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Reduction of postsurgical adhesion formation with hydrogels synthesized by radiation
Nuclear Instruments and Methods in Physics Research B 236 (2005) 277–282 www.elsevier.com/locate/nimb
Reduction of postsurgical adhesion formation with hydrogels synthesized by radiation Young-Chang Nho *, Joon-Ho Lee Radiation Application Division, Korea Atomic Energy Research Institute, P.O. Box 105, Yusong, Daejon 305-600, Korea Available online 10 May 2005
Abstract Biocompatible and biodegradable hydrogels based on carboxymethyl cellulose (CMC) and polyethyleneglycol (PEG) were prepared as physical barriers for preventing surgical adhesions. These interpolymeric hydrogels were synthesized by gamma irradiation crosslinking technique. A 1.5 cm · 1.5 cm of cecal serosa and an adjacent abdominal wall were abraded with bone burr until the serosal surface was disrupted and hemorrhagic but not perforated. The denuded cecum was covered with either CMC/PEG hydrogels or a solution from a CMC/PEG hydrogel. Control rat serosa was not covered. Two weeks later, the rats were sacrificed and the adhesion was scored on a 0–5 scale. Control rat showed a significantly higher incidence of adhesions than either the CMC/PEG hydrogels or a solution from the CMC/PEG hydrogel. In conclusion, these studies demonstrate that CMC/PEG hydrogels have a function of the prevention for an intra abdominal adhesion in a rat model. 2005 Elsevier B.V. All rights reserved. PACS: 61.41.+e; 82.35; 81.40.w Keywords: Hydrogels; Surgical adhesion; Irradiation; Radiation; Crosslinking
1. Introduction Postsurgical adhesions are abnormal tissue attachments that result from cuts or abrasions to tissues during surgery. These adhesions develop as part of the normal wound healing response of *
Corresponding author. Tel.: +82 42 868 8054; fax: +82 42 868 8080. E-mail address: [email protected] (Y.-C. Nho).
the tissues to the trauma and occur in over two thirds of all abdominal surgical patients. The consequences of these adhesions are varied and depend upon the surgical site involved. Problems may include pain, infertility, obstruction of the intestines, and even an increased risk of death after cardiac surgery. The process of adhesion formation initially involves the establishment of a fibrin framework and a normal tissue repair. The normal repair process allows for fibrinolysis alongside a
0168-583X/$ - see front matter 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.nimb.2005.03.254
278
Y.-C. Nho, J.-H. Lee / Nucl. Instr. and Meth. in Phys. Res. B 236 (2005) 277–282
mesothelial repair. However, in a surgical adhesion formation the fibrin matrix matures as the fibroblasts proliferates into the network and angiogenesis occurs resulting in the establishment of an organized adhesion within 3–5 days. Following major abdominal surgery, 60–95% of patients develop adhesions [1]. Adhesions are responsible for about 60% of the bowel obstructions and 20% of all infertilities as well as the substantial costs associated with adhesiolysis and hospitalization [2–4]. Interventional attempts to prevent the formation of postsurgical adhesions have included the use of hydroflotation techniques or barrier devices. Hydroflotation involves the instillation of large volumes of polymer solutions such as dextran or carboxymethyl cellulose [5,6] into the surgical space in an attempt to keep the organs apart. However, this technique has produced marginally beneficial effects in animals or humans. Synthetic barrier membranes made from oxidized regenerated cellulose (Interceed) or polytetrafluroethylene (Gore-tex surgical membrane) have demonstrated some limited inhibition of the adhesion formation in humans. Hydrogels are most often defined as two component systems where one of the components is a hydrophilic polymer, insoluble in water because of the three dimensional network connecting as chains, and the second one is water. The polymer gels have a very low modulus of elasticity, and therefore cause minimal mechanical irritation. They usually show a good biocompatibility in contact with blood, body fluids and tissues. In recent years, much attention has been focused on the research and development of polymer hydrogels for biomaterials, such as contact lenses, wound dressings, enzyme immunoassays, catheters and drug delivery systems. The radiation has been recognized as a very suitable tool for the synthesis of hydrogels owing to the various advantages, such as an easy process control and no necessity to add any initiators and crosslinkers possibly harmful and difficult to remove. It is known that water-soluble polysaccharides such as carboxymethylcellulose are crosslinked by radiation at more than 10% aqueous solution [7].
