mechanical and thermal properties of this system were characterized by FTIR, NMR, DMA, TG et al. The cytotoxicity of materials is evaluated for HeLa cells using a MTT cell-viability assay. The results showed that COPU can cure MPAER and CNTs can increase effectively the properties of MPAER/COPU nanocomposites. The Tg of MPAER/COPU/CNTs has the highest value when CNTs content is 0.4 wt%, which is 52.4 °C higher than the pure MPAER/COPU. Thermal stability of the nanocomposites is enhanced by the addition of CNTs, the initial decomposition temperature Td5 of the sample No. 0.4 has increased from 284.5 to 305.2 °C, which is 20.7 °C higher than No. 0. The impact strength of the No. 0.4 film is 15 kg cm higher than the pure resin system. The survival rate of HeLa cells to the products is greater than 90% within 48 and 72 h, which demonstrate that this material has excellent biocompatibility and no obvious cytotoxicity for HeLa cells, which may be used in the medical treatment.     

Sustainable Polyurethane Networks with High Self-Healing and Mechanical Properties Based on Dual Dynamic Covalent Bonds

Hydroxy-terminated polybutadiene (HTPB) based polyurethanes (PU) networks are broadly applied in industry and aviation, however, their nonrecyclability leads to the waste of petroleum. In this work, a series of novel self-healing, weldable, and recyclable HTPB-based PU networks with dual reversible covalent bonds are fabricated by one-pot polycondensation. To shorten the relaxation time, dual reversible covalent bonds (disulfide bonds and boronic ester bonds) are incorporated into the HTPB-based PU networks. Meanwhile, to promote tensile strength, the rigid isocyanate and cross-link agent are introduced into the networks. Obtained HTPB-based PU network structures are characterized by FTIR, Raman, and DMA measurements. Obtained HHMB-4-20 network shows the best mechanical properties (tensile strength = 6.97 MPa, elongation at break = 302 %), and the mechanical properties almost can be recovered after welding/reprocessing by hot pressing. To satisfy the demands of industrial sustainability, the synthesis of PU networks with capabilities of reprocessing, self-healing, and welding is a feasible approach.     

Repair of Achilles tendon defect with autologous ASCs engineered tendon in a rabbit model

Adipose derived stem cells (ASCs) are an important cell source for tissue regeneration and have been demonstrated the potential of tenogenic differentiation in vitro. This study explored the feasibility of using ASCs for engineered tendon repair in vivo in a rabbit Achilles tendon model. Total 30 rabbits were involved in this study. A composite tendon scaffold composed of an inner part of polyglycolic acid (PGA) unwoven fibers and an outer part of a net knitted with PGA/PLA (polylactic acid) fibers was used to provide mechanical strength. Autologous ASCs were harvested from nuchal subcutaneous adipose tissues and in vitro expanded. The expanded ASCs were harvested and resuspended in culture medium and evenly seeded onto the scaffold in the experimental group, whereas cell-free scaffolds served as the control group. The constructs of both groups were cultured inside a bioreactor under dynamic stretch for 5 weeks. In each of 30 rabbits, a 2 cm defect was created on right side of Achilles tendon followed by the transplantation of a 3 cm cell-seeded scaffold in the experimental group of 15 rabbits, or by the transplantation of a 3 cm cell-free scaffold in the control group of 15 rabbits. Animals were sacrificed at 12, 21 and 45 weeks post-surgery for gross view, histology, and mechanical analysis. The results showed that short term in vitro culture enabled ASCs to produce matrix on the PGA fibers and the constructs showed tensile strength around 50 MPa in both groups (p > 0.05). With the increase of implantation time, cell-seeded constructs gradually form neo-tendon and became more mature at 45 weeks with histological structure similar to that of native tendon and with the presence of bipolar pattern and D-periodic structure of formed collagen fibrils. Additionally, both collagen fibril diameters and tensile strength increased continuously with significant difference among different time points (p < 0.05). In contrast, cell-free constructs failed to form good quality tendon tissue with fibril structure observable only at 45 weeks. There were significant differences in both collagen fibril diameter and tensile strength between two groups at all examined time points (p < 0.05). The results of this study support that ASCs are likely to be a potential cell source for in vivo tendon engineering and regeneration.     

Instantaneous changes in heart rate regulation due to mental load in simulated office work

The cardiac regulation effects of a mental task added to regular office work are described. More insight into the time evolution during the different tasks is created by using time–frequency analysis (TFA). Continuous wavelet transformation was applied to create time series of instantaneous power and frequency in specified frequency bands (LF 0.04–0.15 Hz; HF 0.15–0.4 Hz), in addition to the traditional linear heart rate variability (HRV) parameters. In a laboratory environment, 43 subjects underwent a protocol with three active conditions: a clicking task with low mental load and a clicking task with high mental load (mental arithmetic) performed twice, each followed by a rest condition. The heart rate and measures related to vagal modulation could differentiate the active conditions from the rest condition, meaning that HRV is sensitive to any change in mental or physical state. Differences between physical and mental stress were observed and a higher load in the combined task was observed. Mental stress decreased HF power and caused a shift toward a higher instantaneous frequency in the HF band. TFA revealed habituation to the mental load within the task (after 3 min) and between the two tasks with mental load. In conclusion, the use of TFA in this type of analysis is important as it reveals extra information. The addition of a mental load to a physical task elicited further effect on HRV parameters related to autonomic cardiac modulation.     

