Nelesh Patel

Bio: Nelesh Patel is an academic researcher from University of Cambridge. The author has contributed to research in topics: Carbonate & Resorption. The author has an hindex of 12, co-authored 17 publications receiving 1571 citations.

A comparative study on the in vivo behavior of hydroxyapatite and silicon substituted hydroxyapatite granules

Abstract: Phase pure hydroxyapatite (HA) and a 0.8 wt % silicon substituted hydroxyapatite (SiHA) were prepared by aqueous precipitation methods. Both HA and SiHA were processed into granules 0.5-1.0 mm in diameter and sintered at 1200 degrees C for 2 h. The sintered granules underwent full structural characterization, prior to implantation into the femoral condyle of New Zealand White rabbits for a period of 23 days. The results show that both the HA and SiHA granules were well accepted by the host tissue, with no presence of any inflammatory cells. New bone formation was observed directly on the surfaces and in the spaces between both HA and SiHA granular implants. The quantitative histomorphometry results indicate that the percentage of bone ingrowth for SiHA (37.5%+/-5.9) was significantly greater than that for phase pure HA (22.0%+/-6.5), in addition the percentage of bone/implant coverage was significantly greater for SiHA (59.8%+/-7.3) compared to HA (47.1%+/-3.6). These findings indicate that the early in vivo bioactivity of hydroxyapatite was significantly improved with the incorporation of silicate ions into the HA structure, making SiHA an attractive alternative to conventional HA materials for use as bone substitute ceramics.

Effect of carbonate substitution on the ultrastructural characteristics of hydroxyapatite implants

Abstract: Carbonate ion substitution has been shown to be beneficial for increasing the amount of in vivoosseointegration to hydroxyapatite (HA). Nevertheless, mechanisms by which carbonate ions increase in vivo bioactivity are not fully understood. Sintered granules of HA and carbonate-substituted hydroxyapatite (CHA) were implanted for 6 and 12 weeks in an ovine model. Samples containing the bone-implant interface were prepared for transmission electron microscopy (TEM) and TEM was used to compare the in vivo reactivity of sintered granules of HA and CHA. The current findings demonstrated that CHA (1.2 and 2.05 wt.%) is more soluble than pure HA in vivo. More dissolution was observed from the CHA, at the bone-implant interface and within the implant, when compared to pure HA. A less crystalline phase was formed between the 2.05 wt.% CHA and bone at 12 weeks in vivo. Bone surrounding both the pure HA and 1.2 wt.% CHA was relatively disorganised at 12 weeks. In comparison, bone surrounding the 2.05 wt.% CHA was considerably more organised and in many regions collagen fibrils were present. Despite increased quality of bone surrounding 2.05 wt.% CHA, compared to 1.2 wt.% CHA, the amount of dissolution from both materials was similar.

Phd by thesis

Abstract: Deposits of clastic carbonate-dominated (calciclastic) sedimentary slope systems in the rock record have been identified mostly as linearly-consistent carbonate apron deposits, even though most ancient clastic carbonate slope deposits fit the submarine fan systems better. Calciclastic submarine fans are consequently rarely described and are poorly understood. Subsequently, very little is known especially in mud-dominated calciclastic submarine fan systems. Presented in this study are a sedimentological core and petrographic characterisation of samples from eleven boreholes from the Lower Carboniferous of Bowland Basin (Northwest England) that reveals a >250 m thick calciturbidite complex deposited in a calciclastic submarine fan setting. Seven facies are recognised from core and thin section characterisation and are grouped into three carbonate turbidite sequences. They include: 1) Calciturbidites, comprising mostly of highto low-density, wavy-laminated bioclast-rich facies; 2) low-density densite mudstones which are characterised by planar laminated and unlaminated muddominated facies; and 3) Calcidebrites which are muddy or hyper-concentrated debrisflow deposits occurring as poorly-sorted, chaotic, mud-supported floatstones. These

Biomaterials in orthopaedics.