The goal of this study was to evaluate the efficacy of the CMC/PEG hydrogels as a barrier for reducing postsurgical adhesions in a rat cecal abrasion model.
2. Experimental 2.1. Materials Na-carboxymethylcellulose (CMC, average Mw. 7.0 · 105, DS 0.9) and polyethylene glycol (PEG, average Mw. 4 · 103) were supplied by Aldrich Chemical Company. Distilled water was used as a solvent in all the experiments. 2.2. Preparation of hydrogels CMC/PEG (various weight compositions, Table 1) was dissolved in distilled water of 25 C, and then mixed by a physical blender at room temperature to give a CMC/PEG solution. The dried content of the CMC/PEG was in the range of 11.2–12.3 wt.%, and the weight composition percent of the CMC/PEG was 88/12, 85/15, 82/18, 79/21. The homogeneous paste was then put into the cavity between the plastic plates with a 2 mm spacer. The paste was exposed to 25 kGy of gamma ray to make the hydrogels. 2.3. Preparation of gel solution from hydrogels Cp88/12 as in Table 1 was crosslinked by radiation. It was put in distilled water and agitated
Table 1 Formulation for the preparing hydrogels Abbreviation
Water %
Hydrogel composition Cp88/12 88.8 Cp85/15 88.4 Cp82/18 88.1 Cp79/21 87.7
Composition of CMC/PEG CMC %
PEG %
88 85 82 79
12 15 18 21
CMC Mw = 7.0 · 105, DS = 0.9, Total dose = 2.5 Mrad, Dose rate = 5 kGy/h, PEG Mw = 4.0 · 103.
Y.-C. Nho, J.-H. Lee / Nucl. Instr. and Meth. in Phys. Res. B 236 (2005) 277–282
mildly to make a 2 wt.% concentration of CMC/ PEG in water. This solution consisted of the segregated small particles of the hydrogels in water. It was used for coating for the purpose of the prevention of intra abdominal adhesion in a rat model. 2.4. Degree of swelling The degree of swelling could be described as the water absorptivity (Eq. (1)) of the hydrogels. The gel samples were immersed in distilled water at room temperature. After the water on the surface of the swollen gels was removed with cellulose paper, the mass was determined. The degree of swelling was defined as Eq. (1); where Ws is the weight of the swollen gels and Wd is the initial CMC/PEG weight. Water absorptivity ¼
WsWd . Wd
ð1Þ
2.5. Gel strength A cylindrical hydrogel specimen, with a height of 4.8 mm and a diameter of 12 mm, was used for the compressive strength tests. The compressive strength tests were conducted by using Instron model 4400 Universal testing machine at room temperature. A cylindrical hydrogel specimen was placed on the base and the probe was lowered until a 70% relative deformation was made. The probe was then lowered at 10 mm/min, and then raised. The compressive strength used in this
279
experiment is the value measured at a 70% relative deformation. 2.6. Animal test Female Wistar rats (250–300 g) were purchased form the Kyeryong Science Co. (Daejon, Korea). Rats were anesthetized by an intramuscular injection of ketamine (200 mg/kg) and their ventral hair was removed with electric clippers. Using the aseptic technique, a 7 cm incision was made on the midline of the abdominal wall, and 1.5 cm · 1.5 cm of the cecal serosa and the adjacent abdominal wall were abraded with bone burr until the serosal surface was disrupted and hemorrhagic but not perforated, and the serosa of the cecum was sutured to the abdominal wall 5 mm away from the injured site (Fig. 1). To evaluate the effects of the CMC/PEG hydrogel (Cp8812) or the 2% gel solution from the CMC/ PEG hydrogel (Cp8812) as a physical barrier for the prevention of an intra abdominal adhesion in a rat model, we divided 30 female rats into three equal groups. Group I was the control; in group II a sheet (2 mm) of the CMC/PEG hydrogel was laid over the viscera; in group III the gel solution from the CMC/PEG hydrogel was coated over the viscera. Ten of the animals from each group were sacrificed at postoperative day 14, and the adhesion severity and strength were scored according to VlahosÕ experiment as shown in Table 2 [8]. Some of the model rats were sacrificed at 3, 7 and 14 days after surgery to observe the absorption of the CMC/PEG hydrogel (Cp8812) at the injured site.
