Polycaprolactone coated porous tricalcium phosphate scaffolds for controlled release of protein for tissue engineering.

Polycaprolactone (PCL) was coated on porous tricalcium phosphate (TCP) scaffolds to achieve controlled protein delivery. Porous TCP scaffolds were fabricated using reticulated polyurethane foam as sacrificial scaffold with a porosity of 70-90 vol %. PCL was coated on sintered porous TCP scaffolds by dipping-drying process. The compressive strength of TCP scaffolds increased significantly after PCL coating. The highest strength of 2.41 MPa at a porosity of 70% was obtained for the TCP scaffold coated with 5% PCL solution. Model protein bovine serum albumin (BSA) was encapsulated efficiently within the PCL coating. The amount of BSA encapsulation was controlled by varying proteins' composition in the PCL coating. The FTIR analysis confirmed that BSA retained its structural conformation and did not show significant denaturization during PCL coating. The release kinetics in phosphate buffer solution indicated that the protein release was controlled and sustained, and primarily dependant on protein concentration encapsulated in the PCL coating.

Laser-assisted Zr/ZrO(2) coating on Ti for load-bearing implants.

Oxidized Zr alloys have been shown to exhibit lower friction and superior wear properties, suggesting that they could be used in hip and knee implants. However, conventional oxidation of Zr alloys above 500 degrees C, in dry air, for several hours has been shown to have detrimental effects on the substrate's properties. In this work, we deposited pure Zr on Ti, then oxidized the coating using a continuous-wave Nd:YAG laser, which facilitated localized heating to elevated temperatures without affecting the substrate. Laser-assisted oxidation resulted in a 7microm thick fully dense ZrO(2) layer on Zr in which an increase in oxidation kinetics was evident due to an increase in the laser power and/or the oxygen partial pressure. Due to its high surface energy and wettability, the wear rate of laser-oxidized Zr was two orders of magnitude less compared to that of as-deposited Zr. The oxidized coatings showed comparable in vitro biocompatibility to that of pure Ti and excellent in vitro cell-material interactions. This article reports the processing of Zr/ZrO(2) coatings on Ti using lasers, and the influence of laser parameters and oxygen partial pressure on the coating's mechanical, microstructural, wear and in vitro biological properties using human osteoblast cells.

Mesoporous calcium silicate for controlled release of bovine serum albumin protein.

The purpose of this study is to synthesize mesoporous calcium silicate (CS or wollastonite, CaSiO(3)) and evaluate its possible application in protein/drug delivery. First, calcium silicate was synthesized by wet chemical method and then mesoporosity was created by acid modification of the synthesized CS particle using hydrochloric acid at pH 7, 4.5, and 0.5. The results showed that a hydrated silica gel with abundant Si-OH functional group formed on the surface of calcium silicate due to acid modification. This surface layer had mesoporous structure, with pore diameter between 4 and 5 nm. BET specific average surface area increased to 221, 333, and 356 m(2) g(-1) due to acid modification at pH 7, 4.5, and 0.5, respectively, whereas the surface area for unmodified CS particles was 65 m(2) g(-1). Protein adsorption studies indicated that mesoporous CS has higher ability to adsorb bovine serum albumin and lysozyme compared to unmodified particles. The release kinetics showed that proteins on mesoporous CS released sequentially over one week, whereas the proteins on unmodified particle followed burst release kinetics within a few hours. Human osteoblast cell-material interaction study showed that these materials were biocompatible and promoted excellent bone cell proliferation. In summary, this work has demonstrated the potential to produce mesoporous CS as a carrier for protein/drug delivery for bone regeneration and other biomedical applications.

Fabrication of compositionally and structurally graded Ti-TiO2 structures using laser engineered net shaping (LENS).

Novel structures with functional gradation in composition and structure were successfully made in Ti-TiO(2) combination using laser engineered net shaping. The addition of fully dense, compositionally graded TiO(2) ceramic on porous Ti significantly increased the surface wettability and hardness. The graded structures with varying concentrations of TiO(2) on the top surface were found to be non-toxic and biocompatible. In addition, the higher wettability of surfaces with TiO(2) can enhance their ability to form chemisorbed lubricating films, which can potentially lower the friction coefficient against ultrahigh molecular weight polyethylene liner, thus reducing its wear rate. These unitized structures with open porosity on one side and hard, low friction surface on the other side can eliminate the need for multiple parts with different compositions for load-bearing implants such as total hip prostheses.

Application of laser engineered net shaping (LENS) to manufacture porous and functionally graded structures for load bearing implants.

