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Allograft (Human) Acellular Dermal Matrix represents a viable option in both tissue replacement and reconstruction. The following article looks at two publications from the AlloSource Basic Science series.

Acellular dermal matrices can be used to successfully replace or repair integumental soft tissues compromised by disease, injury or surgical procedures. A number of considerations need to be made when utilizing this biomaterial in vivo, including:

  1. Whether it retains native proteins and growth factors after the decellularization process, which aid in structuring and signalling cellular activity and are critical in a variety of applications.
  2. Its biocompatibility and immunogenicity, both of which influence its incorporation into the surrounding tissue.

AlloSource offer a range of Acellular Allografts: AlloSkin AC and AlloMend.

THE BIOLOGICAL PROPERTIES OF ALLOMEND® ACELLULAR DERMAL MATRIX: GROWTH FACTOR STUDY

The presence of growth factors in an implanted ADM can stimulate healing and revascularization, as well as inhibit scarring1,2 in a variety of procedures, including tendon-to-bone repair and soft tissue repair.

In this study, AlloSource researchers tested for the presence of four specific growth factors widely known to contribute to a healing response following tissue injury:

 

Fibroblast Growth Factor (bFGF). bFGF is essential for coordinated cell activity. It acts as a chemotactic and proliferative marker for fibroblasts and endothelial cells, and a guide for the process of angiogenesis and the development of new membrane layers.1 Applying bFGF to a full-thickness skin graft is reported to improve clinical outcomes by decreasing the incidence of tissue necrosis.3 The application of bFGF has also been shown to be effective in mediating scar-free healing4 and spurring new vessel growth in the healing of surgical wounds,4,5 both of which are essential for soft tissue repair. In tendon repair surgeries, bFGF augmentation has been found to lead to better tendon-to-bone incorporation and strength.6,7 This is especially apparent when acellular dermal matrices are used for the repair.8

Platelet Derived Growth Factor (PDGFbb). PDGFbb helps coordinate a number of steps in the healing process that are especially important for soft tissue repair. It attracts cells to the area of the injury, guides the production of collagen and elastin, and induces cell differentiation. It also directs the signaling cascade to begin the process of reverse remodeling, coordinating the reduction in scarring.9 PDGFbb was the first growth factor to be approved by the FDA for direct application and has proved to be effective in wound healing.10,11 In tendon-to-bone procedures, PDGFbb improves the mechanical strength12 and the histologically-evident healing of the repair.13

Transforming Growth Factor (TGFb). TGFb is an important signaling factor in all stages of the healing process, guiding the proliferation and extracellular protein production of fibroblasts. It also helps prevent over-proliferation and limits the inflammatory response of keratinocytes.14,15 Through the control of the responses of these cells, TGFb mediates scar-free wound healing.16 Conversely, TGFb-deficient mice have been shown to have impaired healing processes.17 TGFb works with other growth factors to coordinate tendon-to-bone incorporation and its presence can reduce the incidence of failure in these procedures.18,19 Studies have also shown that TGFb acts as an important guide for the long term acceptance of allografts.20

Bone Morphogenic Protein 2 (BMP2). BMP2 is a potent osteogenic protein that directs the development and healing of bone and has been proven to affect tendon-type cells, directing differentiation and matrix production.21 This signaling enhances tendon-to-bone healing22 by inducing the production of new cartilage at the insertion site.23 BMP2 is also a potent chemotactic factor for stem cells and serves to drive adipogenesis of such cells.24 This would prove useful for an allograft used in soft tissue reconstructive work such as breast reconstruction

Testing revealed the presence of BMP2, PDGFbb and bFGF in all four of the grafts. TGFb was found in three of the four grafts.

The role each of these proteins plays in a range of procedures is summarised in this table below:

Growth factors in Acellular Dermal Scaffold

The presence of the tested growth factors in AlloMend/AlloSkin AC ADM makes this an ideal acellular graft tissue for numerous types of reconstructive surgeries, including soft tissue repair (e.g., breast reconstruction procedures) sports medicine (e.g., rotator cuff repairs or other tendon-to-bone attachments) and as a tissue replacement in Plastics and Woundcare. Collectively, these growth factors coordinate cellular incorporation, proper bone attachment and proper differentiation of cells. At the same time, they prevent untoward inflammation and necrosis at the implantation site.

Full Paper can be found here: THE BIOLOGICAL PROPERTIES OF ALLOMEND® ACELLULAR DERMAL MATRIX: GROWTH FACTOR STUDY

THE BIOLOGICAL PROPERTIES OF ALLOMEND® ACELLULAR DERMAL MATRIX: GROWTH FACTOR STUDY

The AlloSource proprietary process results in a three dimensional, collagen rich, biocompatible, non-cytotoxic matrix that retains it biomechanics properties. This process and resulting properties help ensure it will be readily accepted by the recipient through subsequent revascularisation and cell repopulation.

The purpose of this study was to evaluate the biocompatibility of the AlloSource ADM through an animal model

 

 

Two days after implantation procedures, visible swelling and erythema were resolved normally, an initial indication of graft incorporation.

Allomend Non Meshed, at two days, two weeks and twelve weeks showed vascularization and graft incorporation. At six weeks the presence of Von Willebrand factor was recorded indicating blood vessels.

  • Animals were deemed healthy by the veterinarian, suggesting there was no significant immunogenic response to the graft.
  • No untoward tissue rejection was apparent at any period.
  • No significant levels of graft encapsulation were observed, indicating the absence of tissue rejection.
  • Histological examination of the explanted tissue indicated cell and vessel infiltration for all three time periods.

*Histological examination of the explanted tissue indicated cell and vessel infiltration for all three of the time periods (figures 4 and 5 below). No significant levels of encapsulation were observed, indicating absence of inflammatory response tissue rejection. Infiltration of blood vessels into the grafts was apparent.

Biocompatibility in AlloSource’s ADM

The lack of untoward biocompatibility response to the implanted AlloMend ADM stands in contrast to the histological record of implanted synthetic mesh materials, which due to their synthetic nature would remain a foreign body and never be fully incorporated. In fact the use of synthetic mesh has led to relatively high incidences of infection¹ even years after implantation.²

This study demonstrated the biocompatibility of AlloSource ADM’s with no untoward tissue reaction or encapsulation. There is strong evidence of tissue incorporation and blood vessel infiltration. No infections notes nor was there discernible impact on metabolism.

Full paper can be found here: THE BIOMECHANICS OF ALLOMEND ACELLULAR DERMAL MATRIX: BIOCOMPATIBILITY STUDY.

¹² – See full paper for references.