Increased bone formation around coated implants

The minipig intraoral dental implant model: A systematic review and meta-analysis

OBJECTIVES

The objective of this report was to provide a review of the minipig intraoral dental implant model including a meta-analysis to estimate osseointegration and crestal bone remodeling.

METHODS

A systematic review including PubMed and EMBASE databases through June 2021 was conducted. Two independent examiners screened titles/abstracts and selected full-text articles. Studies evaluating titanium dental implant osseointegration in native alveolar bone were included. A quality assessment of reporting was performed. Random-effects meta-analyses and meta-regressions were produced for bone-implant contact (BIC), first BIC, and crestal bone level.

RESULTS

125 out of 249 full-text articles were reviewed, 55 original studies were included. Quality of reporting was generally low, omissions included animal characteristics, examiner masking/calibration, and sample size calculation. The typical minipig model protocol included surgical extraction of the mandibular premolars and first molar, 12±4 wks post-extraction healing, placement of three narrow regular length dental implants per jaw quadrant, submerged implant healing and 8 wks of osseointegration. Approximately 90% of studies reported undecalcified incandescent light microscopy histometrics. Overall, mean BIC was 59.88% (95%CI: 57.43-62.33). BIC increased significantly over time (p<0.001): 40.93 (95%CI: 34.95-46.90) at 2 wks, 58.37% (95%CI: 54.38-62.36) at 4 wks, and 66.33% (95%CI: 63.45-69.21) beyond 4 wks. Variability among studies was mainly explained by differences in observation interval post-extraction and post-implant placement, and implant surface. Heterogeneity was high for all studies (I2 > 90%, p<0.001).

CONCLUSIONS

The minipig intraoral dental implant model appears to effectively demonstrate osseointegration and alveolar bone remodeling similar to that observed in humans and canine models.

Biochemical Modification of Titanium Oral Implants: Evidence from In Vivo Studies

The discovery of osseointegration of titanium implants revolutionized the dental prosthesis field. Traditionally, implants have a surface that is processed by additive or subtractive techniques, which have positive effects on the osseointegration process by altering the topography. In the last decade, innovative implant surfaces have been developed, on which biologically active molecules have been immobilized with the aim of increasing stimulation at the implant-biological tissue interface, thus favoring the quality of osseointegration. Among these molecules, some are normally present in the human body, and the techniques for the immobilization of these molecules on the implant surface have been called Biochemical Modification of Titanium Surfaces (BMTiS). Different techniques have been described in order to immobilize those biomolecules on titanium implant surfaces. The aim of the present paper is to present evidence, available from in vivo studies, about the effects of biochemical modification of titanium oral implants on osseointegration.

Influence of a Novel Surface of Bioactive Implants on Osseointegration: A Comparative and Histomorfometric Correlation and Implant Stability Study in Minipigs

Purpose: The objective of this study was to assess the influence of a novel surface of dental implants (ContacTi^®) on the osseointegration process in a minipig model. The surface was compared with other existing surfaces on the market (SLA^® and SLActive^®) by employing bone implant contact analysis (BIC) and implant stability. Method: Twelve minipigs were used with prior authorisation from an ethics committee. Three types of surfaces were tested: SLA^® (sand-blasted acid-etched titanium), SLActive^® (same but hydrophilic, performed under a nitrogen atmosphere), and ContacTi^® (alumina particle bombardment of titanium, bioactivated when treated thermochemically) in 4.1 mm × 8 mm implants with internal connection and a polished neck. Twelve implants of each surface type (N = 36) were placed, sacrificing 1/3 of the animals at 2 weeks of placement, 1/3 at 4 weeks and the remaining 1/3 at 8 weeks. Numerical variables were compared with Analysis of Variance, and the correlation between ISQ and BIC was established with the Spearman’s rank correlation coefficient. Results: SLActive^® and ContacTi^® surfaces showed elevated osteoconductivity at 4 weeks, maintaining a similar evolution at 8 weeks (large amount of mature lamellar tissue with high maturity and bone quality). The SLA^® surface showed slower maturation. The ISQ values in surgery were elevated (above 65), higher at necropsy and higher at 4 and 8 weeks in the SLA^® group than in the other two (SLActive^® and ContacTi^®). No significant correlation was found between ISQ and BIC for each implant surface and necropsy time. Conclusion: The three surfaces analysed showed high RFA and BIC values, which were more favourable for the SLActive^® and ContacTi^® surfaces. No statistical correlation was found between the RFA and BIC values in any of the three surfaces analysed.

