Enhanced wound-healing performance of a phyto-polysaccharide-enriched dressing - a preclinical small and large animal study

Alginate is a natural rich anionic polysaccharide (APS), commonly available as calcium alginate (CAPS). It can maintain a physiologically moist microenvironment, which minimises bacterial infection and facilitates wound healing at a wound site. Patients with burn injuries suffer from pain and an inflammatory response. In this study, we evaluated the CAPS dressing and traditional dressing containing carboxymethyl cellulose (CMC) for wound healing and scar tissue formation in a burn model of rat and swine. In our pilot study of a burn rat model to evaluate inflammatory response and wound healing, we found that the monocyte chemoattractant protein (MCP)-1 and transforming growth factor (TGF)-β were up-regulated in the CAPS treatment group. Next, the burn swine models tested positive for MCP-1 in a Gram-positive bacterial infection, and there was overproduction of TGF-β during the burn wound healing process. Rats were monitored daily for 1 week for cytokine assay and sacrificed on day 28 post-burn injury. The swine were monitored over 6 weeks. We further examined the pain and related factors and inflammatory cytokine expression in a rodent burns model monitored everyday for 7 days post-burn. Our results revealed that the efficacy of the dressing containing CAPS for wound repair post-burn was better than the CMC dressing with respect to natural wound healing and scar formation. The polysaccharide-enriched dressing exerted an antimicrobial effect on burn wounds, regulated the inflammatory response and stimulated anti-inflammatory cytokine release. However, one pain assessment method showed no significant difference in the reduction in levels of adenosine triphosphate in serum of rats after wound dressing in either the CAPS or CMC group. In conclusion, a polysaccharide-enriched dressing outperformed a traditional dressing in reducing wound size, minimising hypertrophic scar formation, regulating cytokines and maximising antimicrobial effects.

In vivo stability and biocompatibility of implanted calcium alginate disks

Alginate is a commonly used biomedical hydrogel whose in vivo degradation behavior is only beginning to be understood. The use of alginate in the central nervous system is gaining popularity as an electrode coating, cell encapsulation matrix, and for duraplasty. However, it is necessary to understand how the hydrogel will behave in vivo to aid in the development of alginate for use as a neural interface material. The goal of the current study was to compare the rheological behavior of explanted alginate disks and the inflammatory response to subcutaneously implanted alginate hydrogels over a 3-month period. Specifically, the effects due to (1) in situ gelling, (2) diffusion gelling, and (3) use of a poly-l-lysine (PLL) coating were investigated. While all samples' complex moduli decreased 80% in the first day, in situ gelled alginate was more stable for the first week of implantation. The PLL coating offered some stability increases for diffusion gelled alginate, but the stability in both conditions remained significantly lower than that in in situ gelled alginate. There were no differences in biocompatibility that clearly suggested one gelation method over another. These results indicate that in situ gelation is the preferred method in neural interface applications where stability is the primary concern.

Biomaterials Used in Injectable Implants (Liquid Embolics) for Percutaneous Filling of Vascular Spaces

The biomaterials currently used in injectable implants (liquid embolics) for minimally invasive image-guided treatment of vascular lesions undergo, once injected in situ, a phase transition based on a variety of physicochemical principles. The mechanisms leading to the formation of a solid implant include polymerization, precipitation and cross-linking through ionic or thermal process. The biomaterial characteristics have to meet the requirements of a variety of treatment conditions. The viscosity of the liquid is adapted to the access instrument, which can range from 0.2 mm to 3 mm in diameter and from a few centimeters up to 200 cm in length. Once such liquid embolics reach the vascular space, they are designed to become occlusive by inducing thrombosis or directly blocking the lesion when hardening of the embolics occurs. The safe delivery of such implants critically depends on their visibility and their hardening mechanism. Once delivered, the safety and effectiveness issues are related to implant functions such as biocompatibility, biodegradability or biomechanical properties. We review here the available and the experimental products with respect to the nature of the polymer, the mechanism of gel cast formation and the key characteristics that govern the choice of effective injectable implants.

Calcium Alginate Provides a High Degree of Embolization in Aneurysm Models: A Specific Comparison to Coil Packing

OBJECTIVE

Although flexible, current coils do not fill intracranial aneurysms to a high degree, and questions remain regarding their thrombogenic capacity. We evaluated the usefulness of calcium alginate as an embolic material for endovascular embolization in aneurysm models.

METHODS

We assessed three endovascular methods of instilling calcium alginate into 10-mm sidewall and 7-mm bifurcation glass aneurysm models using a balloon catheter to seal the aneurysm orifice: 1) instillation of alginate and subsequent instillation of the reactive component calcium chloride (CaCl(2)) via a single-lumen catheter, 2) simultaneous instillation of alginate and CaCl(2) via a side-by-side double-lumen catheter, and 3) instillation of alginate mixed with CaCl(2) delivered from a concentric-tube microcatheter. A 13-mm sidewall silicon aneurysm model was used to measure and compare the volume of calcium alginate occupying the aneurysm models.

RESULTS

Instillation Method 1 did not achieve optimal filling of the aneurysm with calcium alginate. The percentage volumes of calcium alginate occupying the aneurysm were 69.2 +/- 7.7% and 84.6 +/- 5.4% for instillation Methods 2 and 3, respectively. In Method 3, calcium alginate began gelation upon leaving the catheter, entered the aneurysms in a strand form, and gelled to a mass that filled the aneurysm while conforming to its inner contour.

CONCLUSION

Calcium alginate fills aneurysm models to a significantly higher degree than published results of the space filled by coils. Instillation of calcium alginate, especially in strand form, may produce an embolization that better fills and conforms to the contour of aneurysms compared with coils.