Efficacy of platelets in bone healing: A systematic review on animal studies

Editorial Commentary: Platelet-rich plasma (PRP) for rotator cuff repair improves re-tear rate but clinical impact is yet to be seen

Rotator cuff tendon repair has a high failure rate due to the inferior quality of tendon material. Platelet-rich plasma (PRP) is considered a potential solution, though its clinical impact is uncertain. Recent literature indicates that while PRP may reduce re-tear rates radiologically, it does not significantly improve clinical outcomes such as pain and function. Early animal studies showed potential benefits, but initial clinical trials were inconclusive due to small sample sizes and varied PRP methods. Larger, recent studies suggest a possible benefit, yet definitive clinical advantages remain elusive. Advancing PRP research requires a dual approach: deeper understanding of tendon and PRP biology, and larger clinical trials focusing on specific PRP preparations and delivery methods. While current evidence is limited, PRP holds promise for improving rotator cuff repair outcomes, and ongoing research may eventually translate into significant clinical benefits.

The levels of TGFβ1, VEGF, PDGF-BB, and PF4 in platelet-rich plasma of professional soccer players: a cross-sectional pilot study

Background

Regenerative therapy using platelet-rich plasma (PRP), a rich source of growth factors, has become popular in orthopedic sports medicine. Elite athletes prefer PRP therapy for their injured muscles and tendons primarily to avoid the possible risks of surgical treatment. However, the clinical effectiveness of PRP therapy in elite athletes compared to that in non-athletes remains unknown. Therefore, to investigate the effectiveness of PRP therapy in professional athletes (pro-athletes), we focused on the quality of PRP preparations and compared the levels of bioactive molecules between pro-athletes and non-athletes.

Methods

PRP was prepared from healthy, non-smoking male professional soccer players (pro-athletes) (n = 22) and non-athletes (VEGF: n = 34, others: n = 38). The levels of TGFβ1, PDGF-BB, VEGF, and PF4 were determined using ELISA kits. Polyphosphate was probed with 4’,6-diamidino-2-phenylindole and monitored using a fluorometer. The body composition of the donors was determined using a bathroom weighing scale.

Results

The levels of TGFβ1 and VEGF were significantly lower in pro-athletes than in non-athletes, whereas PF4 levels were significantly higher in pro-athletes. No significant difference was found in PDGF-BB levels between these groups. Biomolecule levels were not correlated with polyphosphate levels.

Conclusion

TGFβ1, VEGF, and PDGF-BB levels in pro-athletes were not higher than those in non-athletes. These findings suggest that growth factor levels in PRP may not be a predominant determinant of the clinical effectiveness of PRP therapy in pro-athletes. Increased PF4 levels in pro-athletes suggest an immunological function of PRP that may positively influence tissue regeneration.

Surgical Classification for Preclinical Rat Femoral Bone Defect Model: Standardization Based on Systematic Review, Anatomical Analysis and Virtual Surgery

Though surgical techniques profoundly influence in vivo experiments, significant heterogeneity exists in current surgeries for inducing rat femoral bone defects. Such variations reduce the reproducibility and comparability of preclinical studies, and are detrimental to clinical translation. The purposes of this study were: (1) to conduct a systematic review of rat femoral defect models, summarizing and analyzing the surgical techniques; (2) to analyze surgical design and potential pitfalls via 3D anatomy and virtual surgeries for fostering future precision research; and (3) to establish a surgical classification system, for improving the reproducibility and comparability among studies, avoiding unnecessary repetitive experiments. The online database PubMed was searched to identify studies from January 2000 to June 2022 using keywords, including rat, femur, bone defect. Eligible publications were included for a review of surgical methods. Anatomical analysis and virtual surgeries were conducted based on micro-CT reconstruction of the rat femur for further investigation and establishment of a classification system. A total of 545 publications were included, revealing marked heterogeneity in surgical methods. Four major surgical designs were reported for inducing defects from the proximal to distal femur: bone tunnel, cortical window, segmental defect, and wedge-shaped defect. Anatomical analysis revealed potential pitfalls hindering efficient clinical translation. A classification system was established according to the anatomical region, surgical design, and fixation devices. This systematic review in combination with 3D analysis and virtual surgery provides a general overview of current surgical approaches to inducing femoral defects in rats, and establishes a surgical classification facilitating preclinical research of quality and translational value.

