Morshed Khandaker

Effect of additive particles on mechanical, thermal, and cell functioning properties of poly(methyl methacrylate) cement.

The most common bone cement material used clinically today for orthopedic surgery is poly(methyl methacrylate) (PMMA). Conventional PMMA bone cement has several mechanical, thermal, and biological disadvantages. To overcome these problems, researchers have investigated combinations of PMMA bone cement and several bioactive particles (micrometers to nanometers in size), such as magnesium oxide, hydroxyapatite, chitosan, barium sulfate, and silica. A study comparing the effect of these individual additives on the mechanical, thermal, and cell functional properties of PMMA would be important to enable selection of suitable additives and design improved PMMA cement for orthopedic applications. Therefore, the goal of this study was to determine the effect of inclusion of magnesium oxide, hydroxyapatite, chitosan, barium sulfate, and silica additives in PMMA on the mechanical, thermal, and cell functional performance of PMMA. American Society for Testing and Materials standard three-point bend flexural and fracture tests were conducted to determine the flexural strength, flexural modulus, and fracture toughness of the different PMMA samples. A custom-made temperature measurement system was used to determine maximum curing temperature and the time needed for each PMMA sample to reach its maximum curing temperature. Osteoblast adhesion and proliferation experiments were performed to determine cell viability using the different PMMA cements. We found that flexural strength and fracture toughness were significantly greater for PMMA specimens that incorporated silica than for the other specimens. All additives prolonged the time taken to reach maximum curing temperature and significantly improved cell adhesion of the PMMA samples. The results of this study could be useful for improving the union of implant-PMMA or bone-PMMA interfaces by incorporating nanoparticles into PMMA cement for orthopedic and orthodontic applications.

Micro and nano MgO particles for the improvement of fracture toughness of bone-cement interfaces.

The objective of this study was to determine whether inclusion of magnesium oxide (MgO) in micro and nanoparticulate forms in poly methyl methacrylate (PMMA) cement has any influence on the fracture toughness of bone-cement interfaces. An interfacial fracture mechanics technique was used to compare the values of fracture toughness (KIC) among bone-PMMA, bone-PMMA with micro MgO particles and bone-PMMA with nano MgO particles interfaces. This study found that the values of KIC of bone-PMMA with micro MgO particles and bone-PMMA with nano MgO particles interfaces were significantly higher when compared to the values of KIC of the bone-PMMA interface (p<0.0001). Results indicated that the addition of the micro and nano MgO particles to PMMA improved the quality of bone-cement union.

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.

The Effect of Nanoparticles and Alternative Monomer on the Exothermic Temperature of PMMA Bone Cement

Poly methyl methacrylate (PMMA) cement produce exothermic reaction during its polymerization process, which damage the surrounding bone tissue during orthopedic surgery. Nanoparticles additives (magnesium oxide, hydroxyapatite, chitosan, barium sulfate and silica) and alternative monomers (glycidyl methacrylate(GMA) tri-methaxysilyl propyl methacrylate (3MPMA)), can be incorporated with the PMMA beads and methyl methacrylate (MMA) monomers, respectively, to reduce the exothermic temperature. A comparative study of the addition of these additives and monomer at different concentration on exothermic temperature of PMMA is not known and significant for designing improved PMMA cement for orthopedic applications. The goal of this study is two folds: (1) to evaluate the effect of the inclusion of the above additives with PMMA on the exothermic temperature of PMMA, (2) to evaluate the effect of the inclusion of the above alternative monomers on the exothermic temperature of PMMA. A commercial bone cement was used in this study as PMMA cement. Two wt% and six wt% of the above nanoparticle were mixed with PMMA beads. Two and six wt% of the above alterative monomers were mixed with MMA monomers. Bead and monomer ratio of 2:1 was maintained to prepare the cement samples. A 4-channel thermocouple was used to determine the temperature changes of the samples in an insulated acrylic mold during the curing period. This study found maximum curing temperature on the 2 wt% Magnesium oxide added PMMA specimen was significantly lower than other samples. Addition of 3MPMA and GMA to MMA decreased the maximum curing temperatures and curing time of specimens compared to other samples.

