JBUR-4260; No. of Pages 8 burns xxx (2014) xxx–xxx
Available online at www.sciencedirect.com
ScienceDirect journal homepage: www.elsevier.com/locate/burns
Effect of hydrogel grafting, water and surfactant wetting on the adherence of PET wound dressings Chenxi (Coco) Ning a, Sarvesh Logsetty b, Shivkumar Ghughare a, Song Liu a,c,d,e,* a
Department of Textile Sciences, Faculty of Human Ecology, University of Manitoba, Winnipeg, MB, Canada Manitoba Firefighters Burn Unit, Department of Surgery, Faculty of Medicine, University of Manitoba, Winnipeg, MB, Canada c Department of Chemistry, University of Manitoba, Winnipeg, MB, Canada d Department of Medical Microbiology, University of Manitoba, Winnipeg, MB, Canada e Department of Biosystems Engineering, University of Manitoba, Winnipeg, MB, Canada b
article info
abstract
Article history:
Traditional wound dressings, including cotton gauze, absorbent pads and bandages, can
Accepted 31 December 2013
cause trauma and pain to wounds during dressing changes, leading to a variety of physical and psychosocial sequelae. The aim of this study was to adapt an in vitro model of adherence
Keywords:
to evaluate the effects of various methods to theoretically reduce the adherence of wound
Burn wound care dressing
dressings. Gelatin in liquid form was cast onto poly(ethylene terephthalate) (PET) fabric and
Dressing adherence
allowed to solidify and progressively dry to simulate wound desiccation in the clinical
In vitro dressing adherence test
setting. A 1808 peel test of PET from the gelatin slab yielded adherence data of peeling
Hydrogel grafting
energy. The peeling energy of PET increased with the drying time. It was possible to reduce the force by drying at 75% relative humidity (RH). After drying for 24 h, either 500 mL of water or surfactant solution was added onto the PET surface (16 60 mm2). The peeling energy decreased dramatically with wetting and there was no significant difference between water and surfactant. As a long-term strategy for decreasing adherence, a thin layer of polyacrylamide (PAM) hydrogel was deposited onto PET fabric via UV irradiation. This resulted in a much lower peeling energy without severely compromising fabric flexibility. This hydrogel layer could also serve as a reservoir for bioactive and antimicrobial agents which could be sustainably released to create a microbe-free microenvironment for optimized wound healing. # 2014 Elsevier Ltd and ISBI. All rights reserved.
1.
Introduction
Minimal trauma upon removal has been one of the most important requirements on modern burn wound dressings. According to a worldwide online survey among burn care specialists, out of total 121 participants, 105 identified
non-adhesion as either an essential or a desirable property of an ‘‘ideal’’ dressing [1]. However, many commercially available wound dressings cause second trauma and significant pain upon removal because of adhesion to the wound bed [2]. These dressings can adhere to wounds as exudate dries, and capillary loops and granulation tissue can grow through the dressing fabrics. Pain-induced stress can delay
* Corresponding author at: University of Manitoba, Department of Textile Sciences, 190 Dysart Road, W581 Duff Roblin Building, Winnipeg, MB, Canada. Tel.: +1 204 474 7592/+1 204 474 9616; fax: +1 204 474 7592/+1 20 447 47593. E-mail address: [email protected] (S. Liu). 0305-4179/$36.00 # 2014 Elsevier Ltd and ISBI. All rights reserved. http://dx.doi.org/10.1016/j.burns.2013.12.024 Please cite this article in press as: Ning C, et al. Effect of hydrogel grafting, water and surfactant wetting on the adherence of PET wound dressings. Burns (2014), http://dx.doi.org/10.1016/j.burns.2013.12.024
JBUR-4260; No. of Pages 8
2
burns xxx (2014) xxx–xxx
wound healing and adversely affect patients’ quality of life. A recent study has shown that burn related pain is associated with severe depressive and posttraumatic stress symptoms among patients, increasing incidence of anxiety, depression, and suicidal ideation [3,4]. Traditionally adherence testing has been done with cell adhesion test or in vivo testing. Human skin cells such as keratinocyte and fibroblast were seeded onto the dressings, and the morphology of cells adhered were then observed with a phase contrast microscope after incubating at 37 8C for 1, 2, and 3 days. The number of cells can be quantified using various methods such as MTT cell proliferation assay [5–7]. However, cells