Vegetable oil thermosets reinforced by tannin–lipid formulations

Totally bio-based thermosetting polymers which are comparable to synthetic polyester thermosets have been prepared from copolymerization of condensed tannin–fatty acid esters with vegetable oils. Oxidative copolymerization of tannin linoleate/acetate mixed esters with linseed oil and tung oil produced polymer films ranging from soft rubbers to rigid thermosets. Tannin incorporation into the formulations was essential for the final product to achieve necessary mechanical strength. Films had ambient modulus values between 0.12 and 1.6 GPa, with glass transition temperatures ranging from 32 to 72 °C and calculated crosslink densities of 1020–57,700 mol m^?3. Film stiffness, T_g and crosslink density increase with greater tannin linoeate/acetate content due mainly to this tannin component providing rigidity through polyphenolic aromatic rings and unsaturated chains as crosslinking sites.     

Preparation of Silica Composite Vitrimers via One-Shot Transformation from Simple Polyesters

To solve the conventional problems of chemically cross-linked polymers, the vitrimer concept has attracted great attention because the associative bond-exchange nature in vitrimers provides sustainable functions. So far, various vitrimer designs have been reported using different polymer species with compatible bond exchange mechanisms. However, the biggest barrier for the practical application may be the elaborated functional group modification of the starting components and the limited availability of suitable monomers. As a much simpler preparation, recently, a one-shot preparation of vitrimers from commodity polyesters with no special reactive functional groups by blending and heating with tetra-functional epoxy molecules and base catalysts has been proposed. In this study, further one-shot preparation of composite vitrimers with silica nanoparticles (SNPs) is developed. The effects of SNPs on the cross-linking process and thermo/mechanical properties are first assessed, which reveals the formation of a bound rubber phase on the surfaces of the SNPs. The bound rubber phase also affects the bond exchange features of vitrimers, especially the distribution of relaxation time. Overall, the present facile preparation of composite vitrimers with enhanced mechanical properties could be a hint for practical application, whereas the knowledge on the unique relaxation behaviors of composite vitrimers should be beneficial in the fundamental sense.     

Correlation Between Tensile Strength and Collagen Content in Rat Skin. Effect of Age and Cortisol Treatment

Changes in skin during maturation and ageing as well as after treatment with cortisol acetate were studied in Sprague-Dawley rats. Mechanical parameters (ultimate load and tensile strength) were compared with biochemical parameters, i.e., collagen content and collagen fractions, as well as glycosaminoglycan content and glycosaminoglycan fractions (hyaluronic acid, chondroitin sulfates and heparin sulfate). The values of ultimate load and tensile strength as well as the total collagen and insoluble collagen content showed a biphasic curve during the life span, with a maximum at 4 months or 1 year. Using these parameters, maturation and ageing processes can be distinguished, whereas the other parameters changed only in one direction so that no differentiation between maturation and ageing can be made. Short term treatment with cortisol acetate induced a rise in ultimate load and tensile strength, whereas long term treatment resulted in a decrease in ultimate load and skin thickness and an Increase in tensile strength. Total collagen and insoluble collagen as well as the collagen ratio showed a rise similar to that of tensile strength.

Combining all groups in this study, an excellent correlation between the tensile strength of skin and the content of insoluble collagen was found, resulting in the conclusion that collagen, and not the glycosaminoglycans, is responsible for the tensile strength of rat skin.     

Physicochemical, mechanical, and biological properties of bone cements prepared with functionalized methacrylates

Bone cements prepared with methyl methacrylate (MMA) as a base monomer and either methacrylic acid (MAA) or diethyl amino ethyl methacrylate (DEAEMA) as comonomers were characterized in terms of curing behavior, mechanical properties, and their in vitro biocompatibility.The curing time and setting temperature were found to be composition dependent while the residual monomer was not greatly affected by the presence of either acidic or alkaline comonomers in the bone cements. For samples with MAA comonomer, a faster curing time and higher setting temperature were observed when compared to the cement with DEAEMA comonomer.In terms of mechanical properties, the highest compressive strength was exhibited by formulations containing MAA, while the highest impact strength was shown by the formulations prepared with DEAEMA. There were no differences observed between the two formulations for tensile, shear, and bending strength values. Similarly, fatigue crack propagation studies did not reveal differences with the addition of either DEAEMA or MAA.No differences were observed in the initial number of attached primary rat femur osteoblasts on the different bone cements and positive controls. However, after 48 h there was a reduced proliferation in the cells grown on bone cements containing MAA.     

