About

Dr. Geelsu Hwang is an Associate Professor in the Department of Preventive & Restorative Sciences at Penn Dental Medicine. He holds a B.S. in Chemical Engineering and a Ph.D. in Chemical and Biomolecular Engineering from Yonsei University. Before joining Penn Dental Medicine in 2013, he served as a lecturer in the Department of Chemical Engineering at Seoul National University of Science and Technology. His research focuses on applying engineering principles and tools to understand the pathogenesis of biofilm-associated oral diseases and to develop therapeutic approaches. His work also explores the dynamic interplay between host and microbes in infectious oral disease, utilizing engineering, biochemical/biophysical, confocal imaging methodologies, and mathematical modeling.

Research topics

• Chemistry
• Microbiology
• Materials science
• Biology
• Nanotechnology

Selected publications

• Nanoarchitectonics of Metal–Organic Framework Platforms for Enhanced Enzyme Delivery with Preserved Activity

  ACS Applied Materials & Interfaces · 2026-03-16 · 1 citations

  articleOpen accessSenior authorCorresponding

  The targeted delivery of biomacromolecules remains a critical challenge due to their intrinsic instability, limited permeability across biological barriers, and susceptibility to degradation. Herein, we report postsynthetic enzyme encapsulation in reaction-mechanism-guided metal-organic framework nanocarriers (MOF NCs), enabling selective loading, controlled release, and preserved biological function. The MOF NCs were synthesized via coordination-driven assembly, yielding hybridized porous architectures with high colloidal stability in aqueous media. Enzyme encapsulation was accomplished through nondisruptive interactions, including hydrogen bonding, ionic interactions, covalent anchoring, or van der Waals interactions. The structural integrity of β-Dextranase and endo-1,4-β-mannanase, enzymes known to disrupt oral biofilms, was maintained throughout encapsulation and release, as confirmed by circular dichroism spectroscopy. Environmentally responsive enzyme release was triggered under mildly acidic or alkaline conditions, driven by ligand exchange and hydrolysis at the zinc coordination centers, leading to nanocarrier disassembly and subsequent enzymatic activation. The MOF NCs exhibited excellent biocompatibility and preserved enzyme activity comparable to free enzymes at acidic and basic pH values, demonstrating their potential for targeted therapeutic applications at otherwise inaccessible biological sites.

  PublisherOA PDFDOI

• Research Trends and Citation Patterns in Antifungal Susceptibility Studies of Itraconazole and Terbinafine in Oral and Oropharyngeal Candida: A Bibliometric Analysis

  OSF Preprints (OSF Preprints) · 2026-01-01

  otherOpen access

  This project is a bibliometric and citation analysis investigating research on itraconazole and terbinafine in oral and oropharyngeal Candida infections. The study examines publication trends, citation structures, influential articles, collaboration networks, and thematic patterns related to antifungal susceptibility testing. Analyses are based on the 100 most-cited articles indexed in the Web of Science Core Collection, following the BIBLIO guideline for reporting bibliometric studies.

  PublisherOA PDFDOI

• Hydroxyapatite-Based 3D Tooth Models for Investigating Spatially Resolved Analysis of Biofilm Formation Dynamics

  ACS Applied Bio Materials · 2026-05-08

  articleSenior authorCorresponding

  Experimental oral biofilms have traditionally been cultured on various substrates. Among them, hydroxyapatite (HA), in the form of discs or beads, has been widely used due to its chemical relevance to natural dental tissues. However, these conventional HA substrates fail to replicate the intricate topography of natural teeth, features that significantly influence microbial adhesion and biofilm development. To address this limitation, we developed morphologically accurate HA-based tooth models, including both intact and restored variants. Premolar and molar tooth models were fabricated from patient-derived computed tomography scans using HA powder via cold isostatic pressing and sintering. Restorations (inlays and onlays) were incorporated using permanent dental resin, which was mounted with clinical-grade dental cement. The resulting tooth models were free of visible cracks or macroscopic defects and demonstrated mechanical stability comparable to that of natural human teeth. Results from biofilm experiments using Streptococcus mutans and Candida albicans revealed significantly higher biofilm accumulation on the occlusal surfaces of the mandibular tooth models. In contrast, maxillary tooth models exhibited greater colonization on lateral surfaces. Restored tooth models showed increased biofilm formation on and around inlay and onlay materials. These morphologically accurate tooth models enable spatially resolved analysis of oral biofilms. This approach may enhance our understanding of microbial colonization and biofilm formation mechanisms.

