Organic-inorganic interaction and the growth mechanism of hydroxyapatite crystals in gelatin matrices between 37 and 80 degrees C

Calcium Orthophosphate (CaPO4) Containing Composites for Biomedical Applications: Formulations, Properties, and Applications

The goal of this review is to present a wide range of hybrid formulations and composites containing calcium orthophosphates (abbreviated as CaPO4) that are suitable for use in biomedical applications and currently on the market. The bioactive, biocompatible, and osteoconductive properties of various CaPO4-based formulations make them valuable in the rapidly developing field of biomedical research, both in vitro and in vivo. Due to the brittleness of CaPO4, it is essential to combine the desired osteologic properties of ceramic CaPO4 with those of other compounds to create novel, multifunctional bone graft biomaterials. Consequently, this analysis offers a thorough overview of the hybrid formulations and CaPO4-based composites that are currently known. To do this, a comprehensive search of the literature on the subject was carried out in all significant databases to extract pertinent papers. There have been many formulations found with different material compositions, production methods, structural and bioactive features, and in vitro and in vivo properties. When these formulations contain additional biofunctional ingredients, such as drugs, proteins, enzymes, or antibacterial agents, they offer improved biomedical applications. Moreover, a lot of these formulations allow cell loading and promote the development of smart formulations based on CaPO4. This evaluation also discusses basic problems and scientific difficulties that call for more investigation and advancements. It also indicates perspectives for the future.

Dystrophic calcinosis: structural and morphological composition, and evaluation of ethylenediaminetetraacetic acid ('EDTA') for potential local treatment

BACKGROUND

To perform a detailed morphological analysis of the inorganic portion of two different clinical presentations of calcium-based deposits retrieved from subjects with SSc and identify a chemical dissolution of these deposits suitable for clinical use.

METHODS

Chemical analysis using Fourier Transform IR spectroscopy ('FTIR'), Raman microscopy, Powder X-Ray Diffraction ('PXRD'), and Transmission Electron Microscopy ('TEM') was undertaken of two distinct types of calcinosis deposits: paste and stone. Calcinosis sample titration with ethylenediaminetetraacetic acid ('EDTA') assessed the concentration at which the EDTA dissolved the calcinosis deposits in vitro.

RESULTS

FTIR spectra of the samples displayed peaks characteristic of hydroxyapatite, where signals attributable to the phosphate and carbonate ions were all identified. Polymorph characterization using Raman spectra were identical to a hydroxyapatite reference while the PXRD and electron diffraction patterns conclusively identified the mineral present as hydroxyapatite. TEM analysis showed differences of morphology between the samples. Rounded particles from stone samples were up to a few micron in size, while needle-like crystals from paste samples reached up to 0.5 µm in length. Calcium phosphate deposits were effectively dissolved with 3% aqueous solutions of EDTA, in vitro. Complete dissolution of both types of deposit was achieved in approximately 30 min using a molar ratio of EDTA/HAp of ≈ 300.

CONCLUSIONS

Stone and paste calcium-based deposits both comprise hydroxyapatite, but the constituent crystals vary in size and morphology. Hydroxyapatite is the only crystalline polymorph present in the SSc-related calcinosis deposits. Hydroxyapatite can be dissolved in vitro using a dosage of EDTA considered safe for clinical application. Further research is required to establish the optimal medium to develop the medical product, determine the protocol for clinical application, and to assess the effectiveness of EDTA for local treatment of dystrophic calcinosis.

Factors Influencing the Interactions in Gelatin/Hydroxyapatite Hybrid Materials

The most severe problem in bone regeneration is the defect in the interface. We prepared four types of implantation scaffolds of crosslinked gelatin (GE)/hydroxyapatite (HAp) to study the factors influencing interface interactions, they are film-crosslinked GE scaffold, gel-crosslinked GE scaffold, solid-crosslinked GE/HAp scaffold and gel-crosslinked GE/HAp scaffold. HAp could penetrate the entire GE matrix completely in four successive steps: physical preparation of a gel; chemical crosslinking; incubation in modified simulated body fluid (m-SBF) and freeze-drying. The penetrative nucleation and growth of HAp and the influencing factors in the GE matrix were investigated to ameliorate the interface interactions between organic and inorganic layers. During development of penetrative nucleation and growth, a tight connection was built between organic and inorganic layers, B-type carbonated HAp was formed after incubation with m-BSF, and the apatite content could be controlled. In summary, enhanced interface relies on not only the pre-seeded hydroxyapatite (HAp) as crystal nuclei but also the sufficient space for ions with high concentration to diffuse in.

