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Radiochemical sterilization and its use for sutures
Nuclear Instruments and Methods in Physics Research B 208 (2003) 110–114 www.elsevier.com/locate/nimb
Radiochemical sterilization and its use for sutures S.W. Shalaby a
a,*
, Y. Doyle b, B.L. Anneaux a, K.A. Carpenter a, F.R. Schiretz
a
Poly-Med, Inc., R & D Laboratories, 511 Westinghouse Road, Pendleton, SC 29670, USA b MDS-Nordion, 535 Boulevard Cartier, Laval, Que., Canada H7N 429
Abstract Radiochemical sterilization (RC-S) represents a novel approach to medical device sterilization. It is a hybrid process encompassing the attributes of chemical and high-energy radiation sterilization without the drawbacks associated with the use of the parent processes. It entails the use of a 5–7.5 kGy of c radiation and a polyformaldehyde insert capable of a radiolytic-controlled release of formaldehyde gas in a hermetically sealed package under dry nitrogen. The RC-S process has been applied successfully to radiation-sensitive sutures, namely polypropylene monofilaments and absorbable polyglycolide braids. Ó 2003 Elsevier B.V. All rights reserved. PACS: 61.80; 82.50.G; 82.55; 87.50 Keywords: Radiochemical sterilization; Absorbable sutures; Polypropylene; Sterilization
1. Introduction Radiochemical sterilization (RC-S) represents the first novel approach to medical device sterilization since the early use of ethylene oxide (Et-O) and high-energy radiation [1–4]. It provides the medical device industry with a unique, hybrid process encompassing the attributes of chemical and radiation sterilization (RS) without the drawbacks associated with the use of the parent processes. Limitations on use of the most commonly used methods (namely, traditional RS and Et-O) have grown in the past three decades because of (1)
* Corresponding author. Address: Poly-Med, Inc., 6309 Highway 187, Anderson, SC 29625, USA. Tel.: +1-864-6468544; fax: +1-864-646-8547. E-mail address: [email protected] (S.W. Shalaby).
degradation or undesirable changes of certain polymeric devices, such as those made from absorbable polymers and polypropylene, caused by c radiation; (2) ineffective sterilization of simple and complex devices with Et-O and associated device recalls and (3) toxic and explosive nature of Et-O. In contrast, the RC-S method combines the attributes of chemical sterilants and high-energy radiation and it entails (1) terminal sterilization of devices in a hermetically sealed package; (2) use of precisely generated formaldehyde through controlled radiolytic degradation of a solid polyformaldehyde insert to achieve surface sterility – residual formaldehyde is reabsorbed by its polymeric precursor and (3) about 20% of the traditional radiation dose is used to achieve surface and bulk device sterility. This report outlines the principle of RC-S and describes its successful use to provide sterile sutures
0168-583X/03/$ - see front matter Ó 2003 Elsevier B.V. All rights reserved. doi:10.1016/S0168-583X(03)00654-2
S.W. Shalaby et al. / Nucl. Instr. and Meth. in Phys. Res. B 208 (2003) 110–114
made of radiation-sensitive polymers, without inflicting discernable degradation in their biological properties as would be expected under the traditional sterilization with a nominal dose of 25 kGy [2,5].
2. Radiochemical sterilization and its effectiveness in achieving sterility 2.1. Basic aspects of the RC-S process The RC-S process was conceived and developed on the basis that (1) many polymeric medical devices can be sterilized using a 25 kGy dose of high-energy radiation [6]; (2) formaldehyde gas has been proven as a surface chemical sterilant for certain polymeric devices; (3) polyformaldehyde, particularly in the unstabilized form, undergoes radiolytic depolymerization to yield formaldehyde gas; (4) the amount of generated formaldehyde in a hermetically sealed package can be controlled, precisely, by the mass of irradiated polyformaldehyde and the dose of delivered radiation; (5) dry formaldehyde gas may dissolve in its own polymer or polymerize therein and (6) combinations of a low dose of penetrating high-energy radiation and formaldehyde gas in a dry nitrogen environment may be effective in imparting sterility in hermetically sealed packages. Accordingly, the RC-S process is based on using 10 kGy or less of high-energy radiation to (1) achieve bulk sterility of the specific polymeric device and (2) cause partial radiolytic degradation of a predetermined polyformaldehyde mass to generate, precisely, a limited amount of formaldehyde gas that is sufficient to achieve surface sterilization in conjunction with the prevailing radiation dose. Following the initial verification that 5–10 kGy in the presence of about 200 mg of polyformaldehyde in a sealed 65 ml package are effective in achieving sterility, it was determined that residual formaldehyde in the package is absorbed by the remaining mass of polyformaldehyde in the package. This is consistent with the postulate, relevant to the tenets of the RC-S process, on the fate of formaldehyde gas.
