Harnessing biomolecules for bioinspired dental biomaterials

Abstract

Dental clinicians have relied for centuries on traditional dental materials (polymers, ceramics, metals, and composites) to restore oral health and function to patients. Clinical outcomes for many crucial dental therapies remain poor despite many decades of intense research on these materials. Recent attention has been paid to biomolecules as a chassis for engineered preventive, restorative, and regenerative approaches in dentistry. Indeed, biomolecules represent a uniquely versatile and precise tool to enable the design and development of bioinspired multifunctional dental materials to spur advancements in dentistry. In this review, we survey the range of biomolecules that have been used across dental biomaterials. Our particular focus is on the key biological activity imparted by each biomolecule toward prevention of dental and oral diseases as well as restoration of oral health. Additional emphasis is placed on the structure-function relationships between biomolecules and their biological activity, the unique challenges of each clinical condition, limitations of conventional therapies, and the advantages of each class of biomolecule for said challenge. Biomaterials for bone regeneration are not reviewed as numerous existing reviews on the topic have been recently published. We conclude our narrative review with an outlook on the future of biomolecules in dental biomaterials and potential avenues of innovation for biomaterial-based patient oral care.

Fig. 1

Harnessing biomolecules for bioinspired dental biomaterials. Promising and proven biomolecules include hyaluronic acid, DNA, elastin, peptides, proteins, intrinsically disordered proteins, laminin, minerals, and collagen. Dental biomaterials potentially benefitting from biomolecule incorporation include tissue grafts and membranes, adhesives, and regenerative endodontic obturation materials.

Fig. 2

Chimeric antimicrobial peptides and temperature-sensitive immobilized antimicrobial peptides with in vivo potency. (A) Schematic representation of AMP designed with an implant/titanium binding domain (TiBP) connected to an AMP domain separated by a spacer. Two peptides designs were used in this study: TiBP-AMPA and TiBP-GL13K, which differed in their respective AMPs (AMPA vs. GL13K). (B) Visualization of FITC-labeled peptides using fluorescence microscopy after challenge by S. mutans for 24 hours. The percentage of peptide (TiBP-AMPA vs. TiBP-GL13K) coverage was determined. (C) Fluorescent microscopy images of peptides (TiBP-AMPA and TiBP-GL13K) binding to titanium implant discs, binding with competition from bovine serum albumin, and durability following 1 minute of brushing with an electric toothbrush. (D) Fluorescence microscopy images and quantification of propidium iodide (PI) staining of dead S. mutans bacteria on implant discs after challenge for 24 hours. (E) Scheme of preparation of temperature-sensitive surfaces on Ti; Ti was treated with dopamine to form surface b (Ti-PDA); then, surface b was treated with 2-bromoisobutyryl bromide to form surface c (Ti-Br); by click chemistry, surface c was first converted into surface d by adding NaN₃, and then into surface e (Ti-AMP); surface e (Ti-AMP) contained AMP but lacked pNIPAM; by atom transfer radical polymerization, pNIPAM was formed on surface c to generate surface f (Ti-pNIPAM); by click chemistry, surface f was converted first into surface g (Ti-pNIPAM-N3) by adding NaN₃ and then into surface h (Ti-pNIPAM-AMP) by adding HHC36. Surface f contained AMP conjugated to pNIPAM. (F) Exposure and hiding of HHC36 (fluorescently labelled in green) at lower (left; 25 °C) and higher temperature (right; 37 °C). (G) Quantitative antibacterial activity of different surfaces after incubation against S. aureus and E. coli for 2 h at 25 °C (exposed peptide) and 37 °C (hidden peptide). (H) In vivo characterization of antimicrobial activity and biocompatibility of samples after implantation in infected rabbit tibiae for 7 days; images of the Petri dishes showing the presence of bacteria (yellow spots) on samples after retrieval (left; plain Ti and right; temperature-sensitive with HHC36). (I) Antimicrobial activity of the surfaces of different samples (left) and the tissues surrounding the corresponding samples (right) after in vivo retrieval. Reprinted with permission from ref. (2019) and ref. (2018) American Chemical Society.

Fig. 3

Elastin-like recombinamer coatings on dental implants for anti-biofilm potency. (A) Schematic representation of the modular composition of the antimicrobial-ELR (AM-ELR) and production of self-assembled monolayers (SAMs) on gold surfaces. (B) Live/dead staining biofilms (where green is alive and red is dead) for both (S. aureus and S. epidermidis) after 24 h of culture on negative control gold (Au) surfaces, positive control GL13K peptide surfaces (GL13K), the ELR without an AMP incorporated (VC) and then the antimicrobial AM-ELR (GVC). Reprinted with permission from ref. (2019) American Chemical Society.