Effect of Temperature on Drug Release: Production of 5-FU-Encapsulated Hydroxyapatite-Gelatin Polymer Composites via Spray Drying and Analysis of In Vitro Kinetics

In this study, 5-fluorouracil- (5-FU-) loaded hydroxyapatite-gelatin (HAp-GEL) polymer composites were produced in the presence of a simulated body fluid (SBF) to investigate the effects of temperature and cross-linking agents on drug release. The composites were produced by wet precipitation at pH 7.4 and temperature 37°C using glutaraldehyde (GA) as the cross-linker. The effects of different amounts of glutaraldehyde on drug release profiles were studied. Encapsulation (drug loading) was performed with 5-FU using a spray drier, and the drug release of 5-FU from the HAp-GEL composites was determined at temperatures of 32°C, 37°C, and 42°C. Different mathematical models were used to obtain the release mechanism of the drug. The morphologies and structures of the composites were analyzed by X-ray diffraction, thermal gravimetric analysis, Fourier transform infrared spectroscopy, and scanning electron microscopy. The results demonstrated that for the HAp-GEL composites, the initial burst decreased with increasing GA content at all three studied temperatures. Further, three kinetic models were investigated, and it was determined that all the composites best fit the Higuchi model. It was concluded that the drug-loaded HAp-GEL composites have the potential to be used in drug delivery applications.

The Significance and Utilisation of Biomimetic and Bioinspired Strategies in the Field of Biomedical Material Engineering: The Case of Calcium Phosphat-Protein Template Constructs

This review provides a summary of recent research on biomimetic and bioinspired strategies applied in the field of biomedical material engineering and focusing particularly on calcium phosphate-protein template constructs inspired by biomineralisation. A description of and discussion on the biomineralisation process is followed by a general summary of the application of the biomimetic and bioinspired strategies in the fields of biomedical material engineering and regenerative medicine. Particular attention is devoted to the description of individual peptides and proteins that serve as templates for the biomimetic mineralisation of calcium phosphate. Moreover, the review also presents a description of smart devices including delivery systems and constructs with specific functions. The paper concludes with a summary of and discussion on potential future developments in this field.

Bio-Inspired Synthetic Ivory as a Sustainable Material for Piano Keys

Natural ivory is no longer readily or legally available, as it is obtained primarily from elephant tusks, which now enjoy international protection. Ivory, however, is the best material known for piano keys. We present a hydroxylapatite–gelatin biocomposite that is chemically identical to natural ivory but with functional properties optimized to replace it. As this biocomposite is fabricated from abundant materials in an environmentally friendly process and is furthermore biodegradable, it is a sustainable solution for piano keys with the ideal functional properties of natural ivory.

Functionalized calcium orthophosphates (CaPO4) and their biomedical applications

Due to the chemical similarity to natural calcified tissues (bones and teeth) of mammals, calcium orthophosphates (abbreviated as CaPO₄) appear to be good biomaterials for creation of artificial bone grafts. However, CaPO₄ alone have some restrictions, which limit their biomedical applications. Various ways have been developed to improve the properties of CaPO₄ and their functionalization is one of them. Namely, since surfaces always form the interfaces between implanted grafts and surrounding tissues, the state of CaPO₄ surfaces plays a crucial role in the survival of bone grafts. Although the biomedically relevant CaPO₄ possess the required biocompatible properties, some of their properties could be better. For example, functionalization of CaPO₄ to enhance cell attachment and cell material interactions has been developed. In addition, to prepare stable formulations from nanodimensional CaPO₄ particles and prevent them from agglomerating, the surfaces of CaPO₄ particles are often functionalized by sorption of special chemicals. Furthermore, there are functionalizations in which CaPO₄ are exposed to various types of physical treatments. This review summarizes the available knowledge on CaPO₄ functionalizations and their biomedical applications.