are not the only component in wounds. There are a variety of substances including water, protein, electrolytes, enzymes and waste products that also exist in the wounds. In the in vitro cell adhesion test the cell/sample complexes are not allowed to dry as would happen in wound desiccation. Therefore, it might not appropriately reflect the real situation of wound healing. In vivo evaluation of wound dressing performance on animal models or human beings is more direct but not without drawbacks [8–10]. Using animals in research for screening purposed is of ethical concerns. It’s difficult to obtain a reproducible measurement of adherence forces in the clinical setting as wounds of patients are quite variable and hard to sample. Furthermore, both animal and human models require a substantial commitment of time, effort, and are expensive. In recognition of this problem, we adapted a previously reported in vitro gelatin model to simulate in vivo dressing contact with wounds [11]. Gelatin is a strongly hydrogenbonded proteinaceous material which can adhere to dressing materials similarly to wound exudates. It can be allowed to dry progressively through the gel state into a rigid solid to mimic the process of wound dessication, and different clinical situations can be simulated by allowing the gelatin to dry to different extents. The necessity of a low-adherent dressing drove the current study to explore different strategies for decreasing adherence of common burn wound dressing materials. The short-term strategy was to wet adherent dressings with water or surfactant before the peeling and the long-term strategy to deposit hydrogel onto commonly used dressing materials to reduce adherence. It has been reported that hydrogel dressings can decrease adherence as long as they remain hydrated [12–14]. Poly(ethylene terephthalate) (PET) woven fabric was chosen as the representative dressing material in view of its popularity as dressing base materials in burn dressings (ActicoatTM and Atrauman1) for its readily availability, good biocompatibility and excellent mechanical strength. We present our evaluation of the effect of water and surfactant wetting and hydrogel grafting on the adhesiveness of PET dressings using an in vitro model.
2.
Materials and methods
2.1.
Materials
Acrylamide (AM) and N,N0 -methylene bisacrylamide (MBA, crosslinker) were purchased from Sigma-Aldrich (Oakville,
ON). Gelatin, silver nitrate (AgNO3) and sodium citrate dehydrate (Na3C6H5O2H2O) were purchased from Fisher Scientific (Ottawa, ON). Sodium borohydride (NaBH4) came from Acros (New Jersey, USA). PET plain woven fabric (no. 777H) was purchased from Testfabrics, Inc. (West Pittiston, PA).
2.2.
Preparation of hydrogel coated PET
PET plain woven fabric (6 14 cm) was first extracted with distilled (DI) Water for 24 h to remove impurities before any treatment. The extracted PET fabric was treated with O2 plasma (flow rate of O2: 2–4 standard cubic centimeter per minute) for 20 min to produce peroxide functional groups on the surface of the fabric. 3 mL monomer solution containing 9.8% (w/v) AM and 0.2% (w/v) MBA was uniformly placed onto the plasma treated PET fabric. Then the fabric was sandwiched by two glass plates prior to UV irradiation (365 nm, 3000 mw/ cm2). Crosslinked polyacrylamide (PAM) hydrogel was grown from the surface of PET after UV irradiation (as shown in Scheme 1). After the radical grafting crosslinking copolymerization, the PET sample was extracted with DI water in a 65 8C water bath at the shaking speed of 150 RPM for 16–24 h to remove ungrafted monomers and polymers, dried and stored in a desiccator to reach constant weight. The resultant PET fabric is referred to as ‘‘PET-PAM’’. The amount of hydrogel deposited was calculated by the weight increment of the PET fabrics after the polymerization as follows. Weight increment ¼
ðWt W0 Þ 100% W0
where W0 is the weight of untreated PET and Wt is the weight of sample after t min of UV irradiation, t = 30, 50 and 70 min.
2.2.1.
Swelling ratio test
Before the peeling force test, fabric samples were immersed in DI water for 5 min and centrifuged for 30 s at 2800 rpm to remove the excess water adsorbed on the surface. The swelling process was confirmed by change in weight: the ability for swelling is called ‘‘swelling ratio’’. ðM1 M0 Þ 100% Swelling ratio ¼ M0 where M0 is recorded as the weight of dry sample, and M1 is the weight of swollen sample.
