Mesenchymal stem cells (MSCs) are multipotent in that they naturally replenish the cell types that build our bone, cartilage and adipose tissues. However, their much broader regenerative potential, based on their capacity to migrate and engraft in injured tissues and secrete factors that enhance the formation of new blood vessels, suppress inflammation and cell death, and promote healing, makes them exquisite candidates for cell-based therapies for diseases as varied as cardiovascular, liver, bone and cartilage diseases, lung and spinal cord injuries, autoimmune diseases and even cancer and skin lesions.
Now, a new study reported in Advanced Functional Materials by a team at the Terasaki Institute for Biomedical Innovation in Los Angeles and the University of California, Los Angeles (UCLA) has developed a minimally invasive approach, which deploys "microneedles" that provide a bioactive depot of MSCs.
Microneedles, made of a biomaterial mixed with therapeutic agents, are attached to a strip of tape, needles facing down. The strip is applied to the wound area of the skin and the tape removed. The needles are embedded into the skin and degrade, delivering the therapeutic agent under the skin.
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By embedding comparatively low numbers of MSCs in a gel-like material that prolongs their viability and functionality, and targeting damaged tissues with high spatial precision, the researchers showed their approach to accelerate wound healing in a mouse model with excised skin segments.
"Microneedles have been successfully used in the past to painlessly deliver drugs to target tissues such as skin, blood vessels and eyes. We demonstrate here with 'Detachable Microneedle Depots' that an analogous approach can deploy therapeutic cells at target sites," said co-corresponding author Ali Khademhosseini, the Director and CEO of the Terasaki Institute who was previously Director of the UCLA Center for Minimally Invasive Therapeutics. "To achieve this, we developed an entirely new microneedle patch that supports stem cells' viability, responsiveness to wound stimuli, and ability to accelerate wound healing."
The researchers started by engineering a matrix of gelatin fibers that are cross-linked to each other into a network that could accommodate MSCs. The biomaterial mimicked the normal extracellular environment of tissues that MSCs normally reside in, and it helped to remodel the specific matrix environment in a way that allowed MSCs to take up nutrients and communicate with damaged tissue via soluble factors that they normally receive and dispatch.
The other part of the challenge was to introduce the literal "needle" quality into the cell-delivering device that would enable it to gently penetrate tissues in order to reach their target sites. To this aim, the researcher encased the softer MSC-containing gelatin matrix with a second, much harder biomaterial known as poly(lactic-co-glycolic)acid, in short PLGA. Once the needles were brought into place in a wound bed, the "PLGA shell", which also is biocompatible and biodegradable, slowly degraded, but during the process kept the MSC-containing gelatin matrix in place, allowing MSCs to release their therapeutic factors through emerging gaps in the shell into the damaged tissue.
Finally, the team set out to investigate their microneedle concept in a mouse skin wound model in which a defined excision is made in the epidermal tissue layers. To be able to strategically place individual microneedles within the wound bed, a simple and effective deployment mechanism was devised by attaching an array of microneedles on a small strip of scotch tape with their pointy ends facing away from the tape. Precisely positioning the tape with its patterned microneedle surface on the wound, allowed the individual microneedles to penetrate into the wound bed. Then, the tape was peeled off, causing the microneedles to detach and remain embedded in the wound tissue. Khademhosseini and his co-workers summarized the device's salient features by naming it: "Detachable Hybrid Microneedle Depot" (d-HMND).
MEDICA-tradefair.com; Source: Terasaki Institute for Biomedical Innovation