Study of biocompatibility of particles and rods of polysulfone

Abstracts

Foi estudada comparativamente a resposta do músculo tríceps sural e reto do abdome de ratos Wistar à implantação da polisulfona (PSU) e do polietileno de ultra alto peso molecular (UHMWPE ) sob a forma de bastões e partículas, por um período de até 52 semanas. Ao final, a PSU foi considerada como tendo a mesma biocompatibilidade do UHMWPE, segundo os critérios utilizados.

ARTIGO ORIGINAL

Study of biocompatibility of particles and rods of polysulfone

Sergio Luiz Pavanatti^I; Cecília Amélia Carvalho Zavaglia^II; William Dias Belangero^III; Yoshio Kawano^IV

^IDepto. de Engenharia dos Materiais - FEM/UNICAMP - R. Mendeleiev, 200 - Cid. Universitária Zeferino Vaz - Campinas(SP)

^IIDepto. de Engenharia dos Materiais - FEM/UNICAMP - R. Mendeleiev, 200 - Cid. Universitária Zeferino Vaz - Campinas(SP)

^IIIDepto. de Ortopedia e Traumatologia - FCM/UNICAMP

^IVDepto. Química Fundamental - IQ/USP

SUMMARY

A comparative study was performed of the reaction of triceps sural and abdominal retus muscle of Wistar mice to implantation of polysulfone (PSU) and ultra high molecular weight poliethilene (UHMWPE) as particles and rods, for a period up to 52 weeks. At the end, PSU was considered as having the same biocompatibility as UHMWPE, according to the used method.

INTRODUCTION

Since the forties polymeric use in health applications have been studied. As high performance polymers became available, such as polyethercetones and polysulfones, it was begun to evaluate the possibility of replacing orthopedic implants made of metallic material as 316 L steel and titanium leagues new ones made with this materials.⁽¹⁾

Plates for treatment of tibial fracture, made with thermo-rigid resins reinforced with carbon fibers were successfully used in humans, however, the high cost of its multi-lamination manufacture avoided its large-scale use ⁽¹⁾. So, thermopastic resins, with high thermodinamic properties, as PSU, which besides having lower cost can be molded during the surgical procedures, as metallic material, are the best indicated ⁽³⁾.

Even though there is an interest in using this polymeric resin in clinical practice, there are few publications dealing with long-term biocompatibility in vivo. Thus, it was the objective of this study to evaluate the mouse muscle tissue toleration to this resin and chemical and physical changes happened in the rods after the implantation period, comparing these results to the obtained by UHMWPE, routinely used in orthopedic implant manufacture.

MATERIAL E METHODS

We used 28 male Wistar mice (Rattus novergicus), divided in six groups according to follow-up: 1, 2, 4, 8, 16 and 52 weeks. Each group was composed by 4 animals, except the last one, which had eight.

It was implanted in these animals polyestersulfone (PES), produced by American Oil Company and acquired under the brand UDEL™ P-1800, and ultra high molecular weight polyethylene (UHMWPE), traded by POLIALDEN Petroquímica S.A, under the brand UTEC 3440. These materials were obtained as particles by cold grinding and granulometric distribution of the particles is demonstrated in Graphic 1.

The size of the particles ranged from 53 ì to 300 ì, with predominance between 125 ì and 297 ì; the predominant form was rounded for UHMWPE and irregular for PSU. Rods with 2.0-mm diameter and 10.0 mm length were obtained by hot extrusion of PSU and cold lathering of UHMWPE. All implants, both in form of particles of rods, were sterilized by Gamma radiation at a 3.5 Mrad dose. In each animal it was implanted rods in the abdomen retus muscle, being PSU at left and UHMWPE at right side, while particles were implanted in triceps sural muscle, being, UHMWPE at right and PSU at left side. Techniques for particle and rod implantation followed those already described ^(1,2)

After sacrificed, triceps sural muscle was fixed for 24 hours in a buffered 10% formol solution. Following, a cylindric sample 5 mm thick from the medium third of the muscle (where the material was implanted), for paraffin inclusion. The abdominal retus muscle, after fixation, was longitudinally incised over the rods, allowing its exposure and remotion. Following, the muscles and wrapping formed around the rods were cutted in a transversal direction at its medium portion, from where it was remove a 3 mm thick cylindrical segment, for paraffin inclusion.

Cuts with 5 ì were obtained from these cylinders, and Hematoxylin-Eosin (HE) and Massom Trichromium (TM) stained. Hystological evaluation of triceps sural muscle and abdominal retus muscle was performed according to the methodology decribed by Belangero et al (1993). Besides this analysis, in abdominal retus muscle cuts it was measured the thickness of the wrapping formed between muscle tissue and the rods. This was performed trough an special objective in the optic microscope ( Carl Zeiss 10 x) Measures of maximum and minimum thickness of these wrapping was obtained in 3 different hystological cuts, and for statistical analysis it was considered their arithmetic mean.