2.2.2.
Flexibility test
A Cantilever Bending Tester was used to test the flexibility of fabric samples according to ASTM standard D 1388-96 [15]. Briefly, a fabric sample was immersed in DI water for 5 min and centrifuged for 30 s at 2800 rpm to remove the excess water adsorbed on the surface. Then the swollen sample (2 12 cm2) was put on a horizontal platform and slid gradually in a direction parallel to its long dimension. The length overhang was measured at which the tip of the specimen was depressed under its own mass to the point where the line joining the top to the edge of the platform made a 41.58 angle with the horizontal. Samples were tested at both ends and the two readings were averaged. The bending length c and flexural rigidity were then calculated:
Please cite this article in press as: Ning C, et al. Effect of hydrogel grafting, water and surfactant wetting on the adherence of PET wound dressings. Burns (2014), http://dx.doi.org/10.1016/j.burns.2013.12.024
JBUR-4260; No. of Pages 8 burns xxx (2014) xxx–xxx
3
Scheme 1 – Surface grafting with polyacrylamide (PAM) hydrogel onto PET Dressing via plasma treatment and photopolymerization.
o c ¼ ; where c ¼ bending lengthðcmÞ; o ¼ length of overhangðcmÞ; 2 G ¼ W c3 ; where G ¼ flexural rigidityðmg cmÞ; W ¼ fabric mass per unit areaðmg=cm2 Þ:
2.3.
Peeling force test
An in vitro model was chosen to mimic the environment between human skin and wound dressing: Briefly, a polytetrafluoroethylene (PTFE) window frame with an open area 16 60 mm2 for gelatin casting wad created. All the fabric samples (3 13 cm2) were soaked in DI water for 5 min, centrifuged for 30 s and then spread on a clean bench; one frame was placed onto each piece of fabric. 40 wt% gelatin solution was prepared in 70 8C DI water and then poured into the window frame. To simulate the wound desiccation process, the gelatin/fabric module was dried in the incubator at the skin temperature 32 8C for different time durations while maintaining a dry (
Available online at www.sciencedirect.com
ScienceDirect journal homepage: www.elsevier.com/locate/burns
Effect of hydrogel grafting, water and surfactant wetting on the adherence of PET wound dressings Chenxi (Coco) Ning a, Sarvesh Logsetty b, Shivkumar Ghughare a, Song Liu a,c,d,e,* a
Department of Textile Sciences, Faculty of Human Ecology, University of Manitoba, Winnipeg, MB, Canada Manitoba Firefighters Burn Unit, Department of Surgery, Faculty of Medicine, University of Manitoba, Winnipeg, MB, Canada c Department of Chemistry, University of Manitoba, Winnipeg, MB, Canada d Department of Medical Microbiology, University of Manitoba, Winnipeg, MB, Canada e Department of Biosystems Engineering, University of Manitoba, Winnipeg, MB, Canada b
article info
abstract
Article history:
Traditional wound dressings, including cotton gauze, absorbent pads and bandages, can
Accepted 31 December 2013
cause trauma and pain to wounds during dressing changes, leading to a variety of physical and psychosocial sequelae. The aim of this study was to adapt an in vitro model of adherence
Keywords:
to evaluate the effects of various methods to theoretically reduce the adherence of wound
Burn wound care dressing
dressings. Gelatin in liquid form was cast onto poly(ethylene terephthalate) (PET) fabric and
Dressing adherence
allowed to solidify and progressively dry to simulate wound desiccation in the clinical
In vitro dressing adherence test
setting. A 1808 peel test of PET from the gelatin slab yielded adherence data of peeling
Hydrogel grafting
energy. The peeling energy of PET increased with the drying time. It was possible to reduce the force by drying at 75% relative humidity (RH). After drying for 24 h, either 500 mL of water or surfactant solution was added onto the PET surface (16 60 mm2). The peeling energy decreased dramatically with wetting and there was no significant difference between water and surfactant. As a long-term strategy for decreasing adherence, a thin layer of polyacrylamide (PAM) hydrogel was deposited onto PET fabric via UV irradiation. This resulted in a much lower peeling energy without severely compromising fabric flexibility. This hydrogel layer could also serve as a reservoir for bioactive and antimicrobial agents which could be sustainably released to create a microbe-free microenvironment for optimized wound healing. # 2014 Elsevier Ltd and ISBI. All rights reserved.
