Combined xeno/auto-grafting of a benign osteolytic lesion in a dog, using a novel bovine cancellous bone biomaterial

CASE HISTORY

A 4-year-old female Labrador Retriever was diagnosed with an osteolytic lesion of the right distal radius.

CLINICAL FINDINGS

Radiographs indicated a well-circumscribed radiolucent area 18 x 15 x 8 mm, centred on the distal radial physeal scar.

DIAGNOSIS

Histopathology, performed via Jamshidi needle biopsy and following surgical curettage, was inconclusive but suggested either an aneurysmal bone cyst or fibrous dysplasia.

CLINICAL RELEVANCE

A novel processed cancellous bovine bone xenograft was used in conjunction with autogenous cancellous bone (at a ratio of approximately 4:1) to fill the curetted defect. There were no observed complications associated with the use of this new biomaterial. Osteointegration of the bone graft was followed using conventional radiographs and peripheral quantitative computed tomography (pQCT) for 10 months post-operatively. Radiographically, the osteolytic lesion modelled to resemble metaphyseal trabeculation. The cross-sectional area and the average bone density of the grafted lesion determined using pQCT data increased over time, suggesting healthy osteoconduction and native bone production.

The novel use of waste animal bone from New Zealand agricultural sources as a feedstock for forming plasma sprayed hydroxyapatite coatings on biomedical implant materials

This study presents the feasibility of using animal bone-derived hydroxyapatite (HAP) as feedstock powders for plasma spraying. Bovine, cervine and ovine bone from abattoirs was boiled in a pressure cooker to remove blood, fat and adhering meat tissue. The bone was then placed in a muffler furnace, pyrolyzed at approximately 1000 degrees C to remove collagen and resid-ual organics, cooled and subsequently ground to a powder then digested in nitric acid. Sodium hydroxide was added to the digest to reprecipitate the HAP. Ageing of the precipitate followed by filtration, extensive washing and drying produced the white powder used as the feedstock. X-ray diffractometry (XRD) and Fourier transform infrared spectroscopy (FTIR) confirmed the powder to be poorly crystalline HAP with low-level carbonate. Out of several batches of the sieved powders, one batch was plasma sprayed to produce adherent HAP coatings; therefore, demonstrating that animal bone-derived HAP powders can be seri-ously considered as a feedstock powder, subject to the powder being processed for the correct rheological characteristics for easy flowing within the plasma spray flow lines. The phase composition of the successful plasma sprayed HAP coatings on both stainless steel and titanium were found by XRD to be mainly HAP with minor contributions from á -tricalcium phosphate, tetra-calcium phosphate and CaO; therefore, demonstrating that feedstock decomposition on its passage through the plasma spray torch was insignificant under the conditions employed. Scanning electron microscopy (SEM) micrographs of the coatings indicated that their morphology featured the classical heterogeneous and splat-like appearance expected of plasma sprayed coatings. Young's modulus and Vicker's microhardness tests conducted on the coatings revealed values in the range, respectively, 22-87 GPa and 166-287 (HV200 ) indicating high strength plasma spray HAP coatings had been produced from the feedstock powder.

The processing and characterization of animal-derived bone to yield materials with biomedical applications. Part III: material and mechanical properties of fresh and processed bovine cancellous bone

Conversion of bovine cancellous bone to a useful biomedical xenograft material involves several processing steps which include boiling, defatting and deproteination (i.e. bleaching). This study has shown how these processes can influence cancellous bone modulus and strength. It was found that prolonged boiling in water for six hours followed by NaOCl bleaching had a deleterious effect on the overall strength of the bovine bone. In contrast, bone samples subjected to only moderate boiling (1.5 hours) exhibited a 22% stiffness increase due mainly to the effects of drying. The same stiffened samples, when subjected to the bleaching procedure, retained some strength with only a small reduction in moduli values. It can be concluded that careful control of defatting and bleaching procedures on bovine bone is able to give a strong, albeit, brittle material with preservation of the original bone architecture. The bone xenograft materials are worthy of further investigation in in vivo clinical trials to assess their performance in contact with biological fluids.

The processing and characterization of animal-derived bone to yield materials with biomedical applications. Part II: milled bone powders, reprecipitated hydroxyapatite and the potential uses of these materials

Further studies on the processing and use of animal-bone-derived calcium phosphate materials in biomedical applications are presented. Bone powders sourced either from the direct crushing and milling of bovine, ovine and cervine bone or after being subjected to defatting and acid digestion/NaOH reprecipitation and sodium hypochlorite hydrogen peroxide treatment of animal bones were characterized using Fourier transform infra-red (FTIR) spectroscopy, 13C solid state magic angle spinning (MAS) nuclear magnetic resonance (NMR) spectroscopy, atomic absorption (AA) and inductively coupled plasma (ICP) spectrometric techniques. Bone powders were trialled for their potential use as a substrate for phosphine coupling and enzyme immobilization as well as a feedstock powder for plasma spraying on titanium metal substrates. Results indicated that enzyme immobilization by phosphine coupling could be successfully achieved on milled cervine bone with the immobilized enzyme retaining some activity. It was found that the presence of impurities normally carried down with the processing of the bone materials (viz., fat and collagen) played an important role in influencing the adsorbency and reactivity of the powders. Plasma spraying studies using reprecipitated bovine-derived powders produced highly adherent coatings on titanium metal, the composition of which was mostly hydroxyapatite (Ca10(PO4)6(OH)2) with low levels of alpha-tricalcium phosphate (alpha-Ca3(PO4)2) and tetracalcium phosphate (Ca4P2O9) also detected. In general, animal derived calcium phosphate materials constitute a potentially cheaper source of calcium phosphate materials for biomedical applications and make use of a largely under-utilized resource from abattoir wastes.