Wool-derived keratin hydrogel enhances implant osseointegration in cancellous bone

AIM

This study investigated whether a keratin hydrogel derived from wool enhances ossointegration of dental implants, using a cancellous bone model in sheep.

METHOD

Ten female sheep received one dental implant per hind leg in the distal femoral condyles. Test implants were coated with 1 mL of keratin hydrogel containing sulphonated keratin and hydroxyapatite; control implants remained uncoated; implants were not functionally loaded axially. Biomechanical stability was tested with resonance frequency analysis (RFA) at placement and euthanasia. Animals were sacrificed after 4 weeks and resin-embedded histomorphometry performed.

FINDINGS

Bone appeared denser and more mature around the keratin-treated test implants. Average % bone-implant contact was significantly increased for the test (58.1 ± 4.6 [SD]%) compared to control implants (34.4 ± 7.5%) (p = 0.01). RFA values were lower for control (76.5 ± 4.2 ISQ) than test implants (80.4 ± 1.4) after 4 weeks (p = 0.04).

CONCLUSION

the increase in osseointegration found in this model suggests that keratin hydrogel has the potential to enhance the successful osseointegration of dental implants placed into poor quality bone. © 2017 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 106B: 2447-2454, 2018.

Does incorporating collagen and chondroitin sulfate matrix in implant surfaces enhance osseointegration? A systematic review and meta-analysis

Implant surface modification has been used to improve osseointegration. However, evidence regarding improved new bone formation (NBF) and osseointegration with the use of collagen-chondroitin sulfate (CS) matrix coated implants remains unclear. The aim of this study was to assess the efficacy of collagen-CS matrix coating on the osseointegration of implants. The focused question was "Does the incorporation of collagen-CS matrix in implant surfaces influence osseointegration?" To answer the question, indexed databases were searched up to July 2017 using various combinations of the key words "collagen", "chondroitin sulfate", "osseointegration", and "implants". The initial literature search identified 497 articles, of which 18 reporting experimental studies fulfilled the inclusion criteria. Thirteen of the studies included (72%) reported that implants coated with a collagen-CS matrix presented higher NBF, bone-to-implant contact, and/or bone volume density. The strength of this observation was supported by meta-analysis results. Nevertheless, the results should be interpreted with caution due to the lack of standardization regarding the dosage formulation of collagen-CS, short-term follow-up, and lack of assessment of confounders. On experimental grounds, the incorporation of collagen-CS matrix into implant surfaces appears to promote osseointegration. From a clinical perspective, the results from animal models support phase I studies in healthy humans.

* Extracellular Matrices for Bone Regeneration: A Literature Review

The gold standard material for bone regeneration is still autologous bone, a mesenchymal tissue that consists mainly of extracellular matrix (ECM) (90% v/v) and little cellular content (10% v/v). However, the fact that decellularized allogenic bone grafts often present a clinical performance comparable to autologous bone grafts demonstrates the crucial role of ECM in bone regeneration. For long, the mechanism by which bone allografts function was not clear, but recent research has unveiled many unique characteristics of ECM that seem to play a key role in tissue regeneration. This is further confirmed by the fact that synthetic biomaterials with composition and properties resembling bone ECM present excellent bone regeneration properties. In this context, ECM molecules such as glycosaminoglycans (GAGs) and self-assembly peptides (SAPs) can improve the performance of bone regeneration biomaterials. Moreover, decellularized ECM derived either from native tissues such as bone, cartilage, skin, and tooth germs or from cells such as osteoblasts, chondrocytes, and stem cells has shown promising results in bone regeneration applications. Understanding the role of ECM in bone regeneration is crucial for the development of the next generation of biomaterials for bone tissue engineering. In this sense, this review addresses the state-of-the-art on this subject matter.