1.
Introduction
Minimal trauma upon removal has been one of the most important requirements on modern burn wound dressings. According to a worldwide online survey among burn care specialists, out of total 121 participants, 105 identified
non-adhesion as either an essential or a desirable property of an ‘‘ideal’’ dressing [1]. However, many commercially available wound dressings cause second trauma and significant pain upon removal because of adhesion to the wound bed [2]. These dressings can adhere to wounds as exudate dries, and capillary loops and granulation tissue can grow through the dressing fabrics. Pain-induced stress can delay
* Corresponding author at: University of Manitoba, Department of Textile Sciences, 190 Dysart Road, W581 Duff Roblin Building, Winnipeg, MB, Canada. Tel.: +1 204 474 7592/+1 204 474 9616; fax: +1 204 474 7592/+1 20 447 47593. E-mail address: [email protected] (S. Liu). 0305-4179/$36.00 # 2014 Elsevier Ltd and ISBI. All rights reserved. http://dx.doi.org/10.1016/j.burns.2013.12.024 Please cite this article in press as: Ning C, et al. Effect of hydrogel grafting, water and surfactant wetting on the adherence of PET wound dressings. Burns (2014), http://dx.doi.org/10.1016/j.burns.2013.12.024
JBUR-4260; No. of Pages 8
2
burns xxx (2014) xxx–xxx
wound healing and adversely affect patients’ quality of life. A recent study has shown that burn related pain is associated with severe depressive and posttraumatic stress symptoms among patients, increasing incidence of anxiety, depression, and suicidal ideation [3,4]. Traditionally adherence testing has been done with cell adhesion test or in vivo testing. Human skin cells such as keratinocyte and fibroblast were seeded onto the dressings, and the morphology of cells adhered were then observed with a phase contrast microscope after incubating at 37 8C for 1, 2, and 3 days. The number of cells can be quantified using various methods such as MTT cell proliferation assay [5–7]. However, cells are not the only component in wounds. There are a variety of substances including water, protein, electrolytes, enzymes and waste products that also exist in the wounds. In the in vitro cell adhesion test the cell/sample complexes are not allowed to dry as would happen in wound desiccation. Therefore, it might not appropriately reflect the real situation of wound healing. In vivo evaluation of wound dressing performance on animal models or human beings is more direct but not without drawbacks [8–10]. Using animals in research for screening purposed is of ethical concerns. It’s difficult to obtain a reproducible measurement of adherence forces in the clinical setting as wounds of patients are quite variable and hard to sample. Furthermore, both animal and human models require a substantial commitment of time, effort, and are expensive. In recognition of this problem, we adapted a previously reported in vitro gelatin model to simulate in vivo dressing contact with wounds [11]. Gelatin is a strongly hydrogenbonded proteinaceous material which can adhere to dressing materials similarly to wound exudates. It can be allowed to dry progressively through the gel state into a rigid solid to mimic the process of wound dessication, and different clinical situations can be simulated by allowing the gelatin to dry to different extents. The necessity of a low-adherent dressing drove the current study to explore different strategies for decreasing adherence of common burn wound dressing materials. The short-term strategy was to wet adherent dressings with water or surfactant before the peeling and the long-term strategy to deposit hydrogel onto commonly used dressing materials to reduce adherence. It has been reported that hydrogel dressings can decrease adherence as long as they remain hydrated [12–14]. Poly(ethylene terephthalate) (PET) woven fabric was chosen as the representative dressing material in view of its popularity as dressing base materials in burn dressings (ActicoatTM and Atrauman1) for its readily availability, good biocompatibility and excellent mechanical strength. We present our evaluation of the effect of water and surfactant wetting and hydrogel grafting on the adhesiveness of PET dressings using an in vitro model.
2.
Materials and methods
2.1.