Novel Blend for Producing Porous Chitosan-Based Films Suitable for Biomedical Applications

In this work, a chitosan–gelatin–ferulic acid blend was used in different ratios for preparing novel films that can be used in biomedical applications. Both acetic and formic acid were tested as solvents for the chitosan–gelatin–ferulic acid blend. Glycerol was tested as a plasticizer. The thickness, mechanical strength, static water contact angle and water uptake of the prepared films were determined. Also, the prepared films were characterized using different analysis techniques such as Fourier transform infrared spectroscopy (FT-IR) analysis, X-ray diffraction (XRD), thermal gravimetric analysis (TGA), differential scanning calorimetry (DSC) and scanning electron microscopy (SEM). Acetic acid produced continuous compact surfaces that are not recommended for testing in biomedical applications. The plasticized chitosan–gelatin–ferulic acid blend, using formic acid solvent, produced novel hexagonal porous films with a pore size of around 10–14 µm. This blend is recommended for preparing films (scaffolds) for testing in biomedical applications as it has the advantage of a decreased thickness.

Calcium Orthophosphate-Containing Biocomposites and Hybrid Biomaterials for Biomedical Applications

The state-of-the-art on calcium orthophosphate (CaPO4)-containing biocomposites and hybrid biomaterials suitable for biomedical applications is presented. Since these types of biomaterials offer many significant and exciting possibilities for hard tissue regeneration, this subject belongs to a rapidly expanding area of biomedical research. Through the successful combinations of the desired properties of matrix materials with those of fillers (in such systems, CaPO4 might play either role), innovative bone graft biomaterials can be designed. Various types of CaPO4-based biocomposites and hybrid biomaterials those are either already in use or being investigated for biomedical applications are extensively discussed. Many different formulations in terms of the material constituents, fabrication technologies, structural and bioactive properties, as well as both in vitro and in vivo characteristics have been already proposed. Among the others, the nano-structurally controlled biocomposites, those containing nanodimensional compounds, biomimetically fabricated formulations with collagen, chitin and/or gelatin, as well as various functionally graded structures seem to be the most promising candidates for clinical applications. The specific advantages of using CaPO4-based biocomposites and hybrid biomaterials in the selected applications are highlighted. As the way from a laboratory to a hospital is a long one and the prospective biomedical candidates have to meet many different necessities, the critical issues and scientific challenges that require further research and development are also examined.

Calcium phosphate growth at electropolished titanium surfaces

This work investigated the ability of electropolished Ti surface to induce Hydroxyapatite (HA) nucleation and growth in vitro via a biomimetic method in Simulated Body Fluid (SBF). The HA induction ability of Ti surface upon electropolishing was compared to that of Ti substrates modified with common chemical methods including alkali, acidic and hydrogen peroxide treatments. Our results revealed the excellent ability of electropolished Ti surfaces in inducing the formation of bone-like HA at the Ti/SBF interface. The chemical composition, crystallinity and thickness of the HA coating obtained on the electropolished Ti surface was found to be comparable to that achieved on the surface of alkali treated Ti substrate, one of the most effective and popular chemical treatments. The surface characteristics of electropolished Ti contributing to HA growth were discussed thoroughly.

Biocomposites and hybrid biomaterials based on calcium orthophosphates

The state-of-the-art of biocomposites and hybrid biomaterials based on calcium orthophosphates that are suitable for biomedical applications is presented in this review. Since these types of biomaterials offer many significant and exciting possibilities for hard tissue regeneration, this subject belongs to a rapidly expanding area of biomedical research. Through successful combinations of the desired properties of matrix materials with those of fillers (in such systems, calcium orthophosphates might play either role), innovative bone graft biomaterials can be designed. Various types of biocomposites and hybrid biomaterials based on calcium orthophosphates, either those already in use or being investigated for biomedical applications, are extensively discussed. Many different formulations, in terms of the material constituents, fabrication technologies, structural and bioactive properties as well as both in vitro and in vivo characteristics, have already been proposed. Among the others, the nanostructurally controlled biocomposites, those containing nanodimensional compounds, biomimetically fabricated formulations with collagen, chitin and/or gelatin as well as various functionally graded structures seem to be the most promising candidates for clinical applications. The specific advantages of using biocomposites and hybrid biomaterials based on calcium orthophosphates in the selected applications are highlighted. As the way from the laboratory to the hospital is a long one, and the prospective biomedical candidates have to meet many different necessities, this review also examines the critical issues and scientific challenges that require further research and development.