Dental implant bioactive surface modifications and their effects on osseointegration: a review

BACKGROUND

The purpose of this article is to review and update the current developments of biologically active dental implant surfaces and their effect on osseointegration.

METHODS

PubMed was searched for entries from January 2006 to January 2016. Only in-vivo studies that evaluated the effects of biomolecular coatings on titanium dental implants inserted into the bone of animals or humans were included.

RESULTS

Thirty four non-review studies provided data and observations were included in this review. Within the criteria, four categories of biomolecular coatings were evaluated. The potential biomolecules include bone morphogenetic proteins in 8 articles, other growth factors in 8 articles, peptides in 5 articles, and extracellular matrix in 13 articles. Most articles had a healing period of 1 to 3 months and the longest time of study was 6 months. In addition, all studies comprised of implants inserted in animals except for one, which evaluated implants placed in both animals and humans. The results indicate that dental implant surface modification with biological molecules seem to improve performance as demonstrated by histomorphometric analysis (such as percentage of bone-to-implant contact and peri-implant bone density) and biomechanical testing (such as removal torque, push-out/pull-out tests, and resonance frequency analysis).

CONCLUSIONS

Bioactive surface modifications on implant surfaces do not always offer a beneficial effect on osseointegration. Nevertheless, surface modifications of titanium dental implants with biomolecular coatings seem to promote peri-implant bone formation, resulting in enhanced osseointegration during the early stages of healing. However, long-term clinical studies are needed to validate this result. In addition, clinicians must keep in mind that results from animal experiments need not necessarily reflect the human clinical reality.

Dental implant bioactive surface modifications and their effects on osseointegration: a review

Background

The purpose of this article is to review and update the current developments of biologically active dental implant surfaces and their effect on osseointegration.

Methods

PubMed was searched for entries from January 2006 to January 2016. Only in-vivo studies that evaluated the effects of biomolecular coatings on titanium dental implants inserted into the bone of animals or humans were included.

Results

Thirty four non-review studies provided data and observations were included in this review. Within the criteria, four categories of biomolecular coatings were evaluated. The potential biomolecules include bone morphogenetic proteins in 8 articles, other growth factors in 8 articles, peptides in 5 articles, and extracellular matrix in 13 articles. Most articles had a healing period of 1 to 3 months and the longest time of study was 6 months. In addition, all studies comprised of implants inserted in animals except for one, which evaluated implants placed in both animals and humans. The results indicate that dental implant surface modification with biological molecules seem to improve performance as demonstrated by histomorphometric analysis (such as percentage of bone-to-implant contact and peri-implant bone density) and biomechanical testing (such as removal torque, push-out/pull-out tests, and resonance frequency analysis).

Conclusions

Bioactive surface modifications on implant surfaces do not always offer a beneficial effect on osseointegration. Nevertheless, surface modifications of titanium dental implants with biomolecular coatings seem to promote peri-implant bone formation, resulting in enhanced osseointegration during the early stages of healing. However, long-term clinical studies are needed to validate this result. In addition, clinicians must keep in mind that results from animal experiments need not necessarily reflect the human clinical reality.

The effect of different collagen modifications for titanium and titanium nitrite surfaces on functions of gingival fibroblasts

OBJECTIVES

Targeted modifications of the bulk implant surfaces using bioactive agents provide a promising tool for improvement of the long-term bony and soft tissue integration of dental implants. In this study, we assessed the cellular responses of primary human gingival fibroblasts (HGF) to different surface modifications of titanium (Ti) and titanium nitride (TiN) alloys with type I collagen or cyclic-RGDfK-peptide in order to define a modification improving long-term implants in dental medicine.

MATERIALS AND METHODS

Employing Ti and TiN implants, we compared the performance of simple dip coating and anodic immobilization of type I collagen that provided collagen layers of two different thicknesses. HGF were seeded on the different coated implants, and adhesion, proliferation, and gene expression were analyzed.

