Garima Tripathi

Scaffolds for bone tissue engineering: role of surface patterning on osteoblast response

The fabrication of tissue engineering scaffolds necessitates amalgamation of a multitude of attributes including a desirable porosity to encourage vascular invasion, desired surface chemistry for controlled deposition of calcium phosphate-based mineral as well as ability to support attachment, proliferation, and differentiation of lineage specific progenitor cells. Scaffold fabrication often includes additional surface treatments to bring about desired changes in the surface chemistry. In this perspective, this review documents the important natural and synthetic scaffolds fabricated for bone tissue engineering applications in tandem with the surface treatment techniques to maneuver the biocompatibility of engineered scaffolds. This review begins with a discussion on the fundamental concepts related to biocompatibility as well as the characteristics of the biological micro-environment. The primary focus is to discuss the effects of surface micro/nano patterning on the modulation of bone cell response. Apart from reviewing a host of experimental studies reporting the functionality of osteoblast-like bone cells and stem cells on surface modified or textured bioceramic/biopolymer scaffolds, theoretical insights to predict cell behavior on a scaffold with different topographical features are also briefly analyzed.

Characterization of hydroxyapatite-perovskite (CaTiO3) composites: Phase evaluation and cellular response

In this study, an attempt was made to develop an understanding of the densification behavior, phase stability, and biocompatibility property of HA-CaTiO(3) biocomposite. The composites with varying CaTiO(3) (40-80 wt %) content were sintered at temperatures ranging from 1200°C to 1500°C for 3-5 hr to establish optimum processing parameters. The phase analysis using spectral techniques indicate good thermochemical compatibility between HA and CaTiO(3). The microstructural observations reveal homogeneous distribution of finer CaTiO(3) phase (1-2 μm) along with coarser calcium phosphate phase. In vitro cell culture studies using L929 mouse fibroblast and SaOS2 human osteoblast cell lines provide clear evidence of cell adhesion, spreading, and proliferation as well as the formation of cellular bridges, and, hence, good in vitro biocompatibility of the developed composite can be realized. Also, the number of viable cells was found to increase with incubation period, as revealed by statistical analysis of the 3(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay data.

In vitro cytotoxicity and in vivo osseointergration properties of compression-molded HDPE-HA-Al2O3 hybrid biocomposites.

The aim of this study was to investigate the in vivo biocompatibility in terms of healing of long segmental bone defect in rabbit model as well as in vitro cytotoxicity of eluates of compression-molded High density polyethylene (HDPE)-hydroxyapatite (HA)-aluminum oxide (Al2O3) composite-based implant material. Based on the physical property in terms of modulus and strength properties, as reported in our recent publication, HDPE-40 wt % HA and HDPE-20 wt % HA-20 wt % Al2O3 hybrid composites were used for biocompatibility assessment. Osteoblasts cells were cultured in conditioned media, which contains varying amount of composite eluate (0.01, 0.1, and 1.0 wt %). In vitro, the eluates did not exhibit any significant negative impact on proliferation, mineralization or on morphology of human osteoblast cells. In vivo, the histological assessment revealed neobone formation at the bone/implant interface, characterized by the presence of osteoid and osteoblasts. The observation of osteoclastic activity indicates the process of bone remodeling. No inflammation to any noticeable extent was observed at the implantation site. Overall, the combination of in vitro and in vivo results are suggestive of potential biomedical application of compression-molded HDPE- 20 wt % HA- 20 wt % Al2O3 composites to heal long segmental bone defects without causing any toxicity of bone cells.

In vitro osteogenic cell proliferation, mineralization, and in vivo osseointegration of injection molded high-density polyethylene-based hybrid composites in rabbit animal model:

The present work reports the biocompatibility property of injection molded HDPE-HA-Al2O3 hybrid composites. In vitro cytocompatibility results reveal that osteogenic cell viability and bone mineralization are favorably supported in a statistically significant manner on HDPE-20% HA-20% Al2O3 composite, in comparison to HDPE-40 wt.% HA or HDPE-40 wt.% Al2O3. The difference in cytocompatibility property is explained in terms of difference in substrate wettability/surface energy and importantly, both the cell proliferation at 7 days or bone mineralization at 21 days on HDPE-20% HA-20% Al2O3 composite are either comparable or better than sintered HA. The progressive healing of cylindrical femoral bone defects in rabbit animal model was assessed by implantation experiments over 1, 4 and 12 weeks. Based on the histological analysis as well as histomorphometrical evaluation, a better efficacy of HDPE-20% HA-20% Al2O3 over high-density polyethylene (HDPE) for bone regeneration and neobone formation at host bone-implant interface was established. Taken together, the present study unequivocally establishes that despite the presence of 20% Al2O3, HDPE-based hybrid composites are as biocompatible as HA in vitro or better than HDPE in vivo.

Structures and conformation of a benzo-12-crown-4 containing dipeptide.

Crystal structures of the dipeptide Boc‐12‐Crown‐4‐l‐DOPA‐Gly‐OMe (chi) and Boc‐12‐Crown‐4‐d/l‐DOPA‐Gly‐OMe (rac) were solved by single crystal X‐ray diffraction. Analysis of the packing differences in the crystal reveals that the presence of a water molecule in chi enables intermolecular contacts with the solvent that result in a different conformation of the dipeptide backbone itself. An uncommon NH…N interaction stabilizes the peptide in its solid state.