The functionalization of multi-walled carbon nanotubes by in situ deposition of hydroxyapatite

A simple and effective approach was introduced to functionalize multi-walled carbon nanotubes (MWNTs) by in situ deposition of hydroxyapatite (HA) to improve their hydrophilicity and biocompatibility. Firstly, we prepared two types of pre-functionalized MWNTs: acid-oxidated MWNTs and covalently modified MWNTs by poly (ethylene glycol) (PEG). The influences of the acid-oxidated time, pre-phosphorylation, and PEGylation of MWNTs on in situ growth of HA were further investigated in simulated body fluid (SBF) with ionic concentration: 2, 5 and 10 times, respectively, at 37 degrees C for 24h. The results exhibited that all these factors have positive effects on the HA crystals growth, especially the PEGylation of MWNTs plays a key role during the deposition. Finally, the methyl thiazolyl tetrazolium (MTT) assay was performed to evaluate their cytotoxicity, which showed that the PEGylated MWNTs wrapped by HA crystals have the best biocompatibility.

Hydroxyapatite nucleation and growth mechanism on electrospun fibers functionalized with different chemical groups and their combinations

Controlled nucleation and growth of hydroxyapatite (HA) crystals on electrospun fibers should play important roles in fabrication of composite scaffolds for bone tissue engineering, but no attempt has been made to clarify the effects of chemical group densities and the cooperation of two and more groups on the biomineralization process. The aim of the current study was to investigate into HA nucleation and growth on electrospun poly(dl-lactide) fibers functionalized with carboxyl, hydroxyl and amino groups and their combinations. Electrospun fibers with higher densities of carboxyl groups, combination of hydroxyl and carboxyl groups with the ratio of 3/7, and combination of amino, hydroxyl and carboxyl groups with the ratio of 2/3/5 were favorable for HA nucleation and growth, resulting in higher content and lower crystal size of formed HA. Carboxyl groups were initially combined with calcium ions through electrostatic attraction, and the introduction of hydroxyl groups could modulate the distance between carboxyl groups. The introduction of amino groups may lead to the inner ionic bonding with carboxyl groups, but can accelerate phosphate ions to form HA through a chelate ring with the calcium ion and carbonyl oxygen. The biological evaluation indicated that the mineralized scaffolds acted as an excellent cell support to maintain desirable cell-substrate interactions, to provide favorable conditions for cell proliferation and to stimulate the osteogenic differentiation.

Organic / inorganic bioactive materials Part I: Synthesis, structure and in vitro assessment of collagen/silicocarnotite biocoatings

The silicocarnotite, as an inorganic part of the coatings, has been synthesized using a polystep sol-gel method. The chemical composition of the prepared silicocarnotite sol is described as 58.12 CaO, 29.42 P2O5, 12.45 SiO2 (wt%), where Ca/P+Si = 1,67. The acid soluble type I collagen, as an organic part of the obtained coatings, was mixed with silicocarnotite powder in a weight ratio of 25:75 and 75:25 weight ratio without cross-linkage. The acidity of the obtained mixture was readjust with 25% NH4OH to pH = 9.0. The mixture was then dried at 37°C for 12 h.

The growth of B-type carbonate containing hydroxyapatite (B-type CO3HA) in which CO3 2+→PO4 3− on the surface of collagen/silicocarnotite coatings soaked in 1.5 simulated body fluid (1.5 SBF) was observed. The nucleation of B-type CO3HA was estimated on the obtained coatings after 3 days immersion in 1.5 SBF. The negatively charged carboxylate groups from the collagen surface may be responsible for the HA deposition. This was confirmed by the “red shift” of carboxylate groups of collagen molecules in the FTIR spectra. After soaking in 1.5 SBF, the morphology of prepared coatings and HA formation was observed by SEM.

