Purpose The aim of this study was to examine the in vivo characteristics and levels of integration and degradation of a ready-to-use bone grafting block with elastic properties (elastic block) for the use in surgery. Materials and methods Thirty-six male Wistar rats underwent surgical creation of a well-defined bone defect in the tibia. All created defects – one per animal – were filled with an unsintered nanocrystalline hydroxyapatite embedded either with a non-cross-linked hydrogel carrier (CONT, n=18) or a cross-linked hydrogel carrier (elastic block [EB], n=18) based on polyvinylpyrrolidone (PVP) and silica sol, respectively. The animals were killed after 12 (n=12), 21 (n=12) and 63 days (n=12). The bone formation and defect healing were quantified by histomorphometric measurements made in paraffin sections. Additionally, immunohistochemical (tartrate-resistant acid phosphatase [TRAP] and alkaline phosphatase [aP]), antibody-based examinations (CD68) and energy-dispersive x-ray scattering measurements of silica atom concentration were carried out. Results A larger remaining bone defect area overall was observed in EB after 12 days and 21 days. After 63 days, similar areas of remaining bone defects were found. The amount of the remaining carrier material in EB overall was higher at all times. In CONT no residual carrier material was found at 12 days and later. CD68 analyses showed significantly lower level of CD68-positive marked cells after 21 days in CONT, and nonsignificant differences at 12 and 63 days, respectively. Additionally, a significantly higher level of aP-positive marked cells was observed in CONT after 12 days. Later on, the levels of aP-positive marked cells were slightly higher in EB (21 and 63 days). Furthermore, no significant differences regarding the level of TRAP-positive marked cells in each group were observed. Conclusion The bone substitute (EB) with the cross-linked PVP-based hydrogel carrier leads at the beginning to a higher amount of remaining carrier material and remaining bone substitute. This delayed degradation is supposed to be the reason for the observed lower level of bone remodeling and is caused by the irradiation changes (cross links) in the structure in PVP.

Improved handling characteristics of bone substitute materials may facilitate surgical handling. However, the respective modifications should not alter the biological activity. For comparison of a granular and a putty form of two silicaenhanced bone substitute materials, in 30 rabbits, bilateral bone defects were created in the femoral condyle and randomly filled with (1) sintered, silica-enhanced (0.8 wt%) hydroxyapatite (ACg, n ¼ 15); (2) ACg plus resorbable polymer (ACp, n ¼ 15); (3) non-sintered silica-enhanced hydroxyapatite (hydroxyapatite/SiO 2 ratio:61:39 wt%; NBg, n ¼ 15); and (4) NBg plus matrix of resorbable polymer (NBp, n ¼ 15). After 4, 8, and 12 weeks, respectively, newformed bone, remaining bone substitute materials, and amount of soft tissue were quantified histomorphometrically. After four weeks, new-formed bone was increased for NBg/NBp in which NBp showed significantly less remaining bone substitute materials when compared to ACg. After two months, the highest amount of new-formed bone and the least remaining bone substitute materials were seen for NBg and NBp. ACp had less remaining bone substitute material when compared to ACg. In addition, amount of soft tissue was significantly enhanced in NBp when compared to ACg and NBg. After 12 weeks, NBp had significantly lower remaining bone substitute material when compared to ACg. Amount of soft tissue was significantly increased in NBp when compared to ACg and NBg. In accordance, based on an early increase of new-formed bone, a lower amount of remaining bone substitute material, and as well as a distinct degradation, superiority of the non-sintered bone substitute material to the sintered bone substitute material was seen. The effect of the resorbable polymer to each bone substitute material can be supposed to be rather marginal.

NanoBone®Block is the alternative to autogenous bone blocks and offers doctors a rapid, simple operating procedure in combination with a low risk of complications. Aim of this work was to develop a bone grafting block with elastic properties for dental and orthopedic surgery which is ready to use. An easy handling has to be connected with quick regeneration. Therefore, NB granules have been combined with an elastic hydrogel carrier based on Polyvinylpyrrolidone (PVP) and silica sol. Mechanical properties were optimized for an enhanced handling by cross linking and simultaneous sterilization of the PVP with gamma radiation. Cross linked PVP has the capability of swelling in water without being solved. To approve biocompatibility of adjusted material anin vivostudy was analyzed using a standardized bone defect model in rat tibiae. Defect was filled with elastic bone grafting material. After 21 and 63 days rats were sacrificed and tibias analyzed. Histomorphological analysis showed an increased bone formation but even a decelerated resorption of elastic biomaterial. Quantitative compositional analysis showed a decrease in silicon content of granules as a process of matrix change.

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