Shashwat Banerjee

Direct laser processing of a tantalum coating on titanium for bone replacement structures.

Recently tantalum is gaining more attention as a new metallic biomaterial as it has been shown to be bioactive and biologically bonds to bone. However, the relatively high cost of manufacture and an inability to produce a modular all Ta implant has limited its widespread acceptance. In this study we have successfully deposited a Ta coating on Ti using laser engineered net shaping (LENS) to enhance the osseointegration properties. In vitro biocompatibility study, using human osteoblast cell line hFOB, showed excellent cellular adherence and growth with abundant extracellular matrix formation on the Ta coating surface compared with the Ti surface. A six times higher living cell density was observed on the Ta coating than on the Ti control surface by MMT assay. A high surface energy and wettability of the Ta surface were observed to contribute to its significantly better cell-material interactions. Also, these dense Ta coatings do not suffer from low fatigue resistance due to the absence of porosity and a sharp interface between the coating and the substrate, which is a major concern for porous coatings used for enhanced/early biological fixation.

Understanding the influence of MgO and SrO binary doping on the mechanical and biological properties of β-TCP ceramics

The objective of this study was to evaluate the influence of MgO and SrO doping on the mechanical and biological properties of beta-tricalcium phosphate (beta-TCP). beta-TCP was doped with two different binary compositions, 0.25 and 1.0wt.% SrO along with 1.0wt.% MgO. MgO and SrO doping increased the beta phase stability at a sintering temperature of 1250 degrees C and marginally decreased the compressive strength of beta-TCP. An in vitro cell-material interaction study, using human fetal osteoblast cells (hFOB), indicated that doped beta-TCP was non-toxic, and MgO/SrO dopants improved cell attachment and growth. beta-TCP implants doped with 1.0wt.% MgO and 1.0wt.% SrO showed good in vivo biocompatibility when tested in male Sprague-Dawley rats for 16 weeks. Histomorphology analysis indicated that MgO/SrO-doped beta-TCP promoted more osteogenesis than pure beta-TCP. In vivo osteocalcin and type I collagen assay also revealed faster bone formation in rats with doped beta-TCP implant compared to rats with pure beta-TCP implant. Low Ca(2+) concentration in the urine of rats with doped beta-TCP implant confirmed slower degradation of MgO/SrO-doped beta-TCP than pure beta-TCP.

Zn and Mg Doped Hydroxyapatite Nanoparticles for Controlled Release of Protein

Bovine serum albumin (BSA) protein incorporated with hydroxyapatite (HA) nanoparticles (NPs) were synthesized by an in situ precipitation process. 2 mol % Zn(2+) and Mg(2+) were used as dopants to synthesize Zn(2+)/Mg(2+)-doped HA-BSA NPs. In our study we used BSA as a model protein. The amount of BSA uptake by doped and undoped HA NPs and subsequent release of BSA from NPs were investigated. Zn-doped HA NPs showed the highest amount of BSA uptake, whereas the amount of BSA loaded in undoped HA NPs was the lowest. A two-stage BSA release profile from doped and undoped HA NPs was observed in phosphate buffer solution (PBS) at pH 7.2 +/- 0.2. The initial burst release was due to the desorption of BSA from the HA surface. The later stage of slow release was controlled by the dissolution of BSA incorporated HA NPs. The BSA release rate from Zn-doped HA NPs was found to be the highest, whereas undoped HA NPs released BSA at the slowest rate. Our study showed that the protein release rate from HA NPs can be controlled by the addition of suitable dopants, and doped HA-based NP systems can be used in bone growth factor and drug release study.

