Advances in Nanotechnology Eliminates the Use of Surgical Blades for Controlled Remodeling of Oral Connective Tissues

Malocclusion is a misalignment between the teeth in the upper and lower dental arches when they approach each other as the jaws close. In India, more than one million people are being treated for malocclusion every year. Though misalignment of teeth could occur during teeth development, it could be aggravated by childhood habits such as thumb sucking. The most common cause of misalignment of teeth is considered to be due to relatively smaller size of the jaw when compared to the size of the teeth. The recommended treatments for misaligned teeth could involve a minor surgical procedure and the use of braces to prevent relapse of the repaired teeth. In the gingiva, the teeth and underlying alveolar bone are connected by collagen type-I supracrestal fibers. For patients with severe malocclusion, sectioning of the collagen fibers using a scalpel is necessary to maneuver the teeth to a proper position (Fig. 1(a)). The invasive nature of the surgical procedure and severe pain encountered by patients warrants development of alternate procedures. In recent years, the advancements in nanotechnology has reached new heights in revolutionizing medical care. Researchers at Technion – Israel Institute of Technology lead by Prof. Avi Schroeder along with other researchers at Rambam Medical Center, Moriah Animal Companion Center and Tel Aviv Sourasky Medical Center, Israel have demonstrated a nanotechnology based approach that enabled controlled delivery of proteolytic enzymes, which eliminates the use of surgical blades to correct malocclusion (Fig. 1(b)). They have tested the ability of nanoparticles loaded with a proteolytic enzyme to replace surgical procedures by directly targeting collagen type-I fibers in the oral cavity (Fig. 1(c)).

Fig. 1 (a) Pictorial representation of teeth confined to their natural orientation by soft and hard tissue. Specifically, collagen type-I fibers anchor the teeth to the underlying bone; (b) Nanoparticles (blue spheres) loaded with collagenase, a proteolytic enzyme with specificity towards collagen, are inserted into the sulcus; (c) The nanoparticles maintain the enzyme’s therapeutic release profile and confine the biodistribution to the treatment site.

Collagenase is a proteolytic enzyme and once activated by calcium, it is capable of cleaving the collagen backbone by detaching the peptide link between glycine and leucine. Since the collagenase needs to be activated only after it is placed at the surgical site, it is loaded inside 100 nm liposomes (nanoscale vesicles with an inner aqueous core surrounded by a lipid bilayer membrane). The liposome lipids were not susceptible to degradation by collagenase. Since the liposomal lipid bilayer composed of 1,2-dimyristoyl-sn-glycero-3-phosphocholine is impermeable to Ca²⁺ ions, an early activation of the enzyme is prevented. Once placed in the sulcus, diffusion of collagenase out of the liposomes occurs. Calcium, which is naturally present in the oral cavity, activates the collagenase, which in turn helps to relax the collagen fibers. The degradative activity of the collagenase is responsible for weakening of the collagen fiber, which is evidenced by the extent of increase in weakening of the fibers with an increase in concentration of collagenase. It is important that during treatment, the collagen fibers must be relaxed but should not tear and a collagenase concentration of 0.05-0.1 mg/mL is considered to be optimal.

The change in morphological features of the collagen fiber before treatment, during treatment and during collagen regeneration indicate that the tightly packed fiber structure of collagen (Fig. 2(a)) tends to relax after treatment with collagenase (Fig. 2(b)) but resumes their initial morphology except in some regions wherein the fibers lack a perfect alignment (Fig. 2(c)). It is also important to ensure that as the collagen fibers tend to relax, the bonding between collagen fibers and fibroblasts should be retained. Following the collagenase treatment, the morphology of the fibroblast is changed from an elongated structure to a round structure. Fortunately, the collagen fibers neither detached from the fibroblasts nor impacted their viability. Hence, the adherent fibroblasts could perform the natural reparative processes.

Fig. 2 HR-SEM images of collagen fiber (a) before; (b) during; and (c) after treatment with collagenase indicating the regeneration of collagen.

Comparison of the efficiency of treatments performed on rats by traditional surgical protocol using a scalpel and by the controlled delivery of proteolytic enzymatic surgery over a period of 15 day treatment indicates a similar enhancement in tooth alignment trajectory motion. Groups treated with empty liposomes (without collagenase enzyme) and groups treated with free enzymes (without loading them in liposomes) fails to display any significant improvement in tooth alignment while those treated using liposomal nanoparticulate loaded with the collagenase enzyme exhibits a three-fold improvement in  tooth alignment (Fig. 3). The degree of inflammation appears to be similar; a mild inflammation is observed among all the groups tested. Bone recovery is found to be faster for the liposomal nanoparticulate system when compared to other groups treated with ordinary braces. The occurrence of tooth relapse is relatively less for groups treated using liposomal nanoparticulate loaded with the collagenase enzyme when compared to the control groups. The ability of the liposomal system to protect the collagenase enzyme from deactivation, to prolong its release profile and to confine the spatial distribution of the enzyme to the treatment site is considered responsible for the observed improvement.

Fig. 3 Comparison of the efficiency of treatment for different groups in terms of cumulative tooth movement as a function of time

This nanotechnology based approach enables a controlled delivery of proteolytic enzymes and eliminates the use of surgical blades to correct malocclusion. The success of this treatment approach lies in the appropriate choice of the proteolytic enzyme that can be biologically tailored towards the target organ and ability of the liposomal system to enable a controlled delivery of proteolytic enzymes with a required therapeutic dose confined to the treatment site.

T.S.N. Sankara Narayanan

For more details, the reader may kindly refer Assaf Zinger et al., Proteolytic Nanoparticles Replace a Surgical Blade by Controllably Remodeling the Oral Connective Tissue, ACS Nano, 2018, DOI: 10.1021/acsnano.7b07983

 

Direct delivery of drugs to the brain using ultrathin needle

Parkinson’s disease (PD) is a long-term neurodegenerative disorder of the central nervous system that predominately affects the motor system. Patients affected by PD are deprived of dopamine-producing neurons in the substantia nigra, which leads to a decrease in dopamine levels in their brain. Drugs such as I-dopa often interact with neurotransmitters or the cell receptors. Since the application of these drugs cannot be localized only to the affected site, they could cause severe side effects on all parts of the brain. Will it be possible to deliver the drug within a cubic millimeter of the brain so that we can treat the PD while limiting the side effects of the drug? Researchers at MIT have developed  a miniaturized system that is capable of delivering a very small amount of drug to any specific region of the brain confined to a small space of 1 mm³, without interfering with the normal function of the rest of the brain.

The device was fabricated by microfabrication technique and it consisted of several tubes (diameter: ~30 µm; length: ~ 10 cm) and they are contained within a stainless steel needle (diameter: ~150 µm). The tubes can be connected to small pumps to deliver hundreds of nanoliters of drugs. The device is very stable and robust, and it can be implanted under the skin. Since the device consists of several tubes contained within a needle, which is as thin as a human hair, it would be possible to deliver one or more drugs deep within the brain, with very precise control of the amount of drug and where it should be administrated. In a rat model, they delivered “muscimol” through one of the channels of the device to substantia nigra (one of the regions of the brain) and identified symptoms similar to those seen in PD. However, by delivering a dose of saline thorough another channel, which washes away “muscimol”, the Parkinsonian behaviour is altered. The researchers believe that the device can be customized with different channels to deliver drugs targeting tumours or in treating Parkinson’s or Alzheimer’s disease

T.S.N. Sankara Narayanan

 C. Dagdeviren el al., Science Translational Medicine  24 Jan 2018: Vol. 10, Issue 425, eaan2742