CERRADURA ELECTROMAGNÉTICA

Preparation

Samples

Samples

Samples

Samples

Samples

therefore administered to each animal to achieve anaesthesia. Once general anaesthesia had been achieved, the fur on the dorsum of each animal was shaved to expose the skin. The skin surface was sterilised with 0.5% chorhexidine in alcohol solution, and transcutaneous incisions were made 1 cm on either side of the spinal vertebrae, parallel to the long axis of each animal in order to receive the test materials as shown in Fig. 3.1. The materials were placed transcutaneously and the wounds were sutured with 4/0 braided silk suture material to form crossover mattress sutures over the test materials. The materials were prepared in a T-shape as shown in Fig.3.2 and placed in the wounds so that the horizontal section of the membrane protruded externally and prevented the vertical section from being dislodged from the wound during healing. The crossover mattress sutures were placed over the protruding section so as to hold it in tight apposition to the skin surface stabilising the membrane in situ.

The animals were divided into groups consisting of 3 animals each for the 1 week and 4 week investigations, 6 animals for the 3 day investigation, and a group of 11 animals for the 2 week investigation as illustrated in the study design (Table 3.a). More animals were assigned to the three day and two week groups as a number of additional materials were included for evaluation at these stages.

Prior to each surgical procedure all of the samples under investigation were randomly assigned to one of the eight incisions on each animal allowing for a control site

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T OF THE

Fig. 3.2 DIMENSIONS OF IMPLANT SPECIMENS IN MILLIMETRES

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which received no membrane on each animal. This site was designated the "sham” site in each case.

The materials were left in situ for the designated time period at which time the animals were placed in a COg chamber. After sacrifice the dorsal skin was dissected free, and cut into individual pieces containing the membranes to enable samples to be taken for histological evaluation as shown in Figure 3.3. The medio-posterior corner of each specimen was cut off so as to retain the orientation of the specimen during preparation. The specimens were placed in 10% formalin solution, and subsequently embedded in wax blocks. Serial sections were

cut from each block, ignoring the first 10 cuts.

Subsequently, every 10th cut was mounted for staining with

haematoxylin and eosin tissue stain. In addition,

specimens of the 3 day, 1 week and 4 week periods were stained with Van Gieson's stain for collagen to highlight the maturation of collagen within the healing wounds.

A number of materials were evaluated in the study and these included:

PTFE Millipore filter (Millipore, Harrow, UK)

Gore-Tex Periodontal Membrane (Gore Assocs. Arizona, USA)

Polylactic acid membrane (PLA)

Polyhydroxy butyrate/valerate copolymer P(HB-HV)

Dexon Polyglycolic acid copolymer membrane (Cyanamid, UK)

FIg. 3.3 TO ILLUSTRATE THE CUT SPECIMENS PRIOR TO PROCESSING FOR HISTOLOGICAL INVESTIGATION

The biodegradable polymer membranes were produced by the biomaterials department of Queen Mary College London in 3 separate thicknesses, viz: 0.02 mm, 0.04 mm and 0.07 mm by dissolving the polymers in a chloroform solvent solution and casting the resulting solution onto freshly cleaved, anatomically clean mica. Controlled evaporation was achieved by placing the specimens in a vacuum chamber maintained at room temperature (22°C). The resulting films were then cut into T-shaped pieces illustrated in diagram

3.2. Each piece was packaged and sealed and sterilised prior to surgery. Additionally, a number of other biodegradable materials were assessed only at the two week period to see if the tissue reactions differed markedly between different biodegradable materials. These materials included three samples each of collagen membrane, commercially available polyglycolic acid copolymer membrane, polyhydroxy butyrate/valerate copolymer membrane and polyactic acid membrane with altered surface characteristics to modify the surface free energy of the material.

Prior to the start of the study, the materials were characterised in the laboratory (Galgut et al 1991) to establish the surface hydrophobicity/hydrophilicity of each material as this might affect the cell adhesion and growth properties on the materials. The membranes were prepared and characterised at the biomaterials department (Queen Mary College) prior to the animal study, to ensure that the specifications of size, thickness, purity and sterility

were attained. 3.5 RESULTS

3.5.1 Characterisation of test materials

The contact angles of each material were determined by the research assistant designated to this project (Dr. R. Pitrola), and the surface free energy of each material was calculated by measurement of the angles formed by a number of hydrophobic and hydrophilic liquids placed on the surface of each sample. The results of this calculation are presented in Table 3b which shows the total surface free energy, and also the dispersion and polar components of the total energy. From this table it can be seen that the total surface free energy, as well as the polar and dispersion components were higher for the biodegradable polymers than for the non-biodegradable PTFE materials. This indicates that the biodegradable polymers are more hydrophilic than the PTFE materials. The polar component of surface free energy is directly related to the

hydrophobicity/hydrophilicity of the material under

investigation. It can be seen that the polar component is highest for PLA, less with P(HB-HV) and very low with the PTFE materials. Molecular weight made no difference to the surface free energey of the substance being evaluated. Thus, it would be anticipated that the best cellular adhesion would occur with the most hydrophilic material, which was PLA, and the poorest cell adhesion would be associated with the most hydrophobic materials which were PTFE. Cell adhesion might be less good with the P(HB-HV)