Shafiul Chowdhury

Mechano-morphological studies of aligned nanofibrous scaffolds of polycaprolactone fabricated by electrospinning

Mechanical and morphological studies of aligned nanofibrous meshes of poly(ε-caprolactone) (PCL) fabricated by electrospinning at different collector rotation speeds (0, 3000 and 6000 rpm) for application as bone tissue scaffolds are reported. SEM, XRD and DSC analyses were used for the morphological characterization of the nanofibers. Scaffolds have a nanofibrous morphology with fibers (majority) having a diameter in the range of 550–350 nm (depending on fiber uptake rates) and an interconnected pore structure. With the increase of collector rotation speed, the nanofibers become more aligned and oriented perpendicular to the axis of rotation. Deposition of fibers at higher fiber collection speeds has a profound effect on the morphology and mechanical properties of individual fibers and also the bulk fibrous meshes. Nanoindentation was used for the measurement of nanoscopic mechanical properties of individual fibers of the scaffolds. The hardness and Youngs modulus of aligned fibers measured by nanoindentation decreased with collector rotation speeds. This reveals the difference in the local microscopic structure of the fibers deposited at higher speeds. The sequence of nanoscopic mechanical properties (hardness and modulus) of three fibers is PCL at 0 rpm > PCL at 3000 rpm > PCL at 6000 rpm. This may be explained due to the decrease in crystallinity of fibers at higher uptake rates. However, uni-axial tensile properties of (bulk) scaffolds (tensile strength and modulus) increased with increasing collector rotation speed. The average ultimate tensile strength of scaffolds (along the fiber alignment) increased from 2.21 ± 0.23 MPa for PCL at uptake rate of zero rpm, to a value of 4.21 ± 0.35 MPa for PCL at uptake rate of 3000 rpm and finally to 9.58 ± 0.71 MPa for PCL at 6000 rpm. Similarly, the tensile modulus increased gradually from 6.12 ± 0.8 MPa for PCL at uptake rate of zero rpm, to 11.93 ± 1.22 MPa for PCL at uptake rate of 3000 rpm and to 33.20 ± 1.98 MPa for PCL at 6000 rpm. The sequence of macroscopic mechanical properties (tensile strength and modulus) of three fibers, from highest to lowest, is PCL at 0 rpm < PCL at 3000 rpm < PCL at 6000 rpm. This is attributed to the increased fiber alignment and packing and decrease in inter-fiber pore size at higher uptake rates.

An electrospun triphasic nanofibrous scaffold for bone tissue engineering

A nanofibrous triphasic scaffold was electrospun from a mixture of polycaprolactone (PCL), type-I collagen and hydroxyapatite nanoparticles (nano-HA) with a mixture dry weight ratio of 50/30/20, respectively. Scaffolds were characterized by evaluating fiber morphology and chemical composition, dispersion of HA particles and nanoindentation. Scanning electron microscopy revealed fibers with an average diameter of 180 +/- 50 nm, which coincides well with the collagen fiber bundle diameter characteristic of the native extracellular matrix of bone. The triphasic fibers, stained with calcein and imaged with confocal microscopy, show a uniform dispersion of apatite particles throughout their length with minor agglomeration. Scaffold fibers of triphasic (50/30/20), collagen/nano-HA (80/20), PCL/nano-HA (80/20), pure PCL and pure collagen were each pressure consolidated into non-porous pellets for evaluation by transmission electron microscopy and nanoindentation. While the majority of apatite particles are uniformly dispersed having an average size of 30 nm, agglomerated particles as large as a few microns are sparsely distributed. Nanoindentation of the pressure-consolidated scaffolds showed a range of Youngs modulus (0.50-3.9 GPa), with increasing average modulus in the order of (PCL < PCL/nano-HA < collagen < triphasic < collagen/nano-HA). The modulus data emphasize the importance of collagen and its interaction with other components in affecting mechanical properties of osteoconductive scaffolds.

Mesenchymal stem cell responses to bone-mimetic electrospun matrices composed of polycaprolactone, collagen I and nanoparticulate hydroxyapatite.