  PublisherDOI

• Research Trends and Citation Patterns in Antifungal Susceptibility Studies of Itraconazole and Terbinafine in Oral and Oropharyngeal Candida: A Bibliometric Analysis

  OSF Preprints (OSF Preprints) · 2026-02-04

  other

  This project is a bibliometric and citation analysis investigating research on itraconazole and terbinafine in oral and oropharyngeal Candida infections. The study examines publication trends, citation structures, influential articles, collaboration networks, and thematic patterns related to antifungal susceptibility testing. Analyses are based on the 100 most-cited articles indexed in the Web of Science Core Collection, following the BIBLIO guideline for reporting bibliometric studies.

  Publisher

• Hybrid Bioceramic: A Synergistic Platform for Structural Reinforcement and Bioelectric Stimulation Toward Smart Medical Devices

  Small · 2026-03-18

  article

  ABSTRACT As the rise of smart implants has led to a transformation in healthcare, the hybrid biomaterials have garnered significant attention due to the increasing demand for mechanical stability and functional properties. This study presents a barium titanate (BTO)‐yttria stabilized zirconia (YSZ) bioceramic with varying compositions (between 40 wt.% and 60 wt.%), and sintering temperatures (1250°C–1450°C) to achieve clinically feasible structural integrity, piezoelectricity, mechanical strength, and a cell‐friendly environment. By combining a piezoelectric phase with a mechanically robust ceramic phase, the hybrid system enables energy harvesting from physiological movements while maintaining long‐term mechanical durability. The results demonstrate that both BTO and YSZ exhibit stable coexistence within a single material, segregated in a manner that preserves their respective structural and functional properties. Increasing BTO content enhances the piezoelectric coefficient ( d 33 ), while YSZ contributes to higher hardness and fracture toughness. Optimal sintering at 1350°C yields a dense microstructure that strikes a balance between electrical and mechanical performance. Furthermore, microstructural analysis via Raman spectroscopy, scanning electron microscopy, and X‐ray diffraction confirms phase stability and controlled grain growth. The findings suggest that the BTO–YSZ bioceramic has strong potential for co‐design of biofunctional and mechanically robust hybrid biomaterials, paving the way toward next‐generation smart biomedical implants.

  PublisherDOI

• Comparative Analysis of the Mechanical, Surface, and Dimensional Properties of <scp>3D</scp> ‐Printed Aligners: Influence of Printer Type and Nitrogen‐Assisted Post‐Curing

  Orthodontics and Craniofacial Research · 2026-04-28

  articleOpen access

  OBJECTIVES: This study aimed to compare the mechanical, surface, and dimensional properties of 3D-printed clear aligners (CA) fabricated using liquid crystal display (LCD) and digital light processing (DLP) 3D printing systems with nitrogen treatment. MATERIALS AND METHODS: Specimens were manufactured using LCD (Uniz NBEE) and DLP (Nextdent 5100) printers. Post-processing included residual resin removal and post-curing, with half of the specimens receiving nitrogen treatment. UV intensity was measured for each printer. Mechanical properties were assessed using tensile strength (n = 10), Shore D hardness (n = 8), and nano-indentation (n = 3). Optical and surface properties were assessed using translucency (n = 6) and surface roughness (n = 5). The accuracy of the CAs was assessed using root mean square deviation analysis (n = 4). Statistical analyses were performed using one-way ANOVA with Tukey's test and an independent samples t-test (p < 0.05). RESULTS: The LCD system showed more consistent UV intensity patterns during printing compared to the DLP system, as well as superior mechanical properties with higher tensile strength and Shore D hardness (p < 0.001). Nitrogen treatment significantly enhanced nano-indentation parameters, including Martens hardness and the elastic index in both LCD- and DLP-printed groups (p < 0.001). Both systems exhibited comparable translucency, surface roughness, and accuracy (p > 0.05). CONCLUSION: The choice of 3D printing systems significantly influenced CA properties. The LCD printing system demonstrated superior mechanical performance compared with the DLP system. In addition, nitrogen treatment significantly improved nano-indentation-derived mechanical properties, including Martens hardness and the elastic index. These findings suggest that the selection of the printing system and post-curing conditions may influence the mechanical performance of CAs.

  PublisherDOI

• The Oral Biofilm Microenvironment

  Springer series on biofilms · 2025-01-01

  book-chapter
  PublisherDOI

• Effects of printing layer thickness and build orientation on the mechanical properties and color stability of 3D-printed clear aligners

  The Angle Orthodontist · 2025-03-04 · 9 citations

  articleOpen access

  Objectives: To determine effects of printing layer thickness and build orientation on mechanical properties and color stability of direct 3D-printed clear aligner resin. Materials and Methods: Specimens were printed using 3D printed clear aligner resin with two printing layer thicknesses (50 µm, 100 µm) and three build orientations (90°, 60°, and 45°). Mechanical properties (tensile stress, tensile strain, and elastic modulus), color stability in coffee and artificial saliva, and roughness were then evaluated. Results: Specimens printed with a 50 µm layer thickness and orientation at 90° demonstrated superior color stability in artificial saliva. However, all specimens showed high susceptibility to coffee staining regardless of layer thickness or orientation. Mechanical properties were improved in the order of 90° < 60° < 45° build orientation, showing statistically significant differences (P < .05). Surface roughness was increased in the order of 90° < 60° < 45° build orientation, showing statistically significant differences (P < .05). Conclusions: Printing layer thickness and orientation exerted significant effects on mechanical properties, color stability, and surface roughness of 3D-printed clear aligner resin.

