Topical Applications of Silver Nanoparticles for Wound Healing Enhancement in Various Animals

Wound repair process in healthy individuals depends on several interrelated processes, including the migration of inflammatory cells to colonize the provisional matrix, proliferation of fibroblasts and vascular cells, apoptosis and synthesis of extracellular matrix proteins to reconstitute dermal architecture. Aberrant apoptosis also removes granulation tissues leading to abnormal wound healing (Walker et al., 1988). In animals due to various types of injuries and trauma, the deep extensive wounds are most common encountered conditions, which need emergency attention of veterinarians. The animals are more prone to various wounds on body with multiple complications and the management of such cases become very difficult and challenging. Chronic wounds need long term therapy comprised of complex managemental therapeutics with regular debridement of damaged and necrotic tissues, local and/or systemic infection control, protection of the underlying tissues and induction of cutaneous tissue regeneration (Parmar et al., 2022). Due to strong bactericidal effects of silver compounds and ions, these are extensively used for hygienic and wound management since centuries (Klasen, 2000). Due to the bactericidal properties various silver containing preparations were used for the treatment of chronic wounds in human patients. Apart from antimicrobial properties, having anti-inflammatory properties, it losses rubor in chronic wounds treated with colloidal silver (Demling and DeSanti, 2001). Recently, there has been an increased interest in silver, due to increased resistance of bacteria to antibiotics and improvements in polymer technology. Thus, it has resulted in a large number of silver-containing dressings being available on the market. The recent emergence of nanotechnology has provided a new therapeutic modality in silver nanoparticles for use in wounds. Nonetheless, the beneficial effects of silver nanoparticles on wound healing remain unknown. Nowadays, silver-based topical dressings have been widely used as a treatment for infections in open wounds and chronic ulcers (Mishra et al., 2008). The available literature for the wound healing in veterinary patients especially in clinical cases is very rare. Thus, this paper presents a role of silver nanoparticles for the healing of chronic complicated wounds in different animal species.

Total twenty seven animals of various species viz., dogs (n=20), goats (n=6), cat (n=1) and buffalo (n=1) presented to Veterinary Clinical Complex, College of Veterinary Science and Animal Husbandry, Kamdhenu University, Anand with different types of chronic complicated wounds on different body parts. The details of breed, age, sex, location and type of wound and its duration etc in 20 dogs with would were as presented in Table 1. Amongst the six female goat patients, two years and three years old goats (n=3, each) were presented with chronic deep maggoted wounds on perivalvar region, while an eight months old cat was presented with sloughing of skin at lumber region and a fourth lactation buffalo was presented with extensive skin sloughing on right abdominal region. The evaluation of wound was done and therapeutic management was carried out according to the conditions. The day of presentation was considered as day ‘0’.
       

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 
In all the cases, the wounds were kept open and treated with antiseptic dressing using Betadine 5% along with Inj. Cefrtiaxone and Tazobactum @ 15 mg/kg body weight in dogs and cat, 20 mg/kg body weight in goat and 6 mg/kg body weight in buffalo; and Inj. Meloxicam @ 0.2 mg/kg body weight in dogs, goats and cat and 0.5 mg/kg body weight in buffalo, intravenously, for three days. The cases presented with maggot wounds were treated initially by removing maggots manually, topical antiseptic dressing along with Inj. Ivermectin subcutaneously @ 200 µg/kg body weight in dogs and goats. All the wounds were also treated with topical applications of silver nano particles (AgNPs 100 ppm available as a topical spray) twice a day for the wound healing enhancement. The patients were kept under observations till complete healing of wounds and the duration for granulation, wound contraction and complete healing was recorded. 

Total twenty seven clinical cases of various species, viz., dogs (n=20), goats (n=6), cat (n=1) and buffalo (n=1) age ranging from two months to eleven years were presented with different types of chronic complicated wounds on different body parts. The details of 20 canine wound cases before therapy and the response of silver nano-particles therapy are presented in Table 1. In most of the canine cases, granulation of tissues at the site of wound was noted within 5-10 days with wound contraction in around next 3-5 days and complete healing of wound with or without scar formation was observed in 15-32 days depending upon the site, type, duration and depth of wound.
       
Amongst the six female goat patients, complete wound healing was observed on day 16 to day 19 according to site and depth of wounds. In cat and buffalo patients the granulation was observed on day 12 and 16 and complete wound healing observed on day 28 and 30, respectively. In cat, the granulation formation was slower as compared to other species.
       
In the wounds located on head, peri-vulvar, perineal, abdominal regions showed the marked granulation from day 3 to day 5 along with remarkable wound contraction. The wounds presented on limbs exhibited less granulation compared to wounds presented on other parts. This might be due to constant movement of animals for the locomotion, which interferes in healing process. The granulation was observed from day 5^th on limb region. In all the cases healing period was found variable from day 10 to day 32. This variation might be due to depth of damage, chronicity and location of the wounds on the body of animals. The advantage of topical application of silver nano particles was that it enhanced the healing process compared to duration and chronicity of wounds before treatment and also helped in formation of granulation pad, which is necessary for the wound healing. 
       