The performance of biomaterials designed for bone repair depends, in part, on the ability of the material to support the adhesion and survival of mesenchymal stem cells (MSCs). In this study, a nanofibrous bone-mimicking scaffold was electrospun from a mixture of polycaprolactone (PCL), collagen I, and hydroxyapatite (HA) nanoparticles with a dry weight ratio of 50/30/20 respectively (PCL/col/HA). The cytocompatibility of this tri-component scaffold was compared with three other scaffold formulations: 100% PCL (PCL), 100% collagen I (col), and a bi-component scaffold containing 80% PCL/20% HA (PCL/HA). Scanning electron microscopy, fluorescent live cell imaging, and MTS assays showed that MSCs adhered to the PCL, PCL/HA and PCL/col/HA scaffolds, however more rapid cell spreading and significantly greater cell proliferation was observed for MSCs on the tri-component bone-mimetic scaffolds. In contrast, the col scaffolds did not support cell spreading or survival, possibly due to the low tensile modulus of this material. PCL/col/HA scaffolds adsorbed a substantially greater quantity of the adhesive proteins, fibronectin and vitronectin, than PCL or PCL/HA following in vitro exposure to serum, or placement into rat tibiae, which may have contributed to the favorable cell responses to the tri-component substrates. In addition, cells seeded onto PCL/col/HA scaffolds showed markedly increased levels of phosphorylated FAK, a marker of integrin activation and a signaling molecule known to be important for directing cell survival and osteoblastic differentiation. Collectively these results suggest that electrospun bone-mimetic matrices serve as promising degradable substrates for bone regenerative applications.

Mesenchymal stem cell interaction with ultra smooth nanostructured diamond for wear resistant orthopaedic implants

Ultra-smooth nanostructured diamond (USND) can be applied to greatly increase the wear resistance of orthopaedic implants over conventional designs. Herein we describe surface modification techniques and cytocompatibility studies performed on this new material. We report that hydrogen (H)-terminated USND surfaces supported robust mesenchymal stem cell (MSC) adhesion and survival, while oxygen- (O) and fluorine (F)-terminated surfaces resisted cell adhesion, indicating that USND can be modified to either promote or prevent cell/biomaterial interactions. Given the favorable cell response to H-terminated USND, this material was further compared with two commonly used biocompatible metals, titanium alloy (Ti-6Al-4V) and cobalt chrome (CoCrMo). MSC adhesion and proliferation were significantly improved on USND compared with CoCrMo, although cell adhesion was greatest on Ti-6Al-4V. Comparable amounts of the pro-adhesive protein, fibronectin, were deposited from serum on the three substrates. Finally, MSCs were induced to undergo osteoblastic differentiation on the three materials, and deposition of a mineralized matrix was quantified. Similar amounts of mineral were deposited onto USND and CoCrMo, whereas mineral deposition was slightly higher on Ti-6Al-4V. When coupled with recently published wear studies, these in vitro results suggest that USND has the potential to reduce debris particle release from orthopaedic implants without compromising osseointegration.

In vitro dissolution and mechanical behavior of c-axis preferentially oriented hydroxyapatite thin films fabricated by pulsed laser deposition

Owing to its resemblance to the major inorganic constituent of bone and tooth, hydroxyapatite is recognized as one of the most biocompatible materials and is widely used in systems for bone replacement and regeneration. In this study the pulsed laser deposition technique was chosen to produce hydroxyapatite with different crystallographic orientations in order to investigate some of the material properties, including its in vitro dissolution behavior, as well as mechanical properties. The crystallographic orientations of hydroxyapatite coatings can be carefully controlled, mainly by varying the energy density of the KrF excimer laser (248 nm) used for deposition. Nanoindentation results showed that highly c-axis oriented hydroxyapatite coatings have higher hardness and Youngs modulus values compared with the values of randomly oriented coatings. After 24h immersion in simulated physiological solution the overall surface morphology of the highly oriented coatings was dramatically altered. The porosity was drastically increased and sub-micron pores were formed throughout the coatings, whereas the average size of the grains in the coatings was not significantly changed. The composition of the textured hydroxyapatite coatings remained essentially unchanged. Their c-axis texture, on the other hand, was rather enhanced with an increase in immersion time. The c-axis oriented hydroxyapatite surfaces are likely to promote preferentially oriented growth through a cyclic process of dissolution and reprecipitation, followed by homoepitaxial growth. The remarkable morphological and microstructural changes after dissolution suggest a capability of highly textured hydroxyapatite as a tissue engineering scaffold with an interconnecting porous network that may be beneficial for cellular activity.

