Objectives of research

Figure 1-4 Experiment construction flow chart. Research on Controlled release of drugs is a very important process to achieve the highest therapeutic efficiency. Much research has been carried out in order to develop of new and/or improved drug therapies that are more efficient and, most importantly, more cost-effective. The conventional definition of controlled release is a constant level of drugs in suitable systems. Electrospun fibers was a novel process to prepare and the release characteristics should depend on interaction between polymer and drug pair as much as on the sizes of fibers[28].

Polymeric drug delivery systems plays an important role in conventional dosage forms, such as improved therapeutic effect, reduced toxicity, convenience, and so on. In previous study, the drugs can be capsulated directly into electrospun fibers and these systems show nearly zero-order kinetics of drug release[29].

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Previous studies fabricated effective bacteria inhibiting fiber membranes from Polymer/Silver nanoparticles[30-31] & Polymer/chitosan[32-34] via electrospinning. In addition, when it comes to bacteria inhibiting drug, such as CHX[35], CHX-CA[36], CHX-Digluconate[37], and CHX-gluconate, only the delivery efficiency of Polymer/CHX, or just that of CHX, has been discussed[36-37]. Tests on the inhibiting capability (Inhibition Zone) of Polymer/CHX matrix were rarely done. Evaluations of bacteria inhibiting capability based on Inhibition Zone were only qualitative, not quantitative. This study aimed to discuss whether biodegradable inhibiting drug delivery membranes fabricated from PLLA/CHX via electrospinning possessed the characteristics of drug delivery systems and whether CHX could still inhibit bacteria after being released from PLLA. This experiment quantitatively evaluated bacteria growth in liquid culture by observing Optical Density 600nm (OD) at one-hour intervals, and used the growth curves thus derived to evaluate on a real-time the impacts of drug delivery speeds on the growth rates of bacteria in different phases. Competent cell and plasmid inserted competent cell, bacteria that are of the same strain but grow at different speeds were utilized to interact with biodegradable CHX delivery membranes fabricated via electrospinning to determine whether such drug delivery membranes are a rate-preprogrammed drug delivery system.

A major goal of periodontal regeneration therapy is the regeneration of lost supporting tissue, including the alveolar bone, periodontal ligament, and cementum around a previously diseased tooth root[38-39]. Guided tissue regeneration (GTR) has accomplished this goal, and has become a standard

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procedure for periodontal regeneration therapy since it was initially suggested for such therapy[40-42]. In addition, it has been applied to bone and peri-implant defects, and for bone augmentation procedures prior to implant placement. In such situations, it is sometimes termed guided bone regeneration (GBR)[42-44]. For the membrane to be effective, it must satisfy criteria such as excellent biocompatibility, controllable biodegradability, cytocompatibility, suitable microstructure (pore size and porosity) and mechanical properties[45-47].

In previous studies, although present polymeric products show positive results in clinical studies, their weak mechanical properties and poor bone regeneration capacity are still major challenges[42]. To overcome these problems, recent research efforts have included the incorporation of bone-like ceramics into the membranes, e.g. hydroxyapatite, tricalcium phosphate and calcium carbonate[42, 44, 48-49]. Hydroxyapatite (HA,Ca10[PO4]6[OH]2) is the main mineral component of natural bone and has good biocompatibility, osteoconductivity and bioactivity, and thus it is suitable for making the guided bone regeneration membranes[50]. However, the brittleness of hydroxyapatite limits its applicability[51]. The co-precipitation of HA nanocrystals in soluble collagen has met with partial success in the fabrication of HA–collagen nanocomposites similar to the nanostructure of real bone[52], though with weaker mechanical properties. Calcium carbonate has been recognized as bone filling material and its good osteoconductivity has been approved in recent studies[44, 53-55].

Polymorphism in materials science is the ability of a solid material to exist in more than one form or crystal structure. Polymorphism can potentially be

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found in any crystalline material. Calcium carbonate is one of the most common biological minerals and has polymorphs of calcite, aragonite, and to a less extent amorphous state, vaterite or monohydrate in calcareous structures of organisms[56]. Calcium carbonate can be precipitated in aqueous solution as three anhydrous polymorphs, calcite, aragonite and vaterite, and three hydrated forms, amorphous calcium carbonate, calcium carbonate hexahydrate and calcium carbonate monohydrate[57-58].