Fig. 1. Treatment procedure of the cecal serosa and the adjacent abdominal wall for an adhesion evaluation. (A) Abrasion injury on the cecal serosa. (B) Abrasion injury of the adjacent abnominal. (C) Application of a solution prepared from the hydrogel (Cp88/12) onto the injury.
280
Y.-C. Nho, J.-H. Lee / Nucl. Instr. and Meth. in Phys. Res. B 236 (2005) 277–282
Table 2 Classification of the adhesion and strength
66
Adhesion severity 0 No adhesions 1 One thin filmy adhesion 2 Two or more thin filmy adhesion 3 Thick adhesion with focal point 4 Thick adhesion with plannar attachment 5 Very thick vascularized adhesion Adhesion strength 1 Adhesion was 2 Adhesion was to tear 3 Adhesion was rupture 4 Adhesion was
filmy and easily torn with very light pressure substantial and needed moderate pressure
62
1.20
60 1.15
58 56
1.10
54 1.05
52 50
1.00
48 46
0.95 12
14
16
18
20
22
PEG concentration (%)
heavy and required significant pressure to
Fig. 3. Compressive strength and modulus of the hydrogels prepared by the formulation of Table 1.
very heavy and difficult to rupture
Adhesion according to Vlahos et al. [8].
3. Results and discussion 3.1. Physical properties The radiation crosslinking can be easily adjusted and reproducible by controlling the radiation dose. All the samples prepared by the formulation in Table 1 had very soft and flexible properties. When the prepared hydrogels were kept in water for more than 48 h, the forms of the hydrogels were disintegrated. Fig. 2 shows the degree of swelling for the hydrogels that were synthesized by gamma irradiation. The swelling increased as the amount of PEG in the CMC/PEG 50
CMC/PEG = 88:12 CMC/PEG = 85:15 CMC/PEG = 82:18 CMC/PEG = 79:21
40
Degree of swelling
64
Compressive force Young`s modulus
Young,s modulus (kgf/cm2)
Compressive strength (kgf/cm2)
1.25
increased. Hydrogels are disintegrated 48 h (Cp88/12), 24 h (Cp85/15), 13 h (Cp82/12), 7 h (Cp79/21) after dipping them in water. Polymers are generally divided into those that predominantly crosslink and those that predominantly degrade. CMC and PEG are crosslinked in their homogeneous mixture with water. As the molecular weight of the PEG in these experiments was low, the increase of the PEG in the CMC/PEG solution resulted in a decrease in the gelation of the hydrogels. The compressive strength used in this experiment was the value measured at a 70% relative deformation. The gel strength of the hydrogels was obtained by determining their compressive strength (Fig. 3). The compressive strength and modulus decreased as the concentration of the PEG in the CMC/PEG increased. Because PEG of a low molecular weight does not contribute to the crosslinking, the increase in the PEG in the CMC/PEG resulted in a decrease in the compressive strength and modulus of the hydrogels.
30
3.2. Animal studies 20
10
0 0
10
20
30
40
50
60
Time(hr)
Fig. 2. Swelling behavior for the hydrogels prepared by the formulation of Table 1.
