Biomedical subjects

M Shirkhanzadeh

Publications and source records attributed to M Shirkhanzadeh.

6 recordsLinked to original sources

PubMed2005

Microneedles coated with porous calcium phosphate ceramics: effective vehicles for transdermal delivery of solid trehalose.

Trehalose (alpha-D-glucopyranosyl-alpha-D-glucopyranoside) is recognized as a promising fast-dissolving solid reservoir capable of stabilizing the native structure of proteins and suitable for loading with a wide variety of bioactive substances. Currently, there is a growing interest in developing cost-effective methods for immobilizing solid trehalose on arrays of microneedles for delivering protein-based and DNA-based vaccine to the epidermis. In the present work, micro-porous calcium phosphate coatings were used to provide a biocompatible interface with a large surface area for the effective immobilization of trehalose on microneedles. Calcium phosphate coatings with varying degrees of porosity were electrochemically synthesized on the tips of stainless steel acupuncture needles and loaded with solid trehalose. Skin experiments were designed to determine the ability of micro-porous calcium phosphate coatings to deliver solid trehalose into epidermis without breaking during insertion. The mechanical performance of the coatings was assessed by inserting the tips of the coated needles into human skin to an average depth of 100-300 microm and then removing them for analysis by scanning electron microscopy. Microporous calcium phosphate coatings loaded with trehalose effectively breached the stratum corneum and allowed direct access to the epidermis without breaking and without stimulating nerves in deeper tissues.

Administration, Cutaneous↗

PubMed1998

Direct formation of nanophase hydroxyapatite on cathodically polarized electrodes.

Ultrafine-grained, nanophase coatings of hydroxyapatite were synthesized by electrocrystallization from dilute electrolytes ([Ca]=6.1 x 10-4 M, [phosphate]=3.6 x 10-4 M) at pH values comparable with the biological pH. At these comparatively low supersaturations, hydroxyapatite is shown to be precipitated without the formation of a precursor phase. A description of the sequence of events occurring at the electrode-electrolyte interface is given to explain the mechanism involved in the direct formation of nanophase hydroxyapatite on polarized electrodes.

Journal Article↗

PubMed1998

Nanoporous alkoxy-derived titanium oxide coating: a reactive overlayer for functionalizing titanium surface.

Effective immobilization of bioactive substances such as adhesive proteins, synthetic peptides and growth factors on metallic substrates is required for a number of medical applications. In the present work, evidence is presented to show that an alkoxy-derived nano-porous titanium oxide coating, synthesized electrochemically on titanium in methanolic electrolytes, may act as an effective interface for functionalizing a titanium surface. It is demonstrated that nanoporous oxide coatings could facilitate fast diffusion of small organic molecules within the oxide network and form strong chemical bonds with the functional groups of these molecules at room temperature. Fourier transformed-infrared spectroscopy was used to investigate the nature of the interfacial interactions between the oxide network and a range of molecules containing COOH, OH, NH2, C=O and phosphoric acid functional groups. The results indicate that the nanometre-sized oxide clusters within the coating may play an essential role in effective immobilization of organic molecules by providing numerous binding sites for chemisorption of these species. The surface-derivatized oxide coating may provide a solid phase for the subsequent attachment of a broad range of biochemically active molecules on the titanium surface.

Journal Article↗

PubMed1998

Interaction between self-assembled protein vesicles and microporous apatite surface.

Self-assembled structures such as vesicles have generated immense interest in recent decades due to their potential in mimicking biological membranes and in acting as drug-delivery systems. Despite the importance of the interaction between these organized assemblies and the surface of biomaterials, little is known about the mechanism involved. In this study, the interaction between giant proline-rich mussel adhesive protein (MAP) vesicles and the microporous apatite surface was investigated by scanning electron microscopy (SEM). We have found that MAP vesicles incubated on the apatite surface similar to osteoclasts, induce site-specific resorption of the apatite surface. However, in contrast to the osteoclastic resorption, the vesicle-induced resorption process appears to be accompanied by an organic matrix-mediated remineralization process. This results in the formation of a variety of complex three-dimensional site-specific "remodelled zones" on the apatite surface of micrometre scale. The mechanism of the formation of "remodelled zones" is discussed in terms of surface phenomena, such as adsorption and deformation of vesicles, site-specific release of resorptive agents, organic matrix-directed remineralization, and Ca-induced fusion, collapse and reshaping of the vesicles on the apatite surface.

Journal Article↗

PubMed1998

Formation of carbonate apatite on calcium phosphate coatings containing silver ions.

The prerequisite for bioactive materials to bond to living bone is the formation of biologically equivalent carbonate apatite on their surfaces in the body. Calcium phosphate ceramic surfaces can be transformed to a biological apatite through a series of surface reactions including dissolution-precipitation and ion exchange. In the present work, apatite coatings with different crystallinity, compositions and crystal sizes, including a well-crystallized hydroxyapatite coating, were synthesized electrochemically and doped with silver ions in silver nitrate solution at room temperature. The formation of a new carbonate apatite on the surface of these coatings was investigated in an acellular simulated body fluid with ion concentrations comparable with those of human blood plasma, using scanning electron microscopy and Fourier transform-infrared spectroscopy. The results show that small quantities of silver ions incorporated into apatite coatings may have a strong stimulatory effect on the formation of carbonate apatite without adversely affecting the chemical stability of these coatings.

Journal Article↗

PubMed1997

Immobilization of calcium phosphate nano-clusters into alkoxy-derived porous TiO2 coatings.

Alkoxy-derived porous coatings of titanium oxide were fabricated on commercially pure titanium substrates by an electrochemical method in methanolic electrolytes. Nano-clusters of brushite (CaHPO4. 2H2O) were immobilized into the pores of the oxide network by reacting these coatings in acidic calcium phosphate solutions at 50 degrees C. The acid-base reaction between calcium phosphate solutions and the hydroxyl groups of the oxide network resulted in the formation of nano-clusters of brushite crystals immobilized inside the oxide pores. This treatment resulted in the conversion of the porous oxide network into a coherent mass with improved physical integrity. Nano-clusters of brushite crystals immobilized in the oxide matrix were converted into amorphous calcium phosphate (ACP) and poorly crystallized hydroxyapatite (HA) by further treatment of the oxide in alkaline solutions. The porous oxide coating also reacted strongly with concentrated phosphoric acid. The phosphate-modified oxide resulting from this reaction was further treated in calcium hydroxide solution to form nano-clusters of poorly crystallized HA within the oxide network.

Journal Article↗