Karin A. Hing

Bio: Karin A. Hing is an academic researcher from Queen Mary University of London. The author has contributed to research in topics: Bone regeneration & Apatite. The author has an hindex of 27, co-authored 53 publications receiving 3861 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.

Bone repair in the twenty-first century: biology, chemistry or engineering?

Abstract: Increases in reconstructive orthopaedic surgery, such as total hip replacement and spinal fusion, resulting from advances in surgical practice and the ageing population, have lead to a demand for bone graft that far exceeds supply. Consequently, a number of synthetic bone-graft substitutes (BGSs) have been developed with mixed success and surgical acceptance. Skeletal tissue regeneration requires the interaction of three basic elements: cells, growth factors (GFs) and a permissive scaffold. This can be achieved by pre-loading a synthetic scaffold with GFs or pre-expanded cells; however, a 'simpler' approach is to design intrinsic 'osteoinductivity' into your BGS, i.e. the capability to recruit and stimulate the patient's own GFs and stem cells. Through investigation of the mechanisms controlling bone repair in BGSs, linking interactions between the local chemical and physical environment, scientists are currently developing osteoinductive materials that can stimulate bone regeneration through control of the scaffold chemistry and structure. Moreover, this body of research is providing the foundations for future generations of BGSs and bone-repair therapies and may ultimately contribute towards improving the quality of life through maintenance of the skeleton and reversal of disease states, as opposed to the mending of broken bones that we currently practice. Will we be able to grow our own bones in a bioreactor for use as autologous graft materials in the future? Could surgery be limited to accidental trauma cases, with greater restoration of function through biochemical or gene therapies? The technology and research probes necessary to this task are currently being developed with the advent of nanotechnology, genomics and proteomics: are we about to embark on a chemical revolution in medicine? This paper aims to discuss some of the current thinking on the mechanisms behind bioactivity and biocompatibility in bone and how a fuller understanding of the interactions between cells and the materials used today could bring about completely new approaches for the treatment of bone fracture and disease tomorrow.

Bioceramic Bone Graft Substitutes: Influence of Porosity and Chemistry

Abstract: Bioceramics have been considered for use as synthetic bone graft substitutes (BGSs) for over 30 years, throughout which there have been two primary areas of research: (i) optimization of the physical pore structure and (ii) formulation of an appropriate bioceramic chemistry. While it is well recognized that both the rate of integration and the final volume of regenerated bone are primarily dependent on the macroporosity, there still seems to be some dispute regarding the optimum “type” of porosity. The rate and quality of bone integration have, in turn, been related to a dependence on pore size, porosity volume fraction, and interconnection size and interconnection density, both as a function of structural permeability and mechano-transduction. Moreover, the role of strut microstructure and pore geometry have been considered with respect to their influence on entrapment and recruitment of growth factors (GFs) in addition to its influence on scaffold mechanics. Deconvoluting the relative affects of these parameters is complicated by the use of both resorbable and nonresorbable bioactive bioceramics, which are believed to mediate bioactivity in the osseous environment through two principal mechanisms: (i) directly through dissolution and release of ionic products in vivo, elevating local concentrations of soluble species that interact directly with local cells or influence cell behavior by their effect on local pH, (ii) indirectly through the influence that surface chemistry will have on protein adsorption, GF entrapment, and subsequent cell attachment and function. This article aims to review some of the recent developments in bioceramic BGSs, with a view to understanding how the various physiochemical parameters may be optimized to promote bone healing.

Characterization of porous hydroxyapatite

Abstract: Hydroxyapatite has been considered for use in the repair of osseous defects for the last 20 years. Recent developments have led to interest in the potential of porous hydroxyapatite as a synthetic bone graft. However, despite considerable activity in this field, regarding assessment of the biological response to such materials, the basic materials characterization is often inadequate. This paper documents the characterization of the chemical composition, mechanical integrity, macro- and microstructure of a porous hydroxyapatite, Endobon (E. Merck GmbH), intended for the bone-graft market. Specimens possesed a range of apparent densities from 0.35 to 1.44 g cm(-3). Chemical analysis demonstrated that the natural apatite precursor of Endobon was not converted to pure hydroxyapatite, but retained many of the ionic substituents found in bone mineral, notably carbonate, sodium and magnesium ions. Investigation of the microstructure illustrated that the struts of the material were not fully dense, but had retained some traces of the network of osteocyte lacunae. Macrostructural analysis demonstrated the complex inter-relationship between the structural features of an open pore structure. Both pore size and connectivity were found to be inversely dependent on apparent density. Furthermore, measurement of pore aspect ratio and orientation demonstrated a relationship between apparent density and the degree of macrostructural anisotropy within the specimens, while, it was also noted that pore connectivity was sensitive to anisotropy. Compression testing demonstrated the effect of apparent density and macrostructural anisotropy on the mechanical properties. An increase in apparent density from 0.38 to 1.25 g cm(-3) resulted in increases in ultimate compressive stress and compressive modulus of 1 to 11 MPa and 0.2 to 3.1 GPa, respectively. Furthermore, anisotropic high density (> 0.9 g cm(-3)) specimens were found to possess lower compressive moduli than isotropic specimens with equivalent apparent densities. These results underline the importance of full structural and mechanical characterization of porous ceramic implant materials.

Bioinspired structural materials

Abstract: Natural structural materials are built at ambient temperature from a fairly limited selection of components. They usually comprise hard and soft phases arranged in complex hierarchical architectures, with characteristic dimensions spanning from the nanoscale to the macroscale. The resulting materials are lightweight and often display unique combinations of strength and toughness, but have proven difficult to mimic synthetically. Here, we review the common design motifs of a range of natural structural materials, and discuss the difficulties associated with the design and fabrication of synthetic structures that mimic the structural and mechanical characteristics of their natural counterparts.

Three-dimensional scaffolds for tissue engineering applications : role of porosity and pore size

Abstract: Tissue engineering applications commonly encompass the use of three-dimensional (3D) scaffolds to provide a suitable microenvironment for the incorporation of cells or growth factors to regenerate ...

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.