RESULTS

Although there were no strong differences in initial cell adhesion between the groups at 2 and 4 hours, we found that all surface modifications induced higher proliferation rates as compared to the unmodified controls. Consistently, gene expression levels of cell adhesion markers (focal adhesion kinase (FAK), integrin beta1, and vinculin), cell differentiation markers (FGFR1, TGFb-R1), extracellular protein markers (type I collagen, vimentin), and cytoskeletal protein marker aktinin-1 were consistently higher in all surface modification groups at two different time points of investigation as compared to the unmodified controls.

CONCLUSION

Our results indicate that simple dip coating of Ti and TiN with collagen is sufficient to induce in vitro cellular responses that are comparable to those of more reliable coating methods like anodic adsorption, chemical cross-linking, or RGD coating. TiN alloys do not possess any positive or adverse effects on HGF.

CLINICAL RELEVANCE

Our results demonstrate a simple, yet effective, method for collagen coating on titanium implants to improve the long term integration and stability of dental implants.

The effects of hierarchical micro/nanosurfaces decorated with TiO2 nanotubes on the bioactivity of titanium implants in vitro and in vivo

In the present work, a hierarchical hybrid micro/nanostructured titanium surface was obtained by sandblasting with large grit and acid etching (SLA), and nanotubes of different diameters (30 nm, 50 nm, and 80 nm) were superimposed by anodization. The effect of each SLA-treated surface decorated with nanotubes (SLA + 30 nm, SLA + 50 nm, and SLA + 80 nm) on osteogenesis was studied in vitro and in vivo. The human MG63 osteosarcoma cell line was used for cytocompatibility evaluation, which showed that cell adhesion and proliferation were dramatically enhanced on SLA + 30 nm. In comparison with cells grown on the other tested surfaces, those grown on SLA + 80 nm showed an enhanced expression of osteogenesis-related genes. Cell spread was also enhanced on SLA + 80 nm. A canine model was used for in vivo evaluation of bone bonding. Histological examination demonstrated that new bone was formed more rapidly on SLA-treated surfaces with nanotubes (especially SLA + 80 nm) than on those without nanotubes. All of these results indicate that SLA + 80 nm is favorable for promoting the activity of osteoblasts and early bone bonding.

Assessment of activated porous granules on implant fixation and early bone formation in sheep

Background/Objective

Despite recent progress in regeneration medicine, the repair of large bone defects due to trauma, inflammation and tumor surgery remains a major clinical challenge. This study was designed to produce large amounts of viable bone graft materials in a novel perfusion bioreactor to promote bone formation.

Methods

Cylindrical defects were created bilaterally in the distal femurs of sheep, and titanium implants were inserted. The concentric gap around the implants was randomly filled either with allograft, granules, granules with bone marrow aspirate (BMA) or bioreactor activated granule (BAG). The viable BAG consisted of autologous bone marrow stromal cells (BMSCs) seeded upon porous scaffold granules incubated in a 3D perfusion bioreactor for 2 weeks prior to surgery. 6 weeks after, the bone formation and early implant fixation were assessed by means of micro-CT, histomorphometry, and mechanical test.

Results

Microarchitectural analysis revealed that bone volume fraction and trabecular thickness in the allograft were not statistically different than those (combination of new bone and residue of granule) in the other 3 groups. The structure of the allograft group was typically plate-like, while the other 3 groups were combination of plate and rod. Histomorphometry showed that allograft induced significantly more bone and less fibrous tissue in the concentric gap than the other 3 granule groups, while the bone ingrowth to implant porous surface was not different. No significant differences among the groups were found regarding early implant mechanical fixation.

Conclusion

In conclusion, despite nice bone formation and implant fixation in all groups, bioreactor activated graft material did not convincingly induce early implant fixation similar to allograft, and neither bioreactor nor by adding BMA credited additional benefit for bone formation in this model.