Adhesions are unwanted tissue growths occurring between the layers of adjacent bodily tissues and internal organs. The results of the adhesion scoring are summarized in Table 3. The control animals formed dense adhesions between the cecal and the abdominal wall. Animals treated with the CMC/PEG hydrogel (Cp8812) or the 2 wt.% solution from the CMC/PEG hydrogel
Y.-C. Nho, J.-H. Lee / Nucl. Instr. and Meth. in Phys. Res. B 236 (2005) 277–282 Table 3 Evaluation of the adhesion for the rats treated with the CMC/ PEG hydrogel (Cp8812) or a solution from the CMC/PEG hydrogel (Cp8812) Aggregation
Adhesion degree
Adhesion area (cm2)
Adhesion strength
Controls 2% solution Cp88/12 Hydrogel Cp88/12
4.6 ± 0.5 0.2 ± 0.42*
3.61 ± 0.24 0.0125 ± 0.04*
3.6 ± 0.51 0.3 ± 0.94*
0.1 ± 0.3*
0.0104 ± 0.03*
0.2 ± 0.63*
*
P value < 0.05 versus controls.
(Cp8812) had a significantly lower average adhesion score than the controls. There was not much difference in the adhesion scores between groups II and III. At day 14, no residual HA/CMC hydrogels were visible in the treated animals. The mechanism of the action by which the CMC reduces the adhesion formation is not clear. It has been found that CMC when implanted intraperitoneally attracts fluid in its surrounding and thereby prevents the serosa from a peritoneal contact – the so-called ‘‘hydroflotation effect’’. In addition, there is evidence to suggest that the CMC/PEG coats the intraperitoneal surfaces and reduces the direct apposition of the traumatized structures – the socalled ‘‘siliconizing effect’’ [9]. The other proposed mechanism of the action of the CMC is through its effect on the fibroblastic and cellular activities [10]. At the time of application, the hydrogels adhered readily to the serosal. In both the control and experimental groups, the celiotomy incisions
281
healed normally. The sutures holding the bowel to the abdominal wall were still in place (Fig. 4). The bioresorbability of the CMC/PEG hydrogel (Cp8812) between the skin and the abdominal layer of the rat was evaluated by observing the forms of the hydrogels on the cecal serosa on the 3rd, 7th, 14th days after surgery. The hydrogel was found to be a loose gel on the 3rd postoperative day, and was slightly detectable at the 7th day, but almost not detectable at the 14th postoperative day.
4. Conclusions Hydrogels based on CMC/PEG were prepared as physical barriers for preventing surgical adhesions using radiation. These interpolymeric hydrogels were synthesized by a gamma irradiation crosslinking technique. Animals treated with the CMC/PEG hydrogel (Cp8812) or a gel solution from the CMC/PEG hydrogel (Cp8812) had a significantly lower average adhesion score than the controls. At day 14, almost no residual HA/ CMC hydrogels were visible in the treated animals. Hydrogels prepared by radiation were found to significantly reduce the postsurgical adhesions in a rat cecal abrasion model.
References [1] M.A. Weibel, G. Majno, Am. J. Surg. 126 (1973) 345. [2] H. Ellis, Br. J. Surg. 69 (1982) 241.
Fig. 4. Necropsy taken 14 days after operation of rat to find the difference of adhesion between control (A) and solution prepared from the hydrogel (Cp88/12) (B).
282
Y.-C. Nho, J.-H. Lee / Nucl. Instr. and Meth. in Phys. Res. B 236 (2005) 277–282
[3] M.R. Soules, L. Dennis, A. Boserge, D.E. Moore, Am. J. Obstet. Gynecol. 143 (1982) 829. [4] N.F. Ray, J.W. Larser, R.J. Stillian, R.J. Jacobs, Surg. Gynecol. Obstet. 176 (1993) 271. [5] S.H. Wuster, V. Bonet, A. Mayberry, M. Hadolinott, T. Williams, I.H. Chassdry, J. Surg. Res. 59 (1995) 97. [6] C.K. Ryan, H.C. Sax, Am. J. Surg. 169 (1995) 154.