  PublisherOA PDFDOI

• Usage of Silver Nanoparticles in Orthodontic Appliances

  Materials · 2025-12-29

  articleOpen access

  Orthodontic treatment, offering significant benefits for oral function and facial aesthetics, is in high demand among both adolescent and adult populations. Orthodontic appliances pose challenges for maintaining oral hygiene and increase the risk of dental and periodontal diseases. With advances in dental materials and the use of nanoparticles, a significant amount of research has focused on modifying orthodontic appliances with nanoparticles to reduce bacterial adhesion and biofilm formation. Silver nanoparticles are one of the most popular antibacterial materials in medical research. This article presents current evidence on silver nanoparticle-incorporated orthodontic appliances, including brackets, molar bands, archwires, elastomeric ligatures, mini-implants, and acrylic retainers. Silver nanoparticles and modified silver nanoparticles exhibit robust antibacterial activity when applied to the surfaces of orthodontic appliances. However, there are exceptions in which, on a few orthodontic appliances, the silver nanoparticle incorporation actually increased biofilm formation. Moreover, a silver nanoparticle incorporation may introduce adverse effects, such as cytotoxicity, and increase surface roughness. It is also worth noting that most of the studies were conducted in vitro. Long-term clinical studies are necessary to evaluate the stability, safety, and clinical efficacy of silver nanoparticle-incorporated orthodontic appliances under real-world conditions.

  PublisherOA PDFDOI

• Micro-CT and Histomorphometric Analysis of Degradability and New Bone Formation of Anodized Mg-Ca System

  Biomimetics · 2025-09-03 · 1 citations

  articleOpen accessCorresponding

  The surface treatments and various magnesium alloys are applied to improve the fast degradation rate and resulting negative effects of magnesium alloys. This study aimed to assess the effect of anodic oxidation treatment of magnesium-calcium (Mg-Ca) systems by creating artificial bone defects in the tibia of rats. The cylinder magnesium implants were fabricated using a Mg-xCa (x = 0, 1, 5 wt.%) binary alloy. Degradability and new bone formation were observed at two and six weeks using micro-CT. Histomorphometric parameters were evaluated with Goldner's trichrome staining. The degradation rate decreased depending on the amount of calcium added. The parameters related to bone formation revealed an increasing pattern depending on the addition of calcium, anodic oxidation, and time. The amount of absorbed magnesium to assess degradability of magnesium implants by the histomorphometric analysis revealed a high value in the untreated group at two and six weeks. Bone healing parameters increased depending on the amount of calcium added, anodic oxidation treatment, and region of interest (ROI-0.5 mm, 1.00 mm, 1.5 mm, and 2.0 mm). Biodegradable magnesium systems have the potential to replace bone screws and plates. Combination with calcium combined with anodization surface treatment can improve initial corrosion resistance and promote bone formation.

  PublisherOA PDFDOI

Recent grants

• Enzymatic approach for targeting mannans/EPS to disrupt cross-kingdom cariog

  NIH · $1.7M · 2018–2024

• Collaborative Research: Smart Dental Implant for Ambulatory Dental Care

  NSF · $250k · 2022–2026

• Role of GtfB on S.mutans-C.albicans interactions and cariogenic biofilm formation

  NIH · $160k · 2016–2017

Frequent coauthors

• Hyun Koo

  University of Pennsylvania

  59 shared

• Yuan Liu

  Guangxi University

  46 shared

• Yuan Liu

  University of Pennsylvania

  32 shared

• Atul Dhall

  University of Pennsylvania

  16 shared

• Albert Kim

  14 shared

• Danielle S. W. Benoit

  University of Oregon

  14 shared

• Yang Liu

  China University of Petroleum, Beijing

  13 shared

• Dongyeop Kim

  Jeonbuk National University

  13 shared

Education

• PhD, Chemical and Biomolecular Engineering

  Yonsei University

  2010

• B.Sc, Chemical Engineering

  Yonsei University

  2004

Awards & honors

• The Joseph and Josephine Rabinowitz Award for Excellence in…
• AADR Travel Award, Penn Dental Research Day, University of P…
• AADR Travel Award, Penn Dental Research Retreat, University…
• Member, Hatton Awards Committee of the AADR (2020-2022)
• Proposal Coordinator for Clinical and Translational Science…