The processing and characterization of animal-derived bone to yield materials with biomedical applications: part 1: modifiable porous implants from bovine condyle cancellous bone and characterization of bone materials as a function of processing

A study on the development of a process to form materials suitable for biomedical xenograft implants from bovine cancellous bone is presented. Bone cubes cut from the condyle portion of bovine femurs sourced from abattoir waste were subjected to a defatting and subsequent deproteination procedure to produce shape-modifiable materials in which the biocompatible mineral calcium hydroxycarbonate apatite component was preserved in the original osseous architecture of the bovine bone. Optimum defatting was achieved by (1) thawing of the precut bone cubes in water, (2) pressure cooking at 15 psi in water, (3) soaking in 0.1 mol l(-1) NaOH followed by a thorough rinse under running water, (4) microwave heating of the bone cubes in water, (5) refluxing in methyl acetate and finally (6) removal of internal liquid from the cubes by shaking and then air drying. Subsequent deproteination of the defatted bone cubes was optimally achieved by (1) soaking in 5% sodium hypochlorite solution at ambient temperature using ultrasonication, (2) thorough rinsing of the cubes in water followed by drying. The final product is a defatted/deproteinated, bleached material that can be molded into various shapes for implant use in the body. The bone specimens were characterized by a suite of analytical techniques (i.e. infrared, 31P and 13C solid magic-angle spinning (MAS) nuclear magnetic resonance (NMR), X-ray photoelectron spectroscopies, atomic absorption (AA) spectrometry, inductively coupled plasma (ICP) spectrometry, differential scanning calorimetry (DSC), and scanning electron microscopy (SEM)) in order to follow compositional changes during the various stages of processing. In general, bovine condyles proved to be the best source of xenograft materials with condyles from other animal species (i.e. deer, sheep and ostrich) being too small to constitute a utilizable source of cancellous bone. This study shows how value can be added to a hitherto underutilized abattoir by-product by using simple processing techniques.

Growth of calcium phosphate on phosphorylated chitin fibres

Calcium phosphate growth on chitin phosphorylated fibres was studied using scanning electron microscopy and energy dispersive X-ray analysis (SEM, EDX), micro-Fourier transform infrared spectroscopy (FTIR), and solid state magic angle spinning nuclear magnetic resonance (MAS NMR) techniques. The C6 chemical shift positions of 13C MAS NMR in the chitin fibres phosphorylated using urea and H3PO4 are obvious indicating that phosphorylation takes place not in the C1 but in the C6 region. Micro-FTIR and 31P MAS NMR suggested that ammonium hydrogen phosphate formed during the phosphorylation procedure. Chitin fibres phosphorylated using urea and H3PO4 and then soaked in saturated Ca(OH)2 solution at ambient temperature, which lead to the formation of thin coatings formed by partial hydrolysis of the PO4 functionalities, were found to stimulate the growth of a calcium phosphate coating on their surfaces after soaking in 1.5xSBF solution for as little as one day. The thin layer after Ca(OH)2 treatment functioned as a nucleation layer for further calcium phosphate deposition after soaking in 1.5xSBF solution. EDX-measured Ca : P ratios of the coatings of Ca(OH)2-treated phosphorylated chitin in 1.5xSBF solution suggested that calcium-deficient apatite was formed.

Surface instability of calcium phosphate ceramics in tissue culture medium and the effect on adhesion and growth of anchorage-dependent animal cells

The surface of biocompatible ceramics made of synthesized hydroxyapatite (HAP) and beta-tricalcium phosphate (TCP) was found to be extremely active in tissue culture medium. Using mixed ceramics of HAP and TCP which had been prepared with different Ca/P molar ratios adjusted in stepwise fashion to values of 1.50, 1.55, 1.60, 1.64 and 1.67, the characteristics of the surface were investigated. The time-dependent variation of zeta potential of the TCP-HAP ceramics immersed in distilled water and in culture medium with and without addition of fetal bovine serum showed that the surface was unstable with significant changes in the charge being observed. Dry TCP powder had a zeta potential of -19 mV, which shifted to -7 mV after soaking in water and to -26 mV in culture medium. In contrast, HAP had a zeta potential of -11 mV in a dry state, -9 mV in water and -29 mV in culture medium. Concentrations of calcium and phosphate dissolved in distilled water showed the solubility was higher for TCP than for HAP. In comparison, it was found that dissolved calcium and phosphate in the medium were removed from the solution by deposition on immersed TCP-HAP ceramics. These results suggested that the stability of the surface was closely related to both reactions of association and dissociation of calcium and phosphate in tissue culture medium. The zeta potential analysis also suggested that Ca-deficient HAP, which has a similar crystal structure to HAP with a Ca/P ratio less than 1.67, was generated by degradation and reforming of the surface layer. The most stable structure which was the most suitable for adhesion of L-929 cells was obtained by the mixture of 20% TCP and 80% HAP ceramics. In conclusion, the stability of the surface structure was considered to be the dominant factor for the enhancement of the adhesiveness of cells on TCP-HAP ceramics.