Fatigue testing of implantable specimens: Effect of sample size and branching on the dynamic fatigue properties of polyisobutylene-based biomaterials

Impact of uniaxial tensile fatigue on the evolution of microscopic and mesoscopic structure of carbon black filled natural rubber

This investigation addresses the evolution of the microscopic and mesoscopic structures distribution, and micro-defects of carbon black (CB) filled natural rubber (NR) under uniaxial tensile condition during the fatigue process. NR was filled with three different grades of CB in order to understand the impact of the structural degree and specific surface areas of CB and fatigue degree on the Payne effect. It was found that the Payne effect was initially suppressed and then enhanced by increasing the degree of fatigue. The decrease of the storage modulus in the low strain area was attributed to the CB network destruction and the breakdown of the matrix cross-linking network in the early fatigue stage. However, by further increasing the degree of fatigue, the spatial rearrangement of CB aggregates with the orientation of molecular chains between adjacent CB aggregates will results in mechanical reinforcement before the appearance of micro-defects. Moreover, it has been demonstrated that the structural degree of CB has a stronger impact on the mesoscopic structures than the specific surface area of CB during the tensile fatigue process.

RUBBER CITY GIRL: THE PATH TO THE GOODYEAR MEDAL

An overview of my 40-year career will be provided, spanning both industry and academe, and two continents. During my industrial years at LANXESS (formerly the Rubber Division of Bayer), I solved long-standing (10-yr) major manufacturing problems related to Taktene-55 and developed on-line and off-line process control tools that are still in operation. I also developed new technologies (bimodal butyl, one-step halobutyl, branched butyl, liquid carbon dioxide process) that resulted in patents. After transferring to academe, I continued the development of new polyisobutylene-based materials. I have held the Bayer (LANXESS) Industrial Research Chair for 12 yr, working closely with the rubber industry. My most important accomplishments include developing advanced elastomers and thermoplastic elastomers for health care, enzyme-catalyzed polymer functionalization, a “green” synthesis of disulfide polymers and gels, and research into natural rubber biosynthesis. Poly(styrene-isobutylene-polystyrene) is used in a Food and Drug Administration–approved drug-eluting stent, implanted in more than six million patients, saving lives. The recently patented poly(alloocimene-isobutylene-alloocimene) is also a potential biomaterial and also a potential halogen-free halobutyl rubber. I will also discuss my adventure of a field experiment at a Brazilian Hevea plantation to verify our laboratory discovery that the rubber content of Hevea latex can be increased by 20–50% using a special method of tapping. My goal now is creating safer breast implants with cancer-fighting and healing properties. I am proud that the Rubber World trade journal listed me among the 125 inventors that influenced rubber technology in a profound way. I thank my family, Professor Joseph P. Kennedy, and Dr. Adel Halasa for their mentorship and support.

Highly hydrophobic electrospun fiber mats from polyisobutylene-based thermoplastic elastomers

This paper is the first report of electrospinning neat polyisobutylene-based thermoplastic elastomers. Two generations of these materials are investigated: a linear poly(styrene-b-isobutylene-b-styrene) (L_SIBS) triblock copolymer and a dendritic poly(isobutylene-b-p-methylstyrene) (D_IB-MS), also a candidate for biomedical applications. Cross-polarized optical microscopy shows birefringence, indicating orientation in the electrospun fibers, which undergo large elongation and shear during electrospinning. In contrast to the circular cross section of L_SIBS fibers, D_IB-MS yields dumbbell-shaped fiber cross sections for the combination of processing conditions, molecular weight, and architecture. Hydrophobic surfaces with a water contact angle as high as 146 ± 3° were obtained with D_IB-MS that had the noncircular fiber cross section and a hierarchical arrangement of nano- to micrometer-sized fibers in the mat. These highly water repellent fiber mats were found to serve as an excellent scaffold for bovine chondrocytes to produce cartilage tissue.