From Blood to Bone-The Osteogenic Activity of L-PRF Membranes on the Ex Vivo Embryonic Chick Femur Development Model

(1) Background: To evaluate the effects of the direct and indirect contact of leukocyte and platelet-rich fibrin (L-PRF) on bone development, in an ex vivo embryonic chick femur model. (2) Methods: Both sections of L-PRF membranes (red and yellow portions) were evaluated with scanning electron microscopy and histochemical staining. The in vivo angiogenic activity was evaluated using a chorioallantoic membrane model. The osteogenic activity was assessed with an organotypic culture of embryonic chick femora through direct and indirect contact, and assessment was conducted by microtomographic and histological analysis. Descriptive statistics, One-Way ANOVA and Tukey’s multiple comparisons tests were performed for datasets that presented a normal distribution, and Kruskal-Wallis tests were performed for non-parametric datasets. A significance level of 0.05 was considered. (3) Results: The L-PRF induced angiogenesis reflected by a higher number and a larger and more complex gauge in the vessels that invaded the membrane. The physical presence of the membrane over the bone (direct contact) unleashes the full potential of the L-PRF effects on bone growth enhancement. The greatest increase in mineral content was observed in the diaphysis region. (4) Conclusion: The L-PRF direct contact group presented higher values on mineral content for bone volume, bone surface and bone mineral density than the indirect contact and control groups.

Does PRGF Work? A Prospective Clinical Study in Dogs with A Novel Polylactic Acid Scaffold Injected with PRGF Using the Modified Maquet Technique

Simple Summary

PRGF is a concentration of autologous platelets in a small volume of plasma, which is performed in a specific way and is an accessible resource in veterinary medicine. The PRGF has multiple demonstrated properties as antimicrobial, analgesic and anti-inflammatory but their osteoinductivity potential is controversial. We decided to use PRGF in combination with a PLA bioresorbable scaffold (a specific type of implant with osteoconduction properties) performed by 3D printing, and personalized for each patient, to determinate if the PRGF can produce osteoinduction and as a result, a faster bone healing and a faster patient recovery. Furthermore, in this study PLA scaffolds are proposed as an alternative for metallic implants to avoid the problems that those can cause. The MMT was the technique selected for solving the RCrCL as it is a variant of TTA that follows the same principle for the correction of the patellar tendon angle to neutralize distractive forces; however, this technique needs a lower amount of metallic implants for the scaffold fixation.

Abstract

Tibial tuberosity advancement is a surgical technique to restore the dynamical stability in the knee by advancing the insertion of the patellar ligament, for which it is necessary to advance the tibial crest, being maintained in the desired position usually by a cage and metallic implants. The purpose of this study was to replace the cage with a polylactic acid biodegradable scaffold designed for each patient by 3D printing, inserting platelet-rich in growth factors (PRGF) to demonstrate its osteoinductive properties. To this end, we used the modified Maquet technique to reduce the amount of metal to a minimum. Fifty-three dogs finished the study. The control and PRGF groups did not present any statistically significant differences in terms of ossification degree (p > 0.001) but they demonstrated satisfactory ossification compared to previous publications, although in the PRGF group three of the scaffolds suffered complete reabsorption. The PRGF and control groups did not show any statistically significant differences in terms of lameness degree (p > 0.001). However, the PRGF group showed at the first control some analgesic and anti-inflammatory properties but they were not enough for reducing the functional recovery time in a significant way. The PRGF group did not show any complications or negative results associated with their use.

Effects of Leukocyte-Platelet-Rich Plasma on the Alveolar Bone Changes During Orthodontic Tooth Movement in Rabbits: A Micro-CT Study

Objective: To investigate the effects of leukocyte-platelet-rich plasma (L-PRP) on the alveolar bone changes at the compression and tension sides during orthodontic tooth movement.

Materials and Methods: Around 20 New Zealand white rabbits were used in a split-mouth design. The maxillary first premolar was moved mesially with a nickel-titanium closed-coil spring. One side of the maxilla was randomly injected with L-PRP, while the contralateral side served as the control which received normal saline. The alveolar bone adjacent to the maxillary first premolar was scanned using microcomputed tomography at days 0, 7, 14, and 28. Microstructural parameters including bone volume fraction, trabecular thickness, and trabecular separation of alveolar bone were assessed on the compression and tension sides of the maxillary first premolar.