111
2.2. Effectiveness of RC-S in achieving sterility and optimized packaging development During the early stages of RC-S process development, different types and forms of polyformaldehyde were examined. These included Delrin powder and films as well as Celcon M-90 powder and films. However, it was later shown that unstabilized Celcon M-90 powder is most effective [7]. And using Celcon M-90 as a precursor of formaldehyde and a 5–10 kGy dose of c radiation was shown to achieve sterility under a number of experimental conditions. These included the use of (1) different amounts of Celcon M-90 as package inserts at a constant radiation dose with different sutures; (2) different radiation dose rate at a constant total dose in the presence of spore strips containing 107 spore and (3) different radiation doses at a constant Celcon M-90 mass in the presence of spore strips. A description of representative examples to illustrate the effectiveness of a typical RC-S process and rationale for pursuing key process changes are given below. Results of an earlier study [8] showed that sterility of absorbable suture braids can be achieved by RC-S using combinations of 5 or 7.5 kGy c radiation and a Delrinâ film as a source of radiolytically generated formaldehyde (CH2 O). However, in control packages containing 107 spore strips, the prevailing radiochemical sterilization conditions did not yield complete spore kill or 107 log reduction in a few instances. This was attributed to insufficient radiolytic generation of formaldehyde from the Delrinâ film, and the use of unstabilized Celcon M-90 as a preferred alternative was justified [7]. Accordingly, unstabilized Celcon M-90 powder and uncoated Safilâ polyglycolide braided sutures were procured from Celanese Corporation (Summit, New Jersey) and Aesculap A.G. (Tuttlingen, Germany), respectively. The Celcon was placed in a heat-sealed 1 cm2 pouch made of woven polyethylene terephthalate fabric. The fabric construction is selected so as to allow free diffusion of radiolytically generated formaldehyde gas, while retaining the Celcon M-90â powder in the pouch. All other processes were conducted as described in a previous study [8] and entailed (1) suture coating; (2)
112
S.W. Shalaby et al. / Nucl. Instr. and Meth. in Phys. Res. B 208 (2003) 110–114
packaging, assembling, and sealing; (3) irradiating the sealed packages with 5 kGy dose (using a Co60 source and a dose rate of 32 kGy/h) at MDS Nordion (Laval, Quebec, Canada); (4) measurement of the suture strength prior to sterilization and at least two weeks post-irradiation; (5) verification of suture and control spore strip sterility and (6) measurement of traces of formaldehyde in the irradiated packages. The experimental data generated at the different segments of the study are summarized in Table 1 and indicate that under the prevailing radiochemical sterilization conditions (1) complete suture and control spore strip sterility can be achieved; (2) the amounts of formaldehyde generated due to irradiation in the presence of about 200–500 mg/package of CelconM90 are sufficient to achieve suture and control spore strip sterility and (3) in spite of the original mass of Celcon-M90 ranging from about 10–500 mg, the detectable mass of residual formaldehyde
in the irradiated package ranged from about 9–11 lg. This is consistent with the results of an earlier study in which it was noted that (1) a small fraction of the polyformaldehyde depolymerizes radiolytically to CH2 O gas and (2) excess CH2 O is reabsorbed by its precursor.
