Effects of Processing Parameters on P(L/D)LA 96/4 Fibers and Fibrous Products for Medical Applications

Abstract

Tissue engineering is expected to fulfill its promises to produce knowledge, methods, and products that would benefit the health care sector. The need of a degradable construct is a necessity when trying to grow a living tissue inside a porous structure. The fibers offer a unique approach to this, since the porosity can easily be altered with different methods especially using the textile methods. Textile industry on the other hand offers a broad and variable archive of methods to manufacture products and preforms. These preforms can be further used together with the composite technology to further increase the number of applications to which they can be used. When combining different fields of sciences it is possible to manufacture a living tissue, based on fibrous degradable constructs. Thus fibers and fibrous products are versatile preforms that can be shaped and designed to fulfill many of the demands in the field of tissue engineering. The main objective of this thesis was to study the biodegradable medical grade P(L/D)LA 96/4 polymer fibers and the fibrous products manufactured from them. The thermal degradation behavior of this polymer in single screw extruder environment in melt spinning process was studied. The online hot-drawing was used for fiber orientation. The information based on those studies was analyzed and gathered for future optimization of such melt spinning processes. Different batches and fiber diameters were produced using different processing parameters. Textile methods were further introduced to the melt-spun fibers. The effect of the knitting parameters on fiber properties were studied during the hydrolytic degradation and long term storage. These knits were studied as in vivo soft tissue implant preforms, in vitro spinal fusion cage composite preforms, and in vivo temporomandibular jaw implant preforms. Non-woven fabrics were produced from the melt-spun fibers manufactured by hot-drawing and high-speed drawing. These non-woven felts were used for plasma and solvent based wetting enhancement tests accompanied by cell seeding tests. The felts were also used as a component for temporomandibular jaw implant preforms. The results showed increasing degradation in the extruder barrel in regards to the P(L/D)LA 96/4 polymer molecular weight and viscosity. Lactide monomer was induced into the polymer during the melt spinning process due to the temperature and shear. Monomer content also varied according to the polymer residence time. Fiber showed different hydrolytical degradation behavior depending on the monomer amount. Higher monomer content caused rapid degradation of the mechanical properties and molecular weight. We acquired three different degradation profiles for the fibers that were related to the monomer content. The knitted soft tissue implants degraded faster during the hydrolysis than in in vivo. These knitted soft tissue implants acted as real tissue engineered implants; the cells grew and filled in the scaffolds. While the tissue matured in the scaffolds, the measured mechanical properties of the scaffolds improved despite the loss of mechanical strength of an empty scaffold. Non-woven scaffolds increased their wetting capability due to the oxygen plasma treatment. This also enhanced the cell attachment and proliferation.