Microneedles: A Potent Modern Tool in
Enhancing Transdermal Drug Delivery
Ogundele MI1* and Okafor HK2
1Department of Biomedical Engineering, Binghamton University, USA
2Department of Biochemistry, College of Medicine, University of Lagos, Nigeria
Submission: September 19, 2017; Published: October 23, 2017
*Corresponding author: Ogundele MI, Department of Biomedical Engineering, Binghamton University, USA, Email: firstname.lastname@example.org
How to cite this article: Ogundele M, Okafor H. Microneedles: A Potent Modern Tool in Enhancing Transdermal Drug Delivery. Curr Trends Biomedical
Eng & Biosci. 2017; 10(1): 555776. DOI: 10.19080/CTBEB.2017.09.555776.
The conventional drug delivery methods commonly used are oral administration and injection. However there a limitation posed against the penetration of these substances in therapeutic amounts via the corneum stratum. There has been an increasing emphasis on Transdermal drug delivery which provides a better prospect than the two conventional methods. Transdermal drug delivery provides quite a number of merits which include sustained release, prevention of gastric irritation, improvement in patience compliance as well as removal of pre-systemic first-pass effect. In recent times, microneedles are being proposed for use in enhancing Transdermal drug delivery as the use of microneedles increases skin permeability. This review is a qualitative attempt as discussing the microneedle as a potent modern tool in enhancing transdermal drug delivery. This starts with the explanation of the skin and microneedles. Then the mechanism of action of microneedles, the advantages and disadvantages of microneedles are also discussed. The review ends with the recent advances in the application of microneedles in transdermal drug delivery.
When oral administration of drugs is not feasible because of poor drug absorption or enzymatic degradation in the gastrointestinal tract or liver, injection using a painful hypodermic needle is the most common alternative. An approach that is more appealing to patients and offers the possibility of controlled release over time is drug delivery across the skin using a patch . However, transdermal delivery is severely limited by the inability of the large majority of drugs to cross skin at therapeutic rates given the great barrier imposed by skin’s outer stratum corneum (SC) layer. Chemical/lipid enhancers , electric fields using iontophoresis and electroporation , and pressure waves generated by ultrasound or photo acoustic effects  are some of different approaches to increase permeability of skin have been studied. Although the mechanisms are all different, these methods share the common goal of disrupting SC structure to create ‘‘holes’’ big enough for molecules to pass through. The size of disruptions generated by each of these methods is believed to be of nanometer dimensions, which are large enough to permit transport of small drugs and, in some cases, macromolecules but probably small enough to prevent damage of clinical significance.
Microneedles are used in clinical practice to deliver medications across the skin into the bloodstream. Injections with hypodermic needles are important from a clinical standpoint, but painful . They may also induce hypersensitivity; bruising,
discomfort and bleeding at the site of administration, and in some cases are associated with risks of contamination . There are other concerns linked to their use including accidental needle stick injury and the necessity to train medical staff regarding the proper use of needles . The difficulty in crossing the skin is caused by its anatomical peculiarities. Microneedle arrays markedly increase the skin permeability by up to 3 orders of magnitude . Teo  reviewed microneedle designs that are currently being used for transdermal drug delivery. Arrays of microscopic needles create larger transport pathways of micron dimensions. These pathways are orders of magnitude larger than molecular dimensions and, therefore, should readily permit transport of macromolecules and possibly supramolecular complexes and micro particles. Despite their very large size relative to drug dimensions, on a clinical scale these pathways are small. Although safety studies need to be performed, it is proposed that micron-scale holes in the skin are likely to be safe, given that they are smaller than holes made by hypodermic needles or minor skin abrasions encountered in daily life .
The skin is the largest organ of the body , which accounts for more than 10% of body mass, and the one that enables the body to inter act more intimately with its environment. The skin consists of 4 layers.
The SC, the outer layer of the skin (non-viable epidermis),
forms the main barrier for diffusion for almost all compounds.