[7] F. Yoshii, L. Zhao, R.A. Wach, N. Nagaswa, H. Mitomo, T. Kume, Nucl. Instr. and Meth. B 208 (2003) 320. [8] A. Vlahos, P. Yu, C.E. Lucas, A.M. Ledgerwood, Am. Surg. 67 (2001) 15. [9] T.E. Elkins, F.W. Ling, R.A. Alokas, T.N. Abdella, C.A. Homsey, L.R. Makinak, Fertil. Steril. 41 (1984) 929. [10] C.K. Ryan, H.C. Sax, Am. J. Surg. 169 (1995) 154.
Reduction of postsurgical adhesion formation with hydrogels synthesized by radiation Young-Chang Nho *, Joon-Ho Lee Radiation Application Division, Korea Atomic Energy Research Institute, P.O. Box 105, Yusong, Daejon 305-600, Korea Available online 10 May 2005
Abstract Biocompatible and biodegradable hydrogels based on carboxymethyl cellulose (CMC) and polyethyleneglycol (PEG) were prepared as physical barriers for preventing surgical adhesions. These interpolymeric hydrogels were synthesized by gamma irradiation crosslinking technique. A 1.5 cm · 1.5 cm of cecal serosa and an adjacent abdominal wall were abraded with bone burr until the serosal surface was disrupted and hemorrhagic but not perforated. The denuded cecum was covered with either CMC/PEG hydrogels or a solution from a CMC/PEG hydrogel. Control rat serosa was not covered. Two weeks later, the rats were sacrificed and the adhesion was scored on a 0–5 scale. Control rat showed a significantly higher incidence of adhesions than either the CMC/PEG hydrogels or a solution from the CMC/PEG hydrogel. In conclusion, these studies demonstrate that CMC/PEG hydrogels have a function of the prevention for an intra abdominal adhesion in a rat model. 2005 Elsevier B.V. All rights reserved. PACS: 61.41.+e; 82.35; 81.40.w Keywords: Hydrogels; Surgical adhesion; Irradiation; Radiation; Crosslinking
1. Introduction Postsurgical adhesions are abnormal tissue attachments that result from cuts or abrasions to tissues during surgery. These adhesions develop as part of the normal wound healing response of *
Corresponding author. Tel.: +82 42 868 8054; fax: +82 42 868 8080. E-mail address: [email protected] (Y.-C. Nho).
the tissues to the trauma and occur in over two thirds of all abdominal surgical patients. The consequences of these adhesions are varied and depend upon the surgical site involved. Problems may include pain, infertility, obstruction of the intestines, and even an increased risk of death after cardiac surgery. The process of adhesion formation initially involves the establishment of a fibrin framework and a normal tissue repair. The normal repair process allows for fibrinolysis alongside a
0168-583X/$ - see front matter 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.nimb.2005.03.254
278
Y.-C. Nho, J.-H. Lee / Nucl. Instr. and Meth. in Phys. Res. B 236 (2005) 277–282
mesothelial repair. However, in a surgical adhesion formation the fibrin matrix matures as the fibroblasts proliferates into the network and angiogenesis occurs resulting in the establishment of an organized adhesion within 3–5 days. Following major abdominal surgery, 60–95% of patients develop adhesions [1]. Adhesions are responsible for about 60% of the bowel obstructions and 20% of all infertilities as well as the substantial costs associated with adhesiolysis and hospitalization [2–4]. Interventional attempts to prevent the formation of postsurgical adhesions have included the use of hydroflotation techniques or barrier devices. Hydroflotation involves the instillation of large volumes of polymer solutions such as dextran or carboxymethyl cellulose [5,6] into the surgical space in an attempt to keep the organs apart. However, this technique has produced marginally beneficial effects in animals or humans. Synthetic barrier membranes made from oxidized regenerated cellulose (Interceed) or polytetrafluroethylene (Gore-tex surgical membrane) have demonstrated some limited inhibition of the adhesion formation in humans. Hydrogels are most often defined as two component systems where one of the components is a hydrophilic polymer, insoluble in water because of the three dimensional network connecting as chains, and the second one is water. The polymer gels have a very low modulus of elasticity, and therefore cause minimal mechanical irritation. They usually show a good biocompatibility in contact with blood, body fluids and tissues. In recent years, much attention has been focused on the research and development of polymer hydrogels for biomaterials, such as contact lenses, wound dressings, enzyme immunoassays, catheters and drug delivery systems. The radiation has been recognized as a very suitable tool for the synthesis of hydrogels owing to the various advantages, such as an easy process control and no necessity to add any initiators and crosslinkers possibly harmful and difficult to remove. It is known that water-soluble polysaccharides such as carboxymethylcellulose are crosslinked by radiation at more than 10% aqueous solution [7].
