1. CORROSION AND ELECTROCHEMISTRY
A major concern in today’s metallic implants is the potential for corrosion of the implant alloys. The major alloys of concern include titanium, cobalt-chromium, stainless steel, magnesium, zirconium and tantalum alloys. These systems have passive oxide films on their surface that are susceptible to mechanical disruption and repassivation processes. When mechanically disrupted, the corrosion reactions of these surfaces becomes extremely significant for a transient time period that can give rise to many before known or understood ways. The biological system in which metallic biomaterials are placed is also a highly complex electrochemically active milieu that can affect and be affected by the redox processes at the metal surface. The Gilbert Lab has a major focus on the corrosion and electrochemical interactions of metallic biomaterials with the biological system that includes basic mechanistic studies of bio-tribocorrosion, oxide thin film electrochemical behavior, and biological interactions.
2. CELL AND PROTEIN-SURFACE INTERACTIONS
The interaction of proteins and cells with biomaterials surfaces represents a core focus area for many research programs. In the Gilbert Lab, we approach these subjects with the view of how metal surfaces can interact with cells and proteins in the context of ongoing electrical and electrochemical phenomena present.
3. RETRIEVAL AND FAILURE ANALYSIS
The mechanism of mechanically assisted crevice corrosion (or fretting crevice corrosion) is now one of the major concerns in orthopedic today. The Gilbert Lab has had extensive efforts in understanding corrosion and failure modes associated with metallic biomaterials. This has included, in collaboration with JJ Jacobs and RM Urban at Rush Medical University, the study of retrieval modular total hip replacements which has included investigation of large sets of retrieved implants, case histories of implant failures or corrosion in modular tapers. Head-neck, neck-stem and modular body tapers have all been demonstrated to corrode in the crevices generated by implant modularity. A number of recent papers have shown several never-before seen modes of corrosion in these devices including hydrogen embrittlement of Ti-6Al-4V, extensive pitting attach and selective dissolution of the beta phase of Ti-6Al-4V, and “Oxide-induced stress corrosion cracking” of Ti-6Al-4V. For Co-Cr-Mo alloys, intergranular corrosion attack and etching and selective dissolution have all been identified.
4. SURFACE MICROMECHANICS
The Gilbert lab has developed a series of novel experimental systems capable of performing a wide range on surface mechanical property assessments in a size scale of microns and loading scale between micro Newton and mN. These micromechanical test systems can perform depth sensing indentation testing, frictional measurements, adhesion measurements, viscoelastic surface behaviors all over a large lateral region with X-Y position control, and with micro-scale interactions. These systems have investigated a number of problems related to biomaterials that include: Study of the micromechanics of ultra-high molecular weight polyethylene (UHMWPE), hydrogel indentation testing of surfaces with moduli down to less than 1 kPa and a wide range of other tests. Current efforts are focused on adapting the motion control and positioning systems to adapt this to microimpedance testing, micro-anodization patterning for cell response studies, and friction adhesion and dehydration interactions for contact lenses. The work in this area also involves utilization of heredity integrals and viscoelastic models to study indentation mechanics of soft tissues including spinal cords.
5. PERFORMANCE TESTING AND TEST METHOD DEVELOPMENT
The Gilbert lab, in its efforts to study device-based failure and corrosion mechanisms, has developed a number of instrumented performance tests to study, for example, fretting corrosion of modular hip replacements, spinal instrumentation and other devices engaged in corrosion and mechanical effects. These tests have been able to develop methods to study new materials and designs and can demonstrate the observed clinical mechanisms of corrosion present.
6. BONE CEMENTS AND SELF REINFORCED COMPOSITES
The Gilbert lab, in collaboration with Dr. Julie Hasenwinkel, has been developing modified bone cements that are based on the concept of two high viscosity solutions instead of powder-liquid compositions. This work has investigated a wide range of behaviors of these novel cements including polymerization, residual stress, porosity formation and mechanical properties. Additionally, we have been studying how to utilize deformation processing methods to generate high strength polymer fibers that can be hot compacted into self-reinforced composite (SRC) materials.