3. Application of RC-S in the sterilization of polypropylene (PP) suture For this study, undyed monofilament sutures, size 3-0, were used. The in vivo breaking strength retention (BSR) data of monofilaments sterilized with 5 and 7.5 kGy are summarized in Table 2. The PP monofilaments were packaged under similar conditions to those noted for the polyglycolide braid in Section 4. The results in Table 2 show that under the prevailing RC-S conditions, using 5 and 7.5 kGy of c radiation, the BSR of
Table 1 Effect of RC-S conditions at 5 kGy dose on spore strips and residual formaldehyde using Celcon powder Celcon M-90 (mg)
Dose rate (kGy/h)
Spore strip (DFU/ml)
Spore killing (log reduction)
Residuala H2 O (lg)
Suture sterilityb
9.8 200 300 502 4.8 201 502
18 18 18 18 36 36 36
3:3 102 No growth No growth No growth 1:3 103 No growth No growth
5 7 7 7 4 7 7
9.2 9.7 10.2 11.0 9.1 10.4 11.4
5/0 5/0 5/0 5/0 5/0 5/0 5/0
a b
Residual CH2 O detected in package. Number of sterile/number of non-sterile sutures.
Table 2 In vivo breaking strength retention of sterilized, undyed PP monofilament suturesa Dose (kGy) 0 0 5 5 7.5 7.5 a
21 Day % BSR Relative Non-sterile sutureb
Sterile suturec
96 87 92 91 92 97
96 87 94 96 92 99
Five to six samples/set were tested all containing 150 mg Delrinâ , using Tyvek folders. In vivo % BSR relative to non-sterile suture ¼ tested max. stress/non-sterile max. stress. c In vivo % BSR relative to sterile suture ¼ tested max. stress/sterile max. stress. b
S.W. Shalaby et al. / Nucl. Instr. and Meth. in Phys. Res. B 208 (2003) 110–114
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Table 3 In vivo breaking strength retention of sterilized, dyed RC-S safil PG braided suturesa Dose (kGy)
7 Day % BSR relative
0 0 5 5 7.5 7.5
c
14 Day % BSR relative
21 Day % BSR relative
Non-sterile sutureb
Sterile suture
Non-sterile suture
Sterile suture
Non-sterile suture
Sterile suture
86 90 90 97 90 100
– – 94 111 96 134
87 84 86 82 82 106
– – 90 94 87 127
56 62 58 52 64 64
– – 61 60 68 76
a
Five to six samples/set were tested all containing 150 mg Delrinâ , area 450 mm2 , using Tyvek folders. In vivo % BSR relative to non-sterile suture ¼ tested max. stress/non-sterile max. stress. c In vivo % BSR relative to sterile suture ¼ tested max. stress/sterile max. stress. b
3 do show that the effect of RC-S (using 5 and 7.5 kGy of c radiation) on absorbable braid size 3-0 is minimal at 1-, 2- and 3-week post-implantation. For size 1 suture, the effect of RC-S is slightly more pronounced. The effect of RC-S on BSR values appears to be hardly dependent on whether they are measured in terms of the linear or knot strength. Storage of the sutures in the sealed packages at room temperature for more than 3 months has shown to have no adverse effect on the suture in vivo performance (measured in terms of breaking strength retention, BSR), as would be expected under standard sterilization using 25 kGy.
the PP monofilaments was practically uncompromised.
4. Application of RC-S in the sterilization of commercial absorbable polyglycolide suture braid For this study, coated, dyed sutures size 1 and 30 were used. The BSR data of sutures sterilized using 5 and 7.5 kGy are summarized in Table 3. The sutures were carefully packaged to minimize or eliminate residual moisture and/or traces of oxygen in the packages. And the in vivo BSR data in Table
Table 4 Effect of sterilization of new experimental monofilament suture Suture
Radiation dose (kGy)
Initial strength (kpsi)
% In vitro BSR @ week
% In vivo BSR @ week
1
2
1
2
73 78
72 78
24 51
– –
– –
0.27 – –
90 – –
66 68 52
48 34 28
75 70 58
52 42 29
0 5b 25
0.30 – –
73 – –
72 63 51
36 37 25
77 65 54
52 35 27
0 5b 25
0.14 – –
89 – –
(75)c (72)c (59)c
– (11)c (8)c
73 66 53
68 46 47
Classa
Example
P-SP
22-1-D5 23-1
0 0
26-8-D
0 5b 25
27-5-D1
9-4
L-SP
a
Diameter (mm)
P-SP ¼ polyaxial segmented copolyesters; L-SP ¼ linear segmented copolyester gut suture. Using RC-S protocol. c At 10, 20 and 25 days instead of 1, 2 and 3 weeks. b
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S.W. Shalaby et al. / Nucl. Instr. and Meth. in Phys. Res. B 208 (2003) 110–114
5. Application of RC-S for the sterilization of experimental absorbable monofilament suture Successful application of RC-S to braided suture prompted our pursuit of applying this process to two groups of compliant absorbable monofilament sutures. The first group is based on polyaxial segmented copolyester (P-SP) derived from e-caprolactone, trimethylene carbonate, and glycolide, exemplified by monofilaments nos. 22-1, 23-1, 26-8 and 27-5. The second group of monofilaments is made of linear segmented copolymer (L-SP) trimethylene carbonate and glycolide initiated with a polyalkylene dicarboxylate copolymer and exemplified by monofilament 9-4. Clinically relevant properties of these monofilament sutures before and after sterilization with 25 and 5 kGy (using the RC-S) process are summarized in Table 4. The data in Table 4 show a minor effect of the RC-S process and major changes in properties upon using the traditional 25 kGy dose.