Materials
Acrylamide (AM) and N,N0 -methylene bisacrylamide (MBA, crosslinker) were purchased from Sigma-Aldrich (Oakville,
ON). Gelatin, silver nitrate (AgNO3) and sodium citrate dehydrate (Na3C6H5O2H2O) were purchased from Fisher Scientific (Ottawa, ON). Sodium borohydride (NaBH4) came from Acros (New Jersey, USA). PET plain woven fabric (no. 777H) was purchased from Testfabrics, Inc. (West Pittiston, PA).
2.2.
Preparation of hydrogel coated PET
PET plain woven fabric (6 14 cm) was first extracted with distilled (DI) Water for 24 h to remove impurities before any treatment. The extracted PET fabric was treated with O2 plasma (flow rate of O2: 2–4 standard cubic centimeter per minute) for 20 min to produce peroxide functional groups on the surface of the fabric. 3 mL monomer solution containing 9.8% (w/v) AM and 0.2% (w/v) MBA was uniformly placed onto the plasma treated PET fabric. Then the fabric was sandwiched by two glass plates prior to UV irradiation (365 nm, 3000 mw/ cm2). Crosslinked polyacrylamide (PAM) hydrogel was grown from the surface of PET after UV irradiation (as shown in Scheme 1). After the radical grafting crosslinking copolymerization, the PET sample was extracted with DI water in a 65 8C water bath at the shaking speed of 150 RPM for 16–24 h to remove ungrafted monomers and polymers, dried and stored in a desiccator to reach constant weight. The resultant PET fabric is referred to as ‘‘PET-PAM’’. The amount of hydrogel deposited was calculated by the weight increment of the PET fabrics after the polymerization as follows. Weight increment ¼
ðWt W0 Þ 100% W0
where W0 is the weight of untreated PET and Wt is the weight of sample after t min of UV irradiation, t = 30, 50 and 70 min.
2.2.1.
Swelling ratio test
Before the peeling force test, fabric samples were immersed in DI water for 5 min and centrifuged for 30 s at 2800 rpm to remove the excess water adsorbed on the surface. The swelling process was confirmed by change in weight: the ability for swelling is called ‘‘swelling ratio’’. ðM1 M0 Þ 100% Swelling ratio ¼ M0 where M0 is recorded as the weight of dry sample, and M1 is the weight of swollen sample.
2.2.2.
Flexibility test
A Cantilever Bending Tester was used to test the flexibility of fabric samples according to ASTM standard D 1388-96 [15]. Briefly, a fabric sample was immersed in DI water for 5 min and centrifuged for 30 s at 2800 rpm to remove the excess water adsorbed on the surface. Then the swollen sample (2 12 cm2) was put on a horizontal platform and slid gradually in a direction parallel to its long dimension. The length overhang was measured at which the tip of the specimen was depressed under its own mass to the point where the line joining the top to the edge of the platform made a 41.58 angle with the horizontal. Samples were tested at both ends and the two readings were averaged. The bending length c and flexural rigidity were then calculated:
Please cite this article in press as: Ning C, et al. Effect of hydrogel grafting, water and surfactant wetting on the adherence of PET wound dressings. Burns (2014), http://dx.doi.org/10.1016/j.burns.2013.12.024
JBUR-4260; No. of Pages 8 burns xxx (2014) xxx–xxx
3
Scheme 1 – Surface grafting with polyacrylamide (PAM) hydrogel onto PET Dressing via plasma treatment and photopolymerization.
o c ¼ ; where c ¼ bending lengthðcmÞ; o ¼ length of overhangðcmÞ; 2 G ¼ W c3 ; where G ¼ flexural rigidityðmg cmÞ; W ¼ fabric mass per unit areaðmg=cm2 Þ:
2.3.
Peeling force test
An in vitro model was chosen to mimic the environment between human skin and wound dressing: Briefly, a polytetrafluoroethylene (PTFE) window frame with an open area 16 60 mm2 for gelatin casting wad created. All the fabric samples (3 13 cm2) were soaked in DI water for 5 min, centrifuged for 30 s and then spread on a clean bench; one frame was placed onto each piece of fabric. 40 wt% gelatin solution was prepared in 70 8C DI water and then poured into the window frame. To simulate the wound desiccation process, the gelatin/fabric module was dried in the incubator at the skin temperature 32 8C for different time durations while maintaining a dry (
