| Human skull is a very important part of human body, which can support and protect the brain tissue, as well as resist strikes from outside effectively. Until now, materials used for cranioplasty are divided into two groups: metals and nonmetals. Recently, the most widely used implant materials for skull defects include silicon rubber, titanium, bone cements, fiber reinforced composites, autogenic grafts et al. This paper studies a new type material for skull defects-inorganic fiber reinforced polymethylmethacylate (PMMA)/hydroxyapatite (HA) composite material. The poor mechanical properties of PMMA alone are enhanced by using the composites. Moreover, HA coatings make contributions to the improvement of the implants' biological compatibility.HA miropowder is prepared by making use of hydrothermal method, comminution by gas stream and graded sieving techniques and average particle diameter of such powder is about 280nm. The preparation of PMMA is realized by bulk polymerization of mixing self enhanced additive and MMA monomer liquid. The amount of additive is a key point to the polyreaction because of the initiator of polymerization available in it. By measuring the molecular weight of polymers which are prepared by different proportioning of the powder and liquid, as well as considering the influence of polymer viscosity to practical operations, the self enhanced additive and MMA monomer liquid should be mixed in the proportion of 2:5. In addition, the temperature of polyreaction should be controlled between 45 ℃ and 55 ℃, and the time is 4~5h.The composite materials for skull defects are made by using multilayer composite and compression molding technologies. On the basis of the relationship between thermal properties and compression molding, generally, molding temperature ranges from glass-transition temperature (Tg) to flow temperature (Tf), so as to make sure the resin not only has enough fluidity, but also can be avoided overflowing the mold. Therefore, the scope of technological parameters is preliminarily established as follows, molding temperature: 90~130℃, pressure: 10~ 16MPa and time is about 1.5h.Prepare a group of materials according to following ways: change the pressure whilefixing the temperature at 125℃ and change the temperature while fixing the pressure at 14MPa. Look for the correlation of technological parameters and mechanical properties of such materials through a series of mechanical tests (including bending strength, impact toughness, tensile strength, compressive strength and density) and we can find that the mechanical strengths of the materials reach the peak value when the temperature is 110~120℃ and the pressure is 13~14.5MPa on the foundation of macroscopic and microscopic analysis, otherwise such strengths would fall down when the temperature and pressure is higher or lower. Hence, the optimal parameters adopted for the molding is established as follows, molding temperature: 110~120℃, pressure: 13~ 14.5MPa and time is about 1.5h.Besides mechanical properties, other performances of the materials are tested. Water absorption rate is basically fixed at 0.73% and can no longer exceed 0.75% after 21 days' observation. The result of rubber polymer content is 57.7% by combustion method. Make use of dripping experiment to test the wetting angle of materials undergoing surface treatments, which is 32° . Such properties ensure the favorable mechanical properties and biocompatibility of the composites.In comparison with human skull and PMMA, the artificial composites have preferable mechanical properties which can meet clinical requirements basically.
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