The calcite has a trigonal and the aragonite has an orthorhombic crystal structure. The latter has typically higher elasticity modulus than the powder, better dispersibility due to the surface treatment, increased impact strength, tensile strength and elongation at break[59]. So far, most GTR/GBR membranes are made in the shape of porous foam, created by traditional methods such as particulate leaching, solvent casting or gas foaming[60]. Electrospinning is a simple and versatile method for fibers preparation, which employs electrostatic forces that strength a polymer jet to generate continuous fibers with diameters ranging from micrometers down to several nanometers[22]. Fibers obtained from electrospinning are in the range of 50 nm to a few microns in diameter and generally collected in the form of a non-woven structure[23]. It has already been shown that electrospun membranes have the potential to promote osteoblastic cell function and bone regeneration[42].

When plastics are used for outdoor applications, they often deteriorate fairly rapidly. Theoretical explanation is based upon absorption of ultraviolet energy, raising some bonds to an energy level which exceeds their stability, and thus initiating their breakdown, usually involving atmospheric oxidation and

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sometimes hydrolysis as well. Many of the newer engineering plastics offer high performance in their mechanical, thermal, and chemical properties, but still cannot be recommended for use out-of-doors[61].

Ultraviolet radiation can be classified into UV-A, UV-B, and UV-C regions.

Much less is known about the biological effects of UV-A radiation (320–400 nm), which adjoins the visible light, so the waveband is usually not a topic of discussion. Most observed biological effects of UV-B (280–320 nm) radiation are extremely detrimental to living organisms[62]. Because solar UVR below wavelengths of 290 nm is effectively absorbed by stratospheric ozone, and no such radiation reaches living organisms from natural sources, the wavelength in the UV-C region (200–280 nm) is considered of little detriment to human beings.

Ultraviolet radiation (UV-A、UV-B、UV-C can cause damage to C-H, C-C, O-H, C-Cl, etc. in living organisms, and substance with the same bond energy. In order to solve the polymer composite material is not suitable for outdoor issues, often in the processing additives are added to solve this problem a little[61-63].

Many common additives, such as : UV Absorber : Benzophenone、Phosphite Antioxidant、Hindered Amine Light Stabilizers (HALS)：Hindered Amine Light Stabilizer[64]。

Polylactide (PLA) is one of the most promising biodegradable polymers owing to its mechanical property profile, thermoplastic processibility and biological properties, such as biocompatibility and biodegradability. The use of synthetic degradable polyesters in surgery as suture materials and bone fixation devices has three decades of history. Degradable polyesters derived from three monomers, lactide, glycolide and caprolactone, are commonly used clinically.

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They are characterized by degradation times ranging from days to years, depending on formulation and initial molecular weight[10].

The majority of the studies on electrospinning fibers of PLLA to add Benzophenone -12[65-68] and Chemfos-168[69-70] from solutions, we have reported that molecular structures and antiultraviolet of electrospinning nanofibers. Benzophenone can be used as a photo initiator in UV-curing applications such as inks, imaging and clear coatings in the printing industry.

Benzophenone prevents ultraviolet (UV) light from damaging scents and colours in products such as perfumes and soaps. It can also be added to the plastic packaging as a UV blocker. This allows manufacturers to package the product in clear glass or plastic. Without it, opaque or dark packaging would be used. In laboratories, solvents are often distilled with sodium and benzophenone as desicants. The product of these two chemicals in the absence of air and water is a dark blue ketyl; a solution of this ketyl can be used to qualitatively test for the absence of air and water. Chemfos-168 is an antioxidant is a molecule capable of slowing or preventing the oxidation of other molecules. Oxidation is a chemical reaction that transfers electrons from a substance to an oxidizing agent.

Oxidation reactions can produce free radicals, which start chain reactions that damage cells. Antioxidants terminate these chain reactions by removing free radical intermediates, and inhibit other oxidation reactions by being oxidized themselves. As a result, antioxidants are often reducing agents such as thiols or polyphenols.

In this study, we investigated ultraviolet resistance of the PLLA, PLLA / UV absorption and PLLA / anti-oxidation agents by electrospinning. It is believed that this study could provide a good insight into ultraviolet resistance

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properties of the electrospinning polymer. We also hope to make the ultraviolet resistance electrospinning fibers and have high degree of degradability.

Figure 1- 4 scope of experiments

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Chapter 2 Electrospinning