It is composed of dead, flattened, keratin rich cells, the
corneocytes. These dense cells are surrounded by a complex
mixture of intercellular lipids, namely, ceramides, free fattyacids,
cholesterol, and cholesterolsulfate. Their most important
feature is that they are structured as ordered bilayer arrays .
The predominant diffusional path for a molecule crossing the
SC appears to be intercellular . The other layers are there
maining layers of the epidermis (viable epidermis), the dermis,
and the subcutaneous tissues (Figure 1). Associated appendages
include hair follicles, sweat ducts, apocrineglands, and nails.
Inageneralcon text, the skin’s functions may be classified as
protecting, maintaining home ostasis, and sensing . A lot
of agents are being applied to the epidermal layer of the skin
intentionally or accidentally, resulting to either beneficial or
The pertinent focus in dermal absorption assess mentis
A. Passage via the skin to yield asystemic effect (eg:
B. Dermatological local effects (eg:
C. Surface effects (eg: Sunscreens and cosmetics,)
D. Targeting of deeper tissues (eg: Non-steroidalant
iinflammatory agents)[14-18]; and
E. Unwanted absorption (eg: Solvents in the workplace,
Pesticides, Orallergens) [19,20]. Figure 2 depicts the
pathways of percutaneous absorption.
The skin is popular as a potential site for systemic drug
delivery, on the one hand because of the possibility of avoiding the
problems of stomach emptying, pH effects, enzyme deactivation
associated with gastro intestinal passage, and hepatic first-pass
metabolism and, on the other hand ,because it enables input
Since the past 100 years, hypoderm microneedles as well as
syringes have been utilized to deliver drugs to patients. The year
1844 was the first time the hollow needle was invented, and the
first injection was delivered shortly after , revolutionizing
the practice of medicine (Figure 3). The needle’s still exerts a
strong impact today as a drug delivery vehicle. This is partly
because there is a poor absorption of many pharmaceutical
in the intestine while some are very sensitive to enzymatic
degradation and thus cannot be administered orally.
The syringe and hypodermic needle over the year’s have
evolved into a 2-part device which is disposable. In clinical
practice, the syringe is typically made of plastic and the
needle is made of medical-grade stainless steel. The smallest
needles available for injections are used largely for insulin
administration, measuring 30 gauge for conventional syringes
and 31 gauge for pen injectors.
Microneedles defined as micron-scale needles that are
used for transdermal vaccination and drug delivery . The
possibility that very small needles may be sufficient for transport
across the10- to 20μm-thick SC was first proposed in the 1970s
, but progress was delayed largely because of lack often
chniquestofabricate such small structures. The pioneer work on the utilization of microneedles for transdermal drug delivery
was published in the late 1990s .
Established techniques of the micro electronics industry are
now being adapted and expanded for microneedle fabrication.
Earlier designs of micro-needles used silicon as the fabrication
material because of easy adaptability to microelectronic
fabrication processes. Current designs emphasize metal and
polymeric microneedles. Microneedles used in transdermal
delivery can be classified into 2 categories: solid and hollow
micro-needles . Solid microneedles have been successfully
used to deliver proteins, peptides, oligonucleotides, and
nanoparticles in vitro and in vivo . Hollow microneedles have
a hollow bore, which offers the possibility of rapid bolus dose
drug delivery through flow which is pressure-driven.
The mechanism of action depends on the microneedle design
and is represented in Figure 4. All the types of microneedles are
usually fabricated as an array. Thefinalapproachconsistsofusin
The commonest advantage to all physical methods,
microneedles inclusive (excluding methods using particle
carriers), is that the transport mechanism does not depend on
the uptake functions of the cell; therefore, physical methods
can be applied equally well to all cell types and at all stages of
the cell cycle. The process is, by itself, biologically nontoxic and
The other advantages of microneedles include the following:
1. Solid microneedles could eventually be used with drug
patches to increase diffusion rates; methods to increase
permeability include poking holes in skin and rubbing drug
over area, or coating needles with drug .
2. Microneedles have been fabricated with metals, silicon,
silicon dioxide, polymers, glass, and other materials .
