New Three-Dimensional Bioactive Reinforcing Filler for Improving the Properties of Biomedical Polymers: Synthesis and Application.

In general, the efficiency of reinforcement for filler-based composites is greatly influenced by the filler properties. While much research has been conducted on filler percentage and filler-matrix bonding quality, there is not much research directed to the effect of filler geometry. Therefore, the aim of this article is to examine how a three-dimensional (3D) bioactive filler influences the strength enhancement of biomedical polymers. This was accomplished by first synthesizing highly regular dandelion-like hydroxyapatite (DHA) as a 3D bioactive filler using an optimized hydrothermal method, followed by surface modification with silane molecules. Poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) was then used as a biomedical polymer model to fabricate solution-casted composites by using the as-synthesized DHA particles. The results showed that the composites loaded with the surface-modified DHA particles had significantly higher tensile strength and elastic modulus compared to the neat PHBV and composites having irregular particles. In addition to the mechanical properties, our research found that the 3D DHA filler had a significant impact on the biological characteristics of the PHBV, such as water wettability, biodegradability, bioactivity, and in vitro cell response. These findings suggested that particle geometry can play a more significant role in affecting the biological and mechanical performance of biomedical polymers than previously thought.

Nano-hydroxyapatite structures for bone regenerative medicine: Cell-material interaction.

Bone tissue engineering holds great promise for the regeneration of damaged or severe bone defects. However, several challenges hinder its translation into clinical practice. To address these challenges, interdisciplinary efforts and advances in biomaterials, cell biology, and bioengineering are required. In recent years, nano-hydroxyapatite (nHA)-based scaffolds have emerged as a promising approach for the development of bone regenerative agents. The unique similarity of nHA with minerals found in natural bones promotes remineralization and stimulates bone growth, which are crucial factors for efficient bone regeneration. Moreover, nHA exhibits desirable properties, such as strong chemical interactions with bone and facilitation of tissue growth, without inducing inflammation or toxicity. It also promotes osteoblast survival, adhesion, and proliferation, as well as increasing alkaline phosphatase activity, osteogenic differentiation, and bone-specific gene expression. However, it is important to note that the effect of nHA on osteoblast behavior is dose-dependent, with cytotoxic effects observed at higher doses. Additionally, the particle size of nHA plays a crucial role, with smaller particles having a more significant impact. Therefore, in this review, we highlighted the potential of nHA for improving bone regeneration processes and summarized the available data on bone cell response to nHA-based scaffolds. In addition, an attempt is made to portray the current status of bone tissue engineering using nHA/polymer hybrids and some recent scientific research in the field.

3-Dimensional cell-laden nano-hydroxyapatite/protein hydrogels for bone regeneration applications.

The ability to encapsulate cells in three-dimensional (3D) protein-based hydrogels is potentially of benefit for tissue engineering and regenerative medicine. However, as a result of their poor mechanical strength, protein-based hydrogels have traditionally been considered for soft tissue engineering only. Hence, in this study we tried to render these hydrogels suitable for hard tissue regeneration, simply by incorporation of bioactive nano-hydroxyapatite (HAp) into a photocrosslinkable gelatin hydrogel. Different cell types were also encapsulated in three dimensions in the resulting composites to prepare cell-laden constructs. According to the results, HAp significantly improves the stiffness of gelatin hydrogels, while it maintains their structural integrity and swelling ratio. It was also found that while the bare hydrogel (control) was completely inert in terms of bioactivity, a homogeneous 3D mineralization occurs throughout the nanocomposites after incubation in simulated body fluid. Moreover, encapsulated cells readily elongated, proliferated, and formed a 3D interconnected network with neighboring cells in the nanocomposite, showing the suitability of the nano-HAp/protein hydrogels for cellular growth in 3D. Therefore, the hydrogel nanocomposites developed in this study may be promising candidates for preparing cell-laden tissue-like structures with enhanced stiffness and increased osteoconductivity to induce bone formation in vivo.

Nano-hydroxyapatite reinforced polyhydroxybutyrate composites: a comprehensive study on the structural and in vitro biological properties.