The rods retrieved were washed in ethilic alcohol and, after dried, separated into plastic tubes for chemical analysis through Photoacustic Spectrophotometry at infrared region (BOMEM Specrophotometer , model DA-3 with photoacustic accessory model 200-MTEC), performed at Fundamental Chemistry Department of Instituto de Química da Universidade de São Paulo and for surface changes it was performed a Screening Electronic Microscopy (Cambridge Stereoscan model S4-10), performed at Mechanical Engineering Department of UNICAMP.

Statistical analysis was performed using Mann-Whitney U test with a = 0,05.

RESULTS

Evaluation of Test bodies

In Table 1 number of animals per group, time of follow-up, number of rods retrieved and mean thickness of wrapping around PUS and UHMWEP rods is displayed.

Evaluation performed by Photoacustic spectrum and Raman, in the phase pre and post implantation, did not find any measurable chemical change. Evaluation performed by Screening Electronic Microscopy in pre implantation phase demonstrated that surface finishing of UHMWPE by lathering resulted in clear sulcus, while PES obtained by extrusion presented with smooth surface. After implantation period, it could be observed that there was larger amount of tissue residuals attached to UHMWPE rods (Figures 1,2)

Muscle Tissue evaluation

Related to muscle tissue reaction to particles, in general it was not observed cellular necrosis, neither vascular changes, during the first two weeks. There were small focus of non-specific inflammatory infiltrate, with a prevalence of macrophage and some giant cells, probably caused by the surgical trauma and by the presence of particles, surrounded by muscle fibers in different phases of degeneration and regeneration. In no case it was found the presence of inflammatory cells which could characterize an exudative reaction. In the fourth week it was observed a reduction of inflammatory reaction and cellular population, with a prevalence of fibroblasts over other cells. This reaction became more and more evident during the following weeks, in such a way that, after 52 weeks, particles presented completely surrounded by well defined fibrous beams, formed by thin layers of dense conjunctive tissue, with few cells and with no difference among both materials, according can be observed in Figures 3 and 4.

Hystological evaluation of abdomen retus muscle was similar for both materials. In the group evaluate after 1 week, it was observed the formation of a wrapping, constituted mainly by cells (fibroblasts and fibrocytes), which were placed concentrically surrounding the rods. It was not possible to notice significant differences both in type as in amount of cells present surrounding PES and UHMWPE rods. The thickness of this wrapping reduced by one half starting from the 2^nd week, as well as the cellular population. From this period to the 16^th week, thickness kept stable, however cells amount did reduce very much, and, starting from 8^th week, the wrapping was constituted by fibrous tissue and rare cells. At 52^nd week there was an increase of the thickness of the fibrous layer. The evolution of thickness values of the wrapping surrounding the rods is displayed at Table 1, Graphic 2 and Figures 5,6, 7 and 8.

DISCUSSION

Biocompatibility of any material study involves different phases both of the receptor tissue at a macroscopic and microscopic level, as well as the implant. In this study, Photoacustic Spectrometry did not demonstrate chemical changes both in PSU and UHMWPE after manufacture procedures of rods and after their implantation in abdomen retus muscle. On the other hand, Screening Electronic Microscopy was important to detect differences in surface finish of rods and showing that these irregularities found in the surface of UHMWPE rods favored the adherence of conjunctive tissue of the wrapping formed surrounding it.

The macroscopic analysis gave important information regarding healing process what, even involving a number of inflammatory phenomena was free of complications for both materials in both presentation forms. The findings of a good quality healing, and adequate interaction of the implant, without presence of local hyperemia are early clues of material toleration by receptor tissue. ^(1,5)

Microscopic evaluation, on the other hand, gives not only the cellular, but also the receptor tissues response as a whole, so that immunologic and metabolic systems can participate and express their influence facing substances released by implant degradation. Both testing material and control, must be implanted as particles and rods. Particles aim to increase contact surface and facilitate implant integration, sensitizing the inflammatory response and toxic effects. The comparative analysis of the cellular population both in acute and evolution, as well as quantitative and qualitative features associated to cellular necrosis and vessel neoformation can be important to characterize the implant compatibility.^(1,5,6,8) In this study, in acute phase the inflammatory response was similar and discrete for both materials. In evolution, it could be noticed that at 52 weeks follow-up there were not inflammatory cells, neither granuloma formation surrounding particles, which were involved by conjunctive tissue beams demonstrating the excellent compatibility. ^(3,4,6)

In relation to the rods, the results showed UHMWPE and PSU to be similar in regard to type and intensity of inflammatory reaction of muscular tissue. Measurement of fibrous wrapping formed surrounding the rods was also similar for each moment analyzed. In acute phase, the largest number of cells was found probably due to surgical trauma and presence of the implant. Cellular population reduction, and wrapping of the rods, indicate that there were not toxic stimulus by the implants. ^(4,9) The thickening of fibrous wrapping, observed after 52 weeks, can be justified by interaction between implants and muscles, whose contraction during animal movements produces friction and stimulating dense conjunctive tissue formation. This hypothesis looks to be true, since thickness increase was similar in both material.

REFERÊNCIAS

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Publication Dates

• Publication in this collection
  20 Feb 2006
• Date of issue
  Sept 2001