They can be mass-produced from a range of materials in a
consistent and cost-effective manner.
3. Microneedles are fabricated on the micro scale
(generally 1μm in diameter, ranging from 1 to 100μm in
4. Absence of pain or bleeding makes microneedles more
clinically appropriate (particularly in pediatric vaccination
and for needle-phobic patients) .
5. The mechanism for delivery is not based on diffusion
as it is in other transdermal drug delivery products .
Placement of the drug or vaccine within the epidermis,
where it can more readily reach its site of action.
6. Using microneedles avoids first-pass effect .
Microneedles allow rapid penetration of drugs into the
7. Microneedles can be fabricated to be long enough to
penetrate the SC but short enough not to puncture nerve
8. Microneedles can provide direct controlled delivery of
small molecules, macromolecules, vaccines, or nucleic acids
into the viable epidermis .
9. Using microneedles reduces the chances of pain,
infection, and injury.
10. Hollow needles could eventually be used with drug
patches and timed pumps to deliver drugs at specific times.
11. Very small microneedles could provide highly targeted
drug administration to individual cells .
12. Administration of drugs via microneedles bypasses the
13. Single-use needles are easily disposable and potentially
14. A relatively large surface area can be treated.
15. Drug can be administered at constant rate for a longer
In as much as there are lots of advantages of the use of
microneedles in transdermal drug delivery however there are
a few inherent demerits in its application. They include the
1. Microneedles can be difficult to apply on the skin; the
clinician must learn proper application technique.
2. Local inflammation may result if the amount of drug
is high under the skin. Skin irritation may result because of
allergy or sensitive skin .
3. The needles are very small and much thinner than the
diameter of hair, so the microneedle tips can be broken off
and left under the skin .
5. Advances in the Applications of Microneedles in
Transdermal Drug Delivery
The unique and promising release of drugs by micro-needles
in a minimally invasive way renders them an attractive candidate
as a physical enhancer to administer drugs throughout the skin
[32,33]. The following summarizes the research on microneedles
used in the transdermal administration of drugs.
Another hydrophilic and skin impermeable drug that has
attracted the attention of researchers is naltrexone (NT), a
potent μ-opioid receptor antagonist used to treat opiate and
alcohol dependence. Wermeling et al.  presented a clinical
study for a transdermal patch in healthy human volunteers with
and without pretreatment of the skin with microneedles (array
of 50 microneedles). Whereas delivery from a standard NT
transdermal patch over a 72-hour period yielded undetectable
drug plasma levels, pre- treatment of skin with microneedles
achieved steady- state plasma concentrations within 2 hours
of patch application that were maintained for at least 48 hours.
Microneedles and NT patch were well tolerated, with mild
systemic and application site side effects. This human proofof-
concept study demonstrates systemic administration of a
hydrophilic medication by microneedle-enhanced transdermal
delivery. These findings set the stage for future human studies
of skin-impermeable medications and biopharmaceuticals for
5-aminolevulinic acid (ALA) is used as a protoporphyrin-
IX precursor for the photo- dynamic therapy of superficial
skin cancer and deep or nodular skin tumors. However, the
permeability of hydrophilic ALA across the skin is very low.
Donnelly et al.  used silicon microneedle arrays (with
6×7 arrays of microneedles 270μm in height, with a diameter of
240μm at the base and an inter-spacing of 750μm) to enhance
skin penetration of ALA in vitro and in vivo across excised porcine
skin. There was a significant increase in transdermal delivery of
ALA released from a bioadhesive patch containing 19mg of ALA/
cm2. This clearly has implications for clinical practice, as shorter
application times would mean improved patient and clinician
convenience and would allow more patients to be treated in the
same session. Because ALA is expensive and degrades rapidly
via a second order reaction, reducing the required dose is also
a notable advantage.
The simplest method for reducing the barrier imposed
by the SC is to remove it. An adhesive tape removes a layer of
corneocytes [35,36]. In vivo, removal of the SC by tape stripping
is performed by the repeated application of adhesive tapes
to the skin’s surface. With this in mind, Sivamani et al. 
