Histomorphometric Analysis of Bone Repair in Critical Size Defect in Rats Calvaria Treated with Hydroxyapatite and Zinc-Containing Hydroxyapatite 5%

Structure and biological compatibility of polycaprolactone/zinc-hydroxyapatite electrospun nanofibers for tissue regeneration

Although guided tissue regeneration (GTR) is a useful tool for regenerating lost tissue as bone and periodontal tissue, a biocompatible membrane capable of regenerating large defects has yet to be discovered. This study aimed to characterize the physicochemical properties and biological compatibility of polycaprolactone (PCL) membranes associated with or without nanostructured hydroxyapatite (HA) (PCL/HA) and Zn-doped HA (PCL/ZnHA), produced by electrospinning. PCL, PCL/HA, and PCL/ZnHA were characterized by field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), energy dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD), thermal gravimetric analysis (TGA), and differential scanning calorimetry (DSC). Nanoparticles of HA or ZnHA were homogeneously distributed and dispersed inside the PCL fibers, which decreased the fiber thickness. At 1 wt% of HA or ZnHA, these nanoparticles acted as nucleating agents. Moreover, HA and ZnHA increased the onset of the degradation temperature and thermal stability of the electrospun membrane. All tested membranes showed no cytotoxicity and allowed murine pre-osteoblast adhesion and spreading; however, higher concentrations of PCL/ZnHA showed less cells and an irregular cell morphology compared to PCL and PCL/HA. This article presents a cytocompatible, electrospun, nanocomposite membrane with a novel morphology and physicochemical properties that make it eligible as a scaffold for GTR.

Evaluation of the In Vivo Biocompatibility of Amorphous Calcium Phosphate-Containing Metals

Among the biomaterials based on calcium phosphate, hydroxyapatite has been widely used due to its biocompatibility and osteoconduction. The substitution of the phosphate group by the carbonate group associated with the absence of heat treatment and low synthesis temperature leads to the formation of carbonated hydroxyapatite (CHA). The association of CHA with other metals (strontium, zinc, magnesium, iron, and manganese) produces amorphous calcium phosphate-containing metals (ACPMetals), which can optimize their properties and mimic biological apatite. This study aimed to evaluate the biocompatibility and biodegradation of ACPMetals in mice subcutaneous tissue. The materials were physicochemically characterized with Fourier Transform InfraRed (FTIR), X-Ray Diffraction (XRD), and Atomic Absorption Spectrometry (AAS). Balb-C mice (n = 45) were randomly divided into three groups: carbonated hydroxyapatite, CHA (n = 15), ACPMetals (n = 15), and without implantation of material (SHAM, n = 15). The groups were subdivided into three experimental periods (1, 3, and 9 weeks). The samples were processed histologically for descriptive and semiquantitative evaluation of the biological effect of biomaterials according to ISO 10993-6:2016. The ACPMetals group was partially biodegradable; however, it presented a severe irritating reaction after 1 and 3 weeks and moderately irritating after nine weeks. Future studies with other concentrations and other metals should be carried out to mimic biological apatite.

Zinc as a Therapeutic Agent in Bone Regeneration

Zinc is an essential mineral that is required for normal skeletal growth and bone homeostasis. Furthermore, zinc appears to be able to promote bone regeneration. However, the cellular and molecular pathways through which zinc promotes bone growth, homeostasis, and regeneration are poorly understood. Zinc can positively affect chondrocyte and osteoblast functions, while inhibiting osteoclast activity, consistent with a beneficial role for zinc in bone homeostasis and regeneration. Based on the effects of zinc on skeletal cell populations and the role of zinc in skeletal growth, therapeutic approaches using zinc to improve bone regeneration are being developed. This review focuses on the role of zinc in bone growth, homeostasis, and regeneration while providing an overview of the existing studies that use zinc as a bone regeneration therapeutic.

Biological evaluation of zinc-containing calcium alginate-hydroxyapatite composite microspheres for bone regeneration

Zinc is an important element for bone structure and metabolism. Its interaction with hydroxyapatite has been investigated for the improvement of bone repair. The objective of this study was to evaluate the in vitro and in vivo biological response to nanostructured calcium alginate-hydroxyapatite (HA) and zinc-containing HA (ZnHA). Cytocompatibility was evaluated by applying PrestoBlue reagent after exposing murine pre-osteoblast cells to extracts of each biomaterial microspheres. After physical and chemical characterization, the biomaterial microspheres were implanted in a critical size calvaria defect (8 mm) in Wistar rats (n = 30) that were randomly divided into the HA and ZnHA groups. Tissue samples were evaluated through histological and histomorphometric analyses after 1, 3, and 6 months (n = 5). The results showed cellular viability for both groups compared to the negative control, and no differences in metabolic activity were observed. The HA group presented a significant reduction of biomaterial compared with the ZnHA group in all experimental periods; however, a considerable amount of new bone formation was observed surrounding the ZnHA spheres at the 6-month time point compared with the HA group (p < .05). Both biomaterials were biocompatible, and the combination of zinc with hydroxyapatite was shown to improve bone repair.