The goal of this study was to evaluate the efficacy of the CMC/PEG hydrogels as a barrier for reducing postsurgical adhesions in a rat cecal abrasion model.
2. Experimental 2.1. Materials Na-carboxymethylcellulose (CMC, average Mw. 7.0 · 105, DS 0.9) and polyethylene glycol (PEG, average Mw. 4 · 103) were supplied by Aldrich Chemical Company. Distilled water was used as a solvent in all the experiments. 2.2. Preparation of hydrogels CMC/PEG (various weight compositions, Table 1) was dissolved in distilled water of 25 C, and then mixed by a physical blender at room temperature to give a CMC/PEG solution. The dried content of the CMC/PEG was in the range of 11.2–12.3 wt.%, and the weight composition percent of the CMC/PEG was 88/12, 85/15, 82/18, 79/21. The homogeneous paste was then put into the cavity between the plastic plates with a 2 mm spacer. The paste was exposed to 25 kGy of gamma ray to make the hydrogels. 2.3. Preparation of gel solution from hydrogels Cp88/12 as in Table 1 was crosslinked by radiation. It was put in distilled water and agitated
Table 1 Formulation for the preparing hydrogels Abbreviation
Water %
Hydrogel composition Cp88/12 88.8 Cp85/15 88.4 Cp82/18 88.1 Cp79/21 87.7
Composition of CMC/PEG CMC %
PEG %
88 85 82 79
12 15 18 21
CMC Mw = 7.0 · 105, DS = 0.9, Total dose = 2.5 Mrad, Dose rate = 5 kGy/h, PEG Mw = 4.0 · 103.
Y.-C. Nho, J.-H. Lee / Nucl. Instr. and Meth. in Phys. Res. B 236 (2005) 277–282
mildly to make a 2 wt.% concentration of CMC/ PEG in water. This solution consisted of the segregated small particles of the hydrogels in water. It was used for coating for the purpose of the prevention of intra abdominal adhesion in a rat model. 2.4. Degree of swelling The degree of swelling could be described as the water absorptivity (Eq. (1)) of the hydrogels. The gel samples were immersed in distilled water at room temperature. After the water on the surface of the swollen gels was removed with cellulose paper, the mass was determined. The degree of swelling was defined as Eq. (1); where Ws is the weight of the swollen gels and Wd is the initial CMC/PEG weight. Water absorptivity ¼
WsWd . Wd
ð1Þ
2.5. Gel strength A cylindrical hydrogel specimen, with a height of 4.8 mm and a diameter of 12 mm, was used for the compressive strength tests. The compressive strength tests were conducted by using Instron model 4400 Universal testing machine at room temperature. A cylindrical hydrogel specimen was placed on the base and the probe was lowered until a 70% relative deformation was made. The probe was then lowered at 10 mm/min, and then raised. The compressive strength used in this
279
experiment is the value measured at a 70% relative deformation. 2.6. Animal test Female Wistar rats (250–300 g) were purchased form the Kyeryong Science Co. (Daejon, Korea). Rats were anesthetized by an intramuscular injection of ketamine (200 mg/kg) and their ventral hair was removed with electric clippers. Using the aseptic technique, a 7 cm incision was made on the midline of the abdominal wall, and 1.5 cm · 1.5 cm of the cecal serosa and the adjacent abdominal wall were abraded with bone burr until the serosal surface was disrupted and hemorrhagic but not perforated, and the serosa of the cecum was sutured to the abdominal wall 5 mm away from the injured site (Fig. 1). To evaluate the effects of the CMC/PEG hydrogel (Cp8812) or the 2% gel solution from the CMC/ PEG hydrogel (Cp8812) as a physical barrier for the prevention of an intra abdominal adhesion in a rat model, we divided 30 female rats into three equal groups. Group I was the control; in group II a sheet (2 mm) of the CMC/PEG hydrogel was laid over the viscera; in group III the gel solution from the CMC/PEG hydrogel was coated over the viscera. Ten of the animals from each group were sacrificed at postoperative day 14, and the adhesion severity and strength were scored according to VlahosÕ experiment as shown in Table 2 [8]. Some of the model rats were sacrificed at 3, 7 and 14 days after surgery to observe the absorption of the CMC/PEG hydrogel (Cp8812) at the injured site.