Organic/Inorganic bioactive materials Part III: in vitro bioactivity of gelatin/silicocarnotite hybrids

In this work we present our experimental results on synthesis, structure evolution and in vitro bioactivity assessment of new gelatin/silicocarnotite hybrid materials. The hybrids were obtained by diluting gelatin (G) and silicocarnotite (S) ceramic powder with G:S ratios of 75:25 and 25:75 wt.% in hot (40°C) water. The hybrids were characterized using XRD, FTIR, SEM/EDS and XPS. FTIR depicts that the “red shift” of amide I and COO− could be attributed to the fact that the gelatin prefers to chelate Ca2+ from S. The growth of calcium phosphates on the surface of the hybrids synthesized and then immersed in 1.5 SBF for 3 days was studied by using of FTIR, XRD and SEM/EDS. According to FTIR results, after an immersion of 3 days, A and B-type CO3HA can be observed on the surface. XRD results indicate the presence of hydroxyapatite with well defined crystallinity. SEM/EDS of the precipitated layers show the presence of CO3HA and amorphous calcium phosphate on the surface of samples with different G/S content when immersed in 1.5 SBF. XPS of the G/S hybrid with 25:75 wt.% proved the presence of Ca-deficient hydroxyapatite after an in vitro test for 3 days.

Modification of hydroxyapatite/gelatin nanocomposite using polyacrylamide

A hydroxyapatite (HAp)/gelatin (GEL) nanocomposite was mixed with mineralized polyacrylamide (PAM) to produce a macrocomposite. The mineralization of PAM was carried out by solution-precipitation using Ca(OH)(2) and H(3)PO(4). The crystal growth of HAp in PAM was moderately changed from amorphous-like nanocrystalline to crystalline with the increase of PAM. The dry body of HAp/PAM nanocomposite cracked after the immersion test in water, but the cross-linked sample using glutaraldehyde did not crack. The macrocomposite of HAp/GEL nanocomposite and HAp/PAM nanocomposite showed good toughness, but cracked after the immersion test in water. The cross-linked macrocomposite sample did not crack after the immersion test in water.

Organic-inorganic interaction between hydroxyapatite and gelatin with the aging of gelatin in aqueous phosphoric acid solution

Hydroxyapatite (HAp)/gelatin (GEL) nanocomposite was prepared by the solution-precipitation process using Ca(OH)(2) in water and aqueous solution of H(3)PO(4) in GEL. Before the co precipitation process the GEL powders were dissolved in the aqueous phosphoric acid solution for the phosphorylation of GEL molecules. The chemical variation of the phosphorylated GEL macromolecules was investigated by using attenuated total reflection (ATR) measurement. The crystal growth of HAp became bigger with the long-time aging of the GEL molecules in the phosphoric acid solution, and it resulted from the reduction of length scale of the GEL molecules. The degree of the organic-inorganic interaction was decreased because of the degradation of the GEL macromolecules.

Calcium phosphate formation in gelatin matrix using free ion precursors of Ca2+ and phosphate ions

OBJECTIVES

Hydroxyapatite (HAp)/gelatin (GEL) nanocomposite has been developed as a bone substitute. The nanocomposite formation in the GEL matrix is greatly affected by the reaction between Ca(2+) and phosphate ions. The mineralization of GEL macromolecules was investigated through a co-precipitation of calcium phosphates (Ca-P) by using free ions of Ca(2+) and phosphate ions, Pi. The purpose of this study was to prepare a dense HAp/GEL nanocomposite through a free ion production process.

METHODS

Free ionic calcium, Ca(2+), was produced through electrodialysis process using a cation membrane (CMV). Triprotic acid ions were diffused through an anion membrane (AMV) from an aqueous solution of H(3)PO(4). The HAp/GEL nanocomposite was prepared by the co-precipitation process. As a reference material for comparison, Ca(OH)(2) and H(3)PO(4) were used for the preparation of a HAp/GEL nanocomposite.