Fracture toughness of titanium-cement interfaces: effects of fibers and loading angles

Ideal implant–cement or implant–bone interfaces are required for implant fixation and the filling of tissue defects created by disease. Micron- to nanosize osseointegrated features, such as surface roughness, fibers, porosity, and particles, have been fused with implants for improving the osseointegration of an implant with the host tissue in orthopedics and dentistry. The effects of fibers and loading angles on the interface fracture toughness of implant–cement specimens with and without fibers at the interface are not yet known. Such studies are important for the design of a long-lasting implant for orthopedic applications. The goal of this study was to improve the fracture toughness of an implant–cement interface by deposition of micron- to nanosize fibers on an implant surface. There were two objectives in the study: 1) to evaluate the influence of fibers on the fracture toughness of implant–cement interfaces with and without fibers at the interfaces, and 2) to evaluate the influence of loading angles on implant–cement interfaces with and without fibers at the interfaces. This study used titanium as the implant, poly(methyl methacrylate) (PMMA) as cement, and polycaprolactone (PCL) as fiber materials. An electrospinning unit was fabricated for the deposition of PCL unidirectional fibers on titanium (Ti) plates. The Evex tensile test stage was used to determine the interface fracture toughness (KC) of Ti–PMMA with and without PCL fibers at 0°, 45°, and 90° loading angles, referred to in this article as tension, mixed, and shear tests. The study did not find any significant interaction between fiber and loading angles (P>0.05), although there was a significant difference in the KC means of Ti–PMMA samples for the loading angles (P<0.05). The study also found a significant difference in the KC means of Ti–PMMA samples with and without fibers (P<0.05). The results showed that the addition of the micron- to nanosize PCL fibers on Ti improved the quality of the Ti–PMMA union. The results of the study are essential for fatigue testing and finite-element analysis of implant–cement interfaces to evaluate the performance of orthopedic and orthodontic implants.

Bioactive Additives and Functional Monomers Affect on PMMA Bone Cement: Mechanical and Biocompatibility Properties

The most common bone cement material used clinically today for orthopedic surgeries is poly methyl methacrylate (PMMA). In general, poly Methyl MethAcrylate (PMMA) beads are added to MMA monomer with bead and monomer ratio of 2:1 to prepare the PMMA bone cement. Conventional PMMA bone cement has several mechanical and biological disadvantages. To overcome these disadvantages, researchers investigated several bioactive additives to PMMA bone cement, such as MgO, hydroxyapatite (HAp), chitosan (CS). Additionally, functional monomer, such as glycidyl methacrylate (GMA) was used in addition or substitution to MMA to enhance the properties of PMMA bone cement. A comparative study is required to evaluate the effect that different bioadditives and monomers have on the mechanical and biological performances on PMMA bone cement. The goal of this study is to determine the most suitable additives and alternative monomer for PMMA bone cement that can enhance the mechanical and biological performances of PMMA bone cement. Cobalt™ HV bone cement (referred as CBC), a commercial orthopedic bone cement, was used in this study as PMMA bone cement. MgO, hydroxyapatite (HAp), chitin (CT), chitosan (CS), Barium sulfate (BaSO4 ) and Silica (SiO2 ) were mixed with PMMA beads to prepare CBC-MgO, CBC-HAp, CBC-CT, CBC-CS, CBC-BaSO4 and CBC-SiO2 specimens. Additives included CBC were referred as composite specimen. CBC and composite specimens were further grouped according to the application of GMA as replacement of MMA monomer. Two groups of CBC and composite specimen were prepared. In the first group, CBC and composite specimens were prepared using MMA monomer only, referred as without GMA specimen. In the second group, CBC and composite specimens were prepared using GMA and MMA monomers, referred as with GMA specimen. There are three general research questions: (1) Is there a significant difference in the mechanical and biological performances between CBC (control) and different composite specimens that contain GMA? (2) Is there a significant difference in the in the mechanical and biological performances between CBC (control) and different composite specimens that do not contain GMA? and (3) Is there a significant difference in the mechanical and biological performances between specimens mixed with and without GMA? Elastic and fracture properties of different CBC and composite cements were calculated from three point bend experiments. Osteoblast cell adhesion experiments were performed on different CBC and composite cement on a custom made well plate. This study found that flexural strength and fracture toughness of the CBC specimens that contain GMA is significantly greater than the flexural strengths of all other specimens that contain GMA. In contrast, flexural strength and fracture toughness of the CBC-SiO2 specimens that do not contain GMA is significantly greater than the flexural strengths of all other specimens that contain GMA. This study also found that cell adhesion on the MgO impregnated CBC specimens is significantly greater than the cell adhesion of all other specimens for samples that contain GMA or do not contain GMA.Copyright