Wound healing is a well-orchestrated and complex series of events involving cell-cell and cell-matrix interactions. Various intrinsic and extrinsic factors like diabetes, environmental contamination, animal behaviour are intricate, which affects the wound healing and lead to delayed healing or non-healing. Sometime expansion of the wounds leads to exposure of deeper tissues and bones. The conventional treatment for the wound management like debridement, lavage and antiseptic dressing does not always act effectively. Such cases need advanced therapeutic to regenerate new tissue for enhance healing and to save the affected body parts (Parmar et al., 2022). The healing may be delayed due to various factors, which play a role to make wound more complicated and responsible for suffering of patients and frustration of owner. Thus, sometime the wound management may become a challenge for the veterinarian. 
       
Silver was used as a antimicrobial over a century. In the 17^th and 18^th centuries, silver nitrate was already in use for ulcer treatment and in 1960 it was introduced for the management of burns. After a decrease in the use of silver salts consequent to the introduction of antibiotics in 1940, in more recent years, there has been a renewed interest in silver, due to increased resistance of bacteria to antibiotics and improvements in polymer technology. Silver is applied to burns, either in the form of impregnated bandages or as a cream containing silver sulfadiazine as the active agent, a product that was still considered the benchmark silver product (Hussain and Ferguson, 2006). Silver nitrate used to treat chronic wounds in human causes staining and irritation to contact surface. Silver sulfadiazine was introduced in the 1960s to overcome some of the shortcomings of silver nitrate, but both were limited in the clinics due to the need for a high frequency of application, inactivation of much of the silver by wound fluid and the formation of a pseudo-eschar (Mishra et al., 2008).
       
Nanoparticles (NPs) are defined as particles having one or more dimensions in the order of 100 nm or less. Silver NPs (Ag NPs) had been shown to possess unusual physical, chemical and biological properties (Nair and Laurencin, 2007). Indeed, an active role in wound healing was attributed to silver and, along with its distinctive role in preventing infection, silver nanoparticles can also drive the differentiation of fibroblasts into myofibroblasts, which in turn promotes the wound contraction, quickens the healing rate and stimulates the proliferation and relocation of keratinocytes (Vijayakumar et al., 2019). An ideal Ag + dressing material promotes healing; causes minimal pain to the patient, prevents infection, results in minimal scarring and is inexpensive and easy to use. A dressing which possessed all of these qualities has yet to be developed, but currently many dressing materials met some of these criteria to varying degrees of effectiveness (Rakel et al., 1998). Nanotechnology has provided a way of producing pure silver nanoparticles. This system also markedly increases the rate of silver ion release. In the present study the silver nitrate nano particles in 100 nm was used as a topical dressing material. The bio-availability of silver ion is more and rapid as compared to other silver preparations. In the present study the granulation formation and wound contraction was clearly observed at day 10 in all cases, which might be initiated before day 10.
       
Liu et al., (2010) observed that AgNPs improve the proliferation and migration of keratinocytes from the edge to the centre of the wound and trigger the differentiation and maturation of keratinocytes, thereby promoting wound contraction in rodents. In our study recorded that hair growth was seen in two years old Labrador male dog with injury by hot water and sloughing of skin at head region on day 10. Almost similar healing period was reported by Tian et al., (2007) in thermal wounds of mice treated with silver nanoparticles. The grossly healed wound resembled to normal skin, with less hypertrophic scarring and nearly normal hair growth on the wound surface. These observations indicate that wound healing is accelerated by silver nanoparticles. AgNPs release small silver ions, which carries positive charges, are easily attracted to negatively charged cell membrane of bacteria. It entrapped and penetrated the bacteria, disrupted respiratory processes and caused bacterial death (Jung et al., 2008). Therefore, AgNPs possessed antibacterial property against a wide range of pathogens (Lara et al., 2011). In the present study, all the cases were given antibiotics for three days to encounter the existing infection. Afterwards no antibiotics were given to any patients. The published literature of effects of silver nanoparticles on wound healing are sparse and the mechanism of action remains unknown. This article presents the effects of silver nano particles on chronic complicated wounds in different animals.

In the present study, the topical application of silver nano-particles (AgNPs 100 ppm) in spray form found to be useful to enhance the healing of different chronic complicated wounds in animals as it possessed the antibacterial property and promoted wound healing. The spray form was easy to apply over the site of affections in animals. Topical treatment of chronic complicated wounds with silver nano-particles in spray form was a safe adjunct therapy for skin wound healing in animals.

The authors are grateful to the Dean of the College of Veterinary Science and Animal Husbandry, Kamdhenu University, Anand, Gujarat, India for the facilities provided for this work. The authors are also grateful to Bills Biotech Pvt. Ltd., Vadodara, Gujarat, India for providing silver nano-particles in spray form.

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