Shahram Riahinezhad

Use of Polycaprolactone Electrospun Nanofibers as a Coating for Poly(methyl methacrylate) Bone Cement

Poly(methyl methacrylate) (PMMA) bone cement has limited biocompatibility. Polycaprolactone (PCL) electrospun nanofiber (ENF) has many applications in the biomedical field due to its excellent biocompatibility and degradability. The effect of coating PCL ENF on the surface topography, biocompatibility, and mechanical strength of PMMA bone cement is not currently known. This study is based on the hypothesis that the PCL ENF coating on PMMA will increase PMMA roughness leading to increased biocompatibility without influencing its mechanical properties. This study prepared PMMA samples without and with the PCL ENF coating, which were named the control and ENF coated samples. This study determined the effects on the surface topography and cytocompatibility (osteoblast cell adhesion, proliferation, mineralization, and protein adsorption) properties of each group of PMMA samples. This study also determined the bending properties (strength, modulus, and maximum deflection at fracture) of each group of PMMA samples from an American Society of Testing Metal (ASTM) standard three-point bend test. This study found that the ENF coating on PMMA significantly improved the surface roughness and cytocompatibility properties of PMMA (p < 0.05). This study also found that the bending properties of ENF-coated PMMA samples were not significantly different when compared to those values of the control PMMA samples (p > 0.05). Therefore, the PCL ENF coating technique should be further investigated for its potential in clinical applications.

Peen treatment on a titanium implant: effect of roughness, osteoblast cell functions, and bonding with bone cement

Implant failure due to poor integration of the implant with the surrounding biomaterial is a common problem in various orthopedic and orthodontic surgeries. Implant fixation mostly depends upon the implant surface topography. Micron to nanosize circular-shaped groove architecture with adequate surface roughness can enhance the mechanical interlock and osseointegration of an implant with the host tissue and solve its poor fixation problem. Such groove architecture can be created on a titanium (Ti) alloy implant by laser peening treatment. Laser peening produces deep, residual compressive stresses in the surfaces of metal parts, delivering increased fatigue life and damage tolerance. The scientific novelty of this study is the controlled deposition of circular-shaped rough spot groove using laser peening technique and understanding the effect of the treatment techniques for improving the implant surface properties. The hypothesis of this study was that implant surface grooves created by controlled laser peen treatment can improve the mechanical and biological responses of the implant with the adjoining biomaterial. The objective of this study was to measure how the controlled laser-peened groove architecture on Ti influences its osteoblast cell functions and bonding strength with bone cement. This study determined the surface roughness and morphology of the peen-treated Ti. In addition, this study compared the osteoblast cell functions (adhesion, proliferation, and differentiation) between control and peen-treated Ti samples. Finally, this study measured the fracture strength between each kind of Ti samples and bone cement under static loading. This study found that laser peen treatment on Ti significantly changed the surface architecture of the Ti, which led to enhanced osteoblast cell adhesion and differentiation on Ti implants and fracture strength of Ti–bone cement interfaces compared with values of untreated Ti samples. Therefore, the laser peen treatment method has the potential to improve the biomechanical functions of Ti implants.

Effect of Specimen Holder on Static and Fatigue Tests on Titanium/Cement Interfaces

A tension or compression load was applied onto the Ti rod to test the fracture strength and fatigue life of Ti-cement interface under static and fatigue loadings, respectively. These tests are referred as static and fatigue in this study. A customized holder for the cement is required for the static and fatigue experiments, since the typical wedge, pneumatic, or hydraulic gripper are not suitable for static and fatigue tests on the fracture tests of bi-material samples. The objectives of this study are (1) to evaluate the effect of cement thickness on the fracture strength and fatigue life on Ti-cement union by finite element analysis; (2) to evaluate the effect of plastic cement holder and aluminum cement holder on fracture strength and fatigue life on Ti-cement union by experiment and finite element analysis. Ti-cement union model with 0.22 and 0.11 in. cement, Ti-cement-holder union with plastic and aluminum holders were created and validated using ANSYS in this study to develop a suitable specimen holder for static and fatigue tests. Experimental static tests of Ti-cement with both plastic and aluminum specimen holders were conducted as well. The result clearly showed that both plastic and aluminum holders can be used for static test whereas aluminum holder required much larger fracture load compared to the fracture load on plastic holder. Plastic holder is not suitable for fatigue test, because fatigue test required a stronger and more rigid holder such as aluminum.