ECM inspired coating of embroidered 3D scaffolds enhances calvaria bone regeneration

Resorbable polymeric implants and surface coatings are an emerging technology to treat bone defects and increase bone formation. This approach is of special interest in anatomical regions like the calvaria since adults lose the capacity to heal large calvarial defects. The present study assesses the potential of extracellular matrix inspired, embroidered polycaprolactone-co-lactide (PCL) scaffolds for the treatment of 13 mm full thickness calvarial bone defects in rabbits. Moreover the influence of a collagen/chondroitin sulfate (coll I/cs) coating of PCL scaffolds was evaluated. Defect areas filled with autologous bone and empty defects served as reference. The healing process was monitored over 6 months by combining a novel ultrasonographic method, radiographic imaging, biomechanical testing, and histology. The PCL coll I/cs treated group reached 68% new bone volume compared to the autologous group (100%) and the biomechanical stability of the defect area was similar to that of the gold standard. Histological investigations revealed a significantly more homogenous bone distribution over the whole defect area in the PCL coll I/cs group compared to the noncoated group. The bioactive, coll I/cs coated, highly porous, 3-dimensional PCL scaffold acted as a guide rail for new skull bone formation along and into the implant.

Osseointegration of short titan implants: A pilot study in pigs

Reduced vertical bone level in the implantation area is often considered one of the limiting factors before implant insertion. Inserting implants of reduced length might be useful in order to avoid vertical bone augmentation prior to implantation. To the present day, no official guidelines exist as to the optimal length for these implants. It is nevertheless well known that the stability of an implant depends primarily on its osseointegration, which could otherwise be influenced by modifying implant surface texture. The aim of our study was to evaluate osseointegration in correlation with implant length and surface texture. Three different variations of titan implants (n=5) were compared: two types, each with an acid-etched and ceramic blasted surface, were inserted in the upper jaw of adult female minipigs at different lengths (tioLogic ST Shorty, 5mm length; tioLogic ST, 9mm length) and were compared to a control group (tioLogic ST, 9mm length, ceramic blasted surface). Eight weeks after unloaded healing, bone tissue specimens containing the implants were processed, stained with Masson-Goldner-trichrome and analyzed histologically. Regardless of implant length and surface texture, new bone formation with no signs of inflammation could be detected in the area of the threads. Implants with a modified surface showed no statistically significant difference in bone-implant-contact (BIC) (tioLogic ST Shorty, 56.5%; tioLogic(©)ST; 77.2%), but a statistically significant difference could be found, when the 9mm implants were compared to the control group (BIC 48.9%). Surface modification could positively influence osseointegration as well as contribute to overcoming the adverse effects of length reduction.

Embroidered and surface coated polycaprolactone-co-lactide scaffolds: a potential graft for bone tissue engineering

Tissue engineering and regenerative techniques targeting bone include a broad range of strategies and approaches to repair, augment, replace or regenerate bone tissue. Investigations that are aimed at optimization of these strategies until clinical translation require control of systemic factors as well as modification of a broad range of key parameters.

This article reviews a possible strategy using a tissue engineering approach and systematically describes a series of experiments evaluating the properties of an embroidered and surface coated polycaprolactone-co-lactide scaffold being considered as bone graft substitute for large bone defects. The scaffold design and fabrication, the scaffolds properties, as well as its surface modification and their influence in vitro are evaluated, followed by in vivo analysis of the scaffolds using orthotopic implantation models in small and large animals.

Surface modification of implants in long bone

Coatings of orthopedic implants are investigated to improve the osteoinductive and osteoconductive properties of the implant surfaces and thus to enhance periimplant bone formation. By applying coatings that mimic the extracellular matrix a favorable environment for osteoblasts, osteoclasts and their progenitor cells is provided to promote early and strong fixation of implants. It is known that the early bone ongrowth increases primary implant fixation and reduces the risk of implant failure. This review presents an overview of coating titanium and hydroxyapatite implants with components of the extracellular matrix like collagen type I, chondroitin sulfate and RGD peptide in different small and large animal models. The influence of these components on cells, the inflammation process, new bone formation and bone/implant contact is summarized.