Results: Compared between the groups, the L-PPR group showed a significantly decreased bone volume fraction on the compression side on days 7 and 14 but significantly increased bone volume fraction on the tension side on day 14. However, there were no statistically significant differences in the parameters of trabecular thickness and trabecular separation.

Conclusion: Local administration of L-PRP may promote bone resorption on the compression side and bone formation on the tension side at the initial stage of orthodontic tooth movement.

Synthetic Blocks for Bone Regeneration: A Systematic Review and Meta-Analysis

This systematic review is aimed at evaluating the effectiveness of synthetic block materials for bone augmentation in preclinical in vivo studies. An electronic search was performed on Pubmed, Scopus, EMBASE. Articles selected underwent risk-of-bias assessment. The outcomes were: new bone formation and residual graft with histomorphometry, radiographic bone density, soft tissue parameters, complications. Meta-analysis was performed to compare new bone formation in test (synthetic blocks) vs. control group (autogenous blocks or spontaneous healing). The search yielded 214 articles. After screening, 39 studies were included, all performed on animal models: rabbits (n = 18 studies), dogs (n = 4), rats (n = 7), minipigs (n = 4), goats (n = 4), and sheep (n = 2). The meta-analysis on rabbit studies showed significantly higher new bone formation for synthetic blocks with respect to autogenous blocks both at four-week (mean difference (MD): 5.91%, 95% confidence intervals (CI): 1.04, 10.79%, p = 0.02) and at eight-week healing (MD: 4.44%, 95% CI: 0.71, 8.17%, p = 0.02). Other animal models evidenced a trend for better outcomes with synthetic blocks, though only based on qualitative analysis. Synthetic blocks may represent a viable resource in bone regenerative surgery for achieving new bone formation. Differences in the animal models, the design of included studies, and the bone defects treated should be considered when generalizing the results. Clinical studies are needed to confirm the effectiveness of synthetic blocks in bone augmentation procedures.

Multicenter study of patients' preferences and concerns regarding the origin of bone grafts utilized in dentistry

PURPOSE

Bone graft materials can be obtained from the patient's own body (autologous graft), animals (xenograft), human cadavers (allograft) and synthetic materials (alloplastic bone graft). Patients may have ethical, religious or medical concerns about the origin of bone grafts, which could lead them to reject the use of certain types of bone graft in their treatments. The aim of this multicenter study, which surveyed patients from five university clinics in Portugal, France, Italy, Spain and Chile, was to analyze patients' opinions regarding the source of bone grafts.

PATIENTS AND METHODS

A survey composed of ten questions was translated into local languages and validated. Patients were asked about the degree of acceptance/rejection of each graft and the reasons for rejection. A chi-squared test was used to analyze statistically significant differences.

RESULTS

Three hundred thirty patients were surveyed. The grafts that elicited the highest percentage of refusal were allograft (40.4%), autologous bone graft from an extraoral donor site (34%) and xenograft (32.7%). The grafts with the lowest rate of refusal were alloplastic (6.3%) and autologous bone grafts from an intraoral donor site (24.5%). The main reason for autologous bone rejection was the fear of pain and discomfort, for xenograft it was the fear of disease transmission and the rejection of use of animals for human benefit, and for allograft it was ethical/moral motivations and the fear of disease transmission. Religious affiliation influenced patient's preferences.

CONCLUSION

The origin of bone grafts is still conflictive for a high percentage of patients.

