Vita Zalite

Porous hydroxyapatite for drug delivery

The disadvantages of systemic drug therapy are that only a small fraction of any given dose actually reaches the surgical site, producing low-therapeutic tissue levels. An alternative approach is based on the use of implantable delivery tools, able to release the active substance in a controlled way. Biocompatibility, bioactivity, and osteoconductivity are the main driving forces of calcium phosphate biomaterials, promoting their application as bone substitutes. At the same time, multimodal porous structure and interconnectivity of pores make them promising candidates for site-specific drug delivery. The use of porous hydroxyapatite as a drug delivery system could result in a dual effect: the ability to interact with the bone tissues at the same time ensuring increased drug efficiency, controlled release, and site-specific delivery.

New Biphasic Calcium Phosphate in Orthopedic Surgery: First Clinical Results

This study evaluated first results of biphasic phosphate (BCP) ceramic granules with hydroxyapatite (HAp)/ β-tricalcium phosphate (TCP) ratio of 90/10 as bone substitute for reconstruction of the bone defects in orthopedic surgery, such as fracture and fracture non union treatment, primary and revision arthroplasty and chronic osteomyelitis. We evaluated twelve clinical cases of patients who had undergone surgeries with BCP implantation. Follow up period range from 2 to 8 months, on average 4.5 months. The classification of results was based on clinical and radiographic assessments. The size of defects ranged from 32 cm to 1 cm, average 6.42 cm, median 3 cm. The best results were obtained from patients after elective orthopedic procedures and patients with bone defects less than 3 cm.

The Effect of Pore Forming Agent Particle Size on the Porosity, Microstructure and In Vitro Studies of Hydroxyapatite Ceramics

In situ viscous mass foaming with ammonium bicarbonate (NH4HCO3)as foaming agent was used for the preparation of porous hydroxyapatite ceramics. Three different particle fractions (100-300 μm, 300-500 μm, 500-1000 μm) of NH4HCO3 were used in order to evaluate the particle size effect on the ceramic microstructure. Foamed and dried green bodies were sintered at 1150°C. The porosity and microstructure of ceramics were determined with Archimedes method and scanning electron microscopy. As the NH4HCO3 particle fraction was decrease from 100-300 μm to 500-1000 μm, the open porosity increased from 42 to 54 %. In situ viscous mass foaming leads to the interconnected pore channels with wide pore size range (10-600 μm). In the present work cytotoxicity of obtained porous HA ceramics and fibroblast cell viability was investigated.

Characterization of Different Hydroxyapatite Particles for Tooth Enamel Remineralization

In current research three different prepared calcium deficient hydroxyapatite samples were evaluated for dental application. Lyophilized (lyoCDHAp), spray dried (spCDHAp) powders and wet precipitates (pCDHAp) were characterized by XRD, FTIR, SEM and BET analysis. Results showed, that various drying processes did not affect initial crystallinity, phase and chemical composition of samples. Small agglomerates (up to 2 μm) beside separated particles for lyoCDHAp and spCDHAp were observed in SEM analysis. LyoCDHAp and spCDHAp powders could be used as desensitizing component in the dentifrice, while pCDHAp could be more resorbable due to smaller particle size and induce remineralization of caries sites in the enamel.

Change of Biomechanical Parameters in the Lower Jaws of Rabbits with Experimental Osteoporosis after Implantation of Calcium-Phosphate Bioceramic Material in the Greater Trochanter Region

Investigation of biomechanical properties of the rabbit bone tissue from a corner of the lower jaw was done. Experimental osteoporosis was induced by ovariectomy and following injections of methylprednisolone. The defects in the greater trochanter region was created and filled with granules of a hydroxyapatite and tricalcium phosphate (HAP/TCP 30/70) or HAP/TCP 30/70 together with 5% strontium ranelate. After 3 month animals were euthanased, squared samples have been cut out from a corner of the lower jaw and tested on a bend. Results of research show, that the corner of a lower jaw in rabbit becomes more rigid after filling of defects in the greater trochanter region with granules of a hydroxyapatite and tricalcium phosphate (HAP/TCP 30/70) or granules together with strontium ranelate. The ultimate strain for the bone tissue in the 2nd and 3rd group is less, than for control group. Thus, local uses calcium – phosphatic bioceramic material around the greater trochanter region improves biomechanical parameters of a bone tissue in the lower jaw of animals.

Characterization and Preparation of Calcium Phosphate Model Toothpaste for Tooth Enamel Remineralization

Calcium phosphates are excellent biomaterial for hard tissue regeneration and replacement. Recently, nanohydroxylapatite (HAp) has been intensively studied as remineralization agent for tooth enamel protection and remineralization. In this research, we developed model toothpaste composition, determined viscosity and investigated weather different processed – spray-dried (spCDHAp), lyophilized (lyoCDHAp), wet precipitated (paste-like consistence, pCDHAp) – calcium deficient hydroxyapatite (CDHAp) affect bovine tooth enamel remineralization. Model toothpastes components were CDHAp, 2-hydroxyethylcelluloce, glycerol and water. Viscosity varied from 2.5 to 40 Pa∙s. Model toothpastes with 20 wt% CDHAp showed thixotropic behaviour, thereby we examined them as potential tooth remineralization pastes. After in vitro remineralization enamel surface changes were detected, the texture of demineralized surface and bundles of HAp crystals were not observed. It was suggested, that new calcium phosphate layer was formed on the enamel. In conclusion, CDHAp is very promising material for enamel regeneration, but different pretreatment of CDHAp (resulting as different morphology of agglomerates) did not give distinctive remineralization results.

Ultrastructural Characteristics of Tissue Response after Implantation of Calcium Phosphate Ceramics in the Mandible of Rabbit

This study is undertaken in order to explore interaction between calcium phosphate bioceramics and surrounding tissues in the mandible of rabbit. The tissue response was evaluated 6 months after implantation of ceramics. Three kinds of porous bioceramics were studied: hydroxyapatite (HAp) and HAp mixture with β-tricalcium phosphate (95%HAp/5%β-TCP and 80%HAp/20%β-TCP). X-ray diffractometry (XRD), Fourier transform infrared spectroscopy (FT-IR) and scanning electron microscopy (SEM) were used to characterize porous bioceramic samples. Transmission electron microscopy (TEM), light microscopy and SEM examinations were applied for evaluation of interaction between tissues and bioceramics. The open porosity of obtained samples is in range between 50 to 60%. Pores have not specific form and mainly they are interconnected. The histological studies demonstrated appearance of a thick fibrous collagenous capsule formed around the pure HAp and presented by densely packed fibers and flattened fibrocytes, while addition of b-TCP evidenced highly vascularized adipose tissue.