Eylem Seç
Development of Hydroxyapatite-Based Hybrid Materials for Biomedical Applications
Başlık:
Development of Hydroxyapatite-Based Hybrid Materials for Biomedical Applications
Yazar:
Chan, Gabriela Ruphuy, author.
Yazar Ek Girişi:
Fiziksel Tanımlama:
1 electronic resource (190 pages)
Genel Not:
Source: Dissertation Abstracts International, Volume: 76-07C.
Özet:
This work comprises the development of hybrid inorganic-organic materials based on highly pure nano-hydroxyapatite (n-HAp). Chitosan (CS) was selected as the organic component, in order to develop n-HAp/CS products mimicking bone composition. The following main processing stages were considered: (1) dispersion preparation in which n-HAp is incorporated into the chitosan solution; (2) phase separation/solvent elimination in which the fixation of structural forms takes place; (3) purification and potential sterilization procedures.
Dispersion preparation is a key step since it implies the inclusion of HAp nanoparticles into the chitosan solution. This stage was carried out by physically mixing the HAp nanoparticles with the chitosan solution. The effect of different parameters on the resulting particle size and electrostatic stability (zeta potential) of the dispersions was studied. Results reflected that chitosan acts as a good stabilizer (zeta potential >+30 mV) of HAp nanoparticles in slightly acidic environment (pH 5.5), and such good stability was proven to be consistent along time. Taken into consideration these results, a method for the preparation of n-HAp/CS dispersions by fast stirring (ultraturrax) was developed. With mixing times <100 ms, the used fast stirring set up allowed the production of highly homogeneous and stable n-HAp/CS dispersions (pH 5.5), and it was determined that using HAp/CS weight ratio of 70/30 and n-HAp concentration of 20 g/l, the produced dispersions were suitable materials for the production of n-HAp/CS hybrids in different forms.
In the phase separation/solvent elimination stage, two different structural forms were developed: microparticles and scaffolds. Spray drying was used to produce the hybrid n-HAp/CS microparticles. The effect of pH of the n-HAp/CS dispersion (5.5 and 7.0) and the presence of KCl on the final n-HAp/CS microparticle's properties were studied. It was evidenced that KCl has no beneficial effect on the stability of the n-HAp/CS dispersions, and it appeared as a contaminant on the formed microparticles. Moreover, the generated microparticles presented differences depending on the pH at which the n-HAp/CS dispersion was prepared. Doughnut-like n-HApCS-5.5 microparticles (15.8-im average size in volume) were found preferred over n- HApCS-7.0 microparticles, which require one step more in the productive process and presented a tendency to form large agglomerates. The produced microparticles are advantageous, as they allow HAp's superior properties at the nanoscale to be preserved in the form of microparticles that are suitable materials to develop injectable systems, drug delivery systems, or be shaped into solid substrates with increased surface area.
A simple 3-step production process was developed to produce n-HAp/CS hybrid materials in the form of scaffolds. The process consists in: (1) n-HAp/CS dispersion preparation; (2) freeze-drying stage to fix scaffold shape; and (3) supercritical CO2 (scCO2) extraction to remove acetic acid and promote sterilization. It was shown that scCO2 extraction step is a suitable purification procedure since it allowed the successful removal of acetic acid, with the advantage of not compromising the microarchitecture achieved by freeze-drying unlike other tested methods based on neutralization with alkaline solutions. The produced scaffolds were sterile and exhibited suitable properties for non-load bearing bone graft applications; therefore, the developed 3-step process has great potential to produce ready-to-use n-HAp/CS scaffolds mimicking bone composition and structure.
Given the achieved results, three different n-HAp/CS hybrid products were successfully produced: dispersions, powder (microparticles), and scaffolds. The generated n-HAp/CS hybrid materials mimic bone composition, are composed of highly pure HAp nanoparticles, and displayed suitable properties for different potential applications.
Notlar:
School code: 5896
Tüzel Kişi Ek Girişi:
Mevcut:*
Yer Numarası | Demirbaş Numarası | Shelf Location | Lokasyon / Statüsü / İade Tarihi |
---|---|---|---|
XX(678856.1) | 678856-1001 | Proquest E-Tez Koleksiyonu | Arıyor... |
On Order
Liste seç
Bunu varsayılan liste yap.
Öğeler başarıyla eklendi
Öğeler eklenirken hata oldu. Lütfen tekrar deneyiniz.
:
Select An Item
Data usage warning: You will receive one text message for each title you selected.
Standard text messaging rates apply.