An on-site preparable, novel bone-grafting complex consisting of human platelet-rich fibrin and porous particles made of a recombinant collagen-like protein

Platelet‐rich fibrin (PRF) is widely used in regenerative medicine. Nonetheless, major issues include its controversial effects on bone regeneration and a lack of quality‐assured glass tubes required for coagulation. We used porous particles (FBG) comprising a recombinant RGD motif‐enriched collagen I‐like protein to activate the coagulation pathway and examined the effects of the resulting PRF–FBG complex on bone regeneration. Human whole‐blood samples were mixed with FBG in plastic tubes and centrifuged to prepare a PRF–FBG complex. Platelet‐derived growth factor‐BB (PDGF‐BB) levels and cell growth activity were determined by ELISA and a bioassay using osteoblasts. Bone regenerative activity was assessed using a mouse model of calvarial bone defect. FBG facilitated PRF‐like matrix formation during centrifugation. In this PRF–FBG complex, the microstructure of fibrin fibers was similar to that of PRF prepared conventionally in glass tubes. PDGF‐BB levels and mitogenic action were not significantly influenced by FBG. In the bone defect model, although PRF did not exert any significant positive effects on its own, in combination with FBG, it synergistically stimulated new bone formation. This study demonstrated that incorporation of FBG into whole‐blood samples induces PRF formation without the aid of glass tubes. The resulting PRF–FBG complex could be a promising bone grafting material in clinical settings. © 2018 The Authors. Journal of Biomedical Materials Research Part B: Applied Biomaterials published by Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater 107B: 1420–1430, 2019.

Injectable platelet rich fibrin: cell content, morphological, and protein characterization

OBJECTIVES

The aim of the present study was to evaluate the blood cell content, morphological aspects, gene expression of type I collagen, and release of growth factors on an injectable platelet rich fibrin (i-PRF).

MATERIALS AND METHODS

Blood samples were collected from 15 volunteers to prepare i-PRF samples. Peripheral blood was used as a control group. Blood clot and i-PRF samples were cultured for 10 days. The supernatant of the samples was collected for ELISA immunoassay quantification of PDGF and VEGF growth factors over periods of 1, 8, 24, 72, and 240 h. I-PRF and blood clot samples were biologically characterized using histological and immunohistochemistry analysis for IL-10, osteocalcin, and TGF-β. Scanning electron microscopy (SEM) was used to inspect the fibrin network and distribution of blood platelets and leukocytes. Reverse transcriptase polymerase chain reaction (RT-PCR) method was used to evaluate gene expression for type I collagen.

RESULTS

A higher concentration of platelets and lymphocytes was recorded in i-PRF than in peripheral blood (p < 0.05). The release of VEGF was higher in blood clot samples (1933 ± 704) than that for i-PRF (852 ± 376; p < 0.001). Immunohistochemistry showed upregulation of TGF-B, IL-10, and osteocalcin in the i-PRF group. RT-PCR showed increased type I collagen gene expression in i-PRF (p < 0.05). SEM images revealed agglomeration of platelets in some regions, while a fibrin networking was noticeable in the entire i-PRF sample.

CONCLUSIONS

Injectable platelet rich fibrin becomes a good approach for soft and mineralized tissue healing considering the formation of a three-dimensional fibrin network embedding platelets, leukocytes, type I collagen, osteocalcin, and growth factors. Indeed, the injectable platelet rich fibrin can be indicated in several medical applications regarding bioactivity, simplied technique, and flowable mixing with other biomaterials.

CLINICAL RELEVANCE

Morphological, cell, and protein characterization of platelet rich fibrin provides a better understanding of the clinical effects and improvement of clinical guidelines for several medical applications. Once well physicochemical and biologically characterized, the use of an injectable platelet rich fibrin can be extended to other applications in the field of orthopedics, periodontics, and implant dentistry on the repairing process of both soft and mineralized tissues.

Translational Implications of Platelets as Vascular First Responders

Platelets play a vital role in normal hemostasis to stem blood loss at sites of vascular injury by tethering and adhering to sites of injury, recruiting other platelets and blood cells to the developing clot, releasing vasoactive small molecules and proteins, and assembling and activating plasma coagulation proteins in a tightly regulated temporal and spatial manner. In synchrony with specific end products of coagulation, primarily cross-linked fibrin, a stable thrombus quickly forms. Far beyond physiological hemostasis and pathological thrombosis, emerging evidence supports platelets playing a pivotal role in vascular homeostasis, inflammation, cellular repair, regeneration, and wide range of autocrine and paracrine functions. In essence, platelets play both structural and functional roles as reporters, messengers, and active transporters surveying the vasculature for cues of environmental or developmental stimuli and participating as first responders.1 In this review, we will provide a contemporary perspective of platelet physiology, including fundamental, translational, and clinical constructs that apply directly to human health and disease.