Fabrication of net shape load bearing implants with complex anatomical shapes to meet desired mechanical and biological performance is still a challenge. In this article, an overview of our research activities is discussed focusing on application of Laser Engineered Net Shaping (LENS) toward load bearing implants to increase in vivo life time. We have demonstrated that LENS can fabricate net shape, complex metallic implants with designed porosities up to 70 vol.% to reduce stress-shielding. The effective modulus of Ti, NiTi, and other alloys was tailored to suit the modulus of human cortical bone by introducing 12-42 vol.% porosity. In addition, laser processed porous NiTi alloy samples show a 2-4% recoverable strain, a potentially significant result for load bearing implants. To minimize the wear induced osteolysis, unitized structures with functionally graded Co-Cr-Mo coating on porous Ti6Al4V were also made using LENS, which showed high hardness with excellent bone cell-materials interactions. Finally, LENS is also being used to fabricate porous, net shape implants with a functional gradation in porosity characteristics.

Synthesis and characterization of tricalcium phosphate with Zn and Mg based dopants.

The purpose of this study is to prepare tricalcium phosphate (TCP) ceramic by dual dopants of magnesium (Mg) and zinc (Zn), and investigate the influence of dopants on the physical, mechanical and biological properties of TCP. TCP were synthesized with 1 wt% Mg, 0.3 wt% Zn and dual dopants using the precipitation process. Phase composition and microstructures were characterized. Mechanical properties and dissolution behavior in vitro were investigated. Human osteoblast cell culture was used to determine the influence of dopants on cell-materials interactions. XRD analysis indicated that Mg delayed phase transformation from beta to alpha-TCP and pure beta-TCP phase was obtained for Mg-doped TCP after sintered at 1250 degrees C. Addition of Mg improved densification behavior of TCP. Compression strength also increased from 24.0 MPa to 77.2 MPa after doping with Mg and Zn. Furthermore, Mg additive reduced the solubility of TCP in vitro. Osteoblast culture studies indicated that the presence of Mg stabilized the cell-material interface and thus improved cell attachment and growth. Zn-doped TCP exhibited good bioactivity, which enhanced cell differentiation and alkaline phosphatase (ALP) expression. The highest cell proliferation and ALP expression were found on dual Mg and Zn doped TCP. The results indicate that Mg and Zn dopants play a significant role towards improving mechanical properties and cell-materials interactions of TCP. This work also demonstrates the potential for dual Mg and Zn doped TCP to be used in orthopedics and dentistry, which displays high mechanical strength, low resorption and improved cell-material interaction.

Functionally graded Co-Cr-Mo coating on Ti-6Al-4V alloy structures.

Functionally graded, hard and wear-resistant Co-Cr-Mo alloy was coated on Ti-6Al-4V alloy with a metallurgically sound interface using Laser Engineering Net Shaping (LENS). The addition of the Co-Cr-Mo alloy onto the surface of Ti-6Al-4V alloy significantly increased the surface hardness without any intermetallic phases in the transition region. A 100% Co-Cr-Mo transition from Ti-6Al-4V was difficult to produce due to cracking. However, using optimized LENS processing parameters, crack-free coatings containing up to 86% Co-Cr-Mo were deposited on Ti-6Al-4V alloy with excellent reproducibility. Human osteoblast cells were cultured to test in vitro biocompatibility of the coatings. Based on in vitro biocompatibility, increasing the Co-Cr-Mo concentration in the coating reduced the live cell numbers after 14 days of culture on the coating compared with base Ti-6Al-4V alloy. However, coated samples always showed better bone cell proliferation than 100% Co-Cr-Mo alloy. Producing near net shape components with graded compositions using LENS could potentially be a viable route for manufacturing unitized structures for metal-on-metal prosthetic devices to minimize the wear-induced osteolysis and aseptic loosening that are significant problems in current implant design.

Processing and biocompatibility evaluation of laser processed porous titanium.

The Laser Engineered Net Shaping (LENS) method was used to fabricate porous Ti implants. Porous Ti structures with controlled porosity in the range of 17-58 vol.% and pore size up to 800 microm were produced by controlling LENS parameters, which showed a broad range of mechanical strength of 24-463 MPa and a low Young's modulus of 2.6-44GPa. The effects of porous structure on bone cell responses were evaluated in vitro with human osteoblast cells (OPC1). The results showed that cells spread well on the surface of porous Ti and formed strong local adhesion. MTT assay indicated LENS processed porous Ti provides a preferential surface for bone cell proliferation. Porous Ti samples also stimulated faster OPC1 cell differentiation compared with polished Ti sheet, which could be due to the change in cell morphology within the pores of Ti samples. More extracellular matrix and a higher level of alkaline phosphatase expression were found on the porous samples than on the Ti sheet. This can be beneficial for faster integration of porous implant with host bone tissue. The results obtained also indicated that a critical pore size of 200 microm or higher is needed for cell ingrowth into the pores, below which OPC1 cells bridged the pore surface without any growth in the pores.

Osteoprecursor cell response to strontium-containing hydroxyapatite ceramics.