6. Conclusion and perspective on the future of RC-S This report demonstrates the viability of the RCS process as a preferred alternative to ethylene oxide for effective sterilization of radiation-sensi-
tive medical devices represented by sutures which are made of polypropylene and absorbable polyesters. Following validation of this process, its application to other biomedical devices with complex geometry is expected to represent a major milestone in the field of device sterilization for its demonstrated effectiveness, expected higher safety, and cost advantage as compared with ethylene oxide.
References [1] S.W. Shalaby, C.L. Linden Jr., Radiochemical sterilization, US Patent 5,422,068, 1995. [2] S.W. Shalaby, C.L. Linden Jr., in: R.L. Clough, S.W. Shalaby (Eds.), Irradiation of Polymers, American Chemical Society, Washington, DC, 1996, p. 246. [3] J.D. Kline, D. Correa, S. Barefoot, R. Redshaw, S.W. Shalaby, Trans Soc. Biomater. 22 (1999) 561. [4] J.D. Kline, J.T. Corbett, D. Correa, S.W. Shalaby, Trans Soc. Biomater. 22 (1999) 564. [5] S.W. Shalaby, D.D. Jamiolkowski, Monomer process patent, US Patent 4,435,590 (to Ethicon, Inc.), 1984. [6] K.J.L. Burg, S.W. Shalaby, in: R.L. Clough, S.W. Shalaby (Eds.), Irradiation of Polymers, ACS Symp. Series, 1996, p. 240. [7] J.R. Quirk, B.L. Anneaux, J.T. Corbett, D.E. Linden, S.W. Shalaby, Trans Soc. Biomater. 25 (2002) 657. [8] B.L. Anneaux, G.G. Atkins, D.E. Linden, J.T. Corbett, L.K. Fulton, S.W. Shalaby, Trans. Soc. Biomater. 24 (2001) 157.
Radiochemical sterilization and its use for sutures S.W. Shalaby a
a,*
, Y. Doyle b, B.L. Anneaux a, K.A. Carpenter a, F.R. Schiretz
a
Poly-Med, Inc., R & D Laboratories, 511 Westinghouse Road, Pendleton, SC 29670, USA b MDS-Nordion, 535 Boulevard Cartier, Laval, Que., Canada H7N 429
Abstract Radiochemical sterilization (RC-S) represents a novel approach to medical device sterilization. It is a hybrid process encompassing the attributes of chemical and high-energy radiation sterilization without the drawbacks associated with the use of the parent processes. It entails the use of a 5–7.5 kGy of c radiation and a polyformaldehyde insert capable of a radiolytic-controlled release of formaldehyde gas in a hermetically sealed package under dry nitrogen. The RC-S process has been applied successfully to radiation-sensitive sutures, namely polypropylene monofilaments and absorbable polyglycolide braids. Ó 2003 Elsevier B.V. All rights reserved. PACS: 61.80; 82.50.G; 82.55; 87.50 Keywords: Radiochemical sterilization; Absorbable sutures; Polypropylene; Sterilization
1. Introduction Radiochemical sterilization (RC-S) represents the first novel approach to medical device sterilization since the early use of ethylene oxide (Et-O) and high-energy radiation [1–4]. It provides the medical device industry with a unique, hybrid process encompassing the attributes of chemical and radiation sterilization (RS) without the drawbacks associated with the use of the parent processes. Limitations on use of the most commonly used methods (namely, traditional RS and Et-O) have grown in the past three decades because of (1)
* Corresponding author. Address: Poly-Med, Inc., 6309 Highway 187, Anderson, SC 29625, USA. Tel.: +1-864-6468544; fax: +1-864-646-8547. E-mail address: [email protected] (S.W. Shalaby).
