Judul: Sintesis Hidroksiapatit Berpori dari Cangkang Telur Ayam dengan Matriks Selulosa Nata De Coco dan Natrium Alginat
Abstrak: This research has been done on the synthesis of porous hydroxyapatite from hen eggshells with nata de coco cellulose and Na-alginate matrix. The method used for synthesis of HAp powder is wise drop precipitation, whereas for synthesis of HAp/cellulose and HAp/alginate composites, cellulose immersion and phase separation method were used. The products are HAp powder, scaffold shaped HAp/alginate, and sheet shaped HAp/cellulose composites. XRD characterization results have shown a diffarction pattern that indicated HAp phase with degree of crystallinity more than 80% for HAp powder and more than 50% for composite of HAp/cellulose. FTIR characterization results have shown an absorption spectral clusters of constituent HAp compound and composite of HAp/algiate compound. Scan results using SEM showed that composite of HAp/alginate has porosity structure with enough regularity and size variation start from 93 μm until 182 μm. EDX analysis produced a spectrum of element which present in the composites. The Ca/P ratios based on mass percentage from EDX analysis of HAp/alginate composite are 1.84 and 1.86, while for HAp/cellulose composite are 1.43 and 1.45. The used of CaCl2 as corsslink agent were thought to be the factor that increase the Ca/P ratio in HAp/alginate composite.
Keyword: nata de coco cellulose., Na-alginate, composite, porous hydroxyapatite

Judul: Sintesis Scaffold Hidroksiapatit dari Cangkang Kerang Hijau dengan Matriks Natrium Alginat dan Selulosa Bakteri Nata de coco
Abstrak: Research has been conducted on the synthesis of HA scaffold using sodium alginate matrix with freeze drying method and bacterial cellulose matrix of nata de coco by using immersion method. Synthesis of HA was done with green mussel shells as a source of calcium and phosphate precursor of (NH4)2HPO4. The synthesis results were characterized by using XRD, FTIR, and SEM. XRD results showed that there are phases other than HA such as TCP, ACA and ACB with the degree of crystallinity was obtained above 80%. Spectrum of XRD of HA/cellulose composites showing the typical peaks of cellulose and the typical peak of HA. The results of FTIR test detected that the cluster contained in HA/alginate composite with ratio 70/30 are OH-, PO4 3-, and CO3 2- showed the presence of HA and OH-, COO-, C-O showing the presence of sodium alginate. SEM test results indicated that the pores are formed in HA/alginate composite evenly distributed across the surface with a pore size ranging 65-120 μm, whereas HA/bacterial cellulose composite, HA was decomposed covering the entire surface of bacterial cellulose.
Keyword: Na-alginate., HA scaffold, Bacterial cellulose, Green clam shells

Judul: A Continuous Vaccination Strategy in the SVIR Epidemic Model
Abstrak: Vaccination is conducted to minimize the spread of a disease. The vaccination is usually done several times within a fixed time interval. In the SVIR model, it is assumed that individuals do not get immediate immunity following a vaccination program. So according to process of vaccination on SVIR model, there are two strategies, i.e. the continuous vaccination strategy (CVS) and the pulse vaccination strategy (PVS). In this study, only the CVS strategy in epidemic model SVIR is considered. Results of the study indicate that dynamics of the CVS system depends on the basic reproductive number. If the basic reproductive number is less than one, then the disease-free fixed point is asymptotically stable. It means that the disease will eventually disappear from the population. Conversely, if the basic reproductive number is greater than one, then the endemic fixed point is asymptotically stable, which means that the disease will remain exist in the population. Simulation result shows that the vaccination would minimize the spread of disease by reducing the basic reproductive number. If the time for the vaccinated recipients to obtain the immunity, as well as a possibility of vaccinated recipients to be infected are neglected, then the disease will be eradicated. This condition is called an over-evaluating effect of vaccination.
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