83 compared topical application of hexyl nicotinate (HN) via
injection with hollow microneedle arrays at tape-stripped and
unstripped sites in the volar fore- arms of human volunteers.
Microneedle injections decreased the time to reach maximum
cutaneous blood flow by 3-fold, regardless of whether the SC had
been tape-stripped. Hollow microneedle arrays delivered the
agent past the SC and not into the SC. Therefore microneedles
improve delivery in animals by penetrating past the SC and
would be especially useful in the delivery of lipophilic drugs that
partition slowly from the SC into the epidermis.
Oh et al.  fabricated biocompatible polycarbonate (PC)
microneedle arrays with various depths (200 and 500μm) and
densities (45, 99, and 154ea/cm2) using a micromechanical
process. The skin permeability of a hydrophilic molecule, calcein
(622.5D), was examined according to the delivery systems of
microneedle and drug loading, with vari-ations in depth and
density of the PC microneedle. The skin permeability of calcein
was the highest when the calcein gel was applied to the skin with
the 500μm-depth PC microneedle simultaneously. In addition,
the skin permeability of calcein was the highest when 0.1g of
calcein gel was coupled to the 500μm-depth PC microneedle
(154ea/cm2) as well as longer microneedles and larger density
microneedles. This study suggests that a biocompatible PC
microneedle might be a suitable tool for transdermal drug
delivery system of hydrophilic molecules, with possible
applications to macromolecules such as proteins and peptides.
Henry et al used a reactive ion-etching micro-fabrication
technique to make arrays of microneedles long enough to cross
the permeability barrier but not long enough to stimulate
nerves. These microneedle arrays could be easily inserted into
skin without breaking and increased permeability of human skin
in vitro to a model drug, calcein, by up to 4 orders of magnitude.
Limited tests on human subjects indicated that microneedles
were reported to be painless. This was the first published study
on the use of microfabricated microneedles to enhance drug
delivery across skin
Vemulapalli et al.  investigated transdermal iontophoretic
delivery (0.4mA/cm2 applied for 60 minutes) of methotrexate,
alone or in combination with maltose microneedle array, in vivo
and in vitro by using hairless rat as an animal model. Delivery
was enhanced by iontophoresis and microneedles both in vitro
and in vivo. A synergistic 25-fold enhancement of delivery was
observed in vivo when a combination of microneedles and
iontophoresis was used compared with either modality alone.
Kolli & Banga  characterized solid maltose microneedles
and assessed their ability to increase transdermal drug delivery
of nicardipine hydrochloride (NH) in vitro and in vivo across
hairless rat skin. Transepidermal water loss was measured to
study the skin barrier recovery after treatment. Uniformity in
calcein uptake by the pores was characterized, and percutaneous
penetration of NH was studied in vitro and in vivo across hairless
rat skin. Microneedles penetrated the skin while creating
micro channels measuring about 55.42±8.66mm in diameter.
NH in vitro transport across skin increased significantly after
pretreatment (flux7.05mg/cm2•h) compared with the untreated
skin (flux 1.72mg/cm2•h) and the enhanced delivery was also
demonstrated in vivo in hairless rats.
Microneedles have been widely used in the administration
of insulin [40,41]. During the past few years, considerable effort
has been put into developing novel, more comfortable routes of
insulin administration (eg. gastrointestinal, nasal, and inhalation
therapy). 89,90 Gastrointestinal and nasal administrations have
so far been unsuccessful, whereas inhalation therapy has been
successful. However, the inhalation devices are impractical
in size, and the long-term safety of inhaled formulations has
not been evaluated. Recently, attention has been drawn to the
possibility of using a patch-microneedle hybrid to deliver insulin.
Roxhed et al.  designed and tested a patch-like system
consisting of hollow microneedles and a drug reservoir with an
active electrically controlled dispensing mechanism to achieve
acceptable delivery rates of insulin in vivo in diabetic rats.