Fig. 4

Hybrid antimicrobial biomaterial for endodontics. (A) Schematic representation of study design using a photocrosslinkable gelatin methacryloyl (GelMA) hydrogel with halloysite aluminosilicate nanotube (HNT) for release of chlorohexidine (CHX) for on-demand delivery for endodontic infection ablation. (B) Transmission electron micrographs (TEM) of HNTs. (C) Morphology (scanning electron micrographs) of GelMA hydrogel cross-section. (D) SEM cross-section of GelMA modified with CHX-loaded nanotubes. (E) Antimicrobial activity of GelMA with CHX loaded HNTs against a patient-derived oral microcosm. (F) Degradation profile of hydrogels in collagenase type I solution. (G) Histological analysis of the biopsy of the capsule surrounding indicated samples after 7 and 14 days. Reprinted with permission from ref. (2020) American Chemical Society.

Fig. 5

Polydopamine and whole proteins for improving soft tissue healing around dental implants. (A) Schematic of surface modification of Ti–6Al–4V (Ti). Polished titanium was first coated by a poly-dopamine (PDA) film by self-polymerization of dopamine; then, type I collagen was bonded with the PDA film via a Michael addition or Schiff base reaction. The possible structure of PDA and mechanism of the reaction between PDA and collagen is shown. (B) Adhesion of fibroblasts on (from left to right) Ti, Ti-PDA, and Ti-PDA-Col after 1 day of culture; fluorescent micrographs stained with vinculin in green, actin in red, and nuclei in blue. (C) Fibroblast surface density, vinculin intensity, and cell spreading area after 1 day of culture. (D) Histological (H&E) analysis of the biopsy of the capsule surrounding indicated samples after 30 days of implantation in rats and quantification. Reprinted with permission from ref. (2019) The Royal Society of Chemistry.

Fig. 6

Peptides for enhancing dental implant soft tissue healing. (A) Schematic of surface modification co-immobilizing a peptide derived from ameloblastin (denoted as ABMN) and the laminin α3 globular domain 3 (denoted as LAM) to upregulate hemidesmosome formation on titanium for percutaneous devices such as dental implants. (B) Proliferation of keratinocytes through 48 hours (2 days) of culture on mono- and co-immobilized surfaces. (C) Hemidesmosome formation (immunofluorescence of collagen XVII) after 1 day of culture. Reprinted with permission from ref. (2018) The Royal Society of Chemistry.

Fig. 7

Hard and soft periodontal tissues susceptible to disease and infection necessitating bioinspired dental biomaterial therapies. The tooth, primarily composed of enamel and dentin, is filled with blood vessels and is innervated. The tooth root is covered in cementum and partially anchored into the oral cavity through periodontal ligaments as the tooth sits in a bone socket. The surrounding gingiva, composed of sulcar epithelium and connective tissue, seals the tooth from the harsh oral cavity at the junctional epithelium, near the cemento-enamel junction, and is marked by a distinctive gingival margin and epithelium in healthy individuals.

Fig. 8

Novel bioink biomaterial for increasing bioactivity and bone healing. (A) Representative macrophotographs (upper images) showing the formulation process of the extracellular matrix/amorphous magnesium phosphate (ECM/AMP) bioink, and schematic of the ECM/AMP cell-laden bioink printing and the optical images (lower images) of the cell-free/cell-laden, AMP-based composites with and without cells. (B) Calcein AM (green) and PI (red) staining assay for live and dead analysis of dental pulp stem cells (DPSCs) after short period (1 day) in the cell-laden ECM and ECM/AMP-bioprinted constructs, showing more elongated morphology for DPSCs when combined with the AMP-modified constructs (red arrows denote dead cells). (C) Graphs showing similar cell viability among the tested bioink constructs, but a significant overall increased osteogenic differentiation (alkaline phosphatase activity, Alizarin Red S absorbance, and osteogenic gene expression at days 14 [lower left graph] and 21 [lower right graph]) for the ECM/AMP-modified bioinks as compared with the AMP-free control. (D) Representative macrophotographs for the application of the tested constructs in the in vivo rat model, showing the polytetrafluoroethylene (PTFE) membrane (cytoplast) used as a carrier for the printed constructs (a), its cutting into square-shaped pieces (7 × 7 mm²) (b) and combination with the constructs (c), and implantation in prepared defect (d and e) and suture (f). (E) Micro-CT results showing rat skull 3D rendering at 4 and 8 weeks for defects left empty or filled with the PTFE membrane alone, ECM and 1.0 wt% ECM/AMP-modified (ECM/1.0AMP) constructs; bone volume per total volume (BV/TV) and bone density were substantially higher for defects treated with the AMP-modified material. (F) H&E and MT staining after 8 weeks of implantation of tested groups and controls, indicating healing of the defects with new bone formation restricted to the area close to the border of the defects, with the ECM and ECM/1.0AMP groups showing thicker bone formation; inset legends – connective tissue (CT), osteoblast (OB), new bone (NB), blood vessel (BV), osteocytes (OC), woven bone (WB; blue), lamellar bone (LB; red). Reprinted with permission from ^ref. (2020) American Chemical Society.