degradation or undesirable changes of certain polymeric devices, such as those made from absorbable polymers and polypropylene, caused by c radiation; (2) ineffective sterilization of simple and complex devices with Et-O and associated device recalls and (3) toxic and explosive nature of Et-O. In contrast, the RC-S method combines the attributes of chemical sterilants and high-energy radiation and it entails (1) terminal sterilization of devices in a hermetically sealed package; (2) use of precisely generated formaldehyde through controlled radiolytic degradation of a solid polyformaldehyde insert to achieve surface sterility – residual formaldehyde is reabsorbed by its polymeric precursor and (3) about 20% of the traditional radiation dose is used to achieve surface and bulk device sterility. This report outlines the principle of RC-S and describes its successful use to provide sterile sutures
0168-583X/03/$ - see front matter Ó 2003 Elsevier B.V. All rights reserved. doi:10.1016/S0168-583X(03)00654-2
S.W. Shalaby et al. / Nucl. Instr. and Meth. in Phys. Res. B 208 (2003) 110–114
made of radiation-sensitive polymers, without inflicting discernable degradation in their biological properties as would be expected under the traditional sterilization with a nominal dose of 25 kGy [2,5].
2. Radiochemical sterilization and its effectiveness in achieving sterility 2.1. Basic aspects of the RC-S process The RC-S process was conceived and developed on the basis that (1) many polymeric medical devices can be sterilized using a 25 kGy dose of high-energy radiation [6]; (2) formaldehyde gas has been proven as a surface chemical sterilant for certain polymeric devices; (3) polyformaldehyde, particularly in the unstabilized form, undergoes radiolytic depolymerization to yield formaldehyde gas; (4) the amount of generated formaldehyde in a hermetically sealed package can be controlled, precisely, by the mass of irradiated polyformaldehyde and the dose of delivered radiation; (5) dry formaldehyde gas may dissolve in its own polymer or polymerize therein and (6) combinations of a low dose of penetrating high-energy radiation and formaldehyde gas in a dry nitrogen environment may be effective in imparting sterility in hermetically sealed packages. Accordingly, the RC-S process is based on using 10 kGy or less of high-energy radiation to (1) achieve bulk sterility of the specific polymeric device and (2) cause partial radiolytic degradation of a predetermined polyformaldehyde mass to generate, precisely, a limited amount of formaldehyde gas that is sufficient to achieve surface sterilization in conjunction with the prevailing radiation dose. Following the initial verification that 5–10 kGy in the presence of about 200 mg of polyformaldehyde in a sealed 65 ml package are effective in achieving sterility, it was determined that residual formaldehyde in the package is absorbed by the remaining mass of polyformaldehyde in the package. This is consistent with the postulate, relevant to the tenets of the RC-S process, on the fate of formaldehyde gas.
