This week in lecture we discussed the benefits of using decellularization as a technique for making biomaterials. Decellularization is the process by which cells are removed so that only the extracellular matrix is left. This technique is beneficial because it means that there is a pre-made skeleton that is known to house cells that can be used. Therefore, when using decellularized tissue, you can add in new cells to fill in the pre-made network. This can be beneficial as it allows for the use of cells that will make the implantation of the material more successful.

In the experiment done in the paper, the researchers created a material to aid in wound healing. The material was composed of decellularized human skin tissue and human umbilical cord perivascular cells (HUCPVC). This specific cell type was chosen because it is a stem cell that is known to help in wound healing, specifically within the skin. The way these cells specifically are able to promote wound healing within the skin is because they promote the creation of neovascularization that will allow blood to reach the area of injury. Additionally, these cells do not cause a strong inflammatory response, which indicates that they can be used even when not taken directly from the patient. The paper conducted studies to identify if the scaffold created would be beneficial to use in order to deliver the HUCPVCs to the wound site.

For the experiments run, the researchers first had to be sure that all the native cells on the scaffold were fully removed. This is an important step because it could cause a negative inflammatory effect when inserted in the body if the original cells still remain. Additionally, it is important that the only cells that are focused on are the HUCPVSs rather than another cell present in the scaffold. The next step was to ensure that the HUCPVS cells were able to attach to the scaffold and remain alive, and this proved to be successful. The biomechanical properties of the material with and without the cells were also tested. This test indicated that the present cells did not affect the biomechanical properties. Once, these tests were conducted, it was then safe to move on the in vivo experiments.

For the in vivo experiments, a diabetic rat model was used because it best exemplifies chronic wounds. A control for the experiment included the same wound, but using no material for the healing process. The researchers also tested the scaffold without the cells added, and then another model used the combination of the scaffold with the HUCPVC cells added to it. A figure of the results after 0, 7, 14, and 21 days is shown below.

What the researchers found was the wound that was treated with the combination of the decellularized skin scaffold and the HUCPVS cells had the most promising results because a higher percentage of the wound closed.  More in depth analysis showed that there was more collagen deposited at the area of the wound with the model that had the scaffold and cells. This indicates more matrix production that would aid in the wound healing process. Overall, this new biomaterial was shown to be very effective, and makes practical use of the decellularization process.

Milan, P. B., Lotfibakhshaiesh, N., Joghataie, M. T., Ai, J., Pazouki, A., Kaplan, D. L., … & Samadikuchaksaraei, A. (2016). Accelerated wound healing in a diabetic rat model using decellularized dermal matrix and human umbilical cord perivascular cells. Acta biomaterialia, 45, 234-246.

Now that we have finished covering polymers, ceramics, and metals, we have started to focus on composites. Composites are made up of multiple of materials. In the case of the device I am reviewing, the material is a hydrogel that is composed of both bioglass and agarose-alginate(AA).

The material in the article is a hydrogel and is used as an innovative dressing for wounds. As I’ve discussed in previous blog posts, chronic wounds are a major rising issue especially with the influx of people with diabetes. The body’s inability to repair itself leads to chronic wounds, therefore new materials try to aid the wound healing process This particular material attempts to do this by addressing the humidity at the wound site and also by increasing the ability of angiogenesis.

The material makes use of bioglass’ ability to aid wound healing by promoting angiogenesis, and AA’s ability to create a humid environment. As we learned in lecture, composite materials will not merge together, but instead the composite will have a mixture of properties of the used materials, which in this case would be ceramics and polymers. For this reason, bioglass and AA should both have the same effect that they normally have within the body. However, these materials will work together because the moist environment created by AA allows for the bioglass to release bioactive molecules that will improve the process of creating new blood vessels. If blood is able to effectively flow to the wound site, then there is a higher probability of the wound healing.

The in vivo experiment tested the material at different ratios of agarose and alginate on a rabbit ear’s wound, and it was seen that the models with bioglass and AA performed better (figure shown below). The conclusion was that since more endothelial cells and fibroblasts migrated to the area and due to the increased humidity, then the body was able to heal at a more rapid pace.

When deciding what materials to use, the researches mentioned that although bioglass has useful properties, it is normally used in a powder form which can be difficult to use for a wound site. They were able to fix this issue by combining it with AA, which can make the material temperature dependent for gelation, and thus a material that is both injectable and can solidify at a wound site as need was created.  Ultimately, different materials have their own individual advantages and disadvantages; however, composite materials are able to combine the best aspects of multiple materials to create new biomaterials with the most ideal characteristics.

Zeng, Q., Han, Y., Li, H., & Chang, J. (2015). Design of a thermosensitive bioglass/agarose–alginate composite hydrogel for chronic wound healing. Journal of Materials Chemistry B, 3(45), 8856-8864.