Sensitivity Based Optimum Design Process for MEMS devices

This paper presents an optimum design process of micro-electro-mechanical systems (MEMS) by stochastic optimization to obtain a reliable and optimal design under the structural and fabrication uncertainty. This optimized design process shows the application of probabilistic analysis and optimization methodologies for MEMS design and fabrication. The optimal design of MEMS devices, with a MEMS microswitch as our device example, has been carried out to find the optimum load required for successful operation of the device. The objective of the optimization problem is to minimize adhesion satisfying a set of probabilistic constraints. The optimization problem, which considers both performance and structural reliability, improves yield rate greatly and is essential for successful mass production. This approach, although shown for MEMS structures, can be easily applied to conventional mechanical structures where the reliable optimized performance of the structure is important.

Mechanical Characterization of Polyethylene Glycol Diacrylate (PEGDA) for Tissue Engineering Applications

One of the principal challenges in tissue engineering, especially with the production of large tissue constructs, is the cell survivability within the scaffold. Several researchers developed porous three dimensional (3D) scaffold, where oxygen and nutrients can slowly diffuse for the proper cell growth inside the scaffold. Due to limited diffusion of oxygen and nutrients, the cells placed at a certain depth (usually 3mm) within these tissue construct do not receive adequate nutrients. For which the cells die at that depth which lead to improper tissue regeneration in the scaffold. Currently, there is a necessity to design nutrient conduit networks (referred in this article as channels) within the tissue construct to enable cells to survive in the scaffold. In this study, tissue constructs having the nutrient conduit channels were designed and were fabricated with UV-photopolymerization process. Polyethylene glycol diacrylate (PEGDA) was used as a fabrication material. After the design and fabrication was completed, mechanical characterization was conducted to examine the mechanical properties of the tissue constructs. The study found that PEGDA samples with 0.2% concentration of photoinitiator (PI) has higher cell viability rate compared to the PEGDA samples with higher concentration of PI. Mechanical test results found that PEGDA tissue constructs had higher ultimate tensile strength at room temperature compared to physiological body temperature.

Interfacial Fracture Strength Measurement of Tissue-Biomaterial Systems

The interfacial mechanics at the bone-implant interface is a critical issue for implant fixation and the filling of bone defects created by tumors and/or their excision. The present study is based on the hypothesis that the differences of the surface roughness at bone/ implant interface due to incorporation of micro and nano nanoparticle additives may have significant influence on the quality of bone/implant union. This research studied poly Methyl MethAcrylate (PMMA) bone cement with and without MgO additives as different implant materials. The aims of this research were to determine the influences of a magnesium oxide (MgO) additive particle size to PMMA bone cement on the bonding strength between bone and bone cement specimens. The scope of work for this study were: (1) to quantify elastic properties (Young’s modulus and Poisson’s ratio) of bone cement specimens, (2) to determine whether inclusion of MgO particles with PMMA has any influence on the interface strength between bone and PMMA, and (3) to quantify the effect of surface roughness on the interface fracture strength between bone and PMMA. This study found that the mean interface strength for bone-PMMA is significantly less than the mean interface strengths of bone-PMMA with microsize MgO particles and bone-PMMA with nanosize MgO particles.© 2011 ASME