RESULTS

The dense compact body of dried Ca-P/GEL nanocomposite was obtained through the fine chemical reaction of Ca(2+) and Pi. The free calcium ion Ca(2+), diffused from the CMV of the cation reactor greatly affected the formation of Ca-P phase. Phosphate ion species diffused through the AMV in the anion reactor definitely influenced the reaction with Ca(2+). For the formation of the Ca-P phase in the GEL matrix, the organic-inorganic interaction was analyzed using FT-IR. The crystal growth of HAp in the GEL matrix increased with the increase of GEL from XRD, FT-IR and TEM.

SIGNIFICANCE

The mineralization reaction in GEL macromolecules was critically influenced by the free ions of Ca(2+) and inorganic phosphate ions, Pi. The interaction between Ca(2+) and Pi in the GEL matrix was very fine compared to the HAp/GEL nanocomposite prepared from Ca(OH)(2) and H(3)PO(4) with the GEL. The dense compact body of HAp/GEL nanocomposite was obtained for an artificial bone application.

Fluoride incorporation in hydroxyapatite/gelatin nanocomposite

The incorporation of fluoride ion into hydroxyapatite (HAp)/gelatin (GEL) nanocomposite was investigated. The F(-) ion incorporation into OH(- )site of HAp phase was an energetically active process, which could be confirmed from the spray solution reaction. The precursors of Ca(2+) in water and phosphates in aqueous gelatin were mixed in the humidified air chamber by air spray, and then the precipitates were aged in a reactor. The F(-) ion precursor was dissolved in the starting solution of Ca(OH)(2) in water, and the resulted Ca(OH, F)(2) complex droplets induced the formation of stable fluoroapatite (F, OH)Ap. The reaction kinetics could be assumed from TEM morphology with ED, XRD and FT-IR analysis.

In situ growth of hydroxyapatite within electrospun poly(DL-lactide) fibers

Development of nanocomposites of hydroxyapatite (HA) and polylactic acid (PLA) is attractive, as the advantageous properties of the two types of materials can be combined to suit better the mechanical and biological demands for biomedical uses. To solve the problematic issue of agglomeration of HA crystallites in the PLA matrix, a novel method is introduced in the present study to use electrospun nanofibers as the reaction confinement for composite fabrication. Poly(DL-lactide) ultrafine fibers with calcium nitrate entrapment were prepared by electrospinning and then incubated in phosphate solution to form in situ calcium phosphate on the polymer matrix. The formation of nonstoichiometric nanostructured HA and well dispersion of HA particles on the electrospun fibers were observed. Higher crystalline HA phase was indicated in samples after sintering at 1200 degrees C. The formation of the calcium-phosphate phase was dependent upon the precipitation conditions, and the effects of the incubation time, temperature, and the pH values of the incubation medium were investigated on the spontaneous precipitation and amorphous-crystalline transformation of HA in the current study. Considering the biodegradability of matrix polymer and the crystallinity and uniform dispersal of HA, optimal conditions for composite preparation were incubating calcium-containing ultrafine fibers at 37 degrees C in pH 7.4 or at 25 degrees C in pH 9.0 of diammonium hydrogen phosphate solutions for 7 days. Around 25%-34% of mineral contents can be synthesized in the resulting composites, which was higher than the theoretical value due to the nonstoichiometric HA formed in the composite, and the fiber degradation and partial calcium nitrate involved in the HA formation.

Cross-linkage of hydroxyapatite/gelatin nanocomposite using imide-based zero-length cross-linker

Hydroxyapatite [HAp]/Gelatin [GEL] nanocomposite was prepared at 37 and 48 degrees C through coprecipitation process. The HAp/GEL nanocomposite slurries were cross-linked by imide-based zero-length cross-linking agent such as N-(3-dimethylaminopropyl)-N'-ethylcarbodiimide (EDC) and N-hydroxysuccinimide (NHS). The chemical bond formation and microstructure in HAp/GEL nanocomposite was investigated as a function of cross-linking agents and temperature. The single addition of EDC into the composite slurries resulted in a tougher microstructure in both samples prepared at 37 and 48 degrees C. However, in the case of the simultaneous addition of EDC and NHS the sample prepared at 48 degrees C showed a coarse microstructure. These results were consistent with the fact that the chemical reactivity of NHS is degraded at 48 degrees C whereas the reactivity of EDC increases up to 80 degrees C.