Functionalization of biomaterial surfaces using artificial extracellular matrices

Construction of biomaterials with the ability to guide cell function is a topic of high interest in biomaterial development. One approach is using components native to the ECM of the target tissue to generate in vitro a microenvironment that can also elicit specific responses in cells and tissues—an artificial ECM (aECM). The focus is on collagen as the basic material, which can be modified using a number of different glycoproteins, proteoglycans and glycosaminoglycans. Preparation, immobilization and the biochemical characteristics of such aECM are discussed, as well as the in vitro and in vivo response of cells and tissues, illustrating the potential of such matrices to direct cell fate.

Bone Formation in a Local Defect around Dental Implants Coated with Extracellular Matrix Components

PURPOSE

The coating of implant surfaces with components of the extracellular matrix offers an approach to influence peri-implant bone healing. In this study, bone healing around coated implants is analyzed in a peri-implant defect model.

MATERIALS AND METHODS

Eight months after extraction of the premolar teeth, six dogs received 48 implants (eight per animal) in the mandible. Implant surfaces were sandblasted and acid-etched, and some were additionally coated with collagen type II and chondroitin sulfate (collagen/CS). On each side of the mandible, implants either had no peri-implant defect (control side) or a vertical defect of 5 mm in depth and 0.5, 1.0, or 2.0 mm in width. Implants healed submerged for 8 weeks. Fluorochrome staining, histology, and histomorphometry were used to analyze implant osseointegration.

RESULTS

Fluorochrome labels showed an increased mineralization around collagen/CS-coated surfaces at 4 weeks (p = .031). Histomorphometry generally showed lower vertical and horizontal bone apposition with increasing gap size for both surface types. In gapless sites and 0.5-mm gaps, collagen/CS coated implants showed increased bone volume in areas directly adjacent to the implant, in comparison with uncoated implants (p < .05).

CONCLUSION

The width of the peri-implant gap influences peri-implant bone formation. Complete filling of all gaps by newly formed bone could not be observed around either surface. In proximity to the surface, implant surface coating by collagen/CS positively influenced bone formation.

The comparison between implant stability quotient and bone-implant contact revisited: an experiment in Beagle dog

BACKGROUND

Resonance frequency analysis (RFA) is applied clinically for the assessment of implant stability, and the relevance of this application is widely accepted. However, the relationship between resonance frequency (RF) and other parameters of implant stability, such as the histomorphometrical bone-to-implant contact (BIC) parameter, has become controversial in the last decade.

OBJECTIVE

To analyse and clarify the controversial relationship between RF and histomorphometrical BIC measurements.

MATERIAL AND METHODS

A total of 36 dental implants (9 mm length, Ø 4.0 mm; Biohorizons(®) Implant Systems Inc., Birmingham, AL, USA) with a soluble blasting media (sandblasting with soluble particles) surface were implanted in six beagle dog mandibles. RFA assessments were performed with a magnetic Osstel Mentor(®) device at the time of implant installation, and during the monitoring period at weeks 1, 2, 4, 6 and 8, before implant retrieval. The dogs were sacrificed and the implants were removed in block after 8, 6, 4, 2, 1 and 0 weeks, respectively. One group was obtained at time 0, immediately after the implantation. The samples were embedded in methyl methacrylate polymers (Technovit(®) ) and cut along their long axis. BIC values were assessed by a non-subjective and systematic method based on backscattered scanning electron microscopy (BS-SEM) images. BIC% at the different time points was compared with the corresponding implant stability quotient (ISQ) values of the RFA assessment.

RESULTS

No statistically significant correlation between BIC and ISQ values (Osstell Mentor(®) ) was identified. The absence of a relationship between these two parameters is in agreement with several previous studies in humans and experimental animals.

CONCLUSIONS

The lack of correlation between BIC and ISQ values suggests that ISQ as determined by RFA is not able to identify the relationship between RF and histomorphometrical data.