Fig. 1. Treatment procedure of the cecal serosa and the adjacent abdominal wall for an adhesion evaluation. (A) Abrasion injury on the cecal serosa. (B) Abrasion injury of the adjacent abnominal. (C) Application of a solution prepared from the hydrogel (Cp88/12) onto the injury.
280
Y.-C. Nho, J.-H. Lee / Nucl. Instr. and Meth. in Phys. Res. B 236 (2005) 277–282
Table 2 Classification of the adhesion and strength
66
Adhesion severity 0 No adhesions 1 One thin filmy adhesion 2 Two or more thin filmy adhesion 3 Thick adhesion with focal point 4 Thick adhesion with plannar attachment 5 Very thick vascularized adhesion Adhesion strength 1 Adhesion was 2 Adhesion was to tear 3 Adhesion was rupture 4 Adhesion was
filmy and easily torn with very light pressure substantial and needed moderate pressure
62
1.20
60 1.15
58 56
1.10
54 1.05
52 50
1.00
48 46
0.95 12
14
16
18
20
22
PEG concentration (%)
heavy and required significant pressure to
Fig. 3. Compressive strength and modulus of the hydrogels prepared by the formulation of Table 1.
very heavy and difficult to rupture
Adhesion according to Vlahos et al. [8].
3. Results and discussion 3.1. Physical properties The radiation crosslinking can be easily adjusted and reproducible by controlling the radiation dose. All the samples prepared by the formulation in Table 1 had very soft and flexible properties. When the prepared hydrogels were kept in water for more than 48 h, the forms of the hydrogels were disintegrated. Fig. 2 shows the degree of swelling for the hydrogels that were synthesized by gamma irradiation. The swelling increased as the amount of PEG in the CMC/PEG 50
CMC/PEG = 88:12 CMC/PEG = 85:15 CMC/PEG = 82:18 CMC/PEG = 79:21
40
Degree of swelling
64
Compressive force Young`s modulus
Young,s modulus (kgf/cm2)
Compressive strength (kgf/cm2)
1.25
increased. Hydrogels are disintegrated 48 h (Cp88/12), 24 h (Cp85/15), 13 h (Cp82/12), 7 h (Cp79/21) after dipping them in water. Polymers are generally divided into those that predominantly crosslink and those that predominantly degrade. CMC and PEG are crosslinked in their homogeneous mixture with water. As the molecular weight of the PEG in these experiments was low, the increase of the PEG in the CMC/PEG solution resulted in a decrease in the gelation of the hydrogels. The compressive strength used in this experiment was the value measured at a 70% relative deformation. The gel strength of the hydrogels was obtained by determining their compressive strength (Fig. 3). The compressive strength and modulus decreased as the concentration of the PEG in the CMC/PEG increased. Because PEG of a low molecular weight does not contribute to the crosslinking, the increase in the PEG in the CMC/PEG resulted in a decrease in the compressive strength and modulus of the hydrogels.
30
3.2. Animal studies 20
10
0 0
10
20
30
40
50
60
Time(hr)
Fig. 2. Swelling behavior for the hydrogels prepared by the formulation of Table 1.