Continuous active infusion caused significantly higher insulin
concentrations in blood plasma. After a 3-hour delivery period,
the insulin concentration was 5 times larger compared with
passive delivery. Consistent with insulin concentrations, actively
administered insulin resulted in a significant decrease of blood
glucose levels. This study shows the feasibility of a patch-like
system with on-board liquid storage and dispensing capability.
The proposed device is an important step toward painless and
convenient administration of macromolecular drugs such as
insulin or vaccines.
Nordquist et al.  studied a painless intradermal deliver
of insulin by using a patch microneedle array in male Sprague
Dawley rats with streptozotocin-induced diabetes. Plasma
insulin and blood glucose were measured before, during, and
after subcutaneous or intradermal microneedle infusion of
insulin (0.2IU/h). Administration of insulin resulted in a reduced
plasma glucose independent of administration route.
This study presents a novel possibility of insulin delivery that
is controllable and requires minimal training. This treatment
strategy could improve compliance and thus improve patients’
glycemic control. Martanto et al.  investigated the design
and use of microneedle arrays (105 microneedles from stainless
steel) to deliver insulin into the skin of diabetic hairless rats with
streptozotocin-induced diabetes. During and after microneedle
treatment, an insulin solution (100 or 500U/mL) was placed in
contact with the skin for 4 hours. Microneedles were removed 10
seconds, 10 minutes, or 4 hours after initiation of transdermal
insulin delivery. Arrays of microneedles were fabricated and
demonstrated to insert fully into hairless rat skin in vivo.
Microneedles increased skin permeability to insulin, which
rap- idly and steadily reduced blood glucose levels to an extent
similar to 0.05 to 0.5U of insulin injected subcutaneously. Solid
metal microneedles were capable of increasing transdermal
insulin delivery and lowering blood glucose levels by as much as
80% in diabetic hairless rats in vivo.
In some cases, the combination of different active
enhancement methods has been effective in increasing the
transport of drugs through the skin . For example, Lanke
et al.  investigated the in vitro transdermal delivery of low
molecular weight heparin (LMH) in the hairless rat treated
with various enhancement strategies (passive diffusion,
iontophoresis [0.5mA•cm2 for 4 hours], sonophoresis [55kHz
for 60 seconds], tape stripping [20 pieces of 3M Transpore
adhesive tape removed in each skin section]) and the use of
an array of 28 soluble maltose microneedles. Passive flux was
essentially zero and remained low even after iontophoresis
(0.065U/cm2•h) or application of ultrasound (0.058U/cm2•h).
A significant increase in flux across tape-stripped skin (4.0U/
cm2•h) suggests the interaction of Stratum Corneum. Maltose
microneedles were then used to locally disrupt and bypass
the Stratum Corneum. Microneedles breached the Stratum
Corneum and enhanced LMH permeability (0.175U/cm2•h).
Microneedles when used in conjunction with iontophoresis had
a synergistic effect on LMH delivery, enhancing flux by 14.7 fold
compared with iontophoresis used alone. LMWH was shown to
interact with Stratum Corneum, and therefore tape stripping or
microneedles dramatically increased its delivery by disrupting
the SC skin barrier.