Chondroitin sulfate and sulfated hyaluronan-containing collagen coatings of titanium implants influence peri-implant bone formation in a minipig model

An improved osseous integration of dental implants in patients with lower bone quality is of particular interest. The aim of this study was to evaluate the effect of artificial extracellular matrix implant coatings on early bone formation. The coatings contained collagen (coll) in conjunction with either chondroitin sulfate (CS) or sulfated hyaluronan (sHya). Thirty-six screw-type, grit-blasted, and acid-etched titanium implants were inserted in the mandible of 6 minipigs. Three surface states were tested: (1) uncoated control (2) coll/CS (3) coll/sHya. After healing periods of 4 and 8 weeks, bone implant contact (BIC), bone volume density (BVD) as well as osteoid related parameters were measured. After 4 weeks, control implants showed a BIC of 44% which was comparable to coll/CS coated implants (48%) and significantly higher compared to coll/sHya coatings (37%, p = 0.012). This difference leveled out after 8 weeks. No significant differences could be detected for BVD values after 4 weeks and all surfaces showed reduced BVD values after 8 weeks. However, at that time, BVD around both, coll/CS (30%, p = 0.029), and coll/sHya (32%, p = 0.015), coatings was significantly higher compared to controls (22%). The osteoid implant contact (OIC) showed no significant differences after 4 weeks. After 8 weeks OIC for controls was comparable to coll/CS, the latter being significantly higher compared to coll/sHya (0.9% vs. 0.4%, p = 0.012). There were no significant differences in osteoid volume density. In summary, implant surface coatings by the chosen organic components of the extracellular matrix showed a certain potential to influence osseointegration in vivo.

Poly(L-lactide-co-glycolide) scaffolds coated with collagen and glycosaminoglycans: impact on proliferation and osteogenic differentiation of human mesenchymal stem cells

In this study, we analyzed poly(L-lactide-co-glycolide) (PLGA) scaffolds modified with artificial extracellular matrices (aECM) consisting of collagen type I, chondroitin sulphate, and sulphated hyaluronan (sHya). We investigated the effect of these aECM coatings on proliferation and osteogenic differentiation of human mesenchymal stem cells (hMSC) in vitro. We found that scaffolds were homogeneously coated, and cross-linking of aECM did not significantly influence the amount of collagen immobilized. Cell proliferation was significantly increased on cross-linked surfaces in expansion medium (EM), but was retarded on cross-linked and non-cross-linked collagen/sHya coatings. The alkaline phosphatase activity was increased on sHya-containing coatings in EM even without the presence of differentiation supplements, but was six to ten times higher in differentiation medium (DM) and comparable for cross-linked and non-cross-linked collagen/sHya. The highest amount of calcium phosphate mineral was deposited on day 28 on cross-linked collagen/sHya. Therefore, coatings of PLGA scaffolds with collagen/sHya promoted the osteogenic differentiation of hMSCs in vitro and might be an interesting candidate for the modification of PLGA for bone reconstruction in vivo.

Healing properties of surface-coated polycaprolactone-co-lactide scaffolds: A pilot study in sheep

The aim of this pilot study was to evaluate the bioactive, surface-coated polycaprolactone-co-lactide scaffolds as bone implants in a tibia critical size defect model. Polycaprolactone-co-lactide scaffolds were coated with collagen type I and chondroitin sulfate and 30 piled up polycaprolactone-co-lactide scaffolds were implanted into a 3 cm sheep tibia critical size defect for 3 or 12 months ( n = 5 each). Bone healing was estimated by quantification of bone volume in the defects on computer tomography and microcomputer tomography scans, plain radiographs, biomechanical testing as well as by histological evaluations. New bone formation occurred at the proximal and distal ends of the tibia in both groups. The current pilot study revealed a mean new bone formation of 63% and 172% after 3 and 12 months, respectively. The bioactive, surface coated, highly porous three-dimensional polycaprolactone-co-lactide scaffold stack itself acted as a guide rail for new bone formation along and into the implant. These preliminary data are encouraging for future experiments with a larger group of animals.