Characterization of new acrylic bone cements prepared with oleic acid derivatives

Acrylic bone-cement formulations were prepared with the use of a new tertiary aromatic amine derived from oleic acid, and also by incorporating an acrylic monomer derived from the same acid with the aim of reducing the leaching of toxic residuals and improving mechanical properties. 4-N,N dimethylaminobenzyl oleate (DMAO) was used as an activator in the benzoyl-peroxide radical cold curing of polymethyl methacrylate. Cements that contained DMAO exhibited much lower polymerization exotherm values, ranging between 55 and 62 C, with a setting time around 16--17 min, depending on the amine/BPO molar ratio of the formulation. On curing a commercial bone cement, Palacosreg R with DMAO, a decrease of 20 C in peak temperature and an increase in setting time of 7 min were obtained, the curing parameters remaining well within limits permitted by the standards. In a second stage, partial substitution of MMA by oleyloxyethyl methacrylate (OMA) in the acrylic formulations was performed, the polymerization being initiated with the DMAO/BPO redox system. These formulations exhibited longer setting times and lower peak temperatures with respect to those based on PMMA. The glass transition temperature of the experimental cements were lower than that of PMMA cement because of the presence of long aliphatic chains of both activator and monomer in the cement matrix. Number average molecular weights of the cured cements were in the range of 1.2x10(5). PMMA cements cured with DMAO/BPO revealed a significant (p<0.001) increase in the strain to failure and a significant (p<0.001) decrease in Young's modulus in comparison to Palacosreg R, whereas ultimate tensile strength remained unchanged. When the monomer OMA was incorporated, low concentrations of OMA provided a significant increase in tensile strength and elastic modulus without impairing the strain to failure. The results demonstrate that the experimental cements based on DMAO and OMA have excellent promise for use as orthopaedic and/or dental grouting materials.     

Experimental modelling of aortic aneurysms: Novel applications of silicone rubbers

A range of silicone rubbers were created based on existing commercially available materials. These silicones were designed to be visually different from one another and have distinct material properties, in particular, ultimate tensile strengths and tear strengths. In total, eleven silicone rubbers were manufactured, with the materials designed to have a range of increasing tensile strengths from approximately 2 to 4 MPa, and increasing tear strengths from approximately 0.45 to 0.7 N/mm. The variations in silicones were detected using a standard colour analysis technique. Calibration curves were then created relating colour intensity to individual material properties. All eleven materials were characterised and a 1st order Ogden strain energy function applied. Material coefficients were determined and examined for effectiveness. Six idealised abdominal aortic aneurysm models were also created using the two base materials of the study, with a further model created using a new mixing technique to create a rubber model with randomly assigned material properties. These models were then examined using videoextensometry and compared to numerical results. Colour analysis revealed a statistically significant linear relationship (p < 0.0009) with both tensile strength and tear strength, allowing material strength to be determined using a non-destructive experimental technique. The effectiveness of this technique was assessed by comparing predicted material properties to experimentally measured methods, with good agreement in the results. Videoextensometry and numerical modelling revealed minor percentage differences, with all results achieving significance (p < 0.0009). This study has successfully designed and developed a range of silicone rubbers that have unique colour intensities and material strengths. Strengths can be readily determined using a non-destructive analysis technique with proven effectiveness. These silicones may further aid towards an improved understanding of the biomechanical behaviour of aneurysms using experimental techniques.     

Facile Synthesis of Fluorinated Polyacrylate Elastomer via Emulsion Polymerization Using Adjustable Amphiphilic Star Macro-RAFT Agent as Surfactant

Novel thermoplastic fluorinated polyacrylate films possessing excellent mechanical performance are prepared by emulsion polymerization latex using adjustable amphiphilic star macro-reversible addition-fragmentation chain-transfer (macro-RAFT) agent as surfactants in this work. First, star macro-RAFT agent equipped with six amphiphilic arms is synthesized via two-step RAFT polymerization of acrylic acid (AA) and 2,2,2-trifluoroethyl acrylate (TFEA) in the presence of hexa-functional RAFT agents. The surface activities of the as-synthesized amphiphilic star macro-RAFT agents in aqueous solutions are studied. Subsequently, various fluorinated polyacrylate latexes are obtained by conducting emulsion polymerization of 2,2,3,4,4,4-hexafluorobutyl acrylate (HFBA) and butyl acrylate (BA) using the amphiphilic star macro-RAFT agents as both RAFT agents and surfactants. The latex particle morphologies are studied by transmission electron microscope (TEM) and particle size is measured by dynamic light scattering (DLS). The effects of PAA segment length, HFBA/BA mole ratio, and TFEA segment length on the surface morphologies of the fluorinated polyacrylate films are illustrated by investigating the surface properties using water contact angle test and atomic force microscopy (AFM). Finally, the elastomeric films obtained by directly casting the prepared fluorinated polyacrylate latexes show excellent comprehensive properties such as tensile strength over 4 MPa, elongation at break ≈700%, permanent deformation below 25%. Water absorption test is also provided as a reference.