The objective of this study was to investigate the in vitro bioactivity of strontium-containing hydroxyapatite (Sr-HA), and its effect on cellular attachment, proliferation, and differentiation. The effect of Sr-HA has been compared with that of hydroxyapatite (HA), which is widely used in orthopedics and dentistry. Sr-HA ceramic containing 10 mol % was prepared. The bioactivity of Sr-HA was evaluated in vitro by immersion in simulated body fluid (SBF). After immersion in SBF, Sr-HA exhibited greater ability to induce apatite precipitation on its surface than did HA. The possible effects on cell behavior of Sr-HA were examined by culturing osteoprecursor cells (OPC1) on materials surfaces. Cell shape and cell-material interactions were analyzed by scanning electron microscope (SEM) and the MTT assay was used to determine cell proliferation on samples. When compared with HA, Sr-HA promoted better OPC1 cell attachment and proliferation, and showed no deleterious effects on extracellular matrix formation and mineralization. Confocal scanning microscopy was used to assess the expression of specific osteoblast proteins: alkaline phosphatase (ALP) and osteopontin (OPN). The results obtained indicate that the presence of Sr stimulates OPC1 cell differentiation, and enhances ALP and OPN expression.

Effect of hydroxyapatite coating crystallinity on dissolution and osseointegration in vivo.

Hydroxyapatite (HA) coating with different crystallinities were deposited by plasma spraying and vapor-flame treatment process. Their crystallinities are about 55 and 98%, respectively. These coatings were implanted in cortical bone, muscle, and marrow of dogs. The dissolution and osseointegration behavior were evaluated by scanning electron microscope (SEM) observation histological analysis. The results obtained indicated that after implanted in muscle, a bone-like apatite layer was formed on the surface of as-sprayed coating, which was not observed on the surface of the treated coating. The as-sprayed coating has the ability to induce new bone formation on its surface after implanted in marrow. In contrast, the treated coating displays a limited bone bioactivity. The vapor-flame process diminishes the short-term osseointegration properties of the HA coating, but no significant affection was found after three months implantation. Either in muscle or in cortical bone, treated coating exhibits higher stability than the as-sprayed coating, in some conditions.

In vivo evaluation of plasma-sprayed wollastonite coating.

Wollastonite coatings were prepared by plasma spraying. The bioactivity of wollastonite coatings was investigated in vivo by implanting in dog's muscle, cortical bone and marrow, respectively. The behaviour of bone tissue around wollastonite coatings were examined by histological and SEM observation. After 1 month in the muscle, a bone-like apatite layer was found to form on the surface of the wollastonite coating. When implanted in cortical bone, histological observation demonstrated that bone tissue could extend and grow along the surface of the wollastonite coating. The coating bonded directly to the bone without any fibrous tissue, indicating good biocompatibility and bone conductivity. SEM and EDS analysis revealed that bone did not bond to wollastonite coating directly, but through a Ca/P layer. This suggested that the formation of bone-like apatite layer was very important for bonding to the bone tissue. The amount of bone-implant contact was also measured. Wollastonite coating was shown to stimulate more bone formation on its surface than titanium coating after implantation for 1 month, enhancing the short-term osseointegration properties of implant. The test in marrow indicated that wollastonite coatings could induce new bone formation on their surface showing good bone inductivity property.

In vivo evaluation of plasma-sprayed titanium coating after alkali modification.

In this paper, plasma-sprayed titanium coatings were modified by alkali treatment. The changes in chemical composition and structure of coatings were examined by SEM and AES. The results obtained indicated that a net-like microscopic texture feature, which was full of the interconnected fine porosity, appeared on the surface of alkali-modified titanium coatings. The surface chemical composition was also altered by alkali modification. A sodium titanate compound was formed on the surface of the titanium coating and replaced the native passivating oxide layer. Its thickness was measured as about 150 nm which was about 10 times of that of the as-sprayed coating. The bone bonding ability of titanium coatings were investigated using a canine model. The histological examination and SEM observation demonstrated that more new bone was formed on the surface of alkali-modified implants and grew more rapidly into the porosity. The alkali-modified implants were found to appose directly to the surrounding bone. In contrast, a gap was observed at the interface between the as-sprayed implants and bone. The push-out test showed that alkali-modified implants had a higher shear strength than as-sprayed implants after 1 month of implantation. An interfacial layer, containing Ti, Ca and P, was found to form at the interface between bone and the alkali-modified implant by EDS analysis.

In vivo evaluation of plasma sprayed hydroxyapatite coatings having different crystallinity.

In this paper, hydroxyapatite (HA) coatings having the crystallinities of 56% and 98% were deposited by the plasma spraying and vapor-flame treatment process. The phase composition and crystallinity of the coatings were investigated by X-ray diffraction and infrared spectra. The dissolution behavior of the coatings in tris-buffer solutions was examined. The results obtained indicated that the coating having the high crystallinity showed the lower dissolution as compared to the low crystallinity coating. The bone bonding ability of HA coatings were observed in vivo by implanted in dog's femur. After 3 months implantation, the high crystallinity coating showed the higher shear strengths and remained integrated, whereas the separation of the coating fragments was clearly observed in the coating having low crystallinity.