Abstract: At present, strong requirements in orthopaedics are still to be met, both in bone and joint substitution and in the repair and regeneration of bone defects. In this framework, tremendous advances in the biomaterials field have been made in the last 50 years where materials intended for biomedical purposes have evolved through three different generations, namely first generation (bioinert materials), second generation (bioactive and biodegradable materials) and third generation (materials designed to stimulate specific responses at the molecular level). In this review, the evolution of different metals, ceramics and polymers most commonly used in orthopaedic applications is discussed, as well as the different approaches used to fulfil the challenges faced by this medical field.

Calcium phosphate-based osteoinductive materials.

Abstract: This review focuses on calcium phosphate-based bone substitute materials that are used (or can be used) for teeth or bone replacement, bone repair, augmentation, or regeneration. This review will also include some properties of bone (e.g., interconnected porosity, biodegradability, bioactivity, osteoconductivity) that are being mimicked in the manufacture of calcium phosphate-based biomaterials and some of the reported factors and strategies that can make the calcium phosphate-based biomaterials acquire osteoinductive properties. Archaeological findings showed that attempts to replace missing teeth date back to the prehistoric period. The materials used then included shells, corals, ivory (from elephant tusks), metals, and human (from corpses) and animal bones. Because of the practice of cremation in many societies, not much is known about prehistoric materials used to replace bones lost to accident or disease. Presently, autografts (bones obtained from another anatomic site in the same subject) remain the gold standard for bone repair, substitution, and augmentation followed by allografts (bones from another subject, such as processed cadaver bones). Autografts and allografts while having the important advantage of being osteogenic or osteoinductive (i.e., inducing bone formation), suffer from several disadvantages. With autografts the drawbacks include additional expense and trauma to the patient, possibility of donor site morbidity, and limited availability. In the case of allografts, in addition to limited supply and high cost, potential viral transmission and immunogenicity are of serious concern. Because of the high cost and limited availability of autografts and allografts, there is a great need to develop synthetic alternative biomaterials for bone replacement, repair, and augmentation. Current commercial substitute materials to replace or repair teeth and bones include metals, polymers (natural or synthetic), corals, human bones (processed cadaver bones), animal bones (processed cow bones), corals and coral derived, synthetic ceramics (calcium phosphates, calcium sulfates, calcium carbonate, bioactive glasses), and composites. It is interesting to note that several of the materials used in prehistoric times are similar to the materials used presently (e.g., coral and coral derived, animal bone derived, metals). Generally, depending on the ability to stimulate bone tissue, materials for tooth or bone repair or replacement are classified as bioinert or bioactive. Bioinert materials do not stimulate bone formation but instead stimulate formation of fibrous tissue and therefore do not directly bond to bone and thus form a weak biomaterial-bone interface. Bioactive materials stimulate bone tissue formation and therefore directly bond with bone and thus form a uniquely strong biomaterial-bone interface. Bioinert materials include metals (e.g., titanium or titanium alloys, stainless steel, cobalt-chromium, Co-Cr, alloys), some synthetic polymers (e.g., PEEK, Teflon-type), and some ceramics (e.g., alumina, * To whom correspondence should be addressed. Phone: (212) 998-9580. Fax: (212) 995-4244. E-mail: rzl1@nyu.edu. Racquel Zapanta LeGeros received her Ph.D. degree from New York University. She is currently a Professor and Associate Chair of the Department of Biomaterials and Biomimetics at New York University College of Dentistry. Her pioneering work was on substitution in the apatite structure and effect on properties. Her research interests includes biologic and synthetic apatites and related calcium phosphates, calcium phosphatebased biomaterials in the form of granules, scaffolds, cements, and coatings, and implant surface modifications. Her current research is on the development of calcium phosphate-based biomaterial for prevention of bone loss induced by diseases (e.g., osteoporosis), therapy (e.g., radiation), condition (e.g., mineral deficiency, immobility), and recovery of bone loss. She is married to Dr. John P. LeGeros and mother of Bernard, David, Katherine, and Alessandra. Chem. Rev. 2008, 108, 4742–4753 4742