In lecture we learned that bulk metallic glasses are amorphous metallic alloys and they have properties that are similar to both glass and metals. They have high strength, are very conductive, have high flexibility at high temperature, and can be processed using blow molding in order to create a surface texture. We also learned that some bulk metallic glasses saw a less severe foreign body response as there were less giant body cell formation. Due to its unique properties, bulk metallic glass could be a new leading biomaterial for biomedical applications.

Osteosynthesis is the process of attaching a bone fracture with devices, typically made of metal, in order to immobilize it. This is done so that the bone can heal properly. Lots of studies have been done in order to determine which material would be best to use for these devices as the material has to not fuse with the bone, not elicit an immune response, but still remain strong. Additionally, the material must be able to be removed from the body once the fusing is complete. The figure below shows what a bulk metallic metal used for osteosynthesis looks like once it is implanted. 

In the paper published by Imai and Hiromoto, three different metals were tested for this function: Titanium, stainless steel, and bulk metallic glasses. Since osteosynthesis requires a material that has a high load-bearing potential, titanium and stainless steel are the materials that are most commonly used. However, research into a new material such as bulk metallic glasses could be beneficial as it still has the needed strength and elastic modulus, however it also has a more beneficial impact within the body.

In the experiment conducted, rats were implanted with the three different materials for 12 weeks before the implant was removed. The results showed that bulk metallic glass did not elicit a biological response from the body as there was no infiltration of inflammatory cells or bone resorption. Additionally, the bone healing with bulk metallic glasses was shown to be closer to completion than with titanium or stainless steel. Ultimately, bulk metallic glass seems to be a promising material to be used for osteosynthesis, however my focus is on wound healing.

Based off of lectures and the article studying bulk metallic glass’ performance for osteosynthesis, it seems that BMGs are compatible within the body, due to the lowered inflammatory response. However, for wound healing it is necessary for the material to aid in the inflammatory response. Additionally, it is not as necessary for the material to have a high strength or elastic modulus. Thus, this material may not be as useful for wound healing purposes.

Imai, K., & Hiromoto, S. (2016). In Vivo Evaluation of Bulk Metallic Glasses for Osteosynthesis Devices. Materials, 9(8), 676.

In lecture we briefly discussed bioactive glass as a material. It is a silica-based material that has the capability to bond with bone, and it contains calcium and phosphate. This material is commonly used for bone grafts, as some research suggests that it is osteoconductive properties. However there has been recent research on using this material for wound healing.

In the paper, copper-doped borate bioactive glass microfibers are used as wound dressings to assist in wound healing. Since bioactive glass is known to promote vascularization, then it is a material that can also be helpful during wound healing when the wound site requires vessels to form in order to bring oxygen to the wound site. Furthermore, the incorporation of metallic ions such as copper would further improve angiogenesis which would be more cost effective and safer than using growth factors.

Before this material was tested in vivo, it was first tested in vitro with different concentration of copper incorporated. When comparing the copper-doped bioactive glass microfibers to regular bioactive glass microfibers they found that with copper there was an increase in cell proliferation and an increase in cell migration. Additionally, from the images shown below they claimed that the copper-doped microfibers also promotes angiogenesis as there was a formation of “tube-like structures” by human umbilical vein endothelial cells (HUVECs) and a higher gene expression of growth factors that was not seen with the undoped microfibers. From the in vitro studies they determined that the 3Cu-BG material would be the most optimal to test in vivo as it had the most cell proliferation and migration.

In vivo they created a full-thickness skin wound in a rodent and used regular bioactive glass microfibers and 3CU-bioactive glass microfibers as wound dressing. A wound with no wound dressing served as the control. The image of this experiment is shown below. They found that there was a significant difference in the wound healing with the use of bioactive glass in comparison to no wound dressing. However, although there seemed to be a significant difference between the copper-doped bioactive glass and regular bioactive glass at day 10, by day 14 there seems to be no significant difference.

Although, the use of bioactive glass as a material used for wound healing purposes does appear to have potential, I do not agree with the study’s conclusion that copper-doped bioactive glass is a better material. Although there was an increase in cell proliferation and cell migration, the overall wound closure percentage is very similar regardless of the presence of copper. However, a future step that would give more information about the performance of this biomaterial would be in vivo studies using diabetic rodents. This study will be able to show how the material is able to aid the wound healing process when this process is compromised. In a system were the body cannot properly heal on its own, it is possible that the promotion of angiogenesis that is provide by the presence of copper will prove to be more valuable.

References:

Zhao, Shichang & Li, Le & Wang, Hui & Yadong, Zhang & Cheng, Xiangguo & Zhou, Nai & N. Rahaman, Mohamed & Liu, Zhongtang & Huang, Wenhai & Zhang, Changqing. (2015). Wound dressings composed of copper-doped borate bioactive glass microfibers stimulate angiogenesis and heal full-thickness skin defects in a rodent model. Biomaterials. 53. 10.1016/j.biomaterials.2015.02.112.