Nanocomposites based on polyhydroxybutyrate (PHB) and hydroxyapatite (HAp) have recently been proposed for application in bone repair and regeneration, but very limited studies have investigated the effect of HAp on the rheological and thermal behavior of PHB. More important, the efficiency of a biomaterial depends greatly on its ability to interact with cells, but little is known about this interaction for this kind of nanocomposite. Hence, this paper dealt with some of the characteristics of solution-casted PHB/HAp nanocomposite films, and tried to explore the effect of HAp nanoparticles on cellular responses. The results showed that both rheological and thermal properties can be tailored by incorporating appropriate amounts of nanoparticles. In vitro studies showed a significant increase in proliferation and differentiation of MC3T3-E1 on nanocomposites compared to the neat polymer. Surface examination indicated that topography and chemistry of surface are important factors influencing cellular processes; while no cell differentiation was found on the neat polymer, nanocomposite with 15 wt.% filler content exhibited a pronounced differentiation resulting from high surface roughness and large amount of exposed HAp. These results suggest that HAp particles play a much more important role in determining the biological performance of PHB than has previously been supposed.

Synthesis methods for nanosized hydroxyapatite with diverse structures.

Hydroxyapatite (HAp) is the major mineral constituent of vertebrate bones and teeth. It has been well documented that HAp nanoparticles can significantly increase the biocompatibility and bioactivity of man-made biomaterials. Over the past decade, HAp nanoparticles have therefore increasingly been in demand, and extensive efforts have been devoted to develop many synthetic routes, involving both scientifically and economically new features. Several investigations have also been made to determine how critical properties of HAp can be effectively controlled by varying the processing parameters. With such a wide variety of methods for the preparation of HAp nanoparticles, choosing a specific procedure to synthesize a well-defined powder can be laborious; accordingly, in the present review, we have summarized all the available information on the preparation methodologies of HAp, and highlighted the inherent advantages and disadvantages involved in each method. This article is focused on nanosized HAp, although recent articles on microsized particles, especially those assembled from nanoparticles and/or nanocrystals, have also been reviewed for comparison. We have also provided several scientific figures and discussed a number of critical issues and challenges which require further research and development.

Hydroxyapatite nanorods as novel fillers for improving the properties of dental adhesives: Synthesis and application.

OBJECTIVES: This study evaluates the hypothesis that the incorporation of fibrous hydroxyapatite nanoparticles with high crystallinity and high aspect ratio, synthesized by hydrothermal method, into an experimental ethanol-based one-bottle dentin adhesive, improves the mechanical properties of the adhesive layer, and accordingly increases the bond strength to dentin. METHODS: Hydroxyapatite nanorods were synthesized using a simple hydrothermal procedure. First, the HPO(4)(2)-containing solution was added drop-wise into the Ca(2+)-containing solution while the molar ratio of Ca/P was adjusted at 1.67. The HAp precursor was then treated hydrothermally at 200 degrees C for 60h. The resulting powder was characterized using XRD, FTIR, SEM, TEM, and EDXA. The synthesized HAp nanorods were added to an experimental one-bottle dentin adhesive followed by the characterization of the filled adhesive. The diametral tensile strength, flexural strength, flexural modulus, and the microshear bond strength to the dentin of human premolars of seven adhesive systems containing different nanorod contents were evaluated. The distribution of the filler was determined using EDX-mapping. The depth of cure was also evaluated using scraping technique. Moreover, after microshear testing, the fracture cross-section was observed using SEM to determine the mode of failure involved. The colloidal stability was studied using a separation analyzer and also zeta potential measurement. Data were analyzed using one-way analysis of variance followed by the Tukey test. RESULTS: The results confirmed the high purity, high crystallinity, and high aspect ratio of synthesized HAp nanorods. The diametral tensile strength of nanorod containing adhesive system appeared to increase when 0.2-0.5wt.% HAp nanorods were incorporated (p<0.05). A similar trend was observed in the flexural test providing higher flexural strength at filler contents of 0.2-0.5wt.% while flexural modulus remained unchanged. The highest microshear bond strength was also obtained at 0.2wt.% filler content (p<0.05). The improved properties of the new adhesive system might be due to the high crystallinity and high aspect ratio of the nanorods. SEM observation of debonded surfaces revealed that most specimens showed an adhesive failure from the adhesive-dentin interface. Energy dispersive X-ray (EDX) mapping confirmed the uniform distribution of nanorods in the adhesive matrix. The colloidal stability studies indicated that synthesized hydroxyapatite nanorods have high colloidal stability in the dental adhesive solution. Indeed, the nanorods are well dispersed and protected from aggregation by their high surface charge confirmed by zeta potential measurement. SIGNIFICANCE: Hydroxyapatite-based composites have shown promising bioactivity. However, the knowledge about the influence of the nano-sized HAp on the properties of the dental materials, especially dentin bonding adhesives, is yet insufficient. The nanorod containing adhesive system presented here might be considered to have practical applications in dental clinics.