Synthesis of ultrasmooth nanostructured diamond films by microwave plasma chemical vapor deposition using a He/H2/CH4/N2 gas mixture

Ultrasmooth nanostructured diamond (USND) films were synthesized on Ti-6Al-4V medical grade substrates by adding helium in H(2)/CH(4)/N(2) plasma and changing the N(2)/CH(4) gas flow from 0 to 0.6. We were able to deposit diamond films as smooth as 6 nm (root-mean-square), as measured by an atomic force microscopy (AFM) scan area of 2 μm(2). Grain size was 4-5 nm at 71% He in (H(2) + He) and N(2)/CH(4) gas flow ratio of 0.4 without deteriorating the hardness (~50-60 GPa). The characterization of the films was performed with AFM, scanning electron microscopy, x-ray diffraction (XRD), Raman spectroscopy, and nanoindentation techniques. XRD and Raman results showed the nanocrystalline nature of the diamond films. The plasma species during deposition were monitored by optical emission spectroscopy. With increasing N(2)/CH(4) feedgas ratio (CH(4) was fixed) in He/H(2)/CH(4)/N(2) plasma, a substantial increase of CN radical (normalized by Balmer H(α) line) was observed along with a drop in surface roughness up to a critical N(2)/CH(4) ratio of 0.4. The CN radical concentration in the plasma was thus correlated to the formation of ultrasmooth nanostructured diamond films.

Mechanical Properties of Nanoparticle Hydroxyapatite/gelatin Constructs

Bone consists of up to 70% mostly nanocrystalline hydroxyapatite (HA), and the rest is mostly collagen. One can suggest that synthetic nanoHA/collagen composites could potentially be the closest materials to resemble the bone microarchitecture and prepare resorbable bone substitutes and scaffolds. However, the data on the mechanical properties and property/structure relationships of HA/collagen composites are still scarce. It can be explained, in part, by the high cost of collagen and substantial amounts of materials needed for many tests. However, gelatin is cheap, has many properties similar to collagen, and can be used as a model material for the mechanical testing of HA-based composites. In this study, we report the results of an investigation of some mechanical properties of HA/gelatin composites with 0 to 80% HA nanoparticle (size 15-60 nm) loading by weight. The HA nanoparticle dispersions were mixed with gelatin in trifluoroethanol or in water in different ratios and placed in Teflon molds to produce the sheets with the thickness in the range of 0.4 – 1.0 mm. Nanoindentation technique was used to determine the Youngs modulus and hardness. Bending tests were performed using dynamic mechanical analysis with the amplitudes in the 1 – 50 micron range at 1 Hz. The values of Youngs modulus (1 – 20 GPa), hardness (70 – 500 MPa) and bending modulus (0.3 – 2.4 GPa) were obtained. The highest values of the Youngs modulus and hardness of these composite materials were achieved for 40% – 60% HA content by weight, which was close to the values for similar HA/collagen composites. However, the maximum bending strength was observed for 20 – 35% HA content. We discuss further the observed trends of the mechanical properties and their dependence on other factors such as the test conditions, sample geometry, and HA particle size.

Compositionally Modified Hydroxyapatite Nanocrystals for Polymer/Ceramic Scaffold Applications

The polymer/bioceramic composite materials attract much attention for the development of bioresorbable implants and tissue engineering scaffolds. Hydroxyapatite (HA) is the most commonly used bioceramic material due to its similarity to the major mineral component of the hard tissue. We synthesized carbonated and Mg-substituted HA nanocrystals with various concentrations of CO 3 2− and Mg 2+ ions by chemical precipitation in the range of the process temperatures from 25 °C to 100 °C. The HA nanocrystals were mixed with several polymeric materials (PCL, PLA, PVA, collagen) to fabricate bulk and nanofiber polymer/HA nanoparticle composites with the HA loading up to 80 % by weight. The HA nanocrystals and polymer/HA composites were characterized by X-ray diffraction, FT-IR spectroscopy, scanning electron and atomic force microscopy. Mechanical properties of the composites were investigated using nanoindentation technique.

Analysis of Retrieved Surgical Implant Devices: Alternative Bearing Surfaces

Analyses of orthopaedic devices and prostheses from surgical revisions (failures) have provided considerable and valuable information related to the causes of some unintended clinical outcomes. Thousands of explanted samples have been categorized and hundreds studied over past decades. Forensic approaches for determining cause-effect relationships specific to the prosthesis aspects of clinical performance could lead to recommendations of improvements of existing or design of new systems to further enhance clinical longevities. In the following we provide a summary of methodologies and example results from a series of recent retrieval studies aimed at the analysis of alternative bearing surfaces in orthopaedic implants.Copyright