In lecture this week we covered how the interaction between cells and a particle must be modulated in order to regulate the intake of a drug. One example of a biomaterial that uses this technique are silver nanoparticles. Silver nanoparticles have an antibacterial effect due to the specific properties of silver ions. Due to these properties, the nanoparticles are able to be used for wound healing where there is a desire to limit the inflammatory response that the body may have to the foreign body introduced to the wound.

In the article, the silver nanoparticles were used to treat a wound and the healing process was compared to being treated with silver sulfadiazine and with no treatment. It was found that the use of nanoparticles caused the wound to heal the fastest and also with the best cosmetic outcome, meaning that the wounded area resembled pre-injury the most. The image below depicts the progression of the healing process over 25 days with treatment with silver nanoparticles and treatment with silver sulfadiazine.

Although silver sulfadiazine has been known to be the best treatment for burns, silver nanoparticles performed better for this wound healing experiment.

Overall, it was determined that the silver nanoparticles had the best results due to its antibacterial properties, as well as the ability to modulate cytokines expression. This is exactly what we learned in lecture. By modulating the cell-particle interaction, the nanoparticles are able to have lower levels of IL-6 mRNA, which contributes to inflammation.  Thus, the material is able to have a more beneficiary effect to the healing process.

Although the results of using nanoparticles seem favorable, it is still important to note that the experiments were done only in animals, specifically mice. In order to further understand the true success of this biomaterial, it would be necessary to conduct experiments using a wound healing model that more closely resembles that of a human.

References: Tian, J. , Wong, K. , Ho, C. , Lok, C. , Yu, W. , Che, C. , Chiu, J. and Tam, P. (2007), Topical Delivery of Silver Nanoparticles Promotes Wound Healing. ChemMedChem, 2: 129-136. doi:10.1002/cmdc.200600171

Biomaterials can be used in order to aid skin during wound healing. One such example, is using porous membranes with polymer nanoparticles.  The scaffold itself is made porous in order for it to resemble the extracellular matrix (ECM) of the body. It is made of polylactic acid (PLA) which is biodegradable, and it is made porous through a thermally induced phase separation technique (TIPS). The scaffold is then functionalized with type I collagen in order to create a more biomimetic environment for cells. The image below shows both a control membrane (A) and a porous membrane (B) (scale bar=100mM).

The nanoparticles were made with polycaprolactone (PCL) which a biodegradable polyester and loaded with indomethacin (IND), an anti-inflammatory drug. The nanoparticles were dispersed into the biomaterial and due to their opposite charges, the nanoparticles remained embedded within the material. The image below shows the nanoparticles within the biomaterial.

In lecture we learned about the biodegradability of materials, as well as the use of nanoparticles for drug delivery.  Biodegradability describes the ability of a material to degrade within a living organism. A material can be biodegradable if it is able to be degraded, bioeliminable if it is water soluble and excretable but not degradable, and permanent if it is neither degradable or excretable. Understanding the intended use of a biomaterial is necessary in order to evaluate the biodegradability that is needed. For example, if a material needs to remain in the body for 10 years then it may be necessary to make it permanent whereas a drug delivery material that only needs to remain in the body for a couple of months may need to biodegradable in order to avoid excess surgery to remove it from the body. Nanoparticles tend to be used as vehicles for targeted drug delivery. By using nanoparticles in order to deliver drugs, the release of the drug is able to be controlled and there is also a minimalization to the drug that is lost in circulation.

The biomaterial described in the paper is made of a biodegradable material, PLA. This decision was made because the material is meant to be used for wound healing, which indicates that it should not remain in the body for a long time. Additionally, the material is likely to cause a foreign-body reaction which will lead to inflammation at the site of implantation. In order to combat this issue, the material also contained pores so that it resembles ECM and used nanoparticles to deliver anti-inflammatory drugs. In this material, nanoparticles were used as a drug delivery vehicle because they are able to remain within the material and release the drug over time to the targeted site. Since the current “clinical gold-standard” for skin wounds is transplanting autologous tissue, this biomaterial seems to be a step in the right direction as it is design to mimic human tissue and contains drugs to prevent inflammation. However, the paper focused more on the mechanical characteristics of the material than on the actual biological aspects. Therefore, I believe that the material may be improved if more research is done on the drugs that the nanoparticles are loaded with, as well as testing to see if the changing the rate of drug release can improve the success of wound healing at the site.

When inflicted with a wound, the body automatically works to repair itself. However, there are instances when the body is incapable of healing itself, and biomaterials can be used to aid the process. With the rise of diabetes in the United States, more and more people are dealing with chronic wounds which can lead to amputations. Thus, there has been a push to find better methods to help with chronic wounds. Biomaterials can be used for this purpose, but it still important to understand the pros and cons of the materials currently used, and where there is room for improvement.