Stratum Corneum (SC) presents a significant barrier
to the delivery of gene therapy formulations. To realize the
potential of therapeutic cutaneous gene transfer, delivery strategies are required to overcome this exclusion effect. For
this reason, microneedles have been used for the delivery of
membrane-impermeable molecules into cells, for application in
molecular cell biology, and for the delivery of peptides, proteins,
oligonucleotides, DNA, and other probes that alter or assay cell
Coulman et al.  studied the ability of microfabricated
silicon microneedle arrays to create micron- sized channels
through the Stratum Corneum of ex vivo human skin and the
resulting ability of the conduits to facilitate localized delivery of
charged macromolecules and plasmid DNA (pDNA). The delivery
of a macromolecule, β-galactosidase, and of a “non-viral gene
vector-mimicking” charged fluorescent nano-particle to the
viable epidermis of microneedle-treatedt issue was demonstrated
using light and fluorescent microscopy. Permeation profiles
showed that more than 50% of a colloidal particle suspension
permeated membrane pores in approximately 2 hours. On the
basis of these results, it is probable that micro- needle treatment
of the skin surface would facilitate the cutaneous delivery of lipid
polycation pDNA (LPD) gene vectors, and other related vectors,
to the viable epidermis. Gene expression studies confirmed that
naked pDNA can be expressed in excised human skin following
microneedle disruption of the SC barrier. The presence of a
limited number of microchannels positive for gene expression
indicates that further studies to optimize the microneedle device
morphology, its method of application, and the pDNA formulation
are warranted to facilitate more reproducible cutaneous gene
Li et al.  investigated the microneedle-mediated in vitro
transdermal delivery of human IgG in full- thickness hairless rat
skin. In vitro penetration studies were conducted using freshly
excised full-thickness hairless rat skin, and various parameters
like needle length, number of needles, and effect of donor concentration
were examined. Pathway of IgG transport across skin
was confirmed by immune histochemical (IHC) studies.
A monoclonal antibody was delivered under optimized
conditions. Methylene blue was taken up by micro channels,
indicating disruption of the SC, and cryosections showed
that microneedles just reached the dermis. Human IgG
delivery increased with increases in arrays of microneedles,
concentration, and length of microneedles. IHC studies
demonstrated that IgG follows microchannels for transport
across the skin. Transdermal delivery was also demonstrated
for the monoclonal antibody. Maltose microneedles provide a
means for the transdermal delivery of macromolecules.
is recognized as a promising, fast-dissolving, solid reservoir
capable of stabilizing the native structure of proteins and
suitable for loading with a wide variety of bioactive substances.
There is a growing interest in developing cost-effective methods
for immobilizing solid trehalose on arrays of microneedles to
deliver protein-based and DNA-based vaccine to the epidermis.
Shirkhanzadeh  used microporous calcium phosphate
coatings to provide a biocompatible interface with a large
surface area for the effective immobilization of trehalose on
microneedles. The mechanical performance of the coatings was
assessed by inserting the tips of the coated needles into human
skin to an average depth of 100 to 300μm and then removing
them for analysis by scanning electron microscopy. Microporous
calcium phosphate coatings loaded with trehalose effectively
breached the SC and allowed direct access to the epidermis
without breaking and without stimulating nerves in deeper
Chabri et al.  determined whether silicon-based
microneedles could generate microchannels in human skin
of sufficient dimensions to facilitate access of LPD non-viral
gene therapy vectors. The diffusion of fluorescent polystyrene
nanospheres and LPD complexes through heat-separated human
epidermal sheets was determined in vitro using a Franz-type
diffusion cell. In vitro cell culture with quantification by flow
cytometry was used to determine gene expression in human
keratinocytes (HaCaT cells).
The diffusion of 100-nm-diameter fluorescent polystyrene
nanospheres, used as a readily quantifiable predictive model
for LPD complexes, through epidermal sheets was significantly
enhanced following membrane treatment with microneedles.
The delivery of LPD complexes either into or through the
membrane microchannels was also demonstrated. In both
cases considerable interaction between the particles and the
epidermal sheet was observed. These studies demonstrate the
utility of silicon microneedles in cutaneous gene delivery.
Combination vaccines reduce the total number of injections
required for each component administered separately and
generally provide the same level of disease protection. Yet
physical, chemical, and bio- logical interactions between vaccine
components are often detrimental to vaccine safety or efficacy.