111
2.2. Effectiveness of RC-S in achieving sterility and optimized packaging development During the early stages of RC-S process development, different types and forms of polyformaldehyde were examined. These included Delrin powder and films as well as Celcon M-90 powder and films. However, it was later shown that unstabilized Celcon M-90 powder is most effective [7]. And using Celcon M-90 as a precursor of formaldehyde and a 5–10 kGy dose of c radiation was shown to achieve sterility under a number of experimental conditions. These included the use of (1) different amounts of Celcon M-90 as package inserts at a constant radiation dose with different sutures; (2) different radiation dose rate at a constant total dose in the presence of spore strips containing 107 spore and (3) different radiation doses at a constant Celcon M-90 mass in the presence of spore strips. A description of representative examples to illustrate the effectiveness of a typical RC-S process and rationale for pursuing key process changes are given below. Results of an earlier study [8] showed that sterility of absorbable suture braids can be achieved by RC-S using combinations of 5 or 7.5 kGy c radiation and a Delrinâ film as a source of radiolytically generated formaldehyde (CH2 O). However, in control packages containing 107 spore strips, the prevailing radiochemical sterilization conditions did not yield complete spore kill or 107 log reduction in a few instances. This was attributed to insufficient radiolytic generation of formaldehyde from the Delrinâ film, and the use of unstabilized Celcon M-90 as a preferred alternative was justified [7]. Accordingly, unstabilized Celcon M-90 powder and uncoated Safilâ polyglycolide braided sutures were procured from Celanese Corporation (Summit, New Jersey) and Aesculap A.G. (Tuttlingen, Germany), respectively. The Celcon was placed in a heat-sealed 1 cm2 pouch made of woven polyethylene terephthalate fabric. The fabric construction is selected so as to allow free diffusion of radiolytically generated formaldehyde gas, while retaining the Celcon M-90â powder in the pouch. All other processes were conducted as described in a previous study [8] and entailed (1) suture coating; (2)
112
S.W. Shalaby et al. / Nucl. Instr. and Meth. in Phys. Res. B 208 (2003) 110–114
packaging, assembling, and sealing; (3) irradiating the sealed packages with 5 kGy dose (using a Co60 source and a dose rate of 32 kGy/h) at MDS Nordion (Laval, Quebec, Canada); (4) measurement of the suture strength prior to sterilization and at least two weeks post-irradiation; (5) verification of suture and control spore strip sterility and (6) measurement of traces of formaldehyde in the irradiated packages. The experimental data generated at the different segments of the study are summarized in Table 1 and indicate that under the prevailing radiochemical sterilization conditions (1) complete suture and control spore strip sterility can be achieved; (2) the amounts of formaldehyde generated due to irradiation in the presence of about 200–500 mg/package of CelconM90 are sufficient to achieve suture and control spore strip sterility and (3) in spite of the original mass of Celcon-M90 ranging from about 10–500 mg, the detectable mass of residual formaldehyde
in the irradiated package ranged from about 9–11 lg. This is consistent with the results of an earlier study in which it was noted that (1) a small fraction of the polyformaldehyde depolymerizes radiolytically to CH2 O gas and (2) excess CH2 O is reabsorbed by its precursor.
3. Application of RC-S in the sterilization of polypropylene (PP) suture For this study, undyed monofilament sutures, size 3-0, were used. The in vivo breaking strength retention (BSR) data of monofilaments sterilized with 5 and 7.5 kGy are summarized in Table 2. The PP monofilaments were packaged under similar conditions to those noted for the polyglycolide braid in Section 4. The results in Table 2 show that under the prevailing RC-S conditions, using 5 and 7.5 kGy of c radiation, the BSR of
Table 1 Effect of RC-S conditions at 5 kGy dose on spore strips and residual formaldehyde using Celcon powder Celcon M-90 (mg)
Dose rate (kGy/h)
Spore strip (DFU/ml)
Spore killing (log reduction)
Residuala H2 O (lg)
Suture sterilityb
9.8 200 300 502 4.8 201 502
18 18 18 18 36 36 36
3:3 102 No growth No growth No growth 1:3 103 No growth No growth
5 7 7 7 4 7 7
9.2 9.7 10.2 11.0 9.1 10.4 11.4
5/0 5/0 5/0 5/0 5/0 5/0 5/0
a b
Residual CH2 O detected in package. Number of sterile/number of non-sterile sutures.
