278
12 Collagen
left behind is a cellular architecture which has the right cellular architecture in terms
of pore size and shape to allow for effective cell growth.
12.7.5 Microneedles
Microneedles are transdermal patches which comprise of tiny projections with
micrometer dimensions. They are designed to pierce through the upper layer of the
skin without reaching the dermis where the pain receptors exist and in so doing open
up the skin in a painless manner and creating microconduits through which therapeutics can be delivered. The lower layer of the skin (dermis) is easy reach to the blood
vessels from which the drugs can be absorbed into the bloodstream and to target
cells. These microneedles can be designed for delivery via different modes. One way
is to either pierce the skin, after which it is removed and replaced by a drug loaded
patch which then enters into the lower layer of the skin through the holes created by
the microneedles. These types are referred to as solid microneedles which could be
microfabricated using biocompatible materials such as metals such as stainless steel
or polymers such as silicone and polycarbonate. These solid microneedles could also
be coated with the drugs in the form of a dry coating which will then dissolve into
the skin when inserted and comes in contact with the skin fluid. Microneedles can
also be designed to dissolve into the skin upon piercing and release the drugs loaded
within into the lower layers of the skin from where it can be absorbed. These types
of microneedles are strong and rigid when in the dry state; however, they are soluble in physiological fluid. Such that when they are inserted into the skin and come
into contact with the moisture in the skin, they dissolve off. The production process
usually involves loading the drug within the polymeric formulation in the wet state
followed by forming into microneedles such that the drug is entrapped within the
microneedle structure. These are referred to as dissolving microneedles and are made
from soluble polymers such as hydrolyzed collagen (Olatunji et al. 2014), polylactic
acid (Adamczak et al. 2011) and polyvinyl alcohol (Sullivan et al. 2010). A third
mode is where the microneedle with the drug loaded is inserted into the skin, the
drug is released from the microneedles after which the microneedle is then removed.
These are referred to as hydrogel microneedles. They are made using cross-linked
polymers with the drug embedded within. Cross-linked polymeric structures have
the ability to absorb water and swell. As the water is absorbed and the cross-link
network expands, the drugs which are trapped within the polymer chains are released
into the skin while the microneedle stays intact and can be removed after the drug
is released. Another type of microneedles exists which are the porous microneedles.
These are designed to inject the drug in liquid form into the skin such that it can be
absorbed from the dermis. However, these have been of much less interest due to
the complexity of their production process and high possibility of blockage of the
micron-sized holes upon insertion.
Recently, microneedles produced using fish scale-derived hydrolyzed collagen
hydrogels have been developed (Olatunji and Denloye 2019). These are a form of
12 Collagen
left behind is a cellular architecture which has the right cellular architecture in terms
of pore size and shape to allow for effective cell growth.
12.7.5 Microneedles
Microneedles are transdermal patches which comprise of tiny projections with
micrometer dimensions. They are designed to pierce through the upper layer of the
skin without reaching the dermis where the pain receptors exist and in so doing open
up the skin in a painless manner and creating microconduits through which therapeutics can be delivered. The lower layer of the skin (dermis) is easy reach to the blood
vessels from which the drugs can be absorbed into the bloodstream and to target
cells. These microneedles can be designed for delivery via different modes. One way
is to either pierce the skin, after which it is removed and replaced by a drug loaded
patch which then enters into the lower layer of the skin through the holes created by
the microneedles. These types are referred to as solid microneedles which could be
microfabricated using biocompatible materials such as metals such as stainless steel
or polymers such as silicone and polycarbonate. These solid microneedles could also
be coated with the drugs in the form of a dry coating which will then dissolve into
the skin when inserted and comes in contact with the skin fluid. Microneedles can
also be designed to dissolve into the skin upon piercing and release the drugs loaded
within into the lower layers of the skin from where it can be absorbed. These types
of microneedles are strong and rigid when in the dry state; however, they are soluble in physiological fluid. Such that when they are inserted into the skin and come
into contact with the moisture in the skin, they dissolve off. The production process
usually involves loading the drug within the polymeric formulation in the wet state
followed by forming into microneedles such that the drug is entrapped within the
microneedle structure. These are referred to as dissolving microneedles and are made
from soluble polymers such as hydrolyzed collagen (Olatunji et al. 2014), polylactic
acid (Adamczak et al. 2011) and polyvinyl alcohol (Sullivan et al. 2010). A third
mode is where the microneedle with the drug loaded is inserted into the skin, the
drug is released from the microneedles after which the microneedle is then removed.
These are referred to as hydrogel microneedles. They are made using cross-linked
polymers with the drug embedded within. Cross-linked polymeric structures have
the ability to absorb water and swell. As the water is absorbed and the cross-link
network expands, the drugs which are trapped within the polymer chains are released
into the skin while the microneedle stays intact and can be removed after the drug
is released. Another type of microneedles exists which are the porous microneedles.
These are designed to inject the drug in liquid form into the skin such that it can be
absorbed from the dermis. However, these have been of much less interest due to
the complexity of their production process and high possibility of blockage of the
micron-sized holes upon insertion.
Recently, microneedles produced using fish scale-derived hydrolyzed collagen
hydrogels have been developed (Olatunji and Denloye 2019). These are a form of