Adhesions are unwanted tissue growths occurring between the layers of adjacent bodily tissues and internal organs. The results of the adhesion scoring are summarized in Table 3. The control animals formed dense adhesions between the cecal and the abdominal wall. Animals treated with the CMC/PEG hydrogel (Cp8812) or the 2 wt.% solution from the CMC/PEG hydrogel
Y.-C. Nho, J.-H. Lee / Nucl. Instr. and Meth. in Phys. Res. B 236 (2005) 277–282 Table 3 Evaluation of the adhesion for the rats treated with the CMC/ PEG hydrogel (Cp8812) or a solution from the CMC/PEG hydrogel (Cp8812) Aggregation
Adhesion degree
Adhesion area (cm2)
Adhesion strength
Controls 2% solution Cp88/12 Hydrogel Cp88/12
4.6 ± 0.5 0.2 ± 0.42*
3.61 ± 0.24 0.0125 ± 0.04*
3.6 ± 0.51 0.3 ± 0.94*
0.1 ± 0.3*
0.0104 ± 0.03*
0.2 ± 0.63*
*
P value < 0.05 versus controls.
(Cp8812) had a significantly lower average adhesion score than the controls. There was not much difference in the adhesion scores between groups II and III. At day 14, no residual HA/CMC hydrogels were visible in the treated animals. The mechanism of the action by which the CMC reduces the adhesion formation is not clear. It has been found that CMC when implanted intraperitoneally attracts fluid in its surrounding and thereby prevents the serosa from a peritoneal contact – the so-called ‘‘hydroflotation effect’’. In addition, there is evidence to suggest that the CMC/PEG coats the intraperitoneal surfaces and reduces the direct apposition of the traumatized structures – the socalled ‘‘siliconizing effect’’ [9]. The other proposed mechanism of the action of the CMC is through its effect on the fibroblastic and cellular activities [10]. At the time of application, the hydrogels adhered readily to the serosal. In both the control and experimental groups, the celiotomy incisions
281
healed normally. The sutures holding the bowel to the abdominal wall were still in place (Fig. 4). The bioresorbability of the CMC/PEG hydrogel (Cp8812) between the skin and the abdominal layer of the rat was evaluated by observing the forms of the hydrogels on the cecal serosa on the 3rd, 7th, 14th days after surgery. The hydrogel was found to be a loose gel on the 3rd postoperative day, and was slightly detectable at the 7th day, but almost not detectable at the 14th postoperative day.
4. Conclusions Hydrogels based on CMC/PEG were prepared as physical barriers for preventing surgical adhesions using radiation. These interpolymeric hydrogels were synthesized by a gamma irradiation crosslinking technique. Animals treated with the CMC/PEG hydrogel (Cp8812) or a gel solution from the CMC/PEG hydrogel (Cp8812) had a significantly lower average adhesion score than the controls. At day 14, almost no residual HA/ CMC hydrogels were visible in the treated animals. Hydrogels prepared by radiation were found to significantly reduce the postsurgical adhesions in a rat cecal abrasion model.
References [1] M.A. Weibel, G. Majno, Am. J. Surg. 126 (1973) 345. [2] H. Ellis, Br. J. Surg. 69 (1982) 241.
Fig. 4. Necropsy taken 14 days after operation of rat to find the difference of adhesion between control (A) and solution prepared from the hydrogel (Cp88/12) (B).
282
Y.-C. Nho, J.-H. Lee / Nucl. Instr. and Meth. in Phys. Res. B 236 (2005) 277–282
[3] M.R. Soules, L. Dennis, A. Boserge, D.E. Moore, Am. J. Obstet. Gynecol. 143 (1982) 829. [4] N.F. Ray, J.W. Larser, R.J. Stillian, R.J. Jacobs, Surg. Gynecol. Obstet. 176 (1993) 271. [5] S.H. Wuster, V. Bonet, A. Mayberry, M. Hadolinott, T. Williams, I.H. Chassdry, J. Surg. Res. 59 (1995) 97. [6] C.K. Ryan, H.C. Sax, Am. J. Surg. 169 (1995) 154.
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