Calcium silicate as a graft material for bone fractures: a systematic review

Objective

The goal of this review was to determine whether calcium silicate (wollastonite) as a bone graft material is a viable alternative to autogenous bone or whether the evidence base for its use is weak.

Methods

In this systematic review, electronic databases (MEDLINE/PubMed and BVS) were searched for relevant articles in indexed journals. Articles published in a 10-year period were identified (n = 48). After initial selection, 17 articles were assessed for eligibility; subsequently, seven articles were excluded and 10 articles were included.

Results

Among the studies included, 20% emphasized the importance of randomization, which adds reliability to the study, minimizing the risk of bias. High variability was observed in the material used, such as additives, amounts, dosage, and chemical alterations, rendering direct comparison among these studies impossible. The experimental periods varied considerably; one of the studies did not include statistical analysis, weakening the evaluation. Nonetheless, the true potential of wollastonite as a graft material conducive to new bone formation was reported in all studies.

Conclusion

The results support the use of wollastonite as a bone graft material. The initial research question was answered despite the significant variability observed among these preclinical studies, which hindered the precision of this analysis.

Physico-chemical and Histomorphometric Evaluation of Zinc-containing Hydroxyapatite in Rabbits Calvaria

The aim of this study was to characterize the physico-chemical properties and bone repair after implantation of zinc-containing nanostructured porous hydroxyapatite scaffold (nZnHA) in rabbits' calvaria. nZnHA powder containing 2% wt/wt zinc and stoichiometric nanostructured porous hydroxyapatite (nHA - control group) were shaped into disc (8 mm) and calcined at 550 °C. Two surgical defects were created in the calvaria of six rabbits (nZnHA and nHA). After 12 weeks, the animals were euthanized and the grafted area was removed, fixed in 10% formalin with 0.1 M phosphate buffered saline and embedded in paraffin (n=10) for histomorphometric evaluation. In addition, one sample from each group (n=2) was embedded in methylmethacrylate for the SEM and EDS analyses. The thermal treatment transformed the nZnHA disc into a biphasic implant composed of Zn-containing HA and Zn-containing β-tricalcium phosphate (ZnHA/βZnTCP). The XRD patterns for the nHA disc were highly crystalline compared to the ZnHA disc. Histological analysis revealed that both materials were biologically compatible and promoted osteoconduction. X-ray fluorescence and MEV-EDS of nZnHA confirmed zinc in the samples. Histomorphometric evaluation revealed the presence of new bone formation in both frameworks but without statistically significant differences (p>0.05), based on the Wilcoxon test. The current study confirmed that both biomaterials improve bone repair, are biocompatible and osteoconductive, and that zinc (2wt%) did not increase the bone repair. Additional in vivo studies are required to investigate the effect of doping hydroxyapatite with a higher Zn concentration.

Long-term biocompatibility evaluation of 0.5 % zinc containing hydroxyapatite in rabbits

This study investigates the long-term biocompatibility of 0.5 % zinc-containing hydroxyapatite compared with hydroxyapatite. Spheres (425 < ∅ < 550) of both materials were produced by extrusion of ceramic slurry in calcium chloride and characterized by FTIR, XRD, XRF and SEM. Fifteen White New Zealand rabbits were submitted to general anesthesia, and an perforation (2 mm), was made in each tibia, one for zinc-containing hydroxyapatite sphere implantation and one for hydroxyapatite sphere implantation. After 26, 52 and 78 weeks, the animals were euthanized, and the fragment containing the biomaterial was harvested. A 30-50 μm section was obtained for histological analysis in bright field and polarized light. SEM images revealed similar morphologies between the tested biomaterials. Histological analysis showed that there was no difference between the test groups. The morphometric analysis, however, indicates that there was a greater absorption. The materials are biocompatible, promote osteogenesis and that the zinc-containing hydroxyapatite microspheres were absorbed more quickly.