Table 2 In vivo breaking strength retention of sterilized, undyed PP monofilament suturesa Dose (kGy) 0 0 5 5 7.5 7.5 a
21 Day % BSR Relative Non-sterile sutureb
Sterile suturec
96 87 92 91 92 97
96 87 94 96 92 99
Five to six samples/set were tested all containing 150 mg Delrinâ , using Tyvek folders. In vivo % BSR relative to non-sterile suture ¼ tested max. stress/non-sterile max. stress. c In vivo % BSR relative to sterile suture ¼ tested max. stress/sterile max. stress. b
S.W. Shalaby et al. / Nucl. Instr. and Meth. in Phys. Res. B 208 (2003) 110–114
113
Table 3 In vivo breaking strength retention of sterilized, dyed RC-S safil PG braided suturesa Dose (kGy)
7 Day % BSR relative
0 0 5 5 7.5 7.5
c
14 Day % BSR relative
21 Day % BSR relative
Non-sterile sutureb
Sterile suture
Non-sterile suture
Sterile suture
Non-sterile suture
Sterile suture
86 90 90 97 90 100
– – 94 111 96 134
87 84 86 82 82 106
– – 90 94 87 127
56 62 58 52 64 64
– – 61 60 68 76
a
Five to six samples/set were tested all containing 150 mg Delrinâ , area 450 mm2 , using Tyvek folders. In vivo % BSR relative to non-sterile suture ¼ tested max. stress/non-sterile max. stress. c In vivo % BSR relative to sterile suture ¼ tested max. stress/sterile max. stress. b
3 do show that the effect of RC-S (using 5 and 7.5 kGy of c radiation) on absorbable braid size 3-0 is minimal at 1-, 2- and 3-week post-implantation. For size 1 suture, the effect of RC-S is slightly more pronounced. The effect of RC-S on BSR values appears to be hardly dependent on whether they are measured in terms of the linear or knot strength. Storage of the sutures in the sealed packages at room temperature for more than 3 months has shown to have no adverse effect on the suture in vivo performance (measured in terms of breaking strength retention, BSR), as would be expected under standard sterilization using 25 kGy.
the PP monofilaments was practically uncompromised.
4. Application of RC-S in the sterilization of commercial absorbable polyglycolide suture braid For this study, coated, dyed sutures size 1 and 30 were used. The BSR data of sutures sterilized using 5 and 7.5 kGy are summarized in Table 3. The sutures were carefully packaged to minimize or eliminate residual moisture and/or traces of oxygen in the packages. And the in vivo BSR data in Table
Table 4 Effect of sterilization of new experimental monofilament suture Suture
Radiation dose (kGy)
Initial strength (kpsi)
% In vitro BSR @ week
% In vivo BSR @ week
1
2
1
2
73 78
72 78
24 51
– –
– –
0.27 – –
90 – –
66 68 52
48 34 28
75 70 58
52 42 29
0 5b 25
0.30 – –
73 – –
72 63 51
36 37 25
77 65 54
52 35 27
0 5b 25
0.14 – –
89 – –
(75)c (72)c (59)c
– (11)c (8)c
73 66 53
68 46 47
Classa
Example
P-SP
22-1-D5 23-1
0 0
26-8-D
0 5b 25
27-5-D1
9-4
L-SP
a
Diameter (mm)
P-SP ¼ polyaxial segmented copolyesters; L-SP ¼ linear segmented copolyester gut suture. Using RC-S protocol. c At 10, 20 and 25 days instead of 1, 2 and 3 weeks. b
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S.W. Shalaby et al. / Nucl. Instr. and Meth. in Phys. Res. B 208 (2003) 110–114
5. Application of RC-S for the sterilization of experimental absorbable monofilament suture Successful application of RC-S to braided suture prompted our pursuit of applying this process to two groups of compliant absorbable monofilament sutures. The first group is based on polyaxial segmented copolyester (P-SP) derived from e-caprolactone, trimethylene carbonate, and glycolide, exemplified by monofilaments nos. 22-1, 23-1, 26-8 and 27-5. The second group of monofilaments is made of linear segmented copolymer (L-SP) trimethylene carbonate and glycolide initiated with a polyalkylene dicarboxylate copolymer and exemplified by monofilament 9-4. Clinically relevant properties of these monofilament sutures before and after sterilization with 25 and 5 kGy (using the RC-S) process are summarized in Table 4. The data in Table 4 show a minor effect of the RC-S process and major changes in properties upon using the traditional 25 kGy dose.
6. Conclusion and perspective on the future of RC-S This report demonstrates the viability of the RCS process as a preferred alternative to ethylene oxide for effective sterilization of radiation-sensi-
tive medical devices represented by sutures which are made of polypropylene and absorbable polyesters. Following validation of this process, its application to other biomedical devices with complex geometry is expected to represent a major milestone in the field of device sterilization for its demonstrated effectiveness, expected higher safety, and cost advantage as compared with ethylene oxide.
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