Hydrogel-embedded nanocrystalline hydroxyapatite granules (elastic blocks) based on a cross-linked polyvinylpyrrolidone as bone grafting substitute in a rat tibia model

Abstract

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.

Properties of Calcium Phosphate/Hydrogel Bone Grafting Composite on the Model of Diaphyseal Rat Femur’s Defect: Experimental Study

“…Для каждого об разца проводили вычисление на трех препаратах, всего для каждой группы получалось 18 значений (только для групп «Хронос 3 недели» и «Контроль 6 недель» -15 значений). обСуЖдение Для исследования биологических свойств ма териалов in vivo используются различные моде ли как по выбору животных (мыши [22], крысы [23,24,25,26,27], кролики [28], собаки [29], так и по методике имплантации. Очевидно, что дефект для изучения свойств материалов должен быть критическим, то есть не иметь возможности спон танного замещения.…”

A novel classification of bone graft materials

“…Polymers such as chitosan, 128 pullulan/dextran, 87 and poly(phosphazene) 153 have also been used to make hydrogels and studied in vivo, exhibiting good levels of bone regeneration. However, polyvinylpyrrolidone, when used as a carrier of HAp nanoparticles, underwent slow degradation, and interfered with new bone formation 154 . Injectable hydrogels have been made from hyaluronan, which, when combined with β‐TCP, induced significantly more new bone formation than control defects that were left unfilled 155 .…”

“…However, polyvinylpyrrolidone, when used as a carrier of HAp nanoparticles, underwent slow degradation, and interfered with new bone formation. 154 Injectable hydrogels have been made from hyaluronan, which, when combined with β-TCP, induced significantly more new bone formation than control defects that were left unfilled. 155 Alginate/hyaluronic acid composites have been used as hydrogels with various crosslinking agents to deliver MSCs and BMP-2 to mandibular defects in mini-pigs showing successful osteogenic induction and bone regeneration.…”

In vivo comparison of a granular and putty form of a sintered and a non-sintered silica-enhanced hydroxyapatite bone substitute material

“…13 For example, shape builder like polyvinylpyrrolidone or Poloxamer P407 could be combined with the BSM in order to enhance the respective handling characteristics. 14,15 Besides, they could be used to avoid strong compression forces on the BSM during application [15][16][17] or even as a drug carrier. 18 However, the addition of resorbable polymers to the BSM might have an influence on the respective biological characteristics 14 that should be verified before clinical use.…”

“…14,15 Besides, they could be used to avoid strong compression forces on the BSM during application [15][16][17] or even as a drug carrier. 18 However, the addition of resorbable polymers to the BSM might have an influence on the respective biological characteristics 14 that should be verified before clinical use. Therefore, the aim of the study was to compare the conventional, granular form of two silicon-substituted BSM with their modified putty form.…”