Sulfated hyaluronan/collagen I matrices enhance the osteogenic differentiation of human mesenchymal stromal cells in vitro even in the absence of dexamethasone

Glycosaminoglycans (GAG) are multifunctional components of the extracellular matrix (ECM) involved in different steps of the regulation of cellular differentiation. In this study artificial extracellular matrices (aECM) consisting of collagen (Col) I and different GAG derivatives were used as a substrate for human mesenchymal stromal cells (hMSC) to study osteogenic differentiation in vitro. hMSC were cultured on aECM containing col and hyaluronan sulfates (HyaS) with increasing degrees of sulfation (DS(S)) and were compared with aECM containing col and the natural GAG hyaluronan or chondroitin 4-sulfate. hMSC were analyzed for osteogenic differentiation markers such as calcium phosphate deposition, tissue non-specific alkaline phosphatase (TNAP) and expression of runt-related transcription factor 2 (runx2), osteocalcin (ocn) and bone sialoprotein II (bspII). Compared with aECM containing Col and natural GAG all Col/HyaS-containing aECM induced an increase in calcium phosphate deposition, TNAP activity and tnap expression. These effects were also seen in the absence of dexamethasone (an established osteogenic supplement). The expression of runx2 and ocn was not altered and the expression of bspII was diminished on the col/HyaS-containing aECM. The impact of the Col/HyaS-containing aECM on hMSC differentiation was independent of the DS(S) of the HyaS derivatives, indicating the importance of the primary (C-6) hydroxyl group of N-acetylglucosamine. These results suggest that Col/HyaS-containing aECM are able to stimulate hMSC to undergo osteogenic differentiation even in the absence of dexamethasone, which makes these matrices an interesting tool for hMSC-based tissue engineering applications and biomaterial functionalizations to enhance bone formation.

Biological functionalization of dental implants with collagen and glycosaminoglycans-A comparative study

Biological implant surface coatings are an emerging technology to increase bone formation. Such an approach is of special interest in anatomical regions like the maxilla. In the present study, we hypothesized that the coating of titanium implants with components of the organic extracellular matrix increases bone formation and implant stability compared to an uncoated reference. The implants were coated using collagen-I with either two different concentrations of chondroitin sulfate (CS) or two differentially sulfated hyaluronans. Implant coatings were characterized biochemically and with atomic force microscopy. Histomorphometry was used to assess bone-implant contact (BIC) and bone-volume density (BVD) after 4 and 8 weeks of submerged healing in the maxilla of 20 minipigs. Further, implant stability was measured by resonance frequency analysis (RFA). Implants containing the lower CS concentration had significantly more BIC, compared to the uncoated reference at both times of interest. No significant increase was measured from week 4 to 8. Differences in BVD and RFA were statistically not significant. A higher concentration of CS and the application of sulfated hyaluronans showed no comparable increase in BIC. This study demonstrates a positive effect of a specific collagen-glycosaminoglycan combination on early bone formation in vivo.

Increase of BM-MSC proliferation using L-DOPA on titanium surface in vitro

In order to increase biocompatibility, many dental implants have been studied by immobilization of biomolecules on biomaterials. We used l-3,4-dihydroxyphenylalanine (L-DOPA) as a biomolecule for surface-modified titanium. Water contact angles of nontreated titanium discs (negative control), etched titanium discs (positive control), and titanium discs treated with L-DOPA following the etching process (experimental group) were 82.4 ± 5.7°, 67.1 ± 0.56°, and 44.15 ± 0.91°, respectively. Using atomic force microscopy images, we were able to find L-DOPA, which adhered to the titanium surface. The number of human bone marrow mesenchymal stem cells (BM-MSCs) in the experimental group was much higher than that of cells in any other group. Quantification values of amine groups in the positive control and experimental groups were approximately 3 and 7.5 µg, respectively. Therefore, findings from our research suggested the possibility of a causal link between increased L-DOPA content and cell proliferation in BM-MSCs. Moreover, coating of the discs with L-DOPA can result in greater hydrophilicity of the titanium surface and enhancement of cell adhesion and mitochondrial activity.