Microgroove and Collagen-poly(ε-caprolactone) Nanofiber Mesh Coating Improves the Mechanical Stability and Osseointegration of Titanium Implants

The effect of depositing a collagen (CG)-poly-ε-caprolactone (PCL) nanofiber mesh (NFM) at the microgrooves of titanium (Ti) on the mechanical stability and osseointegration of the implant with bone was investigated using a rabbit model. Three groups of Ti samples were produced: control Ti samples where there were no microgrooves or CG-PCL NFM, groove Ti samples where microgrooves were machined on the circumference of Ti, and groove-NFM Ti samples where CG-PCL NFM was deposited on the machined microgrooves. Each group of Ti samples was implanted in the rabbit femurs for eight weeks. The mechanical stability of the Ti/bone samples were quantified by shear strength from a pullout tension test. Implant osseointegration was evaluated by a histomorphometric analysis of the percentage of bone and connective tissue contact with the implant surface. The bone density around the Ti was measured by micro–computed tomography (μCT) analysis. This study found that the shear strength of groove-NFM Ti/bone samples was significantly higher compared to control and groove Ti/bone samples (p < 0.05) and NFM coating influenced the bone density around Ti samples. In vivo histomorphometric analyses show that bone growth into the Ti surface increased by filling the microgrooves with CG-PCL NFM. The study concludes that a microgroove assisted CG-PCL NFM coating may benefit orthopedic implants.

Electrospin Fiber Affect on the Strength of Metal–Cement Interfaces

The research objectives were to (1) determine electrospun polymer fiber adhesion on Titanium (Ti) using qualitative wear tests; (2) determine the effect of fiber material viscosity on the surface coating of Ti; and (3) determine bonding strength between Ti/ Poly-Methyl-Methacrylate (PMMA) under static load. Polycaprolactone (PCL)-Acetone and PCL-PMMA-Acetone fibers were produced on Ti using electrospinning process. Fiber coated Ti surfaces were scratched using sharp edge needle to evaluate the fiber stickiness to the Ti surface. PCL and PMMA were each mixed with acetone using a sonicator, and then stirred together. Rheometer was used to determine viscosity of PCL-PMMA-Acetone mixtures. Qualitative adhesion tests showed that PCL-PMMA-Acetone solution had greater stickiness compared to PCL-Acetone. Low viscosity of 0.158 ± 0.048 Pa s was achieved for producing PCL-PMMA-Acetone fiber which had averaged size of 1.79 ± 0.4 μm. This study found pull out interface fracture shear strength of PCL-Acetone (1.06 ± 0.23 MPa, n = 3) and PCL-PMMA-Acetone (0.57 ± 0.18 MPa, n = 4) fiber coated implant-PMMA cement interfaces were significantly higher compare to uncoated Ti-PMMA interfaces (0.34 ± 0.04 MPa, n = 3).

Fatigue Tests on Fiber Coated Titanium Implant–Bone Cement Interfaces

The goal is developing an efficient bond interface between the implant and the cement by applying micron to nano size fibers to the surface of the implant through an electrospinning process, utilizing biocompatible fibers. Experimental models have been developed to evaluate the forces experienced on a cemented cylinder shape titanium implant through a static and cyclic tests. Finite element analysis (FEA) model for an uncoated cylindrical cemented titanium model was developed and tested under static and fatigue conditions. Our experimental study on cylindrical model found increase of pull out static strength for fiber coated implant (Mean strength = 1.308 MPa) compare to uncoated implant (Mean strength = 1.098 MPa) for 2 samples. Our experimental study also found no noticeable increase of pull out fatigue life for fiber coated implant (Mean fatigue life = 2019 cycles) compare to uncoated implant (Mean fatigue life = 2015 cycles) for 2 samples. Our FEA study on cylindrical model found the design life to be 1690 cycles with element size of 3.0E-3 m under the minimum stress of 112 kPa and maximum stress of 9.71 MPa according to Modified Goodman theorem.

Effect of Fiber Architecture on the Fracture Strength of Implant/Bio-Material Interfaces

Titanium (Ti) and Ti-based alloys are widely used as implants for hard tissue repair. However, the optimal surface properties for ideal integration of Ti implant with native tissues have not yet been achieved. The goal of this study was to improve the bio-mechanical performances of titanium (Ti) implant by implant surface modification such as coating fiber on the implant surface. It is hypothesized that deposition of fiber with certain architecture can increase mechanical interlock of Ti surface which leads to the increment of in vitro bonding of Ti/cement interfaces. The research objectives were to (1) test the fracture strength of Ti-cement with one round, two rounds and five rounds of PCL fiber under static load to determine the topology effect of electrospun fiber material on the Ti/PMMA cement interface; (2) test the fracture strength of Ti-cement with PCL fiber and PCL-PMMA fiber, with and without heating up Ti before fiber under static load to determine the topography effect of electrospun fiber material on the Ti/PMMA cement interface. PCL and PCL-PMMA fibers coated on the Ti surfaces were produced by electrospinning technique using PCL-acetone fiber solution and PCL-PMMA-acetone solution respectively. Under static conditions, Ti/PMMA union specimen with and without fiber were tested to determine the fracture strength. The result showed one round of PCL fiber has higher fracture strength than two rounds and five rounds of fiber, which suggested that more fibers on the surface were not benefit to the fracture strength of Ti-cement interface. With PMMA added into the polymer fiber solution, the fracture strength of Ti-fiber-cement increased. Heating up the Ti implant to 50°C before coating PCL fiber can help the PCL fiber become stickier to the Ti implant which leads to the increasing of the fracture strength of Ti-cement interface. However, for PCL-PMMA fiber, heating up Ti implant before fiber doesn’t help improve the quality of Ti-cement interface as PCL fiber.Copyright