Understanding in vivo response and mechanical property variation in MgO, SrO and SiO2 doped β-TCP

The aim of this work is to evaluate the influence of MgO, SrO and SiO₂ doping on mechanical and biological properties of β-tricalcium phosphate (β-TCP) to achieve controlled resorption kinetics of β-TCP system for maxillofacial and spinal fusion application. We prepared dense TCP compacts of four different compositions, i) pure β-TCP, ii) β-TCP with 1.0wt.% MgO+1.0wt.% SrO, iii) β-TCP with 1.0wt.% SrO+0.5wt.% SiO₂, and iv) β-TCP with 1.0wt.% MgO+1.0wt.% SrO+0.5wt.% SiO₂, by uniaxial pressing and sintering at 1250°C. β phase stability is observed at 1250°C sintering temperature due to MgO doping in β-TCP. In vitro mineralization in simulated body fluid (SBF) for 16 weeks shows excellent apatite growth on undoped and doped samples. Strength degradation of TCP samples in SBF is significantly influenced by both dopant chemistry and amount of dopant. Compressive strengths for all samples show degradation in SBF over the 16 week time period with varying degradation kinetics. MgO/SrO/SiO₂ doped sample shows no strength loss, while undoped TCP shows the maximum strength loss from 419 ± 28 MPa to 158 ± 28 MPa over the 16 week study. In case of MgO/SrO doped TCP, strength loss is slow and gradual. TCP doped with 1.0wt.% MgO and 1.0wt.% SrO shows excellent in vivo biocompatibility when tested in male Sprague-Dawley rats for 16 weeks. Histomorphology analysis reveals that MgO/SrO doped TCP promoted osteogenesis by excellent early stage bone remodeling as compared to undoped TCP.

Electrically Polarized Biphasic Calcium Phosphates: Adsorption and Release of Bovine Serum Albumin

In this study, we applied electrical polarization technique to increase adsorption and control protein release from biphasic calcium phosphate (BCP). Three different biphasic calcium phosphate (BCP) composites, with hydroxyapatite (HAp) and β-tricalcium phosphate (β-TCP), were processed and electrically polarized. Our study showed that stored charge was increased in the composites with the increase in HAp percentage. Adsorption of bovine serum albumin (BSA), as a model protein, on the poled as well as unpoled surfaces of the composites was studied. The highest amount of BSA adsorption was obtained on positively poled surfaces of each composite. Adsorption isotherm study suggested a multilayer adsorption of BSA on the BCP composites. The effect of electrical polarization on BSA release kinetics from positively charged BCP surfaces was studied. A gradual increase in percent BSA release from positively charged BCP surfaces with decreasing stored charge was observed. Our study showed that the BCP based composites have the potential to be used as a drug or growth factor delivery vehicle.

ZnO, SiO2, and SrO doping in resorbable tricalcium phosphates: Influence on strength degradation, mechanical properties, and in vitro bone–cell material interactions †

To understand the combined effects of ZnO, SiO(2), and SrO doping on mechanical and biological properties of tricalcium phosphate (TCP) ceramics, dense β-TCP compacts of different compositions (pure β-TCP; 1.0 wt % SrO; 0.25 wt % ZnO; 1.0 wt % SrO + 0.5 wt % SiO(2); and 1.0 wt % SrO + 0.25 wt % ZnO) were prepared via dry pressing followed by sintering at 1250°C. X-ray diffraction of sintered compacts revealed that dopants retarded β- to α-TCP phase transformation during sintering. Doping with SrO, SrO/SiO(2), and SrO/ZnO reduced compressive strength of the samples to 56% (173 ± 25 MPa), 57% (170 ± 15 MPa), and 47% (208 ± 72 MPa) of pure β-TCP (396 ± 58 MPa), respectively. However, addition of ZnO resulted in only 7% (365 ± 69 MPa) strength degradation. The impact of dopants on long-term in vitro strength degradation was evaluated by soaking in simulated body fluid (SBF) for a period of 8 weeks. In all cases, excellent apatite growth was observed on doped β-TCP samples. However, strength degradation rates were different depending on dopant chemistry and composition. Maximum degradation was observed in undoped and ZnO-doped β-TCP samples, which degraded to 41% and 68% of the original strength before soaking in SBF. Finally, in vitro cell-materials interaction study using human fetal osteoblast cells demonstrated that addition of dopants improved cell attachment and proliferation. These results indicate that tailorable strength and strength degradation behavior can be achieved in β-TCP via compositional modifications using small amount of dopants.