As a possible alternative to combination vaccines, Morefield
et al.  used specially designed microneedles to inject rhesus
macaques with 4 separate recombinant protein vaccines for
anthrax, botulism, plague, and staphylococcal toxic shock next
to each other just below the surface of the skin, thus avoiding
potentially incompatible vaccine mixtures. The intradermally
administered vaccines retained potent antibody responses and
were well tolerated by rhesus macaques. Tracking of the adjuvant
showed that the vaccines were transported from the dermis to
draining lymph nodes by antigen-presenting cells. Vaccinated
primates were completely protected from an otherwise lethal
aerosol challenge by Bacillus anthracis spores, botulinum
neurotoxin A, or staphylococcal enterotoxin B. The vaccination
method may be scalable to include a greater number of antigens
while avoiding the physical and chemical incompatibilities
encountered by combining multiple vaccines together in one
Influenza, a contagious disease caused by a pathogenic virus
responsible for outbreaks all over the world and thousands of
hospitalizations and deaths every year, has attracted the attention
of researchers. Because of virus antigenic drift and short-lived
immune responses, annual vaccination is required. Koutsonanos
et al.  investigated a novel method for transdermal delivery
(applied in the caudal dorsal skin area of mice) using metal
microneedle arrays coated with inactivated influenza virus (A/
Aichi/2/68,H3N2) to determine whether this route is a simpler
and safer approach than the conventional immunization.
Microneedle vaccination induced a broad spectrum of immune
responses including CD4+ and CD8+ responses in the spleen
and draining lymph node, a high frequency of antigen-secreting
cells in the lung, and induction of virus-specific memory B cells.
The use of microneedles showed a dose-sparing effect and a
strong Th2 bias compared with an intramuscular reference
Delivery of inactivated influenza virus through the skin using
metal microneedle arrays induced strong humoral and cellular
immune responses capable of conferring protection against
virus challenge as efficiently as intramuscular immunization. In
view of the convenience of delivery and the potential for selfadministration,
vaccine-coated metal microneedles may provide
a novel and highly effective immunization method.
Microneedle skin therapy is still in testing and development,
but it seems to show much promise. Microneedle therapy is a
way to rejuvenate the skin without destroying the epidermis. It
is similar to laser treatments but with less damage. Companies
like Clinical Resolution Lab (Los Angeles, California) use
treatments involving microrollers . Microneedles penetrate
the epidermis and break away old collagen strands. The
collagen strands that are destroyed create more collagen under
the epidermis. This leads to youthful looking skin. The only
disadvantage of this method is that it causes blood oozing, which
laser treatments do not. It does, however, have advantages such
as increased collagen, non– sun sensitivity upon treatment, no
breaking of the epidermis, lower cost, and ease of application.
This paper has effectively described some of the frontiers
in Microneedle as a potent modern tool in enhancement of
transdermal drug delivery. This is owing to advances in micro
fabrication technology as well as its scalability in a configuration
of multi array. Oral treatment has some obvious limitations
caused by low surface absorption area and much reduced rate
of enzymatic degradation. Hence the advent of microneedle has
provided a much more needed solution to these challenges as
against oral treatment. Compared with commercially available
hypodermic needles, microneedles enable pain-free insertion,
minimal tissue damage, and increased control over drug dosage,
independent of drug com- position and concentration [1,2].
Buoyed by the numerous advantages of microneedles as already
discussed in this literature review, the interest in the use of
microneedles is ever increasing presently.
It is also well known that most children have phobia for
needles. In addition, many patients suffering from chronic
diseases like diabetics receive multiple injections on daily basis
while a lot of other disease conditions would require the delivery
of therapeutic agents to the skin hence the numerous challenges
associated with needle-based injections has been overcome by
the development of microneedles .
However, valid concerns regarding the use of these
microneedles especially safety issues have also been highlighted.
There are concerns about costs of the delivery system, delayed
onset of action and possible misuse, accidental use, or abuse
. There is a need to investigate further skin pore closure after
MN application especially as it relates to the risk of infections.
It is also essential to ensure that materials which are used for
MN fabrication do not induce skin irritation. Another area is
the need for a balance between increased permeability and
painlessness. It is known that as MN length increases, there is
a high probability that pain receptors located in the dermis may
be stimulated. In spite of the above-mentioned limitations, the
outlook for the use of these devices is promising even as more
work needs to be done for microneedles to become routine drug
delivery systems in clinical practice.